Transport Requirements for P2PSIP

1
Transport Requirements for P2PSIP

• Cullen Jennings
• IETF 71

2
What is P2PSIP?

• A Skype me too
• Conventional SIP uses a network of servers for
  rendezvous
• Replace servers with a peer-to-peer network
• Based on a distributed hash table (DHT)
• Registration information is stored in the DHT
• DHT also used to route messages used to initiate
  connections
• This means a lot of connections between peers
• DHT peers maintain order 10-100 connections each
• Many (most?) peers will be behind NATs
• MUST be able to connect to each other anyway
• With minimal use of relays

3
Transport Requirement

• Operating Systems
• Can download an application and run it without
  special root/admin privileges on at least XP,
  Vista, OS X, Linux
• NAT Traversal
• Needs to work without a relay when both hosts are
  behind different NATs
• Needs to work with type of NATs deployed today
• Reliable Large Object Transfer
• Need to reliably transfer objects that are
  substantially larger than MTU
• High efficiency is not required
• If effective transfer rate was only half of TCP,
  that would be fine
• Success Metric (Thing to optimize)
• Percentage of time it works for clients behind
  two random NATs

4
Straw Man

• Currently in very early stages of clueless
  mucking around for ideas
• Basic thinking
• UDP has best NAT traversal results (90 vs 25
  for TCP)
• Do something simple but safe
• Provide enough feedback so the sender can upgrade
  to much better approach with no change on
  receiver
• Straw man A
• Sender chunks up data and sends over UDP with
  retransmission
• Each UDP packet has a sequence number
• Receiver ACKs each packet and includes a bitmap
  indicating whether the previous 32 sequence
  number packets has been received
• Can be used by sender to compute packet loss
  events
• Retransmission is no more aggressive than TFRC-SP
• Straw man B (Im just the messenger)
• Userland TCP tunneled over UDP