An Improved Kademlia Protocol In a VoIP System

1
An Improved Kademlia Protocol In a VoIP System

• Xiao Wu,Cuiyun Fu and Huiyou Chang
• Department of Computer Science, Zhongshan
  University, Guangzhou, China
• resource2007 IFIP International Conference on
  Network and Parallel Computing Workshops
• reporter69721019 ??? 69721059 ???

2
Outline

• Introduction
• Kademlia
• Improved protocol based by Kademlia
• Improved Route table
• Improved Route protocol
• Backup channel
• Conclusion

3
Outline

• Introduction
• Kademlia
• Improved protocol based by Kademlia
• Improved Route table
• Improved Route protocol
• Backup channel
• Conclusion

4
Introduction

• Standard Kademlia is designed for file sharing
  systems and searching is expected to stop when
  both the desirable peer and k closest peers
  return.

5
Introduction

• When applying to real-time system such as VoIP,
  standard Kademlia should make some modification.
• We proposed an improved kademlia protocol to
  adapt to VoIP systems meeting the need of
  real-time audio service and establishing a
  conversation in short delay.

6
Outline

• Introduction
• Kademlia
• Improved protocol based by Kademlia
• Improved Route table
• Improved Route protocol
• Backup channel
• Conclusion

7
Kademlia

• A peer-to-peer distributed hash table protocol in
  P2P network.
• IDa unique 160-bits identifier that calculated
  by SHA-1 algorithm
• properties
• (1) different inputs bring different values
• (2) distributed in the overlay topology
  uniformly

8
Kademlia

• ltkey, valuegt pairs are stored on nodes
• key 160-bit identifier
• value such as file name in file sharing system
  and phone number in VoIP system.
• distance
• d(x,y) x ? y
• where x and y are two peers node ID

9
Kademlia

• routing tablea binary tree whose leaves are
  k-buckets keeping a list of at most k nodes with
  some common prefix of their node IDs in terms of
  ltIP Address, UDP port, NODE_IDgt triples.
• The prefix is the k-buckets position in the
  routing table.

10
Kademlia
11
Kademlia

• Remote Procedure Control(RPC)
• PING
• FIND_NODE
• STORE
• FIND_VALUE
• Peers will republish their ltkey, valuegt pairs to
  keep them alive periodicallyotherwise,
  ltkey,valuegt pairs would expire and be deleted.

12
Outline

• Introduction
• Kademlia
• Improved protocol based by Kademlia
• Improved Route table
• Improved Route protocol
• Backup channel
• Conclusion

13
Improved protocol based by Kademlia

• When making phone calls, callers use routing
  algorithm FIND_CALLEEID to search callees IP
  addresses and UDP ports in the absence of server.
  Besides, system has a backup channel.
• When entering the network,the newcomer must have
  a contact to an already participating node and
  then it performs a node lookup for its own ID.

14
Outline

• Introduction
• Kademlia
• Improved protocol based by Kademlia
• Improved Route table
• Improved Route protocol
• Backup channel
• Conclusion

15
Improved Route table

• A binary tree similar to Kademlia.
• Each leaf contains a cache-bucket as well as a
  k-bucket, cache-bucket is used as a backup buffer
  of the k-bucket.

16
Improved Route table

• Quaternion ltNode ID, IP address, Port, Stategt.
• Node ID generated by performing SHA-1 operation
  on clients phone number

17
Lookup algorithm
18
Building the routing table

• At the first beginning, the routing table is
  composed of a single TNode, with only one
  k-bucket and one cache-bucket.
• When more than k nodes are being inserted, the
  TNode will be split into two and each child will
  be allocated a k-bucket and a cache-bucket
  respectively.

19
Building the routing table

• Those near the local node ID will be put in the
  right childs k-bucket or cachebucket in
  contrast, those far from the local node ID will
  be moved to the other childs.
• Nodes whose node IDs share common prefix of local
  node ID are put in the right childs.

20
Improved Route table

• The routing table should try its best to stores
  nodes near the local node ID and drop some nodes
  far away to avoid routing table turgid expansion.
• A target TNode is splitable
• RULE1 It is a Local TNode
• RULE2 The right subtree of the minimum subtree,
  containing the Local TNode and the target TNode,
  contains less than k nodes.

21
Splitting TNode algorithm
22
(No Transcript)
23
A compression mechanism

• Compacity
• 1 if This is an TNode that both left and right
  child TNode is a leave TNode and the binary tree
  is not splitable.
• 2 Then Order all nodes in child buckets by time
  first seen
• 3 move nodes from child TNodes to parent and
  prefer old nodes, when bucket is full put
  remaining nodes in replacement cache.
• 4 Order all nodes in child replacement caches by
  time last seen and prefer most recently seen
  nodes
• endif

24
Outline

• Introduction
• Kademlia
• Improved protocol based by Kademlia
• Improved Route table
• Improved Route protocol
• Backup channel
• Conclusion

25
Improved Route protocol

• Caller sends FIND_CALLEEID, with callee ID as its
  parameter, to find the IP address in accordance
  with the ID. Receiver returns k closest peers to
  some given callee ID.
• If Caller gets a response containing the callee
  ID, lookup finishes or else continues to find
  closer peers to callee.
• The searching process terminates when caller has
  queried and gotten responses from the k closest
  peers it has seen and informs the caller that
  search fails.

26
Improved Route protocol

• Avoiding no refreshing in a certain distance,
  every k-bucket without lookup in an hour would
  refresh themselves by doing a callee lookup for a
  random ID in the buckets range.

27
Outline

• Introduction
• Kademlia
• Improved protocol based by Kademlia
• Improved Route table
• Improved Route protocol
• Backup channel
• Conclusion

28
Backup channel

• In our model, backup channels build up a list
  which stores n closest peers in IP network in the
  form of ltIP distance, IP address, port,
  timestamp, nextgt.

29
Backup channel

• We assume that the quaternion would become
  untrusty once it stays longer that average talk
  time and would be offline at any moment. Such
  quaternion should be dropped so that the list
  could be effective to the greatest extent
  thereafter.

30
Backup channel

• When getting the IP address of the callee, caller
  establishes a conversation with the callee and
  caller no longer refreshes its backup channels.
  It sends heartbeat packets to those peers in the
  list to ensure every peer could connect to both
  caller and callee. If peer fails to response,
  caller supposes the peer is offline and deletes
  the quaternion from the list.

31
Backup channel
32
Backup channel

• The backup channels will stop refreshing when ID
  searching is over. Thereby the failure
  probability of backup list is increasing together
  with the increase of the talk time. When backup
  channel is really needed, little useful channel
  could be offered by the list.

33
Backup channel

• When there are less than ß quaternions, caller
  will require all of the remaining peers in the
  list for more backup channels.Those peers will
  return ? closest peers it knows from their own
  backup channels. ßand ?is a system-wide
  parameter.
• Returning peers would update the current backup
  channels. In this rate, local peer would get more
  information to set up a robust backup channel.

34
Outline

• Introduction
• Kademlia
• Improved protocol based by Kademlia
• Improved Route table
• Improved Route protocol
• Backup channel
• Conclusion

35
Conclusion

• In the improved Kademlia protocol we change the
  original FIND_NODE in Kademlia to FIND_CALLEEID,
  which terminates once the caller gets the
  information about callee so that it could set up
  a session as soon as possible.
• Backup channel for circuit switching shortens the
  delay when the connection between caller and
  callee is broken.