Abstract:
A simple supplementary service protocol (SSSP) is provided for implementing functionally based supplementary services using the H.323 standard. According to the preferred embodiment, a generic and expandable protocol is provide for passing supplementary services information between H.323 entities for the provision of over twenty classes of functionally based supplementary services. The protocol of the present invention is relatively lightweight (i.e. not code intensive) compared to H.450 since it does not rely on ASN.1 encoding. In addition, the mixture of functional and stimulus protocol concepts in the design of the inventive protocol results in robust functional characteristics and implementation capability using only lightweight Endpoints.

Description:
CROSS REFERENCE TO RELATED APPLICATION  
       [0001]     This application is a Divisional Application from a U.S. patent application Ser. No. 09/761,136 filed Jan. 16, 2001, which is herein specifically incorporated by reference in its entirety. 
     
    
     FIELD OF THE INVENTION  
       [0002]     The present invention relates in general to network-based voice communications, and more particularly to a method of supporting functionally based supplementary services implemented using H.323 protocol.  
       BACKGROUND OF THE INVENTION  
       [0003]     H.323 is a well known standard for multi-media communication. This standard governs communications between terminals and other entities over a packet switched network. A person of ordinary skill in the art and who is familiar with the H.323 standard will understand the elements of establishing third party call control via a Gatekeeper. Briefly, upon powering up, a H.323 endpoint (desktop) implements a discovery process for determining which Gatekeeper to register with. This can be effected in a number of ways, such as by multicasting a message which identifies the endpoint (i.e. the GRQ message) to a predetermined multicast address. The assigned Gatekeeper then responds (i.e. the GCF/GRJ message) with its RAS channel address (i.e. IP address). Before attempting to place a call, the endpoint must register with the Gatekeeper (i.e. the RRQ message) by advising it of its transport address and any aliases (discussed below). Registration is then confirmed by the Gatekeeper (i.e. via the RCF/RRJ message). Actual call signaling takes place over an established channel between two H.323 endpoints using Q.931 messages. For third party (i.e. Gatekeeper) call control, the originating endpoint sends a H.225 Admission Request (ARQ) to the Gatekeeper over the previously established RAS channel. The Gatekeeper responds with an ACF message which specifies the call signaling transport address to use for the call setup. The originating endpoint then transmits a Setup message to the Gatekeeper which, in turn, sends a Setup message to the destination endpoint. The destination endpoint then sends an admission request (ARQ) to the Gatekeeper and receives an acknowledgment (ACF) therefrom. Finally, a Connect message is sent from the destination endpoint to the Gatekeeper which contains the address of the originating endpoint for H.425 control messages to the originating endpoint.  
         [0004]     The inventor has recognized the desirability of adapting the H.323 standard to voice communications such as traditionally implemented via a PBX. However, the H.323 umbrella protocol standard only provides a limited set of recommendations in terms of supporting functionally based supplementary services between a Gatekeeper (GK) and an Endpoint (EP), due to the relative newness of the standard. Thus, H.323 suffers from limitations in providing a full range of PBX like functionally based supplementary services. The use of a functionally based supplementary service protocol requires a substantial amount of intelligence and knowledge of state within the Endpoint, which tends to make an Endpoint code heavy.  
         [0005]     The H.323 recommendation refers to the H.450 recommendation as the primary method for functionally based supplementary service signaling in the H.323 domain. The H.450 recommendation is new, with support for only eight supplementary services (as of Oct. 99), and expanding at a current rate of only three supplementary services per year. Furthermore, the H.450 protocol is a cumbersome protocol since it is ASN.1 based.  
         [0006]     Another available method of supplementary services signaling is through the use of “DTMF signaling”. This is similar to the use of feature access code signaling methods seen in traditional telephony. However, DTMF signaling is also not an ideal method for providing supplementary services since it usually requires a user to remember a complicated set of access codes and is therefore error prone.  
       SUMMARY OF THE INVENTION  
       [0007]     According to the present invention, a simple supplementary service protocol (SSSP) is provided for implementing functionally based supplementary services using the H.323 standard. According to the preferred embodiment, a generic and expandable protocol is provided for passing supplementary services information between H.323 entities for the provision of over twenty classes of functionally based supplementary services. The protocol of the present invention is relatively lightweight (i.e. not code intensive) compared to H.450 since it does not rely on ASN.1 encoding. In addition, the mixture of functional and stimulus protocol concepts in the design of the inventive protocol results in robust functional characteristics and implementation capability using only lightweight Endpoints.  
         [0008]     According to another aspect of the invention, a user interface is provided at an Endpoint for the purpose of displaying call and feature information relating to a SSSP enabled device, without the requirement of an elaborate state machine. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]     An embodiment of the invention is described below with reference to the accompanying drawings, in which:  
         [0010]      FIG. 1  is a schematic representation of a network-based communication system implemented according to the H.323 standard, including a Gatekeeper, an Application Server and a plurality of H.323 devices;  
         [0011]      FIG. 2  shows message flow between the Gatekeeper and H.323 endpoint for SSSP message transport, according to the preferred embodiment;  
         [0012]      FIG. 3  shows message flow using SSSP for implementing a message waiting indication;  
         [0013]      FIG. 4  shows message flow using SSSP for implementing an endpoint maintenance data indication;  
         [0014]      FIG. 5  shows message flow using SSSP for implementing ACD agent login and logout;  
         [0015]      FIG. 6  shows message flow using SSSP for implementing a make busy, DND, cancel work timer;  
         [0016]      FIG. 7  shows message flow using SSSP for disabling a make busy, DND, cancel work timer;  
         [0017]      FIG. 8  shows message flow using SSSP for unparking a call;  
         [0018]      FIG. 9  shows message flow using SSSP for implementing a back to held feature;  
         [0019]      FIG. 10  shows message flow using SSSP for implementing a force party release;  
         [0020]      FIG. 11  shows message flow using SSSP for implementing a recall feature;  
         [0021]      FIG. 12  shows a first portion of message flow using SSSP for implementing a call transfer with consultation;  
         [0022]      FIG. 13  shows a second portion of message flow using SSSP for implementing a call transfer with consultation;  
         [0023]      FIG. 14  shows a first portion of message flow using SSSP for implementing a blind call transfer;  
         [0024]      FIG. 15  shows a second portion of message flow using SSSP for implementing a blind call transfer;  
         [0025]      FIG. 16  shows message flow using SSSP for implementing a call forward out of service, busy, always feature;  
         [0026]      FIG. 17  shows message flow using SSSP for implementing a call forward no answer feature;  
         [0027]      FIG. 18  shows a first portion of message flow using SSSP for implementing a system camp-on and swap;  
         [0028]      FIG. 19  shows a second portion of message flow using SSSP for implementing a system camp-on and swap;  
         [0029]      FIG. 20  shows a first portion of message flow using SSSP for implementing ad hoc conference expansion;  
         [0030]      FIG. 21  shows a second portion of message flow using SSSP for implementing ad hoc conference expansion;  
         [0031]      FIG. 22  shows a first portion of message flow using SSSP for implementing a conference invite;  
         [0032]      FIG. 23  shows a second portion of message flow using SSSP for implementing a conference invite;  
         [0033]      FIG. 24  shows message flow using SSSP for implementing a group pickup feature;  
         [0034]      FIG. 25  shows message flow using SSSP for implementing a directed pickup feature;  
         [0035]      FIG. 26  shows message flow using SSSP for implementing a night service feature;  
         [0036]      FIG. 27  is a representation of two user interface views for displaying normal call and feature information, according to a further aspect of the invention;  
         [0037]      FIG. 28  is a flowchart showing implementation of a display handler for the user interface of  FIG. 27 ;  
         [0038]      FIG. 29  shows a message flow using SSSP for implementing a call forward busy indication; and  
         [0039]      FIG. 30  is a flowchart showing implementation of a state update handler for the user interface of  FIG. 27 . 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0040]      FIG. 1  shows a typical H.323 system, with H.323 endpoints  1  to  3  and a Gatekeeper  4  connected to a LAN/WAN  5 , according to a fully-routed H.323 Model. An Application Server  6  is also connected to the LAN/WAN  5 , which uses TAPI, TSAPI or JTAPI to control endpoints for telephony applications. The Simple Supplementary Services Protocol (SSSP) of the present invention is a generic communication scheme between a server entity (such as H.323 Gatekeeper  4 ) and an associated Endpoint  1  (such as a H.323 Terminal) or between Endpoints  1 . The SSSP provides a method of call signaling and control signaling that can be carried over existing protocols that support “user-to-user” like information (such as H.323 or ISDN). The following portions of the disclosure describe an encoding method according to the present invention, primitive definition, expandability rules, and the preferred transport method for SSSP. This is followed by illustrations of SSSP as a feature protocol between H.323 Gatekeeper  4  and H.323 Endpoint  1 .  
         [0041]     A generalized method of Alpha Numeric String Encoding and Dual Tone Multiple Frequency (DTMF) String Encoding for a SSSP Protocol Data Unit (PDU) is provided, as set forth below. Alpha Numeric is the preferred method of encoding when used in H.323 systems. The DTMF String Encoding method is restricted to the traditional DTMF character set. As such, it allows SSSP to be ported to non-H.323 communication systems with ease.  
         [0042]     General Encoding Terminology  
                                   AlphaNumericType ::= sequence of characters of set (A, B, C, D, E, F, G,       H, I, J, K, L, M, N, O, P, Q, R, S, T, U, V, W, X, Y, Z,       0, 1, 2, 3, 4, 5, 6, 7, 8, 9}       DirectoryNumberType ::= sequence of characters of       set {0,1,2,3,4,5,6,7,8,9,#,*,!},       NumberType ::= sequence of characters of set {0,1,2,3,4,5,6,7,8,9}       MacAddressType ::= MacParm ‘*‘ MacParam ‘*‘ MacParam ‘*‘               MacParam ‘*‘MacParam ‘*‘MacParam           Where MacParam ::= NumberType (MaxSize(3))                  
 
         [0043]     Alpha Numeric String Encoding  
                                   SSSPTag :: = ‘SP’       PrimitiveName ::= AlphaNumbericType       ParmeterSeperator ::= ‘,’       PDUType ::= ‘I’ | ‘Q’ | ‘R’ | ‘C’ | ‘E’       Parameters ::= DirectoryNumberType | MacAddressType | NumberType       ParameterExtenstions :: = ParameterSeperator Parameters       EndTag ::= NULL (0x00 for ASCII and 0x0000 for Unicode)       PDUName ::= SSSPTag ParameterSeperator PrimitiveName PDUType       SSSP PDU(String Encoding) ::=              PDUName ParameterExtensions EndTag.                  
 
         [0044]     In the foregoing encoding method, the following restrictions apply: 
        SSSPTag is limited to 2 characters wide     PrimitiveName is limited to 3 characters wide. The first 2 characters are unique for each class of supplementary service. For example, all call forwarding features begin with CF and the agent login/logout feature begins with AL.     PDUType is limited to 1 character wide, wherein ‘I’=Indication; ‘Q’=Request; ‘R’=Response; ‘C’=Command; ‘E’=Error     The SSSP PDU (String Encoding) is limited to 16384 characters wide        
 
         [0049]     Thus, for example, a call forward busy indication containing the forwarded destination directory number is formatted as follows: 
        PDUName ::=SP,CFBI     ParameterExtensions ::=DirectoryNumber     SSSP PDU ::=SP,CFBI,DirectoryNumber        
 
         [0053]     DTMF String Encoding  
                                                   FeatureTag ::= ‘AC’           FeatureCode ::= NumberType           ParameterSeperator ::= ‘*’           Params ::= NumberType           ParamExten ::= ParameterSeperator Params           ACEndTag ::= NULL (0x00 for ASCII and 0x0000 for Unicode)           SSSP PDU(Access Code) ::=                FeatureTag FeatureCode ParamExten* ACEndTag                      
 
         [0054]     In the foregoing encoding method, the following restrictions apply: 
        The SSSP PDU (Access Code Encoding) is limited to 16384 characters wide     FeatureCode is limited to 6 characters 
 
 Primitive Definition 
       
 
         [0057]     According to the preferred embodiment at the time of this specification, five PDUTypes have been established including Indication, Command, Request, Response, and Error. The definitions are as follows: 
    Indication: a message that contains information but does not require action or response.     Command: a message that requires action but no explicit response.     Request: a message that results in action by the remote device and requires an immediate response from it.     Response: a message that is the response to a request.     Error: a message indicating exception information.    
 
         [0063]     The following portions of this disclosure illustrate the use of SSSP for providing Gatekeeper implemented supplementary services. Table 1 provides a summary of example SSSP command and indication primitives. Table 2 provides a summary of example SSSP requests and responses. Table 3 lists requests for code enumeration, while Table 4 lists response code enumeration. Table 5 lists SSSP primitive descriptions. Table 6 lists error codes.  
                             TABLE 1                           Command and Indication Primitive Summary.            Primitive Name   Alpha Numeric String Encoding   DTMF String Encoding               AGENT LOGIN COMMAND   SP, AGIC, DirectoryNumber   AC1*DirectoryNumber       AGENT LOGOUT COMMAND   SP, AGOC, DirectoryNumber   AC2       AGENT INDICATION   SP, AGTI, 1   AC3*1       (YOU ARE AN AGENT)       AGENT INDICATION   SP, AGTI, 0   AC3*0       (YOU ARE NOT AN AGENT)       BACK TO HELD COMMAND   SP, BTHC   AC4       CALL FORWARD ALWAYS INDICATION   SP, CFAI, DirectoryNumber   AC5*DirectoryNumber       CALL FORWARD BUSY INDICATION   SP, CFBI, DirectoryNumber   AC6*DirectoryNumber       CALL FORWARD NO ANSWER INDICATION   SP, CFNI, DirectoryNumber   AC7*DirectoryNumber       CALL FORWARD OUT OF SERVICE   SP, CFOI, DirectoryNumber   AC8*DirectoryNumber       INDICATION       CALLING LINE IDENTIFIER INDICATION   SP, CLDI, DirectoryNumber   AC9*DirectoryNumber       CALL PROGRESS INDICATION   SP, CPI, DirectoryNumber   AC10*DirectoryNumber       CALL WAITING INDICATION   SP, CWI, DirectoryNumber   AC11*DirectoryNumber       CANCEL WORK TIMER COMMAND   SP, CWTC, 1   AC12*1       (ENABLE)       CANCEL WORK TIMER COMMAND   SP, CWTC, 0   AC12*0       (DISABLE)       CANCEL WORK TIMER INDICATION   SP, CWTI, 1   AC13*1       (CANCEL WORK TIMER SUCCESSFUL)       CANCEL WORK TIMER INDICATION   SP, CWTI, 0   AC13*0       (CANCEL WORK TIMER UNSUCCESSFUL)       CONFERENCE COMMAND   SP, CONC   AC14       CONFERENCE INDICATION   SP, CONI   AC15       CONSULTATION CALL COMMAND   SP, CCC, DirectoryNumber   AC16*DirectoryNumber       DIRECTED PICKUP COMMAND   SP, DPC, DirectoryNumber   AC17*DirectoryNumber       DO NOT DISTURB COMMAND (DISABLE)   SP, DNDC, 0   AC18*0       DO NOT DISTURB COMMAND (ENABLE)   SP, DNDC, 1   AC18*1       DO NOT DISTURB INDICATION   SP, DNDI, 1   AC19*1       (DO NOT DISTURB IS ON)       DO NOT DISTURB INDICATION   SP, DNDI, 0   AC19*0       (DO NOT DISTURB IS OFF)       ENDPOINT MAINTENANCE DATA   SP, EMDI, VersionIdentifier, Mac   AC20*VersionIdentifier*       INDICATION   Address   MacAddress       ERROR INDICATION   SP, ERRI, ErrorNumber   AC21*ErrorNumber       FORCE PARTY RELEASE COMMAND   SP, FPRC   AC22       GROUP PICKUP COMMAND   SP, GPC   AC23       GROUP PICKUP INDICATION   SP, GPI, 1   AC24*1       (PICKUP AVAILABLE)       GROUP PICKUP INDICATION   SP, GPI, 0   AC24*0       (PICKUP UNAVAILABLE)       HOLD COMMAND   SP, HDC   AC25       HOLD INDICATION   SP, HDI   AC26       MAKE BUSY COMMAND (DISABLE)   SP, MBYC, 0   AC27*0       MAKE BUSY COMMAND (ENABLE)   SP, MBYC, 1   AC27*1       MAKE BUSY INDICATION   SP, MBYI, 1   AC28*1       (MAKE BUSY IS SET)       MAKE BUSY INDICATION   SP, MBYI, 0   AC28*0       (MAKE BUSY IS NOT SET)       MESSAGE WAITING INDICATION   SP, MWI, TotalMessages   AC29*TotalMessages       NIGHT SERVICE PICKUP COMMAND   SP, NPC, DirectoryNumber   AC30*DirectoryNumber       PLAY CONTINUOUS TONE COMMAND   SP, PCTC, ToneNumber   AC31*ToneNumber       PLAY SHORT TONE COMMAND   SP, PSTC, ToneNumber, ToneDuration   AC32*ToneNumber*Tone               Duration       SWAP COMMAND   SP, SWPC   AC33       UN-PARK COMMAND   SP, UPKC, DirectoryNumber   AC34*DirectoryNumber                 Where:            DirectoryNumber ::= DirectoryNumberType (MaxSize(255))            TotalMessages ::= NumberType (MaxSize(5))            MacAddress ::= MacAddressType            ToneNumber ::= NumberType (MaxSize(5))            ToneDuration ::= NumberType (MaxSize(5))            VersionIdentifier ::= NumberType (MaxSize(5))            ErrorNumber ::= NumberType (MaxSize(8))             
 
         [0064]    
       
         
               
             
               
               
               
             
           
               
                 TABLE 2 
               
             
             
               
                   
               
               
                   
               
               
                 Request Response Primitive Summary. 
               
             
          
           
               
                 Primitive Name 
                 Alpha Numeric String Encoding 
                 DTMF String Encoding 
               
               
                   
               
               
                 AGENT LOGIN REQUEST 
                 SP, AGIC, DirectoryNumber 
                 AC35*DirectoryNumber 
               
               
                 AGENT LOGIN RESPONSE 
                 SP, AGTI, ResponseCode 
                 AC36*ResponseCode 
               
               
                 AGENT LOGOUT REQUEST 
                 SP, AGOC, DirectoryNumber 
                 AC37*DirectoryNumber 
               
               
                 AGENT LOGOUT RESPONSE 
                 SP, AGTI, ResponseCode 
                 AC38*ResponseCode 
               
               
                 BACK TO HELD REQUEST 
                 SP, BTHQ 
                 AC39 
               
               
                 BACK TO HELD RESPONSE 
                 SP, BTHR, ResponseGode 
                 AC40*ResponseCode 
               
               
                 CANCEL WORK TIMER REQUEST 
                 SP, CWTC, RequestCode 
                 AC41*RequestCode 
               
               
                 CANCEL WORK TIMER RESPONSE 
                 SP, CWTC, ResponseCode 
                 AC42*ResponseCode 
               
               
                 CONFERENCE REQUEST 
                 SP, CONQ 
                 AC43 
               
               
                 CONFERENCE RESPONSE 
                 SP, CONR, ResponseCode 
                 AC44*ResponseCode 
               
               
                 CONSULTATION CALL REQUEST 
                 SP, CCQ, DirectoryNumber 
                 AC45*DirectoryNumber 
               
               
                 CONSULTATION CALL RESPONSE 
                 SP, CCR, ResponseCode 
                 AC46*ResponseCode 
               
               
                 DIRECTED PICKUP REQUEST 
                 SP, DPQ, DirectoryNumber 
                 AC47*DirectoryNumber 
               
               
                 DIRECTED PICKUP RESPONSE 
                 SP, DPR, ResponseCode 
                 AC48*ResponseCode 
               
               
                 DO NOT DISTURB REQUEST 
                 SP, DNDC, RequestCode 
                 AC49*RequestCode 
               
               
                 DO NOT DISTURB RESPONSE 
                 SP, DNDC, ResponseCode 
                 AC50*ResponseCode 
               
               
                 FORCE PARTY RELEASE REQUEST 
                 SP, FPRQ 
                 AC51 
               
               
                 FORCE PARTY RELEASE RESPONSE 
                 SP, FPRR, ResponseCode 
                 AC52*ResponseCode 
               
               
                 GROUP PICKUP REQUEST 
                 SP, GPQ 
                 AC53 
               
               
                 GROUP PICKUP RESPONSE 
                 SP, GPR, ResponseCode 
                 AC54*ResponseCode 
               
               
                 HOLD REQUEST 
                 SP, HDQ 
                 AC55 
               
               
                 HOLD RESPONSE 
                 SP, HDR, ResponseCode 
                 AC56*ResponseCode 
               
               
                 MAKE BUSY REQUEST 
                 SP, MBYQ, RequestCode 
                 AC57*ResquestCode 
               
               
                 MAKE BUSY RESPONSE 
                 SP, MBYR, ResponseCode 
                 AC58*ResponseCode 
               
               
                 NIGHT SERVICE PICKUP REQUEST 
                 SP, NPQ, DirectoryNumber 
                 AC59*DirectoryNumber 
               
               
                 NIGHT SERVICE PICKUP RESPONSE 
                 SP, NPR, ResponseCode 
                 AC60*ResponseCode 
               
               
                 PLAY CONTINUOUS TONE REQUEST 
                 SP, PCTQ, ToneNumber 
                 AC70*ToneNumber 
               
               
                 PLAY CONTINUOUS TONE RESPONSE 
                 SP, PCTR, ResponseCode 
                 AC71*ResponseCode 
               
               
                 PLAY SHORT TONE REQUEST 
                 SP, PSTQ, ToneNumber, ToneDuration 
                 AC72*ToneNumber*ToneDuration 
               
               
                 PLAY SHORT TONE RESPONSE 
                 SP, PSTR, ResponseCode 
                 AC73*ResponseCode 
               
               
                 SWAP REQUEST 
                 SP, SWPQ 
                 AC74 
               
               
                 SWAP RESPONSE 
                 SP, SWPR, ResponseCode 
                 AC75*ResponseCode 
               
               
                 UN-PARK REQUEST 
                 SP, UPKC, DirectoryNumber 
                 AC76*DirectoryNumber 
               
               
                 UN-PARK RESPONSE 
                 SP, UPKR, ResponseCode 
                 AC77*ResponseCode 
               
               
                   
               
               
                   Where:    
               
               
                   DirectoryNumber ::= DirectoryNumberType (MaxSize(255))    
               
               
                   TotalMessages ::= NumberType (MaxSize(5))    
               
               
                   MacAddress ::= MacAddressType    
               
               
                   ToneNumber ::= NumberType (MaxSize(5))    
               
               
                   ToneDuration ::= NumberType (MaxSize(5))    
               
               
                   VersionIdentifier ::= NumberType (MaxSize(5))    
               
               
                   ErrorNumber ::= NumberType (MaxSize(8))    
               
               
                   ResponseCode ::= NumberType (MaxSize(16))    
               
               
                   RequestCode ::= NumberType (MaxSize(16))    
               
             
          
         
       
     
         [0065]    
       
         
               
             
               
               
               
             
           
               
                 TABLE 3 
               
             
             
               
                   
               
               
                   
               
               
                 Request Code Enumeration. 
               
             
          
           
               
                   
                 Request Code Description 
                 Request Code Value 
               
               
                   
                   
               
               
                   
                 Disable Feature 
                 0 
               
               
                   
                 Enable Feature 
                 1 
               
               
                   
                   
               
             
          
         
       
     
         [0066]    
       
         
               
             
               
               
               
             
           
               
                 TABLE 4 
               
             
             
               
                   
               
               
                   
               
               
                 Response Code Enumeration. 
               
             
          
           
               
                   
                 Response Code Description 
                 Response Code Value 
               
               
                   
                   
               
               
                   
                 Request Failed 
                 0 
               
               
                   
                 Request Successful 
                 1 
               
               
                   
                   
               
             
          
         
       
     
         [0067]    
       
         
               
             
               
               
             
               
             
               
               
             
               
             
               
               
             
               
             
               
               
             
               
             
               
               
             
               
             
               
               
             
               
             
               
               
             
               
             
               
               
             
               
             
               
               
             
               
             
               
               
             
               
             
               
               
             
               
             
               
               
             
               
             
               
               
             
               
             
               
               
             
               
             
               
               
             
               
             
               
               
             
               
             
               
               
             
               
             
               
               
             
               
             
               
               
             
               
             
               
               
             
               
             
               
               
             
               
             
               
               
             
               
             
               
               
             
               
             
               
               
             
               
             
               
               
             
               
             
               
               
             
               
             
               
               
             
               
             
               
               
             
           
               
                 TABLE 5 
               
               
                   
               
               
                   
               
               
                 SSSP Primitive Description. 
               
               
                   
               
             
             
               
                 AGENT LOGIN 
               
             
          
           
               
                 COMMAND 
                 A command sent from an EP to a GK to indicate that the EP wishes to become 
               
               
                   
                 an ACD Agent. 
               
               
                 REQUEST 
                 A request sent from an EP to a GK to indicate that the EP wishes to become an 
               
               
                   
                 ACD Agent. 
               
               
                 RESPONSE 
                 A response to a Agent Login Request indicating if the request was successful or 
               
               
                   
                 not successful. 
               
             
          
           
               
                 AGENT LOGOUT 
               
             
          
           
               
                 COMMAND 
                 A command sent from an EP to a OK to indicate that the EP wishes logout as an 
               
               
                   
                 ACD Agent. 
               
               
                 REQUEST 
                 A request sent from an EP to a GK to indicate that the EP wishes logout as an 
               
               
                   
                 ACD Agent. 
               
               
                 RESPONSE 
                 A response to a Agent Logout Request indicating if the request was successful 
               
               
                   
                 or not successful. 
               
             
          
           
               
                 AGENT 
               
             
          
           
               
                 INDICATION 
                 An indication sent from a GK to an EP indicating the current state of the EP as 
               
               
                   
                 an ACD Agent. The message indicates whether the EP is seen as an ACD 
               
               
                   
                 Agent or not as an ACD agent by the GK. 
               
             
          
           
               
                 BACK TO HELD 
               
             
          
           
               
                 COMMAND 
                 A command sent from an EP to the GK to instruct the OK to release the current 
               
               
                   
                 active call and swap back to the held call on consultation hold. 
               
               
                 REQUEST 
                 A request sent from an EP to the GK to instruct the GK to release the current 
               
               
                   
                 active call and swap back to the held call on consultation hold. 
               
               
                 RESPONSE 
                 A response to a Back to Held Request indicating if the request was successful or 
               
               
                   
                 not successful. 
               
             
          
           
               
                 CALL FORWARD 
               
               
                 ALWAYS 
               
             
          
           
               
                 INDICATION 
                 An indication sent from the GK to an on originating EP that the call has been 
               
               
                   
                 redirected to another endpoint due to the call forward always feature set by 
               
               
                   
                 original destination. 
               
             
          
           
               
                 CALL FORWARD 
               
               
                 BUSY 
               
             
          
           
               
                 INDICATION 
                 An indication sent from the GK to an originating EP that the call has been 
               
               
                   
                 redirected to another endpoint due to the call forward busy feature set by 
               
               
                   
                 original destination. 
               
             
          
           
               
                 CALL FORWARD 
               
               
                 NO ANSWER 
               
             
          
           
               
                 INDICATION 
                 An indication sent from the GK to an originating EP that the. call has been 
               
               
                   
                 redirected to another endpoint due to the call forward no answer feature set by 
               
               
                   
                 original destination. 
               
             
          
           
               
                 CALL FORWARD 
               
               
                 OUT OF SERVICE 
               
             
          
           
               
                 INDICATION 
                 An indication sent from the GK to an originating EP that the call has been 
               
               
                   
                 redirected to another endpoint due to the call forward out of service feature set 
               
               
                   
                 by original destination. 
               
             
          
           
               
                 CALLING LINE 
               
               
                 IDENTIFIER 
               
             
          
           
               
                 INDICATION 
                 An indication sent from the GK to an EP stating the destination alias 
               
               
                   
                 (DirectoryNumber) of the current destination that the Endpoint is in call with. 
               
             
          
           
               
                 CALLING 
               
               
                 PROGRESS 
               
             
          
           
               
                 INDICATION 
                 An indication from the GK to an EP stating that the GK is making a call on 
               
               
                   
                 behalf of that endpoint. 
               
             
          
           
               
                 CALLING WAITING 
               
             
          
           
               
                 INDICATION 
                 An indication from the GK to a busy EP that an EP has been camped on to it by 
               
               
                   
                 the system. 
               
             
          
           
               
                 CANCEL WORK 
               
               
                 TIMER 
               
             
          
           
               
                 COMMAND 
                 A command sent from an EP to the GK to indicate that it wishes to enable or 
               
               
                   
                 disable the Cancel Work Timer feature. 
               
               
                 INDICATION 
                 An indication sent from the GK to an EP indicating the current state of the work 
               
               
                   
                 timer (if the work timer is currently canceled or not). 
               
               
                 REQUEST 
                 A request sent from an EP to the GK to indicate that it wishes to enable or 
               
               
                   
                 disable the Cancel Work Timer feature. 
               
               
                 RESPONSE 
                 A response to a Cancel Work Timer Request indicating if the request was 
               
               
                   
                 successful or not successful. 
               
             
          
           
               
                 CONFERENCE 
               
             
          
           
               
                 COMMAND 
                 A command sent from an EP, that originated a consultation call, to the 
               
               
                   
                 GK/Multipoint Controller (MC) that it wishes to conference in the current party 
               
               
                   
                 into an existing conference that the originating EP is in. If the situation 
               
               
                   
                 involves starting a three party conference, then the party on consultation hold 
               
               
                   
                 will be brought into the active conference (adhoc conference expansion). 
               
               
                 INDICATION 
                 An indication sent from the GK/MC to an endpoint that the conference has. been 
               
               
                   
                 initiated or a new participant has entered the conference. 
               
               
                 REQUEST 
                 A request sent from an EP, that originated a consultation call, to the 
               
               
                   
                 GK/Multipoint Controller (MC) that it wishes to conference in the current party 
               
               
                   
                 into an existing conference that the originating EP is in. If the situation 
               
               
                   
                 involves starting a three party conference, then the party on consultation hold 
               
               
                   
                 will be brought into the active conference (adhoc conference expansion). 
               
               
                 RESPONSE 
                 A response to a Conference Request indicating if the request was successful or 
               
               
                   
                 not successful. 
               
             
          
           
               
                 CONSULTATION 
               
               
                 CALL 
               
             
          
           
               
                 COMMAND 
                 A command sent from an EP to the GK indicating that it wishes to place a 
               
               
                   
                 consultation call to a destination. 
               
               
                 REQUEST 
                 A request sent from an EP to the GK indicating that it wishes to place a 
               
               
                   
                 consultation call to a destination. 
               
               
                 RESPONSE 
                 A response to a Consultation Call Request indicating if the request was 
               
               
                   
                 successful or not successful. 
               
             
          
           
               
                 DIRECTED PICKUP 
               
             
          
           
               
                 COMMAND 
                 A command sent from an EP to the GK to indicate that it wishes to perform a 
               
               
                   
                 directed pickup. 
               
               
                 REQUEST 
                 A request sent from an EP to the GK to indicate that it wishes to perform a 
               
               
                   
                 directed pickup. 
               
               
                 RESPONSE 
                 A response to a Directed Pickup Request indicating if the request was 
               
               
                   
                 successful or not successful. 
               
             
          
           
               
                 DO NOT DISTURB 
               
             
          
           
               
                 COMMAND 
                 A command sent from an EP to the GK to indicate that it wishes to enable or 
               
               
                   
                 disable the Do Not Disturb feature. 
               
               
                 INDICATION 
                 An indication sent from the GK to an EP to indicate the status of the Do Not 
               
               
                   
                 Disturb feature. 
               
               
                 REQUEST 
                 A request sent from an EP to the GK to indicate that it wishes to enable or 
               
               
                   
                 disable the Do Not Disturb feature. 
               
               
                 RESPONSE 
                 A response to a Do not Disturb Request indicating if the request was successful 
               
               
                   
                 or not successful. 
               
             
          
           
               
                 ENDPOINT 
               
               
                 MAINTENANCE 
               
             
          
           
               
                 INDICATION 
                 The purpose of this message is to send any pertinent maintenance information 
               
               
                   
                 from an Endpoint to a GK. 
               
             
          
           
               
                 ERROR 
               
             
          
           
               
                 INDICATION 
                 An indication providing an entity feedback on an exception situation. The 
               
               
                   
                 supported error codes are listed in Table 6. 
               
             
          
           
               
                 FORCE PARTY 
               
               
                 RELEASE 
               
             
          
           
               
                 COMMAND 
                 A command sent from an EP to a GK to instruct the GK to keep the current 
               
               
                   
                 active call and release the party that was placed on consultation hold by the EP 
               
               
                 REQUEST 
                 A request sent from an EP to a GK to instruct the GK to keep the current active 
               
               
                   
                 call and release the party that was placed on consultation hold by the EP 
               
               
                 RESPONSE 
                 A response to a Force Party Release Request indicating if the request was 
               
               
                   
                 successful or not successful. 
               
             
          
           
               
                 GROUP PICKUP 
               
             
          
           
               
                 COMMAND 
                 A command sent from an EP to the GK to indicate that it wishes to perform a 
               
               
                   
                 group pickup. 
               
               
                 INDICATION 
                 An indication sent from the GK to an EP that the group pickup option is 
               
               
                   
                 available or unavailable to the EP 
               
               
                 REQUEST 
                 A request sent from an EP to the GK to indicate that it wishes to perform a 
               
               
                   
                 group pickup. 
               
               
                 RESPONSE 
                 A response to a Group Pickup Request indicating if the request was successful 
               
               
                   
                 or not successful. 
               
             
          
           
               
                 HOLD 
               
             
          
           
               
                 COMMAND 
                 A command sent from an EP to the GK to instruct the GK to place the current 
               
               
                   
                 call the EP is involved in on hold. 
               
               
                 INDICATION 
                 An indication sent from the GK to an EP that it has been placed on hold by the 
               
               
                   
                 GK. 
               
               
                 REQUEST 
                 A request sent from an EP to the GK that asks the GK to place the current call 
               
               
                   
                 the EP is involved in on hold. 
               
               
                 RESPONSE 
                 A response to a Hold Request indicating if the request was successful or not 
               
               
                   
                 successful. 
               
             
          
           
               
                 MAKE BUSY 
               
             
          
           
               
                 COMMAND 
                 A command sent from an EP to the GK to indicate that it wishes to enable or 
               
               
                   
                 disable the Make Busy feature. 
               
               
                 INDICATION 
                 An indication sent from a GK to an EP to indicate the status of the Make Busy 
               
               
                   
                 feature (whether the Make Busy feature is active or not). 
               
               
                 REQUEST 
                 A request sent from an EP to the GK to indicate that it wishes to enable or 
               
               
                   
                 disable the Make Busy feature. 
               
               
                 RESPONSE 
                 A response to a Make Busy Request indicating if the request was successful or 
               
               
                   
                 not successful. 
               
             
          
           
               
                 MESSAGE 
               
               
                 WAITING 
               
             
          
           
               
                 INDICATION 
                 An indication sent from the GK to an Endpoint to indicate that a message is 
               
               
                   
                 available for the user. 
               
             
          
           
               
                 NIGHT SERVICE 
               
               
                 PICKUP 
               
             
          
           
               
                 COMMAND 
                 A command sent from an EP to the GK to indicate that it wishes to pickup a 
               
               
                   
                 night call. 
               
               
                 REQUEST 
                 A request sent from an EP to the GK to indicate that it wishes to pickup a night 
               
               
                   
                 call. 
               
               
                 RESPONSE 
                 A response to a Night Service Pickup Request indicating if the request was 
               
               
                   
                 successful or not successful. 
               
             
          
           
               
                 PLAY CONTINUOUS 
               
               
                 TONE 
               
             
          
           
               
                 COMMAND 
                 A command from the GK to an EP to play a continuous audio tone. 
               
               
                 REQUEST 
               
               
                 RESPONSE 
                 A response to a Play Continuous Tone Request indicating if the request was 
               
               
                   
                 successful or not successful. 
               
             
          
           
               
                 PLAY SHORT TONE 
               
             
          
           
               
                 COMMAND 
                 A command from the GK to an EP to play an audio tone for a finite duration. 
               
               
                 REQUEST 
               
               
                 RESPONSE 
                 A response to a Play Short Tone Request indicating if the request was 
               
               
                   
                 successful or not successful. 
               
             
          
           
               
                 SWAP 
               
             
          
           
               
                 COMMAND 
                 A command sent from an EP to the GK to swap the call that the EP is involved 
               
               
                   
                 with to a camped on call or a call on hold. 
               
               
                 REQUEST 
               
               
                 RESPONSE 
                 A response to a Swap Request indicating if the request was successful or not 
               
               
                   
                 successful. 
               
             
          
           
               
                 UN-PARK 
               
             
          
           
               
                 COMMAND 
                 A command sent from an EP to the GK to retrieve a parked call. 
               
               
                 REQUEST 
                 A request sent from an EP to the GK to retrieve a parked call. 
               
               
                 RESPONSE 
                 A response to a Un-Park Request indicating if the request was successful or not 
               
               
                   
                 successful. 
               
               
                   
               
             
          
         
       
     
         [0068]                                  TABLE 6                           Error Codes for Error Indication.            Error               Number   Error Code Name   Error Code Description               0   Reserved   Not to be used       1   Conference_Unknown_Error   A conference operation has               failed. The reason for failure is               not known.                    
 Rules for Expandability 
 
         [0069]     There are two groups of rules for expanding the SSSP protocol, one for AlphaNumeric String Encoding and the other for DTMF String Encoding.  
         [0070]     When adding new PDUs, the new PDU is defined based on the definition of PrimitiveName as set forth above. For extending existing PDU&#39;s, parameter expansion follows the rule of simply adding additional ParameterExtenstions to the end of the PDU.  
         [0071]     Previously defined parameters are not removed from an existing PDU when new versions of a PDU are implemented, for backward compatibility. Endpoints supporting older versions of SSSP ignore parameters outside the scope of their known PDU templates.  
         [0000]     Alphanumeric String Encoding Expansion Rules  
         [0072]     The following is an example of expanding an existing PDU:  
         [0073]     Pre-Conditions: 
    1. The Consultation Call Command PDU is to be expanded to support an Alias Field.    
 
         [0075]     Additional Encoding:  
         [0076]     Parameter Extensions Required:  
                                                       1.   UNICODESTRINGTYPE ::= sequence of 16 bit characters               (UNICODE).           2.   Parameters ::= DirectoryNumberType | NumberType |               MacAddressType | UNICODESTRINGTYPE                      
 
         [0077]     SSSP PDU:  
                                                   SP,CCC,DirectoryNumber,AliasName           Where:DirectoryNumber ::= DirectoryNumberType (MaxSize(255))              AliasName ::= UNICODESTRINGTYPE (MaxSize(255))                      
 
 DTMF String Code Encoding Expansion Rules 
 
         [0078]     The following is a example of expanding an existing PDU:  
         [0000]     Pre-Conditions:  
         [0000]    
       
          1. The Hold Indication PDU will be expanded to support the IP address of the Music on Hold source to connect to. 
 
 Additional Encoding: 
 
       
     
         [0080]     Parameter Extensions Required:  
                                                       1.   IP4AddressType ::= IP4Parm ‘*‘ IP4Param ‘*‘ IP4Param ‘*‘               IP4Param               Where IP4Param ::= NumberType (MaxSize(3))           2.   Parameters ::= NumberType | IP4AddressType                      
 
         [0081]     SSSP PDU: 
    SP,HDI,MusicOnHoldAddress     Where: MusicOnHoldAddress ::=IP4AddressType 
 
 SSSP Transport 
   
 
         [0084]     Being an application layer protocol, SSSP can be carried within any non-standard data field of a H.225 or H.245 message. For the preferred embodiment set forth herein, SSSP messages are carried within the RAS Location Request (LRQ) and Location Confirmation (LCF) messages in the following examples.  
         [0000]     Using LRQ/LCF for SSSP Transport  
         [0085]     SSSP messages are carried within the nonStandardData field of the LRQ and LCF message. For simplicity the LRQ and LCF are not be used for address translation functionality and the sending and receiving entity regards the LRQ and LCF as a transport mechanism for SSSP only. An independent location request/response exchange is initiated for address translation services.  
         [0086]      FIG. 2  provides illustrations for common SSSP message exchange scenarios between signaling entities. The examples shown are requests from an EP  1  to a GK  4 . Though not shown, the procedures for GK  4  to EP  1  exchange scenarios are the same as for EP  1  to GK  4 .  
         [0087]      FIG. 2  ( a ) is a scenario where a SSSP message (SSSP 1 ) is sent from an EP  1  to the GK  4  with SSSP message piggybacking disabled. The GK  4  receives the message and acknowledges it with a LCF. This is a simple request and acknowledge exchange.  
         [0088]      FIG. 2  ( b ) provides an example where a SSSP request is lost or the acknowledgement for the SSSP request is lost. The timeout and retry mechanism specified by H.323 for LRQ/LCF/LRJ will determine this and the sender entity (EP  1 ) receives a time out error from the protocol stack.  
         [0089]      FIG. 2  ( c ) illustrates a situation where an application proceeds to send two SSSP requests in parallel. This scenario is similar to “windowing” techniques for network protocols.  
         [0090]      FIG. 2  ( d ) represents a “piggyback” situation. A SSSP message (SSSP 2 ) is sent in the acknowledgement LCF to save a round trip delay.  
         [0091]     LRQ/LCF Attribute Encoding  
                             TABLE 7                           Endpoint Sending a SSSP Message in a LRQ.                Attribute   Value                       RequestSeqNum   16 bit value           EndpointIdentifier   Same as the value returned in H.323               Registration Confirmation (RCF) Message           DestinationInfo   Endpoints E.164 alias           NonStandardData   SSSP message           ReplyAddress   Endpoint RAS transport Address           SourceInfo   Not included           CanMapAlias   False           GatekeeperIdentifier   Not included           Tokens   Not included           CryptoTokens   Not included           IntegrityCheckValue   Not included                      
 
         [0092]    
       
         
               
             
               
               
               
             
           
               
                 TABLE 8 
               
             
             
               
                   
               
               
                   
               
               
                 GK Responding to a SSSP Message in a LCF. 
               
             
          
           
               
                   
                 Attribute 
                 Value 
               
               
                   
                   
               
               
                   
                 RequestSeqNum 
                 16 bit value, corresponding to the 
               
               
                   
                   
                 ReguestSeqNum value in LRQ 
               
               
                   
                 CallSignalAddress 
                 IP = 0.0.0.0, Port = 0 
               
               
                   
                 RasAddress 
                 IP = 0.0.0.0, Port = 0 
               
               
                   
                 NonStandardData 
                 Not Included 
               
               
                   
                 DestinationInfo 
                 Not Included 
               
               
                   
                 DestinationCallInfo 
                 Not Included 
               
               
                   
                 DestinationType 
                 Not Included 
               
               
                   
                 RemoteExtensionAddress 
                 Not Included 
               
               
                   
                 AlternateEndpoints 
                 Not Included 
               
               
                   
                 Tokens 
                 Not Included 
               
               
                   
                 CryptoTokens 
                 Not Included 
               
               
                   
                 IntegrityCheckValue 
                 Not Included 
               
               
                   
                   
               
             
          
         
       
     
         [0093]    
       
         
               
             
               
               
               
             
           
               
                 TABLE 9 
               
             
             
               
                   
               
               
                   
               
               
                 GK Sending a SSSP Message in a LRQ. 
               
             
          
           
               
                   
                 Attribute 
                 Value 
               
               
                   
                   
               
               
                   
                 ReguestSeqNum 
                 16 bit value 
               
               
                   
                 EndpointIdentifier 
                 Not Included 
               
               
                   
                 DestinationInfo 
                 Endpoints E.164 alias 
               
               
                   
                 NonStandardData 
                 SSSP message 
               
               
                   
                 ReplyAddress 
                 GK RAS transport Address 
               
               
                   
                 SourceInfo 
                 Not included 
               
               
                   
                 CanMapAlias 
                 False 
               
               
                   
                 GatekeeperIdentifier 
                 Not included 
               
               
                   
                 Tokens 
                 Not included 
               
               
                   
                 CryptoTokens 
                 Not included 
               
               
                   
                 IntegrityCheckValue 
                 Not included 
               
               
                   
                   
               
             
          
         
       
     
         [0094]                                  TABLE 10                           Endpoint Responding to a SSSP Message in a LCF.                Attribute   Value                       RequestSeqNum   16 bit value, corresponding to the               ReguestSeqNum value in LRQ           CallSignalAddress   Endpoints Call Signaling Address           RasAddress   Endpoints RAS Address           NonStandardData   Not Included           DestinationInfo   Not Included           DestinationCallInfo   Not Included           DestinationType   Not Included           RemoteExtensionAddress   Not Included           AlternateEndpoints   Not Included           Tokens   Not Included           CryptoTokens   Not Included           IntegrityCheckValue   Not Included                        
 Message Sequence Charts 
 
         [0095]     The following sub-sections contain message sequence charts (MSCs) to provide guidance for the developer to implement SSSP in Endpoints and Gatekeepers. The format of the MSC is as follows:  
                                   MSC_MESSAGE ::=          H.225/H.245MESSAGENAME ‘(‘ H.225 ‘[‘ SSSPPDU ‘]’ ‘)’       Where:       MSC_MESSAGE is a message in the MSC       H.225/H.245MESSAGENAME is the primitive name for a       H.225/H.245MESSAGE (for example SETUP)       H.225 are parameters within the H.225 message       SSSPPDU represents the SSSP PDU                  
 
         [0096]     H.225 and H.245 parameters that are mandatory within the H.225 and H.245 message are not presented within the message diagrams of FIGS.  3  to  26 , for simplicity. In addition, repetitive and well known interactions, such as the H.245 sequence for basic call, are not presented. The following H.225 parameter clarification should be noted: 
        CALLx: Represents all the necessary identifiers to represent call x. This includes Call Reference Value (CRV), Call Identifier (CallID), and Conference Identifier (ConfID)     DDN: Destination Directory Number (Destination E.164 Alias)        
 
         [0099]     FIGS.  3  to  7  are examples of Call Independednt Supplementary Services, whereas the scenarios of FIGS.  8  to  26  are examples of Call Dependent Supplementary Services.  
         [0100]     In the scenario of  FIG. 3  the GK  4  informs EP 2  when messages are available or unavailable.  
         [0101]     The message sequence is as follows: 
        1. Assume that EP 2  has just registered with the GK  4  and the GK  4  has determined that EP 2  has messages available.     2. The GK  4  sends a Message Waiting Indication SSP PDU with a parameter &gt;0 to indicate that there is a message available for EP 2 . Since the GK  4  does not have the capability of sending the amount of messages available to a user, the number of messages is defaulted to 1. This follows the same behavior for the SX2000 (LW29)     3. Upon receiving the MWI, EP 2  provides visual indication to indicate that one or more messages are available. This could be in the form of a flashing Light Emitting Diode (LED) or an icon on the phone LCD display.     4. Once all the messages have been retrieved by the user at EP 2 , the GK  4  will send a MWI with a parameter of 0 to represent 0 messages available.     5. Upon receiving the MWI with parameter 0, the Endpoint should remove all visual indications representing a waiting message.     6. During the period of EP 2 &#39;s registration with the GK  4 , the GK  4  may determine that more messages are available. If messages are determined to be available sometime after the initial registration on EP 2 , the GK  4  shall follow the procedures outline in step 2 above.        
 
         [0108]     In the scenario of  FIG. 4  EP 2  provides its Maintenance Data to the GK  4  after Registration with the GK  4 .  
         [0109]     The message sequence is as follows: 
        1. After successful registration, EP 2  should provide the GK  4  with maintenance data. Endpoint  2  sends a Endpoint Maintenance Data Indication containing the VersionNumber of 1 (SSSP version 1) and MacAddress of 24*128*0*18*99*255.        
 
         [0111]      FIG. 5  shows ACD Agent Login and Logout.  
         [0112]     The message sequence is as follows:  
         [0000]     To Login:  
         [0000]    
       
         
           
              1. The user at EP 2  has selected the option at the endpoint to login as an ACD Agent.  
           
         
       
     
         [0114]     The Terminal will prompt the user to enter a DN representing the Agent ID, the example has a code of 7658. Once the code is entered, EP 2  will send an AGENT LOGIN COMMAND to the GK  4  containing a parameter of 7658. 
        2. The GK  4  will send back an AGENT LOGIN INDICATION to the Terminal indicating if the user has become an agent or not. A parameter of ‘1’ indicates that the user at EP 2  is considered an ACD Agent by the GK  4  (successful login). The EP should provide a visual indication (e.g. an icon) on the LCD display to indicate that the user is considered an agent. 
 
 To Logout: 
    1. The user then selects the Agent Logout option. The Terminal will prompt the user to enter a DN representing the Agent ID (example 7658). EP 2  sends an AGENT LOGOUT COMMAND with DirectoryNumber equal to the DN entered by the user.     2. The GK  4  will send back an AGENT LOGIN INDICATION to the Terminal indicating if the user is an Agent or not an Agent. A parameter of ‘0’ indicates that the GK  4  does not currently consider the user at EP 2  as an ACD Agent (successful logout). The EP should remove all visual indication related to an Agent (e.g. remove icon).        
 
         [0118]     In the scenario of  FIG. 6  Enable Make Busy, DND, and Cancel Work Timer features are shown.  
         [0119]     The message sequence is as follows: 
        1. The user at EP 2  selects an option at the endpoint to enable the MAKE BUSY, Do Not Disturb, or Cancel Work Timer. When the user selects the enable MAKE BUSY feature. EP 2  will send a MAKE BUSY COMMAND SSSP PDU to the GK  4 . When the user selects enable Do Not Disturb at the EP, EP 2  will send a DO NOT DISTURB COMMAND. EP 2  will send a CANCEL WORK TIMER COMMAND PDU to the GK  4  when the user selects enable Cancel Work Timer. Each of the PDUs will contain a parameter ‘1’ to represent enabling of the feature.     2. The GK  4  will send back the appropriate indications to the Terminal indicating the state of the command. If the feature is enabled, the parameter will be ‘1’. If the feature is still disabled a parameter ‘0’ will be sent.        
 
         [0122]     In the scenario of  FIG. 7  Make Busy, DND, and Cancel Work Timer features previously enabled are disabled.  
         [0123]     The message sequence is as follows: 
        1. The scenario is the reciprocal of the enable feature scenario listed above. The user selects the disable Make Busy, Do Not Disturb, or Cancel Work Timer option to disable the respective feature. The difference between the enabling and disabling scenario is the parameter sent in the SSSP PDU. A parameter of ‘0’ is sent in the MAKE BUSY COMMAND, DO NOT DISTURB COMMAND, or CANCEL WORK TIMER COMMAND to represent disabling of the feature.     2. The GK  4  will send back the appropriate indications to the Terminal indicating the state of the command. If the feature is enabled, the parameter will be ‘1’. If the feature is still disabled a parameter ‘0’ will be sent.        
 
         [0126]     In the scenario of  FIG. 8 , a Unpark a call parked by an attendant feature is shown.  
         [0127]     The message sequence is as follows: 
        1. An attendant has parked EP 2 . Assuming EP 2  is a H.323 Endpoint, the GK  4  will send a HOLD INDICATION SSSP PDU and a PAUSE message (TCS=0). EP 2  should provide the appropriate visual indication that represents hold.     2. The user of EP 1  is notified the parked call by some form of out of band method (such as an overhead page)     3. The user at EP 1  proceeds to un-park the call by selecting the un-park feature option and enters a un-park code of 1200.     4. EP 1  proceeds to initiate a call: 
            Sends an UN-PARK COMMAND SSSP PDU containing a parameter 1200 representing the un-park code.     The ARQ shall contain all mandatory parameters. In addition, the message shall not contain a destination alias. The message shall contain the GK  4  call signaling address as the destination call signaling address.    
            The SETUP message sent shall contain all mandatory parameters. The message shall not contain any source or destination addressing. 
            The CRV, Call ID, and Conference ID should be different than that for EP 2 .    
            5. Once the GK  4  receives the UN-PARK COMMAND, the GK  4  will send a CONNECT message to EP  1  and proceed to send a CALLING LINE IDENTIFIER INDICATION SSSP PDU and a RESUME message (TCS not 0) to EP 2 . EP 2  should display its default talk state display.     6. Normal H.245 procedures occur between EP 1  and EP 2  
 
 In the Scenario of  FIG. 9 a  Back to Held Feature is Shown. 
       
 
         [0138]     The message sequence is as follows: 
        1. The call between EP 1  and EP 2  is on hold and EP 1  is in consultation call with EP 3 .     2. The user at EP 1  decides that he/she wishes to go back to the call with EP 2  by selecting the Back to Held feature option.     3. EP 1  sends a BACK TO HELD COMMAND SSSP PDU to the GK  4  in a H245USERINPUTINDICATION.     4. The GK  4  drops the leg of the call between the GK  4  and EP 3      5. The GK  4  takes EP 2  off hold by sending a TCS not equal 0 to EP 2 , and also sends a CALLING LINE IDENTIFIER INDICATION to EP 2 . EP 2  should display its default talk state display. The GK  4  will also send a CALLING LINE IDENTIFIER SSSP PDU and TCS not equal 0 to EP 1 . EP 1  should display its default talk state display.     6. Normal H.245 connection procedures occur after both TCS not equal to 0. H.245 messages are sent from the GK  4 .        
 
         [0145]     In the scenario of  FIG. 10 a  Force Party Release feature is shown.  
         [0146]     The message sequence is as follows: 
        1. EP 1  has EP 2  on Consultation Hold. In addition EP 1  is in an active consultation call with EP 3 .     2. The user at EP 1  decides to drop the held call with EP 2  by selecting the force party release feature option.     3. EP 1  sends a FORCE PARTY RELEASE COMMAND SSSP PDU to the GK  4 .     4. The GK  4  proxies disconnect procedures with EP 2  and the half call with EP 2  is removed.     1. The GK  4  sends back a PLAY SHORT TONE COMMAND to EP 1  so it will provide audio indication of the outcome of the FORCE PARTY RELEASE COMMAND.        
 
         [0152]     In the scenario of  FIG. 11 a  Recall feature is shown (Single Call Scenario).  
         [0153]     The message sequence is as follows: 
        1. EP 1  has EP 2  on Consultation Hold. EP 1  is also in a consultation call with EP 3 .     2. EP 1  ends the call with EP 3 .     3. Normal disconnect procedures occur between EP 1  and EP 3 . EP 2  is still on hold.     4. The GK  4  proceeds to offer a call to EP 1  after the disconnect on behalf of EP 2 . The CRV, CallID, and ConfID should be the same as the original call between EP 1  and EP 2 .     5. EP 1  sends back ALERTING to indicate that EP 1  is ringing. However, the ALERTING message shall not be passed to EP 2      6. Once the user at EP 1  answers the call, EP 1  sends a CONNECT message back to the GK  4 . The GK  4  proceeds to remove EP 2  off hold and normal H.245 connection procedures occur.        
 
         [0160]     In the scenario of  FIGS. 12 and 13  Call transfer with consultation call is shown.  
         [0161]     The message sequence is as follows: 
        1. Assume EP 1  and EP 2  are in a call (CALL 1 ). The user at EP 1  wants to transfer the user on EP 2  to EP 3 .     2. The user at EP 1  selects the TRANS/CONF option or HOLD key.     3. EP 1  provides a prompt to allow the user to enter a DN. Digits in this state are not taken as DTMF requests.     4. The user at EP 1  enters the DN for EP 3  and presses SEND. After pressing SEND, any additional digits entered are be considered as DTMF requests by the EP.     5. EP 1  sends a CONSULTATION CALL COMMAND PDU containing the DN=1003.     6. The GK  4  sends a PAUSE (TCS=0) command to both EP 1  and EP 2 . EP 2  receives a HOLD INDICATION SSSP PDU prior to the PAUSE message. EP 2  should provide some form of visual indication to inform the user at EP 2  that he/she has been put on hold.     7. The GK  4  places a new call to EP 3 . EP 3  should have a different CRV and Call ID than EP 1 , and the same Conference ID as EP 1 . Once the SETUP message is sent to EP 3  from the GK  4 , the GK  4  will send a CALL PROGRESS INDICATION PDU containing DN=1003 back to EP 1 . EP 1  should provide visual indication to the user that a call is proceeding with EP 3  who&#39;s DN is 1003.     8. Once EP 3  is ringing (ALERTING), the GK  4  instructs EP 1  to play local ringing through a PLAY TONE COMMAND SSSP PDU. Assume that a ToneNumber of 5 represents local ringing.     9. Once EP 3  answers the consultation call, the GK  4  disables local ringing by sending a PLAY TONE COMMAND SSSP PDU with a ToneNumber of 0. In addition, the GK  4  will send a CALLING LINE IDENTIFIER SSSP PDU to EP 1 . EP 1  should display the default talk state display at this point.     10. The GK  4  sends a RESUME (TCS not 0) message to EP 1  and normal H.245 call procedures occur between EP 1  and EP 3 .     11. The user at EP 1  completes the call transfer by releasing the call. EP 1  sends a RELEASE COMPLETE to the GK  4 . The GK  4  proxies the disconnect so only the leg between the GK  4  and EP 1  is dropped.     12. The GK  4  sends a CALLING LINE IDENTIFIER INDICATION SSSP PDU (containing the DN of EP 2 ) to EP 3  and a CALLING LINE IDENTIFIER INDICATION SSSP PDU (containing the DN of EP 3 ) to EP 2 . EP 2  and EP 3  should display their default talk state display.     13. The GK  4  pauses EP 3  with a PAUSE message     14. The GK  4  sends a RESUME message to both EP 2  and EP 3 , and normal H.245 call procedures occur.        
 
         [0176]     In  FIGS. 14 and 15  Blind transfer with consultation call is shown.  
         [0177]     The message sequence is as follows: 
        1. Steps 1 to 7 from  FIGS. 12 and 13  are followed.     2. Once EP 3  is ringing (ALERTING), the GK  4  instructs EP 1  to play local ringing through a PLAY TONE COMMAND SSSP PDU. Assume that a ToneNumber of 5 represents local ringing.     3. The user at EP 1  decides to complete the call transfer at this point by hanging up the call (blind transfer). On reception of RELEASE COMPLETE, the GK  4  will send a PLAY TONE COMMAND to disable ringing. Note, the user may decide to hang-up prior to hearing local ringing to initiate the blind transfer. Basically, before EP 1  receives the PLAY TONE COMMAND. If this is the case, a PLAY TONE COMMAND will not be sent to EP 1  and the sequence continues with NSM(CALL 2 , [SP,CPI, 1002]).     4. The GK  4  sends a CALL PROGRESS INDICATION SSSP PDU (containing the DN of EP 2 ) to EP 3 . EP 3  should display the proper visual indication to show that a call is proceeding with EP 2 .     5. The GK  4  sends a CALL PROGRESS INDICATION SSSP PDU (containing the DN of EP 3 ) to EP 2 . EP 2  should display the proper visual indication to show that a call is proceeding with EP 3 . The GK  4  will also send a PLAY TONE COMMAND to EP 2  so that it would play ringing tone to the user.     6. Once the user at EP 3  answers the call, EP 3  sends a CONNECT message to the GK  4 .     7. The GK  4  instructs EP 2  to stop ringing with a PLAY TONE COMMAND. The GK  4  also sends a RESUME (TCS not 0) message to EP 2 , and normal H.245 call procedures occur.     8. The GK  4  sends A CALLING LINE IDENTIFIER SSSP PDU to EP 2  and EP 3 . EP 2  and EP 3  should display the default talk state display at this point.        
 
         [0186]     In the scenario of  FIG. 16  Call Forward Out of Service, Busy, or Always is shown.  
         [0187]     The message sequence is as follows: 
        1. The user at EP 1  wants to make a call to EP 2  and proceeds with normal call operations     2. EP 2  is either Out of Service, Busy, or has Call Forward Always activated. Assume the call forwarding destination is set to EP 3      3. The GK  4  re-routes the call to EP 3  and normal call procedures between EP 1  and EP 3  occur with the following exception. Once the SETUP message is sent to EP 3 , the GK  4  will send either a CALL FORWARD OUT OF SERVICE INDICATION (CFOI), CALL FORWARD BUSY INDICATION (CFBI), or CALL FORWARD ALWAYS INDICATION (CFAI) SSSP PDU to EP 1  in a NSM. The message sent depends on state at EP 2 . EP 2  should have a different CRV than EP 1 , and the same Call ID and conference ID as EP 1 . EP 1  should provide the correct visual indication stating the type of call forwarding that has occurred and to which destination the call has been forwarded to.     4. Once the user at EP 3  answers the call, a CONNECT message is sent by EP 3  to EP 1  through the GK  4 . At this point, normal H.245 procedures occur. In addition, the GK  4  sends a CALLING LINE IDENTIFIER INDICATION SSSP PDU to EP 1 . EP 1  should display its default talk state display at this point.        
 
         [0192]     In the scenario of  FIG. 17  Call Forward No Answer is shown.  
         [0193]     The message sequence is as follows: 
        1. The user at EP 1  wants to make a call to EP 2  and proceeds with normal call operations     2. No user is available to answer the call at EP 2  and the ring timer in the GK  4  expires. Assume Call Forward No Answer is set for EP 2  with a forwarding destination of EP 3 . The GK  4  proceeds to release the half call with EP 2 .     3. The GK  4  makes a new call with EP 3 . Once the SETUP message is sent to EP 3 , the GK  4  will send a CALL FORWARD NO ANSWER INDICATION with the DN of EP 3  to EP 1 . Assume EP 1  is still ringing. EP 2  should have a different CRV than EP 1 , and the same Call ID and conference ID as EP 1 . EP 1  should provide the correct visual indication stating the type of call forwarding that has occurred and to which destination the call has been forwarded to.     4. Normal call operations between EP 1  and EP 3  occur once EP 3  sends a CONNECT message to the GK  4 . EP 1  should display its default talk state display when the CALLING LINE IDENTIFIER INDICATION is received by the Endpoint.        
 
         [0198]     In the scenario of  FIGS. 18 and 19  System Camp-on and Swap is shown.  
         [0199]     The message sequence is as follows: 
        1. EP 2  and EP 3  are in a call.     2. The user at EP 1  proceeds to make a new call to EP 3 . Note the CRV, Call ID, and Conference ID used by EP 1  is different than the one used for the call between EP 2  and EP 3 .     3. Assume system camp-on is enabled for the user of EP 1 . The GK  4  determines EP 3  is busy and sends a CALL WAITING INDICATION SSSP PDU (with the DirectoryNumber Parameter 1001) to EP 3 . EP 3  should provide some form visual indication indicating a camped on call to the user. The GK  4  will also instruct EP 3  to play a short tone to provide audio indication to the user.     4. The GK  4  sends a CONNECT message to EP 1  and proceeds to PAUSE the call initiated by EP 1 . A HOLD INDICATION is sent to EP 1  from the GK  4  and a PAUSE (TCS=0) message. EP 1  should provide some form of visual indication to indicate that EP 3  has been placed on hold by the system.     5. The user at EP 3  decides to swap the current call to EP 1  by selecting the swap feature option.     6. EP 3  sends a SWAP COMMAND SSSP PDU to the GK  4 . The GK  4  proceeds to place EP 2  on hold by sending a HOLD INDICATION SSSP PDU and a PAUSE message. EP 2  should provide some form of visual indication to the user that they have been placed on hold.     7. The GK  4  sends a PAUSE message to EP 3      8. The GK  4  sends a CALLING LINE IDENTIFIER INDICATION to EP 1 . EP 1  should provide its default talk state display at this point.     9. The GK  4  sends a CALLING LINE IDENTIFIER INDICATION to EP 3 . EP 1  should provide its default talk state display at this point.     10. The GK  4  sends a RESUME (TCS not 0) to both EP 1  and EP 3  and normal H.245 call procedures follow.        
 
         [0210]     In the scenario of  FIGS. 20 and 21  Adhoc Conference Expansion is shown.  
         [0211]     The message sequence is as follows: 
        2. The user at EP 1  completes the conference by selecting the conference feature option.     3. EP 1  sends a CONFERENCE COMMAND SSSP PDU in a NSM to the GK  4 .     4. The GK  4  pauses EP 1  and EP 3  by sending a PAUSE message to both EP 1  and EP 3 .     5. The GK  4  sends a CONFERENCE INDICATION SSSP PDU to EP 1 , EP 2 , and EP 3 . Each endpoint shall provide some form of visual indication to the user to inform him/her that a conference event has occurred. The PLAY SHORT TONE COMMAND SSSP PDU is also sent to each EP after CONFERENCE INDICATION to provide each user with a comfort tone (100 ms of tone in this example).     6. The GK  4  sends a RESUME message to EP 1 , EP 2 , and EP 3 . The GK  4  will proxy the H.245 negotiation to move EP 1 , EP 2 , and EP 3  to the conference bridge. This involves negotiating all the necessary Terminal Capability, Master Slave, and Open Logical exchanges on behalf of the conference bridge to get EP 1 , EP 2 , and EP 3 &#39;s RTP stream to the bridge.        
 
         [0217]     In the scenario of  FIGS. 22 and 23  Conference Invite is shown.  
         [0218]     The message sequence is as follows: 
        1. Assume EP 1  EP 2 , and EP 3  are in a conference. The user at EP 1  wishes to invite the user at EP 3 B into the conference.     2. The user at EP 1  selects the consultation call option.     3. EP 1  provides a prompt to allow the user to enter digits or the user can select a feature option that does not require a prompt for digits. Digits in this state are not taken as DTMF requests.     4. The user at EP 1  enters the address for EP  3 B. After entering the address for EP 3  B, any additional digits entered shall be considered as DTMF requests.     5. EP 1  sends a CONSULTATION CALL COMMAND PDU containing the DN=1003.     6. The GK  4  sends a PAUSE (TCS=0) command to both EP 1 .     7. The GK  4  places a new call to EP 3 B. EP 3 B should have a different CRV and Call ID than EP 1 &#39;s original call, and the same Conference ID as EP 1 . Once the SETUP message is sent to EP  3 B from the GK  4 , the GK  4  will send a CALL PROGRESS INDICATION PDU containing DN=1003 back to EP 1 . EP 1  should provide visual indication to the user that a call is proceeding with EP 3  who&#39;s DN is 1004.     8. Once EP  3 B is ringing (ALERTING), the GK  4  instructs EP 1  to play local ringing through a PLAY TONE COMMAND SSSP PDU. Assume that a ToneNumber of 5 represents local ringing.     9. Once EP  3 B answers the consultation call, the GK  4  disables local ringing by sending a PLAY TONE COMMAND SSSP PDU with a ToneNumber of 0. In addition, the GK  4  will send a CALLING LINE IDENTIFIER SSSP PDU to EP 1 . EP 1  should display the default talk state display at this point.     10. The GK  4  sends a RESUME (TCS not 0) message to EP 1  and normal H.245 call procedures occur between EP 1  and EP  3 B.     11. The user at EP 1  completes the conference invite by selecting the conference feature     12. EP 1  sends a CONFERENCE COMMAND SSSP PDU in a H245USERINPUTINDICATION to the GK  4 .     13. The GK  4  pauses EP 1  and EP  3 B by sending a PAUSE message to both EP 1  and EP 4   3 B     14. The GK  4  sends a CONFERENCE INDICATION SSSP PDU to EP 1 , EP 2 , EP 3 , and EP  3 B. Each endpoint should provide some form of visual indication to the user to inform him/her that a conference event has occurred. The PLAY SHORT TONE COMMAND SSSP PDU is also sent to each EP after CONFERENCE INDICATION to provide each user with a comfort tone (100 ms of tone in this example).     15. The GK  4  sends a RESUME message to EP 1  and EP  3 B. The GK  4  will proxy the H.245 negotiation to move EP 1  and EP  3 B to the conference bridge.        
 
         [0234]     In the scenario of  FIG. 24 a  Group Pickup feature is shown.  
         [0235]     The message sequence is as follows: 
        1. EP 1  calls a pickup group and assume EP 1  is in the alerting state.     2. The GK  4  informs EP 2  that a group pickup is available by sending it a GROUP PICKUP INDICATION SSSP PDU. EP 2  should provide visual indication to the user at EP 2  of an available group pickup.     3. The user at EP 2  wishes to perform a group pickup and selects the directed pickup feature option at EP 2 .     4. EP 2  proceeds to initiate a call: 
            Send a GROUP PICKUP COMMAND SSSP PDU to the GK  4      The ARQ shall contain all mandatory parameters. In addition, the message shall not contain a destination alias. The message shall contain the GK  4  call signaling address as the destination call signaling address.     The SETUP message sent shall contain all mandatory parameters. The message shall not contain any source or destination addressing.     The CRV, Call ID, and Conference ID should be different than that for EP 1 .    
            5. The GK  4  sends a CONNECT message to EP 2  and EP 1 .     6. Normal H.245 call procedures between EP 1  and EP 2         
 
         [0246]     In the scenario of  FIG. 25 a  Directed Pickup feature is shown.  
         [0247]     The message sequence is as follows: 
        1. EP 1  calls EP 3  and both EP 1  and EP 3  are in the alerting state.     2. The user at EP 2  wishes to perform a directed pickup and selects the directed pickup feature option at EP 2  and then enters the pickup code.     3. EP 2  proceeds to initiate a call: 
            Send a DIRECTED PICKUP COMMAND SSSP PDU containing the pickup code (6500) as a parameter.     The ARQ shall contain all mandatory parameters. In addition, the message shall not contain a destination alias. The message shall contain the GK  4  call signaling address as the destination call signaling address.     The SETUP message sent shall contain all mandatory parameters. The message shall not contain any source or destination addressing.     The CRV, Call ID, and Conference ID should be different than that for EP 1 .    
            4. The GK  4  releases the half call between EP 2 .     5. The GK  4  sends a CONNECT message to EP 2  and EP 1 .     6. Normal H.245 call procedures between EP 1  and EP 2 .        
 
         [0258]     In the scenario of  FIG. 26 a  Night Service feature is shown.  
         [0259]     The message sequence is as follows: 
        1. Assume Night Service is active.     2. An incoming call to the GK  4  from EP 1  is in progress. EP 1  is in the alerting state.     3. An out of band indication representing a night call is occurring.     4. The user at EP 2  wishes to perform a night service pickup and selects the night service feature option at EP 2  and then enters the night service code.     5. EP 2  proceeds to initiate a call: 
            Send a NIGHT SERVICE PICKUP COMMAND SSSP PDU containing the night service code (7000) as a parameter     The ARQ shall contain all mandatory parameters. In addition, the message shall not contain a destination alias. The message shall contain the GK  4  call signaling address as the destination call signaling address.     The SETUP message sent shall contain all mandatory parameters. The message shall not contain any source or destination addressing.     The CRV, Call ID, and Conference ID should be different than that for EP 1 .    
            6. The GK  4  sends a CONNECT message to EP 2  and EP 1 .     7. Normal H.245 call procedures between EP 1  and EP 2 .        
 
       User Interface Support for SSSP  
       [0271]     A complicated state machine is traditionally required to keep user interfaces (UIs) in the correct context for displaying information related to a functionally based supplementary services protocol. The following portion of this disclosure provides a simplified implementation for providing a UI at an Endpoint for the purpose of display normal call and feature information related to a SSSP enabled device.  
         [0272]     The state handling required for UI display is simplified in the present invention by dividing the display into two views: a feature display, which handles all feature related displays needed during SSSP interaction, and a default display, which handles all non-SSSP related display information. By flipping between feature and default displays according to a small finite set of rules, an Endpoint can provide an effective UI without a need for a completed state machine, as set forth below.  
         [0273]     The term Default Display represents the normal status display view that a H.323 Terminal supports (if the Terminal has a display capability). For optimal support of SSSP feature indications, according to the present invention the H.323 Terminal supports an additional view (referred to herein as the Feature Display) for display of feature information. The Feature Display is driven by SSSP indications and has the same visual dimensions as the Default Display. According to the invention, the H.323 terminal runs both views (Default and Feature) at any given time. Both displays are updated in real time. However, only one display is placed in the foreground (displayed) to the user at any given time. Based on set rules, the Feature Display and Default Display toggle back and forth from foreground to background.  
         [0274]      FIG. 28 , along with the information from Table 11, provides a summary of the logic required for toggling between the Default Display and Feature Display. As seen in  FIG. 28 , there is a specific set of messages and events that cause the Default or Feature display to be placed into the foreground. The Feature Display is placed in the foreground on reception of specific SSSP indications listed in the table. The Default display is only placed in the foreground under a condition where the user ends the call, or on reception of a CALLING LINE IDENTIFIER INDICATION SSSP message.  
                             TABLE 11                           Messaging that Changes Feature and Default Display.            Message   Back to Feature Display   Back to Default Display               CPI, DirectoryNumber   Terminal displays:   Drop call, CLDI.           Line1: Call Proceeding           Line2: {DirectoryNumber}           on the display       HLDI   Terminal displays:   Drop call, CLDI           Line 1: ON HOLD       CFBI, DirectoryNumber   The Terminal can optionally display:   Drop call, CLDI           Line1: CF—Busy           Line2: {Directory Number}       CFOI, DirectoryNumber   The Terminal can optionally display:   Drop call, CLDI           Line1: CF—Out of Service           Line2: {Directory Number}       CFAI, DirectoryNumber   The Terminal can optionally display:   Drop call, CLDI           Line1: CF—Always           Line2: {Directory Number}       CFNI, DirectoryNumber   The Terminal can optionally display:   Drop call, CLDI           Line1: CF—No Answer           Line2: {Directory Number}       CONI   The Terminal will display:   Drop call, CLDI           Line1: In Conference       CWI, DirectoryNumber   The Terminal will display:   Drop call, CLDI           Line1: Call Waiting           Line2: {Directory Number}       ERRI, ErrorNumber   The display text will be dependent on the   Drop call, CLDI           ErrorNumber.           By default the Terminal will display:           Line1: Error − {Error#}           Where {Error#} is the value of           ErrorNumber.           For ErrorNumber 1           (Conference_Unknown_Error), the           Terminal will display:           Line 1: Conference           Line2: Operation Failed                    
         [0275]     The contents of the display shown in Table 11 is for example purposes only. The display text may be customized to the capability of the end device. In addition, the terms “line1:” and “line2:” represent the line location to display the text on the Terminal.  
         [0276]      FIG. 29  illustrates how the principles discussed above provide an effective user interface, having regard to a Call Forward message exchange which illustrates toggling between the Default Display and Feature Display. 
        1. Scenario starts with a user at EP 1  calling a user at EP 3 .     2. The Default Display is in the foreground at EP 1      b  3 . The user at EP 1  dials  1002  and presses send.     4. The Default Display is updated to indicate that the call is proceeding as usual     5. The GK  4  determines EP 2  is busy and reroutes the call to EP 3      6. The GK  4  sends CALL FORWARD BUSY INDICATION with DN  1003  to EP 1      7. EP 1  updates the Feature Display view with “CALL FORWARD BUSY:  1003 ”. In addition, it sees that this is a message listed on Table 11 that will cause the Feature Display to move to the foreground. EP 1  flips the Feature Display to the foreground.     8. The user at EP 3  sees and incoming call and answers the call. EP 3  is showing the Default Display and providing to usual basic call feedback to the user.     9. The GK  4  passes the CONNECT message to EP 1      10. EP 1  updates its Default Display indicating the call is connected to  1002 . For example, ¢In Call:  1002 ”. EP 1  still believes it is talking to EP 2  since it is not interpreting the CALL FORWARD BUSY INDICATION. It is simply displaying it. The Default Display is in the background so the user still sees “CALL FORWARD BUSY:  1003 ”.     11. The GK  4  will send a CALLING LINE IDENTIFIER INDICATION (CLDI) message to EP 1  after the CONNECT message     12. EP 1  sees the CLDI message and updates its current called party to  1003 . It then updates the Default Display to say “In Call:  1003 ”. Since CLDI is a message that will cause the Default Display to be moved to the foreground, EP 1  does so and the user sees the correct visual display. Why CLDI updates the default display will be shown in Section  0 .     13. Note: Feature Display still shows “CALL FORWARD BUSY:  1003 ”. However, it is in the background and not shown to the user. 
 
 Override of Operations from Indication Messages 
         
         [0290]     When the Terminal receives a message from Table 11, it cancels any existing operation that has been started. Then the Terminal displays the correct Feature or Default display in the foreground.  
         [0291]     For example: 
        1. Terminal 1  is in call with Terminal 2      2. The user on Terminal 2  presses a key and a list appears on Terminal 2 &#39;s display. The user on Terminal 2  is undecided on what to do and the list stays on the screen.     3. In the meantime, a HDI SSSP message is sent to Terminal 2 .     4. Terminal 2  then cancels the list, brings the Feature Display to the foreground and displays a hold message on the Feature Display. 
 
 Indications that Affect State Value 
       
 
         [0296]     The discussion above illustrates how SSSP indications that manipulate the Feature Display so as to toggle the Feature Display from background to foreground. The rest of the SSSP indications change internal parameter/state values, particularly if a value is set or not.  
                         TABLE 12                           Messaging Affecting State.            Message   Change               CLDI,   Terminal updates the current party called default       DirectoryNumber   display with a directory number of           {DirectoryNumber}       MWI, 1 or MWI, 0   Terminal displays message waiting icon or           removes the message waiting icon. This could be           simply flashing the LED or have a specific icon           on the display to represent message waiting       AGTI, 1 or AGTI, 0   Terminal displays the agent icon on the display or           removes the agent icon off its display       MBYI, 1 or MBYI, 0   Terminal updates its menu item to display make           busy feature is enabled or disabled       DNDI, 1 or DNDI, 0   Terminal updates its menu item to display the Do           Not Disturb feature is enabled or disabled       CWTI, 1 or CWTI, 0   Terminal updates its menu item to display the           cancel work timer feature is enabled or disabled       GPI, 1 or GPI, 0   Terminal displays a group pickup icon on the           display or removes the group pickup icon from           the display                  
 
         [0297]     As shown in Table 12, the indications sent to the Endpoint cause the endpoint to update its current parameter/state value for a particular feature. This includes whether to turn on an icon or off an icon, showing if a feature is enabled or disabled in a feature list, or updating it&#39;s current calling line identifier display. On reception of a message listed in Table 12, the Endpoint follows the procedures listed in  FIG. 30 . Following the example discussed above with reference to  FIG. 29 , EP 1  receives a CLDI message from the GK  4 . EP 1  follows the rules in Table 12 and updates its parameter that stores the calling line identifier from  1002  to  1003  refreshes the Default Display. The Default Display is still in the background. EP 1  checks the rules stated by Table 11 and the Default Display is brought up to the foreground.  
         [0298]     Alternatives and variations of the invention are possible. For example, although H.2323 protocol is set forth as the existing protocol within which SSSP is transported, the principles of SSSP may be applied to ISDN, Ti or any other user-to-user communication protocol (i.e. any protocol which supports transparent tunneling of information. Also, although the specific implementation examples are directed to exchanges between the Gatekeeper and Endpoints, it will be understood by a person of skill in the art that SSSP may also be extended to communications between Endpoints. All such alternative embodiments and variations are believed to be within the sphere and scope of the claims appended hereto.