Prospects of Peer-to-Peer SIP for Mobile Operators

1. Prospects of Peer-to-Peer SIP for Mobile Operators 8.7.2007 Master’s Thesis Author Juho Seppänen Supervisor Jörg Ott

2. Agenda • Background • Problem statement • Methodology • Locating SIP servers in SIP [RFC 3263] • DHT overlay network • P2PSIP • Mobile operators’ role in P2PSIP • Conclusions

3. Background • P2P applications developed since Napster and gained wide popularity • 60-80% of all Internet traffic is generated by ~30% of all subscribers (of which BitTorrent alone account for 30%) • Skype has become a rival for traditional telecom operators (with over 170M users) • Uses P2P technology to avoid heavy infrastructure costs • P2P is now being applied to SIP in order to have a open standard for P2P person communication (Skype has shown the need and interest for such a system) • The evolution of voice trunking is changing from traditional circuit-switched networks to digital packets-switched networks • The intelligence of the end-points can be exploited to push the intelligence from the network to the terminals • Has enabled the convergence of telecom operated personal communication environment with the Internet environment

4. Problem Statement • General nature of user communication is person-to-person • The usage of P2P networking for user communication appears a very logic approach • Network intelligence is diminishing, and even intelligent terminals can access Internet more easily • Operators are challenged to adapt to upcoming changes in order to preserve their revenues • Cost-effective P2P-based networks for user communication can be regarded as a threat for telecom operators • Network intelligence is diminishing (vendors driving the evolution out from closed telecom environments) • P2PSIP makes it even more challenging • Instead of regarding P2PSIP as a threat, a telecom operator could find how to make profit of it

5. Methodology • The study is conducted in two parts 1. Literature study • Technical background of the P2PSIP components (P2P&SIP) • P2P overlay operations model • Mobile Operator (MO) role evaluation • Interworking • Operator solutions (in own infra and for public infra) • Impacts of P2PSIP on telecom operators

6. Locating SIP servers in SIP [RFC 3263] • SIP servers in conventional SIP are located as per RFC 3263 • The Session Initiation Protocol (SIP) uses DNS procedures to allow a client to resolve a SIP Uniform Resource Identifier (URI) into the IP address, port, and transport protocol of the next hop to contact. • It also uses DNS to allow a server to send a response to a backup client if the primary client has failed. This document describes those DNS procedures in detail. • P2PSIP replaces this procedure by using a structured DHT overlay A conventional SIP session establishment procedure, where DNS procedures (not shown) are used to find SIP servers

7. DHT overlay network 1/2 • P2PSIP uses DHT (Distributed Hash Table) to form the overlay • Different DHT implementations allowed (Chord support required) • Distributed algorithms in structured P2P overlay networks implement the DHT abstraction to construct an identifier space for resource discovery within the overlay. • Every peer has a responsibility area of the entire key space (keys hashed e.g. from SIP URI) • Overlay has a deterministic structure • Messages can be sent to the direction where (i.e. whereabouts) the destination is known to be • Typically O(logN) hops required to reach a service, where N is the number of peers within the overlay (In a client-server architecture only O(1) hops required)

8. DHT overlay network 2/2 • Chord (among other DHT implementations) uses DHT as a substrate for the overlay structure • Chord is the most prominent DHT algorithm for P2PSIP to be required • Other DHT implementations exists (Bamboo, CAN, Pastry, Kademlia etc.)

9. Peer-to-Peer SIP (P2PSIP) 1/4 General info • Developed in the IETF (still under development, ready 2008/2009) • Main goal of P2PSIP: • Replace the procedure of locating SIP servers (RFC 3263) in SIP with a structured P2P overlay • P2PSIP does not need dedicated servers or managed infrastructure (aims to be a pure P2P system) • Functionality of P2PSIP could be, however, enhanced with some servers • enrolment server and bootstrap server to increase security and to help finding some peer of the overlay to be joined • SIP is reused in P2PSIP (includes some new headers) • Reused for routing session establishment analogous to the conventional SIP) • P2PSIP (just like SIP) is not meant as a replacement for existing TDM (Time Division Multiplexing) telephony systems, such as 2G/3G and PSTN.

10. Peer-to-Peer SIP (P2PSIP) 2/4 P2PSIP Overlay • Peer connections based on a DHT overlay connections (Chord used in this example) • NAT traversal is taken care of, as NATs introduce the problem of non-transitive connectivity • Solved using either superpeer or fully-distributed approach • Superpeers widely used in current P2P networks • Fully-distributed uses persistent connections between equal peers. These connections are used to traverse NATs • Different kind of resources are possible (new ones can be developed)

11. Peer-to-Peer SIP (P2PSIP) 3/4 Interworking 1 • Interworking is important for wide acceptance of P2PSIP, but also for telecom operators and service providers to benefit in providing rich services for users • Interworking supported by the P2PSIP standard • Conventional SIP (supported in the P2PSIP standard) • Other P2PSIP overlays running different DHT • Other possible (i.e. feasible) interworking cases • Fixed and mobile networks (PSTN&PLMN gateway) • IMS networks and its services • Other IMS-based networks • DOCSIS (cable network) • TISPAN (standardization body for convergence of fixed networks and Internet convergence)

12. Peer-to-Peer SIP (P2PSIP) 4/4 Interworking 2 • Interworking between a conventional SIP domain and P2PSIP overlay supported in P2PSIP • P2PSIP Proxy Peer (and Relay Agent Peer) as enablers for interworking • Proxy Peer as a gateway (converts the signalling) Interworking between Conventional SIP and P2PSIP

13. Mobile operators’ role in P2PSIP 1/3 • As the P2PSIP is an open standard, it can be used also for commercial purposes (as SIP can be to provide VoIP solutions) • What a MO can do (in general)? • Ignore the P2P traffic • Provide only the data pipe • Impede • Filter P2P traffic and force to use their IMS • Fill the gaps • Provide access-level-service for upgrading reachability • Provide “some” services to applications • We focus on the last one in identifying the MOs’ role in P2PSIP • MO can find its role in P2PSIP environment, but it is possible that as it wins, it also loses (if the P2PSIP services rival with current services) • In the long run, MOs might only lose, if not participating by just providing the data pipe

14. Mobile operators’ role in P2PSIP 2/3 • Potential identified roles for MOs (list includes only some possible roles) • Providing services for outside (e.g. private) P2PSIP networks • Providing access to services e.g. PSTN gateway and IMS (e.g. by providing a superpeer for outside overlays as a gateway) • Emergency calls • Security authority (e.g. enrolment service (e.g. SIM auth) & bootstrap server) • Directory of other public P2PSIP networks as a rendez-vous point (and possibly with integrated security service)

15. Mobile operators’ role in P2PSIP 3/3 • In MOs own network • Provide PSTN/PLMN gateway for access to telephony network (as is in Skype) • Use P2PSIP as a signalling protocol to implement distributed apps, grid computing etc. • Provide a VoIP solution by providing entire P2PSIP networks for customers (e.g. companies) • (Lawful interception may be required, if operator run a public P2PSIP network) • Scalable server farms (DHT running among the servers) • IMS (partly or entirely) • To replace e.g. HSS with a distributed directory • AS an alternative for IMS • Operators are buying their infrastructure from vendors. If vendors provide infrastructures that use P2PSIP, operators could be interested (as the infrastructure would be more lightweight)

16. Conclusions • P2P networking has evolved a powerful tool for communication without servers (today ~70% of Internet traffic is P2P) • Main P2P networks are for file sharing (e.g. BitTorrent). Skype dominant in VoIP. • The proprietary Skype has shown the feasibility of a cost-effective global VoIP service (even for free calls) using P2P networking • P2PSIP gives a standard P2P VoIP (and other multimedia) protocol using SIP. Enables everyone to form Skype-like networks. • Mobile operators (MOs) are challenged to adapt to upcoming changes in order to preserve their revenues • P2P networking enables global VoIP services without need of heavy infrastructures • Terminals are more capable and not tied to operator environment anymore • MOs can identify roles in P2PSIP environment without hindering current segments of services portfolio. • not just ignore (i.e. provide only the data pipe) or try to impede the P2P traffic, but provide access-level-service for upgrading reachability and “some” services to applications

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18. Mobile Operator to adopt P2PSIP • The MOs will adopt P2PSIP under the following circumstances 1. It puts the issue of recurring revenues to bed long enough for a bond issue 2. It permits a level of certainty regarding customer retention 3. It allows them to offer different services at different prices to different people 4. It allows them to shrink their OPEX enough to make more and charge less 5. It keeps happy enough emergency and government entities (e.g. lawful interception) 6. It allows them to do what they do best, bury costs in ongoing charges and fees