Specifications

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Cisco AS5800 Operations, Administration, Maintenance, and Provisioning Guide
DOC-7810814=
Chapter 3 Operations
Verifying Modem Performance
To achieve 33600 bps, the channel must deliver:
• A response from 244 to 3674 Hz
• A SNR of 38 dB or better
In practice, toll-quality voiceband circuits support V.34 at speeds of 21600 to 33600 bps.
The following six items reduce the achieved V.34 speed:
1. Robbed-bit signaling links in the circuit, which reduce SNR.
2. Extra analog-to-digital conversions. For example, nonintegrated or universal subscriber line
concentrators (SLCs) reduce bandwidth and SNR.
3. Load coils on the local loop, which reduce bandwidth.
4. Long local loops, which reduce bandwidth and SNR.
5. The following electrical disturbances in the house wiring, which reduce SNR:
– Cross talk from two lines in the same quad cable
– Corroded connectors
– Bridge-tapped lines running parallel to fluorescent lights
– Flat silver-satin cables running parallel to power cables
– Extra electrical equipment sharing the same power jack as the modem
6. Voiceband circuits that pass through sub-64k coding, such as a cellular or 32K ADPCM link.
With 32k ADMCM, the speed is typically 9600 to 16800 bps.
V.90 Basic Rules
Many circuit components work together to deliver V.90 modulation. See Figure 3-4.
Figure 3-4 V.90 Network Components
Here are the V.90 basic rules:
• Select recommended modem code. The following are reliable V.90 releases at the time of this
publication:
– MICA Portware Version 2.6.2.0
– Microcom Firmware Version 5.2.1.0
The latest modem code is posted on CCO at the following URL:
http://www.cisco.com/kobayashi/sw-center/sw-access.shtml
• Run a Cisco IOS release that is compatible with V.90. Table 3-3 shows the V.90 supported
Cisco IOS releases at the time of this publication.
33171
PSTN
Client
DTE
Client
DCE
House
wiring
Local
loop
DS0
circuit
through
PSTN
Digital
line
NAS
Digital
modem