CBT, Core Based Trees

Description Glossary RFCs Publications Obsolete RFCs


Protocol suite: TCP/IP.
Protocol type:Transport layer multicast routing protocol.
Multicast addresses: (routers).
IP protocol:7.
MIME subtype:
Working groups: idmr, Inter-Domain Multicast Routing.

RFC 2189, page 1:

CBT builds a shared multicast distribution tree per group, and is suited to inter- and intra-domain multicast routing. CBT may use a separate multicast routing table, or it may use that of underlying unicast routing, to establish paths between senders and receivers.

RFC 2201, page 1:

Abstract CBT is a multicast routing architecture that builds a single delivery tree per group which is shared by all of the group's senders and receivers. Most multicast algorithms build one multicast tree per sender (subnetwork), the tree being rooted at the sender's subnetwork. The primary advantage of the shared tree approach is that it typically offers more favourable scaling characteristics than all other multicast algorithms.

The CBT protocol is a network layer multicast routing protocol that builds and maintains a shared delivery tree for a multicast group. The sending and receiving of multicast data by hosts on a subnetwork conforms to the traditional IP multicast service model.

MAC header IP header CBT header Data :::

CBT header, version 2:

0001020304050607 0809101112131415 1617181920212223 2425262728293031
Version Type Address length Checksum
Data :::

Version. 4 bits.
CBT version number.

Type. 4 bits.
CBT message.

1Join request.
2Join ack.
3Quit notification.
4Echo request.
5Echo reply.
6Flush tree.
7Bootstrap message.
8Candidate Core Advertisement.

Address length. 8 bits.
Size of the unicast or multicast addresses carried in the control packet in bytes.

Checksum. 16 bits.
16-bit one's complement of the one's complement sum of the entire CBT control packet.



[RFC 1949] Scalable Multicast Key Distribution.

[RFC 2189] Core Based Trees (CBT version 2) Multicast Routing Protocol Specification.

[RFC 2201] Core Based Trees (CBT) Multicast Routing Architecture.

[RFC 2715] Interoperability Rules for Multicast Routing Protocols.


Obsolete RFCs:

Description Glossary RFCs Publications Obsolete RFCs