The Critical Role of Sip&H.323 Internetworking in Next-Generation Telephony

1. The Critical Role of Sip&H.323 Internetworking in Next-Generation Telephony Dr. Samir Chatterjee Associate Professor School of Information Science 909-607-4651; samir.chatterjee@cgu.edu

2. Outline • Definition of SIP and H.323 • Comparison of SIP and H.323 • Complexity • Extensibility • Scalability • Services • Security Mechanisms used in SIP and H.323 • Market Analysis • Conclusions

3. Definition – H.323 • ITU H.323 series of recommendations (“Packet Based Multimedia Communications Systems”) defines protocols and procedures for multimedia communications on the Internet. • It is an umbrella standard that provides a well-defined system architecture and implementation guidelines. • It includes • H.245 for control • H.225.0 for connection establishment • H.332 for large conferences • H.450(.1,.2,.3) for supplementary services • H.235 for security • H.246 for interoperability with circuit-switched services.

4. Definition – SIP • The Session Initiation Protocol (SIP), developed by MMUSIC working group of the IETF, is a signaling protocol for establishing real-time calls and conferences over IP networks. • It resembles HTTP and SMTP. • It uses SDP for media description. • It is not as strictly defined as a complete system like H.323. Therefore, it is flexible and can be adapted to a number of implementations. • It allows for the use of established protocols from other applications, such as HTTP and HTML.

5. Definition - Functional Entities Terminal Terminal Gatekeeper Terminal H.323 Zone PSTN MCU Gateway H.323/SIP gateway H.323 network UA (softphone) SIP telephony gateway SIP network Proxy/ Registrar Enterprise network Redirect server SIP Realm UA (IP phone)

6. H.323 Rather complex protocol Defines hundreds of elements Uses binary representation for its messages → therefore it requires special code generators to parse Uses several protocol components →therefore, many services require interaction between many of them → this also complicates firewall traversal SIP Simpler protocol Defines only 37 headers Encodes its messages as text, similar to HTTP → this allows simple parsing and generation Uses a single request that contains all necessary information Comparison - Complexity Source: schulzrinne and Rosenberg

7. H.323 Provides extensibility generally by use of nonstandardParam fields → this allows for different vendors to develop their own extensions Extensions are limited only to those places where a non-standard parameter has been added It has no mechanisms for allowing terminals to exchange information about which extensions each supports. SIP Built in a rich set of extensibility and compatibility functions Numerical error codes are hierarchically organized → this allows for additional features to be added by defining semantics for the error codes in a class, while achieving compatibility Uses textual encoding which is self describing → this enables developers to determine usage from the name Comparison - Extensibility Source: schulzrinne and Rosenberg

8. H.323 Large Number of Domains It provides no easy way to perform loop detection in complex multi-domain searches. Server Processing The complexity of signaling makes it less scalable. Conference Sizes Three distinct mechanisms exits to support different conference sizes. Comparison - Scalability SIP • Large Number of Domains • It uses a loop detection algorithm which can be performed in a stateless manner. • Server Processing • Simple signaling mechanism makes it more scalable. • Conference Sizes • It scales all different conference sizes. Source: schulzrinne and Rosenberg

9. Comparison - Services • H.323 and SIP offer roughly equivalent call control services. • H.323 provides a much richer set of functionality for capabilities exchange services. • SIP provides rich support for personal mobility services. • H.323 supports various conference control services. Sip does not provide conference control, rather it relies on other protocols for this service. Source: schulzrinne and Rosenberg

10. H.323/H.235 Two mechanisms that provide Authentication or/and Integrity are: Annex D - Baseline Security Profile Hop-by-hop processing Password based security Shared Secret-Key Digest (Hashing) Algorithm Annex E - Signature Security Profile Signature Profile – Public Key Infrastructure (PKI) Certificate Based Security Scalable - applicable for “Global” IP Telephony Hop-by-Hop and End-to-End security Digest Algorithms (Source: Radvision PPT) SIP End-to-end mechanisms Basic authentication Digest authentication S/MIME Hop-by-hop mechanisms Transport Layer Security (TLS) IP Security (IPSec) The SIPS URI schema (source: Ben Campbell presentation) Security Mechanisms

11. SIP Authentication SIP Server SIP Client REQUEST Generate the Nonce value CHALLENGE Nonce, realm Compute response = F(nonce, Username, password, realm) F= MD5 REQUEST Nonce, realm, Username, response Authenticate: compute F(nonce, username, password, realm) And compare with response

12. Chart 1 summarizes the technology supported by the 77 products. (source: Wind River White Paper) Chart 2 summarizes the technology supported by VoIP Service Providers. (source: Wind River White Paper) Market Analysis

13. Interoperability Source: Ho et al.

14. Conclusion • If SIP is better, why is H.323 important? • Huge installed base and backward compatibility is important. • However, newer products may not need H.323. • In videoconferencing world, H.323 is still a dominant player. • Most VoIP products support H.323 and SIP together. But this has the potential to increase the cost, size and power requirements of the products. • An all-SIP network is simple and cleaner to run/manage but we will see H.323/SIP for a long time. • Security mechanisms (authentication, privacy, authorization, integrity, non-repudiation) may well decide their fate.

15. References • www.ietf.org drafts and RFCs (3261, 2543) for SIP • ITU-T and H.323 specifications. • SIP Vs. H.323:A Business Analysis, white paper from WindRiver. • SIP versus H.323, iptel.org/info/trends/sip.html • H.323 versus SIP: A Comparison, packetizer analysis at http://www.packetizer.com/iptel/h323_vs_sip/ • A Comparison of SIP and H.323 for Internet Telephony • Henning Schulzrinne and Jonathan RosenbergNetwork and Operating System Support for Digital Audio and Video (NOSSDAV), (Cambridge, England), July 1998. • For our work on SIP/H.323 security, see http://middleware.internet2.edu/video/