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Cisco IOS Dial Services Configuration Guide: Network Services, Release 12.1
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About the Cisco IOS Software Documentation
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Using Cisco IOS Software
- Part 1: Large-Scale Dial Solutions
- Part 2: Cost-Control Solutions
- Part 3: Virtual Private Networks
- Part 4: X.25 on ISDN Solutions
- Part 5: Telco Solutions
- Part 6: Dial-Related Addressing Services
- Part 7: Interworking Dial Access Scenarios
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Table Of Contents
Configuring the Cisco SS7/C7
Dial Access Solution SystemCisco SS7/C7 Dial Access Overview
Configuring the Access Server for RLM
Configuring the Cisco SS7/C7
Dial Access Solution System
This chapter describes how to configure the Cisco Signalling System 7 (SS7)/C7 Dial Access Solution System feature. It includes the following main sections:
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Cisco SS7/C7 Dial Access Overview
The Cisco SS7/C7 Dial Access Solution System feature runs on the Cisco AS5200, AS5300, AS5800, and Cisco AccessPath TS and TS3 access servers in conjunction with the following Cisco technologies:
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For additional software configuration information, refer to the following publications:
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For a complete description of the commands mentioned in this chapter, see the Cisco IOS Dial Services Command Reference publication. To locate documentation of other commands that appear in this chapter, use the command reference master index or search online.
Cisco SS7/C7 Dial Access Overview
The Cisco SS7/C7 Dial Access Solution System feature enhances capabilities previously introduced in the Cisco IOS software. These capabilities include:
Provided is support for IP connection to SS7/C7 signalling controller and associated continuity testing. This support allows carrier customers to connect their access servers to the Public Switch Telephone Network (PSTN) directly by using SS7/C7 signalling protocols. The SS7/C7 signalling links terminate on a separate UNIX system called the Signalling Controller (SC2200). The SC2200 maps incoming calls, which are signalled via SS7/C7, to bearers on the access servers. The access servers and SC2200 interact to set up and tear down calls using an extended Q.931 protocol over Q.921 and the User Data gram Protocol (UDP). In this manner, the access servers and SC2200 form a system that emulates an end-office switch in the PSTN.
The Cisco SS7/C7 Dial Access Solution System uses the ISDN Q.931 and Q.921 protocols over an RLM module. RLM makes use of UDP to transfer information from the network access server to the CSC and vice versa. The ISDN module works in conjunction with the RLM.
Redundant Link Management
The goal of RLM is to primarily provide virtual link management over multiple IP networks so that the Q.931 signalling protocol and other proprietary protocols can be transported on top of multiple redundant links between the CSC and the network access server. RLM opens, maintains, and closes multiple links, manages buffers of queued signalling messages, and monitors whether links are active for link failover and signalling controller failover. The user can create more than one IP connection between the CSC and the network access server.
The client or server side must support the RLM protocol, which manages those redundant links between the server and client and handles the link and server failover mechanism.
We recommend that all access servers use at least two IP interfaces to connect to the primary and alternative IP interfaces of the CSC. Otherwise, the control traffic will be impacted by the data traffic by sharing the same interface for both types of traffic; refer to Figure 28.
The RLM goes beyond Q.921, because it allows for future use of different upper layers, and more importantly, it allows for multiple, redundant paths to be treated as one path by upper layers.
Figure 28 Release 2 Architecture
The protocol stack is listed in Figure 29.
Figure 29 RLM Protocol Stack
Extended Q.931 provides call control and maintenance functions. The Q.931 implementation is based on the Cisco National ISDN (NI) switch type with custom enhancements. The signalling controller appears as one or more signalling points in an SS7 network, and performs interworking between the various SS7 protocols in use worldwide to the extended NI protocol used between the Cisco SC2200 and network access server.
Q.921 is used to encapsulate the Q.931 messages. It guarantees the in-sequence transmission of Extended Q.931 messages and provides for retransmission. UDP provides for the connectionless transfer of signalling messages across the subnetworks (LAN or WAN), connecting the access servers to the signalling controller.
Continuity Test Subsystem
The SS7 network, in order to detect failures of DS0 channels, will at times request a COT of a channel before establishing a call. ITU-based networks use only the loopback method for continuity test. However, ANSI-based network usage varies. Some use only the loopback method and others use both tone and loopback methods. Only the loopback method is supported in Cisco IOS Release12.1 of the SS7 system.
Continuity test requests are received over an SS7 signalling path and processed within the Signalling Access Server (SAS). The SAS requests that the network access server put the particular bearer in external loopback mode (loopback incoming receive to outgoing transmit) or to insert a transponder in the incoming circuit. The continuity test lasts until a COT message is received.
The COT subsystem supports continuity testing, which is required by the SS7 network to conduct loopback and tone check testing on the path before a circuit is established. COT will detect any failure of DS0 channels. It is required for North American SS7 compliance. You must have installed MICA technologies 2.6.1.0 portware, which supports the COT feature.
ISDN Module
The ISDN module ensures that the ISDN protocol stack functions properly while the D-channel information (Q.931 and the Q.921 frames) is transported over possibly multiple IP networks via UDP, across links managed by the RLM.
Do not use this feature or other SS7 dial access solutions if you are using a PRI interface. The RLM group should have already been configured. If not, see the section "Configuring the Access Server for RLM" later in this chapter to complete this task.
RLM Configuration Task List
Perform the following tasks to configure RLM:
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Configuring the Access Server for RLM
To configure the access server interfaces for RLM, use the following commands beginning in global configuration mode:
Verifying RLM
To verify RLM, perform the following tasks:
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Router# show rlm group 1 statusRLM Group 1 StatusUser/Port: RLM_MGR/3000Link State: Up Last Link Status Reported: UpNext tx TID: 1 Last rx TID: 0Server Link Group[r1-server]:link [10.1.1.1(Loopback1), 10.1.4.1] = socket[active]link [10.1.1.2(Loopback2), 10.1.4.2] = socket[standby]Server Link Group[r2-server]:link [10.1.1.1(Loopback1), 10.1.5.1] = socket[opening]link [10.1.1.2(Loopback2), 10.1.5.2] = socket[opening]Note the following:
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Router# show isdn statusGlobal ISDN Switchtype = primary-niISDN Serial1:23 interfacedsl 0, interface ISDN Switchtype = primary-ni :Primary D channel of nfas group 0Layer 1 Status:ACTIVELayer 2 Status:TEI = 0, Ces = 1, SAPI = 0, State = MULTIPLE_FRAME_ESTABLISHEDLayer 3 Status:0 Active Layer 3 Call(s)Activated dsl 0 CCBs = 0ISDN Serial2:23 interfacedsl 1, interface ISDN Switchtype = primary-ni :Group member of nfas group 0Layer 1 & 2 Status Not ApplicableLayer 3 Status:0 Active Layer 3 Call(s)Activated dsl 1 CCBs = 0Total Allocated ISDN CCBs = 0Note the following information for Serial1:23 (the first half of the messages):
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The second half of the messages display information for Serial2:23.
RLM Troubleshooting Tips
If you are having trouble, check for the following:
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