Troubleshooting guide

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Cisco Broadband Local Integrated Services Solution Troubleshooting Guide
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Chapter 1 Solution Overview
Solution Components
Edge Routers
Cisco GSR 12000 (optional)—the Cisco GSR 12000 Gigabit Switch Router can be used to connect
CMTSs to the rest of the IP network. It can be located in a headend, in the regional backbone, or in a
service providers Internet Protocol Central Office (IPCO).
Trunking Components
The Media Gateway Control Protocol (MGCP) 1.0 is used to control Voice over IP (VoIP) calls by
external call-control elements known as call agents (CAs). It is described in detail in IETF RFC 2705.
MGCP 1.0 is the call control protocol that runs between call agents and trunking gateways (TGWs) in a
packet cable / IP telephony network.
PacketCable Labs developed the NCS and TGCP protocols, which contain extensions and modifications
to MGCP while preserving the basic MGCP architecture and constructs. NCS is designed for use with
analog, single-line user equipment on residential gateways (MTAs), while TGCP is intended for use in
VoIP-to-PSTN trunking gateways in a packet cable environment.
As in the earlier implementations of the protocol, the trunking gateway handles the translation between
audio signals from the PSTN and the packet cable network. The trunking gateways interact with the Call
Agent, which performs signal and call processing on the gateways’ calls. Call support has been expanded
to include MTAs, which provide an interface between analog (RJ11) calls and the VoIP over cable
network.
MGCP 1.0, including the NCS 1.0 and TGCP 1.0 profiles feature, provides protocols for MTAs and
trunking gateways (TGWs), which sit at the edge of the packet network to provide interfaces between
traditional, circuit-based voice services and the packet network. MTAs offer a small number of analog
line interfaces, while trunking gateways generally manage a large number of digital trunk circuits.
In the Cisco BLISS for Cable solution, the Cisco BTS 10200 Softswitch communicates with SS7-based
PSTN switches and service control points (SCPs) using a SIGTRAN-based signaling gateway (SG). The
SIGTRAN interface carries all SS7 messages encapsulated in IP packets. The Cisco IP Transfer Point
(ITP) is one of the SGs used with the Cisco BTS 10200 Softswitch for this purpose.
Bearer traffic connections to the PSTN are through ISDN User Part (ISUP) trunks with a TGW providing
the bearer connections (for example, T1 carrier connections to the Cisco MGX8850). Either ISUP or
multifrequency (MF), Feature Group-D (FGD), OS signaling trunks are used to interconnect to a service
bureau (or ILEC) providing operator services, directory services and positions for 311, 611 and 711
services. E911 calls are routed to an E911 tandem, which has the appropriate databases and interfaces
with the Presentation-Service Access Points (PSAP).
Connectivity to other networks includes PSTN connectivity, IP Backbone connectivity, and Internet
connectivity. IP backbone and Internet connectivity is accomplished via the GSR 12000 in the IPCO.
Cisco MGX8850 Trunking Gateway
This section describes the Cisco MGX 8850 trunking gateway (TGW) in the Call Agent node.
The Cisco MGX 8850 is the primary ISUP trunk, 911 trunk, and Operator Services/411 TGW.
All TGWs must support redundant IP network interfaces with each interface able to handle the full
capacity for media streams based on fully loaded PSTN interconnect.
TGWs can be configured with a virtual IP address associated with a loop-back port—independent of the
two IP addresses associated with the Ethernet interfaces. This loop-back IP address is the one that the
Call Agent should know about when talking to the TGW. It provides the optimum way of communicating
with the TGW in cases where one of the Ethernet interfaces (or the switch) fails.