CPSC441

1
CPSC441
Computer Communication
2
What this Course is About?

• Provide an introduction to modern
  telecommunications and computer networks,
  including information about
• the physical characteristics of current
  transmission media
• layered protocol hierarchies commonly used for
  the organization of modern networks
• standards and protocols for several of these
  layers.

3
Topics

• INTRODUCTION
• PHYSICAL LAYER
• DATA LINK LAYER
• NETWORK LAYER
• TRANSPORT LAYER
• APPLICATION LAYER
• TCP/IP SECURITY

4
Topics

• INTRODUCTION
• HISTORY
• TYPES OF NETWORKS LAN, WAN
• TYPES OF NETWORKS Client - Server, Peer to Peer
• THEORETICAL NETWORK OSI model, TCP/IP model
• EXAMPLES OF NETWORKS, SERVICES
• PHYSICAL LAYER
• DATA LINK LAYER
• NETWORK LAYER
• TRANSPORT LAYER
• APPLICATION LAYER
• TCP/IP SECURITY

5
Topics

• INTRODUCTION
• PHYSICAL LAYER
• SOME PHYSICS
• TRANSMISSION MEDIA, MODULATION
• TELEPHONE SYSTEM, MODEMS
• BASEBAND, BROADBAND TRANSMISSION
• ATM TRANSMISSION
• DATA LINK LAYER
• NETWORK LAYER
• TRANSPORT LAYER
• APPLICATION LAYER
• TCP/IP SECURITY

6
Topics

• INTRODUCTION
• PHYSICAL LAYER
• DATA LINK LAYER
• FRAMES, FRAME MANAGEMENT
• ERROR CHECKING
• DATA LINK PROTOCOLS
• EXAMPLES ETHERNET, TOKEN RING, others
• NETWORK LAYER
• TRANSPORT LAYER
• APPLICATION LAYER
• TCP/IP SECURITY

7
Topics

• INTRODUCTION
• PHYSICAL LAYER
• DATA LINK LAYER
• NETWORK LAYER
• ROUTING, ROUTING PROTOCOLS
• IP ADDRESSING, SUBNETS, NETMASK
• TRANSPORT LAYER
• APPLICATION LAYER
• TCP/IP SECURITY

8
Topics

• INTRODUCTION
• PHYSICAL LAYER
• DATA LINK LAYER
• NETWORK LAYER
• TRANSPORT LAYER
• TCP, UDP protocols
• SOCKET PROGRAMMING
• APPLICATION LAYER
• TCP/IP SECURITY

9
Topics

• INTRODUCTION
• PHYSICAL LAYER
• DATA LINK LAYER
• NETWORK LAYER
• TRANSPORT LAYER
• APPLICATION LAYER
• Domain Name Service (DNS)
• BASIC INTERNET SERVICES
• TCP/IP SECURITY

10
Topics

• INTRODUCTION
• PHYSICAL LAYER
• DATA LINK LAYER
• NETWORK LAYER
• TRANSPORT LAYER
• APPLICATION LAYER
• TCP/IP SECURITY
• INTRO TO CRYPTOGRAPHY
• Secure Socket Layer (SSL)
• FIREWALLS

11
Quotes

• Computers in the future may weigh no more than
  1.5 tons
• I think there is a world market for maybe five
  computers. Thomas Watson Chairman of IBM 1943
• There is no reason anyone would want a computer
  in their home Ken Olson president DEC 1977
• 640K ought to be enough for anybody Bill Gates
  1981

12
History of Data Communications

• Communications industry was already established
  at the beginning of the computer era.
• First type of data communication was terminals
  attached to mainframes via modems and telephone
  lines.

13
History of Data Communications

• Development of Semi-Automatic Business Research
  Environment (SABRE)
• Development of Packet Distribution Network (PDN),
  allowed Advanced Research Projects Agency (ARPA)
  to develop ARPANET.

14
History of Data Communications

• Development of other Proprietary Computer
  Networks (works on one manufacturers equipment)
• Systems Network Architecture (SNA) developed by
  IBM
• Decnet Developed by Digital
• Telnet developed by General Telephone and
  Electronics (GTE)

15
Historical Events

• 1948 first commercial computer installed UNIVAC I
• 1958 first U.S. communication satellite
• 1964 SABRE airline reservation system packet
  switching network (purposed by RAND)
• 1969 ARPANET first packet switching network
  begins operation

16
Historical Events

• 1971 first computer chip
• 4 bit, 2,300 transistors
• 1972 Ethernet specifications formulated
• 1974 IBM introduces SNA
• 1975 Altair 8800 first commercial microcomputer
  sold as kit

17
Historical Events

• 1975 Paul Alan / Bill Gates wrote a BASIC
  language interpreter for the Altair, they formed
  Microsoft
• 1976 Woznaik and Jobs built Apple I and formed
  Apple Computer Company
• 1979 VisiCalc first commercial spread sheet
  introduced

18
Historical Events

• 1981 IBM introduced IBM PC one floppy
• 1983 TCP/IP becomes the official protocol on
  ARPANET
• 1984 Apple introduced GUI with Apple Macintosh
• 1986 PC Convertible (first laptop (luggable))

19
Historical Events

• 1988 OS/2 shipped by IBM first multitasking
  operating system for PC 1989 Intel releases 486
• 1989 Microsoft releases Windows 3.0 1991
• 1989 NSF replaces ARPANET as internet backbone
• 1991 WWW invented by CERN physicist Tim
  Berners-Lee

20
Historical Events

• 1992 Mosaic release first GUI web browser
• 1995 Netscape goes from startup to 2.9 billion
  in one year
• 2000 .com melt down

21
Data Communications
Data Communications
Terminal to Computer
Computer to Computer
Local Area Networks
Wide Area Networks
Peer to Peer
Client Server
22
PC as an Information tool

• Local Area Network (LAN)
• number of computers connected together
• usually a small geographical area
• office, floor, classroom
• share resources (software, hardware)

23
PC as an Information Tool

• Wide Area Network (WAN)
• connection of LANs
• connected by wire, microwave, satellite

24
Resource Sharing

• Sharing of Information
• Types
• Mission critical data
• Frequently used data (form letters)
• Policy / procedure manuals
• Who needs what access
• update
• read only

25
Information Sharing

• What information is vital to your organization
• What information do you need to keep consistent,
  or restricted, or in one place for everyone to
  access
• Consider how a network (centralized control)
  would help

26
Hardware Sharing

• Allows sharing of devices such as
• Printers
• Fax modems
• Scanners
• Disk drives
• CD ROM's
• Tape Backup units
• Plotters

27
Software Sharing

• Software need not be installed on every computer
• One install, one central location for updates
• Consistent configuration
• Grant or deny access to a program

28
Software Sharing

• License considerations
• single user
• license per user
• site license

29
Backup

• Backup of central server or disk
• Hard to backup a number of stand alone computers
• Usually backup of workstation is responsibility
  of the user

30
Computer Roles in a Network

• Clients
• use network resources
• provide no resources to the network
• run their own operating system
• Servers
• provide resources to the network
• Peers
• use and provide services

31
Operating systems

• Server
• Novel NetWare
• Windows NT
• Client
• Windows 2000
• DOS
• OS/2
• Peer
• Windows 2000

32
Categories of Networks

• Client / Server
• contains clients and supporting servers
• may be dedicated or non dedicated
• server centric
• network centric

33
Categories of Networks

• Peer to Peer
• network of computers sharing resources with no
  dedicated server

34
Server Based Networks

• Advantages
• Strong central security
• Central file storage (backup, data organization)
• Share hardware and software
• Optimize dedicated servers for special purpose
• Less intrusive security (network centric)
• manages shared resources
• manages users

35
Server Based Networks

• Disadvantages
• Expensive hardware
• Expensive software
• Dedicated network administrator

36
Peer to Peer

• Advantages
• no extra hardware or software
• easy setup
• no network administrator
• users control resource sharing
• no reliance on other computers for their
  operation
• lower cost for small networks

37
Peer to Peer

• Disadvantages
• additional load on computers because of resource
  sharing
• smaller networks
• lack of central organization, harder to find data
• no central point of storage (backup)
• user administer their network
• weak security
• no central management

38
Peer Security /Server Security

• Peer to Peer
• less secure than client server
• security is controlled by access to a share
  directory (password)
• each resource requires a separate password
• cannot distinguish between users
• Client / Server
• network logins
• permissions granted to users for files /
  resources

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Home Network Applications (2)

• In peer-to-peer system there are no fixed
  clients and servers.

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Selecting the Network type

• Cost
• Expertise
• Security issues
• Number of work stations
• Types of applications

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Types of servers

• Servers can designed for a specialized purpose
• file servers
• print servers
• Application servers
• Message servers
• database servers
• Web servers
• One server (hardware / software) may perform one
  or more functions

42
File Servers

• Offer services that allow users to share files
• Typical operating systems
• Novel NetWare, Windows NT
• Services include
• file transfer
• file storage and data migration
• file update synchronization
• file archiving

43
File ServersFile Transfer

• The ability to transfer files from one computer
  to another
• Need for security (who has what access to which
  files)
• Historical done by sneaker net

44
File ServersFile Storage and Data Migration

• Vast amounts of data is stored (exabytes)
• Must be able to efficiently manage the storage of
  this data
• Categories of file storage
• Online storage
• Offline storage

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File StorageOnline

• Online storage consists mostly of hard drives
• Online information is immediately available

46
File StorageOffline

• Offline storage include media such as tape,
  optical disk
• High capacity, low price
• Not immediately available
• Need for operator intervention
• Best for rarely used data (backup)

47
File ServerFile Archiving

• Process of backing up files on offline devices
• Most systems backup file server data
• Some backup client workstations
• Usually the backup of the client (workstation) is
  the users responsibility

48
Print Servers

• Manages and controls printing on the network
• allows users to share printers
• place printers where convenient
• better workstation performance by using high
  speed data transfer, print queues and spooling
• ability to send and receive faxes directly from
  the work station

49
Application Servers

• Allow sharing of extra computing of expensive
  software applications that reside on a shared
  computer

50
Message Servers

• Message services coordinate interactions between
  users, documents and applications
• Interactions may be graphics, audio, video, etc.
• Types of message services
• Electronic mail
• Workgroup applications
• Object oriented
• Directory services

51
Database Servers

• Allows relatively weak clients to access powerful
  database capabilities
• Usually runs in a client server model
• Client runs interface
• Server runs database operations such as
• managing the database
• processing queries

52
Network Topology

• The way in which connections between devices in a
  network is called the topology

53
Network Topology Bus
4
1
2
3
5

• Components connected together by one or more
  wires
• Passive topology no active electronics
• Messages sent by one node are received by all
• Only the node to which the message is addressed
  accepts the message

54
Network TopologyBus

• Only one node can transmit at one time
• A bus topology must be terminated
• An unterminated bus will cause the signal to echo
  back (ringing)

1
2
3
4
5
55
Network TopologyBus

• Advantages
• Simple, reliable in small networks
• Easy to use
• Requires least amount of cable
• Easy to extend
• Can be extended by using a repeater

56
Network TopologyBus

• Disadvantages
• Degrades with heavy traffic
• Each connector weakens the signal
• Difficult to troubleshoot

57
Network TopologyStar

• Cables run from central hub to each computer
• Each node communicates with central hub
• Central hub can resend message to all nodes
  (broadcast star)
• Central hub can resend only to destination node
  (switched star)

58
Network TopologyStar

• Active hubs regenerate the signal
• Active hubs and switches require power
• Passive hubs such as wiring panels or punch down
  blocks act as a connection point
• Some hubs allow more than on type of cable

59
Network TopologyStar

• Advantages
• Easy to modify
• Easy to diagnose
• Single computer failure does not affect the rest
  of the network
• Use multiple types of cables

60
Network TopologyStar

• Disadvantages
• Central hub is a single point of failure
• More costly

61
Network TopologyRing

• Each computer is connected to the next in line
  the last computer is connected to the first
• Most use token passing
• Only the node with the token can send a message

62
Network TopologyRing

• Advantages
• Equal access to the network
• Still functions under heavy load
• Disadvantages
• Failure of one computer could cause of the
  failure of the ring
• Difficult to troubleshoot
• Adding or removing a node disrupts the network
• Usually more expensive

63
Network TopologyMesh Networks

• Advantages
• Fault tolerant
• Easy to troubleshoot
• Disadvantages
• Cost

64
Failure of one computer could cause of the
failure of the network ? avoided using
Logical/Physical Topologies
1
2
3
4
5
Physical Bus ? errors
Logical Bus Physical Star ? OK
1
2
3
4
5
65
Failure of one computer could cause of the
failure of the network ? avoided using
Logical/Physical Topologies
1
5
4
Physical Ring ? errors
2
3
1
5
Logical Ring Physical Star ? OK
2
4
3
66
What Goes Wrong in the Network?

• Bit-level errors (electrical interference)
• Packet-level errors (congestion)
• Link and node failures
• Messages are delayed
• Messages are deliver out-of-order
• Third parties eavesdrop

67
Network SoftwareProtocol Hierarchies

68
Protocol Hierarchies

• Example information flow supporting virtual
  communication in layer 5.

69
Connection-Oriented and Connectionless Services

• Six different types of service.

70
Services to Protocols Relationship

71
OSI Model

• The International Organization for
  Standardization (ISO) began developing the Open
  Systems Interconnection (OSI) model in 1977
• It is now the most accepted standard for network
  modeling

72
OSI Model

• Defines rules that apply to the following issues
• how network devices contact each other
• how network devices communicate with each other
• who has the right to transmit data
• are transmissions received correctly and by the
  right node

73
OSI Model

• Defines rules that apply to the following issues
• how physical media are arranged and connected
• ensure that network devices maintain a proper
  rate of data flow
• how bits are represented on the network media

74
OSI Model

• Not implemented but many models very close (SNA)
• OSI model divides tasks into seven layers
• Layers are software and hardware standards

75
OSI Model

• The seven layers
• Physical
• Data link
• Network
• Transport
• Session
• Presentation
• Application

76
OSI Model

• Protocol Stack
• a group of protocols each communicating with it's
  neighbour
• Layer N receives information from layer N-1 and
  provides information to layer N1
• for computers to communicate with each other both
  must be running the same protocol stack

77
OSI Model

• Protocol stack
• each layer creates / uses information used by /
  created by it's peer protocol
• computers may be running different operating
  system but running the same protocol stack
• ie Mac running TCP/IP communicating with DOS
  running TCP/IP
• A computer may run more than one protocol stack
  at the same time

78
OSI Model
79
Peer Level Communication

• Message sent from one application to another
  application on different hosts
• travels down the layers of the sending machine
• each layer adds a header to be used by it's
  corresponding peer level
• bottom layer (physical) sends the message to the
  receiving machine

80
Peer level Communication

• Sending Message (continued)
• received on receiving side
• passed up through each layer
• each layer reads the corresponding header

81
Peer Level Communication
82
OSI Model 7 Protocol Layers

• Physical ? how to transmit bits
• Data link ? how to transmit frames
• Network ? how to route packets to the node
• Transport ? how to send packets to the
  application
• Session ? manage connections
• Presentation ? encode/decode msgs, security
• Application ? everything else!

83
Physical Layer

• Physical is responsible for sending bits from one
  computer to another
• Is not concerned with the meaning of the bits
• Defines electrical details (what represents a 0
  or 1)
• Mechanical connections shape and number of
  connector

84
Physical Layer

• What signals are sent on which pins
• Devices at the physical layer
• Simple Hubs (passive and active)
• Couplers , T connectors, terminators, cables,
  and cabling, repeaters
• Transceivers on the (NIC)
• Repeaters, multiplexers

85
Physical Layer

• The following are addressed at the physical layer
• Network connections
• multipoint, point to point
• Physical topologies
• bus, star, or ring
• Analog / digital signaling
• Bit synchronization
• Baseband / Broadband
• Multiplexing

86
Data Link Layer

• Provides for error free transfer of FRAMES over a
  single link from one device to another
• Link
• the circuit established between two adjacent
  nodes, with no intervening nodes
• Path
• a group of links that allows a message to move
  from origin to destination

87
Links and paths
88
Data Link Layer

• Adds Cyclic Redundancy Check (CRC) to detect
  damaged frames
• Adds control information
• frame type
• segmentation details
• Detects when a frame is lost and asks for
  retransmission

89
Data Link Layer

• Broadcast networks
• all devices on the LAN receive the data
  transmission
• Point to Point
• only the destination computer receives the
  message
• Uses physical address (NIC ID)

90
Data Link Layer

• Split into two sublayers
• Media Access Control (MAC)
• Controls how devices share the same media
• Logical Link Control (LLC)
• establishing and maintaining links between
  communicating devices
• synchronization
• flow control
• error checking

91
Data Link Layer

• Devices
• Bridges
• intelligent hubs
• NICs

92
Network Layer

• Makes routing decisions for devices that are
  farther than one link away
• Translates logical address into physical address
• Routers work at the network layer
• Example IP addressing

93
Transport Layer

• Responsible for process to process (end to end)
  delivery of messages
• Breaks messages into segments
• Can be Connection-type or Connection-less.
  Example TCP or UDP

94
Session Layer

• Allows applications on different computers to
  share a connection
• Provides for checkpoints (if a connection is lost
  only the required info is resent
• Dialog control who can transmit

95
Presentation Layer

• Handles the format of the data
• protocol conversion
• data translation (ASCII)
• Compression
• Encryption

96
Application Layer

• Provides services to support user applications
  such as
• FTP (file transfer)
• TELNET (remote login)
• SMTP (simple mail transfer protocol ) e-mail

97
OSI Model
98
A
Subnet 2
B
Subnet 1
Subnet 4
Gateway
Subnet 3
Subnet 2
Router
Node
Subnet 1
99
Node
Application
AP
Creates a new end point allocates table space
for it within the transport layer
Socket interface
Identification of application (port )
Transport
Network
Identifies the node
Data Link
Frames
NA
NIC card identified by NIC card address
100
Node 0
Node 1
AP0
AP1
hello
Buffer ?
Buffer ?
Socket interface
Socket interface
Transport
Transport
Network
Network
Data Link
Data Link
NA0
NA1
101
Node 0
Node 1
AP0
AP1
hello
Buffer ?
Buffer ?
hello
Socket interface
Socket interface
Transport
Transport
Network
Network
Data Link
Data Link
NA0
NA1
102
Node 0
Node 1
AP0
AP1
hello
Buffer ?
Buffer ?
Socket interface
Socket interface
Transport
hello
AP1
AP0
Transport
Network
Network
Data Link
Data Link
NA0
NA1
103
Node 0
Node 1
AP0
AP1
hello
Buffer ?
Buffer ?
Socket interface
Socket interface
Transport
Transport
Network
Node 1
Node 0
Network
hello
AP1
AP0
Data Link
Data Link
NA0
NA1
104
Node 0
Node 1
AP0
AP1
hello
Buffer ?
Buffer ?
Socket interface
Socket interface
Transport
Transport
Network
Network
Data Link
Node 1
Node 0
Data Link
hello
AP1
AP0
NA0
NA1
Is Node 1 in my subnet?
YES
105
Node 0
Node 1
AP1
AP0
hello
Buffer ?
Buffer ?
Socket interface
Socket interface
Transport
Transport
Network
Network
Data Link
NA1
NA0
Node 1
Node 0
Data Link
hello
AP1
AP0
NA0
NA1
106
Node 0
Node 1
AP0
AP1
hello
Buffer ?
hello
Buffer ?
Socket interface
Socket interface
Transport
Transport
Network
Network
Data Link
Data Link
NA0
NA1
hello
AP1
AP0
NA1
NA0
Node 0
Node 1
107
Node 0
Node 1
AP1
AP0
hello
Buffer ?
Buffer ?
Socket interface
Socket interface
Transport
Transport
Network
Network
Data Link
Node X
Node 0
Data Link
hello
AP1
AP0
NA0
Is Node X in my subnet?
NA1
NO
Call ROUTER
108
Backbone
Routing Tables
Router
Routing tables
Subnet 30
Node X
Router
Node 0
Node 1
NAR0
Subnet 20
hello
AP1
AP0
Node X
Node 0
NAR0
NA0
109
Gateway
Backbone
Router
Routing Tables
Subnet 30
Router
Node 0
Node 1
Subnet 20
110
Reference Models

111
Reference ModelsTCP / IP

• Protocols and networks in the TCP/IP model
  initially.

112
TCP/IP Model ? The Internet Layer
Packet-switching network based on a
connectionless internetwork layer Permit hosts
to inject packets, independent travel to
destination
Official packet format and protocol IP (Internet
Protocol) IP packets delivered where they are
supposed to go
113
TCP/IP Model ? The Transport Layer
Allows peers on the source and destination hosts
to carry on a conversation. Protocols TCP and
UDP
TCP (Transmission Control Protocol) ? reliable,
connection-oriented, error-free byte stream
delivering handles flow control UDP (User
Datagram Protocol) ? unreliable, connectionless
No TCPs flow control applications where prompt
delivery more important than accurate delivery
(speech, video, )
114
IEEE

• Institute of Electrical and Electronic Engineers
  defined standards relating to the physical
  cabling and data transmission relating to the
  physical and Data Link layers
• 802.x standards

115
Example Networks

• The Internet
• Connection-Oriented Networks X.25, Frame
  Relay, and ATM
• Ethernet
• Wireless LANs 80211

116
Architecture of the Internet

• Overview of the Internet.

117
ATM Virtual Circuits

118
ATM Virtual Circuits (2)

• An ATM cell.

119
The ATM Reference Model

• The ATM reference model.

120
The ATM Reference Model

121
Ethernet

122
Wireless LANs

• (a) Wireless networking with a base station.
• (b) Ad hoc networking.

123
Wireless LANs (2)

124
Wireless LANs (3)