ECE 4436A & 9303
NETWORKING: PRINCIPLES, PROTOCOLS, AND
ARCHITECTURES
DR. ABDALLAH SHAMI
September 13th, 2019
Department of Electrical and Computer Engineering
University of Western Ontario
SLIDES ADAPTED FROM KUROSE AND ROSS NOTES PROVIDED THROUGH PUBLISHER. THE AUTHOR’S AND PUBLISHER’S
COPYRIGHT HOLDS THROUGHOUT.
CHAPTER 1: ROADMAP
1.1 what is the Internet?
1.2 network edge
 end systems, access networks, links
1.3 network core
 packet switching, circuit switching, network structure
1.4 delay, loss, throughput in networks
1.5 protocol layers, service models
1.6 networks under attack: security
1.7 history
2
HOW DO LOSS AND DELAY OCCUR?
packets queue in router buffers
 packet arrival rate to link (temporarily) exceeds output link capacity
 packets queue, wait for turn
packet being transmitted (delay)
Edge devices (user)
A
Routers
(core network devices)
Packets
B
packets queueing (delay)
free (available) buffers: arriving packets
dropped (loss) if no free buffers
3
THE FOUR SOURCES OF PACKET DELAY
transmission
A
propagation
dproc: nodal
processing
dqueue:
queueing
delay
dprop:
propagation
delay:
dtrans:
transmission
delay:
place
at in
each
node
i.e.
router
Takes
Takes
place
medium
of transmission
thethe
output
of the
node
 Air,
electric
cable,
or
fiber optic
cable etc.
check
bit
errors

After
processing
done
 The
time
taken
toisconvert
the packet
intospeed
energy
signals
compatible
 information
s:
(~2x108
m/sec)
determine
output
link (path)
to being
use with

Is propagation
the totalwhich
time
spent
waiting
before
the
transmission
mediums
discussed
earlier
allowed
onto
the
output
link
for
transmission
 d:
of<<
physical
link
Is length
typically
1 msec
 electrical ,light, radio, micro waves.
 Packet resides inside router memory known as
 dprop = d/s
 L:the
packet
bufferlength (bits)
 R:
link bandwidth
(bps) level of router

depends
on congestion
 dtrans = L/R
B
nodal
processing
queueing
dnodal = dproc + dqueue + dtrans + dprop
4
THE FOUR SOURCES OF PACKET DELAY
 Q. The length of wire that a packet must travel impacts which of the four delays?

A. Processing

B. Queueing

C. Transmission

D. Propagation
5
THE FOUR SOURCES OF PACKET DELAY
 Q. The time it takes a router to ascertain which path to place a packet on is considered a part of which delay?

A. Processing

B. Queueing

C. Transmission

D. Propagation
6
QUEUEING DELAY (REVISITED)
 R: link bandwidth (bps)
 a: average packet arrival rate
 La/R ~ 0: avg. queueing delay small
 La/R -> 1: avg. queueing delay large
 La/R > 1: more “work” arriving than
can be serviced, average delay infinite!
La/R ~ 0
average queueing
delay
 L: packet length (bits)
traffic intensity
= La/R
La/R -> 1
7
PACKET LOSS
 queue (aka buffer) preceding link in buffer has finite capacity
 packet arriving to full queue dropped (aka lost)
 lost packet may be retransmitted by previous node, by source end system, or not at
all
8
THROUGHPUT
 throughput: rate (bits/time unit) at which bits transferred between sender/receiver
 instantaneous: rate at given point in time
 average: rate over longer period of time
server,
withbits
server
sends
file of into
F bitspipe
(fluid)
to send to client
linkpipe
capacity
that can carry
Rs bits/sec
fluid at rate
Rs bits/sec)
linkpipe
capacity
that can carry
Rc bits/sec
fluid at rate
Rc bits/sec)
9
THROUGHPUT
 Rs < Rc What is average end-end throughput?
Rs bits/sec
Rc bits/sec
 Rs > Rc What is average end-end throughput?
Rs bits/sec
Rc bits/sec
10
THROUGHPUT
 Rs < Rc What is average end-end throughput?
Rs bits/sec
Rc bits/sec
 Rs > Rc What is average end-end throughput?
Rs bits/sec
Rc bits/sec
bottleneck link
link on end-end path that constrains end-end throughput
11
THROUGHPUT: INTERNET SCENARIO
10 connections (fairly) share
backbone bottleneck link R bits/sec
Rs
Rs
Rs
R
 per-connection end-end throughput:
min(Rc ,Rs,R/10)
Rc
Rc
Rc
 in practice: Rc or Rs is often bottleneck
12
THROUGHPUT
3 b/sec
 Pinpoint the bottleneck in the following
network.
2 b/sec
4 b/sec
6 b/sec
1 b/sec
3 b/sec
2 b/sec
13