DiffServ

ENTC 345Dr. Ana GoulartAssistant Professor

Announcement

Homework#6 due next Monday

Announcements

Syllabus Course Topics

Network Simulation – Introduction to Opnet Protocol Architecture Wide Area Networks –Frame Relay Local Area Networks

Ethernet WLANs

Internet and Transport Protocols Quality of Service Architectures Internet Applications – Multimedia and Internet Telephony

Announcements

Today (Monday)Quality of Service (Ch. 19)

WFQ with different weights DS codepoint (TOS byte)

Voice-over-IP (Ch. 24)Reminder – Throughput calculation of WLANs

Generalized Processor Sharing (GPS) WFQ calculates the finish number for each packet as if it

was served by GPS, and then use this finish number to order the service of packets.

schedulerN ConnectionsEqual weights

Bandwidth

1N

Bandwidth to eachConnection

Generalized Processor Sharing (GPS) For different weights:

scheduler

w1

Bandwidth

Scheduler servers an infinitesimal from each connection in turn.

w2

wn

Queue with weight w1 will have afraction equal to w1/(Σi wi) of the total bandwidth of the outgoing link.

Computing finish numbers

Packet size/weight + the greater ofThe finish number of the previous packet in

the same queueThe current round number

F(i, k, t) = P(i, K, t) + max { F(i, k-1, t) , R(t) }

i = connection identifierk = packet identifiert = time t

wi

Weighted Fair Queuing Example (1st part) Assume a WFQ Scheduler with 3 queues

(connections) wA = 1, wB=2, wC= 1 Packets of size 1, 2, and 2 units arrive at

time 0 on connections A, B, and C. The link rate is 1.0 unit/second Initialize the system with R(t) = 0.

WFQ Example – t = 0

A (1) B (2) C(1)

Time Connections Round Finish #

Rem. Finish # Rem. Finish # Rem.

T=0 3 0 1 1 1 2 2 2

WFQ Example – t = 1

A B C

Time Connections Round Finish #

Rem. Finish # Rem. Finish # Rem.

T=0 3 0 1 1 1 2 2 2

T=1 3 0.25 1 0.75 1 1.5 2 1.75

WFQ Example – t = 2

A B C

Time Connections Round Finish #

Rem. Finish # Rem. Finish # Rem.

T=0 3 0 1 1 1 2 2 2

T=1 3 0.25 1 0.75 1 1.5 2 1.75

T=2 3 0.5 1 0.5 1 1 2 1.5

WFQ Example – t = 3

A B C

Time Connections Round Finish #

Rem. Finish # Rem. Finish # Rem.

T=0 3 0 1 1 1 2 2 2

T=1 3 0.25 1 0.75 1 1.5 2 1.75

T=2 3 0.5 1 0.5 1 1 2 1.5

T=3 3 0.75 1 0.25 1 0.5 2 1.25

WFQ Example – t = 4

A B C

Time Connections Round Finish #

Rem. Finish # Rem. Finish # Rem.

T=0 3 0 1 1 1 2 2 2

T=1 3 0.25 1 0.75 1 1.5 2 1.75

T=2 3 0.5 1 0.5 1 1 2 1.5

T=3 3 0.75 1 0.25 1 0.5 2 1.25

T=4 3 1 1 0 1 0 2 1

WFQ Example – t = 4

A B C

Time Connections Round Finish #

Rem. Finish # Rem. Finish # Rem.

T=0 3 0 1 1 2 2 2 2

T=4 3 1 1 0* 1 0* 2 1

After 4 units of time, each connection has received 4*0.25 = 1 units of service.

That is enough service for the first and second packets to depart, but onlyhalf enough for connection C.

WFQ Example – t = 5

A B C

Time Connections Round Finish #

Rem. Finish # Rem. Finish # Rem.

T=0 3 0 1 1 2 2 2 2

T=4 3 1 1 0* 1 0* 2 1

T=5 1 2 1 0* 1 0* 2 0*

Actual delivery times

Note the finish numbers are not the times when the packets complete service.

The first packet to be serviced is packet 1 from A or packet 1 from B. Assume scheduler chooses to deliver packet from B. Service is completed at time 2.

The second packet to be serviced is packet from A, which completes at time 3.

The third packet to be serviced is packet from C, which completes at time 5.

B B A C C

T=5

Differentiated Services

Differentiated Services - Overview IP packets are labeled using the DS

field (or TOS – Type of Service field) All traffic with the same DS octet is

treated the same by the network service

VERS HLEN TOTAL LENGTH

0 4 8 16 19 24 31

IDENTIFICATION FLAGS FRAGMENT OFFSET

TIME TO LIVE PROTOCOL HEADER CHECKSUM

SOURCE IP ADDRESS

DESTINATION IP ADDRESS

PADDINGIP OPTIONS (IF ANY)

DATA

SERVICE TYPE

…

IP Header - originally

IP Header

Service type TOS byte – Type of service

D T R

3 1(Unused

bit)Precedence higher => better service

routers don’t look atthese bits (DTRM)

•DS (Differentiated Services) octet

M

IPv4 Precedence Service

IPv4 TOS field included subfields precedence (3 bit) - datagram urgency/priorityTOS(4 bit) - guidance on selecting next hop

D T R

3 1(Unused

bit)Precedence higher => better service

M

IPv4 Precedence Service

IPv4 TOS field included subfields precedence (3 bit) - datagram urgency/priorityTOS(4 bit) - guidance on selecting next hop

D T R

3 1(Unused

bit)Precedence higher => better service

M

Precedence: 111 – Network Control 110 – Internetwork control 101 – Critical 100 – Flash Override … 000 - Routine

Recommended values for TOS field

Application Minimize delay

Maximize throughput

Maximize

reliability

Minimize

Monetary cost

Telnet 1 0 0 0

FTP - data 0 1 0 0

TFTP 1 0 0 0

DNS (UDP) 1 0 0 0

SNMP 0 0 1 0

NNTP 0 0 0 1

However, most routers do not look at those bits.

Differentiated Services

Routers deal with each packet individually and do not have to save state information on packet flows -> per-hop behavior (phb)

Services (specified in TOS bits): Expedited Forwarding PHBAssured Forwarding PHB

DS Field (6 bits) Keeps compatibility with originalprecedence bits

Differentiated Services Domains

DS Configuration and Operation

within domain, interpretation of DS code points is uniform

interior nodes implement simple mechanisms per-hop behavior (PHB) on all routers

boundary nodes have PHB & more sophisticated mechanisms hence most of complexity

DS Traffic Conditioner