Cisco SS7 Interconnect for Access Servers Configuration Options and Components

This chapter briefly describes the various Cisco SS7 Interconnect for Access Servers Solution configuration options and the required and optional components:

Cisco SS7 Interconnect for Access Servers Solution Configurations

The Cisco SS7 Interconnect for Access Servers Solution provides the following configuration options:

Simplex and Redundancy Options

You can deploy the Cisco SS7 Interconnect for Access Servers Solution in one of three ways:

Simplex Configuration

A simplex configuration is an SC node that consists of a single SC host (Sun Netra t 112x) operating with one or more Cisco SLTs. The SC application is run on the SC host and the SS7 signaling links are terminated on the Cisco SLT. An IP control LAN is used to interconnect the host server with the Cisco SLTs. One or more network access servers provide for bearer channel termination. See Figure 2-1.

Note Simplex configurations provide no fault tolerance and are typically used for solution testing or validation or noncritical installations. If the host fails, calls are dropped, and service is discontinued.

Figure 2-1: Simplex Configuration Example

Fault-Tolerant Configuration

A fault-tolerant configuration is similar to a simplex configuration; however, the SC host must be a Sun Netra t 1400 server platform providing redundant components. If any redundant component fails, the backup component takes over; established calls are maintained.

Continuous-Service Configuration

A continuous-service configuration is an Cisco SC zone that consists of a pair of Cisco SC hosts running in active mode and standby mode, operating with one or more network access servers and two or more Cisco SLTs. An error-checking function runs continuously between the two Cisco SC hosts monitoring the primary Cisco SC host. When the function detects an error condition on the primary Cisco SC host, responsibility for call processing is switched to the secondary Cisco SC host. The secondary Cisco SC host now becomes the primary Cisco SC host, and call preservation is maintained.

Figure 2-2 shows an example of a continuous-service configuration with redundant signaling links terminating on a pair of Cisco SLTs with bearer traffic terminating on the NAS.

Figure 2-2: Continuous-Service Configuration Example

Signaling Network Connections

The Cisco SS7 Interconnect for Access Servers Solution performs functions to exchange telephone control messages between the following components that support the end user's signaling network connection:

Cisco Signaling Controller—Provides a signaling protocol conversion and network Q.931 call control to communicate with the NASs. One signaling controller might provide signaling and call-processing services for multiple NASs in geographically distributed locations.

Cisco SLT—Handles the incoming and outgoing SS7 messages (MTP layer 1 and 2) from the A-links connected to Signal Transfer Points (STPs) or F-links connected to other service switching points (SSPs). Also, when used in Drop and Insert mode, the Cisco SLT grooms off the terminating signaling link from F-links (fully associated links) and then sends the bearer channels to the NAS.

Cisco Network Access Server—Provides termination for bearer trunks. A NAS functions as a server to the bearer links. The NAS has at least two IP network interfaces: one to carry IP packet data onto one or more of the ISP's backbones and another to connect to the ISP's secure management, signaling, and Q.931 control network.

Your Cisco SS7 Interconnect for Access Servers Solution can be deployed in three ways, as described in the "Simplex and Redundancy Options" section with the following SS7 signaling network connections.

Note Type of connection would depend on your specific network requirements.

A-Link with Cisco SLT

In the A-link SLT signaling configuration, the Cisco SLT processes the two lowest-layer SS7 signaling protocols, MTP1 and MTP2. The upper layer protocols are then forwarded to the Cisco MGC host over the control signaling network. Each SLT supports two signaling network connections, and multiple SLTs can be used to support additional signaling channels or provide redundant signal paths between the signaling network and the control signaling network.

The A-link SLT signaling configuration supports V.35, T1, and E1 interfaces using signaling interfaces installed in the Cisco SLT. The A-link SLT configuration can be used with simplex and continuous-service configurations. Each interface supports a single DS0 signaling channel, as illustrated in Figure 2-3.

Figure 2-3: A-Link SLT Signaling Configuration

F-Link with Cisco SLT

F-link SLT signaling configurations are similar to A-link SLT configurations. The SS7 network connection is made through fully associated links that connect an SSP or SCP to the Cisco SLT.

The F-link SLT signaling configuration supports V.35, T1, and E1 interfaces using signaling interfaces installed in the Cisco SLT. The F-link SLT configuration can be used with simplex and continuous-service host configurations. Each interface supports a single DS0 signaling channel.

A-Link or F-Link with Cisco SLT (Drop and Insert)

An A-link or F-link with Cisco SLT (Drop and Insert) signaling connection is similar, respectively, to an A-Link or F-link SLT signaling connection. Fully associated links directly connect an SSP or SCP to the Cisco SLT. The difference is that A-link and F-link Drop and Insert configurations support a single DS0 signaling channel per link and additional bearer traffic channels up to the capacity of the T1 or E1 link, as shown in Figure 2-4.

Note The A-Link and F-link Drop and Insert techniques are also known as time-division multiplexing (TDM) cross-connect.

Figure 2-4: F-Link Drop and Insert Configuration

The F-link drop and insert signaling configuration supports T1 and E1 interfaces using signaling interface cards installed in the Cisco SLT. The Drop and Insert cards are special two-port cards designed for this application. Signal and bearer traffic enter one port together, the Cisco SLT grooms the bearer traffic and then routes it out the second port.

The F-link Drop and Insert configuration can be used with simplex and continuous-service host configurations. Each interface card supports a single DS0 signaling channel.

Control Signaling Network Options

Designing your network to handle control signaling is a complex and sophisticated task beyond the scope of this document. This section briefly describes what control signaling network options are available and some network engineering guidelines to consider.

Customer-Provided Equipment

Your control network consists of a number of hubs, switches, or routers configured together to support the number of ports in your point of presence (POP), the traffic characteristics of incoming calls, the geographic location of the Cisco SS7 Interconnect for Access Servers Solution components and the level of redundancy that you require. Other factors to consider are:

Design of the network (topology and hardware components)
Security (physical, packet encryption, packet filtering)
Quality of service (delay, bandwidth, throughput, queuing techniques)
Traffic segregation (access lists and route filters)
Configuration of the components (Redundant Link Manager (RLM) with the required SC host and NAS, Cisco SLT redundancy, and timers)

Control traffic (signaling) should be segregated from the bearer traffic on the QoS packet network (towards the Internet/intranet). This optimizes control traffic latency and provides added security. Redundancy in your control network can be provided by duplicating your Cisco SS7 Interconnect for Access Servers Solution components. In the event that the control network fails or connectivity to it fails, the QoS packet network is used for signaling.

In the simplest case, your Cisco SS7 Interconnect for Access Servers Solution components are co-located, and a pair of LAN switches serves as your control network. Cisco Systems recommends that the Cisco SLT not be deployed in remote configurations from the Cisco SC2200. The remote configurations include, but are not limited to, remote configurations based on dedicated ATM connections or other similar dedicated facilities. Installing the Cisco SLT remotely from the Cisco SC2200 compromises the SS7 link stability and can eventually cause the SS7 link to fail during high traffic.

IP Connectivity with LAN

Figure 2-2 shows a sample continuous-service configuration with a mated Cisco SLT pair (for redundancy) on the control signaling network. Redundant signaling controllers support two or four Fast Ethernet connections each.

In this continuous-service configuration example, the control signaling network functions are:

Checkpointing traffic (RUDP/UDP/IP)
Heartbeat (UDP; 50 bytes/sec)
SNMP management of components
Cisco SC/Cisco NAS signaling and communications (Q.931+/Q921/UDP/IP-RLM)
Cisco SC/Cisco SLT signaling and communications (MTP-3+ISUP/SM/RUPD/UDP/IP)

The QoS packet network functions are:

PSTN traffic over IP from and toward the Internet/intranet
Network access server/RPMS traffic
Network access server/AAA (Radius/TACACS+server traffic)

IP Connectivity with WAN

Distributed IP control networks operating over a WAN is necessary when:

Multiple POPs in geographically different locations are controlled by the same Cisco SC host.
Redundant Cisco SC hosts are in geographically different locations.

Note The NAS is equipped with serial ports providing WAN termination.

IP Control Network Combinations

The following IP control network combinations are recommended:

One single subnet for all traffic.
Two redundant subnets: one for dedicated to control traffic and the other for user data traffic and as alternative path for the control traffic.
Four redundant subnets: two redundant subnets for Cisco SLT/SC host traffic; two redundant subnets for NAS/SC host traffic. Note: One of these subnet pairs must also run user data traffic.
Any combination of the above with WAN links and dedicated routers providing IP connectivity between the SC host/NAS subnets and the SC host subnet.
Any combination of the above with VLANs configured in shared switches.

Note The subnet mentioned in your IP control network can be a dedicated hub or switch running at 10 or 100 Mbps (10 Mbps for SLTs) or a VLAN configured in a switch sharing backplane bandwidth with other VLANs.

Engineering Considerations

When engineering your network, you must consider the following issues:

There should be no packet loss, and the packets should not be received out of order between the signaling controller and the NASs. This could impact the performance of the Cisco SS7 Interconnect for Access Servers Solution, and the call setup time might become unacceptable.
Do not enable load balancing in the control network. If you must use load balancing, then you must also enable destination-based load balancing. In this case, use Cisco Express Forwarding (CEF) if available. If you do not use CEF, load balancing could cause out-of-sequence delivery when the cache ages out.
If you are using Weighted Fair Queuing (WFQ) or any other type of queuing feature, make sure that all signaling packets from the NASs to the signaling controller (and vice versa) show up in the same queues. Fancy Queuing is not recommended in the control network unless absolutely necessary.
If you are using dynamic routing protocols in the control network, out-of-sequence delivery could occur on a change of adjacency or topology. This should not be a normal occurrence in a stable network.

Cisco SS7 Interconnect for Access Servers Solution Components

Figure 2-5 displays the components of the Cisco SS7 Interconnect for Access Servers Solution.

See the "SS7 Technology Overview" appendix for information about how the Cisco SS7 Interconnect for Access Servers Solution components operate within the SS7 hierarchy.

Figure 2-5: Cisco SS7 Interconnect for Access Servers Solution Components

Cisco SC Node Products

The Cisco SC node is the combination of hardware and software that provides the signaling controller function and transports the signaling traffic between the Cisco SC hosts and the SS7 signaling network. The Cisco SC node in the Cisco SS7 Interconnect for Access Servers Solution consists of one or more SC hosts, one or more Cisco SLTs, the signaling controller software, and ancillary equipment.

This section describes the Cisco SC hosts, signaling and Ethernet interface options, and the ancillary hardware requirements. For details on software requirements, refer to the Cisco SS7 Interconnect for Access Servers Upgrade Guide.

SC Hosts

An SC host is a Sun hardware platform running signaling controller software.

Table 2-1 lists supported SC hosts for the Cisco SC2200 product.

.
Table 2-1: Supported SC Hosts

SC Host Description

Sun Ultra Enterprise 450 (E450)

The Sun Ultra Enterprise 450 is a high-performance, shared-memory, multiprocessing, general-purpose
Sun Ultra SPARC server.

Note The Sun E450 is not NEBS compliant.

Note The Sun E450 can no longer be ordered. Cisco supports the existing installation base only.

Sun Netra t 1120/1125

The Sun Netra t 112x is a general-purpose Sun Ultra SPARC server. The Sun Netra t 112x is rack-mountable and is NEBS and ETSI compliant. The Sun Netra 1120 uses DC power and the
Sun Netra 1125 uses AC power.

Sun Netra t 1400

The Sun Netra t 1400 is a fault-tolerant, dual modular, redundant architecture. Additional lockstep operations give this host the ability to isolate and recover from hardware failure. The
Sun Netra t 1400 is NEBS and ETSI compliant.

Sun Netra ft 1800

The Sun Netra ft 1800 is a fault-tolerant, dual modular, redundant system with the Overriding Principle design. Overriding Principle means that no single point of failure will occur, and all active modules can be removed and replaced online.

The Sun Netra ft 1800 is ETSI compliant and is fully certified to level 3 of the NEBS standard.

SC Host Features

The primary functions of the signaling controller is performing protocol conversion and call screening. The signaling controller is responsible for:

Interworking a variety of user protocols
Translating dialed digit information into data address information A-number and B-number analysis
Issuing control commands to the Transport layer to create, modify, or delete a call session
Generating comprehensive CDR on a call-by-call basis
Providing element management information and statistics
Providing comprehensive signaling debugging capabilities

Table 2-2 lists the features for the SC host.

.
Table 2-2: SC Host Features

Feature Support for ...

Call performance per signaling controller

As many as 100 calls per second with 30 K to 50 K simultaneous calls

As many as 200 calls per second with 100,000 simultaneous calls and with Cisco SC2200 call-processing software optimization

Management interfaces

Provisioning from MML or from an SNMP manager

Dynamic reconfiguration of point codes, linksets, trunk groups, and trunks

MML commands and responses

Application-level checking of call states and circuit states

Signaling protocols

SS7 with MTP2 configured on the Cisco SLT

Support for national protocols of many countries

Scaling of point codes

250+ DPCs and 6 OPCs

Faults and alarms management

SNMP traps

Millisecond time stamp

Millisecond time stamps on log records of diagnostic messages, set and clear alarm messages (sets and clears), alarm messages recorded by the Data Dumper, and alarm messages in the responses for the MML commands "rtrv-alms" and "rtrv-alms:CONT".

Logging enhancements for Release 2.2

Improved system logging efficiency and ability to diagnose problems.

The logging utility is enhanced in the following areas:

Enhanced log format: consistent, text-based message logs and separate logs for the system and users.

Improved system efficiency: dynamic and
non-service- interrupting filtering capabilities for specific logging.

Improved user efficiency: ability to work with other tools (for example, grep utility) and improved log reliability.

Configuration management

Cisco MGC Manager (CMM), a TCL/tk graphic user interface (GUI) that uses simple network management protocol (SNMP) commands to provision the Cisco SC host.

Man-Machine Language (MML), a command-line interface to the Cisco SC host.

Accounting

CDR (CSV format) support for international carrier requirements

Resource management

Keeps track of circuit IDs for assigning calls on NAS ports

Manages adds, moves, and changes of NAS resources

Performance measurements and statistics

Supports carrier requirements

Security

Structured system of passwords

Operating system

Sun Solaris 2.6.x

Dial Plan Provisioning Enhancements

Enables you to input the shortest digit sequence to the Cisco SC2200 number analysis table to define a range of digit strings for the same digit analysis treatment.

For example, for North America Numbering Plan (NANP) dial plans, the shortest digit sequence to identify the range of digit strings from 1-703-484-3000 through 1-703-484-3999 for the same digit analysis treatment would be 1-703-484-3.

MML-control of call processing resources

Provides a MML command interface to allow or reject any new calls.

Route List Display

Displays the symbolic name of a route list in the Telephony Controller Manager (TCM).

Configuration Upload/Download

Provides new configuration management capabilities using both the SNMP and MML interfaces to upload or download all the non-static configuration information.

MML Names in Log

Displays component IDs in the terms of MML names in system logs.

Bearer Channel Level Tracing

Provides a call tracing capability through the MML interface to generate machine-readable traces to be used by Call Trace Viewer (CTV) applications.

Viewer Tools

Provides the following new viewing aids for system-generated data files:

Call Trace Viewer: a tool to display the specified call trace file.

CDR Viewer: a GUI-based tool to retrieve and display the specified CDR file or files.

Log Viewer: a GUI-based tool to retrieve and display the specified Cisco SC2200 log file or files.

Route Verification Viewer: a tool to display the summary of route translation by simulating the specified call through the active dial plan.

Memory Reduction

Provides a per-call, post-answer memory reduction mechanism to accommodate 100,000 simultaneous calls on the Cisco SC host.

Caution The Memory Reduction mechanism may degrade the calls-per-second (CPS) rate. If CPS degrades by more than 5 percent, Cisco recommends that you disable this feature. Cisco also recommends that you never allow CPS to degrade by more than 20 percent.

Scalable D-channel connection

Provides enhanced Cisco SC host infrastructure to support as many as 1500 simultaneous D-channel connections.

Signaling and Ethernet Interface Options

Table 2-3 shows the signaling and Ethernet interface options for the Cisco SC2200.

Table 2-3: SC Signaling and Ethernet Interface Options

Interface Option Sun Netra t 1120 Sun Netra t 1400 Sun Netra ft 1800 Sun E450¹

ITK T1/E1 card

Supported

Not supported

Not supported

Supported

PTI V3.5 card

Supported

Not supported

Not supported

Supported

Sun Ethernet 1-port card

Required

Required

Not supported

Required

Cisco SLT

Supported

Supported

Supported

Supported

¹ Starting with Release 2.1, Sun E450 can no longer be ordered. Cisco supports the existing installation base only.

Interface Option	Sun Netra t 1120	Sun Netra t 1400	Sun Netra ft 1800	Sun E450¹
ITK T1/E1 card	Supported	Not supported	Not supported	Supported
PTI V3.5 card	Supported	Not supported	Not supported	Supported
Sun Ethernet 1-port card	Required	Required	Not supported	Required
Cisco SLT	Supported	Supported	Supported	Supported

Note Cisco recommends that you upgrade to the Cisco SLT to terminate the telephony signaling links. Starting with Release 2.1, ITK T1/E1 and PTI V.35 cards can no longer be ordered. Cisco supports the existing installation base only.

Ancillary Hardware Requirements

Table 2-4 shows the ancillary hardware requirements for the Cisco SC2200.

Table 2-4: SC Ancillary Hardware Requirements

Component Sun Netra t 1120 Sun Netra t 1400 Sun Netra ft 1800 Sun E450¹

Dataprobe Alarm Relay Unit (ARU)

Supported²

Not supported

Not supported

Supported and required only for alarm functions

Dataprobe A/B Switch

Required with use of ITK T1/E1 or PTI V.35 cards³

Not supported

Not supported

Required with use of ITK T1/E1 or PTI V.35 cards³

Asynch Extension

Optional for simplex configurations; required with use of Dataprobe A/B switch

Not supported

Not supported

Optional for simplex configurations; required with use of Dataprobe A/B switch

¹Starting with Release 2.1, Sun E450 can no longer be ordered. Cisco supports the existing installation base only.
²Cisco does not recommend using Dataprobe ARU. You should use the built-in alarm card and software.
³ Call preservation upon switchover or failover is not supported with the A/B switch.

Component	Sun Netra t 1120	Sun Netra t 1400	Sun Netra ft 1800	Sun E450¹
Dataprobe Alarm Relay Unit (ARU)	Supported²	Not supported	Not supported	Supported and required only for alarm functions
Dataprobe A/B Switch	Required with use of ITK T1/E1 or PTI V.35 cards³	Not supported	Not supported	Required with use of ITK T1/E1 or PTI V.35 cards³
Asynch Extension	Optional for simplex configurations; required with use of Dataprobe A/B switch	Not supported	Not supported	Optional for simplex configurations; required with use of Dataprobe A/B switch

Cisco SLTs

The Cisco SLT handles the incoming and outgoing SS7 messages (MTP layer 1 and 2) that arrive from the PSTN Signal Transfer Points (STPs) or Service Switching Points (SSPs). When used in the proper configurations, the Cisco SLTs improve fault tolerance by providing for multiple communications paths between the SS7 signaling network and multiple SC hosts.

Cisco SLT Features

Table 2-5 lists the features for the Cisco SLT.

Table 2-5: Cisco SLT Features

Feature Support for...

SS7 link termination on a high-availability platform

SS7 network access and interconnection requires a high degree of reliability in the signaling links and associated equipment. The Cisco SLT provides the reliability of a dedicated signaling link termination device and maximizes the availability of the SS7 signaling links.

Distributed SS7 MTP processing

Processor-intensive parts of the SS7 Message Transfer Part (levels1 and 2) are offloaded from the signaling controller to the Cisco SLT. This distributed MTP model allows the signaling controller to better utilize its resources to provide optimal call control.

Call control

Signaling backhaul provides a means for integrating the Cisco Signaling Link Terminals into a virtual switch with the call control intelligence centralized in the signaling controller system.

Standard Physical Interfaces

Interconnection with SS7 network elements is supported using the most popular SS7 physical interface standards: T1, E1, V.35, RS-449, and RS-530.

Drop and Insert

Cisco T1/E1 Multiflex Voice/WAN interface cards (VWICs) support Drop and Insert (also called TDM Cross-Connect), which allows individual T1/E1 channels to be transparently passed, uncompressed, between T1/E1 ports. This feature enables direct termination of SS7 F-links in T1 or E1 carriers, while the remaining bearer channels are hairpinned back to a gateway device for processing.

Feature	Support for...
SS7 link termination on a high-availability platform	SS7 network access and interconnection requires a high degree of reliability in the signaling links and associated equipment. The Cisco SLT provides the reliability of a dedicated signaling link termination device and maximizes the availability of the SS7 signaling links.
Distributed SS7 MTP processing	Processor-intensive parts of the SS7 Message Transfer Part (levels1 and 2) are offloaded from the signaling controller to the Cisco SLT. This distributed MTP model allows the signaling controller to better utilize its resources to provide optimal call control.
Call control	Signaling backhaul provides a means for integrating the Cisco Signaling Link Terminals into a virtual switch with the call control intelligence centralized in the signaling controller system.
Standard Physical Interfaces	Interconnection with SS7 network elements is supported using the most popular SS7 physical interface standards: T1, E1, V.35, RS-449, and RS-530.
Drop and Insert	Cisco T1/E1 Multiflex Voice/WAN interface cards (VWICs) support Drop and Insert (also called TDM Cross-Connect), which allows individual T1/E1 channels to be transparently passed, uncompressed, between T1/E1 ports. This feature enables direct termination of SS7 F-links in T1 or E1 carriers, while the remaining bearer channels are hairpinned back to a gateway device for processing.

Network Access Servers

The NAS terminates the PSTN trunks, also referred to as bearer channels, that carry the call traffic. The PSTN trunks are T1 or E1 PRI interfaces.

Note Cisco IOS Release 12.1(3) or later releases run on the NAS.

Table 2-6 lists the features for the Cisco AS5x00.

Table 2-6: Cisco AS5x00 Features

Feature Support for...

Continuity testing

Automated diagnostic procedure.

Redundant Link Manager

Virtual link management.

Resource Pool Management

Shared dial resources for wholesale and retail dial network services on a single NAS.

Resource Pool Management Server

Shared dial resources for wholesale and retail dial network services across multiple NAS stacks.

Feature	Support for...
Continuity testing	Automated diagnostic procedure.
Redundant Link Manager	Virtual link management.
Resource Pool Management	Shared dial resources for wholesale and retail dial network services on a single NAS.
Resource Pool Management Server	Shared dial resources for wholesale and retail dial network services across multiple NAS stacks.

LAN Switches (Optional)

The control signaling network for the Cisco SS7 Interconnect for Access Servers Solution often consists of a LAN switch and the cabling required to interconnect the solution components in an SC zone. The Cisco SS7 Interconnect for Access Servers Solution supports a LAN switch from the Cisco Catalyst switch family. This switch can extend VLANs across platforms through backbone Fast Ethernet, Gigabit, or ATM connections, when necessary.

Note The Catalyst LAN switch is not provided with the Cisco SC2200 product.

Table of Contents

Cisco SS7 Interconnect for Access Servers Configuration Options and Components

SC Host Features

Cisco SLT Features