WELCOME to COMP 421 CMPET 401

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WELCOME to COMP 421 /CMPET 401

• COMMUNICATIONS and NETWORKING
• Class 1

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COURSE OUTLINE

• Overview of Communications
• Introduction
• Protocols and Architecture
• Data Communications
• Data Transmission
• Transmission Media
• Data Encoding
• Data Link Control
• Multiplexing

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COURSE OUTLINE (continued)

• Local and Wide Area Networks
• LAN WAN Protocols
• Switching Techniques
• Bridges and Routers
• High Speed Networks
• Internetworking
• Internet Resources
• Network Operating Systems

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TELECOMMUNICATIONS

• Telecommunications is the technique of
  transmitting a message from one point to another
• knowing how much information, if any, is likely
  to be lost in the process.
• Hence the term TELECOMUNICATIONS covers all forms
  of distance communications
• including
• Radio
• Telegraph
• Television
• Telephony
• Data Communications
• Computer Networking

• The elements of a telecommunication system are
• Transmitter
• Channel
• Line
• Receiver
• The transmitter is a device that transforms or
  codes the message into a physical
• phenomenon called the transmission channel, by
  its physical nature it is likely to
• modify or degrade the signal on it path from the
  transmitter to the receiver.

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TELECOMMUNICATIONS
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TELECOMMUNICATIONS
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The Communications Model
output information
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Communication Tasks

• Communication Tasks Include
• Transmission System Utilization
• Interfacing
• Signal Generation
• Synchronization
• Exchange Management
• Error Correction and Detection
• Flow Control
• Addressing
• Routing
• Recovery
• Message Formatting
• Security
• Network Management

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Data Communication Network
Communication Network Node
Network Station
Communication Network
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Data Communication Networking

• Networks are used to link devices together
• Distant - Network is called a Wide Area Network
  (WAN)
• Circuit Switched
• Packet Switched
• Frame Relay
• ATM
• Public Switched Telephone Network (PSTN)
• Leased lines
• Public switched data network (PSDN)
• Integrated services digital network (ISDN)
• Local - Network is called a Local Area
  Network (LAN)
• Intermediate - Network is called a Metropolitan
  Area
• Network (MAN)

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PSTN

• modem link via PSTN

PSTN
modem
modem
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LAN
station
4th floor

• confined geographical area
• under single management
• high data rate

station
3rd floor
station
2nd floor
1st floor
server
router
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Leased lines

• Lease pubic circuits to connect different
  sites
• Communication channel is private

LAN
Voice
leased circuit
LAN
Voice
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PSDN

• PSDN is designed specifically for the
  transmission of data rather than voice
• Communication is shared

LAN
PSDN Public Switched Data Network
LAN
PSDN
LAN
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ISDN
ISDN is an acronym for integrated Services
Digital Network ISDN provides integrated voice
and data over the Telephone company facilities.
3 Telephone Lines
1 ISDN Line
Telco Central Office
Telco Central Office
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Standards

• Standards are required in the telecommunications
  industry to govern
• the physical, electrical and procedural
  characteristics of communications
• equipment.
• Some organizations whom exist, at least
  partially, to create these
• standards are
• The Internet Society
• ISO
• ITU-T (formerly CCITT)
• The ATM Forum
• IEEE

RFC - Request for Comment
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Standards
ISO ITU-T
Integrated computer and telecommunications
industry
International Standards (Open Systems
Interconnection)
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Standards

• The Standardization Process of the Internet
  Organizations is
• Be stable well understood
• Be technically competent
• Have multiple independent and interoperable
• implementations with substantial
  operational experience
• Enjoy significant public support
• Be recognizable useful in some or all parts of
  the Internet

The key difference between theses criteria and
this used for the international standards from
ISO and ITU-U is the emphasis on operational
experience
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Standards
Internet Draft
The process a specification goes through to
become a standard is defined by RFC 2026
Proposed Standard
Experimental
International
Draft Standard
Internet Standard
Historic
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An Example 802.11 Wireless LAN
802.11 Initial 1 2 Mbps 802.11a High Rate
5.7Ghz 802.11b 5.5 and 11 Mbps 802.11c MAC
Bridge 802.11d Regulating Domains 802.11e Qualit
y of Service 802.11f Multi-Vendor Inter-Access
Port 802.11g High Rate 2.4Ghz 802.11h Power
Control/Frequency Selection 802.11i Enhanced
Security 802.11j 4.9-5Ghz in Japan 802.11k Radio
Resonance Management
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TOPOLOGIES
A network topology is the geometric arrangement
of nodes and cable links in a LAN, and is used in
two general configurations bus and star. These
two topologies define how nodes are connected to
one another. A node is an active device connected
to the network, such as a computer or a printer.
A node can also be a piece of networking
equipment such as a hub, switch or a router. A
bus topology consists of nodes linked together in
a series with each node connected to a long cable
or bus. Many nodes can tap into the bus and begin
communication with all other nodes on that cable
segment. A break anywhere in the cable will
usually cause the entire segment to be inoperable
until the break is repaired. Examples of bus
topology include 10BASE2 and 10BASE5.
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TOPOLOGY
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Computer Networks

• A computer network is a system for communication
  among two or more computers
• Computer network may be categorized by Range
• PAN
• LANMANWAN
• Computer network applications may be categorized
  with respect to the functional
• relationships between components
• Client-server
• Multi-tier architecture
• peer to peer

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PANs
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MANs

• Distances between 5 and 50 km
• Data rate above 1 Mbps
• Standards IEEE 802.6 DQDB, FDDI, and ATM

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LANs (Local Area Networks)

• Maximum distance not more than a few kms
• Ownership by a single organization
• Transmission speed of at least several Mbps (tens
  to hundreds are economical)

• Some widely used standards include
• IEEE 803.3 - Ethernet
• IEEE 803.5 - Token ring
• FDDI
• ATM
• An important issue in broadcast LANs is the
  allocation of the shared channel (media access
  control)
• Control may be static (time division
  multiplexing) or dynamic (contention or
  arbitration)

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WANs (Wide Area Networks)
Often a network is located in multiple physical
locations. Wide area networking combines multiple
LANs that are geographically separate. This is
accomplished by connecting the different LANs
using services such as dedicated leased phone
lines, dial-up phone lines both synchronous and
asynchronous, satellite links, and data packet
carrier services. Wide area networking can be as
simple as a modem and remote access server for
employees to dial into, or it can be as complex
as hundreds of branch offices globally linked
using special routing protocols and filters to
minimize the expense of sending data sent over
vast distances.
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WAN

• WAN (Wide Area Network)
• Spans entire states or countries
• Data rate of 1.544 (T1), and 45 (T3) Mbps common
• Higher data rates are available with the wide
  deployment of ATM backbone networks
• Often owned by multiple organizations

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WAN

• Usually separate communications functions from
  application functions
• Transmission lines circuits, channels or trunks
• Switching elements
• Specialized computers connecting two or more
  circuits

• Intermediate Systems, Packet Switching Node, Data
  Switching Exchange, Router, etc.
• Intermediate systems store a complete packet
  before forwarding it
• store-and-forward packet switched
  point-to-point network

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Computer Networks
Computer Networks may be implemented using a
variety of network protocol stack architectures
computer buses or combinations of media and
protocol layers incorporating one or more of the
following ARCNETDECNETEthernet IP TCP AppleTalk
Token Ring IPX FDDIHSSI ATM RS-232 USBFirewire
X.25 Blue Tooth WiFi Frame Relay
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Network Software

• Network software is highly structured
• This technique has been immensely successful
• The key is Layered design
• Each layer provides a service to the layer above
• Each layer hides details of how the service is
  provided to the layer above
• The Nth layer on one machine talks to or
  interacts with the Nth layer on another machine

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Understanding Services and Protocols

• Protocol is set of rules about the format and
  meaning of data units exchanged by peers
• Protocol is used by entities to implement
  services
• Protocol and/or its implementation can change and
  as long as the Service (interface) remains
  unchanged, higher layers are happy and continue
  to work
• Like in abstract data types or object
  orientation, we decouple interface and
  implementation

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Protocols
Although each network protocol is different, they
all share the same physical cabling. This common
method of accessing the physical network allows
multiple protocols to peacefully coexist over the
network media, and allows the builder of a
network to use common hardware for a variety of
protocols. This concept is known as "protocol
independence," which means that devices that are
compatible at the physical and data link layers
allow the user to run many different protocols
over the same medium.
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Protocols
A Structured Set of Modules implements the
communications function
That structure is referred to as a Protocol
Architecture
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Protocols

• The Key Elements of Protocols are
• SYNTAX - Data format and signal levels
• SEMANTICS- Control information for coordination
• error handling
• TIMING - speed matching and sequencing

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Network Software - Protocols

• Conventions and rules governing this interaction
  are specified by the Layer N Protocol
• A protocol is an agreement about how
  communications are to proceed
• Without a protocol, communication can be
  difficult or even impossible
• E.g. Telephone conversation, Postal addresses

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Network Software - Protocols

• The set of protocols and layers together make up
  the Network Architecture
• A Network Architecture Specification must provide
  enough information to allow implementation in
  hardware/software
• Implementation specific details are not part of
  the architecture and should be irrelevant for
  inter-operation
• With one protocol per layer we have a Protocol
  Stack

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Network Software - Protocols

• Information is not actually transferred directly
  between peer layer N entities
• Peer layer N entities carry on a virtual
  communication using the services of the layers
  below
• Layer N passes data and control information down
  to (or receives data and control from) Layer N-1
  until the physical medium is reached

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The benefits of Layered Protocols

• Network Architectures, Protocols and Protocol
  stacks are the Fundamentals of Computer Networks
• They form the foundation for the very
  considerable success of computer networks in the
  real world
• Multilayer communications protocols allow
• ready adaptation of successful protocols to new
  technology (prevent obsolescence)
• migration of protocols from software
  implementation (slow) to hardware (fast) as they
  evolve

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More Benefits of Layered Protocols

• Separate data and control information
• Support differing levels of abstraction (message,
  packet, frame) with different sizes
• Allow segmentation of large messages
• Peer process abstraction facilitates reduction of
  difficult design task (a network architecture)
  into smaller manageable tasks (protocol layer
  architecture)
• Typically lower layer protocols of network
  software are implemented in silicon (hardware)

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Network Software - Interfaces Services

• Interfaces exist between each layer
• Interface defines which primitive functions and
  services layer N-1 provides to layer N
• Want layers to
• Perform a well defined, logically related set of
  functions
• Minimize the amount of information needed to pass
  between layers
• Keep interfaces clean to allow easy and
  transparent replacement of layers

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The 3 Layer Model
This layer is concerned with the exchange of
data between the computer and the network

• Network access Layer -
• Transport Layer -
• Application Layer -

This layer is concerned with reliable and orderly
exchange of data
This layer provides the logic required to support
the various user applications
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A Simple Architecture
SAPs
( ) ( ) ( ) ( )
Network Address
Comms Network
( ) ( ) ( ) ( )
( ) ( ) ( ) ( )

• Each computer contains software at all three
  layers.
• Every entity on the network must have a unique
  address
• Actually two layers of addressing are required
• A unique network address
• Each application of the computer must have a
  unique address
• This application address allows the transport
  layer to support
• applications on each computer and are known as
• Service Access Points (SAPs)

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Simplified Architecture
Computer A
Computer B
Application Protocol
Transport Protocol
Comms \Network
Network Access Protocol
Network Access Protocol
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PDUs
Protocol Data Unit (PDU) -
is the combination of data from the next higher
layer and control information
Application data
Transport protocol data unit (TPDU)
Application data
Transport header
Transport header
Application data
Network protocol data unit (NPDU)
Transport header
Transport header
Network header
Network header
Application data
Application data

• control info data in each layer protocol
  data unit (PDU)

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Network Operation
Information in Transport Header
Destination SAP - Tells the destination
Transport layer to whom to deliver the
message Sequence Number - Tells the destination
what order the PDU was sent by numbering
them Error-Detection Code - The sending
transport sends a code that is a function of the
contents
of the PDU. The receiving entity
performs the same calculation
and compares the
two numbers.
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Network Operation
Information in Network Header
Destination Computer Address - Tells the network
to which computer the
data
is to be delivered Facilities Requests - Tells
the network to make use of certain facilities
(i.e. Priority)
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Operation of Protocol Architecture
Source X
Destination Y
Application
Application
Record
Record
Transport
Transport
DSAP

DSAP
Transport PDU
Network Access
Network Access




DHost
DHost
Packet
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Network Operation

• Computer X desires to send a record to computer Y
• Computer X hands the record via a procedure call
  to the Transport layer
• The Transport layer adds its header creating the
  Transport PDU
• This is passed down to the Network layer
• The Network layer adds its header creating the
  Network PDU
• The Network accepts the network PDU from X and
  delivers it to Y
• The network access module in Y receives the PDU
  and strips off the header
• It transfers the transport PDU to its transport
  layer
• The Transport layer examines the transport header
  and on the basis of the
• SAP field delivers the enclosed record

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The components of a basic Network
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Why establish a computer network

• Program and file sharing
• Network resource sharing
• Database sharing
• Economical expansion of the PC base
• Workgroup capabilities
• Centralized management
• Security
• Interconnectivity
• Enhancement of corporate structure

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Distributed computing
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Access methods in a distributed computing
environment
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A local area network (LAN) and an internetwork
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A network communication model
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Circuit Switching
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Circuit Switching
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Circuit Switching
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Packet Switching
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Packet Switching
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Packet Switching
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Internet
The Internet is a system of linked networks that
are worldwide in scope and facilitates data
communication service such as remote login, file
transfer, electronic mail, the World Wide Web and
newsgroups. With the meteoric rise of demand for
connectivity, the Internet has become the
communications highway for millions of users. The
Internet was initially restricted to military and
academic institutions in its infancy but now it
is a full-fledged information channel for any and
all forms of information and commerce. Internet
websites now provide personal, educational,
political and economic resources to every corner
of the planet.
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Intranet
With the advancements made in browser-based
software for the Internet, there is now a
phenomenon developed by private organizations
called an intranet. An intranet is a private
network utilizing Internet-type tools, but
available only within that organization. For
large organizations, an intranet provides an easy
access mode to corporate information for
employees.
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