CSE 422 Computer Networks

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CSE 422Computer Networks

• CSE 422

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Technology Over The Centuries

• 18th Century Mechanical Systems Accompanying The
  Industrial Revolution
• 19th Century Age of The Steam Engine
• 20th Century Information Gathering, Processing,
  and Distribution e.g.,
• Worldwide Telephone Network
• Invention of Radio and TV
• Computer Industry
• Launching of Communication Satellites

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Internet Growth (by Number of Computers)
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Computer Networks

• Definition
• Interconnected Collection of Autonomous Computers
• Goals
• Resource Sharing
• Lower Communication Costs
• Client-Server Model
• High Reliability
• Communication Medium Among Widely Separated
  People
• Smooth System Growth
• Simpler Software Design

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Applications of Networks

• Access to Remote Programs
• Simulation
• Computer Aided Ed.,
• Medical Diagnosis
• Access to Remote Data Bases
• Reservations For Hotels, Airplanes
• Home Banking
• Automated Newspaper
• Automated Library
• Access to Information System (e.g. World Wide
  Web)

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Applications of Networks (cont.)

• Communication Medium
• Electronic Funds Transfer System
• Electronic Mail
• Teleconferencing
• Worldwide Newsgroups
• International Contacts by Humans
• Entertainment Industry
• Video On Demand
• Multiperson real-time simulation games
• Selecting any movie/TV program ever made
• Live TV may becomes interactive with audience

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Social Issues

• Views on politics, religion, sex, etc.
  distributed
• Newsgroups debate sensitive issues
• Network operators risk being sued for contents
• Rights to free speech may be violated
• Anonymous messages can be desirable, but ...

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Classification of interconnected processors by
physical size
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Network Structure

• Communication Subnet (Subnet)
• Switching Elements (Routers)
• Transmission Lines (Circuits)

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Types of Design For Subnets

• Point-to-Point Circuits (Channels)
• Example of Topologies

Some possible topologies for a point-to-point
subnet (a) Star (b) Loop (c) Tree (d) Complete
(e) Intersecting loops (f) Irregular
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Types of Design For Subnets (cont.)

• Broadcast Channels
• Examples of Topologies

Communication subnet using broadcasting (a) Bus
(b) Satellite or Radio (c) Ring
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Types of Design For Subnets (cont.)

• Note Broadcast Subnets May Allocate Channel By
• 1. Static Methods
• TDMA
• 2. Dynamic Methods
• Centralized
• Decentralized

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Summary of Network types -LANs, MANs, WANs

• Local area networks (LANs)-are privately owned
  networks within a single building or campus of up
  to a few kilometers in size
• LANs-have three distinguished characteristics
  (1) size, (2) transmission technology, (3)
  topology
• Metropolitan area networks (MANs)-basically a
  larger version of LANs, and uses similar
  technology
• MAN-has just one or two cables and contains no
  switching elements

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Network Types (Cont.)-LANs, MANs, WANs

• MAN standard-Distributed Queue and Dual Bus
  (DQDB), consists of two unidirectional buses
  (cables) to which all computers are
  connected
• WAN-spans a large geographical area it consists
  of several hosts, connected to a subnet, which in
  turn is connected via transmission lines and
  switching elements

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Network Types (Cont.)-LANs, MANs, WANs

• Architecture of DQDB metropolitan area network

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Network Types (Cont.)-Wireless Networks

• Mobile computing, (e.g., notebook computers
  portable digital assistants (PDA) is growing at a
  rapid rate)
• Users want network connectivity in cars,
  airplanes, other remote sites
• The use of a portable computer capable of
  wireless networking will very likely
  revolutionize the way we use computers
• Possible uses portable office, fleets of trucks,
  taxis, buses, and repairpersons (keeping in
  contact with home)

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Network Types (Cont.)-Wireless Networks

• Other uses workers at disaster sites (fires,
  floods, etc.) where telephone system is
  destroyed military operations
• Some disadvantages low bandwidth (1-2 Mbps),
  high error rates, frequent disconnections
• Wireless networks communicate via modulating
  radio waves or pulsing infrared light
• Wireless communication linked to wired network
  infrastructure by transceivers

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Network Types (Cont.)-Wireless Networks

• Cell-
• area cover by an individual transceiver's
  signal the cell sizes vary widely
• Wireless networks comes in many forms. Some
  universities have installed antennas all over
  campus to allow students to access the library
  card catalog, while sitting under the trees
• Security is a problem, because connection to
  wireless is so easy challenge for software
  designers
• Address migration also presents a challenge

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Examples of Networks

• Commercial Networks
• DECNET
• SNA
• National Network
• ARPANET
• NREN
• EDUNET
• USENET

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Examples of Networks (cont.)

• Local Area Networks
• NOVELL NETWARE
• MAP and TOP
• Packet Carriers
• TYMNET
• TELENET

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The Internet Emerges-funded by ARPA

• Need to interconnect LANs, MANs, and WANs
• Initially interconnected NSFNET and ARPANET
• Results Internet, with TCP/IP Software
• Growth continues exponentially, doubles each yr.
• Main applications Email, Remote Login, News,
  File Transfer
• New application WWW, with Internet Explorer,
  further increased the Internet usage

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Data Communications Organizations

• ISO CCITT
• ANSI State Dept.
• EIA
• Carriers Other NTIA
• NCS Org.
• Government Agencies

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A Simplified Architecture for File Transfer
Computer X
Computer Y
File transfer application
File transfer application
File and file transfer command
Communications Service module
Communications Service module
Communications-related data units
Network access Module
Network access Module
Network interface logic
Network interface logic
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Network Architectures

• Protocols
• Layers

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The ISO Reference Model (Basic Principles)

• 1. A layer should be created where a different
  level of abstraction is needed.
• 2. Each layer should perform a well defined
  function.
• 3. The function of each layer should be chosen
  with an eye toward defining internationally
  standardized protocols.

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The ISO Reference Model (Basic Principles)
(cont.)

• 4. The layer boundaries should be chosen to
  minimize the information flow across the
  interfaces.
• 5. The number of layers should be large enough
  that distinct functions need not be thrown
  together in the same layer out of necessity, and
  small enough that the architecture does not
  become unwieldy.

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Design Issues For The Layers

• Mechanism For Connection Establishment
• Mechanism For Connection Termination
• Rules for Data Transfer
• Simplex
• Half Duplex
• Full Duplex
• Error Control
• Properly Sequencing Messages

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Design Issues For The Layers (cont.)

• Flow Control
• Routing
• Multiplexing Conversations
• Mechanism For Handling Arbitrarily Long Messages

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Layers, protocols, and Interfaces
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Example information flow supporting virtual comm.
in layer 7.
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Physical Layer

• Concerned with Transmitting Raw Bits over a
  Communication Channel.
• Design Issues
• Mechanical, Electrical, Procedural Interfacing to
  Subnet
• Implemented in Hardware

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Data Link Layer

• Takes a Raw Transmission Facility Transforms It
  To a Line Which Appears Free of Transmission
  Errors to The Network Layer.
• Breaks Input Data Into Frames, Transmitting
  Frames Sequentially, Process Acknowledgment
  Frames.
• Design Issues
• Solve Problems Caused By Damaged, Lost, or
  Duplicate Frames.
• How to Keep Fast Transmitters From Drowning Slow
  Receiver.

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Network Layer --- Communication Subnet Layer

• Determines Chief Characteristics of IMP Host
  Interface How Packets Are Routed Within The
  Subnet.
• Software Accepts Messages From The Source Host,
  Converts Them To Packets, See That Packets Are
  Routed Correctly.

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Network Layer --- Comm. Subnet Layer (cont.)

• Design Issues
• The Division of Labor Between The IMPs The Host
  (i.e., Who Should Ensure That All Packets Are
  Correctly Received at Their Destination, in
  Proper Order.)
• How The Route is Determined? By Using Static
  Tables, Dynamic Tables, or ?
• Implemented in Host by I/O Drivers

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Transport Layer --- Host to Host Layer

• Provides a flow of data between two hosts, for
  the application layer above.
• Accepts Data From Session Layer, Splits It Into
  Smaller Units, If Needed, Passes to Network
  Layer, Ensures That All Pieces Arrive Correctly
  at Other End.
• Determines The Type of Service Provided to The
  Session Layer. e.g.,
• Error --- Free (Virtual) Point-to-Point Channel
  That Delivers Messages in The Order They Were
  Sent.

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Transport Layer --- Host to Host Layer (cont.)

• Transport of Isolated Messages With No Guarantee
  About The Order of Delivery.
• Broadcasting of Messages to Multiple
  Destinations.
• Design Issues
• Mechanism to Regulate The Flow of Information
  From One Host to Another.
• Determine Which Message Belongs to Which
  Connection.
• Implemented as Part of The Host OS.

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Session Layer --- User Interface Layer

• User Negotiate to Establish a Connection with a
  Process on Another Machine.
• Manages The Session Once It Has Been Set Up,
  (e.g., If Transport Connections are Unreliable,
  The Session Layer May Be Required To Recover From
  Broken Transport Connections.)
• Implemented as Part of The OS.

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Presentation Layer

• Represents Information to Communication
  Application-Entities In a Way That Preserves
  Meaning While Resolving Syntax Differences.
  Typical Functions Include
• Text Compression
• Encryption for Security
• Syntax Selection
• Conversion Between Character Codes (e.g., ASCII
  to EBCDIC)

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Application Layer

• Based on Request From User, This Layer Selects
  Appropriate Services To Be Supplied From Lower
  Layers. e.g.
• Identification of Intended Communication Partners
  Their Availability Authenticity.
• Determination of Cost Allocation Methodology.
• Establishment of Error Recovery Responsibility.
• Agreement on Required Privacy.

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Application Layer (cont.)

• Design Issues
• Problem of Partitioning to Gain Maximum Advantage
  of Network.
• Questions of Network Transparency, Hiding The
  Physical Distribution of Resources From The User.

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Approximate correspondences between the various
networks
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A Critique of the OSI Model and Protocols

• Bad timing
• Bad technology
• Bad implementation
• Bad Politics

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A Critique of the TCP/IP Reference Model

• Does not distinguish concepts of service,
  interface, and Protocol clearly
• Not at all general, poorly suited to describing
  any other protocol stack
• Host-to-network layer is not really a layer, but
  an interface between the network and the
  data-link layers
• Does not distinguish between physical and data
  link layers
• IP and TCP were well thought out, but the other
  protocols were ad hoc

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Relation Between Layers at an Interface
In order to transfer the SDU, the layer N entity
may have to fragment it into several pieces, each
of which is given a header and sent as a
separate PDU such as a packet
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Layering of TCP/IP-based protocols
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Six different types of services

• Service Example
• Reliable message stream Sequence of
  pages
• Reliable byte stream Remote login
• Unreliable connection Digitized voice
• Unreliable datagram Electronic junk
  mail
• Acknowledged datagram Registered mail
• Request-reply Database query

Connection- oriented
Connection- less
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Service Primitives
request
response
Layer N1
2
4
Layer N
1
3
confirm
indication
Physical channel
Host 1
Host 2
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Service Primitives (cont.)

• Request An entity wants the service to do some
  work
• Indication An entity is to be informed about an
  event
• Response An entity wants to respond to an event
• Confirm An entity is to be informed about its
  request

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Service Primitives (cont.)

• To make the concept of a service more concrete,
  let us consider as an example a simple
  connection-oriented service with eight service
  primitives as follows
• 1. CONNECT.request --- Request a connection to be
  established.
• 2. CONNECT.indication --- Signal the called
  party.
• 3. CONNECT.response --- Used by the callee to
  accept/reject calls.
• 4. CONNECT.confirm --- Tell the caller whether
  the call was accepted.

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Service Primitives (cont.)

• 5. DATA.request --- Request that data be sent.
• 6. DATA.indication --- Signal the arrival of
  data.
• 7. DISCONNECT.request --- Request that a
  connection be released.
• 8. DISCONNECT.indication --- Signal the peer
  about the request.
• In this example, CONNECT is a confirmed service
  (an explicit response is required) whereas
  DISCONNECT is unconfirmed (no response).

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Example Data Communication Services

• Switched Multimegabit Data Services
  (SMDS)-connecting LANs
• SMDS is designed to handle bursty traffic
• SMDS service simple connectionless packet
  service
• A useful feature of SMDS is broadcasting
• Another useful feature is address screening on
  both incoming outgoing packets

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Example Data Communication Services (cont.)
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Data Commun. Services (Cont.)- X.25 Networks

• Standard developed during the 1970s by CCITT
• Provides an interface between public packet
  networks their customers
• X.25 comprises the physical layer, the data link
  layer the network layer
• X.25 is connection-oriented supports both
  switched virtual circuits permanent ones
• Provides ACKs and flow control

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Data Commun. Services (Cont.)-X.25 Networks

• Note some older terminals still do not speak
  X.25 need yet another way to connect (Packet
  Assembler Disassembler)
• Multiplexing switching of logical connections
  take place in layer 3
• Call control signaling is carried on the same
  logical connection as user data

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Data Commun. Services (Cont.)-Frame Relay

• An absolute connection-oriented service
• Goal move bits from A to B at reasonable speed
  low cost
• Can be thought as a virtual leased line
• Does not provide ACKs or flow control
• Variable size packets (Frames) may be up to 1600
  bytes
• Designed to operate at user data rates of up to 2
  Mbps

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Data Commun. Services (Cont.)-Frame Relay

• Lower delay higher thru put, since internal
  processing is reduced, as is the protocol
  functionality at the user-network interface
• Call control signaling is on a separate logical
  connection from user data
• Multiplexing switching of logical connections
  take place in layer 2

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Data Commun. Services (Cont.)- B-ISDN and ATM

• Asynchronous Transfer Mode (ATM), Universal
  information carrier voice, data, video
• ATM networks are connection-oriented
• Example services video on demand, live TV from
  many sources, full motion multimedia E-mail,
  CD-quality music, high-speed data transport, LAN
  interconnection
• Small fixed-sized packets (cells), 53 bytes long,
  of which 5 bytes are header 48 bytes are payload

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Data Commun. Services (Cont.)- B-ISDN and ATM

• ATM is called cell relay- a cell-switching
  technology
• Cell delivery is not guaranteed, but the order is
• Cell-switching highly flexible, can handle
  both VBR CBR traffic, digital switching of cell
  is easy via fiber optics, facilitates TV
  distribution broadcasting
• Normal speed for ATM networks is 155 Mbps, 622
  Mbps, and gigabit speed later
• The ATM Forum an international group that guides
  the future of ATM

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Data Commun. Services (Cont.)- B-ISDN and ATM
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Data Commun. Services (Cont.)- B-ISDN and ATM

• The ATM layers and sublayers, and their functions

OSI layer
ATM layer
ATM sublayer
Functionality
Providing the standard interface(convergence)
CS
3/4
AAL
SAR
Segmentation and reassembly
Flow control cell header generation/extraction vir
tual circuit/path management Cell
multiplexing/demultiplexing
2/3
ATM
Cell rate decoupling Header checksum generation
and verification Cell generation Packing/unpacking
cells from the enclosing envelope Frame
generation
2
TC
Physical
Bit timing Physical network access
1
PMD
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Data Commun. Services (Cont.)- B-ISDN and ATM

• Different networking services.
• Issue DQDB SMDS X.25
  Frame relay ATM
• Connection oriented Yes No
  Yes Yes
  Yes
• Normal speed(Mbps) 45 45
  .064 2
  155
• Switched No
  Yes Yes No
  Yes
• Fixed-size payload Yes
  No No No
  Yes
• Max payload 44
  9188 128 1600
  48
• Permanent VCs No
  No Yes Yes
  Yes
• Multicasting No
  Yes No No
  Yes

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Gigabits Testbeds

• Michigan State University High-Speed Networking
  Performance Research Laboratory (HSNP)
• ARPA NSF financed a number of
  university-industry gigabit testbeds
• MIT, U of Penn., IBM Watson Lab, and Bellcore
  Aurora- (a testbed linking four sites in the
  Northeast)
• AT\T Bell Labs, Berkley, the U of Wis Blanca-
  (research issues protocols, host interfaces, etc)

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Gigabit Testbeds Cont.

• Cal Tech, JPL, Los Alamos, San Diego Super
  Computer Center CASA- (aimed at doing research
  on super computer applications
• CMU Nectar- (an experimental MAN from CMU to
  Pittsburgh, interested in applications involving
  chemical process flowsheeting Oper. Res.)
• U of NC, NC State U, IBM Res. Triangle Park
  VISTAnet- research focuses on 3D images to plan
  radiation therapy for cancer patients)