TBCP Tree Building Control Protocol

1
TBCPTree Building Control Protocol
2
Introduction

• Building an overlay spanning tree among hosts
  presents a significant challenge.
• The process of building the tree should not rely
  on any network support that is not already
  ubiquitous.
• One of major requirement is to design a tree
  building control protocol that operate between
  end-systems exclusively.

3
Introduction (cont.)

• End systems can only gain knowledge about
  network through host-to-host measurement
  samples.
• TBCP is a tree-first distributed overlay spanning
  tree building protocol, whose strategy is to
  place members in a (near) optimal position at
  joining time.

4
TBCP Join Procedure

• The root of the spanning tree is used as a
  rendezvous point for the associated TBCP tree.
• Therefore, new nodes join the tree at the root
• Each TBCP entity (including the tree root) fixes
  the maximum number of children. Its called
  fanout.

5
TBCP Join Procedure (cont.)

• A newcomer N contacts a candidate parent P with a
  HELLO message.
• P sends back to N the list of its existing
  children Ci in a HELLO_ACK.

6
TBCP Join Procedure (cont.)

• P starts timer T0 and wait for a JOIN message
  from N.
• This time is needed because, for consistency
  reasons, P cannot accept any new HELLO message
  until it has finished dealing with the current
  newcomer.

7
TBCP Join Procedure (cont.)

• N estimates its distance from P and all Cis and
  sends this information to P in a JOIN
  message.
• If P has not received this JOIN message within
  its timer T0, P sends a RESET message to N,
  meaning that N needs to restart the procedure
  from the beginning.

8
TBCP Join Procedure (cont.)

• P finds a place for N by evaluating all possible
  local configurations.
• A score function is used to evaluate how good
  each configuration is.
• The evaluation based on the distance estimates
  among P, N and the Cis.

9
Join Procedure Condition

• If N is accepted as a child of P, P sends
  WELCOME message to N.
• N then acknowledges immediately.

10
Join Procedure Condition (cont.)

• If N or Cj is to be redirected to one of Ps
  children (say Ck), that node is sent a GO(Ck)
  message.
• Then N or Cj starts a join procedure with Ck (the
  procedure in the beginning), and send GO_ACK
  message to P.

11
Additional Rules

• If fanout of P4
• If fanout of Plt4

12
Cost Function and Measurements
?
13
Cost Function and Measurements (cont.)

• Distance D(i,j) round trip time (RTT) between
  node i and node j along the tree.
• Score function max M?CiUN D(P,M)Where Ci
  is the set of Ps children and N is the newcomer
• Then the chosen configuration is the one with the
  smallest score.

14
Conclusions

• The efficient and scalable TBCP
  algorithm/protocol has been developed to build
  such an overlay spanning tree.
• The join procedure is very efficient since its
  developed with decentralized algorithm.
• The leave procedure is not yet designed in this
  paper.