||Residential Broadband Physical Interfaces Specification
||This specification defines physical layer (PHY) interfaces for residential broadband (RBB)
deployment. It references, where appropriate, other standards and specifications.
This specification defines physical layers for the 25.6/51.2 Mb/s Private UNI. Devices
meeting this specification shall be able to operate at the 25.6 Mb/s rate and may also operate
at the 51.2 Mb/s rate. Automatic speed detection of the ATM End System shall be
implemented where the local device has 25.6/51.2 Mb/s capability.
The physical layer is divided into a Physical Media Dependent sublayer (PMD) and a
Transmission Convergence (TC) sublayer. The PMD sublayer provides the specifications
for the transmitter, the receiver, timing recovery, media interface connector and the channel
transmission media. The TC sublayer defines the line coding, scrambling, data framing
and synchronization. This specification defines both a metallic twisted pair and plastic
optical fiber PMD, using a common TC. The TC is based on the one specified in the ATM
Forum specification \"Physical Interface Specification for Twisted Pair Cable\" (af-phy-0040.000)
but with some modifications to improve RF egress. The PMD for metallic
twisted pair is such that components meeting the above specifications will interoperate at
25.6 Mb/s over Category 5 metallic channels of up to 50m length as described in this
specification. Although such interoperability is supported, it is recommended that use of
devices conforming to af-phy-0040.000 is minimized in the home environment, and the
devices used shall normally conform to this specification. Devices conforming to this
specification have improved RF egress characteristics intended to allow coexistence of
home networks with residential activities sensitive to RF egress, such as amateur band and
shortwave radio listening.
The bit rate used throughout this document refers to the logical information rate, before line
coding. The term line symbol rate will be used when referring to the rate after line coding
(25.6 Mb/s bit rate results in a 32 Mbaud line symbol rate after 4B5B encoding, 51.2 Mb/s
bit rate results in a 64 Mbaud line symbol rate after 4B5B encoding).
Within the context of this document, specifications are presented as requirements, denoted
by (R), conditional requirements, denoted by (CR), recommendations, denoted by (REC)
or optional requirements, denoted by (O). In this document requirements are functions that
are necessary for operational compatibility. Conditional requirements are functions that are
necessary for operational compatibility if the stated conditional clause is satisfied
Recommendations are provided as guidelines and usually refer to measurement criteria.
Optional requirements indicate functions, which if implemented, should be according to the
stated methodology for compatibility.