ITU-T G.994.1 PDF

This Recommendation defines signals, messages and procedures for exchanging these between digital subscriber line (DSL) equipment, when the modes of operation of the equipment need to be automatically established and selected, but before signals are exchanged which are specific to a particular DSL Recommendation.

For interrelationships of this Recommendation with other ITU-T G.99x-series Recommendations, see Recommendation ITU-T G.995.1 (informative).

The principal characteristics of this Recommendation are as follows:

a) use over metallic local loops;

b) provisions to exchange capabilities information between DSL equipment to identify common modes of operation;

c) provisions for DSL equipment at either end of the loop to select a common mode of operation or to request the other end to select the mode;

d) provisions for exchanging non-standard information between DSL equipment;

e) provisions to exchange and request service and application-related information;

f) support for both duplex and half-duplex transmission modes;

g) support for multi-pair operation;

h) provisions for DSL equipment at the remote end of the loop (xTU-R) to propose a common mode of operation (new in version 2 of the Recommendation through the use of new message type MP and its associated transactions);

i) support for a re-transmission mechanism (new in version 3 of the Recommendation through the use of new message type REQ-RTX).

j) support for exchanging the relative transmit and receive level of individual carriers in order to estimate loop characteristics.