A Cooperative SIP Infrastructure for Highly Reliable Telecommunication Services

1
A Cooperative SIP Infrastructure for Highly
Reliable Telecommunication Services

• Ali Fessi, Heiko Niedermayer,
• Holger Kinkelin, Georg Carle
• IPTComm 2007, 19th-20th July, New York, USA

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Overview

• Motivation
• Properties of server-based SIP networks
• Properties of P2P-based SIP networks
• Our solution for SIP reliability Cooperative
  SIP (CoSIP)
• CoSIP Overview
• Sample Applications
• Implementation
• Evaluation
• Improving reliability and security with CoSIP
• Initial functional tests results
• Conclusions

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Motivation

• Some open issues with VoIP still need to be
  solved
• reliability, security, QoS, SPIT, etc.
• Users are used to the nearly 100 reliable PSTN
• Good news
• Peer-to-peer (P2P) networks provide higher
  reliability
• Bad news
• P2P network have also their bad side
• Security in P2P networks is much harder to cope
  with due to decentralization
• Goals
• How can we make SIP networks more reliable?
• How can we benefit from the advantages of both
  architectures
• server vs. P2P

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Properties of Server-based SIP Networks

• Sufficient security mechanisms
• UA authentication
• Integrity and confidentiality
• High lookup performance of SIP URI
• O(1) messages
• Complex service infrastructure
• SIP proxies, registrars, AAA servers, location
  database, DNS server, routers, etc
• Network and service failures may propagate
  quickly
• Server infrastructures are vulnerable to DoS
  attacks

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Properties of P2P-SIP Networks

• Self-organization
• Recoverability from local failures
• Robustness against DoS attacks
• ? P2P network can also survive under
  difficult conditions
• Scalability
• Lookup performance of the Contact URI in a DHT in
  the avg case
• O( log ( N ) ) messages N is the number of peers
• Several security issues can not be solved in
  pure P2P network
• Attacks on the routing of lookup requests
• Attacks on the content of the P2P network
• Sybil attacks, partitioning attacks, etc.
• Open P2P-SIP networks are an invitation for SPIT!

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Cooperative SIP (CoSIP)

• Basic idea
• Design a hybrid architecture that benefits from
  the advantages of both server-based and P2P-based
  SIP networks
• SIP User Agents organize themselves into a P2P
  network
• SIP infrastructure and SIP User Agents cooperate
  in order to provide the best service
• ? Cooperative SIP architecture CoSIP
• Improve reliability, survivability, security and
  lookup performance

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CoSIP UA Registration

• A SIP UA is registered to the SIP infrastructure
  as well as to the DHT
• Use REGISTER for registration to the
  infrastructure
• Use put for the registration to the DHT
• put (H(SIP_URI), Contact_URI)

REGISTER
put(H(SIP_URI), Contact_URI)
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CoSIP Session Establishment

• Signaling to the SIP infrastructure with INVITE
• In parallel resolve the Contact-URI in the DHT
  with a get
• get (H(SIP_URI)) Contact_URI
• Server does not answer or DHT is faster?
• ? use the Contact-URI provided by the DHT
  lookup
• ? perform direct signaling to the peer
• Lookup performance
• under normal conditions
• O(1) messages
• in case of failures of the infrastructure
• O( log ( N ) ) messages

INVITE
get(SIP_URI)
INVITE
Session
200 OK
Contact_URI
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CoSIP Sample Applications

• Large enterprise/ academic SIP networks with e.g.
  20-30 k-users
• CoSIP can be used to bridge
• network and service failures
• maintenance downtimes

CoSIP-enabled SIP Network
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CoSIP Sample Applications (2)

• CoSIP adapter/ proxy in DSL routers
• CoSIP adapters organize themselves into a P2P
  network

Small Office and Home Network (SOHO)
Internet/VoIP Provider
DSL Router with a CoSIP adapter / CoSIP proxy
SOHO
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Implementation of CoSIP as an external Proxy
Application
SIP Express Router (SER)

• The CoSIP proxy is an adapter to connect regular
  SIP UA
• CoSIP Proxy communicates with the SIP
  infrastructure and the P2P network
• DHT Bamboo/ Pastry
• Formal specification of the CoSIP protocol
  with SDL
• Programming language Python
• When the SIP infrastructure fails P2P signaling
  between the CoSIP proxies

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Specification of CoSIP - Goody

• State machines switchable to different modes
• Cooperative mode (DHT SIP server)
• DHT-only mode (basically P2P-SIP with Bamboo as a
  DHT)
• Server-only mode
• DHT-only mode successfully tested with OpenDHT

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SIP UA running with CoSIP Proxy in the background
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Evaluation

• Improving reliability with CoSIP
• P2P network provide high reliability and
  self-organization
• Local failures can be recovered autonomically by
  neighboring peers
• Data is replicated on a set of nodes (replica
  set)
• Even large failures affect only a part of the
  network
• In the ideal case (uncorrelated failures), the
  probability of a service failure with CoSIP would
  be
• ? CoSIP provides even better reliability and
  survivability than
• P2P-SIP networks
• server-based SIP networks

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Evaluation

• Improving security with CoSIP
• Managing security in large P2P-SIP networks is
  not possible without central severs
• However, PKI / CA is not enough
• A CA is not able to detect an attack in the P2P
  network and shut down the attacker
• A security solution for P2PSIP requires
• more SIP specific knowledge
• knowledge about the P2P network
• CoSIP servers can provide Identity Management for
  the P2P-SIP network
• CoSIP servers can make sure that peers in the
  P2P-SIP network behave well
• How can you provide Intrusion Detection in a
  large P2P network?
• ? a CoSIP server can help to do this job
• More work is still required on this topic

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Evaluation

• Initial tests have been run on PlanetLab
• Each used PlanetLab node hosts
• a SIP UA
• a CoSIP proxy
• a Bamboo DHT node
• High variance of the RTT on PlanetLab noticed
• SIP server failure emulated
• Successful recoverability from service failure
• No interruption of service is noticed
• Time required to establish a session between UAC
  and UAS increases slightly but is still
  acceptable
• Performance results will be published soon

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CoSIP Summary

• CoSIP provides a low-cost solution for
  significantly improving the reliability of SIP
  networks
• Implementation
• CoSIP as an external proxy application ?
  compatible to existing SIP networks
• Cooperative (server DHT) as well as DHT-only
  mode possible
• CoSIP is a hybrid architecture which provides
  better reliability, survivability, security and
  performance simultaneously
• Could CoSIP be useful for catastrophic failures /
  emergency calls?
• Future work
• Integration of security mechanisms to CoSIP ?
  Improve security of P2P-SIP
• CoSIP is still a single domain concept ?
  Peering of several domains with CoSIP
• Improving geometry and routing in the DHT for
  higher connectivity in case of network failures

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Questions / Discussion / Feedback
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P2P-SIP

• Basic idea SIP without server
• Registration
• Phase1 Node registration P2P-SIP node joins
  the DHT
• Phase 2 User registration storing the Contact
  URI with SIP URI as lookup key in the DHT
• Session establishment
• Resolving the SIP URI to a Contact URI using the
  DHT
• Subsequent signaling can occur between the two
  peers

Node registration
User registration
Session establishment
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Evaluation - PlanetLab

• Global research network
• 784 nodes
• 382 institutions
• Cons
• Very variable performance and load of PlanetLab
  nodes
• High variance in the RTT
• ? Causes high variance in the measurement
  results
• High instability and unreliability of the
  PlanetLab nodes
• Upgrade PlanetLab 3.0 to 4.0
• More than 50 nodes barely manageable

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CoSIP State Machines

• Formal specification of the CoSIP protocol using
  SDL
• Logical separation between the state machines of
  different SIP UAs
• The CoSIP proxy processes
• requests from UA
• messages from the server
• messages from the DHT
• timeouts for limiting the pending time
• Events are processed FIFO

SDL diagram for the processing of an INVITE
message in state IDLE
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CoSIP State Machines (2)
High Level INVITE Session State Machine
High Level REGISTER Session State Machine
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Related Work

• P2PSIP
• Secure Overlay Services (SOS)
• Resilient Overlay Networks (RON)
• Skype
• CoDNS

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Overview Tesbed
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OpenDHT

• OpenDHT Bamboo running on PlanetLab
• publicly accessible
• put
• get
• remove

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CoSIP Implementation Overview

• Threading for transport of SIP messages
• and communication with the DHT
• Event-based processing of
• SIP messages
• DHT messages
• Timeouts
• Events are processed
• FIFO
• Programming language
• Python
• Platform independent
• (CoSIP tested with Linux / Windows)
• Code size ca. 5 kLoC

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SIP UA running with CoSIP Proxy in the background
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Evaluation Recovery from Service Interruption
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Evaluation (VI)