MAC-PHY Interface for copper PHY

		   Sailesh Rao    SDE Inc.
                 George Eisler    Brooktree Corp.
                     T-J. Shan    Lucent Bell Labs


OBJECTIVES

 o To call for a clear-cut delineation of MAC functionality from 
   PHY functionality.

 o To call for a simple, logical MAC-PHY interface that is independent of the 
   PHY media.

 o To call for sufficient commonality in MAC-PHY interface with 100Base-T 
   to allow for simple 100/1000 copper media designs.


REQUIREMENTS FOR COPPER PHY

 o Copper PHY will not use 8B/10B coding because of the intrinsic 25% data-rate 
   penalty. Hence, MAC functionality should not be defined in the 10B domain, 
   since 8B/10B is a Fiber-PHY-specific feature.

 o Copper PHY will require 
    o at least a 2-byte preamble/SFD for the Start of Packet.
    o at least a 2-byte IPG for EOP
    o Byte-aligned packet data

 o Copper PHY should have sufficient in-band code redundancy for signalling
    o Defer signal during idle
    o Carrier Extension
    o Error Indication 
    o Other potential control code signalling

 o Copper PHY should be Full Duplex capable.


MAC-SPECIFIC FUNCTIONALITY

 o SOP/EOP generation/handling

 o Packet Data generation/handling- assumed to be byte-aligned.

 o Defer bit generation/handling

 o Carrier Extension generation/handling

 o Other control code generation/handling

 o Error Indication generation/handling

 o All of the above are independent of Copper/Fiber media.
   They should be specified/debated without assuming
   8B/10B coding.


PHY SPECIFIC FUNCTIONALITY

 o Capability signalling and negotiation
   o Fiber PHY may do this with C codes
   o Copper PHY may choose to use Clause 28 primitives to be
     compatible with 100Base-T

 o Link Status signalling
   o Fiber PHY may use F codes
   o Copper PHY may use scrambled idle patterns to indicate link 
     OK/NOT_OK

 o Error Propagation Signalling
   o Fiber PHY may use ? codes
   o Copper PHY may use scrambled ESC patterns to propagate Errors

 o Transmission of SOP/EOP 
   o Fiber PHY may use I codes and may require 16-bit word alignment
   o Copper PHY may use scrambled ESC patterns for SOP/EOP

 o Transmission of Data
   o Fiber PHY may use 8B/10B coded 1.25Gb/s serialized data transfer
   o Copper PHY may use scrambled multi-pair multi-level signalling
     without 8B/10B pre-coding.

 o Transmission of Carrier Extension
   o Fiber PHY may use a string of R codes for carrier extension
   o Copper PHY may use scrambled idle patterns for carrier extension


THREE VIEWS OF THE MAC-PHY INTERFACE

    (3 block-diagrams for elucidation)


PROPOSED MAC-PHY INTERFACE 

    Assume Byte-Aligned Data

    Signal        Transmit             Receive
    ------        --------             -------
    Clock          Tx_CLK               Rx_CLK

    Data/
    Control Code   Tx_D[7:0]            Rx_D[7:0]

    Control        Tx_C[1:0]            Rx_C[1:0]
    
   o Allows for 10-bit MAC/PHY interface
 
   o Similar to ANSI FC-10


PROPOSED DEFINITION OF CONTROL CODES
     
    Tx_C[1:0]     Tx_D[7:0]         Interpretation
    Rx_C[1:0]     Rx_D[7:0]     
    ---------     ---------         --------------
      00          XXXXXXXX           Normal Idle
      01          DDDDDDDD           Normal Data
      10          XXXXXXX1           Carrier Extend
      10          XXXXXX10           Defer
      10          ........           Other Control Codes
      11          XXXXXXXX           Error Indication

  o Simple, logical, extensible MAC-PHY interface
  o Easily Backward compatible with 100Base-T MII
  o Easily Compatible with ANSI FC-10 interface


CONCLUSIONS

 o Defined a simple, logical MAC-PHY interface that is independent of the 
   PHY media,

    o To separate MAC functionality from PHY functionality

    o To be backward compatible with 100Base-T to allow 
      for simple 100/1000 copper media designs

    o To avoid having to decipher 10B-speak for understanding 
      common requirements