Ethernet

Question 0

List the pin pairs in RJ45 T568B.

Answer 0

Pair 2 = 1, 2
Pair 3 = 3, 6
Pair 1 = 4, 5
Pair 4 = 7, 8

Question 1

List the pin pairs in RJ45 T568A.

Answer 1

Pair 3 = 1, 2
Pair 2 = 3, 6
Pair 1 = 4, 5
Pair 4 = 7, 8

Question 2

What is the maximum length of a 1000BaseSX run using 50 micron multimode fibre?

Answer 2

550m

Question 3

What is the maximum length of a 1000BaseSX run using 62.5 micron multimode fibre?

Answer 3

220m

Question 4

What is the purpose of the 802.3 SNAP header?

Answer 4

It is used by vendors for proprietary protocols (like CDP, VTP etc). By adding the SNAP header to an IEEE 802.3 frame a 3 byte OUI and 2 byte DIX Ethertype can be defined.

When using a SNAP header the 802.2 SSAP and DSAP fields are set to 0xAA and the control field is set to 0x03.

Question 5

What is the main difference between an 802.3 (SAP) frame and a DIX Ethernet II frame?

Answer 5

A DIX frame uses a 2 byte Type field to specify Ethertypes but has no Length field. The 802.3 frame includes a 2 byte Length field and 1 byte SSAP, DSAP, and Control fields. The SAP fields serve the same purpose as the DIX Type field but allow specification of both source and destination types.

Question 6

What types of traffic use 802.3 Ethernet I frames?

Answer 6

Ethernet I frames are used by protocols that require error recovery and flow control at layer 2 such as Netbui and SNA.

Question 7

What type of traffic uses DIX Ethernet II frames?

Answer 7

Protocols that have error recovery and flow control implemented at higher layers such as IP.