provider link state bridging (802.1) (PLSB)

Provider Link State Bridging (PLSB) is a technology developed by Nortel that evolved from Provider Backbone Bridges(PBB) specified in 802.1ah and Ethernet OAM - Operation, Administration, and Maintenance - specified in IEEE 802.1ag. As can be seen from the name Provider Link State Bridging, PLSB uses a link state protocol. Each dedicated VLAN of the backbone, B-VLAN, operates with Link State Advertisements( LSA) and the Intermediate System to Intermediate System Protocol( IS-IS) to discover the network structure and exchange state information.

PLSB nodes inform each other about the immediate neighboring nodes and which nodes are connected and how. The Intermediate System to Intermediate System Protocol(IS-IS), standardized by the International Standards Organization ( ISO), is ideally suited for this purpose because of its flexibility and supports a wide variety of network protocols. In PLSB bridging, Intermediate System to Intermediate System (IS-IS) is used to exchange Layer 2 information, namely backbone MAC addresses (B-MAC) and I-Component Service Identifiers (I- SID).

Frame of Provider Backbone Bridges (PBB) according to IEEE 802.1ah

Since PLSB uses the frame format of Provider Backbone Bridges, the Customer MAC addresses (C-MAC) are located in the MAC addresses of the backbones (B-MAC). This eliminates the need to learn the Customer MAC addresses from the backbone and also preserves the integrity of the information.

PLSB applies the SPF algorithm, Shortest Path First (SPF), and stores the calculated signal paths in the routing tables of the PLSB nodes. This gives each individual node its own view of the shortest transmission paths.