Intel SIU520 SS7 User Manual

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Communications
Building Fault-tolerant SS7 Systems Using the Intel
®
NetStructure™
Application Note
Building Fault-tolerant SS7 Systems Using the Intel®NetStructure™ SIU520 SS7 Signaling Gateway Application Note
Table of Contents
Abstract 1
Introduction 1
Overview of SIU Operation 2
Circuit-switched API Operation 2
Transaction-based API Operation 3
Management Interface 3
Potential Points of Failure 3
Failure of SS7 Links 4
Failure of Routes 5
Failure of Power Supply 6
Failure of Signaling Interface Unit 6
Routing Architectures of a Dual-resilient SIU System 7 Dual SIU architecture for Circuit-switched Applications 10
Dual SIU architecture for Transaction-based Applications 13 Failure of IP Subnetwork 15 Failure of Application 15
Configuring a Dual SIU Pair 17
Hardware Requirements 17
System Configuration 18
Changes to the config.txt Parameter File 18
Configuring the Inter-SIU Link 18 Routing Configuration 19 Circuit Group Configuration 19 Example Configuration 19
Run-time Operations of a Dual-resilient SIU System 20
Connecting a Host to Two SIUs 20
Communicating with Both SIUA and SIUB 21
Transferring Control of a Circuit Group between SIUs 21
Activating and Deactivating Circuit Groups 21 System Initialization 21 Failure Detection 21 Transferring the Circuit Group 22 Re-synchronization of the Circuit Sate Information 22 Recovery of the Failed Unit 23 Transferring Control Back 23 Circuit Group Conflict 23
Appendix A: Frequently Asked Questions 24
Appendix B: For More Information 24
Appendix C: Abbreviations 24
Application Note Building Fault-tolerant SS7 Systems Using the Intel®NetStructure™ SIU520 SS7 Signaling Gateway
Table of Figures
Figure 1 Structure of the Intel®NetStructure™ SIU520 SS7 Signaling Gateway 2
Figure 2 Integrating the SIU520 3
Figure 3 SIU Connected to Adjacent Node with Two Links in Link Set 4
Figure 4 SIU520 Connected to Mated STP Pair Providing Route Resiliency 5
Figure 5 Dual SIU Architecture 6
Figure 6 Transmit Routing to a Single Destination 7
Figure 7 Dual-resilient SIUs Connected to a Mated STP Pair in a Straight Line 8
Configuration
Figure 8 Dual-resilient SIUs Connected to a Mated STP Pair in a Crossed Link 8
Configuration
Figure 9 Transmit Routing Through Mated STPs 9
Figure 10 Normal Routing for Circuit Group 0 When Controlled by SIUA 10
Figure 11 Routing When All Local Links Have Failed, Group 0 Controlled by SIUA 11
Figure 12 Routing Following Failure of SIUA 12
Figure 13 Two Different Architectures for a TCAP Processing SIU System 13
Figure 14 Message Flow on a Dual-resilient System Running 14
the SS7 Stack up to TCAP
Figure 15 Dual LAN Operation on the SIU520 15
Figure 16 TCAP Dialogue Groups Example 16
Figure 17 Inter-SIU Link over Crossed E-1/T-1 Cable 17
Figure 18 Inter-SIU Link Set over V.11 18
Figure 19 Example Configuration to an Adjacent SSP/SCP 19
Figure 20 Example Configuration to an Adjacent STP Pair 20
Abstract
In order to achieve five-nines (99.999%) reliability and a high degree of fault tolerance in an SS7 environment 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. Splitting the protocol processing functionality of a signaling point by implementing an SS7 node over two SIUs isolates the hardware processors on the chassis from each other. This separation lets one processor continue if the other fails, allowing the system to remain in service. Distributing application processing of a signaling point on multiple application servers not only increases the total capacity of a system, but also offers a higher level of fault tolerance in the user application space.
Intel NetStructure SS7 products are designed for this dual-processor approach and provide the architecture for splitting a point code over two active SS7 protocol engines. Using this technique, the links in an SS7 link set can be spread between two separate chassis when Intel NetStructure SS7 boards are installed in each.
This document describes the features of the SIU520 SS7 signaling gateway that are available to build SS7 solutions and reach the five-nines requirements of telco-grade service platforms.
Introduction
This application note describes the architecture of the Intel NetStructure SIU520 signaling gateway, reviews the most common potential points of failure of an SS7 system based on this product, and explains methods that can mitigate each of these potential failure points. This document also explains in detail the configuration and run-time operation considerations of a dual-resilient SIU520-based system.
Because of the high expectation of service reliability by the users of public telephone networks, equipment manufacturers and system integrators demand high levels of fault tolerance and availability, often citing the five-nines for availability (requiring a system to be operational for 99.999% of the time).
These systems need to continue to offer service even when partial hardware or software failure has occurred. There are several well-known methods of achieving this type of reaction to partial failure in the signaling component of communications networks, including:
Multiple signaling paths (SS7 links and link sets) to each end point
Distribution of these paths through independent inter­faces and cabling
Distribution of the processing of SS7 terminations at a single signaling point between multiple processing cards in a single SIU
Physical isolation and duplication of the SS7 interface for a single signaling point on independent protocol engines sharing a single point code
Splitting the functionality of the application layer between multiple application servers
The first method can be achieved by implementing multi­ple links (64 Kb/s or 56 Kb/s channels) between two adjacent inter-communicating points. (By definition, these links will all be in the same link set.) The last two can be accomplished by using two independent, but co-operat­ing, SIU520s relaying the SS7 signaling to a distributed application layer split over multiple application hosts.
Note: Readers should be familiar with Signaling System 7 (SS7) concepts. They should also be aware that the information contained in this application note is provided as a complement to the Intel NetStructure SIU520 Developer’s Manual; hence, an understanding of the terms defined in the developer’s manual is assumed.
Building Fault-tolerant SS7 Systems Using the Intel®NetStructure™ SIU520 SS7 Signaling Gateway Application Note
1
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 net­work (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 modula­tion (PCM) trunk interface or over multiple PCM trunks. The SIU examines the timeslots carrying the SS7 informa­tion 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 direc­tion, 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 termi­nates and hence controls a fixed range of physical cir­cuits, or circuit identification codes (CICs). CICs are con­figured 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
Figure 1. Structure of the Intel®NetStructure™ SIU520 SS7 Signaling Gateway
Application
#0
Configuration
and
Management
Application
#1
API Layer/Ethernet Driver
MAP or INAP or IS41
TCAP
SCCP
MTP Levels 1-3
Application
#N
Ethernet
ISUP TUP
SIU 520
Transaction-based API Operation
TCAP-based applications can be distributed on multiple application hosts using two different methods which are explained in details further in this document (see “Failure of Applications”, pg. 15). These methods imply running TC-user application parts (such as GSM-MAP, INAP, or IS-41) on each application host. When running any application part above TCAP on the SIU520 itself, the product allows operation of a single host application.
Management Interface
The SIU520 constantly monitors the state of its physical connections, PCM trunk inputs, the communication channel via TCP/IP Ethernet to the host processors and reports status information to an application process running on a user-defined host. The host elected to receive management messages can be selected by sending an API_MSG_COMMAND management request. (See the Intel NetStructure SIU520 Developer’s Manual for more information.) Host 0 is used by default.
Potential Points of Failure
In this section, the most critical points of failure of an Intel NetStructure SIU520 SS7 signaling gateway-based sys­tem are reviewed. The list of potential points of failure include:
SS7 links
SS7 routes
Power supply
Signaling interface unit
IP subnetwork
Application host
For each of these points of failure, a solution is provided and implementation details are given.
Building Fault-tolerant SS7 Systems Using the Intel®NetStructure™ SIU520 SS7 Signaling Gateway Application Note
3
Figure 2. Integrating the SIU520
E-1 or T-1 Trunks,
Voice Circuits
CT Application Platform
Only
}
SIU520
E-1 or T-1 Trunks
SS7
Information
CT Application Platform
with SS7 Channel and Voice Circuits
}
Ethernet
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. By definition, such links are said to belong to the same link set, which can contain up to 16 links. Ideally, the links of a link set should not be carried over a unique physical medium (such as an E-1 or T-1 trunk) but, instead, should be split over independent physical trunks.
Link failure management is a standard MTP3 operation and is not an SIU520-specific feature. In other words, failure between links in a same link set will happen in a completely transparent way for the user application.
Details — In an SIU520 system configuration, two commands are used in config.txt to configure link sets and links: MTP_LINKSET and MTP_LINK. In this example, two SS7 links are defined between local point code 0x100 and adjacent point code 0x200 on time slot 16 of PCM ports 1 and 2. (Also see Figure 3.)
Application Note Building Fault-tolerant SS7 Systems Using the Intel®NetStructure™ SIU520 SS7 Signaling Gateway
4
Figure 3. SIU Connected to Adjacent Node with Two Links in Link Set
A
* MTP_LINKSET <linkset_id> <adjacent_spc> <num_links> <flags> <local_spc> <ssf> MTP_LINKSET 0 0x200 2 0x0000 0x100 0x08
* MTP_LINK <link_id> <linkset_id> <link_ref> <slc> <bpos> <blink> <bpos2> *<stream> <timeslot> <flags> MTP_LINK 0 0 0 0 0 0 0 0 16 0x0006 MTP_LINK 1 0 1 1 0 1 0 1 16 0x0006
) Load sharing between link 0 and link 1 under normal conditions
SIU520
Point Code
0x100
Link Set id 0
B) Traffic sent over link 1 under failure of link 0
SIU520
Point Code
0x100
Link id 0, slc 0
Link id 1, slc 1
SSP/SCP
Point Code
0x200
SSP/SCP
Point Code
0x200
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 require any specific action from the user application.
Solution — To eliminate this single point of failure, an alternative link set can be provided in the SIU520 system configuration to reach the same DPC. Route failover is a standard MTP3 operation which does not require any specific action from the user application.
Note: When an alternative route to a given DPC is
defined in an SIU520 configuration file, a choice must be made between two different traffic modes: load sharing or failover. In load-sharing mode, traffic sent towards the remote signaling point is shared between the two link sets. In failover mode, all traffic sent towards the remote signaling point will normally be sent using the primary link set, unless this link set fails, in which case the traffic will use the alternative link set. See the Intel NetStructure SIU520 Developer’s Manual for more information on the selection of traffic mode in the MTP_ROUTE command.
Details — This example (see Figure 4) shows two link sets (each containing one link) being used in load-sharing mode to reach destination point code 0x400.
Building Fault-tolerant SS7 Systems Using the Intel®NetStructure™ SIU520 SS7 Signaling Gateway Application Note
5
Figure 4. SIU520 Connected to Mated STP Pair Providing Route Resiliency
* MTP_LINKSET <linkset_id> <adjacent_spc> <num_links> <flags> <local_spc> <ssf> MTP_LINKSET 0 0x200 2 0x0000 0x100 0x08 MTP_LINKSET 1 0x300 2 0x0000 0x100 0x08
* MTP_LINK <link_id> <linkset_id> <link_ref> <slc> <bpos> <blink> <bpos2> *<stream> <timeslot> <flags> MTP_LINK 0 0 0 0 0 0 0 0 16 0x0006 MTP_LINK 1 0 1 1 0 1 0 1 16 0x0006 MTP_LINK 2 1 0 0 0 2 0 2 16 0x0006 MTP_LINK 3 1 1 1 0 3 0 3 16 0x0006
* MTP_ROUTE <dpc> <linkset_id> <user_part_mask> <flags> <second_ls> <pc_mask> MTP_ROUTE 0x400 0 0x0020 0x0003 1 0x00000000
A) Load sharing between link set 0 and link set 1 under normal
Link Set id 0
STPA
Link id 0, slc 0
SIU520
L
Point Code
0x100
Link Set id 1
B) Traffic sent over link set 1 under failure of STP
Link Set id 0
SIU520
Point Code
0x100
Link Set id 1
ink id 1, s
Link id 0, slc 0
L
ink id 1, slc 0
Point Code
0x200
lc 0
STPB
Point Code
0x300
STPB
Point Code
0x300
SSP/SCP
Point Code
0x400
SSP/SCP
Point Code
0x400
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 redundant and hot swappable power supply.
Details — Please refer to Intel NetStructure SIU520/Intel NetStructure SG430 Hardware User Manual, Issue 3 to
obtain part numbers for redundant power supplies for the SIU520.
Failure of Signaling Interface Unit
Problem — Since the SIU520 provides an SS7 interface to a distributed application, it is usually deployed for high-density service platforms. Should the SIU of a single SIU-based system fail, many resources (telephony cir­cuits to TCAP dialogues) would become unavailable and would cause major service disruption.
Solution — A major feature of the SIU architecture is that two units can be configured to operate as a single entity, sharing the same local SS7 point code. In normal operation, signaling can be shared between two units. In the event of a failure, signaling is maintained by the remaining unit.
Details — In a dual configuration, one unit is assigned as SIUA, the other as SIUB. Under normal operation, the application uses both the resources of SIUA and SIUB (see Figure 5).
The distributed layer 4 management is achieved using a LAN connection and allows SS7 messages for any trans­action or call to be received by either unit, regardless of the unit that is actually processing the call or transaction.
The distributed MTP3 functionality is achieved using a specially configured inter-SIU link set, containing one or more signaling links. Transmit messages from each SIU are load shared between links that connect to the local SIU, if these are available. If all local network-facing SS7 links have failed, transmit messages are relayed to the
Application Note Building Fault-tolerant SS7 Systems Using the Intel®NetStructure™ SIU520 SS7 Signaling Gateway
6
Figure 5. Dual SIU Architecture
Application
Ethernet
SIUA SIUB
API Layer/Ethernet Driver
MAP or INAP
or IS41
TCAP
SCCP
MTP Levels 1-3
ISUP TUP
SS7
Distributed Layer 4
Management
Distributed MTP3
Management
Link Set
Ethernet
API Layer/Ethernet Driver
MAP or INAP
or IS41
TCAP
SCCP
MTP Levels 1-3
SS7
ISUP TUP
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