The ITU-T has defined a suite of digital subscriber line (DSL) Recommendations that include symmetric and asymmetric DSL transceivers. Each of the DSL Recommendations contains numerous options and capabilities, and before proper operation can begin, the transceivers need to negotiate and agree on a common set of parameters. ITU-T Recommendation G.994.1 defines handshake (HS) procedures for DSL transceivers to exchange transceiver capabilities and to negotiate and select a common mode of operation. Handshake Recommendation G.994.1 (also referred to as G.hs) defines the modulation method, protocol, and messages for exchanging capabilities information and negotiating session configuration. The initial issues of G.hs apply to ADSL and SHDSL systems. We expect that later revisions of G.hs will apply to VDSL when the transmission approach is defined in the ITU-T. This chapter provides an overview of the handshake mechanism defined in G.994.1 [1]. The goal is to provide assistance toward the understanding of the handshake mechanism for DSL systems. We describe the handshake signals and modulation method, initialization and clear-down, the set of commands, message structure, message coding format, and example transaction sequences. |
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