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Overview

The SBC maximizes the probability of completing a call, with minimal post dial delay through the following enhancements:

  • The SBC skips blacklisted routes even though the PSX returns all peers

  • The number of routes to try is specified

  • Alternate routes are attempted for completing the call


Note

The SBC supports this feature only when the PSX acts as a policy server over D+ interface, only for the SBC.

The dynamic view of routes at the SBC is used at the SBC and the static view at the PSX is communicated to its clients.

Backward compatibility is maintained across all products and during upgrades. This is achieved by each product communicating to the PSX if it supports the Routes to Try feature.

The SBC adds the following enhancements for the feature:

  • The SBC sends a bit to the PSX in the Policy Request, indicating that it supports Skip Blacklisted Peers feature.

  • The SBC receives Routes to Try for each group from the PSX and increment the counter if the route is not blacklisted.

  • The SBC tries routes as per the Routes to Try values received in the PSX query response for the following scenarios:

    • Heavy weight dip

    • Light weight dip

    • More routes request

    • FQDN request

    • IP Peers request

    • GW- GW request

    • If the SBC gets 3xx response

    • Non-INVITE messages. For DNS failures, the SBC does not move to the next route and ends the call.

    • REGISTER messages.

  • The SBC adds SIP In Core support for the Routes to Try feature.

Use Cases

In the following use cases, Routes to Try is enabled and the number of routes to try is configured in the PSX.

The SBC uses ARS service to blacklist entries (based on ARS profile) and uses PATHCHECK service to blacklist entries (based on PATHCHECK profile).

In the figures below:

  • P11 stands for IPSPG1 Peer1
  • P12 stands for IPSPG1 Peer 2
  • IP1 stands for IP Peer 1
  • IP2 stands for IP Peer 2

IP Signaling Peer Groups Provisioned in the PSX - SBC Does a Heavy Weight Dip

IP Signaling Peer Groups provisioned in PSX - SBC Heavy Weight Dip


IP Signaling Peer Groups Provisioned in the PSX - SBC Does a Light Weight Dip

IP Signaling Peer Groups Provisioned in PSX - SBC Light Weight Dip


IP Signaling Peer Groups Provisioned in the PSX - SBC Does a Heavy Weight Dip Followed by a More Routes Request


Note

The first route of a More Routes request is always attempted.


IP Signaling Peer Groups Provisioned in the PSX - SBC Does a Heavy Weight Dip Followed by a More Routes Request



IP Signaling Peer Groups Provisioned with FQDNs in the PSX - SBC Does a Heavy Weight Dip

IP Signaling Peer Groups Provisioned with FQDNs in the PSX - SBC Does a Heavy Weight Dip


IP Peers are Provisioned in the PSX - SBC Does a Heavy Weight Dip

IP Peers are Provisioned in the PSX - SBC does a Heavy Weight Dip


IP Signaling Peer Groups and GW-GW routes are Provisioned in the PSX - SBC Does a Heavy Weight Dip

IP Signaling Peer Groups and GW-GW routes are Provisioned in the PSX - SBC Does a Heavy Weight Dip