1 The Critical Role of Sip&H.323 Internetworking in Next- Generation Telephony Dr. Samir Chatterjee Associate Professor School of Information Science ;

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 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 MCU Gateway PSTN H.323 Zone Enterprise network UA (softphone) UA (IP phone) Proxy/ Registrar Redirect server SIP telephony gateway H.323/SIP gateway SIP Realm SIP network H.323 network

6 Comparison - Complexity 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 Source: schulzrinne and Rosenberg

7 Comparison - Extensibility 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 Source: schulzrinne and Rosenberg

8 Comparison - Scalability 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. Source: schulzrinne and Rosenberg 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.

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 Security Mechanisms 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)

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

12 Market Analysis 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)

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 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 A Comparison of SIP and H.323 for Internet Telephony Henning Schulzrinne and Jonathan Rosenberg Network and Operating System Support for Digital Audio and Video (NOSSDAV), (Cambridge, England), July For our work on SIP/H.323 security, see