Table of Contents

Introduction
Architecture
Interfaces

External Interfaces
Internal Interfaces

Understanding Terminology
Features
Scalability and Performance

Virtual Switch Controller Management
Cisco Signaling Link Terminal Management

Cisco SS7 PRI Gateway Solution Introduction

The Cisco SS7 PRI Gateway Solution consists of hardware and software to offload data traffic from the CLEC TDM switches and terminate ISDN-PRI interfaces and Inter-Machine Trunks (IMTs) under the control of an SS7 enabled call agent.

This chapter introduces the architecture, products, interfaces and features of the
Cisco SS7 PRI Gateway Solution in the following sections:

• Architecture

• Interfaces

• Understanding Terminology

• Features

• Scalability and Performance

Introduction

The explosive growth of Internet dialup traffic is causing congestion problems for the telecommunication service providers (carriers), both Incumbent Local Exchanges Carriers (ILECs) and the competitive local exchange carriers (CLECs). Traditional time-division multiplexing (TDM) networks, originally designed to carry circuit-switch voice only, need additional transport and switching capacity to relieve congestion and accommodate the additional dial load from Internet service providers (ISPs).

ISPs typically connect to the CLEC TDM switches (5ESS or DMS-100) using ISDN PRI lines. Problems occur when an incumbent local exchange carrier (ILEC), using the three or six leading digits (NPA or NPA-NXX) of a dialed number, routes calls to the CLEC's TDM switch. Because the ILEC does not use the final four digits of the dialed number (XXXX), the CLEC switch is unable to offload ISP dialup traffic from the TDM switch directly onto an SS7 enabled network access server (NAS).

As ISP PRI terminations grow, the CLEC switches become increasingly congested while handling the typically long dialup calls. The result is a degraded quality of service that forces the CLEC to move PRIs to other parts of the switch to balance the traffic load, or to buy additional switching capacity.

The Cisco SS7 PRI Gateway Solution solves this problem by placing a high-density, low-cost TDM switching fabric (gateway) between the ILEC and CLEC TDM switches on the interconnecting trunk group. The gateway terminates ISDN PRI interfaces and Inter-Machine Trunks (IMTs) under the control of an SS7 enabled call agent. Figure 1-1 shows an example of the Cisco SS7 PRI Gateway configuration.

Upon receiving a call from the ILEC, the Cisco SS7 PRI Gateway analyzes all ten of the dialed digits and determines whether or not the call should be routed to an ISP PRI provisioned off the gateway. When a call is destined for an ISP on the gateway, a connection is completed between the incoming IMT and the PRI to the ISP NAS. All other calls destined for the CLEC are routed to the CLEC circuit-switch by establishing a connection between the incoming and outgoing IMTs.

Note Some product labels and packaging might use the term telephony controller. Any references to the telephony controller apply to the Cisco Media Gateway Controller (MGC).

Architecture

The system consists of the required components shown in Table 1-1. Each is described in detail in the "Cisco SS7 PRI Gateway Solution Introduction" section in Chapter 2.

Table 1-1: SS7 PRI Gateway Components

Virtual Switch Controller (Cisco VSC3000)	The Cisco VSC3000 software runs on Sun carrier grade servers: Sun Netra t 112x series and Sun Netra t 140x series. The software provides SS7 and ISDN protocol support (and conversion) for various countries and variants, Media Gateway Controller Protocol (MGCP 0.1) call control, and ISDN backhaul.
Cisco MGX 8260 Media Gateway Release 1.1	Provides high-density TDM and ISDN ports to terminate DS-3 interfaces to the ILEC and CLEC switches as well as to the ISP Network Servers. Under direction of MGCP messages from Cisco VSC3000, performs TDM (IMT to IMT, or IMT to NAS) connection. Also performs ISDN/PRI layer 2 (Q.921) functions and backhauls Q.931 (using RUDP) messages to the VSC.
Cisco Signaling Link Terminal (Cisco SLT) Cisco IOS 12.0 (7) XR	Provides the physical interface to the SS7 network. Supports termination of SS7 links (MTP L1/L2) with T1/E1, or V.35 interfaces. Supports SS7 signaling backhauling at the MTP L2/L3 split (MTP L3, ISUP, SCCP, and TCAP) using RUDP to the VSC. Each Cisco SLT terminates two SS7 links. Links in a linkset can be configured across Cisco SLTs in order to provide reliability.
LAN Switch (Cisco Catalyst Switch Family)	Provides the LAN/WAN connectivity required for the IP Control Network across platforms through backbone Fast Ethernet, Gigabit, or ATM connections. Uses VLANs to segregate traffic for bandwidth load optimization. Two LAN switches provide redundancy.
Cisco MGC Node Manager (CMNM)	Provides element management for the virtual switch controller, the Cisco MGX 8260, and the Cisco SLTs.
Billing Mediation Facility	Provides the ability to format call detail records (CDRs) into the Bellcore Automatic Message Accounting Format (BAF) billing records.
Voice Service Provisioning Tool	Provisions the Cisco VSC3000 and the Cisco MGX 8260.

Figure 1-2 provides a graphical presentation of how the components interconnect.

Interfaces

The solution provides SS7 interfaces (signaling channels and bearer channels) and ISDN interfaces (D-channel for signaling and B-channels for voice or data). SS7 signaling interfaces can use DS1 or V.35 facilities. SS7 bearer channels and ISDN PRI are transported over DS1 or DS3 facilities.

The Cisco SS7 PRI Gateway Solution supports SS7 ISDN User Part (ISUP) to SS7 ISUP calls, and SS7 ISUP to ISDN PRI calls. The incoming call is analyzed on the VSC and routing is performed based on the ISUP initial address message (IAM). LNP trigger is also supported through an LNP query launched during B-number analysis of the NPA-NXX prefix, if it is identified as ported.

The SS7 PRI Gateway Solution external and internal interfaces are described in the sections that follow.

External Interfaces

The following interfaces are used to connect the system to external equipment:

• SS7 signaling links over T1/E1 or V.35---In a typical configuration, these connect to a mated pair of STPs. The T1/E1 or V.35 terminates on a Cisco SLT that terminates SS7 MTP Level 1 and MTP Level 2. Higher levels are backhauled to the VSC host.

• SS7 bearer channels (DS0 circuits) over DS1 or DS3---These connect to a Class 4 or Class 5 switch. The DS3 terminates on a Cisco MGX 8260 (no DS1 interface; however, DS1 is transported in DS3) that extracts the DS0 circuits and cross-connects them as instructed by the VSC host.

• Primary ISDN interfaces over DS1 and DS3---The Cisco MGX 8260 supports the multiplexing of 28 ISDN PRI DS1 into a DS3. In a typical ISDN PRI DS1, B-channels 1 through 23 are for voice or data circuits, and D-channel 24 provides ISDN signaling.

• SNMP MIBs are available on every component for external management systems and to provide traps for alarms.

• Cisco VSC3000 to Billing and Measurement (BAM) interface--- This interface uses the File Transfer Protocol (FTP) to transfer call detail records (CDR) from the Cisco VSC3000 to the BAM. The BAM system retrieves and formats these records into industry standard formatted billing records and metrics for transfer to upstream (external) mediation and billing platforms.

Internal Interfaces

The SS7 PRI Gateway Solution is a distributed solution that connects the components over an IP cloud with the following Ethernet and Fast Ethernet interfaces:

• SS7 backhaul signaling between VSC host and Cisco SLT

• Between the active and standby MGC for failover, checkpointing, and configuration synchronization

• MGCP messages between VSC host and Cisco MGX 8260

• ISDN PRI backhaul signaling between VSC host and Cisco MGX 8260

• SNMP interface between the network management platform and the following:

  • VSC host

  • Cisco SLT

  • Catalyst 5500 LAN switch

  • Cisco MGX 8260

• Web interface between Cisco MGX 8260 and web browser running on the network management platform.

• Cisco VSC3000 to BAM interface---To support transfer of call detail files from the Cisco VSC3000 to the BAM data server, and the corresponding handshake protocol to verify status of the file transfer operations.

• MGCP interface between the VSC and Cisco MGX 8260

Understanding Terminology

The key terms used to describe the Cisco SS7 PRI Gateway Solution architecture are:

• Cisco VSC3000---A hardware and software package that provides the virtual switch controller function. Typically this includes two VSC hosts configured in a redundant manner for increased availability.

• VSC host---A Sun host running Solaris and virtual switch controller software.

• VSC host node---A combination of hardware (Sun workstations and Cisco SLTs) and software that provides the virtual switch controller function and transports the signaling traffic between the VSC hosts and the SS7 signaling network.

• VSC host zone---The combination of a VSC host node and the Cisco MGX 8260 gateways that provide signaling services.

• Virtual switch---The combined function of all the virtual switch zones that share the same virtual switch controller.

Features

The features of the Cisco SS7 PRI Gateway Solution are listed below.

• 100 calls per second (CPS) POTS without AIN query (raw CPU call setup capability)

• 100,000 simultaneous active calls

• Cisco MGX 8260 single chassis control (phase 1)

• 500 PRIs per Cisco MGX 8260 chassis (phase 1)

• Media Control Gateway Protocol (MGCP)--- MGCP 0.1 November 9, 1998

• PRI Signaling Backhaul---ISDN PRI at the Q.921/Q.931 split

• SS7 Signaling Backhaul---SS7 ISUP at the MTP L2/L3 split

• Non-Facility Associated Signaling (NFAS) with 16 T1 spans per NFAS group (D-channel backup is not supported)

• Advanced Intelligent Network (AIN) Services

  • Info-Analyzed and Analyze-Route query/response message support to handle Local Number Portability (ANSI)

• TCAP Enhancements

  • SCP Selection

  • Signaling interface for LNP as specified in the Telcordia and ANSI generic requirements for switching and SCP application

• Enhanced COT support

  • Origination (same tone and different tone) and termination (loopback and dual tone)

  • Manual Continuity Check Request (CCR)

• Enhanced call detail record (CDR) support

• Mirrored disks

  • Enhanced fault tolerance

  • Geographically separate active and standby VSC computing elements

  • Controlled active to standby switchover

• Enhanced call processing

  • Support for the North American Numbering Plan (NANP)

  • Digit Analysis

  • Digit Manipulation---Capability at the node level at any point in the digit tree, to configure the dial plan to move the current pointer to the right or left and resume analysis from that point

  • Pre-Analysis---Provides routing and digit insertion/deletion capabilities prior to the actual analysis of the called party number

  • Calling Party Analysis---Analyzes the Calling Party Number after NOA analysis is completed but before Called Party Number analysis begins

  • Called Party Number Analysis---provides capabilities that support called party digit analysis

  • Screening Capabilities---Supports a rich set of capabilities to provide screening functionality

• Circuit Advance---Flexible circuit selection capability

Scalability and Performance

The Cisco SS7 PRI Gateway Solution is scalable and cost-effective:

• Scales up to 24,000 DS0 ports

• 100 calls per second (CPS) throughput

• 100,000 simultaneous calls

• Support for 200+ destination point codes (DPCs)

• Support for 6 origination point codes (OPCs)

• Quasi-associated or fully-associated signaling

• Complete continuity check (two-wire and four-wire)

• NEBS Level 3 compliant

• MGC platform options

  • Sun Netra t 112x

  • Sun Netra t 140x

For maximum reliability and resilience, we recommend:

• Deploying the Cisco SS7 PRI Gateway Solution in a continuous service configuration at your site. The continuous-service configuration consists of an active server and a standby server, linked through a heartbeat function. 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 supports:

  • ISL trunking protocol configured between the two switches

  • One Route Switch Module (RSM), which routes traffic between the VLANs when necessary

• Using 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 both the LAN switches, VSC hosts, and Cisco SLTs.

Virtual Switch Controller Management

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

Table 1-2: Virtual Switch Controller Management Components

Management Component	Description
Dial Provisioning Plan (DPP)	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.
VSM	Supports configuration of the VSC host and voice-related configurations of the Cisco MGX 8260.
Interim Provisioning Tool	This is a graphical user interface tool for configuring, and provisioning the Cisco VSC3000 host and the Cisco MGX 8260. This tool will be able to accept an MML batch file from a current configuration to allow editing or cloning of the configuration for deployment on another Cisco VSC3000 host.
Alarms	The MGC 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 Measurement	You can get a variety of usage statistics from the signaling controller. The data is recorded real time and written to a file. You can specify the statistics to be collected and the time intervals for collection and writing to file. Each performance measurement record includes: Start time Duration Measured value Category Element measured
Accounting	Every call that passes through the Cisco MGC produces call detail information that 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.

Cisco Signaling Link Terminal Management

The Cisco SLT architecture provides for a separation of the signal terminal function from the Cisco MGC call-processing function. The Cisco SLT provides MTP Level 1 and MTP Level 2 interconnect to the STPs, as well as MTP level 3, ISUP, and SCCP backhaul over Cisco Reliable UDP to the Cisco  MGC.

For information about Cisco SLT management, refer to Cisco Media Gateway Controller Software Release 7 Installation and Configuration Guide.

Posted: Thu Jun 15 09:56:40 PDT 2000
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