Routing Overview

Service Provider personnel statically maintain signaling endpoint routing tables. The routing table identifies the links, linksets, primary routes, and alternate routes for each DPC. All links in the linkset share the traffic load equally. When a particular destination has more than one linkset, the linksets involved share the traffic load equally.

Priority codes identify primary and alternate routes. The direct, most-direct, or fewest-hop-count route (or link) is always the first choice as the outgoing link. The routes are chosen based on link type (A- to F-links) and signaling endpoint type (SSP, STP, or SCP). An F-link between two SSPs, for example, is the first route choice for messages between these two endpoints. A most-direct-route example is an E-link; if available, this link is the second choice for messages between the (E-link-attached) SSP and the destination SSP.

The SNM function reroutes traffic in the SS7 network. The SMH handles the following during network link failures:

• Linkset rerouting

• Alternate link rerouting

• Traffic flow rerouting to specific endpoints

The SNM process handles the rerouting of traffic through alternate links or linksets during network link failures. The SNM process also controls the flow of traffic to specific endpoints during network link failures.

SNM is divided into three functions:

• Link Management—Monitors and controls the individual links of the signaling endpoint. Link management manages the link interfaces of the signaling endpoint as opposed to the end-to-end link. The link management function is divided into three parts—Link Activation, Link Restoration, and Link Deactivation—described here:

o The Link Activation process uses the LSSU to inform the adjacent endpoint of the link status. Signaling Link Test Messages (SLTMs) activate links between endpoints. The SLTM acknowledgment (SLTA) restores the link to service and enables traffic to flow over the link. o The Link Restoration process uses the LSSU to inform the adjacent endpoint of L3 alignment activities. When the alignment procedures are complete, the link activation process is initiated. o The Link Deactivation process places links into alignment procedures when links are failed or in error. Link deactivation uses local MTP2 information and remote information provided by the

LSSU to initiate alignment procedures. Link deactivation triggers traffic management procedures when link failures or errors are detected.

• Route Management—Exchanges routing information and status between signaling endpoints. Routing problems are transmitted using transfer messages to redirect traffic during network failure conditions. This enables the other signaling endpoints to choose alternate routes.

You can use several types of transfer messages for normal and cluster routing management. The functionality and capabilities of these messages are outside the context of this book. The following is a list of the transfer messages used when failures are identified:

o Transfer Prohibited o Transfer Allowed o Transfer Restricted o Transfer Controlled o Signaling Route Set and Congestion Test o Cluster Router Set Test

• Traffic Management—Used to reroute or divert traffic and control congestion during network failure conditions. The traffic management process receives link availability information from SNM Link Management and is advised of routing problems to particular destinations from SNM Route Management. Traffic management also has the capability of advising SMH and the upper-layer protocols of failure conditions. Traffic management uses the following:

o An interface to SMH to reroute or divert messages over an alternate route o Primitives to advise the upper-level protocols about the status of signaling links o MSU to transmit messages to SNM peer processes in other signaling points o Commands to MTP2 for signaling links

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