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Peer-to-Peer SIP

Peer-to-Peer SIP. David Bryan July 27, 2005. p2psip.org. Affiliation(s). Overview. Motivation What is Peer-to-Peer? Why P2P SIP? P2P basics Approaches to P2P SIP P2P SIP/SOSIMPLE Problems, barriers, and future work. What is Peer-to-Peer?. Peer-to-Peer (P2P) technology

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Peer-to-Peer SIP

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  1. Peer-to-Peer SIP David Bryan July 27, 2005

  2. p2psip.org Affiliation(s)

  3. Overview • Motivation • What is Peer-to-Peer? • Why P2P SIP? • P2P basics • Approaches to P2P SIP • P2P SIP/SOSIMPLE • Problems, barriers, and future work

  4. What is Peer-to-Peer? • Peer-to-Peer (P2P) technology • Fundamentally different than client server • Nodes cooperate to provide (collectively) the functionality a central server would provide • Not all nodes provide all services/know everything, but as a group they do

  5. What is Peer-to-Peer? Client Server:    

  6. What is Peer-to-Peer? Peer-to-Peer    

  7. Motivating Cases • Small deployments • Security • Lack of resource • Limited/No Internet connectivity • Ad-Hoc and ephemeral groups • Censorship or impeded access • Large scale decentralized communications • Skype (sort of)

  8. Client/Server Session

  9. Organization B Internet Organization A Problem w/Remote Server

  10. Why P2P? • Infrastructure independence • No central servers • Don’t need connectivity • Simple discovery and setup • Privacy • Highly scalable • Lack of central control • Dynamic DNS doesn’t offer all of this

  11. P2P Session

  12. Why SIP? • Widely established protocol • Standards based • Compatibility with existing equipment • Reuse existing software components • Many problems already solved • SIP is already “mostly” P2P • SIP vs. H.323 • Support for both IM and VoIP • SIP/SIMPLE vs. XMPP

  13. Related Work • Skype • Not as P2P as they imply, non-standard • EarthLink’s SIP Share • Use SIP messages to encode filesharing DHT • Others in this area • Kundan Singh/Henning Schulzrinne at Columbia University

  14. P2P Basics • Most famous use of P2P is file sharing • Most famous infamous use of P2P is file sharing • Each user stores some number of files on the network, ask peers for the file • Can also share other resources or services, no need to be files • Connected to each other in a logical network called an overlay

  15. Overlay Network • Collection of nodes, connected logically in some way • The connections in the overlay are frequently not related to those in the physical network

  16. Flooding w/TTL Node broadcasts to neighbors Node(s) respond directly TTL = 1 TTL = 2 TTL = 3

  17. Problems w/Flood • Inefficient! • Lots of network traffic • Multiple nodes respond (can be good or bad) • No guarantee of completion – some outside of TTL “horizon” • Nodes working on behalf of others • DOS risk, but doubles traffic otherwise • Gnutella was a flood based design

  18. Structured P2P • Basic idea is that what you are looking for has an identifier • Locate items in the overlay based on the identifier • Distributed Hash Table (DHT), Content Addressable Networks (CAN) • Since “everything has its place”, eliminate false negatives • Since you can go (close to) directly to the item you want, more efficient

  19. Distributed Hash Tables • Every resource has a keyword, hashed to produce a Resource ID, or key • Every node participating hashes a unique property (IP address) to produce a Node ID • The resource itself, or information about how to find it, for a particular Resource ID is stored at a node with a similar Node ID

  20. Chord • Algorithm/Implementation for a DHT in a circular namespace • 0 and max ID are neighbors • A resource w/key k is stored by the first node with Node ID ≥ k • This node is called the successor node of key k

  21. Example namespace is 0-31 Wraps at 0/31 Values increase clockwise Sometimes called an identifier circle Example Chord Ring 0 31 1 2 3 4 5 6 7 15

  22. Example Chord Ring Node A Node-ID 2 Item A, key = 5 Stores: Item C, key = 30 Node D Node-ID 29 Item B, key = 18 Item C, key = 30 Node C Node-ID 18 Stores: Item B, key = 18 Node B Node-ID 13 Stores: Item A, key = 5 IDs/key namespace is 0-31

  23. Finger Tables • Each node keeps n “fingers” spaced around the ring to route messages (where address space is 2n) • Fingers point 1, 2, 4, …2n-1 away from the node the ring, so nodes know more about neighbors than distant nodes • Most distant finger is ½ the distance across the identifier ring, so all fingers are in the node’s “half” • If no node at the exact value the finger should point to, points to the next actual node

  24. Example Finger Table • Namespace 0-31 is size 25, so 5 fingers • Node is 3, so fingers are: 0 31 1 2 3 4 5 6 7 15

  25. Example Finger Table • Namespace 0-31 is size 25, so 5 fingers • Node is 3, so fingers are: 3 4 5 7 19 11

  26. Example Finger Table • If only nodes 3, 6, 11 are in the overlay: 3 6 11

  27. Routing in Chord • Chord routes by sending messages to some node nearer the desired resource • The nearer node sends to an even closer node on behalf of sender • Process repeats until a node receiving the message knows its successor controls that space • Returns address of successor, sender and responsible node then exchange data

  28. Applying this to SIP • Use pure DHT to find the other UAs • Could leverage standards for DHT, but there aren’t any • Some firewalls block DHT traffic as “file sharing” • Use DHT for location, but implemented as SIP messages • Essentially, use DHT as another registration/location mechanism • Requires some “tweaks” to Chord • Use standard SIP to signal once resources are located

  29. SOSIMPLE • Protocol suggested by myself and Cullen Jennings of Cisco • Available as IETF Internet-Draft • Implemented and being studied at William & Mary • Implements a Chord-like DHT using SIP • All traffic is SIP messages • Very similar to Chord, only slight changes

  30. Node vs. User Operations • Operations can be either Node operations, or User operations • Node operations are DHT related – a node joining, a node leaving, a node updating its finger table • Use REGISTER for much of this • User operations are completely separate • More traditional SIP registration here • Registration is stored by Resource ID of hashed username • A user’s node has a Node ID, but their User ID, and thus registration, will be stored at a different node • Once a user’s node joins, only means the node is in the DHT. Still need to do a user registration to make calls

  31. Node Joining Joining Node Node-ID 503 1. REGISTER Bootstrap Node Node-ID 023 302 Node B 2. REGISTER Node B Node-ID 245 302 Node C 3. REGISTER Differences from Chord: node answers for itself – doesn’t return successor that controls, iterative vs. recursive 200 OK Node C Node-ID 520 4. Joining node after join Node-ID 503

  32. 302 Node B • REGISTER • Alice Alice (User ID 234) 2. REGISTER Alice 200 OK User Registration Node A Node-ID 023 Node B Node-ID 245 Stores: Alice’s Registration Node C Node-ID 520 Alice’s Node Node-ID 503

  33. Session Establishment Alice hashes Bob and gets 011 Alice searches for a registration with User ID 011, sends invite to Node A (023) Node A Node-ID 023 Bob-> Bob’s Node Bob’s Node Node-ID 683 • INVITE • Bob Alice (User ID 234) Node B Node-ID 245 Bob (User ID 011) Node C Node-ID 520 Alice-> Alice’s Node Alice’s Node Node-ID 503

  34. Session Establishment Node A stores a registration for Bob (User ID 011) and returns Bob’s Node as a contact in a 302 Node A Node-ID 023 Bob-> Bob’s Node Bob’s Node Node-ID 683 • INVITE • Bob Alice (User ID 234) 302 Contact: Bob’s Node Node B Node-ID 245 Bob (User ID 011) Node C Node-ID 520 Alice-> Alice’s Node Alice’s Node Node-ID 503

  35. Session Establishment Alice’s UA now invites Bob’s UA Call set up proceeds as normal Node A Node-ID 023 Bob-> Bob’s Node Bob’s Node Node-ID 683 Alice (User ID 234) 2. INVITE Bob Node B Node-ID 245 Bob (User ID 011) 100, 180, 200 Node C Node-ID 520 Alice-> Alice’s Node Alice’s Node Node-ID 503

  36. Session Establishment Node A Node-ID 023 Bob-> Bob’s Node Bob’s Node Node-ID 683 Media and further signaling flow directly between UAs Alice (User ID 234) Node B Node-ID 245 Bob (User ID 011) Node C Node-ID 520 Alice-> Alice’s Node Alice’s Node Node-ID 503

  37. Presence/Buddies • Subscribe/Notify used for presence • Subscribe to all available buddies at startup and periodically • Serve as additional finger table entries

  38. Encoding P2P in SIP • SIP URI parameters • alg : (defined in draft-ietf-sip-identity) to convey hash algorithm used • user=node : used when messages are about node operations, rather than user • resourceID : used on user messages to indicate what a resource hashes to • overlay-name : indicates name of the particular overlay (can be more than 1)

  39. Encoding P2P in SIP • New headers • DHT-NodeID : defines sending node’s node ID • DHT-Link : used by nodes to exchange information about fingers, successors, predecessors

  40. Encoding P2P in SIP Register for a node first joining the overlay: REGISTER sip:10.7.7.1 SIP/2.0 To: sip:4737a8fe3d@10.4.2.2;user=node;alg=rsa-sha1;overlay=chat From: sip:4737a8fe3d@10.4.2.2;user=node;alg=rsa-sha1;overlay=chat Contact: sip:4737a8fe3d@10.4.2.2;user=node;alg=rsa-sha1;overlay=chat Expires: 600 DHT-NodeID: rsa-sha1 4737a8fe3d 10.4.2.2 Require: dht Supported: dht

  41. Encoding P2P in SIP Response from accepting node: SIP/2.0 200 OK To: sip:4737a8fe3d@10.4.2.2;user=node;alg=rsa-sha1;overlay=chat From: sip:4737a8fe3d@10.4.2.2;user=node;alg=rsa-sha1;overlay=chat Contact: sip:4737a8fe3d@10.4.2.2;user=node;alg=rsa-sha1;overlay=chat Expires: 600 DHT-NodeID: rsa-sha1 34f2a82eee 10.7.7.1 DHT-Link: P 1 rsa-sha1 312a18dd12 10.8.7.5 DHT-Link: S 1 rsa-sha1 3863a23ad1 10.11.22.233 DHT-Link: F 2 rsa-sha1 459a1211df 10.101.0.45 DHT-Link: F 3 rsa-sha1 a61bd8c100 10.210.78.101 Supported: dht Require: dht

  42. Encoding P2P in SIP User Registration: REGISTER sip:10.5.22.112 SIP/2.0 To: sip:alice@10.4.2.2; alg=rsa-sha1;overlay=chat;resource-ID=51a6f9098d From: sip:alice@10.4.2.2;alg=rsa-sha1;overlay=chat;resource-ID=51a6f9098d Contact: sip:alice@10.4.2.2;alg=rsa-sha1;overlay=chat;resource-ID=51a6f9098d Expires: 600 DHT-NodeID: rsa-sha1 4737a8fe3d 10.4.2.2 Require: dht Supported: dht

  43. Problems with P2P SIP • Like most things SIP, NATs • Same problems, plus some new ones • Super nodes? • Security • Sybil attacks • DOS (through traffic and true denial) • Encryption • Information “leakage” • Choosing node locations to divert/block

  44. Future Work • Improved Security • Adding features • Configuration information, VM storage • Using overlay for voice traffic as well • Alternate methods for routing • Comparing different P2P approaches

  45. References • draft-bryan-sipping-p2p-01 • D. A. Bryan, B. B. Lowekamp and C. Jennings, SOSIMPLE: Towards a Serverless, Standards-based, P2P Communication System, AAA-IDEA, June 2005 • Stoica et al., Chord: A Scalable Peer-to-Peer Lookup Protocol for Internet Applications, IEEE/ACM Transactions on Networking (to appear) • (Don’t use the algorithms from SIGCOMM paper by same authors with same title – it contains some algorithmic errors) • I maintain a list of references at http://www.p2psip.org • Contact me via email bryan [at] ethernot [dot] org

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