Network design and evolution

1
Network design and evolution

• Network functions and network topology
• Telegraph networkmessage switching
• Telephone networkcircuit switching
• Computer networks and the Internet---packet
  switching

2
Network Design

• Applications impose requirements on the services
  provided by a network
• delay reliability accuracy
• volume and rate
• cost convenience
• The network design
• meets these requirements cost- effectively
• must address a common set of functions
• may take fundamentally different approaches

3
Essential Network Functions

• Basic user service
• --Voice connections or packet transfer
• Switching approach the means of transferring
• information flows between communication lines
• Terminal the end system that connects to the
  network, telephone or computer
• Information representation the format of the
• information handled by the network, voice or
  bits

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Essential Network Functions (cont.)

• Transmission system the means for transmitting
• information across a physical medium copper
  telephone wires, coaxial TV cable, optical fiber
• Addressing the means for identifying points
  of
• connection to the network telephone number
  or IP address
• Routing the means for determining the path
  across the network
• Multiplexing the means for connecting multiple
• information flows into shared connection
  lines.

5
Network Topology How a Network Grows

• A network involves the interconnection of
  transmission lines using switches to convey
  information between users
• The growth of a network from a few users in
  close
• proximity to a very large community over a
  wide
• geographic region leads to a hierarchical
  network structure

6
A Network transfers information among
users (A single block of information or a stream
of information)
Network
Figure 1.6
7
(a) A switch provides the network to a cluster
of users
n lines
n(n-1)/2 lines
Network
Access network
(b) A multiplexer connects two access networks
Figure 1.7
8
1
a
(a)
b
Metropolitan network A consists of access
subnetworks a, b, c, d.
2
4
3
A
c
d
Metropolitan
(b)
National network consists of regional subnetworks
a, b, g. Metropolitan network A is part of
regional subnetwork ?.
?
?
g
Hierarchical network topology
Figure 1.8
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Approaches to Network Design
10
Approaches to Network Design (cont.)
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Telegraphy Networks message switching

• Samuel B. Morse invented telegraph in 1837
• binary communications using dots dashes
• Morse code maps alphabet to sequences of dots/
  dashes
• text messages transmitted hop- by- hop across
  a
• network of relay stations
• Manual routing, routing decision is done by a
  operator
• Operator stores a message, finds next station
  according to the destination and forwards it, so
  message switching
• Multiplexing, the symbols from several
  operators into the same communication line.
  (20bits/sec?120bits/sec)

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Morse code
13
Telephone networkcall set up
Telephone Office
1.
The caller picks up the phone triggering the flow
of current in wires that connect to the telephone
office.
The current is detected and a dial tone is
transmitted by the telephone office to indicate
that it is ready to receive the destination
number.
Telephone Office
2.
The caller sends this number by pushing the keys
on the telephone set. Each key generates a pair
of tones that specify a number. (In the older
phone sets the user dials a number which in turn
generates a corresponding number of pulses.)
Telephone Office
3.
The equipment in the telephone office then uses
the telephone network to attempt a connection.
If the destination telephone busy, then a busy
tone is returned to the caller. If the
destination telephone is idle, then ringing
signals are sent to both the originating and
destination telephones.
4.
Telephone Office
Telephone Office
5.
The ringing signals are discontinued when the
destination phone is picked up and communication
can then proceed.
Telephone Office
6.
Either of the users terminate the call by putting
down a receiver.
Figure 1.1
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Telephone networks circuit switching

• 1875, Alexander G. Bell invented telephone
• Voice (analog) signal, telephone terminal is very
  simple, anybody can use it
• Switches were introduced because of the vast
  cost of dedicated lines (recall n(n-1) lines to
  n lines)
• Human operator performs switching, manual routing
• Connection-oriented, dedicated end-to-end
  connection (dedicated lines and switches),
  therefore, circuit switching
• Routing decision at setting up of the connection

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(a) A switch in the form of an operator with a
patch cord panel (not shown)
(b) Cords interconnect user sockets providing
end-to-end connection
Figure 1.10
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Advances of telephone networks

• Digital (0,1) transmission, PCM technique
• Multiplexing 20 voice calls, 1.5Mbps
• Digital switches
• Hierarchical telephone networks local/
  tandem/toll switches
• Hierarchical numbering (addressing) system area
  code exchange number phone number
• Automatic connection by computer
• A separate singling network for management
• Enhanced telephone servicescredit-card call,
  long distance call, 800, caller ID, voice mail,
  cellular phone (mobility).

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CO Center Office switch
Tandem switch Toll switch
Hierarchical telephone network structure
Figure 1.11
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Topics discussed (a brief summary)
What is a communication network?
An infrastructure to transfer information over
space
What is the purpose of it?
Provides services
What are the main requirements?
Delay, reliability, accuracy
What are four typical interactions?
Gathering, distribution, request/reply, two
multiple way interaction
What does connection-oriented mean?
A connection between two parties must be set up
ahead of information transmission
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Topics discussed (a brief summarycont.)
What are the main network functions?
Switching, information representing, addressing,
routing, multiplexing
What are approaches implementing the functions?
In telegraph networks
Message switching, Morse code, geographical
address, manual routing, charmessage
multiplexing
In telephone networks
Circuit switching, analog or digital,
hierarchical numbering, call setup
manually/automatically, circuit multiplexing
What is the generic network topology?
Hierarchical network structure
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What is a protocol?

• A set of rules that governs how two parties are
  to interact.
• The purpose of a protocol is to provide a server
  to its users.
• Protocols stack/layers

protocol
Horizontal
Service to its user
Vertical
protocol
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Computer networks packet switching

• Internet Protocol (IP) provides a means of
  transferring information across multiple
  heterogeneous networks
• A message may divide into multiple packets, each
  of which may be transferred independently,
  therefore, packet switching
• Typical computer networks terminal-oriented
  networks, computer-to-computer networks, the
  ARPANET, Ethernet local area networks, the
  Internet. (i.e., the evolution of computer
  networks)

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Terminal-oriented networks

• (a) Time-Shared Computers Cables for Input
  Devices
• (b) Dial In

T
C
. . .
T
T
. . .
C
T
T
Modem Pool
PSTN
Modem
T
T terminal
Allow expensive host computers shared by a number
of terminals
What is the problem of this system?
Figure 1.12
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Terminal-oriented networks
(Line sharing techniques)
Poll to terminal
C
Response from terminal
T
T
T
T
--Transmissions from terminals very bursty, so
dedicated lines inefficient --Polling protocols
for controlling the sharing of a transmission
line were developed
Figure 1.13
24
Terminal-oriented networks
(Statistical Multiplexing Techniques)
T
. . .
Host
T
Address Info
T
Statistical multiplexers developed to allow the
sharing of a transmission line Messages from a
terminal encapsulated in a frame that has a
header that contains the terminal address A
message must wait for line (buffer) to become
available Framing technique to delineate the
beginning and end of each message Error
control techniques and check bits
Figure 1.14
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Typical terminal-oriented networks
Host
High-speed lines
Low-speed lines
San Francisco
New York City
T
T
. . .
Chicago
Atlanta
T
Tree- topology network connecting terminals to
centralized shared computers, routing and
forwarding is straightforward. What is the
limitation of this kind of networks?
Not flexible could not handle proliferation of
computers applications
Figure 1.15
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Computer-to-Computer Networks

• The proliferation of computers leds to a need
  to develop networks to interconnect computers
• Fundamentally different than connecting
  terminals to computers, because now both parties
  are intelligent
• Interactive applications require quick response
• implying that messages cannot be too long,
  because this will cause long delays
• Solution Packet switching
• variable-length messages up to some maximum
  allowed
• longer messages are broken into several
  packets
• connectionless transfer vs. connection-oriented
  transfer, i.e., IP datagram vs. ATM VC.

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The ARPANET
AMES
UTAH
BOULDER
GWC
CASE
McCLELLAN
RADC
ILL
CARN
LINC
USC
AMES
MIT
MITRE
UCSB
STAN
SCD
ETAC
UCLA
RAND
TINKER
NBS
HARV
BBN

• developed in 1960s by U.S. DoD
• Testbed for wide-area network packet switching
  research
• Interconnection of computers using a mesh
  networks
• There exist multiple paths between any pair of
  hosts
• Packet switches route packets from source to
  destination

Figure 1.16
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ARPANET Packet Switching Innovations

• Flexible interconnection of computers
• Connectionless transfer of packets
• Distributed synthesis of routes
• Adaptation to failures and traffic variations
• Layered architecture
• Investigation of complex network dynamics

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Local Area Networks (LAN)
Development of workstations leds to LANs to
allow sharing of resources (file servers,
printers, ...) LAN different than WAN
bandwidth is cheap, transmission relatively
error-free use broadcast packet transmissions,
flat address space
transceivers
? ? ? ? ? ?
(a)
(b)
Bus topology
Star topology
Figure 1.17
30
Internetworking (Internet)

• Different protocols were developed to transmit
  packets across different types of networks
• packet switch networks, radio networks,
  satellite
• networks
• Problem How to exchange information between
• computers attached to any of these networks?
• Internet Protocol (IP) creating a network of
  networks

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Gateways provide interconnection across
networks IP packets sent from gateway to gateway
net 3
G
net 1
G
G
G
net 5
net 2
net 4
G
G gateway
An internetwork
Figure 1.18
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Definition of the Internet

• Internet, the global information system that
• is logically linked together by a globally
  unique address space
• based on the Internet Protocol (IP) or its
  subsequent extensions/ follow-ons
• is able to support communications using the
  TCP/ IP suite or its subsequent extensions/
  follow-ons, and/ or other IP- compatible
  protocols
• provides, uses or makes accessible, either
  publicly or privately, high level services
  layered on the communications and related
  infrastructure described herein

33
Internet Innovations

• Keep gateways simple, complexity at the edge
• Best-effort transfer of IP datagrams try best
  to deliver packets but no guarantee
• Route IP packets according to destination
  address
• Domain Name System to map between host names
• (people-friendly) and IP addresses
  (machine-friendly)
• Transmission Control Protocol (TCP) to provide
• reliable connections over unreliable datagram
  transfer
• Any application that can run over TCP/ IP can
• immediately run over the entire Internet

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Discussion on switching approaches

• Telephone network
• Real-time voice
• Connection-oriented
• Resources allocated once set up and guaranteed
• All messages along the same route (circuit)
• Reliable
• Fast transfer

• Internet
• Good for various applications
• (IP is) Connectionless
• No set up, no latency
• Each packet routed independently
• Robust around failure point
• No state information in routers, burden put on
  edge computers

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Discussion on switching approaches (cont.)

• Telephone network
• Not for other data transfer
• Latency at the beginning
• Poor utilization of bandwidth
• New set up when failure
• State information in switches

• Internet
• TCP not good for real-time applications
• Extra address overhead in each packet
• Overhead on routing for each packet
• Packets may lost, delay, out of order

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Key factors determining success of a new service
Will it inter-operate?
Can it be built?
Technology
Standards
Will it sell?
Market
Regulation
Is it allowed?
Figure 1.19