Intel SIU520 SS7 manual 7 SS

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

Application

SIUA

	TCAP
Ethernet	instance = 0

SCCP

MTP

Inter-chassis	SS
communication	7
(RSI)

MTP

SCCP

TCAP instance = 1

SIUB

Transmit message for transaction handled by TCAP B

Message received for transaction handled by TCAP B

SS7

7 SS

Adjacent

Signaling

Point

Figure 14. Message Flow on a Dual-resilient System Running the SS7 Stack up to TCAP

In the second case, each unit controls half of the total available transactions. (The Intel NetStructure SIU520 SS7 signaling gateway supports up to 16,384 transac- tions. A dual-resilient system can consequently handle up to 32,768 simultaneous transactions.) Each transaction is processed for its entire duration by the SIU that processed the first TCAP message. The user application must therefore direct all messages for a transaction to the same SIU, and load balance outgoing dialogues between the two units. An incoming TCAP dialogue mes- sage other than BEGIN or QUERY is handled by the SIU that processed the first TCAP message for that dialogue received from the SS7 network. When an SIU receives a TCAP message that belongs to a transaction that was initiated on the other unit, it will pass this message to its peer SIU over the RSI connection. This is shown in

Figure 14. Failure of an SIU reduces the number of avail- able transactions to one-half.

In a dual-resilient transaction-based SIU system running the SS7 stack up to SCCP on the SIU, and TCAP (and above) on the application host, each host controls a fixed number of transactions. Each transaction is processed for its entire duration by the application host that processed the first TCAP message. Upon failure of one SIU unit, the TCAP capacity and ongoing transaction are totally unaffected.

The architectural decision taken on where the TCAP module is running also has consequences on the level of application resiliency and total system capacity. These consequences are explained in more details in “Failure of Application”, pg. 15.

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