Cisco SS7 Interconnect for Voice Gateways Solution Introduction

This chapter introduces the Cisco SS7 Interconnect for Voice Gateways Solution and includes the following sections:

Overview

When you make calls using your telephone or PC with modem connection, you generally use the Public Switched Telephone Network (PSTN). You hear progress tones such as a dial tone or a busy tone that tell you your call is being processed. These are alerting tones that are produced by the PSTN. Alerting tones are used to communicate from the PSTN to users, and telecommunications computers, or "switches," communicate with each other through standards-based signaling. Signaling is the backbone for interconnection between carrier, cellular, and wireless networks. Signals are the medium that set up and tear down your calls.

A major breakthrough in signaling networks was to separate the signaling path from voice and data conversations. This is called "common channel interoffice signaling (CCS)." CCS, also known as out-of-band signaling, is a data network that overlays a carrier's switching network. Using CCS increases network intelligence, efficiency, automation, and functionality. CCS has evolved into a standard called Signaling System 7 (SS7), a protocol that lowered costs and increased network reliability even further. With SS7, all carriers are able to interoperate as a consistent and seamless network. Services such as global billing, wireless roaming, and 800 number calling rely on the SS7 protocol to exchange messages reliably.

The Cisco SS7 Interconnect for Voice Gateways Solution is a distributed system that provides SS7 connectivity for Voice-over-IP (VoIP) access gateways by using the Cisco Signaling Controller (also referred to as the Cisco SC2200 product) and the access gateways as a bridge from the H.323 IP network to the PSTN network. This solution interacts over the IP network with other Cisco H.323 VoIP access gateways. In addition, the Cisco SS7 Interconnect for Voice Gateways Solution can interoperate with H.323 endpoints, using non-SS7 signaling such as ISDN PRI and channelized T1.

Figure 1-1 illustrates where the Cisco SS7 Interconnect for Voice Gateways Solution is located when it is dropped into a PSTN to offload calls. By placing the solution as close to the ingress switch as possible, voice and data traffic ties up fewer PSTN resources. The direct connection of the Cisco SS7 Interconnect for Voice Gateways Solution to the SS7 network provides advantages such as faster call setups and teardowns, and SS7's look-ahead capabilities for rerouting to avoid downed network nodes and links.

Cisco Signaling Controller Product Information

The Cisco signaling controller (Cisco SC2200) product is an application supported by the Cisco media gateway controller (Cisco MGC) product line that addresses the scalability of ISP dial modem traffic. The Cisco MGC is a powerful call control application that can be used to facilitate a wide variety of telecommunication services using data infrastructures. This new world architecture allows end users to realize the benefits of deploying a single network to address both data and voice applications.

Note

Your Cisco SS7 Interconnect for Voice Gateways Solution documentation suite includes the Cisco MGC reference books.

Note

Some product labels and packaging might use the term Cisco telephony controller. Any references to the Cisco telephony controller apply to the Cisco media gateway controller.

Understanding Terminology

The key terms used to describe the Cisco SS7 Interconnect for Voice Gateways Solution architecture are:

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Cisco SC2200—A hardware and software package that provides the signaling controller function. Typically this includes two SC hosts configured in a redundant manner for increased availability.

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SC node—The combination of hardware (Sun servers and Cisco SLTs) and software that provides the signaling controller function and transports the signaling traffic between the SC hosts and the SS7 signaling network.

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SC zone—The combination of an SC node and the Cisco access gateways that are provided with signaling services.

Architecture

The Cisco SS7 Interconnect for Voice Gateways Solution architecture provides SS7 connectivity for voice gateways, by way of the SC host as a protocol translator, using ISDN Q.931 and SS7 as control protocols.

Table 1-1 Components for the Cisco SS7 Interconnect for Voice Gateways Solution
Component	Description
Cisco Signaling Controller Host	Cisco SC2200—operates as an SS7-to-ISDN protocol converter for the Cisco access gateways.
Cisco Signaling Link Terminal	Cisco SLT—used for physical SS7 link termination. •SLT 2611 •SLT 2651
Cisco Media Gateway	Used for bearer channel termination. •Cisco AS5300 •Cisco AS5350 •Cisco AS5400 •Cisco AS5800 •Cisco AS5850
Gatekeeper	Cisco 3640—manages other nodes in a VoIP network. (Optional.) Note This solution uses the Cisco 3640 gatekeeper, but supports any H.323 compliant gatekeeper used in your IP network.
LAN Switch	Cisco Catalyst Switch Family—a switch to extend Virtual Local Area Networks (VLANs) across platforms through backbone Fast Ethernet, Gigabit, or ATM connections. Connects multiple Cisco SLTs to the active and standby hosts within the SC node. Connects the media gateways with their controlling SC node. Connects the originating SC zone to the terminating SC node between SC zones. Note The switch is a customer premise equipment and is not provided with the Cisco signaling controller.
Cisco Media Gateway Controller Node Manager (CMNM)	Integrates the management interfaces and functionality of the Cisco MGC node components into a comprehensive human interface and data repository. (Optional.)
Cisco Voice Services Provisioning Tool (VSPT)	Provides a graphical user interface for the creation, modification, and execution of signaling connections, trunk groups, trunks, routes, and dial plans. (Optional.)
Cisco Internetwork Performance Monitor	Enables you to troubleshoot network-wide performance to diagnose congestion and latency problems. For more information, refer to the following URL: http://www.cisco.com/warp/public/cc/pd/wr2k/nemo/index.shtml
Cisco Resource Manager Essentials	A suite of Web-based applications offering network management solutions for Cisco switches, access servers, and routers. For more information, refer to the following URL: http://www.cisco.com/warp/public/cc/pd/wr2k/rsmn/index.shtml

Benefits

Using the Cisco SS7 Interconnect for Voice Gateways Solution provides the following benefits:

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Provides wholesale dial services, dial-up Virtual Private Networks (VPNs), Internet access, and voice services, while interconnecting as a carrier.

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Addresses voice network congestion by using the SS7 interfaces to make features such as rerouting on overflow conditions and the use of IN functions possible, which further drives down operating costs.

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Integrates the access gateways directly into the SS7 network, using the Cisco SS7 Interconnect for Voice Gateways Solution, and thus remove the need for two switch ports on the PSTN circuit switch for each NAS port installed.

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Increases the signaling channel to bearer channel ratios, thus decreasing the number of signaling channels needed and the overall complexity of the system or network.

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Provides economical reliability of SS7 link termination by using channelized T1/E1/T3 software on the Cisco SLT.

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Transparently passes individual and uncompressed T1/E1/T3 channels between T1/E1/T3 ports using Drop and Insert interfaces.

Features

Table 1-2 briefly lists features that are provided with your Cisco SS7 Interconnect for Voice Gateways Solution. For an overview of scalability and performance, system redundancy, management, and software requirements, see subsequent sections of this document.

Table 1-2 Features for the Cisco SS7 Interconnect for Voice Gateways Solution
Feature	Purpose
Directly connects access gateways to PSTN in a peer-to-peer interconnect	•Reduces network costs •Interconnects with more favorable tariffs and rates
Supports Cisco H.323 access gateways and gatekeepers	Provides SS7 connectivity for intelligent H.323 endpoints: •Offers long-distance and international low-rate telephony services •Uses packet telephony technology for cost-effective offloading of voice traffic from congested PSTN networks
Supports co-located and distributed access gateways	•Cost savings; scalable and flexible
Terminates and originates switching-system functions	•Enables new services •Fast time to market •Dial-out and dial-in •Meets interconnect requirements
Worldwide protocol support using Cisco Message Definition Language (MDL).	•Is certified worldwide •Fast time to market
Provides software upgrade of: •Cisco IOS •Signaling controller and Sun OS software •Cisco Signaling Link Terminal	•Protects Cisco investments •Provides low cost of ownership •Is part of a complete solution with Cisco IOS software
Provides a reliable IP link between signaling controllers and access gateways with Redundant Link Manager (RLM)	No single point of failure in connection between access gateways and signaling controllers
•RADIUS or TACACS+ AAA functions, including authentication based on calling or called number •Provides call detail records for PSTN billing •RADIUS Proxy (GRS)	Meet PSTN requirements to create new service opportunities
Provides facility associated signaling through the Cisco SLTs	•Grooms the bearer channels and then delivers, or hairpins, them to the access gateway •Backhauls MTP-3 to the Cisco SC2200 over Reliable User Data Protocol/Internet Protocol (RUDP/IP)
Fault-tolerant platform	•Provides no more than 6 seconds of downtime per year
Continuous service platform	•Established calls are maintained upon failover
Sun OS 2.6.1	•Y2K compliant •Open computing platform
Cisco MGC Manager (CMM)	•Full SNMP configuration

Scalability and Performance

The Cisco SS7 Interconnect for Voice Gateways Solution includes the following scalability and performance features:

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Ability to process 80 calls per second with 100,000 simultaneous calls of 20 minute call hold time

System Redundancy

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Deploying the Cisco SS7 Interconnect for Voice Gateways Solution continuous service configuration at your site. The continuous service configuration consists of an active server and a standby server, linked by a heartbeat function. All configuration changes made to the active server are replicated on the standby server.

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Using a minimum of two LAN switches from the Cisco Catalyst switch family that support:

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Inter-Switch Link (ISL) trunking protocol configured between the two switches.

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One route-switch module (RSM), which routes traffic between the VLANs when necessary.

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Using a minimum of two links per linkset if signaling links are connected to the Cisco signaling controllers. The links should be split across separate T1/E1 interface cards on the LAN switches, SC hosts, and Cisco SLTs.

Signaling Controller Management

Table 1-3 provides an overview of the management components of the signaling controller.

Table 1-3 Management Components of the Signaling Controller
Management Component	Description
Configuration Management	Dial Provisioning Plan (DPP) is used to format the dial plan and routing data for deployment on the signaling controller. Dial plan and routing data is defined in a flat file, and this information is parsed by the DPP to generate the configuration files for deployment on the signaling controller.
Fault Management	The signaling controller supports a comprehensive set of alarms: •Configuration •Resource •Operating system •I/O card •Signaling channel failure •Line interface loss of signal You can customize the severity of alarm and thresholds to match your carrier's severity level definitions. You can also configure the system to generate real-time alarms to local or remote terminals. All alarms are written to a log file in an uncompressed format for easy retrieval.
Performance Management	You can get a variety of usage statistics from the signaling controller. The data is recorded real-time and is written to a file. You can specify the statistics to be collected and the time intervals for collection and writing to the file. Each performance measurement record includes: •Start time •Duration •Measured value •Category •Element measured
Accounting Management	Every call that passes through the signaling controller produces call detail information, which includes: •CLI pretranslated •CLI posttranslated •Dialed number pretranslated •Dialed number posttranslated •Start, seizure, supervision, and disconnect time stamps •Circuit path information Call detail records are written to a spool file that is automatically closed at defined intervals or when the file exceeds a specified size. You can also specify when to retrieve or send closed files to processing systems.

Access Gateway Management

The Cisco IOS software installed on the access gateways provides an array of network management components (described in Table 1-4) designed to meet the needs of today's large, complex networks.

Cisco's integrated management simplifies administrative procedures and shortens the time required to diagnose and fix geographically dispersed networks with a small, centrally located staff of experts. Configuration services reduce the cost of installing, upgrading, and reconfiguring network equipment.

Table 1-4 Network Management Components
Management Component	Description
SNMP and RMON Support	Access gateways are fully manageable by using the Simple Network Management Protocol (SNMP) and imbedded Remote Monitoring (RMON) capabilities: •SNMP provides for the collection of information about each controller and interface, which can be polled through any SNMP-compatible network management system. •RMON acts as a remote protocol analyzer and LAN probe. By using the Alarm RMON group, you can set a threshold on any integer-valued Management Information Base (MIB) variable. When the threshold is crossed, an event, defined in the Event RMON group, is triggered. With these capabilities, the system can detect and analyze overloaded conditions and congestion in real time.
Network Management Systems	The access gateways both support CLI and CiscoView graphical user interface (GUI) for comprehensive, flexible network management. CiscoView provides dynamic status, statistics, and comprehensive configuration information for Cisco switches, routers, access gateways, Cisco SLTs, concentrators, and adapters. It displays a graphical view of Cisco devices, provides configuring and monitoring functions, and offers basic troubleshooting.
Modem Management	Cisco offers two types of modems: basic and managed. Managed modems offer superior reporting and statistics in the CiscoView application, including troubleshooting and monitoring modem connections on individual or groups of modems, while calls are in progress. You can manage modems using the same tools used to manage the rest of the network. In addition, managed modems provide an out-of-band management feature that allows you to reduce problem detection and resolution time from a remote site. Through out-of-band management, you can view real-time information (for current or previous calls) such as modem modulation scheme, modem protocol, modem EIA/TIA-232 signal states, modem transmit and receive states, and analog signal-to-noise ratio.

Cisco Signaling Link Terminal Management

The Session Manager software, running on the Cisco SLT, manages the communication sessions between two SC hosts.

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Maintains separate communication sessions with each signaling controller in the pair

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In a continuous service configuration, handles additional traffic in the event of a single Cisco SLT failure, with no impact to call processing

Applications

The Cisco SS7 Interconnect for Voice Gateways Solution preserves full capabilities on the IP side, including existing H.323 access gateway functionality, interoperability with H.323 gatekeepers, two stage dialing, mixed gateway environment, and PSTN voice and fax traffic offload. This solution targets the following key applications that support phone to phone, PC to phone, and fax relay packet telephony services:

Settlement providers require services such as two-stage dialing, international toll bypass, and open settlements, as illustrated in Figure 1-3.

Two-Stage-Dial Toll Bypass

This application enables the service provider to leverage its WAN infrastructure and offer long-distance toll bypass services. Each customer is assigned an account number and a personal identification number (PIN). The user dials a local or a 1-800 Internet Telephony Service Provider (ITSP) number and is connected to the local VoIP point of presence.

In Figure 1-3, the first leg of the call is terminated by the access gateway through the ISUP to Q.931+/IP translation. The user is prompted by the interactive voice response (IVR) to input account and PIN numbers, and (following an authentication by the RADIUS server) then a secondary dial tone allows the desired phone number to be entered. Also, the RADIUS authentication can be accomplished based on the combination of calling number ID (ANI) and called number (DNIS).

For fax services, the PIN number is automatically dialed by the redialer that is attached to the fax machine. An E.164 destination phone number, dialed by the user, is mapped by the local-zone gatekeeper to an IP address of a remote-zone gatekeeper. The remote-zone gatekeeper selects an access gateway to terminate the call. During the call setup, end-to-end ISUP signaling transparency is supported. After the call setup is complete, the voice is encoded by the access gateway using standard algorithms (including G.711, G.729, G.729a, and G.723.1), encapsulated in Real-Time Transport Protocol (RTP) packets, and then routed over the WAN to the remote access gateway that decodes the voice and delivers it to the receiver.

PSTN Voice and Fax Traffic Offload

This application offloads PSTN traffic from congested PSTN networks. The offloaded traffic is then forwarded to a tandem switch connected in a peer-to-peer configuration to the Cisco SS7 Interconnect for Voice Gateways Solution through access gateways. The configuration uses Direct Inward Dialing (DID) functionality, and no ANI or CDR billing is required.

Packet Telephony and Data Wholesale Services

This application enables the wholesale service provider to extend services to a specific geographical area. Again, voice and fax traffic is offloaded from PSTN onto data networks, as well as support scalable routing and Quality of Service (QoS), across data networks, to effectively route the calls to their final destination. Routing and authorization between multiple service carriers, and real-time selection of a cost-effective service provider and reciprocal billing arrangements are required. Resource pooling is required for data, but not for voice.

The Open Settlement Protocol (OSP) is a communications protocol between H.323 equipment and back-end services, such as authorization, route determination, and call detail record (CDR) collection and settlement. With OSP, interdomain CDR records are forwarded to the settlement system, processed, and then transmitted as settled records to billing system platforms. The access gateways in your Cisco SS7 Interconnect for Voice Gateways Solution generate intradomain records and are accessed by any accounting and billing system based on RADIUS.

Table Of Contents

Introduction