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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.
Building Fault-tolerant SS7 Systems Using the Intel
®
NetStructure™ SIU520 SS7 Signaling Gateway Application Note
15
Figure 15. Dual LAN Operation on the SIU520
Application
Host
SIU520
Application
Host
Subnetwork 1
Subnetwork 1
Subnetwork 2
S
ubnetw
or
k 2