Specifications

3-3
Cisco AS5800 Operations, Administration, Maintenance, and Provisioning Guide
DOC-7810814=
Chapter 3 Operations
Verifying Modem Performance
Figure 3-2 Modem Access Connectivity Path
To understand the general call-processing sequence, match the following numbered list with the
numbers shown in Figure 3-2:
1. 64K DS0 circuits extend from the NAS modems, through the internal TDM CSM bus, and through
the circuit network (PSTN).
2. The NAS modems demodulate digital streams into analog-voiceband modulation. The virtual
EIA/TIA-232 interface connects the modems (DCE) to the TTY lines.
3. The TTY lines are mapped into asynchronous interfaces. Interfaces are Cisco IOS software objects
that move packets. TTY lines function at Layer 1. Interfaces function at Layer 2 and Layer 3.
4. The packets are delivered into the IP network.
33185
Inside a Cisco
network access server
Asynchronous
interfaces
Asynchronous
Characters
Modems
TTY lines
64K DS0
TDM CSM bus
T1 controllers
Packet-
switched
half
Circuit-
switched
half
Circuit network
(PSTN)
Client PC
Client
modem
PSTN interface
(T1, E1, BRI)
Packet interface
(Ethernet, frame
relay,etc.)
Routing and
switching engine
IP
network
3
4
2
1