Banana Tree Protocol

1
Banana Tree Protocol
2
Properties

• Banana Tree Protocol (BTP) is based on a tree
  topology
• Each host in the group is a node in the tree
• The node may be a parent or a child or both
• The host that created the tree is the root node
  and has no parent. Consequently, all other nodes
  have a parent

3
Properties (2)

• The parent is the next node on the path to the
  root
• A node may have multiple children
• Nodes parent or children are also its neighbors
• Other children of a nodes parent is called
  siblings

4
Properties (3)
toward root
parent
node
child
node
node
sibling
sibling
5
Joining Group

• A host joins a group by becoming the child of a
  nodes currently in the tree (e.g. the root node)
• We assume the existence of a bootstrap protocol
• With bootstrapping protocol, host can learn of a
  node in a multicast group
• A node that joining a multicast group with no
  member become the root node

6
Switching in The Group

• Nodes can change parent in some situations, its
  called switch
• Example node A switches to node C

root
root
C
B
B
C
A
A
7
Sending Packets

• To send a multicast packet, a node sends the
  packet to its neighbors
• When a node receives a multicast packet from its
  neighbor, it forwards the packet to its other
  neighbors

8
Partitioning

• If nodes parent leaves or fails, a partition is
  formed.
• The node then reconnect to the root
• This cant create a loop because the root cant
  be the nodes descendant
• If the nodes child fails, the node does nothing,
  because if the child had children, they will
  reconnect to the root themselves

9
Optimization Algorithm

• Nodes can switch parents to optimize the tree
• For avoiding loop, a node cant switch to an
  arbitrary node
• A node can only switch to 1. root 2.
  siblingbecause a root and a sibling is not
  descendant of the node

10
Optimization Algorithm (2)

• Looping case

root
root
3
3
3
3
1
1
Loop
3
3
11
Optimization Algorithm (3)

• The purpose of switching to a sibling is to
  optimize the tree for low cost. Because BTP is
  designed without considering low latency.

R
R
R
3
3
A
B
A
B
A
B
1
Tree cost 6
Tree cost 4
12
Optimization Algorithm (4)

• When a node is switching to a sibling, another
  rules are 1. the sibling is still the nodes
  sibling 2. the sibling is not trying to switch
  to another node at the same time

13
Switching Algorithm

• Assume a node has received a list of its siblings
  from its parent and has found a sibling closer
  than its parent.
• That node may find this sibling by pinging each
  sibling.
• This sibling is called potential parent.

14
Switching Algorithm (2)

• When a node wants to switch to a potential
  parent, it must first send a switch request to
  the potential parent.
• The node has to wait for an acceptance or
  rejection message.

15
Switching Algorithm (3)

• Problem
• To ensure that siblings do not try to switch each
  other at the same time, a node which is trying to
  switch to a potential parent will always reject a
  request from the potential parent to switch to it.

16
Switching Algorithm (4)

• Problem
• To prevent such loops from happening, BTP adopted
  the policy that a node will reject all attempts
  at switching if it is itself in the process of
  switching parents.

17
Switching Algorithm (5)

• For avoiding an out-of-date information, the node
  has to include the current parent information in
  the switch request.
• The potential parent checks that the node and
  itself are actually sharing the same parent.

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Closeness Metric

• Closeness Metric, C ds/dc
• ds the distance from node to the closest
  node found by switching dc the distance from
  node to the closest possible node in the
  tree C 1, but if C 1 ? ideal

19
BTSMP and BTFTP

• There are two protocols built on top of BTP that
  give additional features 1. Banana Tree Simple
  Multicast Protocol (BTSMP) 2. Banana Tree
  File Transfer Protocol (BTFTP)
• BTSMP provide many-to-many group communication
  for sending and receiving packets.
• BTFTP provides one-to-many file distribution.

20
BTSMP and BTFTP (2)

• The only feature of BTSMP is caching. Each node
  can keep a cache of the last few packet sent or
  received.
• The good thing is when a new node joins the tree,
  it can request the contents of the cache from its
  parent.
• BTFTP provides reliable one-to-many file
  transfer. It is assumed that the root has the
  file.

21
Related Work

• Several end-host multicast protocols related to
  this protocol are1. Yoid2. Narada3. AMRoute