Queuing Mechanisms Objectives

Weight in WFQ Scheduling

• Flow with P=001

• Flow with P=000

• WFQ System (Real-Size Packets)

• 1

• 1

• 2

• 2

• 3

• Flow with P=001

• Flow with P=000

• WFQ System (Virtual-Size Packets)

• 1

• 1

• 2

• 2

• 3

• Precedence-1 packets appear half the real size.

• Hardware FIFO Queue

• 1

• 2

• 3

• 1

• 2

• 3

• 4

• 3

• Precedence-1 flow gets twice as much bandwidth as Precedence-0 flow.

• Virtual Packet Size = Real Packet Size / (IP Precedence + 1)

Weighted Fair Queuing Finish Time Calculation

• If Flow F Active, Then FT(Pk+1) = FT(Pk) + Size(Pk+1)/(IPPrec+1) Otherwise FT(P0) = Now + Size(P0)/(IPPrec+1)

• If Flow F active, then FT(Pk+1) = FT(Pk) + Size(Pk+1)*4096/(IPPrec+1) otherwise FT(P0) = Now + Size(P0)*4096/(IPPrec+1)

• The finish time is adjusted based on the IP precedence of the packet.

• IOS implementation scales the finish time to allow integer arithmetic.

• RSVP packets and high-priority internal packets (PAK-Priority) have special weights (4 and 128).

IP Precedence to Weight Mapping

• RSVP packets and high-priority internal packets (PAK-Priority) have special weights (4 and 128).
• Lower weight makes packets appear smaller (preferred).

• 1024 (virtual IP Precedence)

• 32 (virtual IP Precedence)

• 7

• 6

• 5

• 4

• 3

• 2

• 1

• 0

• IP Precedence

• 4 (RSVP)

• 128 (PAK-Priority)

• 512

• 585

• 682

• 819

• 1024

• 1365

• 2048

• 4096

• Weight