Network Working Group Hans Hannu, Ericsson (Editor) INTERNET-DRAFT Sweden Expires: March 2002 September 5, 2001 Signaling Compression Requirements & Assumptions Status of this memo This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC2026. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet-Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or cite them other than as "work in progress". The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/lid-abstracts.txt The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html This document is a submission of the IETF ROHC WG. Comments should be directed to its mailing list, rohc@cdt.luth.se. Abstract The purpose of this document is to outline requirements on a signaling compression scheme which is able to compress/decompress messages from signaling protocols, such as SIP/SDP. Hannu [Page 1] INTERNET-DRAFT Signaling Compression req. & assumptions Sept. 05 , 2001 0. Document History - June 7, 2001, version 00. First version - July 06, 2001, version 01. Updated with additional requirements - September 05, 2001, version 02. Part of the problem draft, , has been included. Deleted requirements from previous version: Number 9 and 12. Changed requirements (previous->current): 13->6, 11->9, 6->10, 10-modified->7, 8-modified->8, 10-modified->7, 7-modified->11, New requirements: Number 3a and 12. TABLE OF CONTENTS 1. Introduction..................................................3 1.2. Protocol characteristics....................................3 1.2.1. SIP.......................................................3 1.2.2. SDP.......................................................3 1.2.3. RTSP......................................................4 1.2.4. Protocol similarities.....................................4 1.3. Cellular system radio characteristics.......................4 2. Motivation for signaling reduction............................5 2.1. Estimation of Call Setup Delay using SIP/SDP................5 2.1.1. Delay results.............................................6 3. Alternatives for signaling reduction..........................7 4. Requirements..................................................8 4.1. General requirements........................................8 4.2. Performance requirements....................................9 4.2.1. Robustness...............................................10 4.2.2. Compression efficiency...................................10 5. Security considerations.......................................11 6. IANA considerations...........................................11 7. Editor's address..............................................11 8. References....................................................11 Appendix A. Test sequences.......................................12 Hannu [Page 2] INTERNET-DRAFT Signaling Compression req. & assumptions Sept. 05 , 2001 1. Introduction In wireless environments and especially in cellular systems, such as GSM/GPRS, there is a need to maximize the transport efficiency of data over the radio interface. The radio spectrum is rather expensive and must be used carefully. Therefore the cellular systems must support a sufficient number of users to make them economical feasible. Thus, there is a limitation in the per user bandwidth. Compressing the headers of the IP-protocols used for carrying user data is one way to make more efficient use of the scarce radio resources [ROHC]. However, compression of the messages from signaling protocols, such as SIP/SDP, should also be considered to increase the radio resource usage even further. Compression will also improve the service quality, by reducing the user idle time, at e.g. call setup. When IP will be used end-to-end, new applications, such as streaming, will be brought to the cellular devices. This will introduce additional traffic in cellular systems. Compression of signaling messages, such as RTSP [RTSP], should also be considered to improve both the service availability and quality. New services with their corresponding signaling protocols make it reasonable to consider a scheme that is generic. The scheme should be generic in the meaning that the scheme efficiently can be applied to arbitrary protocols with certain characteristics, such as the ASCII based protocols SIP and RTSP. 1.2. Protocol characteristics The following application signaling protocols will be used in future cellular systems. Some of their characteristics are described below. 1.2.1 SIP The Session Initiation Protocol [SIP] is an application layer protocol for establishing, modifying and terminating multimedia sessions or calls. These sessions include Internet multimedia conferences, Internet telephony and similar applications. SIP can be used over either TCP [TCP] or UDP [UDP]. SIP is a text based protocol, using ISO 10646 in UTF-8 encoding. 1.2.2 SDP The Session Description Protocol [SDP] is used to advertise multimedia conferences and communicate conference addresses and conference tool specific information. It is also used for general real-time multimedia session description purposes. SDP is carried in the message body of SIP and RTSP messages. SDP is text based using the ISO 10646 character set in UTF-8 encoding. Hannu [Page 3] INTERNET-DRAFT Signaling Compression req. & assumptions Sept. 05 , 2001 1.2.3 RTSP The Real Time Streaming Protocol [RTSP] is an application level protocol for controlling delivery of data with real-time properties, such as audio and video. RTSP may use UDP or TCP (or other) as transport protocol. RTSP is text based using the ISO 10646 character set in UTF-8 encoding. 1.2.4 Protocol similarities The above protocols have many similarities. These similarities will have implications on solutions to the problems they create in conjunction with the cellular radio access. The similarities include: -Requests and reply characteristics. When a sender sends a request, it stays idle until it has received a response. Hence, it typically takes a number of round trip times to conclude e.g. a SIP session. -They are ASCII based. -They are generous in size in order to provide the necessary information to the session participants. -SIP and RTSP share many common header field names, methods and status codes. The traffic patterns are also similar. The signaling is carried out primarily under the set up phase. For SIP this means that the majority of the signaling is carried out to set up a phone call or multimedia session. For RTSP the majority of the signaling is done before the transmission of application data. 1.3. Cellular system radio characteristics Partly to enable high utilization of cellular systems and partly due to the unreliable nature of the radio media, cellular links have characteristics that differ somewhat from a typical fixed link, e.g. copper or fiber. The most important characteristics are the lossy behavior of cellular links and the large round trip times. The quality in a radio system typically changes from one radio frame to another due to fading in the radio channel. Due to the nature of the radio media and interference from other radio users, the average bit error rate (BER) can be 10e-3 with a variation roughly between 10e-2 to 10e-4. To be able to use the radio media with its error characteristics, methods such as forward error correction (FEC) and interleaving are used. If these methods were not used, the BER of a cellular radio channel would be around 10 %. Thus, radio links are by nature error prone. The final packet loss rate may be further reduced by applying low level retransmissions (ARQ) over the radio channel; this, however, trades decreased packet loss rate for a larger delay. Hannu [Page 4] INTERNET-DRAFT Signaling Compression req. & assumptions Sept. 05 , 2001 By applying methods to decrease BER, the system delay is increased. In some cellular systems, the algorithmic channel round trip delay is in the order of 80 ms. Other sources of delays are DSP-processing, node-internal delay and transmission. A general value for the RTT is difficult to state, but it might be as high as 200 ms. For cellular systems it is of vital importance to have a sufficient number of users per cell; otherwise the system cost would prohibit deployment. It is crucial to use the existing bandwidth carefully; hence the average user bit rate is typically relatively low compared to the average user bit rate in wired line systems. This is especially important for mass market services like voice. 2. Motivation for signaling reduction The need for solving the problems caused by the signaling protocol messages is exemplified in this chapter by looking at a typical SIP/SDP Call Setup sequence over a narrow band cellular channel. 2.1 Estimation of Call Setup Delay using SIP/SDP Figure 2.1 shows an example of SIP signaling between two termination points with a wireless link between, and the resulting delay under certain system assumptions. It should be noted that the used figures represent a very narrow band link even if e.g. a WCDMA system can provide maximum bit rates up to 2 Mbits/s in ideal conditions. However, this requires that one user consumes all radio resources in a cell. For a mass market service such as voice, it is always crucial to reduce the bandwidth requirements for each user. The one way delay is calculated according to the following equation: OneWayDelay = MessageSize[bits]/LinkSpeed[bits/sec] + RTT[sec] / 2 (eq. 1) The following values have been used: RTT/2: 70 ms LinkSpeed 9.6 kbps The delay formula is based on an approximation of a WCDMA radio access method for speech services. The approximation is rather crude. For instance, delays caused by possible retransmissions due to errors are ignored. Further, these calculations also assume that there is only one cellular link in the path and also take delays in an eventual intermediate IP-network into account. Even if this Hannu [Page 5] INTERNET-DRAFT Signaling Compression req. & assumptions Sept. 05 , 2001 approximation is crude, it is still sufficient to provide representative numbers and enable comparisons. The message size given in Figure 2.1, is typical for a SIP/SDP call setup sequence. Client Network-Proxy Size [bytes] Time [ms] | | |---------- INVITE --------->| 620 517+70=587 | | |<-- 183 Session progress ---| 500 417+70=487 | | |---------- PRACK ---------->| 250 208+70=278 | | |<----- 200 OK (PRACK) ------| 300 250+70=320 : : |<...... RSVP and SM .......>| : : |---------- COMET ---------->| 620 517+70=587 | | |<----- 200 OK (COMET) ------| 450 | | + |<------ 180 Ringing --------| 230 567+70=637 | | |---------- PRACK ---------->| 250 208+70=278 | | |<----- 200 OK (PRACK) ------| 300 | | + |<--------- 200 OK ----------| 450 625+70=695 | | |----------- ACK ----------->| 230 192+70=262 Figure 2.1. SIP signaling delays assuming a link speed of 9600 bits/sec and a RTT of 140 ms. 2.1.1 Delay results Applying equation 1 to each SIP/SDP message shown in the example of Figure 2.1 gives a total delay of 4131 ms from the first SIP/SDP message to the last. The RSVP and Session Management (Radio Bearer setup), displayed in Figure 2.1 will add approximately 1.5 seconds to the total delay, using equation 1. However, there will also be RSVP and SM signaling prior to the SIP INVITE message to establish the radio bearer, which would add approximately another 1.5 seconds. In [TSG] there is a comparison between GERAN call setup using SIP and ordinary GSM call setup. For a typical GSM call setup the time is about 3.6 seconds, and for the case when using SIP, the call setup is approximately 7.9 seconds. Hannu [Page 6] INTERNET-DRAFT Signaling Compression req. & assumptions Sept. 05 , 2001 Another situation that would benefit from reduced signaling is when carrying signaling messages over narrow bandwidth links in mid-call. For GERAN, this will result in frame stealing with degraded speech quality as a result. Thus, solutions are needed to reduce the signaling delay and the required bandwidth when considering both system bandwidth requirements and service setup delays. 3. Alternatives for signaling reduction More or less attractive solutions to the previously mentioned problems can be outlined: * Increase the user bit rate. An increase of the bit rate per user will decrease the number of users per cell. There exist systems (for example WCDMA) which can provide high bit rates and even variable rates for instance at setup of new sessions. However, there are also systems, e.g. GSM/EDGE, where it is not possible to reach these high bit rates in all situations. At the cell borders, for example, the signal strength to noise ratio will be lower and result in a lower bit rate. In general, an unnecessary increase of the bit rate should be avoided due to the higher system cost introduced and the possibility of denial of service. The latter could for example be caused by lack of enough bandwidth to support sending of the large setup message within a required time period, which is set for QoS reasons. * Decrease the RTT of the cellular link Decreasing the RTT would require substantial system changes and is thus not feasible. Further, the RTT-delay due to interleaving and FEC will always have to be present regardless of which system is used. Otherwise the BER will be too high for the received data to be useful, or alternatively trigger retransmissions giving an average total delay of the same or higher magnitude. * Optimize message sequence for the protocols. If the request/response pattern could be eased up, then "keeping the pipe full" could be a way forward. Thus, instead of following the message sequence described in Figure 4.2, more than one message would be sent in row, even though no response has been received. However, this would entail protocol changes and may be difficult at current date. Hannu [Page 7] INTERNET-DRAFT Signaling Compression req. & assumptions Sept. 05 , 2001 * Protocol stripping. Removing fields from a message would decrease the size of the messages to some extent. However, this would cause loss of transparency and thus violate the End-to-End principle and is thus not desirable. * Compression. By compressing messages, the impact of the mentioned problems could be decreased. Compared to the other possible solutions compression can be made, and must be, transparent to the end-user application. Thus, compression seems to be the most attractive way forward. 4. Requirements This chapter states requirements for a signaling compression scheme to be developed in the IETF ROHC WG. The requirements are divided into two parts. Section 4.1 sets general requirements concerning the Internet infrastructure, while Section 4.2 sets requirements on the scheme itself. 4.1. General requirements 1. Transparency: When a message is compressed and then decompressed the result must be bitwise identical to the original message. The transparency must be maintained independently of the payload. Justification: This is to ensure that the compression scheme will not cause problems for any current or future part of the Internet infrastructure. Note: See also requirement 8. 2. Header compression coexistence: The compression scheme must be able to coexist with header compression, especially the ROHC protocol. Justification: Signaling compression is used because there is a need to conserve bandwidth usage. In that case, header compression will likely be needed too. 3a. Compatibility: The compression scheme must be constructed in such a way that it does not exclude other protocols' mechanisms to negotiate whether the compression scheme is to be applied or not. Hannu [Page 8] INTERNET-DRAFT Signaling Compression req. & assumptions Sept. 05 , 2001 Justification: Two entities must be able to communicate regardless if the signaling compression scheme is implemented at both entities or not. 3b. Ubiquity: Modifications to the protocols, which generate the messages that are to be compressed, must not be required for the compression scheme to work. Justification: This will simplify deployment of the compression scheme. Note: This does not preclude making extensions, which are related to the signaling compression scheme, to existing protocols, as long as the extensions are backward compatible. 4. Generality: Compression of arbitrary message streams must be supported. The signaling compression scheme must not be limited to certain protocols, traffic patterns or sessions. It must not assume any message pattern to be able to perform compression. Justification: There might be a future need for compression of different ASCII based signaling protocols. This requirement will minimize future work. Note: This does not preclude optimization for certain streams. 5. Unidirectional routes: The compression scheme must operate on unidirectional routes, i.e. without explicit feedback messages from the decompressor. Note: Implementations on unidirectional routes might possibly show a degraded performance compared to implementations on bi-directional routes. 4.2. Performance requirements 6. Scalability: The scheme must be flexible to accommodate a range of compressor/decompressor with varying memory and processor capabilities. Justification: A primary target for the signaling compression scheme is cellular systems, where the mobile terminals have varying capabilities. 7. Delay: The signaling compression must not noticeably add to the delay experienced by the end user. Hannu [Page 9] INTERNET-DRAFT Signaling Compression req. & assumptions Sept. 05 , 2001 Justification: Reduction of the user experienced delay is the main purpose of signaling compression. Note: This requirement is intended to prevent schemes that achieve compression efficiency at the expense of delay, i.e. queuing of messages to improve the compression efficiency should be avoided. The section on scheme specific requirements is divided into two subsections, a robustness section and a compression efficiency section. 4.2.1. Robustness The requirements in this section concern the issue when compressed messages should be correctly decompressed. The transparency requirement (first requirement), covers the issue with faulty decompressed messages. 8. Residual errors: The compression scheme must be resilient against errors undetected by lower layers, i.e. the probability of incorrect decompression caused by such undetected errors must be low. Justification: A primary target for the signaling compression scheme is cellular systems, were undetected errors might be introduced on the cellular link. 9. Error propagation: Propagation of errors due to signaling compression should be kept at an absolute minimum. Loss or damage to a single or several messages, between compressor and decompressor should not prevent compression and decompression of later messages. Justification: Error propagation reduces resource utilization and quality. 10. Delay: The compression scheme must be able to perform compression and decompression of messages under all expected delay conditions. 4.2.2. Compression efficiency This section states requirements concerning compression efficiency. 11. Message loss: Loss or damage to a single or several messages, on the link between compressor and decompressor, should not prevent the usage of later messages in the compression and decompression process. Hannu [Page 10] INTERNET-DRAFT Signaling Compression req. & assumptions Sept. 05 , 2001 12. Moderate message misordering: The scheme should be able to decompress moderate misordered (1-2 messages) messages between compressor and decompressor. The scheme should not prevent the usage of later message in the compression and decompression process. Justification: Misordering is frequent on the Internet, and this kind of misordering is common. 5. Security considerations A protocol specified to meet these requirements must be able to cope with packets that has undergone security measures, such as encryption, without adding any security risks. This document by itself, however, does not add any security risks. 6. IANA considerations A protocol which meets these requirements will require the IANA to assign various numbers. This document by itself, however, does not require any IANA involvement. 7. Editor's Address Hans Hannu Tel: +46 920 20 21 84 Ericsson Erisoft AB Lulea, Sweden EMail: Hans.Hannu@epl.ericsson.se 8. References [ROHC] C. Bormann, Et. al., RObust Header Compression, RFC 3095, July 2001. [RTSP] H. Schulzrinne, A. Rao and R. Lanphier, Real Time Streaming Protocol (RTSP), RFC 2326, April 1998. [SDP] M. Handley and V. Jacobson, SDP: Session Description Protocol, RFC 2327, April 1998. [SIP] M. Handley, H. Schulzrinne, E. Schooler and J. Rosenberg, SIP: Session Initiation Protocol, RFC 2543, August 2000. [TCP] J. Postel, Transmission Control Protocol, RFC 793, September 1981. [TSG] Nortel Networks, A Comparison Between GERAN Packet- Switched Call Setup Using SIP and GSM Circuit-Switched Hannu [Page 11] INTERNET-DRAFT Signaling Compression req. & assumptions Sept. 05 , 2001 Call Setup Using RIL3-CC, RIL3-MM, RIL3-RR, and DTAP, 3GPP TSG GERAN #2, GP-000508, 6-10 November 2000. [UDP] J. Postel, User Datagram Protocol, RFC 761, August 1980. This Internet-Draft expires in January 2002. Appendix A. Test sequences The SIP message sequences depicted in figure A1 and A2, should be used to test the compression scheme for compression efficiency and processing and memory requirements. Call Setup delays should be calculated according to equation (1) in section 2.1. User A User B | | | INVITE F1 | |----------------------->| | (100 Trying) F2 | |<-----------------------| | 180 Ringing F3 | |<-----------------------| | | | 200 OK F4 | |<-----------------------| | ACK F5 | |----------------------->| | Both Way RTP Media | |<======================>| | | | BYE F6 | |<-----------------------| | 200 OK F7 | |----------------------->| | | Figure A1. From "draft-ietf-sip-call-flows-05.txt". Message Details: F1 INVITE User A -> User B INVITE sip:UserB@there.com SIP/2.0 Via: SIP/2.0/UDP here.com:5060 From: BigGuy To: LittleGuy Call-ID: 12345601@here.com CSeq: 1 INVITE Contact: Content-Type: application/sdp Hannu [Page 12] INTERNET-DRAFT Signaling Compression req. & assumptions Sept. 05 , 2001 Content-Length: 147 v=0 o=UserA 2890844526 2890844526 IN IP4 here.com s=Session SDP c=IN IP4 100.101.102.103 t=0 0 m=audio 49172 RTP/AVP 0 a=rtpmap:0 PCMU/8000 F2 (100 Trying) User B -> User A SIP/2.0 100 Trying Via: SIP/2.0/UDP here.com:5060 From: BigGuy To: LittleGuy Call-ID: 12345601@here.com CSeq: 1 INVITE Content-Length: 0 F3 180 Ringing User B -> User A SIP/2.0 180 Ringing Via: SIP/2.0/UDP here.com:5060 From: BigGuy To: LittleGuy ;tag=8321234356 Call-ID: 12345601@here.com CSeq: 1 INVITE Content-Length: 0 F4 200 OK User B -> User A SIP/2.0 200 OK Via: SIP/2.0/UDP here.com:5060 From: BigGuy To: LittleGuy ;tag=8321234356 Call-ID: 12345601@here.com CSeq: 1 INVITE Contact: Content-Type: application/sdp Content-Length: 147 v=0 o=UserB 2890844527 2890844527 IN IP4 there.com s=Session SDP c=IN IP4 110.111.112.113 t=0 0 m=audio 3456 RTP/AVP 0 a=rtpmap:0 PCMU/8000 F5 ACK User A -> User B Hannu [Page 13] INTERNET-DRAFT Signaling Compression req. & assumptions Sept. 05 , 2001 ACK sip:UserB@there.com SIP/2.0 Via: SIP/2.0/UDP here.com:5060 From: BigGuy To: LittleGuy ;tag=8321234356 Call-ID: 12345601@here.com CSeq: 1 ACK Content-Length: 0 F6 BYE User B -> User A BYE sip:UserA@here.com SIP/2.0 Via: SIP/2.0/UDP there.com:5060 From: LittleGuy ;tag=8321234356 To: BigGuy Call-ID: 12345601@here.com CSeq: 1 BYE Content-Length: 0 F7 200 OK User A -> User B SIP/2.0 200 OK Via: SIP/2.0/UDP there.com:5060 From: LittleGuy ;tag=8321234356 To: BigGuy Call-ID: 12345601@here.com CSeq: 1 BYE Content-Length: 0 Entity A Entity B | | | INVITE F1 | |----------------------->| | (100 Trying) F2 | |<-----------------------| | 183 Session Progress F3| |<-----------------------| | PRACK F4 | |----------------------->| | 200 OK F5 | |<-----------------------| | COMET F6 | |----------------------->| | 200 OK F7 | |<-----------------------| | 180 Ringing F8 | |<-----------------------| | PRACK F9 | |----------------------->| | 200 OK F10 | Hannu [Page 14] INTERNET-DRAFT Signaling Compression req. & assumptions Sept. 05 , 2001 |<-----------------------| | 200 OK F11 | |<-----------------------| | ACK F12 | |----------------------->| | Both Way RTP Media | |<======================>| | BYE F13 | |----------------------->| | 200 OK F14 | |<-----------------------| | | Figure A2. From "3GPP TS 24.228 (v0.4.0 March/2001)". Message Details: F1 INVITE Entity A -> Entity B INVITE sip:+1-212-555-2222@home.net;user=phone SIP/2.0 Via: SIP/2.0/UDP [5555::aaa:bbb:ccc:ddd] Supported: 100rel Remote-Party-ID: John Doe Proxy-Require: privacy Anonymity: Off From: Alien Blaster ; tag=171828 To: sip:B36(SHA-1(+1-212-555-2222; time=36123E5B; seq=73))@localhost Call-ID: B36(SHA-1(555-1111;time=36123E5B;seq=72))@localhost Cseq: 127 INVITE Contact: sip:[5555::aaa:bbb:ccc:ddd] Content-Type: application/sdp Content-length: 253 v=0 o=- 2987933615 2987933615 IN IP6 5555::aaa:bbb:ccc:ddd s=- c= IN IP6 5555::aaa:bbb:ccc:ddd b=AS:64 t=907165275 0 m=audio 3456 RTP/AVP 97 3 96 a=rtpmap:97 AMR a=fmtp:97 mode-set=0,2,5,7; maxframes=2 a=rtpmap:96 G726-32/8000 a=qos:mandatory sendrecv F2 (100 Trying) Entity B -> Entity A SIP/2.0 100 Trying Via: SIP/2.0/UDP [5555::aaa:bbb:ccc:ddd] Hannu [Page 15] INTERNET-DRAFT Signaling Compression req. & assumptions Sept. 05 , 2001 From: Alien Blaster ; tag=171828 To: sip:B36(SHA-1(+1-212-555-2222; time=36123E5B; seq=73))@localhost Call-ID: B36(SHA-1(555-1111;time=36123E5B;seq=72))@localhost CSeq: 127 INVITE Content-length: 0 F3 183 Session Progress Entity B -> Entity A SIP/2.0 183 Session Progress Via: SIP/2.0/UDP [5555::aaa:bbb:ccc:ddd] Media-Authorization: 9BV3072 Remote-Party-ID: John Smith Anonymity: Off From: Alien Blaster ; tag=171828 To: sip:B36(SHA-1(+1-212-555-2222; time=36123E5B; seq=73))@localhost; tag=314159 Call-ID: B36(SHA-1(555-1111;time=36123E5B;seq=72))@localhost Cseq: 127 INVITE Contact: sip:token1@pcscf1.home.net RSeq: 9021 Content-Disposition: precondition Content-Type: application/sdp Content-length: 232 v=0 o=- 2987933615 2987933615 IN IP6 5555::aaa:bbb:ccc:ddd s=- c= IN IP6 5555::eee:fff:aaa:bbb b=AS:64 t=907165275 0 m=audio 6544 RTP/AVP 97 3 a=rtpmap:97 AMR a=fmtp:97 mode-set=0,2,5,7; maxframes=2 a=qos:mandatory sendrecv confirm F4 PRACK Entity A -> Entity B PRACK sip:token1@pcscf1.home.net SIP/2.0 Via: SIP/2.0/UDP [5555::aaa:bbb:ccc:ddd] From: Alien Blaster ;tag=171828 To: ;tag=314159 Call-ID: B36(SHA-1(555-1111;time=36123E5B;seq=72))@localhost Cseq: 128 PRACK Contact: sip:[5555::aaa:bbb:ccc:ddd] Rack: 9021 127 INVITE Content-Type: application/sdp Hannu [Page 16] INTERNET-DRAFT Signaling Compression req. & assumptions Sept. 05 , 2001 Content-length: 222 v=0 o=- 2987933615 2987933615 IN IP6 5555::aaa:bbb:ccc:ddd s=- c= IN IP6 5555::aaa:bbb:ccc:ddd b=AS:64 t=907165275 0 m=audio 3456 RTP/AVP 97 a=rtpmap:97 AMR a=fmtp:97 mode-set=0,2,5,7; maxframes=2 a=qos:mandatory sendrecv F5 200 OK Entity B -> Entity A SIP/2.0 200 OK Via: SIP/2.0/UDP [5555::aaa:bbb:ccc:ddd] From: Alien Blaster ;tag=171828 To: ;tag=314159 Call-ID: B36(SHA-1(555-1111;time=36123E5B;seq=72))@localhost Cseq: 128 PRACK Contact: sip:token2@pcscf1.home.net Content-Length: 0 F6 COMET Entity A -> Entity B COMET sip:token2@pcscf1.home.net SIP/2.0 Via: SIP/2.0/UDP [5555::aaa:bbb:ccc:ddd] From: Alien Blaster ;tag=171828 To: ;tag=314159 Call-ID: B36(SHA-1(555-1111;time=36123E5B;seq=72))@localhost Cseq: 129 COMET Contact: sip:[5555::aaa:bbb:ccc:ddd] Content-Type: application/sdp Content-length: 220 v=0 o=- 2987933615 2987933615 IN IP6 5555::aaa:bbb:ccc:ddd s=- c= IN IP6 5555::aaa:bbb:ccc:ddd b=AS:64 t=907165275 0 m=audio 3456 RTP/AVP 97 a=rtpmap:97 AMR a=fmtp:97 mode-set=0,2,5,7; maxframes=2 a=qos:success sendonly Hannu [Page 17] INTERNET-DRAFT Signaling Compression req. & assumptions Sept. 05 , 2001 F7 200 OK Entity B -> Entity A SIP/2.0 200 OK Via: SIP/2.0/UDP [5555::aaa:bbb:ccc:ddd] From: Alien Blaster ;tag=171828 To: ;tag=314159 Call-ID: B36(SHA-1(555-1111;time=36123E5B;seq=72))@localhost Cseq: 129 COMET Contact: sip:token3@pcscf1.home.net Content-Length: 0 F8 180 Ringing Entity B -> Entity A SIP/2.0 180 Ringing Via: SIP/2.0/UDP [5555::aaa:bbb:ccc:ddd] From: Alien Blaster ;tag=171828 To: ;tag=314159 Call-ID: B36(SHA-1(555-1111;time=36123E5B;seq=72))@localhost Cseq: 129 COMET Content-length: 0 F9 PRACK Entity A -> Entity B PRACK sip:token4@pcscf1.home.net SIP/2.0 Via: SIP/2.0/UDP [5555::aaa:bbb:ccc:ddd] From: Alien Blaster ;tag=171828 To: ;tag=314159 Call-ID: B36(SHA-1(555-1111;time=36123E5B;seq=72))@localhost Cseq: 130 PRACK Contact: sip:[5555::aaa:bbb:ccc:ddd] Rack: 9022 127 INVITE Content-length: 0 F10 200 OK Entity B -> Entity A SIP/2.0 200 OK Via: SIP/2.0/UDP [5555::aaa:bbb:ccc:ddd] From: Alien Blaster ;tag=171828 To: ;tag=314159 Call-ID: B36(SHA-1(555-1111;time=36123E5B;seq=72))@localhost Cseq: 130 PRACK Contact: sip:token5@pcscf1.home.net Content-Length: 0 Hannu [Page 18] INTERNET-DRAFT Signaling Compression req. & assumptions Sept. 05 , 2001 F11 200 OK Entity B -> Entity A SIP/2.0 200 OK Via: SIP/2.0/UDP [5555::aaa:bbb:ccc:ddd] From: Alien Blaster ;tag=171828 To: ;tag=314159 Call-ID: B36(SHA-1(555-1111;time=36123E5B;seq=72))@localhost Cseq: 130 PRACK Contact: sip:token6@pcscf1.home.net Content-Length: 0 F12 ACK Entity A -> Entity B ACK sip:token6@pcscf1.home.net SIP/2.0 Via: SIP/2.0/UDP [5555::aaa:bbb:ccc:ddd] From: Alien Blaster ;tag=171828 To: ;tag=314159 Call-ID: B36(SHA-1(555-1111;time=36123E5B;seq=72))@localhost Cseq: 131 ACK Contact: sip:[5555::aaa:bbb:ccc:ddd] Content-length: 0 F13 BYE Entity A -> Entity B BYE sip:+1-212-555-2222@home.net;user=phone SIP/2.0 Via: SIP/2.0/UDP [5555::aaa:bbb:ccc:ddd] From: Alien Blaster ; tag=171828 To: sip:B36(SHA-1(+1-212-555-2222; time=36123E5B; seq=73))@localhost Call-ID: B36(SHA-1(555-1111;time=36123E5B;seq=72))@localhost CSeq: 132 BYE Content-Length: 0 F14 200 OK Entity B -> Entity A SIP/2.0 200 OK Via: SIP/2.0/UDP [5555::aaa:bbb:ccc:ddd] From: Alien Blaster ; tag=171828 To: sip:B36(SHA-1(+1-212-555-2222; time=36123E5B; seq=73))@localhost Call-ID: B36(SHA-1(555-1111;time=36123E5B;seq=72))@localhost CSeq: 132 BYE Content-Length: 0 Hannu [Page 19]