peer-to-peer sip
DESCRIPTION
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 - PowerPoint PPT PresentationTRANSCRIPT
Peer-to-Peer SIP
David Bryan
July 27, 2005
www.p2psip.org
Affiliation(s)
p2psip.org
www.p2psip.org
Overview
• Motivation
• What is Peer-to-Peer?
• Why P2P SIP?
• P2P basics
• Approaches to P2P SIP
• P2P SIP/SOSIMPLE
• Problems, barriers, and future work
www.p2psip.org
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
www.p2psip.org
What is Peer-to-Peer?
Client Server:
www.p2psip.org
What is Peer-to-Peer?
Peer-to-Peer
www.p2psip.org
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)
www.p2psip.org
Client/Server Session
www.p2psip.org
Problem w/Remote Server
Organization B
InternetOrganization A
www.p2psip.org
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
www.p2psip.org
P2P Session
www.p2psip.org
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
www.p2psip.org
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
www.p2psip.org
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
www.p2psip.org
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
www.p2psip.org
Flooding w/TTL
TTL = 1TTL = 2TTL = 3
Node broadcasts to neighborsNode(s) respond directly
www.p2psip.org
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
www.p2psip.org
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
www.p2psip.org
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
www.p2psip.org
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
www.p2psip.org
Example Chord Ring
• Example namespace is 0-31
• Wraps at 0/31• Values increase
clockwise• Sometimes called
an identifier circle
0
15
31
7
1 23
45
6
www.p2psip.org
Example Chord Ring
IDs/key namespace is 0-31
Node DNode-ID 29
Node ANode-ID 2
Node CNode-ID 18
Node BNode-ID 13
Item A, key = 5
Item B, key = 18
Item C, key = 30
Stores:Item A, key = 5
Stores:Item B, key = 18
Stores:Item C, key = 30
www.p2psip.org
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
www.p2psip.org
Example Finger Table
• Namespace 0-31 is size 25, so 5 fingers
• Node is 3, so fingers are:
0
15
31
7
1 23
45
6
f[0] Offset 20=1 Points to 3+1=4
f[1] Offset 21=2 Points to 3+2=5
f[2] Offset 22=4 Points to 3+4=7
f[3] Offset 23=8 Points to 3+8=11
f[4] Offset 24=16 Points to 3+16=19
www.p2psip.org
Example Finger Table
• Namespace 0-31 is size 25, so 5 fingers
• Node is 3, so fingers are:
f[0] Offset 20=1 Points to 3+1=4
f[1] Offset 21=2 Points to 3+2=5
f[2] Offset 22=4 Points to 3+4=7
f[3] Offset 23=8 Points to 3+8=11
f[4] Offset 24=16 Points to 3+16=19
3
4
5
7
1119
www.p2psip.org
11
Example Finger Table
• If only nodes 3, 6, 11 are in the overlay:
f[0] Offset 20=1 Points to 3+1=4(6)
f[1] Offset 21=2 Points to 3+2=5(6)
f[2] Offset 23=4 Points to 3+4=7(11)
f[3] Offset 24=8 Points to 3+8=11(11)
f[4] Offset 25=16 Points to 3+16=19(3)
3
6
www.p2psip.org
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
www.p2psip.org
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
www.p2psip.org
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
www.p2psip.org
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
www.p2psip.org
Node Joining
Bootstrap NodeNode-ID 023
Node BNode-ID 245
Joining NodeNode-ID 503
1. REGISTER
302 Node B
2. REGISTER
302 Node C3. REGISTER
200 OK
4. Joining node after joinNode-ID 503
Node CNode-ID 520
Differences from Chord: node answers for itself – doesn’t return successor that controls, iterative vs. recursive
www.p2psip.org
User Registration
Node ANode-ID 023
Node BNode-ID 245
Alice’s NodeNode-ID 503
1. REGISTERAlice
302 Node B
2. REGISTER Alice
200 OK
Node CNode-ID 520
Alice (User ID 234)
Stores:Alice’s Registration
www.p2psip.org
Session Establishment
Node ANode-ID 023
Node BNode-ID 245
Node CNode-ID 520
Alice’s NodeNode-ID 503
Alice-> Alice’s Node
Bob-> Bob’s Node
Bob’s NodeNode-ID 683
1. INVITEBob
Alice (User ID 234)
Bob (User ID 011)
Alice hashes Bob and gets 011Alice searches for a registrationwith User ID 011, sends invite
to Node A (023)
www.p2psip.org
Session Establishment
Node ANode-ID 023
Node BNode-ID 245
Node CNode-ID 520
Alice’s NodeNode-ID 503
Alice-> Alice’s Node
Bob-> Bob’s Node
Bob’s NodeNode-ID 683
1. INVITEBob
302 Contact: Bob’s Node
Alice (User ID 234)
Bob (User ID 011)
Node A stores a registration for Bob (User ID 011) and returns
Bob’s Node as a contact in a 302
www.p2psip.org
Session Establishment
Node ANode-ID 023
Node BNode-ID 245
Node CNode-ID 520
Alice’s NodeNode-ID 503
Alice-> Alice’s Node
Bob-> Bob’s Node
Bob’s NodeNode-ID 683
Alice (User ID 234)
Bob (User ID 011)
Alice’s UA now invites Bob’s UACall set up proceeds as normal
100, 180, 200
2. INVITEBob
www.p2psip.org
Session Establishment
Node ANode-ID 023
Node BNode-ID 245
Node CNode-ID 520
Alice’s NodeNode-ID 503
Alice-> Alice’s Node
Bob-> Bob’s Node
Bob’s NodeNode-ID 683
Alice (User ID 234)
Bob (User ID 011)
Media and further signaling flow directly
between UAs
www.p2psip.org
Presence/Buddies
• Subscribe/Notify used for presence• Subscribe to all available buddies at startup and
periodically• Serve as additional finger table entries
www.p2psip.org
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)
www.p2psip.org
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
www.p2psip.org
Encoding P2P in SIP
REGISTER sip:10.7.7.1 SIP/2.0
To: sip:[email protected];user=node;alg=rsa-sha1;overlay=chat
From: sip:[email protected];user=node;alg=rsa-sha1;overlay=chat
Contact: sip:[email protected];user=node;alg=rsa-sha1;overlay=chat
Expires: 600
DHT-NodeID: rsa-sha1 4737a8fe3d 10.4.2.2
Require: dht
Supported: dht
Register for a node first joining the overlay:
www.p2psip.org
Encoding P2P in SIP
SIP/2.0 200 OK
To: sip:[email protected];user=node;alg=rsa-sha1;overlay=chat
From: sip:[email protected];user=node;alg=rsa-sha1;overlay=chat
Contact: sip:[email protected];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
Response from accepting node:
www.p2psip.org
Encoding P2P in SIP
REGISTER sip:10.5.22.112 SIP/2.0
To: sip:[email protected]; alg=rsa-sha1;overlay=chat;resource-ID=51a6f9098d
From: sip:[email protected];alg=rsa-sha1;overlay=chat;resource-ID=51a6f9098d
Contact: sip:[email protected];alg=rsa-sha1;overlay=chat;resource-ID=51a6f9098d
Expires: 600
DHT-NodeID: rsa-sha1 4737a8fe3d 10.4.2.2
Require: dht
Supported: dht
User Registration:
www.p2psip.org
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
www.p2psip.org
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
www.p2psip.org
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