Download Introduction - School of Computing and Information Sciences

CEN 4500
Data Communications
Chapter 1: Introduction
Instructor: S. Masoud Sadjadi
http://www.cs.fiu.edu/~sadjadi/Teaching/
sadjadi At cs Dot fiu Dot edu
Agenda
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Introduction
Network Hardware
Network Software
Reference Models
Example Networks
Network Standardization
Summary
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History
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18th Century
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19th Century
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The Great Mechanical Systems
Industrial Revolution
The age of the Steam Engine
20th Century
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Information gathering, processing, and
distribution
Telephone, Radio, TV, Computer, and Satellites
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History
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Computer industry
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is still young
comparing to automobiles and air transportation
has made much better progress
First two decades
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Highly centralized, usually within a single large room
A medium-sized company or university might have 1
Larger institutions had at most a few dozen
Twenty years later
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Equally powerful computers smaller than postage
stamps
At the time, this would be science fiction!
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History
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Merging of Computers and Communications
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“Computer Center” is now obsolete
Old Model
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New Model
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A single computer serving everyone in an organization
A large number of separated but interconnected
computers do the job
These systems are called Computer Networks
We study the design and organization of these systems
Future Model ?
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Computer Network
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A collection of autonomous computers
interconnected by a single technology
Two computers are interconnected
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If they are able to exchange information
The connection can be via
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Copper wire, Fiber optics, Microwaves, Infrared, or
Communication satellites
How about Internet and WWW?
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Internet is a network of networks
WWW is a distributed system on top of Internet
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Distributed System
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Should not be confused or used
interchangeably with Computer Network
So, then what is a distributed system?
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In a distributed system, a collection of
independent computers appears to its users as a
single coherent system
Usually, it is a single paradigm or model that it
presents to the users (WWW & documents)
Often a layer of software on top of operating
system (called middleware) is responsible for
implementing this model
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Uses of Computer Networks
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Business Applications
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Resource sharing: programs, equipment, data
Communication medium: e-mial, IM, SMS, etc.
Doing business with suppliers (B2B)
E-Commerce (doing business with customers, B2C)
Home Applications
Mobile Users
Social Issues
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Business Applications of Networks
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Resource sharing using client-server model
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Data are stored in a powerful machine
Employees have a simpler machine called clients
A network with two clients and one server.
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Business Applications of Networks
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The client-server model
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Two processes are involved: one on the client
machine and one on the server machine
Communication takes place by the client process
sending a request and the server process sending a
reply to the request.
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Uses of Computer Networks
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Business Applications
Home Applications
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Access to remote information (Web surfing)
Person-to-person communication (IM, Chat room)
Interactive entertainment (VoD, Game, etc)
Electronic commerce (shopping, paying bills, etc)
Mobile Users
Social Issues
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Home Network Applications
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Person to person communication via P2P
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In peer-to-peer system there are no fixed clients
and servers.
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Home Network Applications
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Some forms of e-commerce.
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Mobile Network Users
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Combinations of wireless networks and mobile computing.
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m-commerce
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PDA cell phones as an electronic wallet, replacing …
Location-dependent services using GPS on cell phones
Personal area networks
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Wearable computers
Pervasive computing
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Agenda
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Introduction
Network Hardware
Network Software
Reference Models
Example Networks
Network Standardization
Summary
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Taxonomy of Computer Networks
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There is no widely accepted taxonomy
Two dimensions that stand out
1. Transmission Technology
2. Scale
1. Transmission Technologies
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Broadcast links (usually smaller networks)
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Have single, shared communication channel
Short messages (packets) sent are received by all
Point-to-point links (usually larger networks)
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Consists of many connections between individual pairs
Packets may have to visit some intermediate machines
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Taxonomy of Computer Networks
2. Scale
Classification of interconnected processors by scale.
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Network Hardware
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Local Area Networks
Metropolitan Area Networks
Wide Area Networks
Wireless Networks
Home Networks
Internetworks
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Local Area Networks
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LANs
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Are privately-owned networks within a single
building or campus of up to few kilometers
Two broadcast networks
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(a) Bus (e.g., IEEE 802.3 or Ethernet, up to 10 Gbps)
(b) Ring (e.g., IEEE 802.5 or IBM token ring, FDDI)
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Metropolitan Area Networks
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MAN covers a city
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Cable TV grew from community antenna systems in the
areas with poor over-the-air TV reception)
Broadband wireless
A metropolitan area network based on cable TV.
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Wide Area Networks
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WAN spans a large geographical area
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Contains a collection of hosts interconnected by a
communication subnet
Subnets: transmission lines move bits and switching
elements (routers) connect two or more tls.
Relation between hosts on LANs and the subnet.
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Wide Area Networks
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Store-and-forward or packet-switched subnet
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Each packet will be received in its entirety on
each router and stored there until an output line is
free, and then forwarded
Cells: if the packets are small and the same size
A stream of packets from sender to receiver.
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Wide Area Networks
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Routing decisions are make locally
How to make a routing decision is called
routing algorithm.
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Not all WANs are packet-switched
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Satellite systems
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Each router has an antenna to send and receive packets
Satellite networks are inherently broadcast and are
most useful when the broadcast property is important.
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Wireless Networks
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Not a new idea
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Ship-to-shore wireless telegraph in 1901
Categories of wireless networks:
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System interconnection
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Wireless LANs
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Ease of operation
IEEE 802.11
Wireless WANs
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Cellular phones
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Wireless Networks
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(a) Bluetooth configuration
(b) Wireless LAN
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Wireless Networks
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Almost all wireless network hook up to wired
network at some point
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(a) Individual mobile computers
(b) A flying LAN
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Future of wireless networks
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Wireless is the wave of the future
“Mobile wireless computers are like mobile
pipeless bathrooms—portapotties. They will
be common on vehicles, and at constructions
sites, and rock concerts. My advice is to wire
up your home and stay there.”
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(Metcalfe, 1995)
“Four or five computers should be enough for
the entire world until the year 2000.”
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(IBM chairman T.J. Watson, 1945)
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Home Network Categories
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Computers
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desktop PC, PDA, shared peripherals
Entertainment
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TV, DVD, VCR, camera, stereo, MP3
Telecomm
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telephone, cell phone, intercom, fax
Appliances
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microwave, fridge, clock, furnace, AC
Telemetry
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utility meter, burglar alarm, babycam
Wired or Wireless?
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Cost favors wireless, but privacy favors wired!
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Internetworks
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A collection of interconnect networks is called an
internetwork or internet.
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“Internet” with capital “I” is one specific internet.
Subnets do not include the hosts, but WANs do.
The combination of a subnet and its hosts forms a
WAN
The combination of he cables and the hosts forms a
LAN (no subnet in a LAN).
Rule of thumb
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If different organizations paid to construct different parts
of the network and each maintains its part, we have an
internet
If the underlying technology is different.
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Agenda
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Introduction
Network Hardware
Network Software
Reference Models
Example Networks
Network Standardization
Summary
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Network Software
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Why a layered organization?
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To address complexity most network are
organized as a stack of layers or levels, each one
is built upon the one below it.
The number, name, content, and function of
layers are different from one network to the other
The purpose of each layer is to offer certain
services to the higher layers, shielding those
layers from the implementation details
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Network Software
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Protocol Hierarchies
Design Issues for the Layers
Connection-Oriented and Connectionless
Services
Service Primitives
The Relationship of Services to Protocols
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Protocol Hierarchies
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Layer n Protocol
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The rules and conventions
used in for two layer n of a
network on two machines to
communicate.
An agreement between the
communication parties on
how communication is to
proceed
Peers
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The entities comprising the
corresponding layers on each
different machines.
It is the peers that
communicate by using the
protocols.
Interface
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Defines which primitive
operations and services the
lower layer makes available
to the upper layer.
Layers, protocols, and interfaces.
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Network Architecture
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A set of layers and protocols are called a network
architecture.
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The specification of a network architecture must have
enough information to allow an implementer to write a
program or develop the hardware for each layer so that it
will correctly obey the appropriate protocols.
Neither the details of implementation nor the specification
of interfaces is part of the architecture because these are
hidden inside a machine and not visible from the outside.
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Protocol Stack
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A list of protocols used by a certain system, one protocol
per layer, is called a protocol stack.
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Protocol Hierarchies
The philosopher-translator-secretary architecture.
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Protocol Hierarchies
Example information flow supporting virtual communication in layer 5.
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Design Issues for the Layers
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Addressing
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Every layer needs a mechanism for identifying senders
and receivers
Error Control
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Physical communication circuits are not perfect
Flow Control
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How to keep a fast sender from swamping a slow receiver
with data
Multiplexing
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Not every arbitrarily long messages can be sent without
disassembling, transmitting, and reassembling
Routing
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When there are multiple path between the senders and
receivers
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Services
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Connection-Oriented Services
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Modeled after telephone systems
Pick up the phone, dial a number, talk, hang up.
Acts like a tube
In most cases, the order is preserved, so that the bits
will arrive in the same order they were sent.
Connectionless Services
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Modeled after postal system.
Each letter carries the full destination address
Each is routed throughout the system independently.
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Services
Six different types of service.
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Service Primitives
Five service primitives for implementing a simple connection-oriented service.
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Service Primitives (2)
Packets sent in a simple client-server interaction on a connection-oriented network.
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Services to Protocols Relationship
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Service
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A set of primitives (operations) that a layer provides to the layer
above it, which relates to the interface between the layers
Protocol
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A set of rules governing the format and meaning of the packets, or
messages that are exchanged by the peer entities within a layer
The relationship between a service and a protocol.
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Agenda
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Introduction
Network Hardware
Network Software
Reference Models
Example Networks
Network Standardization
Summary
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Reference Models
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The ISO OSI Reference Model
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Open systems: systems that are open for
communication with other systems.
Not a network architecture, because it does not
specify the exact services and protocols to be
used in each layer.
The TCP/IP Reference Model
A Comparison of OSI and TCP/IP
A Critique of the OSI Model and Protocols
A Critique of the TCP/IP Reference Model
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Reference Models
The OSI
reference
model.
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The ISO OSI Reference Model
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Physical layer
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Is concerned with the transmission of raw bits over a communication channel.
Data link layer
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Is to transform a raw transmission facility into a line that appears free of
undetected transmission errors.
Network layer
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Controls the operation of the subnet.
Transport layer
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End-to-end. Accepts data from above, split it up into smaller units if need be,
pass these to the network layer, and ensures that the pieces all arrive correctly
at the other end.
Session layer
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Allows users on different machines to establish a session.
Presentation layer
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Concerned with the syntax and semantics of the information transmitted.
Application layer
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Contains a variety of protocols that are commonly uses
HTTP, FTP, SMTP, NTTP, etc.
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Reference Models
The TCP/IP reference model.
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Reference Models
Protocols and networks in the TCP/IP model initially.
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Comparing OSI and TCP/IP
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Concepts central to the OSI model
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Services (layer semantics)
Interfaces (layer syntax)
Protocols (layer’s own business)
TCP/IP
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Did not originally clearly distinguish between
service, interface, and protocol
People have tried to retrofit it after the fact to
make it more OSI-like
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A Critique of the OSI Model & Protocols
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Why OSI did not take over the world
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Bad timing
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Bad technology
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Both the model and protocols are flawed (the choice of
layers were mostly political than technical)
Bad implementations
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The competing TCP/IP protocols were already in
widespread use by research universities by the time
OSI protocols appeared.
Initial implementation were huge, unwieldy, and slow
Bad politics
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Push by the European and then US government.
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Bad Timing
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If the interval between the two elephants is very
short (because everyone is in hurry to get started),
the people developing the standards may get
crushed!
The apocalypse of the two elephants.
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A Critique of the TCP/IP
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Problems:
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Service, interface, and protocol not distinguished
Not a general model
Host-to-network “layer” not really a layer, it is
just an interface between the network and data
link layers
No mention of physical and data link layers
Minor protocols deeply entrenched (ad hoc), hard
to replace
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Telnet was designed for a ten char per second
mechanical Teletype terminal
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Hybrid Model
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The hybrid reference model to be used in this
book.
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Agenda
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Introduction
Network Hardware
Network Software
Reference Models
Example Networks
Network Standardization
Summary
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Example Networks
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The Internet
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Connection-Oriented Networks:
X.25, Frame Relay, and ATM
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Ethernet
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Wireless LANs: 802:11
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The Internet
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Is not a network at all, but a vast collection of
different networks that use certain common
protocols and provide certain common
services.
It is an unusual system that
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is NOT planned by anyone
And is NOT controlled by anyone
It all started in the late 1950’s (cold war)
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The DoD wanted a command-and-control
network that could survive the nuclear war.
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The ARPANET
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(a) Structure of the telephone system. Vulnerable!
(b) Baran’s proposed distributed switching system.
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The ARPANET (2)
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The original ARPANET design.
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IMP: Interface Message Processors
Software: Subnet and Host
BBN and UC Berkeley: Berkeley UNIX Sockets
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The ARPANET (3)
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Growth of the ARPANET (a) December 1969. (b) July 1970. (c) March
1971. (d) April 1972. (e) September 1972.
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NSFNET
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In late 1970s, to get to the ARPANET, a university had to have a research
contract with the DoD, which many did not have
NSF response was to design a successor to ARPANET
The NSFNET backbone in 1988.
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Internet Usage
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Traditional applications (1970 – 1990)
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E-mail
News
Remote login
File transfer
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Architecture of the Internet
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Overview of the Internet.
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ATM Virtual Circuits
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A virtual circuit.
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Connections are often called virtual circuits in analogy
with physical circuits used within the telephone systems
A permanent virtual circuit is also supported in ATM
Cells are 53 (48+5) bytes long
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ATM Virtual Circuits (2)
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An ATM cell.
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Cell is a small and fixed sized packet.
ATM networks
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Are organized like traditional WANs, with lines
and switches (routers).
155 Mbps and 622 Mbps (or higher).
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For compatibility with AT&T’s SONET transmission
system
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The ATM Reference Model
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The ATM reference model.
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The ATM Reference Model (2)
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The ATM layers and sublayers and their functions.
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Ethernet
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Architecture of the original Ethernet.
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Wireless LANs
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(a) Wireless networking with a base station.
(b) Ad hoc networking.
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Wireless LANs (2)
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The range of a single radio may not cover the
entire system.
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Wireless LANs (3)
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A multicell 802.11 network.
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Agenda
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Introduction
Network Hardware
Network Software
Reference Models
Example Networks
Network Standardization
Summary
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Network Standardization
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Who’s Who in the Telecommunications
World
Who’s Who in the International Standards
World
Who’s Who in the Internet Standards World
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ITU
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Main sectors
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Radiocommunications
Telecommunications Standardization
Development
Classes of Members
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National governments
Sector members
Associate members
Regulatory agencies
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IEEE 802 Standards
The 802 working groups. The important ones are
marked with *. The ones marked with  are
hibernating. The
oneS. Masoud
marked
with † gave up.
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Metric Units
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The principal metric prefixes.
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Agenda
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Introduction
Network Hardware
Network Software
Reference Models
Example Networks
Network Standardization
Summary
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Summary
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Computer networks can be used for numerous
services for companies and individuals.
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Client-Server and Peer-2-Peer models.
Networks can be divided into LANs, MANs, WANs,
and internetworks.
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LANs and MANs are unswitched (no routers).
Network software consists of protocols, which are
rules by which processes communicate.
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Connectionless or Connection-oriented
Protocol hierarchy and protocol stack; OSI and TCP/IP
models
Design issues: multiplexing, flow control, error control,
etc.
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Examples: Internet, ATM, Ethernet, IEEE 802.11.
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