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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 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 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.
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.
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Note Your Cisco SS7 Interconnect for Voice Gateways Solution documentation suite includes the Cisco MGC reference books. |
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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. |
The key terms used to describe the Cisco SS7 Interconnect for Voice Gateways Solution architecture are:
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.
The solution consists of the following required components that are described in more detail in the "Cisco SS7 Interconnect for Voice Gateways Solution Components" section of this document.
Component
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Using the Cisco SS7 Interconnect for Voice Gateways Solution provides the following benefits:
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.
| Feature | Purpose |
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Directly connects access gateways to PSTN in a peer-to-peer interconnect |
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Supports Cisco H.323 access gateways and gatekeepers | Provides SS7 connectivity for intelligent H.323 endpoints:
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Supports co-located and distributed access gateways |
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Terminates and originates switching-system functions |
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Worldwide protocol support using Cisco Message Definition Language (MDL). |
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Provides software upgrade of:
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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 |
| Meet PSTN requirements to create new service opportunities |
Provides facility associated signaling through the Cisco SLTs |
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Fault-tolerant platform |
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Continuous service platform |
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Sun OS 2.6.1 |
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Cisco MGC Manager (CMM) |
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The Cisco SS7 Interconnect for Voice Gateways Solution. includes the following scalability and performance features:
For maximum reliability and resilience, Cisco recommend the following options:
Table 1-3 provides an overview of the management components of the signaling controller.
| Management Component | Description |
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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:
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:
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Accounting Management | Every call that passes through the signaling controller produces call detail information, which includes:
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. |
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.
These management features do the following:
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.
| Management Component | Description |
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SNMP and RMON Support | Access gateways are fully manageable by using the Simple Network Management Protocol (SNMP) and imbedded Remote Monitoring (RMON) capabilities:
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. |
The Session Manager software, running on the Cisco SLT, manages the communication sessions between two SC hosts.
The session manager:
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.
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 AS5300) 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.
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.
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.
Posted: Wed Sep 6 08:21:39 PDT 2000
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