In this section:


In the following network configuration (see the following figure)

  • C and D are DSC - SP2000 Platforms
  • A and B are switches
  • E and F are core STPs
  • X is a switch that is beyond the core STPs that A and B have to access
Note

Typically, in this scenario, nodes C and D behave as STPs. If A is required to send a message signaling unit (MSU) to B, this MSU would be sent through C or D and it would be routed using standard MTP Level 3 routing procedures.

Routing MSUs Using MTP Level 3 Routing Procedures

Enabling the traffic flow shown in the following figure with traditional MTP3 routing (based on DPC only) is not possible for the following reasons:

  • E and F refuses to send the MSUs back to C and D, because of circular routing rules (GR-246).
  • If C and D route based on DPC, the MSUs from E or F with DPC B is routed back to E or F, and the circular routing rules cause the MSU to be discarded.

Forcing MSUs Through Core STP E

Routing on Incoming Linkset

Note

The routing on incoming linkset feature is license-dependent. For information about license availability and pricing, contact your Sales Representative


To allow the traffic flows presented in the preceding illustrations, the allows routing of messages not only on the DPC, as defined in SS7 standards, but also on a per incoming linkset basis.

In this case, when routing traffic is destined to B, nodes C and D must route messages originating from A through E or F. However, traffic originating from F destined to B is routed directly to B. To obtain this traffic pattern, the operator must provision two routeset lists that are assigned directionally (see the following figure)

Routing on Incoming Linkset (RTIL)

Asymmetric Routing

When the Edge devices are configured with appropriate routing tables, the core STPs must also allow the appropriate traffic flow.

For STPs that use standard SS7 routing, one solution is to provision routes asymmetrically.

Using this method, the links between C, D, E, and F carry unidirectional traffic. E receives traffic from C, but sends traffic to D (see the following figure).

Asymmetric Routing Example


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