R2511-HP MSR Router Series Interface Configuration Guide(V5)

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Overview
ADSL technologies
Asymmetric Digital Subscriber Line (ADSL) is an asymmetric transmission technology that implements
high-speed data transmission over twisted-pair copper wire by using unused high frequency ranges in
the regular telephone line with a different modulation method. With standard ADSL, the band from 26
kHz to 138 kHz is used for upstream communication, while 138 kHz to 1.104 MHz is used for
downstream communication. Theoretically, the upstream rate is up to 640 kbps, and the downstream
rate is up to 8 Mbps.
Some latest ADSL technologies, however, can provide faster transmission rates by improving modulation
rate, coding gain, initialization state machine, by reducing frame head overhead, and by using
enhanced signal processing methods. For example, given the same bands, ADSL2 can provide the
upstream transmission rate up to 1024 kbps and downstream transmission rate up to 12 Mbps. By
expanding the downstream band from 1.104 MHz to 2.208 MHz, ADSL2+ can even provide a
downstream rate as fast as 24 Mbps.
The transmission rate of ADSL is susceptible to the transmission distance and line quality. An increased
transmission distance means decreased line quality and transmission rate, and a decreased transmission
distance means the contrary. When setting up a link, ADSL can automatically tune the rate taking into
consideration actual line conditions such as distance and noise.
Two types of ADSL modules/cards are available: ADSL over POTS and ADSL over ISDN (ADSL-I).
Typical network topology for ADSL routers
Figure 8 shows a typical network topology for routers with ADSL interfaces, where:
• DSLAM at the central office end works as the central office (CO) equipment.
• The router works as the Customer Premises Equipment (CPE).
Figure 8 Network diagram
Line activation and deactivation
Before transmitting traffic, the CPE must activate the line. This is done through handshake training and
information exchange between the CO equipment and the CPE.
A typical activation process lasts 30 seconds, beginning with line negotiation until the line comes up.
During this process, the two parties examine line distance and conditions against the line configuration
template (which defines the ADSL criteria, channel mode, upstream and downstream speeds, and noise
tolerance) and attempts to reach an agreement. If the activation succeeds, a communication connection