Data Sheet

Interconnects—Ethernet Controller I210
93
3.7.3.3.1 8B10B Encoding/Decoding
The GbE PCS circuitry uses the same transmission-coding scheme used in the fiber channel physical
layer specification. The 8B10B-coding scheme was chosen by the standards committee in order to
provide a balanced, continuous stream with sufficient transition density to allow for clock recovery at
the receiving station. There is a 25% overhead for this transmission code, which accounts for the data-
signaling rate of 1250 Mb/s with 1000 Mb/s of actual data.
3.7.3.3.2 Code Groups and Ordered Sets
Code group and ordered set definitions are defined in clause 36 of the IEEE 802.3z standard. These
represent special symbols used in the encapsulation of GbE packets. The following table contains a brief
description of defined ordered sets and included for informational purposes only. Refer to clause 36 of
the IEEE 802.3z specification for more details.
Table 3-23. Brief Description of Defined Ordered Sets
Code Ordered_Set
# of Code
Groups
Usage
/C/ Configuration 4
General reference to configuration ordered sets, either /C1/ or /C2/, which
is used during auto-negotiation to advertise and negotiate link operation
information between link partners. Last 2 code groups contain
configuration base and next page registers.
/C1/ Configuration 1 4
See /C/. Differs from /C2
/
in 2nd code group for maintaining proper
signaling disparity
1
.
1. The concept of running disparity is defined in the standard. In summary, this refers to the 1-0 and 0-1 transitions within 8B10B
code groups.
/C2/ Configuration 2 4
See /C/. Differs from /C1
/
in 2nd code group for maintaining proper
signaling disparity
1
.
/I/ IDLE 2
General reference to idle ordered sets. Idle characters are continually
transmitted by the end stations and are replaced by encapsulated packet
data. The transitions in the idle stream enable the SerDes to maintain
clock and symbol synchronization between link partners.
/I1/ IDLE 1 2
See /I/. Differs from /I2
/
in 2nd code group for maintaining proper
signaling disparity
1
.
/I2/ IDLE 2 2
See /I/. Differs from /I1
/
in 2nd code group for maintaining proper
signaling disparity
1
.
/R/ Carrier_Extend 1
This ordered set is used to indicate carrier extension to the receiving PCS.
It is also used as part of the end_of_packet encapsulation delimiter as well
as IPG for packets in a burst of packets.
/S/ Start_of_Packet 1
The SPD (start_of_packet delimiter) ordered set is used to indicate the
starting boundary of a packet transmission. This symbol replaces the last
byte of the preamble received from the MAC layer.
/T/ End_of_Packet 1
The EPD (end_of_packet delimiter) is comprised of three ordered sets. The
/T/ symbol is always the first of these and indicates the ending boundary
of a packet.
/V/ Error_Propagation 1
The /V/ ordered set is used by the PCS to indicate error propagation
between stations. This is normally intended to be used by repeaters to
indicate collisions.