Overview

A substantial amount of information has to be exchanged between the CO-modem and a CPE-modem before an EFM Copper link can be brought into a mode where it can transport user data. This is accomplished by means of different initialization mechanisms. The actual sequence of events is different for 2BASE-TL and 10PASS-TS, but both rely on handshaking as described in ITU-T Recommendation G.994.1 to start initialization.

ITU-T Recommendation G.994.1 specifies handshaking procedures for xDSL transceivers. These procedures allow for an exchange of essential initialization information between an xTU-O and an xTU-R transceiver, prior to the establishment of an end-to-end data link. The EFM PHYs for point-to-point copper are based on xDSL, and therefore use the same handshaking procedures with different codepoints.

Handshake messages are exchanged by modulating certain sets of carriers, belonging either to the 4 kHz carrier family (used by SHDSL and QAM-VDSL) or the 4.3125 kHz carrier family (used by all DMT-based xDSL systems). For each of the different xDSL transceivers standardized by ITU-T, there is a mandatory minimum carrier set to be used for handshaking, but use of other additional carrier sets is encouraged. Using additional carrier sets allows detection of other xDSL flavors on the link, which can yield useful troubleshooting information, even when the peer in the handshaking transaction is not an interoperable xDSL flavor. The carrier sets used for EFM PHYs are shown in Table 3.5.