Table 1 compares the advantages and disadvantages of these methods.
Table 1. Comparison of a Straight Link Configuration vs. a Crossed Link Configuration
Comparison Subject Straight Configuration Crossed Configuration
Load sharing -+
STPA can only load share traffic Each STP can load share between the two SIUs,
for SIUA and vice-versa optimizing the resource utilization
Network-facing links +-
failure SIUA can rely on SIUB to send When an SIU loses its network-facing links, the
outgoing traffic upon failure of its application must activate circuit groups on the
entire network-facing links surviving SIU (for ISUP-based application)
Inter-SIU link set -+
dimensioning Need to allocate 1/4 of all Need to allocate a single link, maximizing the
network facing links (e.g., 16 number of network-facing links (e.g., 22 network facing
network facing links and four links and one inter-SIU link). Allocating a single link means
inter-SIU links) there are two single points of failure in the system.
For best resilience, the inter-SIU link set should contain
two links spread across two cards in each SIU.
Building Fault-tolerant SS7 Systems Using the Intel
®
NetStructure™ SIU520 SS7 Signaling Gateway Application Note
9
