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This chapter briefly describes the Cisco SS7 PRI Gateway Solution configuration options and the required and optional components:
The Cisco SS7 PRI Gateway Solution provides the following configuration options:
You can deploy the Cisco SS7 PRI Gateway Solution in the following ways:
A continuous-service configuration is a VSC zone that consists of a pair of VSC hosts running in a primary (active) and secondary (inactive) mode, operating with one or moreCisco Cisco MGX 8260s and one or more Cisco SLTs. An error-checking function runs continuously between the two VSC hosts monitoring the primary VSC host. In addition, call information is checkpointed from the active VSC host to the standby VSC host.
When the function detects an error condition on the primary VSC host, responsibility for call processing is switched to the secondary VSC host. The secondary VSC host now becomes the primary VSC host, and call preservation is maintained. Further, the Cisco SLTs provide for physical SS7 link termination.
Figure 2-1 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 Cisco MGX 8260.
A simplex configuration is a VSC zone that consists of a single VSC host (Sun Netra t 112x or t 140x) operating with one or more Cisco SLTs. The VSC application is run on the VSC 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 Cisco MGX 8260s are required for bearer channel termination. See Figure 2-1.
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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. |
The Cisco SS7 PRI Gateway Solution performs functions to exchange telephone control messages between the following components that support the end user's signaling network connection:
Cisco Virtual Signaling Controller---Provides a signaling protocol conversion, and network Q.931 call control to communicate with the Cisco MGX 8260s. One signaling controller may provide signaling and call-processing services for multiple Cisco MGX 8260s in geographically distributed locations, over redundant IP links used for ISDN signaling.
Cisco SLT---Handles the incoming and outgoing SS7 message (MTP layer 1 and 2) from the A-links (access links) connected to Signal Transfer Points (STPs). Also, it grooms off the signaling links and the bearer channels (ISUP) from F-links (fully associated links) and sends them to the Cisco MGX .8260
Cisco MGX 8260---Provides termination for PSTN trunks. A Cisco MGX 8260 functions as a server to the SS7 bearer links. The Cisco MGX 8260 has two (four with two SCCs) IP network interfaces: to connect to the ISP's secure management, signaling, and Q.931 control network.
Your Cisco SS7 PRI Gateway Solution can be deployed in three ways, as described in "Simplex and Redundancy Options," with several options to address SS7 signaling network connections. Options would depend on your specific network requirements. Those options are:
An A-link with Cisco SLT signaling configuration option is an access link from the PSTN Signal Transfer Point (STP) connected to the Cisco SLT of the VSC node, using a V.35 or T1/E1 interface card. On the LAN side, the Cisco SLTs connect to the Ethernet card on the VSC host by way of a LAN switch connection. See Figure 2-1 for an example.
An F-link with Cisco SLT signaling connection is a fully associated link from the PSTN to the
Cisco SLT of the VSC node. F-links connect the VSC host directly to a Service Switching Point (SSP) or a Service Control Point (SCP) in the SS7 network; they do not make an intermediate connection through STPs.
The F-link SLT signaling configuration supports RS-449, RS-530, V.35, and T1/E1 interfaces that are installed in the Cisco SLT. The F-link SLT configuration can be used with simplex and continuous-service VSC host configurations. Each interface supports a single DS0 signaling channel.
An F-link with Cisco SLT (Drop and Insert) signaling connection is similar to an F-link SLT signaling connection. Fully associated links directly connect an SSP or SCP to the Cisco SLT. The difference is that an F-link Drop and Insert configuration supports 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 2-2.
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Note The F-link Drop and Insert technique is also known as time-division multiplexing (TDM) cross-connect. |
Figure 2-3 shows an example of PRI signaling Backhaul. Signaling backhaul is the ability to reliably transport the signaling (Q.931 and above layers) from a PRI trunk that is physically connected to a trunking gateway to a VSC host for processing; in addition, the VSC host can send the response signaling out the same interface.
The reliable transport is provided by a Session Manager and a Reliable User Datagram Protocol (RUDP) mechanism that will be delivered on the VSC and media gateways. Reliable UDP provides in-sequence, guaranteed delivery. Session Manager provides packet network and virtual switch controller redundancy support.
The PRI backhaul takes place between an Cisco MGX 8260 and the Cisco VSC3000 host, which provides call processing. For ISDN, the boundary is between Q.921 and Q.931; for SS7, the boundary is between MTP2 and MTP3.
This section briefly describes the available control signaling network options and network engineering assumptions to consider.
Your control network consists of a number of hubs, switches, or routers configured together to support the number of ports, the traffic characteristics of incoming calls, the geographic location of the Cisco SS7 PRI Gateway Solution components and the level of redundancy that you require. Other factors to consider are:
Control traffic (signaling) should be segregated from the bearer data IP traffic (towards the internet/intranet) onto a different network. This optimizes control traffic latency and provides added security. Redundancy in your control network can be provided by duplicating your
Cisco SS7 PRI Gateway Solution components.
In the simplest case, your Cisco SS7 PRI Gateway Solution components are co-located, and a pair of LAN switches serves as your control network. However, it is also possible that Cisco SLTs and
Cisco MGX 8260s are geographically separate from the VSC hosts requiring a control network with WAN links and separate routers to provide the WAN connection.
Figure 2-1 shows a sample continuous-service configuration with two LAN switches and one or more Cisco SLTs (for redundancy) on the control or signaling network. Redundant signaling controllers support two or four Fast Ethernet connections each.
In this continuous-service configuration example, the control network functions are:
Distributed IP control networks operating over a WAN are necessary when redundant VSC hosts are in geographically different locations.
The following IP control network combinations are recommended:
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Note The subnet mentioned in your IP control network can be a dedicated hub or switch running at 10 or 100 Mbps or a VLAN configured in a switch sharing backplane bandwidth with other VLANs. |
When engineering your network, you need to consider the following issues:
The VSC node is the combination of hardware and software that provides the virtual switch controller function and transports the signaling traffic between the VSC hosts and the SS7 signaling network. The VSC node in the Cisco SS7 PRI Gateway Solution consists of the components listed below and shown in Figure 2-4. Each component is addressed in detailing the following pages. See the
"Cisco SS7 PRI Gateway Solution Documentation Suite" section for detailed information.
The Cisco VSC3000 hosts provides all necessary call agent functions (for example, call routing, charging, and maintenance of gateway resources) and solution signaling processing, in this case SS7 to PRI. The VSC host analyzes the parameters within the signaling bit streams and makes routing decisions based on its provisioned data tables. The VSC hosts communicate with each other, the Cisco SLTs, and the Cisco MGX 8260 over an interconnecting IP LAN/WAN.
A VSC host is a Sun hardware platform running signaling controller software. Table 2-1 provides a detailed description of the supported VSC host platforms.
| SC Host | Description |
|---|---|
Sun Netra t 112x | The Sun Netra t 112x is a carrier-grade Sun Ultra SPARC server. The Sun Netra t 112x is rack-mountable and is NEBS and ETSI compliant. |
Sun Netra t 140x series | The Sun Netra t 140x is a carrier-grade Sun Ultra SPARC server. The Sun Netra t 140x is rack-mountable and is NEBS and ETSI compliant. |
Two redundant VSC hosts share the same database configuration and operate in an active or "warm" standby configuration. Call processing takes place on the active VSC host while call state information is copied in real time to the standby VSC host. In the event of a failure in the active VSC host, the standby VSC host takes over and, after a short period (2-3 seconds), resumes call processing. Stable calls are maintained during the switchover.
The primary function of the VSC host is to perform routing and protocol conversion and is responsible for:
Table 2-2 lists the features for the VSC host.
| Feature | Support for ... |
|---|---|
Call performance per signaling controller (simplex configuration) |
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Call performance per signaling controller (continuous-service configuration) |
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Configuration/operation |
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Configuration management |
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Signaling protocols |
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100,000 simultaneous calls | 100 call per second (CPS) POTS (raw CPU call setup capability) |
Media Control Gateway Protocol (MGCP) ---MGCP 0.1 | Communication between the VSC hosts and the Cisco MGX 8260. |
PRI Signaling Backhaul | SDN PRI at the Q.921/Q.931 split |
SS7 Signaling Backhaul | SS7 ISUP at the MTP L2/L3 split |
Advanced Intelligent Network (AIN) Services | Local Number Portability (LNP) |
Complete COT support |
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Enhanced call detail record (CDR) support | Upstream mediation and billing platforms |
Enhanced fault tolerance |
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Enhanced call processing |
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Scaling of point codes | 200+ DPCs and 6 OPCs |
Network management interfaces | IP |
Faults and alarms management | SNMP traps |
Enhanced logging facility |
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Accounting | CDR (TLV format) support for worldwide carrier requirements |
Performance measurements and statistics | Supports carrier requirements |
Security | Structured system of passwords |
Operating system | Sun Solaris 2.6.x |
The Cisco SS7 PRI Gateway Solution VSC3000 product requires the following software release levels listed in Table 2-3
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| Software Release Level | Support for... |
|---|---|
Cisco MGC Software Release 7.4.7 | Virtual switch controller software running on the VSC host. It provides SS7 and ISDN protocol support (and conversion) for various countries and variants, MGCP 0.1 call control, and ISDN backhaul. |
Cisco IOS 12.0(7)T or later releases | Cisco IOS release running on the Cisco SLT. |
Sun Solaris 2.6.x | Operating system running on the VSC host. |
Each Cisco Signaling Link Terminal (SLT) terminates as many as two SS7 links (V.35 or DS1) and backhauls MTP L3, ISUP, and TCAP/SCCP SS7 messages over IP to the active VSC host. Cisco SLTs connect to the CLEC STP through V.35 SS7 links or DS1.
The Cisco SLT handles the incoming and outgoing SS7 messages (MTP layer 1 and 2) with DS1, E1, or V.35 interfaces. It supports SS7 signaling backhauling at the MTP L2/L3 split (MTP L3, ISUP, SCCP, and TCAP) through Reliable User Datagram Protocol (RUDP) and Session Manager to the VSC.
Each Cisco SLT terminates two SS7 links. Ideally, links in a linkset are spread across Cisco SLTs for redundancy (to increase availability). This permits each Cisco SLT to communicate with both STPs of the carrier's mated pair.
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 VSC hosts. Table 2-4 lists the features for the Cisco SLT
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| 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 (levels 1 and 2) are off-loaded 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 combining gateways 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 | T1/E1 interface cards 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 A-links or F-links in T1 or E1 carriers, while the remaining bearer channels are passed on to a gateway device for processing. |
The Cisco MGX 8260 terminates DS-3 interfaces to the ILEC and CLEC switches as well as to ISP network servers.
The Cisco MGX 8260 provides the termination of SS7 bearer channels from the PSTN. It also provides SS7 bearer channels out to the PSTN or PRI bearers out to a RAS or modem pool device.
The VSC can set up TDM connections on the Cisco MGX 8260 through MGCP messages. The
Cisco MGX 8260 also performs ISDN/PRI layer 2 (Q.921) functions and backhauls Q.931 messages to the VSC.
Signaling backhaul passes as many layers of a protocol stack as possible through a gateway directly to the VSC. In ISDN, the backhaul takes place at the Layer 2 (Q.921)/ Layer 3 (Q.931) boundary. The lower levels of the protocol are performed on the gateway, by the Cisco MGX 8260. This provides the advantage of distributing the protocol processing to allow for greater expendability and suitability. Reliable UDP (RUDP) over IP is used to transport Q.931 over the packet network. RUDP provides a socket-like interface but also provides autonomous notification of connected sessions and failed sessions.
Cisco MGX 8260 Release 1.1 includes the following hardware products:
Table 2-5 lists the features for the Cisco MGX 8260.
| Feature | Support for... |
|---|---|
T3 TDM (to DS0) interface | 6 T3 per BSC, max 36 T3 per chassis (108 DS3 per 7' rack) |
NEBS level 3 compliance | Compliance with telecommunication standards for performance, quality, environment, and safety |
Hot swappable cards | Redundancy. No active calls are lost during hardware or software switchover. |
220-MB solid state flash disk | All software images, configuration files, log files, and announcement files are stored in SCC hard disk. |
Environment monitoring | Temperature, voltage, and fan management |
Primary and secondary clock sources can be configured as |
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Redundancy (hot standby) | No active calls lost during HW or SW failovers |
Integrated alarm |
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System monitoring and error recovery | Derived operational measurements and reliability |
Network management |
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ISDN PRI and NFAS backhaul | Q.921 running on BSC and NSC. Q.931 is transported to VSC (Feature Set 1). |
COT loopback and transponder modes for both originating and terminating | Bearer channel status verification |
The control signaling network for the Cisco SS7 PRI Gateway Solution often consists of
Catalyst 5500 LAN switches and the cabling required to interconnect the solution components in a VSC zone.
The LAN switches provide the LAN/WAN connectivity required for the IP Control Network. They are configured to interconnect IP segments using VLANs. Using VLANs traffic can be segregated to optimize bandwidth load. Two LAN switches are used for redundancy.
The Cisco SS7 PRI Gateway Solution components can be managed using the command line interface, the SNMP, or the network management applications as described in the sections that follow.
Every component of the solution is SNMP enabled. For a description of the supported MIBs, refer to each component's documentation.
The following integrated network management applications are available:
Posted: Thu Jun 15 09:57:22 PDT 2000
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