3com 3031 Instruccion De Instalación

C

HAPTER

 15: ATM/DSL I

NTERFACE

 C

ONFIGURATION

ATM interface loopback is generally used for testing some special functions.

Perform the following configuration in ATM interface view.

By default, loopback function is disabled.

ADSL is an asymmetric transmission technology that implements the high-speed 
data transmission over the twisted-pair copper wire by making use of the unused 
high frequency ranges in the regular telephone line with different modulation 
method. Where, the uplink band is 26kHz-138kHz that can provide a speed of 
640 Kbps, and the downlink band is 138kHz-1.104MHz that can provide a speed 
of 8 Mbps. The transmission speed of ADSL is susceptible to the transmission 
distance and the line quality. Normally, a longer transmission distance means a 
poorer line quality and a lower transmission rate, and a shorter distance. When 
setting up a link, ADSL can automatically make tuning for a reasonable speed 
taking into consideration the actual line state information such as distance, noise 
and some other elements.

The following figure shows a networking topology that is commonly adopted for 
the routers with ADSL interfaces. DSLAM at the central office end works as the CO 
equipment, the router works as the Customer Premises Equipment (CPE 
equipment), the DSL interface card provides the WAN interface, and the Ethernet 
card provides the connection to the subscriber LAN. When making the connection, 
connect the input line of the subscriber’s telephone line, the ADSL port on the 
router and the phone-set respectively to the Line port, the DSL port and the Phone 
port on the splitter. As the transmission speed of ADSL is susceptible to the 
transmission distance and the line quality, you should use the standard twisted 
pairs and guarantee proper connection. .

Before transmitting the service, the CPE equipment must activate the line. 
Activation refers to a series of operations that the CO equipment at the central 
office end and the CPE make in handshake training and information exchanging. 
The activation procedure will be specified in compliance with the ADSL standard, 
channel mode, uplink and downlink speeds, and the noise tolerance specified in 
the line configuration template. It will test the line distance and state, make the 
central office and the remote device make negotiation, and confirm whether the 
normal operation is allowed in the above conditions. If the activation succeeds, a 
communication connection will be set up between the central office and the 
remote device for service transmission. When line activation negotiates connection 
parameters, CO device plays a master role, while CPE device plays a slave role, in 
other words, most connection parameters are provided and decided by CO device.

Table 236   Setting loopback mode of ATM OC-3c/STM-1 interface

Enable the ATM interface to make local cell loopback

Enable the ATM interface to work as a local loop

Enable the ATM interface to work as a remote loop

Disable the ATM interface to make loopback