An Overview of Analog Dialup Modem Performance, Environments, and Impairments.

REVISED 7/20/98 13
DOC. NUM. PRT/005A/0798
Bps – Bits Per Second. This is the unit of measurement used when describing data rate of a modem.
CO – Central Office. This is the telco facility that directly provides telephone service to the
customer.
ITU-T – International Telecommunications Union. This is the international standard-setting body
that publishes the V.xx Recommendations for modem communications.
K56flex™ – proprietary PCM protocol developed jointly by Rockwell and Lucent. Not
interoperable with x2 or V.90.
LAPM – Link Access Procedures for Modems. This is the primary error-correction protocol speci-
fied in ITU-T Recommendation V.42.
Loop – copper network or circuit between the customer and the CO.
MNP2-4 – error correction protocol developed by Microcom, which is specified as an alternate er-
ror-correction protocol under V.42.
PCM – Pulse-coded modulation.
PSTN – Public Switched Telephone Network, alternately referred to as POTS (Plain Old Telephone
System).
RBOC – Regional Bell Operating Company (Baby Bell)
RBS – Robbed-bit signaling. This uses certain bits from the digital data stream to perform call
control and switching.
SLC – subscriber loop concentrator. This is a device used on the loop circuit to aggregate a large
number of phone lines into a single connection back to the central office.
SNR – Signal-to-Noise ratio
V.34 – ITU-T standard modulation protocol for speeds up to 33.6Kbps.
V.42 – ITU-T standard for the negotiation of an error-correcting link.
V.90 – ITU-T draft standard modulation protocol for speeds up to 56,000bps.
x2 - proprietary PCM protocol developed by U.S. Robotics (now 3Com)