Intel SIU520 SS7 manual Failure of SS7 Links

Application Note Building Fault-tolerant SS7 Systems Using the Intel® NetStructure™ SIU520 SS7 Signaling Gateway

A) Load sharing between link 0 and link 1 under normal conditions

Link id 0, slc 0

SIU520

Link id 1, slc 1

Point Code

0x100

Link Set id 0

B) Traffic sent over link 1 under failure of link 0

SIU520

Point Code

0x100

SSP/SCP

Point Code

0x200

SSP/SCP

Point Code

0x200

Figure 3. SIU Connected to Adjacent Node with Two Links in Link Set

Failure of SS7 Links

Problem — With a single link to the adjacent signaling point, service is disrupted if the link goes down for some reason (i.e., layer 1 alarm, congestion).

Solution — Link resiliency is achieved by using multiple links between a local point code and an adjacent point code. By definition, such links are said to belong to the same link set, which can contain up to 16 links. Ideally, the links of a link set should not be carried over a unique physical medium (such as an E-1 or T-1 trunk) but, instead, should be split over independent physical trunks.

Link failure management is a standard MTP3 operation and is not an SIU520-specific feature. In other words, failure between links in a same link set will happen in a completely transparent way for the user application.

Details — In an SIU520 system configuration, two commands are used in config.txt to configure link sets and links: MTP_LINKSET and MTP_LINK. In this example, two SS7 links are defined between local point code 0x100 and adjacent point code 0x200 on time slot 16 of PCM ports 1 and 2. (Also see Figure 3.)

* MTP_LINKSET <linkset_id> <adjacent_spc> <num_links> <flags> <local_spc> <ssf> MTP_LINKSET 0 0x200 2 0x0000 0x100 0x08

*MTP_LINK <link_id> <linkset_id> <link_ref> <slc> <bpos> <blink> <bpos2> *<stream> <timeslot> <flags>

MTP_LINK 0 0 0 0 0 0 0 0 16 0x0006 MTP_LINK 1 0 1 1 0 1 0 1 16 0x0006

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