scope:

The scope of this document is as follows:

a) In bridged networks running MTBP, ports shall be identified as either a meshed tree port that participates in the meshed tree resolution, or a host port, to which a local host is connected. Only meshed tree ports are allowed to participate in the meshed tree resolution.

b) MTBP provides superior fault tolerance by preconfiguring several logical trees from a root. One of these logical trees is considered the primary tree and is used for forwarding broadcast frames. In the event of a network component failure and immediately on failure detection of the primary branch, broadcast frame forwarding is taken over by any one of the other preconfigured tree branches. This is achieved with minimal message dissemination and delay.

c) The addition of a bridge configured to run MTBP will allow the bridge to send a request to join (via MT_JOIN message) message to all other bridges to which it is connected. The new bridge will join the bridges already in the topology. The new bridge then receives multiple invitations from its neighbors to join tree branches that they are already part of. The new bridge decides to join the multiple tree branches and stores the multiple paths in order of preference. One of these paths shall be the path for broadcast frame forwarding.

d) Upon a network component failure detection, the active topology will stabilize within a short, deterministic, maximized probability interval, reducing the time for which the service is unavailable for communication between any pair of end stations.

e) The active topology will be predictable and reproducible, and may be selected by management of the parameters of the algorithm, thus allowing the application of configuration management, following traffic analysis, to meet the goals of performance management.

f) The MTBP operates transparently to the end stations.

g) The communications bandwidth consumed by the MTBP on any particular LAN is designed to consume a negligible fraction of the total available bandwidth and is independent of the total traffic supported by the network regardless of the total number of bridges.

h) The memory requirements associated with each bridge port are independent of the number of bridges in the network.

i) The MTBP describes the use of meshed tree paths to reduce transit delay from one path to another with minimal convergence delay upon topology changes.

j) The MTBP permits the learning of end station MAC addresses via special host address advertisement (HAA) messages.

k) The MTBP specifies the use of meshed tree bridging protocol data units (MT_BPDUs) for the creation of the active topologies in meshed tree bridging and learning end station addresses.

l) The MTBP shall allow designation of multiple roots to provide redundancy for the root MTB. Upon detection of primary root failure, the secondary root takes over immediately. The number of predefined roots is implementation specific.

Purpose

The purpose of this standard is to specify the methods for establishing several tree-like structures on an existing topology. The protocol leverages any useable path rather than eliminating possible alternate links. Upon changes to the topology, the meshed tree protocol will converge in zero time through the immediate use of alternate predetermined viable pathways on failure detection.

MTBP allows for maintenance of multiple active topologies by adopting the MTA (described in Clause 5). The concept of meshed trees is novel in that they do not use the traditionally prevailing concept of a single tree from one root. They allow for multiple trees or subtrees to be constructed from a root and thus maintain multiple paths in readiness to take over in the event of a link or path failure. Meshed trees thus address the path redundancy in bridged networks by providing multiple loop-free tree paths between a root bridge and a non-root bridge. Meshed trees also address immediate failover upon link failure detection because they allow several logical pathways to exist between any two communicating bridges. To cut down on the delays due to root election and re-election in the event of current root failure, the MMT concept allows for multiple meshed trees to be constructed from multiple predesignated roots.