Cisco SS7 Interconnect for Voice Gateways Solution Introduction

When you make calls using your telephone or PC terminal and modem, 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 conversation. 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 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, as well as 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 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 media gateway controller (MGC) reference books.

Note

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

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.


Cisco Signaling Controller Host (Cisco SC2200)	Operates as an SS7 to ISDN protocol converter front-end to the Cisco access gateways.
Cisco Signaling Link Terminal (Cisco SLT)	Used for physical SS7 link termination.
Cisco Access Gateway (Cisco AS5300)	Used for bearer channel termination.
Gatekeeper (Cisco 3640)	Manages other nodes in an H.323 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 VLANs across platforms through backbone Fast Ethernet, Gigabit, or ATM connections, when necessary. Connects multiple Cisco SLTs to the active and standby hosts within the SC node. Connects the Network Access Servers with their controlling SC node. Connects the originating SC zone to the terminating SC nodebetween SC zones. Note The switch is customer premise equipment and is not provided with the Cisco signaling 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.

Benefits

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

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Provides wholesale dial services, dial-up 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 E1/T1 software on the Cisco SLT.

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Transparently passes individual and uncompressed T1 or E1 channels between T1 or E1 ports by using Drop and Insert interfaces.

Features

Table 1-1 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 1-1 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 signaling controller over 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 Table 1-2 lists the scalability and performance of the Cisco SS7 Interconnect for Voice Gateways Solution.

Table 1-2 Scalability and Performance of the Cisco SS7 Interconnect for Voice Gateways Solution
Feature	Benefit
•Scaling up to 50,000 DS-0 ports •As many as 50 calls per second throughput •180,000 busy hour call attempts	•Scale cost-effectively to central-office size
•Support for 250+ destination point codes (DPCs) •Support for 6 originating point codes (OPCs) •Quasi-associated or fully associated signaling •Complete continuity check (two-wire and four-wire) •NEBS Level 3 compliant •Three signaling controller platform options	•Flexible and scalable •Ready for international markets •Meets interconnect requirements •Telco ready •Cost-effective options

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. Also, 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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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	The Cisco MGC Manager (CMM) is a graphical user interface (GUI) that uses SNMP to configure and provision your solution network. You can access the CCM remotely, using Xterminals, and manage all the TCHOSTs in your network with a single CMM system. 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

Cisco SS7 Interconnect for Voice Gateways Solution 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 (Cisco 5300) 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 QoS, across data networks, to effectively route the calls to their final destination. Routing and authorization between multiple service carriers, as well as 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.

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