Chapter 14 - QoS

Question 1

802.1Q

Answer 1

An IEEE specification that defines the use of the 3-bit Priority Code Point (PCP) field to provide different classes of service. The PCP field is contained within the TCI field, which is part of the 802.1Q header.

Question 2

802.1p

Answer 2

An IEEE specification that defines the use of the 3-bit Priority Code Point (PCP) field to provide different classes of service. The PCP field is contained within the TCI field, which is part of the 802.1Q header.

Question 3

Differentiated Services (DiffServ)

Answer 3

A field that uses the same 8 bits of the IP header that were previously used for the ToS and IPV6 Traffic Class fields. This allows it to be backward compatible with IP Precedence. The DiffServ field is composed of a 6-bit Differentiated Services Code Point (DSCP) field that allows for classification of up to 64 values (0 to 63) and a 2-bit Explicit Congestion Notification (ECN) field.

Question 4

Differentiated Services Code Point (DSCP)

Answer 4

A 6-bit field within the DiffServ field that allows for classification of up to 64 values (0 to 63).

Question 5

per-hop behavior (PHB)

Answer 5

The QoS action applied to a packet (expediting, delaying, or dropping) on a hop-by-hop basis, based on its DSCP value.

Question 6

Type of Service (TOS)

Answer 6

An 8-bit field where only the first 3 bits, referred to as IP Precedence (IPP), are used for marking, and the rest of the bits are unused. IPP values range from 0 to 7 and allow the traffic to be partitioned into up to six usable classes of service; IPP 6 and 7 are reserved for internal network use.