Cisco VPOP-DAP Solution Introduction

Overview

Cisco Signaling Controller Product Information

Architecture

Understanding Terminology

Benefits

Features

Scalability and Performance

System Redundancy

Signaling Controller Management

Network Access Server Management

Cisco Signaling Link Terminal Management

Cisco VPOP-DAP Solution Introduction

Overview

The Cisco Virtual Point-of-Presence Dial Access Platform (VPOP-DAP) Solution is a distributed system used for interconnecting Cisco network access servers (NASs) to a circuit-switched TDM network using Signaling System #7 (SS7) protocols for signaling. The interconnections are achieved using a protocol conversion platform called the Cisco Signaling Controller combined with the Cisco Signaling Link Terminal. The Cisco SC2200 comprises the hardware and software package that provides the signaling controller function in the Cisco VPOP-DAP Solution. It provides high availability, high performance, and key scaling.

When large points of presence (POPs) receive calls from the Public Switched Telephone Network (PSTN), the traffic is running over legacy architectures that use in-band signaling (such as Integrated Services Digital Network Primary Rate Interfaces (ISDN PRIs), in-band channel-associated signaling (CAS), or single analog lines) rather than out-of-band signaling like SS7. With both signaling and bearer traffic running over the lines, these legacy switches become congested with modem traffic and limited circuits. Cisco offers the Cisco VPOP-DAP Solution that offloads the signaling to an out-of-band network so that available bandwidth increases.

The Cisco VPOP-DAP Solution is a distributed system that adds SS7 signaling interfaces to large ISP POPs. SS7 interfaces are connected to the PSTN by using the same signaling technology as a PSTN switch. The Cisco VPOP-DAP Solution consists of the Cisco signaling controller (also referred to as the Cisco SC2200 product), which includes the Cisco Signaling Link Terminal (Cisco SLT) and the network access server (NAS). The Cisco VPOP-DAP Solution turns a POP into an end-office switching system in the PSTN, allowing direct peer-to-peer signaling connectivity. The POP, as a switch, connects directly to the rest of the network as a peer. After connections to the Internet are aggregated at a POP, streams of user packets are statistically multiplexed for efficient transport over the backbone network.

Figure 1-1 illustrates the PSTN-to-POP network without a Cisco VPOP-DAP Solution. Because of Internet and additional data calls with hold times that average 30 minutes, the PSTN network experiences more busy signals and overloads network resources.

Figure 1-1: Without the Cisco VPOP-DAP Solution

Figure 1-2 illustrates where the Cisco VPOP-DAP Solution is located when it is dropped into a PSTN, so as to offload calls. Note that the NAS are connected with a Cisco SS2200. By placing the Cisco VPOP-DAP Solution as close to the ingress switch as possible, data traffic ties up fewer PSTN resources. The direct connection of the Cisco VPOP-DAP 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.

Figure 1-2: With the Cisco VPOP-DAP Solution

Cisco Signaling Controller Product Information

The Cisco SC2200 product is a signaling controller (SC) that converts telephony signals from one format to another. For example, the Cisco SC2200 converts Signaling System 7 (SS7) signaling information from the PSTN to the signaling format required to establish calls between the PSTN and a packet data network.

The Cisco SC2200 product is part of the Cisco Media Gateway Controller (MGC) product line. The Cisco MGC product line consists of hardware and software packages that you can use to connect your packet data network to the Public Switched Telephone Network (PSTN). Cisco MGC products manage call signaling conversion between the PSTN and the packet data network, and depending on the product, Cisco MGC products can control the routing of calls across the PSTN or packet data network .

Note Your Cisco VPOP-DAP Solution documentation suite includes Cisco 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 VPOP-DAP Solution architecture, shown in Figure 1-3, provides SS7 signaling connectivity for network access servers (NASs) to operate in an environment where SS7 is used to establish calls on bearer channels on T1/E1 trunks connected to the NAS.

The solution consists of the following required components that are described in more detail in the Cisco VPOP-DAP Solution Components section of this document:

 Cisco SignalingController Host (Cisco SC2200)

 At MTP3 and higher layers, operates as an SS7 to ISDN protocol converter front-end to the NASs.

 Cisco SignalingLinkTerminal (CiscoSLT)

 Used for physical SS7 link termination and MTP1 and MTP2 termination.

 Cisco NetworkAccessServer (Cisco AS5800)

 Used for data ISUP trunk termination.

 LAN Switch (Cisco Catalyst Switch Family)

 Provides infrastructure for the redundant and reliable Cisco SC2200 architecture. 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 node between SC zones.



Note   The switch is customer premises equipment and is not provided with the Cisco signaling controller.

Figure 1-3: Cisco SS7 DAS Architecture

Understanding Terminology

The following key terms are used in this document to describe the Cisco VPOP-DAP Solution architecture:

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 continuous service.
Cisco SC host—A Sun host running signaling controller software.
Cisco 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.
Cisco SC zone—The combination of an SC node and the Cisco network access servers that are provided with signaling services.

Benefits

Using the Cisco VPOP-DAP Solution provides the following benefits:

Provides wholesale dial services, dialup VPNs, Internet access, and voice services, while interconnecting as a carrier.
Addresses voice network congestion by using the SS7 interfaces to make features such as rerouting on overflow conditions and the use of Intelligent Network (IN) functions possible, which further drives down operating costs.
Replaces ISDN PRIs with bearer trunks and separate the signaling to increase bandwidth.
Installs an SS7 POP in a new location without the added expense of a switch.
Integrates the NASs directly into the SS7 network, using the Cisco VPOP-DAP Solution and thus remove the need for two switch ports on the PSTN circuit switch for each NAS port installed.
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.
Provides economical reliability of SS7 link termination by using channelized E1/T1 software on the Cisco SLT.
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 VPOP-DAP 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 VPOP-DAP Solution

Feature	Purpose
Directly connects access servers to PSTN in a peer-to-peer interconnect	Reduces network costs. Interconnects with more favorable tariffs and rates.
Intelligent Network (IN) triggers	TCAP over IP. TCAP local number portability (LNP) support. 800/900 number translation.
Provides a reliable IP link between signaling controllers and NASs with Redundant Link Manager (RLM)	No single point of failure in connection between NAS and signaling controller.
Dial outsourcing	Signaling controller and NAS can be provisioned by telephone service providers and local exchange carriers. Calls can be directed to NASs belonging to various ISPs.
Facility-associated signaling provided by the Cisco Signaling Link Terminals (Cisco SLTs)	Grooms off the bearer channels and then delivers them to the NAS. Delivers MTP-3 to the signaling controller over RUDP.
Resource management	Shares modems across POPs among various wholesale customers. Single point of management.
Introduces services such as wholesale dial, Virtual Private Dial-up Networks (VPDNs), and virtual modem pooling	Realizes new revenues. Reduces PSTN congestion.
Supports co-located and distributed access servers	Cost savings; scalable and flexible.
Supports Cisco AS5800	Investment in Cisco equipment protected.
Terminates and originates switching-system functions	Enables new services. Fast time to market. Dial-out and dial-in. Meets interconnect requirements.
Provides software upgrade of: Cisco IOS MICA Portware Signaling controller and Sun OS software on signaling controller Cisco Signaling Link Terminals	Protects investments. Provides low-cost ownership. Is part of a complete solution with Cisco IOS software.
VPDN with L2F and L2TP Dial-out for callback and dial-on demand routing (DDR) Current remote access servers data features	New revenue opportunities. Complete services. Investment protection.
Radius or TACACS+ AAA functions, including authentication based on calling or called number Call detail records for PSTN billing Radius Proxy (GRS)	Meet PSTN requirements to create new service opportunities.
Call Tracker support	Captures data for active and historical call sessions, allowing external applications to access the data via SNMP, CLI, or SYSLOG
Exec-VPDN support	Enables IP traffic to travel securely over a public TCP/IP network by encrypting all traffic from one network to another.
Attribute 8 support	Allows a network access server (NAS) to provide the RADIUS server with a hint of the user IP address in advance of user authentication
RPMS support	Enables telephone companies and Internet service providers (ISPs) to share dial resources for wholesale and retail dial network services

Scalability and Performance

The Table 1-2 lists the scalability and performance of the Cisco VPOP-DAP Solution

Table 1-2: Scalability and Performance of the Cisco VPOP-DAP Solution

Feature	Benefit
Scaling up to 50,000 DS-0 ports Up to 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 Thirty-two signaling links	Flexible and scalable Ready for international markets Meets interconnect requirements Telco ready Cost-effective options

System Redundancy

For maximum reliability and resilience, we recommend the following options:

Deploying the Cisco VPOP-DAP 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.
Using a minimum of two LAN switches from the Cisco Catalyst switch family that support
- ISL trunking protocol configured between the two switches.
- One Route-Switch Module (RSM), which routes traffic between the VLANs when necessary.
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 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 Cisco SC2200. You can access the CMM remotely, using Xterminals, and manage all the signaling controllers 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.
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. The signaling controller is SNMP capable, and MIBs are available.
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. The signalling controller is SNMP capable, and MIBs are available. Each performance measurement record includes: Start time Duration (START-STOP) Measured value Category Element measured
Accounting Management	Every call that passes through the signaling controller produces call detail records (CDRs), which include: 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.

Network Access Server Management

The Cisco IOS software installed on the NASs provides an array of network management components (described in Table 1-4). These management features do the following:

Reduce network bandwidth and processing overhead
Offload management servers
Conserve resources
Ease system configuration tasks

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	NASs 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 server, 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 NASs both support CLI and the CiscoView graphical user interface (GUI) for comprehensive, flexible network management. CiscoView provides dynamic status, statistics, and comprehensive configuration information for Cisco switches, routers, NASs, Cisco SLTs, concentrators, and adapters. It displays a graphical view of Cisco devices, provides configuring and monitoring functions, and offers basic troubleshooting.
RPMS Support	Cisco Resource Pool Manager Server (Cisco RPMS) enables telephone companies and Internet service providers (ISPs) to count, control, manage, and provides accounting data for shared resources for wholesale Virtual Private Dial-up Network (VPDN) and retail dial network services across one or more network access server (NAS) stacks. Cisco RPMS offers a web browser-based configuration utility that enables you to: Manage customers' use of shared resources such as modems or HDLC controllers for data calls. Offer advanced wholesale dial up services using VPDN to enterprise accounts and ISPs. Efficiently use resource groups such as modems to offer differing over-subscription rates and dial service level agreements. Maintain the flexibility to include local retail dial services in the same NAS stack with the wholesale dial customers. Deploy Data over Voice Bearer Service (DOVBS). Accept or reject a call based on the incoming DNIS prior to answering the call. View reports. Collect accounting data. Set threshold notifications. Configure backup Cisco RPMS servers for fault tolerance and resiliency.
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 the SLT and the SC host.

The session manager:

Maintains separate communication sessions with each signaling controller in the pair
Uses RUDP to communicate between the Cisco SLT and the signaling controller
In a continuous service configuration, handles additional traffic in the event of a single Cisco SLT failure, with no impact to call processing

Table of Contents

Cisco VPOP-DAP Solution Introduction