ENEE 426: Introduction
Richard J. La
Spring 2005
What is a Communication
Network?

Communication network – a set of interconnected
resources that support information transfer between
geographically distributed users


Main function or service is “transfer of information” over
shared communication resources
Examples



Telegraph networks (message)
Telephone networks (voice)
Computer networks (data)
History of Communication
Networks – Telegraph
1.
Telegraph network – transmission of text messages
over long distances

1837 Samuel B. Morse demonstrated a practical
telegraph that provided the basis for telegram service
(most successful version)

Morse code – long and short pulses
e.g. A =
, B=

Precursor of modern digital communication system

Led to development of codes (and information theory)
History of Communication
Networks - Telegraph
1.
Telegraph network (cont’d)

Routing of a message


Message or telegram arrives at a telegraph station
An operator makes a “routing” decision based on the
destination “address”
telegraph
station
telegraph
station
Store-andforward
Message Switching
telegraph
station
History of Communication
Networks - Telephone
2.
Telephone network



Telephone developed in 1876 by Alexander Graham Bell
Used analog transmission system
Requires setting up a connection before transfer of
information can take place (called “circuit switching”)

“connection-oriented”

Reservation of resources

Dedicated end-to-end connection

Routing decision made when the path is set up
History of Communication
Networks - Telephone
2.
Telephone network (cont’d)

With transition to digital transmission and wide-spread user of
computers for control, a separate “signaling network” is introduced

Enables new services

e.g., 800 number services, call forwarding, voicemail, etc.
History of Communication
Networks – Computer Network
3.
Evolution from telephone networks to data networks to
the Internet


1960s – expensive mainframes were time shared by many
users

Tree-topology terminal-oriented networks
With emergence of more intelligent personal computers,
dumb terminals were replaced by intelligent terminals and it
became necessary to develop networks more flexible
connecting many computers

More complex protocols and network topology
History of Communication
Networks – Computer Network
3.
ARPANET



Wanted to develop a resilient and robust communication
network that can tolerate link/node failures (courtesy of Cold
War!)
Kleinrock advocates the use of “packet-switching” over “circuitswitching” for reliability and efficiency (1961)
Leads to ARPANET project (1969)

Beginning of the Internet
SRI
UCSB
UTAH
UCLA – first Interface Message Processor (IMP)
History of Communication
Networks – Computer Network
3. ARPANET (cont’d)
Host-host protocol
Host-IMP
protocol
Host
Source IMP to destination
IMP protocol
Subnet
IMP-IMP
protocol
IMP
History of Communication
Networks – Computer Network
3.
NSFNET (1986)

Created to provide access to NSF-sponsored supercomputing
centers




Serve as a primary backbone linking together regional networks
Used to connect regional networks
Restriction on commercial use lifted in 1991
Privatized and decommissioned in 1995

Private service providers provide backbone service
History of Communication
Networks – Computer Network
Local ISP
Regional ISP
NSP B
Private Peering
NAP
NSP A
Regional ISP
Local ISP
NAP
History of Communication
Networks – Computer Network

Current Internet

Hierarchical structure

End systems connected to local Internet service providers
(ISPs) through access networks



e.g. local area network within a company or university, a dial
telephone line with a modem, or a high-speed cable-based or
phone-based access network
Local ISPs in turn connected to regional ISPs
Regional ISPs connected to national service providers (NSPs)

Can directly connect to network access points (NAPs) as well
History of Communication
Networks – Computer Network

National Service Providers (NSPs)





Form independent backbone networks that span
North American (and extend abroad as well)
internetMCI, SprintLink, etc.
Links ranging from 1.5 Mbps to tera bps
Provides hubs that interconnect its links and at which
regional ISPs can tap into the NSP
NSPs interconnected at switching centers, called
network access points (NAPs)

Many NAPs run by regional Bell operating companies
(RBOCs)
Message switching, packet
switching, & circuit-switching

Circuit-switched network

Resources needed along a path (buffers, link bandwidth) to
provide for communication between the end systems reserved
for the duration of the system at the set-up phase


E.g. telephone network
Message or packet-switched network


Resources not reserved
Messages or packets use the resource on demand

May need to wait due to lack of reservation


Queueing delay
E.g. telegraph network, computer networks
Telephone network
10 Regional Offices
(fully connected)
Sectional Offices
Primary Offices
Toll Offices
End Offices
Telephone network
Resource Reserved
on all links
Message-switch vs. packetswitching

In packet-switching


Message may need to be segmented into smaller “packets”
and reassembled at the edge nodes
Advantages:



Smaller end-to-end delay
Smaller probability of packet error
Disadvantage:

Larger overhead – source address, destination address, etc.
need to padded to the packets
Message-switch vs. packetswitching
7.5 Mbits long message
1.5 Mbps
1.5 Mbps
1.5 Mbps
0
5
10
15
Message-switch vs. packetswitching
7.5 Mbits long message -> segmented into
5,000 1.5 kbits packets
1.5 Mbps
1.5 Mbps
1.5 Mbps
0
5
5.0002
Connection-oriented vs.
Connectionless

Connection-oriented

Telephone network


Connection-oriented data connection (TCP)


A “circuit” must be established before a conversation can
start
Three-way handshake
Connectionless

Connectionless data connection (UDP)


No set-up phase
Telegraph network