In this section:

On an incoming MSU destined for the SCCP Relay point, if the destination is available, perform the necessary mapping always using the primary routing PCs. If the remote primary destination is unavailable but the mate and secondary destination are available, get MTP3 to send on the C-link using the MTP3 VNode Rerouting option (refer to MTP3 VNode for more information in the appropriate guide in the Documentation Library). Prior to sending traffic on the C-link, the Gateway Screening (GWS) information on the incoming linkset is validated. If the incoming linkset is that of the mate, circular routing would ensue, so the mate LPC is considered as unavailable. The DPC of the incoming message is changed to the secondary mirror PC if this PC is different from the primary. This PC swap is required when the mirror PC is set to a local point code, because there can be no VNode for an LPC or a routeset to itself.

If the remote primary and the mate LPC are all unavailable, but the remote secondary LPC is available, then the message is converted but the DPC is set to the remote variant SCCP Relay mate LPC. The SCCP PCs are set to the secondary values. Therefore, when the MTP3 receives these secondary values, it automatically sends the values to the other Level 4 Converter. This Level 4 Converter now checks to see if the OPC is that of its mate LPC. If it is, then secondary routing applies and the OPC is converted to the incoming DPC (local LPC) and uses the first (only) route mapping to determine the DPC based on the primary home PC.

Note

The secondary routing only applies to traffic destined to the variant with an LPC setup, because the primary and secondary is never distinct if a VNode is involved.

The secondary routing is required as R4-8 feature at MTP3 only applies to user traffic and not C-Link transfer. The OPC cannot be set to the secondary PC as MTP3 considers this a circular routed MSU.

If the primary, secondary, and mate LPCs are all unavailable, return a (X)UDTS if required (refer to SCCP Relay Point Configuration).

Example 1 – Japan to ITU All Linkset Available

DPC 20.15.86, OPC 01.01.001.

The Level 4 Converter on mate 1 receives the message. Japan PCs 20.15.86 and 01.01.001 Route Mappings found and primary destination is available. Conversion from 20.15.86 to 1.1.1 and 01.01.001 to 1.2.3 are used. Message is sent to ITU STP 1.1.1 for routing.

Example 2 – ITU to Japan with Primary Unavailable

The linkset to Japan 01.01.001 is down and message is received at ITU STP 1.1.1.

DPC 1.1.3, OPC 4.84.1

The Level 4 Converter on mate 1 receives the message. ITU PC 1.1.3 Route Mapping is found. Primary destination is down, but mate LPC 1.1.2 and 02.02.002 are available. The message is not originally from the C-link, so message is sent back to ITU STP 1.1.1 using C-link to 1.1.2. The DPC is still 1.1.3 as the secondary mirror PC is the set to the VNode.

The Level 4 Converter on mate 2 receives the message. ITU PC 1.1.3 Route Mapping found. ITU 4.84.1 Route Mapping found. Conversion from 1.1.3 to primary 02.02.002 and 4.84.1 to primary 20.15.87 are used. Message is sent to Japan STP 20.15.87 for routing.

Example 3 – Japan to ITU with ITU Mate 2 Unavailable (C-link and 2 ITU links down)

DPC 20.15.87, OPC 02.02.002.

Level 4 Converter on mate 2 receives the message. Japan PC 20.15.87 Route Mapping is found. Primary (and secondary – identical) is down but mate LPC 20.15.86 is available. The message is not originally from the C-link so message is sent back to Japan STP 20.15.87 but with DPC set to 20.15.86 to be sent using C-link.

Level 4 Converter on mate 1 receives the message. Japan PCs 20.15.86 and 02.02.002 primary Route Mappings are found. Conversion from 20.15.86 to 1.2.3 and 02.02.002 to 1.1.1 are used. Message is sent to ITU STP 1.1.1 for routing.

 

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