Intel SIU520 SS7 manual Failure of IP Subnetwork, Failure of Application

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

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SIU520

Figure 15. Dual LAN Operation on the SIU520

Failure of IP Subnetwork

Problem — Should one subnetwork go down due to a network component failure, the hosts connected to the SIU over the other subnetworks will remain active and attempt to preserve half of the total system capacity.

Solution — There are two Ethernet ports on the SIU520. This allows splitting the IP connections between the SIU and the application hosts onto two physically separated subnetworks, as shown in Figure 15. This eliminates the risk of losing all IP connectivity in the event of a switch/router/hub failure in the LAN.

Details — “Failure of Application”, below, shows how to take advantage of the dynamic configuration features offered by the SIU520 to failover the affected application hosts to the surviving subnetwork.

Failure of Application

Problem —The failure of an application host leads to the loss of a portion of system resources.

Solution —The most basic feature ensuring this is that the application can be deployed on multiple hosts. In a software release bigger than v1.06, the SIU520 supports up to 64 hosts. For circuit-switched applications, failure of a host generally means loss of the physical trunk interface; hence, there is no need of transferring the logic to other (surviving) hosts. More sophisticated features are

available to allow TCAP-based applications to failover to other hosts.

Details — For TCAP-based applications, the SIU allows operation of multiple application hosts interfacing directly to TCAP, hence giving a certain level of resiliency in the user application space. Two methods are available for this purpose and are explained here.

TCAP Resiliency Based on Dialogue Groups

Fixed ranges of TCAP dialogues can be created in the SIU520 configuration file and assigned to different application hosts. (TCAP dialogue groups are defined using the TCAP_CFG_DGRP command in config.txt. More information about this command can be found in the Intel NetStructure SIU520 Developer’s Manual.) The application program running on each host must therefore ensure that only dialogue identifiers from the assigned range are used. Optionally, a TCAP-user layer such as MAP, INAP, or IS41 can run on each application host to provide some application part functionalities. Figure 16 describes such a distributed architecture where TCAP transactions are handled by four different hosts, each of them running MAP and a MAP application. The total number of TCAP dialogues for the whole system is 16,384 and this number does not depend on the number of hosts.

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