ELEC 6851-

Introduction to Telecommunication Networks

Concordia University

Chadi Assi
EV9.179
 Text books

n “Communication Networks: Fundamental

Concepts and Key Architectures” by Alberto
Leon-Garcia and Indra Widjaja

n Wireless Communications & Networks, 2/E Pearson

Higher Education, (W. Stallings)
 Course outline
§ Introduction to Computer networks
§ Transport Layer (Principles of error detection and control ,
principles of Flow and congestion control, TCP)
§ Network Layer (forwarding, switching, routing, addressing and
internetworking, SDN, etc.)
§ Link Layer (Error detection and control, Access methods:
deterministic and random, Aloha and S-Aloha,
CSMA/CD, Ethernet, STP protocol)
§ Wireless and cellular communication (Cellular, Mobile IP,
Wireless LANs, MAC modeling, IEEE 802.11)
 Course outline

§ Chadi Assi, chadi.assi@concordia.ca

• Office : EV 9.179
• Office Phone: 5799
• Office Hours : Thursday 4PM-5:30PM

§ Marking Scheme:
o Midterm 20%
o Final 50%
o Project 30%

§ More info: ENCS Moodle

Chapter 1
Introduction

All material copyright 1996-2016

J.F Kurose and K.W. Ross, All Rights Reserved

Introduction 1-5
Chapter 1: introduction
overview:
§ what’s the Internet?
§ what’s a protocol?
§ network edge; hosts, access net, physical media
§ network core: packet/circuit switching, Internet structure
§ performance: loss, delay, throughput
§ security
§ protocol layers, service models
§ history

Introduction 1-6
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

Introduction 1-7
 Area T
(1
IoE Hyper-HSR

Where are we heading umMTC

Space Travel

LDHMC
(a)

Peak Data Rate User-Experienced

(Tb/s) Data Rate (Gb/s)

≥1
1
IMT-2030 (6G)
0.1 0.1
Area Traffic Capacity
(Gb/s/m2) 0.02
Spectrum
1
Efficiency
0.1 5×
0.01 1x

1×
10×
100× 500
Mobility
Network Energy ≥1,000 (km/h)
Efficiency IMT-2020 (5G)
106 1

107 0.01–0.1

Connectivity Density Latency (ms)

(Devices/km2)
(b) Introduction 1-18
 1.1 • WHAT IS THE INTERN

1.1 • WHAT IS THE INTERNET? 3

What’s the Internet: “nuts and bolts” view National or

Global ISP

National or

§ billions of connected Global ISP

computing devices: Mobile Network

Mobile Network Datacenter Network

• hosts = end systems Datacenter Network

• running network apps

Datacenter Network

§ communication links Datacenter Network

• fiber, copper, radio, Local or

satellite Home Network

Home Network
Local or
Regional ISP
Regional ISP
Content Provider Network
Content Provider Network

• transmission rate:
bandwidth

§ packet switches: forward

packets (chunks of data) Key:
Key:
Enterprise Network
Enterprise Network

• routers and switches

Host Host
Server Server
Mobile Mobile Link-layer
Router Router Base
Link-layerSmartphone
Base Smartphone
Cell phone Cell phone
(= end system)Computer
(= end system) Computer switch switch or station
station tablet or tablet
tower tower

WorkstationWorkstation
Datacenter Datacenter Traffic light Traffic light
Thermostat Thermostat
Fridge Fridge Introduction 1-8
 1.1 • WHA

1.1 • WHAT IS THE INTE

What’s the Internet: “nuts and bolts” view National or

Global ISP

National or
Global ISP

§ Internet: “network of
Mobile Network

Datacenter Netw
networks”
Mobile Network

Datacenter Network

• Interconnected ISPs
§ protocols control sending,
receiving of messages
Datacenter Netw

Datacenter Network

• e.g., TCP, IP, HTTP, Skype, Local or

802.11 Home Network
Home Network
Local or
Regional ISP
Content Provider Network
Regional ISP

§ Internet standards
Content Provider Network

• RFC: Request for

comments
• IETF: Internet Engineering
Task Force Enterprise Network
Enterprise Network
Key:
Key:

Host Host
Server Server
Mobile Mobile Link-layer
Router Router Base
Link-layerSmartphone
Base Smartphone
Cell phone Cell phone
(= end system)Computer
(= end system) Computer switch switch or station
station tablet or tablet
tower tower

WorkstationWorkstation
Datacenter Datacenter Traffic light Traffic light
Thermostat Thermostat
Fridge Fridge Introduction 1-19
 1.1 • WHA

What’s the Internet: a service view

1.1 • WHAT IS THE INTE

National or
Global ISP

National or
Global ISP

Mobile Network

§ infrastructure that provides Mobile Network Datacenter Netw

services to applications: Datacenter Network

• Web, VoIP, email, games, e-

commerce, social nets, … Datacenter Netw

Datacenter Network

§ provides programming Local or

interface to apps
Home Network Regional ISP
Local or Content Provider Network
Home Network Regional ISP
Content Provider Network

• hooks that allow sending

and receiving app programs
to “connect” to Internet
• provides service options, Enterprise Network

analogous to postal service

Enterprise Network
Key:
Key:

Host Host
Server Server
Mobile Mobile Link-layer
Router Router Base
Link-layerSmartphone
Base Smartphone
Cell phone Cell phone
(= end system)Computer
(= end system) Computer switch switch or station
station tablet or tablet
tower tower

WorkstationWorkstation
Datacenter Datacenter Traffic light Traffic light
Thermostat Thermostat
Fridge Fridge Introduction 1-20
What’s a protocol?
human protocols: network protocols:
§ “what’s the time?” § machines rather than
§ “I have a question” humans
§ introductions § all communication activity
in Internet governed by
… specific messages sent protocols
… specific actions taken
when messages protocols define format, order of
received, or other
events messages sent and received
among network entities, and
actions taken on message
transmission, receipt
Introduction 1-21
What’s a protocol?
a human protocol and a computer network protocol:

Hi TCP connection
request
Hi TCP connection
response
Got the
time? Get http://www.awl.com/kurose-ross
2:00
<file>
time

Introduction 1-22
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

Introduction 1-23
 1.1 • WHA

1.1 • WHAT IS THE INTE

A closer look at network structure: National or

Global ISP

National or
Global ISP

§ network edge: WAT Mobile Network

• hosts: clients and servers

Mobile Network Datacenter Netw

Datacenter Network

• servers often in data

centers Datacenter Netw

§ access networks, physical

Datacenter Network

media: wired, wireless

Local or
Home Network Regional ISP
Local or Content Provider Network
Home Network Regional ISP

communication links
Content Provider Network

Router
Switch
Server

§ network core:
• interconnected routers
Enterprise Network
Enterprise Network
Key:
Key:

• network of networks
Host Host
Server Server
Mobile Mobile Link-layer
Router Router Base
Link-layerSmartphone
Base Smartphone
Cell phone Cell phone
(= end system)Computer
(= end system) Computer switch switch or station
station tablet or tablet
tower tower

WorkstationWorkstation
Datacenter Datacenter Traffic light Traffic light
Thermostat Thermostat
Fridge Fridge Introduction 1-24
 1.1 • WHA

1.1 • WHAT IS THE INTE

Access networks and physical media National or

Global ISP

National or
Global ISP

Q: How to connect end Mobile Network

systems to edge router? Mobile Network Datacenter Netw

Datacenter Network

§ residential access nets

§ institutional access Datacenter Netw
networks (school, company) Datacenter Network

§ mobile access networks Home Network

Local or
Regional ISP
Local or Content Provider Network
Home Network Regional ISP

keep in mind:
Content Provider Network

§ bandwidth (bits per second)

of access network?
§ shared or dedicated?
Enterprise Network
Enterprise Network
Key:
Key:

Host Host
Server Server
Mobile Mobile Link-layer
Router Router Base
Link-layerSmartphone
Base Smartphone
Cell phone Cell phone
(= end system)Computer
(= end system) Computer switch switch or station
station tablet or tablet
tower tower

WorkstationWorkstation
Datacenter Datacenter Traffic light Traffic light
Thermostat Thermostat
Fridge Fridge Introduction 1-25
Access network: digital subscriber line (DSL)
central office telephone
network

DSL splitter
modem DSLAM

ISP
voice, data transmitted
at different frequencies over DSL access
dedicated line to central office multiplexer

§ use existing telephone line to central office DSLAM

• data over DSL phone line goes to Internet
• voice over DSL phone line goes to telephone net
§ < 2.5 Mbps upstream transmission rate (typically < 1 Mbps)
§ < 24 Mbps downstream transmission rate (typically < 10 Mbps)
§ Rates may vary with the standard used.
Introduction 1-26
§ Rates vary with distance (~5-10 Miles)
Access network: cable network
cable headend

cable splitter
modem

C
O
V V V V V V N
I I I I I I D D T
D D D D D D A A R
E E E E E E T T O
O O O O O O A A L

1 2 3 4 5 6 7 8 9

Channels

frequency division multiplexing: different channels transmitted

in different frequency bands
Introduction 1-27
 1.6, fiber optics connect the cable head end to neighborhood-level junctions, from which traditional
coaxial cable is then used to reach individual houses and apartments. Each neighborhood junction

Access network: cable network

typically supports 500 to 5,000 homes. Because both fiber and coaxial cable are employed in this
system, it is often referred to as hybrid fiber coax (HFC).

cable headend

cable splitter cable modem

modem CMTS termination system

data, TV transmitted at different

frequencies over shared cable ISP
distribution network

§ HFC: hybrid fiber coax

• asymmetric: up to 30Mbps downstream transmission rate, 2
Figure 1.6 A hybrid fiber-coaxial access network
Mbps upstream transmission rate
§ network of cable, fiber attaches homes to ISP router
Cable internet access requires special modems, called cable modems. As with a DSL modem, the cable
• homes share access network to cable headend
• unlike DSL, which has dedicated access to central office
Introduction 1-28
Access network: FTTH

Figure 1.7 FTTH Internet access

§ FTTH Internet Access

Uponto
than• 100) toa single,
Gbpsshared rates (with
optical typical
fiber, which average
connects rates
to an optical of 20Mbps
line terminator or
(OLT) in the

more)
telco’s CO. The OLT, providing conversion between optical and electrical signals, connects to the
Internet via a telco router. In the home, users connect a home router (typically a wireless router) to the
PON,
§ ONT EPON,
and access GPON,
the Internet LR-PON,
via this home etc.
router. In the PON architecture, all packets sent from OLT
to the splitter are replicated at the splitter (similar to a cable head end).

FTTH can potentially provide Internet access rates in the gigabits per second range. However, most
Introduction 1-29
 Access network: typical home network
wireless
devices

to/from headend or
central office
often combined
in single box

cable or DSL modem

Address
wireless access router, firewall, NAT Network
point (54 Mbps) Translation
wired Ethernet (1 Gbps)

Introduction 1-30
Enterprise access networks (Ethernet)

institutional link to
ISP (Internet)
institutional router

Ethernet institutional mail,

switch web servers

Cach Hit Rate

§ typically used in companies, universities, etc.

§ 10 Mbps, 100Mbps, 1Gbps, 10Gbps transmission rates
§ today, end systems typically connect into Ethernet switch

Introduction 1-31
 & [
Interne
Mombps
X

·
Enter a
Interneti
Total Delay
>

delay
OI
E
request Access Delay
8
.

each LEN Delay

Request
Cashing Example Imbits

15 request/see
I
requests 1 Mbit ! "
Loud
oig
IS * 1Mbit =
15 Mbps
Loud on access link : ups-1 delay High
15Mbps
Load on Enterprise Network
= 0 .
15
delay
wo
When Cash Added 60 % goes through Access
Link
0 60 * 15 9 Mbit/se
. *
1 Mbps =

Load on access link ps = 0 6

.

15Mbps
Wireless access networks
§ shared wireless access network connects end system to router
• via base station aka “access point”

wireless LANs: wide-area wireless access

§ within building (100 ft.) § provided by telco (cellular)
§ 802.11b/g/n (WiFi): 11, 54, 450 operator, 10’s km
Mbps transmission rate § between 1 and 10 Mbps
§ 3G, 4G: LTE

to Internet

to Internet

Introduction 1-32
Host: sends packets of data
host sending function:
§ takes application message
§ breaks into smaller two packets,
chunks, known as packets, L bits each
of length L bits
§ transmits packet into
access network at 2 1
transmission rate R R: link transmission rate
• link transmission rate, host
aka link capacity, aka
link bandwidth

packet time needed to L (bits)

transmission = transmit L-bit =
delay packet into link R (bits/sec)
Introduction 1-33
Physical media
§ bit: propagates between
transmitter/receiver pairs
§ physical link: what lies twisted pair (TP)
between transmitter & § two insulated copper
receiver wires
§ guided media: • Category 5: 100 Mbps, 1
Gbps Ethernet
• signals propagate in solid • Category 6: 10Gbps
media: copper, fiber, coax
§ unguided media:
• signals propagate freely,
e.g., radio

Introduction 1-34
Physical media: coax, fiber
coaxial cable: fiber optic cable:
§ two concentric copper § glass fiber carrying light
conductors pulses, each pulse a bit
§ Bidirectional § high-speed operation:
§ Common in cable TV • high-speed point-to-point
transmission (e.g., 10’s-100’s
§ broadband: Gbps transmission rate)
• multiple channels on cable
§ low error rate:
• HFC
• repeaters spaced far apart
• immune to electromagnetic
noise

Introduction 1-35
Physical media: radio
§ signal carried in radio link types:
electromagnetic spectrum § terrestrial microwave
§ no physical “wire” • e.g. up to 45 Mbps channels
§ bidirectional § LAN (e.g., WiFi)
§ propagation environment • 54 Mbps
effects: § wide-area (e.g., cellular)
• reflection • 4G cellular: ~ 10 Mbps
• obstruction by objects • 5G: 100MBps-2GBps?
• 6G? 1Tbps
• interference
§ satellite
• Kbps to 45Mbps channel (or
multiple smaller channels)
• 270 msec end-end delay
• geosynchronous versus low
altitude
Introduction 1-36
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

Introduction 1-37
The network core
§ mesh of interconnected
routers
§ packet-switching: hosts
break application-layer
messages into packets
• forward packets from one
router to the next, across
links on path from source
to destination
• each packet transmitted at
full link capacity

Introduction 1-38
Packet-switching: store-and-forward
At what time will the
third packet arrive at
the destination?
L bits
per packet

3 2 1
source destination
R bps R bps

§ takes L/R seconds to transmit one-hop numerical example:

(push out) L-bit packet into
link at R bps § L = 7.5 Mbits
§ store and forward: entire § R = 1.5 Mbps
packet must arrive at router § one-hop transmission
before it can be transmitted delay = 5 sec
on next link
§ end-end delay = 2L/R (assuming
zero propagation delay) more on delay shortly …
Introduction 1-39
Packet Switching: queueing delay, loss

R = 100 Mb/s C
A
D
R = 1.5 Mb/s
B
E
/queing
queue of packets
waiting for output link

queuing and loss:

§ if arrival rate (in bits) to link exceeds transmission rate of link
for a period of time:
• packets will queue, wait to be transmitted on link
• packets can be dropped (lost) if memory (buffer) fills up

Introduction 1-40
 Two key network-core functions
routing: determines source-
destination route taken by forwarding: move packets from
packets router’s input to appropriate
§ routing algorithms router output

routing algorithm

local forwarding table

header value output link
0100 3 1
0101 2
0111 2 3 2
1001 1
1
011

destination address in arriving

packet’s header
Introduction 1-41
Alternative core: circuit switching
end-end resources allocated
to, reserved for “call”
between source & dest:
§ in diagram, each link has four
circuits.
• call gets 2nd circuit in top
link and 1st circuit in right
link.
§ dedicated resources: no sharing
• circuit-like (guaranteed)
performance
§ circuit segment idle if not used
by call (no sharing)
§ commonly used in traditional
telephone networks
Introduction 1-42
Circuit switching: FDM versus TDM
Example:
FDM
4 users

frequency

time
TDM

frequency

time
Introduction 1-43
 Packet switching versus circuit switching
packet switching allows more users to use network!

example:
§ 1 Mb/s link
§ each user: N

…..
users
• 100 kb/s when “active” new
users usery )
• active 10% of time Ni 33 Inactive Pr
p
-
0
.
- 1 Mbps link

Defining
D -() 0

s up
in
6
I L =
"
Pr 1

Pinc
§ circuit-switching: own
• 10 users
§ packet switching: Q: how did we get value 0.0004?
• with 35 users, probability >
10 active at same time is less Q: what happens if > 35 users ?
than .0004 *
* Check out the online interactive exercises for more examples: http://gaia.cs.umass.edu/kurose_ross/interactive/
Introduction 1-44
Internet structure: network of networks
§ End systems connect to Internet via access ISPs (Internet
Service Providers)
• residential, company and university ISPs
§ Access ISPs in turn must be interconnected.
• so that any two hosts can send packets to each other
§ Resulting network of networks is very complex
• evolution was driven by economics and national policies

Introduction 1-45
Internet structure: network of networks
Question: given millions of access ISPs, how to connect them
together?

… access
net
access
net …
access
net
access
access net
net
access
access net
net
…

…
access access
net net

access
net
access
net

access
net
access
net
… access access …
net access net
net

Introduction 1-46
Internet structure: network of networks
Option: connect each access ISP to every other access ISP?

… access
net
access
net …
access
net
access
access
net
… … net

access
access net
net

connecting each access ISP

…

…
to each other directly doesn’t

…
access access
…

net
scale: O(N2) connections. net

access
net
access
net

access
net
access
…

net
… access access …
net access net
net

Introduction 1-47
Internet structure: network of networks
Option: connect each access ISP to one global transit ISP?
Customer and provider ISPs have economic agreement.
… access
net
access
net …
access
net
access
access net
net
access
access net
net
…

…
global
access
net
ISP access
net

access
net
access
net

access
net
access
net
… access access …
net access net
net

Introduction 1-48
Internet structure: network of networks
But if one global ISP is viable business, there will be competitors
….

… access
net
access
net …
access
net
access
access net
net
access
access net
net
ISP A
…

…
access
net ISP B access
net

access
net
ISP C
access
net

access
net
access
net
… access access …
net access net
net

Introduction 1-49
Internet structure: network of networks
But if one global ISP is viable business, there will be competitors
…. which must be interconnected
Internet exchange point
…
access access
net net …
access
net
access
access net
net

access
IXP access
net
net
ISP A
…

…
access
net
IXP ISP B access
net

access
net
ISP C
access
net

access peering link

net
access
net
… access access …
net access net
net

Introduction 1-50
Internet structure: network of networks
… and regional networks may arise to connect access nets to
ISPs

… access
net
access
net …
access
net
access
access net
net

access
IXP access
net
net
ISP A
…

…
access
net
IXP ISP B access
net

access
net
ISP C
access
net

access
net regional net
access
net
… access access …
net access net
net

Introduction 1-51
 Internet structure: network of networks
… and content provider networks (e.g., Google, Microsoft,
Akamai) may run their own network, to bring services, content
close to end users
… access
net
access
net …
access

side
net
access
access net
net

access
IXP access
net
net
ISP A
…

…
Content provider network
access
net
IXP ISP B access
net

access
net
ISP C
access
net

access
net regional net
access
net
… access access …
net access net
net

Introduction 1-52
Internet structure: network of networks

Tier 1 ISP Tier 1 ISP Google

IXP IXP IXP

Regional ISP Regional ISP

access access access access access access access access

ISP ISP ISP ISP ISP ISP ISP ISP

§ at center: small # of well-connected large networks

• “tier-1” commercial ISPs (e.g., Level 3, Sprint, AT&T, NTT), national &
international coverage
• content provider network (e.g., Google): private network that connects
it data centers to Internet, often bypassing tier-1, regional ISPs Introduction 1-53
Tier-1 ISP: e.g., Sprint

POP: point-of-presence
to/from backbone

peering
… …
…

to/from customers

Introduction 1-54
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

Introduction 1-55
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)

B
packets queueing (delay)
free (available) buffers: arriving packets
dropped (loss) if no free buffers

Introduction 1-56
Four sources of packet delay
transmission
A propagation

B
nodal
processing queueing

dnodal = dproc + dqueue + dtrans + dprop

dproc: nodal processing dqueue: queueing delay

§ check bit errors § time waiting at output link
§ determine output link for transmission
§ typically < msec § depends on congestion
level of router
Introduction 1-57
Four sources of packet delay
transmission
A propagation

B
nodal
processing queueing

dnodal = dproc + dqueue + dtrans + dprop

dtrans: transmission delay: dprop: propagation delay:

§ L: packet length (bits) § d: length of physical link
§ R: link bandwidth (bps) § s: propagation speed (~2x108 m/sec)
§ dtrans = L/R dtrans and dprop § dprop = d/s
very different
* Check out the online interactive exercises for more examples: http://gaia.cs.umass.edu/kurose_ross/interactive/
* Check out the Java applet for an interactive animation on trans vs. prop delay Introduction 1-58
Caravan analogy
100 km 100 km
ten-car toll toll
caravan booth booth

§ cars “propagate” at § time to “push” entire

100 km/hr caravan through toll
§ toll booth takes 12 sec to booth onto highway =
service car (bit transmission 12*10 = 120 sec
time) § time for last car to
§ car ~ bit; caravan ~ packet propagate from 1st to
§ Q: How long until caravan is 2nd toll both:
lined up before 2nd toll 100km/(100km/hr)= 1
booth? hr
§ A: 62 minutes
Introduction 1-59
Caravan analogy (more)
100 km 100 km
ten-car toll toll
caravan booth booth

§ suppose cars now “propagate” at 1000 km/hr

§ and suppose toll booth now takes one min to service a car
§ Q: Will cars arrive to 2nd booth before all cars serviced at first
booth?
• A: Yes! after 7 min, first car arrives at second booth; three
cars still at first booth

Introduction 1-60
Queueing delay (revisited)

average queueing
§ R: link bandwidth (bps)

delay
§ L: packet length (bits)
§ a: average packet arrival
rate
traffic intensity
= La/R
§ La/R ~ 0: avg. queueing delay small La/R ~ 0

§ La/R -> 1: avg. queueing delay large

§ La/R > 1: more “work” arriving
than can be serviced, average delay infinite!

La/R -> 1
* Check online interactive animation on queuing and loss
Introduction 1-61
Example

§ Consider sending a large file of F bits from Host A to Host B.

There are three links (and two switches) between A and B,
and the links are uncongested (that is, no queuing delays).
Host A segments the file into segments of S bits each and
adds 80 bits of header to each segment, forming packets of
L=80 + S bits. Each link has a transmission rate of R bps.
Find the value of S that minimizes the delay of moving the file
from Host A to Host B. Disregard propagation delay.

S540

Introduction 1-62