DiffServ

1
DiffServ

• ENTC 345
• Dr. Ana Goulart
• Assistant Professor

2
Announcement

• Homework6 due next Monday

3
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

4
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

5
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.

Bandwidth
scheduler
N Connections Equal weights
1 N
Bandwidth to each Connection
6
Generalized Processor Sharing (GPS)

• For different weights

w1
Bandwidth
w2
scheduler
Queue with weight w1 will have a fraction equal
to w1/(Si wi) of the total bandwidth of the
outgoing link.
wn
Scheduler servers an infinitesimal from each
connection in turn.
7
Computing finish numbers

• Packet size/weight the greater of
• The finish number of the previous packet in the
  same queue
• The current round number

F(i, k, t) P(i, K, t) max F(i, k-1, t) ,
R(t)
wi
i connection identifier k packet identifier t
time t
8
Weighted Fair Queuing Example (1st part)

• Assume a WFQ Scheduler with 3 queues
  (connections)
• wA 1, wB2, 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.

9
WFQ Example t 0
A (1) B (2) C(1)
Time Connections Round Finish Rem. Finish Rem. Finish Rem.
T0 3 0 1 1 1 2 2 2
10
WFQ Example t 1
A B C
Time Connections Round Finish Rem. Finish Rem. Finish Rem.
T0 3 0 1 1 1 2 2 2
T1 3 0.25 1 0.75 1 1.5 2 1.75
11
WFQ Example t 2
A B C
Time Connections Round Finish Rem. Finish Rem. Finish Rem.
T0 3 0 1 1 1 2 2 2
T1 3 0.25 1 0.75 1 1.5 2 1.75
T2 3 0.5 1 0.5 1 1 2 1.5
12
WFQ Example t 3
A B C
Time Connections Round Finish Rem. Finish Rem. Finish Rem.
T0 3 0 1 1 1 2 2 2
T1 3 0.25 1 0.75 1 1.5 2 1.75
T2 3 0.5 1 0.5 1 1 2 1.5
T3 3 0.75 1 0.25 1 0.5 2 1.25
13
WFQ Example t 4
A B C
Time Connections Round Finish Rem. Finish Rem. Finish Rem.
T0 3 0 1 1 1 2 2 2
T1 3 0.25 1 0.75 1 1.5 2 1.75
T2 3 0.5 1 0.5 1 1 2 1.5
T3 3 0.75 1 0.25 1 0.5 2 1.25
T4 3 1 1 0 1 0 2 1
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WFQ Example t 4
A B C
Time Connections Round Finish Rem. Finish Rem. Finish Rem.
T0 3 0 1 1 2 2 2 2
T4 3 1 1 0 1 0 2 1
After 4 units of time, each connection has
received 40.25 1 units of service. That is
enough service for the first and second packets
to depart, but only half enough for connection C.
15
WFQ Example t 5
A B C
Time Connections Round Finish Rem. Finish Rem. Finish Rem.
T0 3 0 1 1 2 2 2 2
T4 3 1 1 0 1 0 2 1
T5 1 2 1 0 1 0 2 0
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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
T5
17
Differentiated Services
18
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

19
IP Header - originally
0
4
8
16
19
24
31
SERVICE TYPE
HLEN

TOTAL LENGTH
VERS
FLAGS
FRAGMENT OFFSET
IDENTIFICATION
TIME TO LIVE
PROTOCOL
HEADER CHECKSUM
SOURCE IP ADDRESS
DESTINATION IP ADDRESS
PADDING
IP OPTIONS (IF ANY)
DATA

20
IP Header

• Service type
• TOS byte Type of service

routers dont look at these bits (DTRM)
D
T
R
M
3
1 (Unused bit)
Precedence higher gt better service

• DS (Differentiated Services) octet

21
IPv4 Precedence Service

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

D
T
R
M
3
1 (Unused bit)
Precedence higher gt better service
22
IPv4 Precedence Service

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

D
T
R
M
3
1 (Unused bit)
Precedence higher gt better service
Precedence 111 Network Control
110 Internetwork control
101 Critical 100
Flash Override
000 - Routine
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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.
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Differentiated Services

• Routers deal with each packet individually and do
  not have to save state information on packet
  flows -gt per-hop behavior (phb)
• Services (specified in TOS bits)
• Expedited Forwarding PHB
• Assured Forwarding PHB

25
DS Field (6 bits)
Keeps compatibility with original precedence bits
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Differentiated Services Domains
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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

28
DS Traffic Conditioner