Intel SIU520 SS7 manual Comparison Subject, Straight Configuration, Crossed Configuration

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

A)Normal routing case (both network link sets available) Single Point Code

Link Set id 1

Inter-SIU

Link Set

Link Set id 0

SIUA

SIUB

A-Links

Link Set id 2

STPA SSP/SCP

C-Links

STPB

B) Routing under failure of network link set between SIUA and adjacent STP
Single Point Code
Inter-SIU	Link Set id 1
Link Set
SIUA		SSP/SCP
Link Set id 0	A-Links
SIUB		C-Links
	Link Set id 2	STPB
Transmit Traffic from SIUA
Transmit Traffic from SIUB
	Figure 9. Transmit Routing Through Mated STPs

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.

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