IEEE Std 1910.1-2020 pdf download
IEEE Std 1910.1-2020 pdf download.IEEE Standard for Meshed Tree Bridging with Loop-Free Forwarding.
5. Mesh tree algorithm and the protocol
The MFA allows construction of logically meshed subtrees from a single root bridge in a distributed manner using local information shared among neighbor MTBs. The MTA is first described using a flowchart in Figure 1. A root is preselected or designated. Preselcction or designation does not impact the MTBP operation (see 7.2.4). Annex A provides formal definitions for meshed trees.
In MTBP, for the construction and maintenance of multiple subtrecs from a single root in a bridged network, virtual identifiers (VIDs) are assigned to the communicating bridges. A single communicating non-root bridge can acquire multiple VIDs. The VID is henceforth called meshed tree IID (MTVID). Each MT_VID derived in MTBP defines a non-looping path from the communicating bridge to the root bridge. This is true for all communicating bridges except the root bridge. The root bridge has a single MT_VID that shall be assigned to it, when it is predesignated to be the root bridge.
NOTE—For an implementation of MTBP, a root bridge is designated and assigned a V ID.6
6. Meshed tree algorithm
The MTA supports construction of multiple subtrees from a single root. The flow chart for the MTA using a connected graph is given in Figure 1. In this graph, a vertex is defined to be the root. The meshed tree construction starts with all vertices checking if they have the root status or not. The vertex that has this status sends out path invitations (P1) to its neighboring vertices. If a neighbor accepts the invitation, the root notes this neighbor as part of its meshed tree. Vertices that do not have the root status listen for PIs. When they receive a P1. they first perform a loop-check, and if the P1 does not result in loop formation with already accepted PIs, the vertex accepts the new P1. It then stores all PIs in a list and sorts them in order of hop count from the root. The extent of meshing among the subtrees can be restricted to Krnax, i.e., a vertex can reside in a maximum of Kinax subtrees from a root. After sorting its P1 list, a vertex checks if the length of the list is > Kinax. Entries greater than are removed. A vertex that has Pis now offers Pis to its neighbors. The vertex also continues to listen to PIs in their neighborhood and update their P1 list. Thus, all vertices are a part of the multiple subtrees originating from the root.
To implement the Pis and allow each node in a bridged network to reside on multiple subtrees and carry this information without conflict, the specified numbering scheme is used in the MTBP. This numbering scheme uses MT VIDs, which are used for creating the PIs. An MT_VID provides a path from a non-root bridge to the root bridge. The use of MT_VIDs in the protocol is explained next. Meshed tree construction from a designated root in a bridged network is covered in 7.3.
Meshed trees construction: To construct meshed trees, a numbering technique to maintain the multiple tree branches and to distinguish them is used. The technique is based on meshed tree VIDs (MT_VIDs). An MT_VID is a string of integers separated by a ‘dot’. This technique is described with an example. In this example, the metric used for tree construction is hop count. Several bridges are connected in a partial mesh topology. One bridge (normally the one with the best processing capacity) is preselected to be the root from which the meshed trees are constructed. Preselecting a root bridge and its rationale is discussed in 7.2.4. The root bridge is assigned an MT VID when it is designated to be the root bridge. In this example, the root bridge is assigned an MT_VID = 1.
All other bridges are to be administratively configured as non-root bridges. The non-root bridges wait to receive a P1. i.e.. an MT_VID offer or advertisement (as described in algorithm flow chart in Figure 1) as the meshed trees are constructed from the root. The operation of MTBP is based on the numbering schemes adopted for the MT_VIDs.
