Abstract:
A method for transferring time-synchronous data, particularly voice and video data, over a network, particularly the Internet, between at least two terminals, where between the terminals a connection is established using a SIP server and where the SIP protocol is used for establishing the connection, is—with respect to high Quality of Service for transferring time-synchronous data and with a technically simple and cost effective design—developed in a way that the SIP server analyzes the connection and/or the terminals or the like and that based on the analysis it determines an ideal bandwidth for optimizing the transfer of time-synchronous data.

Description:
BACKGROUND OF THE INVENTION 
     The invention concerns a method for time-synchronous data transfer, particularly of voice and video messages, over a network, particularly the Internet, between at least two terminals where a connection between the terminals is set up using the SIP protocol and at least one SIP server. 
     Methods for transfer of time-synchronous data, such as voice data, over networks, particularly over the Internet, are gaining importance, because for private users as well as for enterprises cost saving on telephone calls are possible. For conducting telephone calls between two terminals over a network, particularly using the Internet protocol, means for signalling call set-up and tear-down are required. SIP, the Session Initiation Protocol is one of the protocols used for this purpose. It was standardized by the IETF, the Internet Engineering Task Force. 
     A caller may send a SIP message for setting up a call by using his/her terminal. The message notifies the callee that the caller intends to set up a call. The terminal of the callee would then for example ring and notify the terminal of the caller by another SIP message that ringing has started. If the callee operates her/his terminal such that it accepts the call, then the terminal sends another SIP message to the terminal of the caller for notifying it that now transmission of time-synchronous data, for example voice or video data, can start. The SIP protocol is also used for signalling tear-down of a connection. 
     Establishing a concrete voice connection and coding and sending time-synchronous voice data is not supported by SIP. For this, the terminals communicate with each other, for example, by negotiating about the kind of connection or data transfer to use and a coding method for voice data. SIP supports establishing a connection insofar, as it includes an exchange of terminal properties. This includes the kinds of voice coding that the terminals support, the addresses of the terminals to which voice traffic is to be sent, and some other terminal specific properties. 
     Another functionality of SIP is finding a callee at his/her current location. The first message from a caller to a callee if typically not sent directly to the callee&#39;s terminal, but to a SIP server, which is usually configured as SIP proxy server. At this server, a company XYZ provides an address sip://customer@xyz.de to one of its customers. 
     Now, the customer can register her/his current terminal at the SIP proxy server provided by company XYZ. His current terminal might be his work phone, his home phone, his mobile phone, or any other SIP-enabled phone. The terminal of the caller then sends the first message to sip://customer@xyz.de. There the proxy server forwards this message to the terminal that the customer has registered. The SIP server would also forward the reply of customer&#39;s terminal in the opposite direction. 
     As for the conventional technique, the following references are known. 
     Reference for Differentiated Services:
         “RFC 2475 An Architecture for Differentiated Service,” S. Blake, D. Black, M. Carlson, E. Davis, Z. Wang, W. Weiss, December 1998 (Format: TXT=94786 bytes) (Updated by RFC3260) (Status: INFORMATIONAL)       

     Reference for RSVP:
         “RFC 2205 Resource ReSerVation Protocol (RSVP), Version 1 Functional Specification,” R. Braden, Ed., L. Zhang, S. Berson, S. Herzog, S. Jamin, September 1997 (Format: TXT=223974 bytes) (Updated by RFC2750) (Status: PROPOSES STANDARD);   “RFC 2210 The Use of RSVP with IETF Integrated Services,” J. Wroclawski, September 1997 (Format: TXT=77613 bytes) (Status: PROPOSED STANDARD)       

     Reference for SIP:
         “RFC 3261 SIP: Session Initiation Protocol,” J. Rosenberg, H. Schulzrinne, G. Camarillo, A. Johnston, J. Peterson, R. Sparks, M. Handley, E. Schooler, June 2002 (Format: TXT=647976 bytes) (Obsoletes RFC 2543) (Updated by RFC 3265) (Status: PROPOSED STANDARD).       

     For the known methods of transferring time-synchronous data over the basic Internet, there is the particular problem that they give no guarantees for Quality of Service (QoS), for example available bandwidth and packet delay of a connection. This may lead to bad quality of voice transmission, because packets containing the coded voice arrive in an order different to the one they were sent in, because packets are damaged or dropped during transfer, or because packets are transferred with high delay. For time-synchronous data, such as voice or video, this leads to bad QoS. The lack of QoS is one of the reasons for the limited acceptance of time-synchronous services, particularly Internet telephony, so far. Also SIP does not have any built-in mechanism to support Quality of Service (QoS) to the time-synchronous data transfer it signals. 
     Enhancements of the basic Internet, such as Integrated Services and Differentiated Services support QoS for Internet connections, but it requires additional signalling and network management functions. Integrating SIP signalled IP telephony or video transfer with these methods for QoS provisioning would be a significant technology improvement and it would increase the acceptance of Internet telephony, but its available is very limited, so far. 
     Existing suggestions on how to perform this integration are based on the idea that the telephony terminals themselves try to reserve resources for their calls by using other means of signalling, independent of SIP. An example is the Resource reSerVation Protocol (RSVP) of Integrated Services. However, this approaches do not scale sufficiently with an increasing number of users, such that existing QoS provisioning systems cannot deal with a high rate of reservation requests. 
     BRIEF SUMMARY OF THE INVENTION 
     Therefore, this invention is targeted at defining a method for transferring time-synchronous data with high quality, which is technically simple and cost-effective. 
     According to the invention, the goal described above is achieved by a method for transferring time-synchronous data according to patent claim  1 . This method is designed and developed in a way that the SIP server analyzes the connections and/or the terminals in a way that based on this analysis an ideal bandwidth for optimizing the transfer of time-synchronous data is determined. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will be more apparent from the following description of preferred embodiments taking in conjunction with the accompanying drawings, in which: 
         FIG. 1  shows a network which is used for explaining a method according to the present invention and which includes a SIP server and traffic trunks; and 
         FIGS. 2(   a ), ( b ), and ( c ) show schematic views of describing trunk control operations of the present invention; and which: 
       Reference numerals are added to the respective structural elements in  FIGS. 1 and 2  for a better understanding of the present invention and, specifically,  1  is representative of a phone terminal;  2 , an edge router;  3 , a control IP network;  4 , traffic trunks;  5 , a SIP server;  6 , SIP signaling;  7 , trunk control; and  8 , data connection. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Within the invention it is found that for achieving sufficient QoS, no additional functionality is required for the terminals and/or the network, but that the required QoS can be achieved in a particularly simple and cost-effective way by extending the SIP server such that the connection, particularly the SIP message exchanged for signalling, and or the terminals are analyzed. Based on this analysis and with knowledge of the coding and decoding methods, an optimal bandwidth for optimizing the transfer of time-synchronous data is determined. A sufficient QoS for the data transfer can therefore be achieved without requiring additional functionality of terminals or the network, which saves costs significantly. 
     Now, in a very advantageous way, based on the analysis of the connection and or the terminals, a bandwidth reservation for the transfer of time-synchronous data can be made for ensuring QoS. The reservation of bandwidth could be performed by the SIP server, which is extended by this functionality. The QoS would be ensured with respect to loss of data during data transfer, as far as the transfer data rate is within the reserved bandwidth. Particularly for voice and video transmission, this method ensures good QoS. 
     In order to determine the required bandwidth to be reserved in a very simple way, at the analysis,the properties of the connection and/or the terminals and/or the used coding method and/or the used decoding method for time-synchronous data transfer could be determined. The analysis of the used coding method and/or decoding method is very simple, since these methods are mentioned explicitly in the SIP messages. 
     In an again very simple way, the reservation of bandwidth could be performed using a QoS management system. The QoS management system could be external to the SIP server and receive reservation requests from the SIP server. The QoS management system could, for example, be designed as a bandwidth broker, also called QoS server. Then bandwidth broker performs the complex task of forwarding the reservations to the individual devices in the network. 
     Now, if several connections between different devices are established, then these bandwidth reservations for different connections can be aggregated to at least one traffic trunk, preferably by the SIP server. This could be used for achieving scalability of the methods described above in the network. 
     With respect to high flexibility, the bandwidth of the traffic trunk could be chosen larger than the actual bandwidth required by the connections. This would allow quickly providing bandwidth to new connections to be established, without requesting additional bandwidth at the bandwidth management system. 
     With respect to an effective reservation of bandwidth, a traffic trunk could aggregate reservations between two end points, particularly access routers or edge routers. Access routers or edge routers could be devices connecting a large number of terminals to the Internet. 
     With respect to high flexibility concerning new connections to be established, a new connection between a first terminal and a second terminal via at least two end points could be mapped to the respective traffic trunk. This trunk would be the already existing traffic trunk between the two end points. This would largely avoid the creation of new traffic trunk at connection establishment as well as the related effort. 
     For ensuring good QoS, the SIP server could reject establishment of a new connection, if the required bandwidth of the new connection exceeds the remaining available bandwidth of the trunk. This would ensure that the QoS of already existing connections would not be deteriorated. 
     Alternatively, the SIP server could reserve additional bandwidth for the concerned traffic trunk, if the required bandwidth of a new connection to be established exceeds the remaining available bandwidth of the trunk. This would ensure that very few requested connections would be rejected, and that in most cases a connection would be established. 
     With respect to cost-effectiveness, the SIP server could reduce the reserved bandwidth for a traffic trunk if the bandwidth required by the connections is much less that the reserved bandwidth. 
     With respect to flexibility, the reservation of bandwidth, particularly between all end points server by the SIP server, could be performed before any connection is established. This can be based on an analysis of reservations in the past. 
     When the invented method is available, terminals have—with some restrictions—a free choice of the SIP server to use. The SIP server is realized In general as a SIP proxy server. A service provider could offer two different SIP servers, one offering QoS according to the methods described above, and a conventional one without this function. Then the service provider could charge a higher price for connections with QoS guarantees, while also offering connections without QoS guarantees for a lower price or free of charge to users who do not require QoS guarantees. 
     Several variants of the invention can be implemented. Particularly, for the selection of the SIP server that performs the analysis, particularly of the SIP messages, and the reservation of resources for a traffic trunk as well as the modifications of reservations for the traffic trunks. The SIP server could be selected out of a chain of SIP servers involved in forwarding SIP signalling messages. The reservation and modification of reservation for traffic trunks could be based on the observation of actual observed usage of resources. 
     Another variant would be an explicit signalling of QoS requirements of coding methods and decoding methods used by the terminals to the SIP server. For this purpose, for example an extension of the SIP protocol could be defined and used. This would imply that the SIP server no longer would need to analyze SIP messages with respect to properties of the terminals, particularly concerning the used coding method in order to determine the required QoS parameters of the connection. Instead, it would receive these parameters directly from the terminals using the SIP extensions for signalling. 
     The invention offers a technically feasible and scalable way of integrating SIP-signalled transfer of time-synchronous data with QoS guarantees in networks. Preferably, the QoS parameters are derived from an analysis of SIP messages while the messages are forwarded by the SIP server. An advantage of the invention is that no extensions of the SIP protocol are required for offering QoS guarantees. Resource reservations for individual connections are aggregated by the SIP server into traffic trunks. These traffic trunks can then be adapted to the observed usage of the trunks. This way, the invention is a highly scalable method that can be used for installing large Internet telephony networks. The investment in the new technology is relatively small, because only the SIP server needs to be extended. A change of the terminals is not required.