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Overview of SIU Operation
The Intel NetStructure SIU520 SS7 signaling gateway is
an SS7 network access product that provides a resilient
interface to SS7 networks via a TCP/IP local area net-
work (LAN). As shown in Figure 1, SIU520 software
includes SS7 protocol layers, as well as a configuration
and management module. The SIU520 supports multiple
SS7 signaling links within the same pulse code modula-
tion (PCM) trunk interface or over multiple PCM trunks.
The SIU examines the timeslots carrying the SS7 informa-
tion and processes them accordingly, outputting this data
to the LAN using TCP/IP. Similarly, it takes commands
from the TCP/IP LAN and converts those to SS7 signals
for transmission to the SS7 network. In the receive direc-
tion, information is conveyed to the user application in
structured messages placed in a sequential queue.
For both circuit- and transaction-related operations, the
SIU520 provides the ability to automatically distribute
signaling information between a number of physically
independent application platforms, thus providing a
degree of fault tolerance within the application space.
The SS7 signaling may be presented from the network
multiplexed in a timeslot on an E-1 (2.048 MB/s) or T-1
(1.544 MB/s, also known as DS1) bearer or by a V.35
(56/64 kb/s) synchronous serial interface.
For telephony operation (using a telephony layer 4 protocol
such as ISUP or TUP), if the SS7 signaling is multiplexed
onto a PCM bearer, the voice circuits may be passed
transparently through the SIU to the application platform
that terminates the physical circuits (see Figure 2).
Circuit-switched API Operation
The message-based application programming interface
(API) operates transparently over TCP/IP Ethernet, using
software modules provided by Intel. For circuit-switched
(telephony) applications, each application platform termi-
nates and hence controls a fixed range of physical cir-
cuits, or circuit identification codes (CICs). CICs are con-
figured in groups of up to 32, each group normally
equating to all the circuits in a single E-1 or T-1 trunk.
Each group is terminated on a fixed application platform
or host processor, enabling the SIU to automatically
direct API messages to the correct platform.
Application Note Building Fault-tolerant SS7 Systems Using the Intel
®
NetStructure™ SIU520 SS7 Signaling Gateway
2
Application
#0
Application
#1
Application
#N
API Layer/Ethernet Driver
Configuration
and
Management
MAP or INAP or IS41
TCAP
SCCP
MTP Levels 1-3
ISUP TUP
Ethernet
SIU 520
Figure 1. Structure of the Intel
®
NetStructure™ SIU520 SS7 Signaling Gateway