Patent Publication Number: US-6993030-B2

Title: AAL2 negotiation procedure

Description:
RELATED APPLICATION 
     This application is a continuation of U.S. patent application Ser. No. 09/140,865, filed Aug. 27, 1998 now U.S. Pat. No. 6,788,691. 
    
    
     FIELD OF THE INVENTION 
     The invention relates to digital communications networks, and particularly, although not exclusively to an arrangement and method for enabling a plurality of channels to occupy a single asynchronous transfer mode (ATM) connection. 
     BACKGROUND TO THE INVENTION 
     The known asynchronous transfer mode (ATM) transmission technique is a modern telecommunications switching technique which is able to switch connections for a wide range of different data types at a wide range of different bit rates. ATM technology provides a flexible form of transmission which allows various types of service traffic data, eg. voice data, video data, or computer generated data to be multiplexed together onto a common physical means of transmission, Currently, several trends are encouraging the widespread introduction of ATM; for example the availability of high speed, low error rate communication links between switching centers, an availability of technology to digitize video and speech, and pressure to reduce operating costs by integrating previously separate telephony and data network. ATM technology allows speech data, video and inter-computer data to be carried across a single communications network. The information carried in each of these services is reduced to digitized strings of numbers which are transmitted across such a communications network from point to point. 
     Referring to  FIG. 1  herein, there is illustrated schematically a pair of known interworking functions  101  and  102  connected by an ATM virtual channel connection (ATM VCC)  103  across an ATM network  100 .  FIG. 1  illustrates a pair of interworking functions which may be residing at a pair of distinct telecoms resources eg switches, cross connects, comprising processing means and memory means. It will be understood by those skilled in the art that a plurality of interworking functions may be interconnected over a plurality of ATM VCC. Incoming to first interworking function  101  are, for example, a plurality of digitized voice signals multiplexed together using the E1 or T1 mutiplexing systems. First and second interworking functions  101  and  102  are configured to convert data arriving in a plurality of forms and conforming to a plurality of different data standards into a form suitable for transmission over ATM VCC  103  across ATM network  100 . Interworking functions  101  and  102  are also configured to perform conversion of data sets across ATM network  100  back into a plurality of different data standards. Each of these incoming channels may carry data at a bit rate of 64 kilobits per second (kbits/s). 
     There is a financial cost associated with leasing sufficient bandwidth between interworking functions  101  and  102  to transmit a plurality of uncompressed 64 kbits/s channels down a single ATM virtual circuit  103 . Therefore, it is known to apply a range of different data compression techniques in order to make more efficient use of the available band width. For example, the known G series data compression techniques can be used to compress streams of data having a bit rate of 64 kbits/s down to bit rates of 40 kbits/s or 8 kbits/s. In addition, speech activity detection (SAD) techniques can be used to suppress pauses in speech data allowing other data to be inserted in the gaps. After compression, there may exist a plurality of compressed 8 kbits/s data to be transferred between interworking functions  101  and  102  across ATM virtual channel  103  via ATM network  100 . The plurality of compressed channels of data may represent a plurality of calls between a plurality of users. 
     Referring to  FIG. 2  herein, there is illustrated schematically first and second interworking functions  101 ,  102  represented as a set of functional layers. Each interworking function comprises the following protocol stack of functional layers:
         a Service Specific Conversion Sub-layer (SSCS)  201  into which compressed voiced data are input and output;   a Common Part Sub-layer (CPS)  202 ;   an ATM Sub-layer  203 ; and   a Physical Sub-layer  204 .       

     The set of functional layers  201  to  204  are well known in the art. Each functional layer within the protocol stack is configured to exchange information with the functional layer above it and the functional layer below it. The exchange of information between functional layers within the protocol stack enables each functional layer to provide a service for the functional layer immediately above it. Each functional layer can be considered to exchange information directly with the same functional layer within a protocol stack residing within a distant interworking function across a virtual channel. The exchange of information between interworking functions  101  and  102  is actually effected by the exchange of information across a physical connection between physical sub-layers  204  and  208 . Compressed voice data which are input into the interworking function  101  by the Service Specific Conversion Sub-layer  201  are transferred across an ATM network to the remote second interworking function  102  which comprises a similar protocol stack to interworking function  101 . The output of Service Specific Conversion Sub-layer  205  of first interworking function  102  is compressed voice data. 
     Whilst transmission of compressed voice data is shown in one direction in  FIG. 1 , the protocol stacks are bi-directional and transmission can occur in both directions between first and second interworking functions  101 ,  102 . 
     In  FIG. 2  herein there is illustrated a single Service Specific Conversion Sub-layer  201  associated with interworking function  101 . In a real network there may be a plurality of such Service Specific Conversion Sub-layers receiving a plurality of compressed voice data channels. The Common Part Sub-layer  202  is configured to receive a plurality of compressed voice data channels from the plurality of Service Specific Conversion Sub-Layers and multiplex the plurality of compressed voice data channels together. The combination of Service Specific Conversion Sub-layers  201  and Common Part Sub-layer  202  in interworking function  101  are also known in the prior art as ATM Adaption Layer Type 2 (AAL2). 
     In order to make best use of the available band width over a single ATM. VCC it is known to have a plurality of channels carrying a plurality of, for example, compressed voice data channels. In order to be able to carry a plurality of separate streams of digital data across a network using a plurality of ATM AAL 2 channels over a single ATM virtual channel connection (VCC), there is a need to be able to identify individual ATM AAL 2 channels at both interworking functions. 
     SUMMARY OF THE INVENTION 
     Specific embodiments and methods according to the present invention aim to facilitate the establishment of a plurality of ATM AAL2 channels across a single ATM virtual circuit, thereby providing a more efficient use of available band width in communications networks. 
     According to a first aspect of the present invention there is provided a method of communicating a plurality of AAL2 channels over an ATM virtual channel connection between first and second communications entities, said method comprising the steps of: 
     maintaining a stored record of a plurality of channel identifiers relating to a plurality of AAL2 channels; and 
     establishing an AAL2 channel on a virtual channel connection by sending and receiving a plurality of messages over an AAL2 channel between said first and second communication entities, 
     wherein said messages operate on said stored record of channel identifiers to modify said channel identifiers into an assigned state indicating an AAL2 channel has been assigned to a virtual channel connection, or an unassigned state, indicating an AAL2 channel is unassigned to a virtual channel connection. 
     The invention includes a method of establishing an AAL2 channel over an ATM virtual channel connection comprising the steps of: 
     maintaining a stored record of a plurality of channel identifiers relating to a corresponding plurality of AAL2 channels; and 
     modifying a status of said stored channel identifier indicating a corresponding said AAL2 channel is assigned to a virtual channel connection. 
     Said status may be modified in response to a set of primitive messages received from a system management means. 
     The invention includes a method of de-establishing an AAL2 channel from an ATM virtual channel connection, said method comprising the steps of: 
     maintaining a stored record of a plurality of channel identifiers relating to a plurality of AAL2 channels; and 
     modifying a status of a said stored channel identifier to indicate a said corresponding AAL2 channel is unasssigned to a virtual channel connection. 
     The status may be modified in response to a set of primitive messages received from the system management means. 
     The status may be modified in response to at least one peer to peer message received from a communications network. 
     According to a second aspect of the present invention there is provided an ATM communications entity capable of communicating a plurality of AAL2 channels over a single ATM virtual channel connection (VCC), said device comprising: 
     means for storing a plurality of records describing a status of a plurality of AAL2 channel identifiers; 
     means for generating a set of messages operating on said stored channel identifier records; 
     means for generating a plurality of originating procedure messages for creating a plurality of AAL2 channels; and 
     means for generating a plurality of terminating procedure messages complementary to the originating procedure messages for creating a plurality of AAL2 channels; and 
     means for generating a plurality of originating procedure messages for releasing a plurality of AAL2 channels; and 
     means for generating a plurality of terminating procedure messages complementary to the originating procedure messages for releasing a plurality of AAL2 channels. 
     According to a third aspect of the present invention there is provided a method of assigning a plurality of AAL2 channels to an ATM virtual channel connection (VCC), said method comprising the steps of: 
     to set up a said AAL2 channel; 
     generating an assignment request message for sending to an ATM communications entity to request assignment of an AAL2 channel in response to said request message; 
     receiving a first assignment confirmation message confirming receipt of said assignment request message; and 
     sending a second assignment confirmation message for confirming receipt of said first assignment confirmation message. 
     Preferably the method further comprises the steps of: 
     if said first assignment confirmation message is not received within a predetermined period, sending a second assignment request message to request assignment of an AAL2 channel in response to said second assignment request message. 
     Preferably the method further comprises the step of: 
     if neither said assignment request message nor said second assignment confirmation message is received within a predetermined period after the sending of said first assignment confirmation message, the assignment of said AAL2 channel to said ATM VCC is assumed to be complete. 
     According to a fourth aspect of the present invention there is provided a method of releasing an AAL2 channel carried over an ATM virtual channel connection (VCC) said method comprising the steps of: 
     sending a first release request message, said first release request message requesting disconnection of an AAL2 channel from a virtual channel connection; 
     receiving a first release confirm message confirming release of a said AAL2 channel; and 
     sending a second release confirm message confirming receipt of said first release confirm message. 
     Preferably, the method further comprises the step of: 
     if said first release confirm message is not received within a predetermined time, sending a second release request message requesting release of said AAL2 channel. 
     Preferably the method further comprises the step of: 
     if neither a release request message nor a release confirm message is received within a predetermined time after sending said second release confirm message, the release of said AAL2 channel is assumed to be complete. 
     The invention includes a method for transmitting a plurality of streams of digital data using at least one of a plurality of channels over a communications network, said method comprising the steps of: 
     identifying an unused channel amongst said plurality of channels, wherein said plurality of channels are configurable to connect a transmitting function to a receiving function; 
     sending a message from said transmitting function to said receiving function requesting to use said identified channel to connect said transmitting function to said receiving function; 
     sending a message from said receiving function to said transmitting function confirming that said identified channel is available to transmit said digital data between said transmitting function and said receiving function; 
     exchanging said stream of digital data between said transmitting function and said receiving function using said identified channels; and 
     releasing said identified used channel. 
     Preferably said step of identifying an unused channel amongst said plurality of channels comprises the steps of: 
     sending a first message from a first functional block of said transmitting function to a second functional block of said transmitting function requesting an unused channel; 
     sending a second message from said second functional block of said transmitting function to a third functional block of said transmitting function to identify an unused channel amongst said plurality of channels and to mark as assigned said unused channel; 
     sending a third message from said second functional block of said transmitting function to said first functional block of said transmitting function confirming that said unused channel is available. 
     Preferably said step of sending a message from a transmitting function to a receiving function comprises sending a message from a second functional block within said transmitting function to a corresponding second functional block within said receiving function. 
     Preferably said step of sending a message from said receiving function to said transmitting function confirming said identified channel, comprises the steps of: 
     sending a fourth message from said corresponding second functional block within said receiving function to a first functional block within said receiving function said message identifying said unused channel; 
     sending a fifth message from said first functional block within said receiving function to said second functional block within said receiving function accepting said unused channel; 
     sending a sixth message from said second functional block of said receiving function to a third functional block within said receive function to mark as assigned said unused channel; 
     sending a seventh message from said second functional block of said receiving function to said second functional block of said transmitting function confirming that said identified unused channel is acceptable; and 
     sending an eighth message from said second functional block of said transmitting function to said first functional block of said transmitting function confirming that said identified unused channel is acceptable. 
     Preferably said step of releasing said identified used channel comprises the steps of: 
     sending a ninth message from said first functional block of said transmitting function to said second functional block of said transmitting function requesting to release said identified used channel; 
     sending a tenth message from said second functional block of said transmitting function to said third functional block of said transmitting function requesting to mark said identified used channel as unassigned; 
     sending an eleventh message from said second functional block of said transmitting function to said corresponding second functional block of said receiving function requesting to release said identified used channel; 
     sending a twelfth message from said second functional block of said receiving function to said first functional block of said receiving function requesting to release said identified used channel; 
     sending an thirteenth message from said first functional block of said receiving function to said second functional block of said receiving function confirming release of said identified used channel; 
     sending a fourteenth message from said second functional block of said receiving function to said third functional block of said receiving function requesting to mark said identified used channel as unassigned; 
     sending a fifteenth message from said second functional block of said receiving function to said second functional block of said transmitting function confirming release of said identified used channel; and 
     sending a sixteenth message from said second functional block of said transmitting function to said first functional block of said transmitting function confirming release of said identified used channel. 
     Preferably said plurality of channels comprise a plurality of ATM adaption layer type 2 channels. 
     A said transmitting and said receiving function may each comprise an interworking function. 
     The invention includes a network comprising: 
     a plurality of physical resources comprising a plurality of processors, and a plurality of memory means; 
     a means for communicating between said plurality of physical resources; 
     a plurality of functions residing at said plurality of processors and said plurality of memory means, wherein at least one function of said plurality of functions is sub-divided into a first set of functional blocks; 
     at least one functional block of said first set of functional blocks is sub-divided into a second set of functional blocks, wherein members of said first set of functional blocks are configurable to exchange a first set of messages with members of said second set of functional blocks; and 
     members of said second set of functional blocks within a first function residing at a first set of processors and a first set of memory means are configurable to exchange a second set of messages with corresponding members of a second set of functional blocks within a second function residing at a second set of physical resources and a second set of memory means. 
     Preferably said communicating means comprises an ATM adaption layer type 2 virtual channel connection. 
     Said second set of functional blocks within said first function and said second set of functional blocks within said second function may comprise: 
     a means for originating a plurality of channels between said first function and said second function; 
     a means for terminating a plurality of channels between said first function and said second function; and 
     a means for storing a status of a channel of said plurality of channels between said first function and said second function, wherein said status of a channel indicates whether said channel is in use. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a better understanding of the invention and to show how the same may be carried into effect, there will now be described by way of example only, specific embodiments, methods and processes according to the present invention with reference to the accompanying drawings in which: 
         FIG. 1  illustrates schematically a pair of known interworking functions connected by an ATM virtual channel connection (ATM VCC) across an ATM network; 
         FIG. 2  illustrates schematically the pair of known interworking functions represented as a set of functional layers; 
         FIG. 3  illustrates schematically functional blocks within first and second interworking functions according to a first specific implementation of the present invention; 
         FIG. 4  illustrates schematically, in more detail, the functional blocks within an ANP layer management according to the first specific implementation of the present invention; 
         FIG. 5  illustrates schematically functional blocks within a pair of interworking functions and according to a second specific implementation of the present invention; 
         FIG. 6  illustrates schematically, in more detail, functional blocks within an AAL2 Connection Control; 
         FIG. 7  illustrates, by way of example, a Table used to store information concerning whether an individual AAL2 connection within one ATM virtual channel is assigned/unassigned or activated/de-activated; 
         FIG. 8  lists a set of primitives exchanged between a System Management means, a Status Record means, AAL2 Connection Control means, Call Handing means and either a signaling ATM adaptation layer (SAAL) or AAL2; 
         FIG. 9  illustrates, by way of example, a message sequence chart for establishing an AAL2 connection between first and second interworking functions and according to the first specific implementation of the present invention; and 
         FIG. 10  illustrates schematically message sequences for releasing an AAL2 connection between first and second interworking functions according to a second specific implementation of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE BEST MODE FOR CARRYING OUT THE INVENTION 
     There will now be described by way of example the best mode contemplated by the inventors for carrying out the invention. In the following description numerous specific details are set forth in order to provide a thorough understanding of the present invention. It will be apparent however, to one skilled in the art, that the present invention may be practiced without limitation to these specific details. In other instances, well known methods and structures have not been described in detail so as not to unnecessarily obscure the present invention. 
     ATM Adaptation Layer Type 2 (AAL2) allows a user to have multiple AAL connections per ATM connection. This is achieved by multiplexing “packets” of data in the common part sub-layer (CPS). A number of packets can be placed within an ATM cell. The default length for user data in a CPS packet is up to 45 octets—with a 3 octet CPS packet header. This guarantees that the full CPS packet will be no longer than 48 octets and can fit into the payload of a single ATM cell. An AAL2 CPS packet comprises a channel identifier (CID), a length indicator (LI), a user to user identification (UUI), and a header error control (HEC) as is known in the prior art. The specification for AAL2 can be found in ITU-T I.363.2, B-ISDN ATM Adaptation Layer Type 2 Specification, Toronto, September 1997. 
     Referring to  FIG. 3  herein, there are shown a set of functional blocks, which are also known as entities herein, comprising first and second interworking functions  301  and  302  according to a first specific implementation of the present invention. Such entities may reside at first and second telecoms resources, eg switches, connects, routers. Each functional bock comprises a means for performing a function, which in the best mode herein are implemented as application specific integrated circuits (ASICS), or by data processors operating in accordance with algorithms stored in electronic form in electronic memories. It will be understood by those skilled in the art that only those functional blocks concerned with the control of AAL2 channels between interworking functions  301  and  302  are shown in  FIG. 3 . In order to carry a plurality of separate streams of data across a network, using a plurality of ATM AAL2 channels over a single ATM virtual channel connection (VCC), individual ATM AAL2 channels need to be identified at both first and second interworking functions. The channel identifier (CID) of each AAL2 channel is used for this purpose as follows: 
     At first interworking function  301 , System Management entity  303  exchanges information with ANP layer management entity  304  via a service access point (SAP)  305 . The ANP layer management entity  304  exchanges information with the protocol stack comprising functional layers  307  to  310 . Information is exchanged across service access points by means of the exchange of predefined sets of messages. The predefined sets of messages are known herein as ‘primitives’. 
     System Management entity  303  is configured to control inputs to ANP layer management entity  304  which in turn controls the protocol stack  307 – 310  which controls the connections which enables a plurality of AAL2 channels to be created on a single ATM virtual channel connection  311 . 
     Second interworking function  302  is constructed similarly to first interworking function  301  and comprises a service specific convergence sub-layer  312 ; a common part sub-layer  313 ; an ATM layer  314 ; a physical layer  315  connected to physical layer  310  of the first interworking function  301 ; a second ANP layer management entity  316  connected to service specific convergence sub-layer  312  via a service access point  317 ; and a second system management entity  318  connected to second ANP management entity  316  via a service access point  319 . 
     Referring to  FIG. 4  herein, there is illustrated an architecture of ANP layer management entity  304  according to the first specific implementation of the present invention. The ANP layer management entity is organized and configured into a plurality of functional means, which carry out a set of logical operations. A similar set of logical operations are provided at second ANP layer management entity  316 . A System Management entity  303  exchanges information across service access point  305  with the ANP layer management entity  304  by means of a set of primitives. Each primitive within the set of primitives for communication between the ANP layer management entity  304  and the System Management entity  303  contains parameters which are assigned values when the primitive is used. The primitives exchanged between the System Management entity  303  and the ANP layer management entity  304  are summarized in Table 1 herein. The following parameters are defined for use with the primitives: 
     Channel identifier (CID)—the CID parameter indicates a CID value for the AAL2 channel being used; 
     Connection parameters (Conn — Parms)—this parameter is used with primitives that deal with AAL2 channels. It contains parametric elements necessary to configure the AAL2 channel including details of any voice encoding used; 
     Cause—the cause parameter is used with the Reject, Release and Fault primitives to indicate the reason for a CID assignment rejection, a CID release, or a fault indication; 
     TransactionID—the TransactionID parameter is used with all primitives except for ‘Activate’ and ‘Deactivate’. Its purpose is to associate a current transaction with a given call between users across ATM VCC  311 , so that any concurrent transactions may be distinguished. Its use is local to a user of the ANP layer management entity  304 . 
     
       
         
           
               
               
             
               
                   
                 TABLE 1 
               
             
            
               
                   
                   
               
               
                   
                 Type 
               
            
           
           
               
               
               
               
               
            
               
                 Primitive Generic Name 
                 Request 
                 Indication 
                 Response 
                 Confirm 
               
               
                   
               
               
                 Assign 
                 TransactionID 
                 TransactionID 
                 TransactionID 
                 TransactionID 
               
               
                   
                 Conn — Parms 
                 CID 
                 CID 
                 CID 
               
               
                 Reject 
                 (Note 1) 
                 TransactionID 
                 TransactionID 
                 (Note 1) 
               
               
                   
                   
                 CID 
                 CID 
               
               
                   
                   
                 Cause 
                 Cause 
               
               
                 Release 
                 TransactionID 
                 TransactionID 
                 TransactionID 
                 TransactionID 
               
               
                   
                 CID 
                 CID 
                 CID 
                 CID 
               
               
                   
                 Cause 
                 Cause 
               
               
                 Ready-for-Use 
                 (Note 1) 
                 CID 
                 (Note 1) 
                 (Note 1) 
               
               
                   
                   
                 TransactionID 
               
               
                 Fault 
                 (Note 1) 
                 TransactionID 
                 (Note 1) 
                 (Note 1) 
               
               
                   
                   
                 Cause 
               
               
                 Activate 
                 CID 
                 CID 
                 CID 
                 CID 
               
               
                 Deactivate 
                 CID 
                 CID 
                 CID 
                 CID 
               
               
                   
               
               
                 Note 1: 
               
               
                 This primitive not defined 
               
            
           
         
       
     
     According to the best mode described herein., operation of the ANP layer management entity is subdivided into a set of ‘Originating’ procedures  406  and a set of ‘Terminating’ procedures  409 . The Originating procedures  406  are further subdivided into two further functional blocks ‘Assign’  407  and ‘Release’  408 . The Terminating procedures  409  are subdivided into functional blocks ‘Assign’  410  and ‘Release’  411 . 
     The Originating procedure ‘Assign’  407  is invoked when the local system management entity within an interworking function requests the assignment of an AAL2 channel identifier (CID) to a particular AAL2 connection. The Originating procedure ‘Release  408 ’ is invoked when the local system management entity within an interworking function requests the release of the CID associated with a particular AAL2 channel. 
     The Terminating procedure ‘Assign’  410  is invoked when the system management entity within the distant peer interworking function requests the assignment of an AAL2 channel identifier (CID) to a particular AAL2 connection. The Terminating procedure ‘Release  411 ’ is invoked when the system management entity within the distant peer interworking function requests the release of the CID associated with a particular AAL2 channel. 
     It will be understood by those skilled in the art that both first interworking function  301  and second interworking function  302  are each configurable to generate Originating procedures and Terminating procedures. 
     Within the ANP layer management entity  304  there is a third functional block referred to herein as “Status Record”  412 . Status Record  412  comprises a memory and processor resource configurable to store a plurality of numbers identifying a plurality of AAL2 channels associated with a single ATM VCC. In addition, Status Record  412  is configured to store information indicating whether an individual AAL2 channel amongst the plurality of AAL2 channels is in use. According to the best mode described herein, a single ATM VCC can carry up to 256 different AAL2 channels. The limit on the number of channels per ATM VCC is imposed by the size of an addressing field appended to each block of data by the Common Part Sub-layer function layer  202 . On any ATM VCC a part of the bandwidth assigned to any individual AAL2 channel is concerned with identifying that channel. An AAL2 channel is identified by a channel identifier (CID). In order to ensure that each AAL2 channel within an ATM VCC has a unique identifier there is only one Status Record  412  per ATM VCC. However, there may be a plurality of Originating procedures  406  and a plurality of Terminating procedures  409  per ATM VCC. In addition, a plurality of ATM VCC&#39;s can share a single set of Originating plus Terminating procedures. 
     In order to create a new AAL2 channel between first and second interworking functions  301  and  302 , System Management layer entity  303  exchanges a sequence of primitives with ANP layer management entity  304 . If, by way of example, System Management layer entity  303  indicates that there is a need for a new AAL2 channel then the Originating procedures  406  within the ANP layer management entity interrogate Status Record means  412  to obtain an unassigned CID value. In order to establish an AAL2 channel between interworking functions  301  and  302  it is necessary that both interworking functions have knowledge of the CID value assigned to a channel prior to establishing that channel. To accomplish this the ANP layer management entity  304  institutes an exchange of messages with ANP layer management entity  316  associated with interworking function  302 . The process of assigning a particular CID value to an AAL2 channel between interworking functions  301  and  302  is a service which the ANP layer management entities  304  and  316  provides for the corresponding System Management layer entities  303  and  318 . The provision of services between peer ANP layers involves the exchange of ANP messages between ANP transmitting (Tx) and receiving (Rx) entities. As described herein the phrase “peer ANP layers” means separate and equivalent ANP layer management entities within separate interworking functions. The list of services provided by the ANP layer  304  to the System Management layer  303  comprises:
         AAL2 channel assignment—establishes an AAL2 channel between peer ANP transmitting and ANP receiving layer management entities. Included among the parameters that are negotiated and/or conveyed between transmitting and receiving ANP layer management entities are the following: CID; and TransactionID which is used to associate a current transaction with a request from a System Management layer entity to establish a new AAL2 channel.   AAL2 channel release—this service is used to release a currently assigned AAL2 channel and to de-allocate the CID value identifying the assigned AAL 2 channel.   AAL2 channel pre-assignment—this service allows AAL2 channels to be pre-assigned for particular users.       

     Referring to  FIG. 5  herein there is illustrated schematically a second specific implementation according to the present invention.  FIG. 5  illustrates a method of establishing a plurality of AAL2 channels across a single ATM VCC between first and second interworking functions  501  and  502 . Each interworking layer comprises a protocol stack comprising a service specific convergence sub-layer  503 ,  504 , a common part sub-layer  505 ,  506  an ATM layer  507 ,  508  and a physical layer  509 ,  510 ; a signaling ATM adaptation layer (SAAL)  504 ,  520  connected via a corresponding respective service access point to said ATM layer  507 ,  508 ; an AAL2 connection control block  513 ,  514  connected to said signaling ATM adaptation layer via a corresponding service access point; a call handling block  515 ,  516  communicating with said AAL2 connection control and said SAAL via corresponding service access points, and optionally communicating with said service specific convergence sub-layer  503 ,  504  via a corresponding service access point; and a system management layer  517 ,  518  communicating with said AAL2 connection control block via a further service access point. The call handling blocks communicate with each other via a connection control application  519  which carries peer to peer signalling messages. The service specific convergence sublayers communicate with the application services (voice, data) represented by application block  519 . AAL2 connection control (AAL2 CC)  513  which is also known herein as ANP layer management entity communicates with the ATM layer  507  of the protocol stack via a Signaling ATM Adaption Layer (SAAL)  504 . Communication between AAL2 Connection Control  513  and SAAL  504  is achieved through the exchange of a set of primitives across a service access point (SAP). Communication between SAAL  504  and ATM layer  507  is achieved by exchange of a set of primitives across another service access point. 
     Referring to  FIG. 6  herein, there are illustrated schematically a set of functional blocks within AAL2 Connection Control  513  according to the second specific implementation of the present invention. AAL2 Connection Control  513  is subdivided into a set of functional blocks comprising a plurality of Originating procedures  600 , Terminating procedures  610  and AAL2 Channel Status Record procedures  620 . The Originating procedures  600  are invoked when a local Call Handling entity  515  originates either a CID assignment to establish a new AAL2 channel between interworking functions  501  and  502  or a CID release to release an AAL2 channel between interworking functions  501  and  502  which had been previously assigned. Terminating procedures  610  are invoked when call handling entity  515  within distant interworking function  502  originates either a CID assignment or a CID release. The AAL2 Channel Status Record procedures  620  are responsible for keeping a record of the status of individual CID values. AAL2 Channel Status Record procedures may be updated and queried by System Management entity  630  by the exchange of a set of primitives according to the best mode presented herein. 
     Call handling entity  515  is configured to send primitives to AAL2 Connection Control  513  that are responsible for assigning a CID value and releasing a CID value. In response to the primitives received from Call Handling  515  the AAL2 Connection Control  513  is configured to respond with primitives that confirm or deny the requests that Call Handling  515  makes. The primitives and parameters exchanged between AAL2 connection control  513  and call handling entity  515  are listed in Table 2. 
     
       
         
           
               
               
             
               
                   
                 TABLE 2 
               
             
            
               
                   
                   
               
               
                   
                 Type 
               
            
           
           
               
               
               
               
               
            
               
                 Primitive Generic Name 
                 Request 
                 Indication 
                 Response 
                 Confirm 
               
               
                   
               
               
                 Assign 
                 TransactionID 
                 TransactionID 
                 TransactionID 
                 TransactionID 
               
               
                   
                 Conn — Parms 
                 CID 
                 CID 
                 CID 
               
               
                   
                 Routing — Info 
                 Conn — Parms 
               
               
                   
                   
                 Routing — Info 
               
               
                 Reject 
                 (Note 1) 
                 TransactionID 
                 TransactionID 
                 (Note 1) 
               
               
                   
                   
                 CID 
                 CID 
               
               
                   
                   
                 Cause 
                 Cause 
               
               
                 Release 
                 TransactionID 
                 TransactionID 
                 TransactionID 
                 TransactionID 
               
               
                   
                 CID 
                 CID 
                 CID 
                 CID 
               
               
                   
                 Cause 
                 Cause 
               
               
                 Ready-for-Use 
                 (Note 1) 
                 CID 
                 (Note 1) 
                 (Note 1) 
               
               
                   
                   
                 TransactionID 
               
               
                 Activate 
                 CID 
                 CID 
                 CID 
                 CID 
               
               
                   
                 Conn — Parms 
                 Conn — Parms 
               
               
                 Deactivate 
                 CID 
                 CID 
                 CID 
                 CID 
               
               
                   
               
               
                 Note 1: 
               
               
                 This primitive as not defined 
               
            
           
         
       
     
     The Routing — Info parameter is used in AAL2 switched connection control. 
     According to the best mode presented herein, a set of primitives are defined between the AAL2 Channel Status Record procedures  620  and System Management entity  630  to enable System Management entity  630  to control both the number of CIDs allocated and the number of CIDs pre-assigned as well as to determine the status of individual CIDs. The set of primitives that are exchanged between AAL2 Channel Status Record procedure  620  and System Management entity  630  are listed in Table 3 herein. 
     
       
         
           
               
               
               
               
             
               
                   
                 TABLE 3 
               
             
            
               
                   
                   
               
               
                   
                 Primitive 
                 Type 
                   
               
            
           
           
               
               
               
               
               
            
               
                   
                 Generic Name 
                 Request 
                 Indication 
                 Confirm 
               
               
                   
                   
               
               
                   
                 Preassign — CIDs 
                 No — CID 
                   
                 No — CID 
               
               
                   
                 Allocate — CIDs 
                 No — CID 
                 (Note 1) 
                 No — CID 
               
               
                   
                   
                 Coll — Res 
                   
                 Coll — Res 
               
               
                   
                 Query — CIDs 
                 (Note 2) 
                 No — CIDs 
                 (Note 1) 
               
               
                   
                 Increment — CIDs 
                 No — CID 
                 (Note 1) 
                 No — CID 
               
               
                   
                 Decrement — CIDs 
                 No — CID 
                 (Note 1) 
                 No — CID 
               
               
                   
                 Status 
                 CID 
                 CID 
                 (Note 1) 
               
               
                   
                   
                   
                 CIDState 
               
               
                   
                   
               
               
                   
                 Note 1: 
               
               
                   
                 This primitive is not defined. 
               
               
                   
                 Note 2: 
               
               
                   
                 No parameter with this primitive. 
               
            
           
         
       
     
     The primitives listed in Table 3 herein are described as follows:
         Pre-assign — CIDs is used to allow a plurality of CID values to be semi-permanently associated with AAL 2 channels.   Allocate — CIDs enables System Management entity  630  to set the number of CID values for use on ATM VCC  519 ;   Query — CIDs enables System Management entity  630  to determine the number of currently assigned CID values;   Increment — CIDs allows the number of allocatable CID values to be incremented;   Decrement — CIDs allows the number of allocatable CID values to be decremented;   Status allows the current state of a CID to be determined.       

     Preferably, the following parameters are defined for use with the primitives listed in Table 3 herein:
         CID indicates the CID value associated with the primitive;   Coll — Res carries a value of either TRUE or FALSE. If Coll — Res has a value TRUE then the originating assignment of allocated CID values will start from the lowest available value towards the highest; if Coll — Res has a value FALSE then originating assignment will start from the highest available value towards the lowest;   No — CID is used to indicate the number of CID values associated with is the primitive; and   CIDState is used to indicate the current value of the CID for which status request has been received. CIDstate can only have two possible values, either assigned or unassigned.       

     In the best mode herein, primitives are defined to be exchanged between AAL2 Connection Control Originating procedures  600  and Terminating procedures  610  and AAL 2 Channel Status Record procedures  620  to control a current state of a given CID value. The primitives exchanged between AAL2 connection control Originating procedures  600  and Terminating procedure  610  and AAL2 Channel Status Record procedure  620  are listed in Table 4 herein: 
     
       
         
           
               
               
               
               
             
               
                   
                 TABLE 4 
               
             
            
               
                   
                   
               
               
                   
                 Primitive 
                 Type 
                   
               
            
           
           
               
               
               
               
            
               
                   
                 Generic Name 
                 Request 
                 Indication 
               
               
                   
                   
               
               
                   
                 Assign — CID 
                 (Note 2) 
                 CID 
               
               
                   
                 Activate — CID 
                 CID 
                 (Note 1) 
               
               
                   
                 Reject — CID 
                 (Note 1) 
                 Cause 
               
               
                   
                 Release — CID 
                 CID 
                 (Note 1) 
               
               
                   
                 Deactivate — CID 
                 CID 
                 (Note 1) 
               
               
                   
                   
               
               
                   
                 Note 1: 
               
               
                   
                 This primitive is not defined 
               
               
                   
                 Note 2: 
               
               
                   
                 CID parameter only used for terminating assignment and not for originating assignment. 
               
            
           
         
       
     
     Preferably, the following parameters are defined for use with primitives listed in table 4:
         CID indicated CID value for the AAL 2 channel to be assigned/activated or released/deactivated; and   Cause is used with reject — CID.indication primitive to convey to AAL2 Connection Control that, due to unavailability, request for CID assignments cannot be met.       

     Referring to  FIG. 7  herein, there is illustrated, by way of example, a Status Record containing 256 AAL2 channel identifiers. According to the best mode presented herein, it is possible to semi-permanently assign certain CID values to particular applications. Semi-permanently assigned connections are also known as preassigned AAL 2 channels. Referring to  FIG. 7 , the contiguous set of AAL2 channels numbered  230 – 240  have been pre-assigned. When any of pre-assigned AAL2 channels  230 – 240  are in use they are activated, and when not in use they are de-activated. In contrast, other channels comprising one ATM VCC are assigned when in use and unassigned when not in use. 
     Referring to  FIG. 8  herein, there is illustrated schematically the sets of primitives exchanged between System Management  630 , AAL2 Channel Status Record procedures  620 , AAL2 Connection Control procedures  600  and  610 , Call Handling  515  and the underlying protocol SAAL  504  according to a second method of the present invention. 
     Referring to  FIG. 9  herein, there is illustrated an example of a message sequence chart illustrating the primitives exchanged between functional blocks within interworking functions  301  and  302  and messages exchanged between corresponding functional blocks of interworking functions  301  and  302  during an attempt to assign a new AAL2 channel in the first implementation herein. Operation in the second implementation is similar. 
     System Management entity  303  sends an Assign — Request primitive  900  to transmitting ANP layer  304 . Transmitting ANP layer management entity  304  responds by sending a first message ASSIGN — REQUEST (1) 901 to receiving ANP layer management entity  316  within distant interworking function  302 . At substantially a same instant of time that ANP layer  304  sends the message to receiving ANP layer management entity  316 , transmitting ANP layer management entity  304  also starts a first timing means called Tassign. If receiving ANP layer management entity  316  receives ASSIGN — REQUEST (1) message  901  then receiving ANP layer management entity  316  sends an Assign — Indication primitive  902  to System Management layer entity  318 . System Management layer entity  318  responds by sending an Assign — Accept primitive  903  to receiving ANP layer management entity  316 . Receiving ANP layer  316  responds by sending an ASSIGN — CONFIRM (2) message  904  to transmitting ANP layer  304 , while at substantially the same time also starting a second timing means called Tconfirm. If the time duration between transmitting ANP layer  304  sending the ASSIGN — REQUEST (1) message and receiving the ASSIGN — CONFIRM (2) message is less than a pre-determined value Tassign then transmitting ANP layer management entity  304  responds by sending an Assign — Confirm primitive  905  to System Management layer entity  303  and sends ASSIGN — CONFIRM (3) message  906  to receiving ANP layer management entity  316 . Preferably, the first pre-determined time Tassign is equal to 200 ms. 
     If receiving ANP layer  316  receives ASSIGN — CONFIRM (3) message  906  within a time less than predetermined value Tconfirm then receiving ANP layer  316  sends a Ready — for — Use primitive  910  to System Management layer entity  318  and a new AAL2 channel is successfully established. Preferably, the second pre-determined time duration Tconfirm is 200 ms. If receiving ANP layer  316  does not receive ASSIGN — CONFIRM (3) message  906  within the pre-determined time Tconfirm then it is inferred that transmitting ANP layer  304  has sent ASSIGN — CONFIRM (3) message  906  which has been corrupted in transmission. Receiving ANP layer  316  sends a Ready — for — Use primitive to System Management layer entity  318  and a new AAL2 channel is successfully established. 
     If transmitting ANP layer management entity  304  does not receive the ASSIGN — CONFIRM (2) message  904  within the first pre-determined time, Tassign then it sends another ASSIGN — REQUEST (1) message  907  to receiving ANP layer  316  and restarts timing means Tassign. If receiving ANP layer  316  receives another ASSIGN — REQUEST (1) message  907  after having sent ASSIGN — CONFIRM (2) message then it can be inferred that transmitting ANP layer management entity  304  did not receive ASSIGN — CONFIRM (2) message  904  within the predetermined time Tassign. In that case, receiving NP layer  316  then resends ASSIGN — CONFIRM (2) message  908  and restarts second timing means. If transmitting ANP layer management entity  304  receives the ASSIGN — CONFIRM (2) message  908  within the first pre-determined time Tassign then it sends an Assign — Confirm primitive to System management layer entity  303  and sends ASSIGN — CONFIRM (3) message  909  to receiving ANP layer  316 . If receiving ANP layer  316  receives ASSIGN — CONFIRM (3) message  909  within time Tconfirm then receiving ANP layer  316  sends a Ready — for — Use primitive to System Management layer entity  318  and a new AAL2 channel is successfully established. If receiving ANP layer  316  does not receive ASSIGN — CONFIRM (3) message  909  within the second pre-determined time Tconfirm then it is inferred that transmitting ANP layer  304  has sent ASSIGN — CONFIRM (3) message  909  which has been corrupted in transmission. Receiving ANP layer  316  sends a Ready — for — Use primitive to System Management layer entity  318  and a new AAL2 channel is successfully established. 
     The use of timing means Tassign and Tconfirm for the retransmission of messages that are lost or corrupted during transmission may be invoked as many times as required to ensure satisfactory message delivery. Thus, the signaling method described herein before for establishing a new AAL2 connection between interworking functions is sufficiently robust to withstand the loss of individual messages used in assigning a new AAL2 channel. 
     Referring to  FIG. 10  herein, in a like manner, when a previously established AAL2 channel is no longer required system Management entity  303  sends a Release — Request primitive  1000  to transmitting ANP layer management entity  304 . Transmitting ANP layer management entity  304  responds by sending a first message RELEASE — REQUEST (1) 1001 to receiving ANP layer management entity  316  within distant second interworking function  302 . At substantially the same instant of time that ANP layer management entity  304  sends a message to receiving ANP layer management entity  316  transmitting ANP layer management entity  304  also starts a third timing means called Trelease. If receiving ANP layer management entity  316  receives first RELEASE — REQ (1) message  1001  then receiving ANP layer management entity  316  sends a Release — Indication primitive  1002  to system management layer entity  318 . System management layer entity  318  responds by sending a Release — Confirm primitive  1003  to receiving ANP layer management entity  316 . Receiving ANP layer management entity  316  responds by sending a first RELEASE — CONFIRM (2) message  1004  to transmitting ANP layer management entity  304 , while at substantially the same time starting said second timing means Tconfirm. If the time duration between transmitting ANP layer management entity  304  sending RELEASE — REQ (1) message  1001  and receiving the RELEASE — CONFIRM (2) message  1004  is less than a third pre-determined value Trelease then transmitting ANP layer management entity  304  responds by sending a Release — Confirm primitive  1005  to system management layer entity  303  and sends RELEASE — CONFIRM (3) message  1006  to receiving ANP layer management entity  316 . Preferably, the third pre-determined time Trelease has a value of 200 ms. The channel identifier associated with the AAL2 channel is set to unassigned within Status Record  412  and the released AAL2 channel is now, once again, available for use. 
     If receiving ANP layer  316  receives RELEASE — CONFIRM (3) message  1006  within a time less than predetermined value Tconfirm then the channel identifier associated with the AAL2 channel is set to unassigned within Status Record  412  and the released AAL2 channel is now, once again, available for use. If receiving ANP layer  316  does not receive RELEASE — CONFIRM (3) message  1006  within the pre-determined time Tconfirm then it is inferred that transmitting ANP layer  304  has sent RELEASE — CONFIRM (3) message  1006  which has been corrupted in transmission. As before, the channel identifier associated with the AAL2 channel is set to unassigned within Status Record  412  and the released AAL2 channel is now, once again, available for use. 
     If transmitting ANP layer management entity  304  does not receive first RELEASE — CONFIRM (2) message  1004  within the third pre-determined time, Trelease then sends a second RELEASE — REQ (1) message  1007  to receiving ANP layer management entity  316 . If receiving ANP layer management entity  316  receives a second RELEASE — REQ (1) message  1007  after having sent first RELEASE — CONFIRM (2) message  1004  then it can be inferred that transmitting ANP layer management entity  304  did not receive RELEASE — CONFIRM (2) message  1004 . In that case, receiving ANP layer management entity  316  then sends a second RELEASE — CONFIRM (2) message  1008  and restarts the second timing means which stores a time duration Tconfirm. Transmitting ANP layer management entity  304  if it receives second RELEASE — CONFIRM (2) message  1008 , then sends a Release — Confirm primitive  1010  to system management entity  303  and sends RELEASE — CONFIRM (3) message  1009  to receiving ANP layer management entity  316  and the channel identifier associated with the AAL2 channel is set to unassigned within Status Record  412  and the released AAL2 channel is now, once again, available for use. 
     If receiving ANP layer management entity  316  receives RELEASE — CONFIRM (3) message  1009  within the second pre-determined time Tconfirm then the channel identifier associated with the AAL2 channel is set to unassigned within Status Record  412  and the released AAL2 channel is now, once again, available for use. If receiving ANP layer management entity  316  does not receive RELEASE — CONFIRM (3) message  1009  within the second pre-determined time Tconfirm, then it is inferred that transmitting ANP layer  304  has sent RELEASE — CONFIRM (3) message  1009  which has been corrupted in transmission. In this case, receiving ANP layer management entity  316  sets the channel identifier associated with the AAL2 channel to unassigned exactly as before. The use of timing means Trelease and Tconfirm for the retransmission of messages that are lost or corrupted during transmission may be invoked as many times as required to ensure satisfactory message delivery.