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Intel in Communications Building Fault-tolerant SS7 Systems Using the Intel ® NetStructur e™ SIU520 SS7 Signaling Gateway Application Note.
Building Fault-tolerant SS7 Systems Using the Intel ® NetStructure™ SIU520 SS7 Signaling Gateway Application Note T able of Contents Abstract 1 Introduction 1 Overview of SIU Operation 2 Circuit-sw.
Application Note Building Fault-tolerant SS7 Systems Using the Intel ® NetStructure™ SIU520 SS7 Signaling Gateway T able of Figur es Figure 1 Structure of the Intel ® NetStructur e™ SIU520 SS7 S.
Abstract In order to achieve five-nines (99.999%) r eliability and a high degree of fault tolerance in an SS7 envir onment using Intel ® NetStructure™ SIU520 signaling gateways, an SS7 end point spread over two signaling interface units (SIUs) and multiple application servers can be configured and deployed.
Overview of SIU Operation The Intel NetStructure SIU520 SS7 signaling gateway is an SS7 network access product that pr ovides a resilient interface to SS7 networks via a TCP/IP local area net- work (LAN). As shown in Figure 1, SIU520 softwar e includes SS7 protocol layers, as well as a configuration and management module.
T ransaction-based API Operation TCAP-based applications can be distributed on multiple application hosts using two differ ent methods which are explained in details further in this document (see “Failure of Applications”, pg.
Failure of SS7 Links Problem — With a single link to the adjacent signaling point, service is disrupted if the link goes down for some reason (i.e., layer 1 alarm, congestion). Solution — Link resiliency is achieved by using multiple links between a local point code and an adjacent point code.
Failure of Routes Problem — With a single route to a destination point code (DPC), service can be disrupted if all the links of the link set used to reach that signaling node fail. Route failover is a standard MTP3 operation which does not requir e any specific action from the user application.
Failure of Power Supply Problem — Ensuring that the unit survives the loss of one power supply and making it possible to replace a failed power supply without affecting the availability of the system. Solution — The Intel NetStructure SIU520 SS7 signaling gateway can be optionally configured with a r edundant and hot swappable power supply .
partner SIU across the inter -SIU link set and sent out to the adjacent signaling point by the partner unit. The inter - SIU link set also provides the capability of message retrieval and r etransmission when a changeover operation occurs between the two units.
In case (A), since the F-links all exist in the same link set, messages may be sent from the adjacent SSP/SCP to either SIUA or SIUB. If an SIU receives a message fr om the SS7 network for a circuit or transaction that it does not control, this r eceive message is passed automatically to the other SIU for processing via the TCP/IP LAN.
T able 1 compares the advantages and disadvantages of these methods. T able 1. Comparison of a Straight Link Configuration vs. a Crossed Link Configuration Comparison Subject Straight Configuration Cr.
Dual SIU Architectur e for Circuit-Switched Applications Within the SIU environment, circuits ar e configured in groups, each gr oup equating to all the circuits multiplexed onto a single E-1 or T -1 PCM trunk.
If all the links between the controlling SIU and the adjacent signaling point fail, all transmit traffic is automatically routed to the adjacent signaling point through the inter -SIU link set as shown in Figure 11. The application should continue to use the SIU as before, directing all outgoing cir cuit requests to SIUA.
The circuit gr oup control will then appear as shown in Figure 12. The user application software should r eset all idle circuits following a transfer , and reset all r emaining circuits as they become idle. When the failed unit recovers, contr ol of the circuits may be transferred back by the application.
Dual SIU Architectur e for T ransaction-based Applications There ar e two ways of architecting a dual-r esilient SIU520-based system for processing TCAP transactions.
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.
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 ar e two Ethernet ports on the SIU520.
TCAP Resiliency Based on DTS/DTC Option Alternatively , it is possible to distribute SCCP traffic to multiple application hosts using the distributed transac- tion server/distributed transaction client (DTS/DTC) soft- ware option, as shown on Part B of Figur e 13.
Configuring a Dual SIU Pair T o create a dual-r esilient configuration for the Intel NetStructure SIU520 SS7 signaling gateway , modifications are r equired to both the system configuration (done using the man machine interface [MMI]) and the protocol configuration (in the config.
The inter -SIU signaling link set can be configur ed to use any signaling processor on any signaling car d and may be carried on any of the available interfaces on the signaling card.
using the MTP_LINK command, assigning incrementing <link_ref> and <slc> values as normal. The <bpos> and <blink> parameters define which SS7 processor (there ar e three on each signaling car d) manages each link. If a V .11 port is being used, <blink> must be either 1 or 2.
For an SIU pair connected to a mated STP pair , carrying the inter -SIU link over the second E-1 port of the first signaling card the configuration (Figur e 20) would be: For SIUA MTP_CONFIG 0 0 0x000.
Communicating with Both SIUA and SIUB The user application exchanges information with the SIU via API messages (MSG). In a dual SIU environment, each time the user application sends a message to the SIU, this should be directed to either SIUA or SIUB using a library function GCT_set_instance .
conc_id on the host ( conc_id is set when the RSI link was started, optionally by rsicmd ). This message will only be received by the application if the RSI link is con- figured with the conc_id set to the application’ s module ID.
Recovery of the Failed Unit The host application is informed of recovery of the communication to the SIU with the same method used for notification of the failure. The RSI_MSG_LINK_ ST A TUS message in this case contains a status value of 1 (link to SIU recover ed).
Appendix A: Frequently Asked Questions Q: How can I tell if an SIU fails? A: The status of the communication between the host and the SIU is indicated by RSI_MSG_ST A TUS messages.
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