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SIP-Based or DHT-Based?

SIP-Based or DHT-Based?. P2P SIP Ad-hoc Meeting IETF64, Vancouver. November 12, 2005 Eunsoo Shim Panasonic Digital Networking Laboratory. Why Distributed Hash Tables (DHTs)?. High success rate of search If all the DHT routing tables are correct, 100% success.

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SIP-Based or DHT-Based?

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

  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. 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 10 SIP Layer SIP Layer SIP Layer SIP Layer 3 9 6 7 8 4 5 2 1 DHT Layer DHT Layer DHT Layer DHT Layer INVITE message flow

  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. 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 7 6 SIP Layer SIP Layer SIP Layer 1 5 DHT Layer DHT Layer DHT Layer DHT Layer 2 3 4 INVITE message flow

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

  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?

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