Specifications

3-9
Cisco AS5800 Operations, Administration, Maintenance, and Provisioning Guide
DOC-7810814=
Chapter 3 Operations
Verifying Modem Performance
• Exactly one digital to analog conversion must exist in the circuit. The digital line must connect into
a digital switch, not a channel bank. V.90 requires PRI (64k clear-channel DS0s). Channel banks
destroy V.90 by adding additional analog-to-digital conversions. Telcos occasionally refer to
channel banks as line-side services. Digital switches are sometimes referred to as trunk-side
services. Figure 3-5 shows this.
Figure 3-5 No Channel Banks for V.90
•
In the local loop, less than three miles of twisted-pair copper line with no load coils is ideal. Load
coils limit frequencies (passband). V.90 requires a 3000 Hz passband. A circuit that does not deliver
a 3200 Hz passband will most likely not deliver V.90. Load coils are common in long loops in
North America (at the 3.5 mile mark).
• Sometimes the PSTN switch fabric is extended by a digital carrier. It is then converted to analog by
a SLC. This setup complies with V.90. The digital-to-analog conversion is moved closer to the
subscriber. However, non-integrated or universal SLCs do not comply to V.90.
• Use a recommended V.90 client modem.
• Electrical house wiring sometimes causes V.90 trainup to fail. For details, see the “V.34 Basic
Rules” section on page 3-7.
Initiating a Modem Loopback Test Call
Test the access server’s ability to initiate and terminate a modem call. Similar to sending a ping to the
next-hop router, this test verifies basic connectivity for modem operations. Successfully performing this
test gives you a strong indication that remote clients should be able to dial into the NAS. Figure 3-6
shows this test.
After completing this test, dial into the EXEC from a client PC and a client modem (no PPP).
Table 3-3 V.90 Supported Cisco IOS Releases
Chassis Modem Type Cisco IOS Release
Cisco AS5800 MICA 11.3(6+)AA
12.0(1+)T
Line side service
Channel bank
Trunk side service
Digital switch
Digital switch NAS
NAS
33173