AT&T SS7 Linkset Is Either Unavailable or
Inaccessible
Document ID: 20514
Contents
Introduction
Prerequisites
Requirements
Components Used
Conventions
Background Information
Cisco ICM 4.1 and Earlier Versions
Cisco ICM 4.2 and Later Versions
Problem
Cause
Solution
Cisco ICM 4.1 and Earlier Versions
Cisco ICM 4.2 and Later Versions
Related Information
Introduction
This document provides a background and solutions for AT&T SS7 Linkset error messages such as, "SS7
linkset unavailable" and "SS7 network inaccessible".
Prerequisites
Requirements
There are no specific requirements for this document.
Components Used
This document is not restricted to specific software and hardware versions.
Conventions
Refer to Cisco Technical Tips Conventions for more information on document conventions.
Background Information
In older versions of Cisco Intelligent Contact Management (ICM), which include ICM 4.1 and earlier, the
Network Interface Controller (NIC) and the gateway act as a single process that runs on a DOS machine. In
ICM 4.2 and later versions, the NIC is a process that runs on the Router node while the SS7 gateway is a
separate node.
Cisco ICM 4.1 and Earlier Versions
Intelligent Call Processing (ICP), a service of AT&T, allows customer premises equipment to participate in
call routing at the network level. The ICM CallRouter uses ICP to receive call routing requests, and to return
call routing responses to the AT&T SS7 signaling network.
Within ICM, the ICP interface is implemented as a dedicated computer and process, called the Network
Interface Controller (NIC). Figure 1 represents the relationship between the NIC and the AT&T ICP network.
Figure 1 Relationship Between the NIC and the AT&T ICP Network: ICM Version 4.1 and Earlier
When ICM is connected to the AT&T ICP network, ICM is considered as a Customer Routing Point (CRP).
ICM communicates with the AT&T network through SS7 links to a pair of mated Signal Transfer Points
(STPs). The STPs carry message traffic between nodes and the Network Control Point (NCP). The NCP is an
AT&T network node that processes 800−number call routing requests received from telephone switches in the
AT&T network.
The AT&T NIC connects the ICM CallRouter to a pair of STPs in the network through two 56−Kbps circuits
called A−links. AT&T provides these links as part of the ICP service. The A−Links come as a pair, which
means that link redundancy is a standard feature. Each A−Link terminates in an SS7 card in the ICP NIC
platform.
Cisco ICM 4.2 and Later Versions
SS7 gateways are ICM nodes that provide SS7 network connectivity for various NICs in an ICM deployment.
All gateways provide the SS7 Message Transfer Part 2 (MTP2), Message Transfer Part 3 (MTP3), and SCCP
SS7 network layers. Some gateways also implement the Transaction Capabilities Application Part (TCAP) of
SS7 and TCAP User layers as well.
SS7 gateways can use ISA SS7, or PCI Quad SS7 network interface cards. Note that ISA SS7 interface cards
are not supported in versions later than ICM 6.0.
Figure 2 shows a full "mated pair" configuration where two routers with two NICs are connected to two
gateways that each are connected to two STP (Signaling Transfer Points). This fully redundant configuration
allows for any single point of failure in ICM without affecting the ability of ICM to route calls.
Figure 2 Relationship Between the NIC and the AT&T ICP Network: ICM Version 4.2 and Later
One or more signaling links help to achieve connection to an SS7 network. The physical link interface
implementation is through adapter cards inserted into the gateway PC. The gateway can support up to two PCI
SS7 adapter cards although one card is adequate for most installations. Each adapter card provides four
signaling links and requires a dedicated PCI slot within the machine. You can use one, two, three or four links
per card as necessary.
Each adapter card supports four 56 or 64 Kbit/sec SS7 links over a V.35 electrical interface. The clocking
provided from the network (CSU/DSU) determines the actual baud rate. Four 10−foot DTE cables accompany
each card. Each cable terminates in a 34−pin male block connector with a standard V.35 pinout.
Problem
AT&T SS7 Linkset is either unavailable or inaccessible, and either of these messages appears in Monitor ICR
on an Admin Workstation (AW) or in Alarm Tracker:
• "SS7 linkset unavailable."
• "SS7 network inaccessible."
Cause
These error messages usually indicate that there is a network fault somewhere between the Cisco ICM NIC
and the AT&T network, or directly in the AT&T network.
Solution
Cisco ICM 4.1 and Earlier Versions
Specifically, these types of messages indicate that the Cisco ICM NIC does not receive digital clock pulses
from the AT&T network.
As a first step, cold−boot the problematic Cisco ICM NIC. If the problem persists, open a trouble ticket with
both Cisco and AT&T for further investigation.
Contact Technical Support to open, check, or update a service request with the Cisco Technical Assistance
Center (TAC).
Cisco ICM 4.2 and Later Versions
Specifically, these types of messages indicate that the Cisco ICM SS7 gateway does not receive digital clock
pulses from the AT&T network.
As a first step, cold−boot the problematic Cisco ICM SS7 gateway. If the problem persists after you cold boot
the Cisco ICM SS7 gateway, open a trouble ticket with both Cisco and AT&T for further investigation.
Contact Technical Support to open, check, or update a service request with the Cisco Technical Assistance
Center (TAC)
Related Information
• Technical Support & Documentation − Cisco Systems
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Updated: Feb 10, 2005
Document ID: 20514