What is a protocol?
• A set of rules that governs how two parties
are to interact.
protocol
Horizontal
• The purpose of a protocol is to provide a
server to its users.
Service to its user
• Protocols stack/layers
• See a protocol example
protocol
CIS.IUPUI (from Leon-garcia)
Vertical
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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
.
.
.
C
T
T
(b) Dial In
C
.
.
.
T
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?
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Figure 1.12
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
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Figure 1.13
Terminal-oriented networks
(Statistical Multiplexing Techniques)
Host
Mux
.
.
.
T
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 (FIFO)
• Framing technique to delineate the beginning and end of
each message
• Error control techniques and check bits
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Figure 1.14
Typical terminal-oriented networks
Host
High-speed lines
Low-speed lines
San
Francisco
New York
City
T
T
Chicago
T
Atlanta
• 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 CIS.IUPUI (from Leon-garcia)
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Figure 1.15
Computer-to-Computer Networks
• The proliferation of computers led 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
McCLELLAN
UTAH
BOULDER
GWC
CASE
RADC
ILL
CARN
LINC
USC
AMES
MIT
MITRE
UCSB
STAN
SCD
ETAC
UCLA
RAND
TINKER
BBN
HARV
NBS
• 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
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Figure 1.16
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 led 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
-- Frame structure to delineate individual transmission
-- Media access control (MAC) to coordinate
transceivers
(a)
  
 

(b)
Bus topology
Star topology
Star is better than bus in two ways:
1. twisted-pair is cheaper than coaxial wire. 2. fault tolerant.
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Figure 1.17
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
H
H
net 3
G
net 1
G
G
G
H
net 2
net 5
G
net 4
G
H
G = gateway
An internetwork
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Figure 1.18
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, 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
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Internet Innovations
• Keep gateways simple, put 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: host names  IP addresses
–
(people-friendly) (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
Internet (IP)
Telephone network
• Real-time voice
• Connection-oriented
• Resources allocated once
set up and guaranteed
• All messages along the
same route (circuit)
• Reliable
• Fast transfer
•
•
•
•
Good for various applications
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?
Regulation
Market
Is it allowed?
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Figure 1.19