1. SIP-Based or DHT-Based? November 12, 2005 Eunsoo Shim Panasonic Digital Networking Laboratory P2P SIP Ad-hoc Meeting IETF64, Vancouver

2. 2 Why Distributed Hash Tables (DHTs)? High success rate of search If all the DHT routing tables are correct, 100% success. Even for data with little replication Smaller number of replications are easier to maintain consistency for dynamic data  User locations are of dynamic data. Slow delay increase Delay – O(log(N)) hops where N: number of active nodes. Low cost for search No (or few) duplicate query messages High cost for maintenance

3. 3 SIP-Based : Use SIP for Distributed Data Access and Overlay Maintenance SIP Node Registration is used for DHT JOIN. SIP Node Registration expiration is used for DHT LEAVE. User record is created via SIP User Registration INVITE is routed along the path dictated by DHT. DHT layer is a thin layer just maintaining DHT routing table. DHT key information is carried as a part of SIP messages. Additional DHT maintenance information is carried by SIP Registration messages. Existing designs --- Kundan/Henning, Cullen/David DHT Layer SIP Layer 1 5 3 4 6 2 DHT Layer SIP Layer DHT Layer SIP Layer DHT Layer SIP Layer 8 7 9 10 INVITE message flow

4. 4 Pros & Cons of SIP-Based Approach Pros Efficiency: SIP signaling can be combined with search and overlay maintenance  Smaller number of messages, Less delay Can consider SIP semantics in search processes and overlay maintenance.  Ex) Call forking Protocol Reuse: May be able to reuse many things from existing SIP messages Cons Complexity Reusing existing SIP methods may be confusing --- different semantics need more care (Pointed in Alan Johnston’s draft) Only P2P-SIP nodes can participate in the overlay network. Challenge --- how to support different overlay algorithms?

5. 5 DHT-Based DHT layer provides the following interface. Lookup(in key, in type, out data) Place(in key, in type, in data) Resource search is managed by DHT layer. SIP is just an application over DHT layer. DHT provides a kind of distributed data base functions to its applications. DHT lookup messages are generic ---- independent of SIP call semantics or resource types DHT Layer SIP Layer 1 5 3 4 6 2 DHT Layer SIP Layer DHT Layer SIP Layer 7 INVITE message flow

6. 6 About Trapezoid Routing Preserving the trapezoid routing No trapezoid routing DHT UA Proxy UA DHT UA

7. 7 Pros & Cons of DHT-based Approach Pros Clarity No confusion with semantics of existing SIP messages Flexibility Easier to support different overlay algorithms with little change in SIP messages Sharing the overlay network --- common lookup mechanism for many things! No change in DHT operation required to support advanced features of SIP-based P2P VoIP, IM, and Presence Can share the same overlay network with more applications beyond basic VoIP call or IM.  For example, for P2P-based conferencing later. Nodes without SIP entity can participate in the overlay network. Cons Less efficiency No optimization of search and overlay maintenance by using SIP call semantics Separate lookup from call signaling (Invite messages) Defining new protocols Challenge: Can we reuse any existing protocol? Challenge: Can we define a common protocol with extensions for different overlay algorithms?