Information Distribution Component
Traffic engineering requires detailed knowledge about the network topology as well as dynamic information about network loading. To implement the information distribution component, simple extensions to the IGPs are defined. Link attributes are included as part of each router’s link-state advertisement. IS-IS extensions include the definition of new type length values (TLVs), whereas OSPF extensions are implemented with opaque link-state advertisements (LSAs). The standard flooding algorithm used by the link-state IGPs ensures that link attributes are distributed to all routers in the routing domain. Some of the traffic engineering extensions to be added to the IGP link-state advertisement include maximum link bandwidth, maximum reserved link bandwidth, current bandwidth reservation, and link coloring.
Each router maintains network link attributes and topology information in a specialized traffic engineering database. The traffic engineering database is used exclusively for calculating explicit paths for the placement of LSPs across the physical topology. A separate database is maintained so that the subsequent traffic engineering computation is independent of the IGP and the IGP’s link-state database. Meanwhile, the IGP continues its operation without modification, performing the traditional shortest-path calculation based on information contained in the router’s link-state database.