IEEE 802.3 Auto-Negotiation
Selector Field definitions

Auto-Negotiation Selector Field values are not allocated until a draft Standard reaches the Sponsor Ballot stage.

The Selector Field, S[4:0] in the Link Code Word, is used to identify the type of message being sent by Auto-Negotiation. Table 1 below identifies the types of messages that may be sent. As new messages are developed, this table will be updated accordingly. Note that this table may contain recently assigned values that are in the process of being added to the IEEE802.3 standard.

The Selector Field uses a 5-bit binary encoding, which allows 32 messages to be defined. All unspecified combinations are reserved. Reserved combinations shall not be transmitted.

S4	S3	S2	S1	S0	Selector description
0	0	0	0	0	Reserved for future Auto-Negotiation development
0	0	0	0	1	IEEE Std 802.3
0	0	0	1	0	IEEE Std 802.9 ISLAN-16T
0	0	0	1	1	IEEE Std 802.5
0	0	1	0	0	IEEE Std 1394
0	0	1	0	1	INCITS
0	0	1	1	X	Reserved for future Auto-Negotiation development
0	1	X	X	X	Reserved for future Auto-Negotiation development
1	X	X	X	X	Reserved for future Auto-Negotiation development

Note - In the event of conflict between IEEE Std 802.3 and the table above, the IEEE 802.3 standard contains the normative requirements.