Overview and Network Models
Textbook: Ch.1 and Ch.2
SEHH2238: Computer Networking
SEHH2238 Lecture 1 1
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SEHH2238: Computer Networking
Main Topics
Computer Networking
Connection and Transmission Mode
Topology
Categories of Networks and Internetworks
Protocols, Standards and Standard Organizations OSI Model: Open System Interconnection by ISO TCP/IP Protocol Suite
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SEHH2238: Computer Networking
1. Computer Networking
Computer Networking facilitates data communication among computing devices
Data communications :The exchange of data between two devices via some form of transmission medium.
Communication effectiveness depends on Delivery (to the correct destination) Accuracy
Timeliness
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A network is a set of devices (called nodes) connected by media links (called communication channels).
What is a good network?
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Anumberofmeasurements,e.g. Propagation/Transmission time
Response time
Performance
Performance is often evaluated by two networking metrics: Throughput
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Catastrophe
Fire , earthquake, etc. Backup system Contingency plan
Resistant to: Unauthorized access Data damage Viruses
Reliability
Frequency of failure
Recovery time of a network after a failure
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2. Types of Connections
Defines the attachment of communication devices to a link
Two Types:
Point-to-point: a dedicated link between two
Multipoint (multidrop): more than two devices share a single link
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Figure 1.3 Types of connections: point-to-point and multipoint
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3. Transmission Mode
Refers to the direction of information flow
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WCB/McGraw-Hill The McGraw-Hill Companies, Inc.,
SEHH2238: Computer Networking
(simplex, half-duplex, and full-duplex)
– Communication is unidirectional.
– Each station can both transmit and receive, but not at the same time.
– Both stations can transmit and receive simultaneously.
Figure 1.2 Data flow (simplex, half-duplex, and full-duplex)
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4.T opology
Defines the physical or logical arrangement of links in a network
It is the geometric representation of the relationship of all the links and nodes to each other (simply speaking, the shape of the network)
A consideration when choosing a topology is the relative status of the devices to be linked
Relationships: Peer-to peer or Primary-secondary SEHH2238 Lecture 1 11
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Figure 1.4 Categories of topology
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Mesh Topology
Afullyconnectedmeshtopology(fivedevices) How many links are needed?
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SEHH2238: Computer Networking
Mesh Topology
Every device has a dedicated point-to-point link to every other device
A fully connected mesh network has n(n-1)/2 physical channels
to link n devices
Convenient for peer-to-peer transmission
What are the advantages of Mesh topology?
What are the costs?
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SEHH2238: Computer Networking
Advantages
Mesh Topology
Dedicated links eliminate the traffic problem
Robust: failure of one link does not affect the whole network
Privacy/Security provided by dedicated links Easy fault identification and isolation
Disadvantages
Expensive
cost of cabling and the I/O ports
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Star Topology
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Star Topology
Each device has a dedicated link only to a central controller (called a hub) which acts as an exchange
No direct traffic between devices
Advantages:
Less expensive for cabling and I/O ports Robustness, easy fault identification and isolation
Disadvantage:
Single point of failure (what if the hub goes down?) SEHH2238 Lecture 1 17
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Bus Topology
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A broadcast channel
Bus Topology
One long cable acts as a backbone to link all the devices
Easy installation, least cabling
Due to power loss; no. of taps and distance between taps are limited
Difficult reconfiguration and fault isolation SEHH2238 Lecture 1 19
SEHH2238: Computer Networking
Ring Topology
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Ring Topology
Each device has a dedicated link only with the two neighbor devices
A signal is passed along the ring in one direction from device to device (which has a repeater)
Relatively easy to install and reconfigure
Constraints on maximum ring length & no. of
Unidirectional traffic: a break in the ring can
disable the entire network
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Hybrid Topology
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Hybrid Topology
Figure 1.9 A hybrid topology: a star backbone with three bus networks SEHH2238 Lecture 1 23
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WCB/McGraw-Hill
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5. Categories of Networks
Classify by its size, ownership, covering distance and physical architecture
SEHH2238: Computer Networking
or campus.
Local Area Network
LAN is usually privately owned
Connecting hosts in a single office, building,
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WCB/McGraw-Hill The McGraw-Hill Companies, Inc
SEHH2238: Computer Networking
Wide Area Network
Connecting devices in a wider geographical area, e.g. town, country, or even the world.
Figure 1.11 WANs: a switched WAN and a point-to-point WAN
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Internetwork
(Internet) is a network of networks
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SEHH2238: Computer Networking
Example of LAN and WAN
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Figure 1.12 A heterogeneous network made of four WANs and two LANs
SEHH2238: Computer Networking
6. Protocols
A set of rules (conventions) that govern all aspects of information exchange.
The key elements:
Syntax : Structure or format of the data Semantics : Meaning of different part Timing : When to send and how fast
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Provides a model for development that makes it possible for a product to work regardless of the individual manufacturer.
Ensures that products from different manufacturers can work together
ISO – International Standards Organization
ANSI – American National Standards Institute
IEEE – Institute of Electrical and Electronics Engineers
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SEHH2238: Computer Networking
Layering in Network Models
Data communication systems consists of a lot of rules and procedures for different functions
Divide the complex tasks into layers for simpler implementation and maintenance
Each layer only focuses on its own task Protocols are designed for specific layers
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Consider the scenario
Figure 2.1 Tasks involved in sending a letter
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7- layered architecture
Provides guidelines for the development of universally compatible architecture, hardware and software
Each layer
provides services to the layer above
While utilizing the services of the layer below
Communications between computers is a peer- to-peer process using the protocols appropriate
to a given layer
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Figure 2.15
Functions of layers
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Figure 2.3 The interaction between layers in the OSI model
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TCP/IP Protocol Suite
5-layered architecture
Being used by current Internet
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Figure 2.12: TCP/IP and OSI model
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Communication through the Internet
Figure 2.5: Communication through an Internet SEHH2238 Lecture 1 38
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How data is transmitted
Figure 2.8: Encapsulation / Decapsulation SEHH2238 Lecture 1 39
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Figure 2.16
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Examples of Protocols
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1.Types of connection: Point-to-point and Multipoint
2.Transmission Mode: Simplex, … 3.Topology: Mesh, bus, ring, star, hybrid 4.OSI Model, TCP/IP protocol suite
Revision Quiz: Chapter 1
• http://highered.mheducation.com/sites/0073376221/student_view0/chapter1/quizzes.html Chapter 2
• http://highered.mheducation.com/sites/0073376221/student_view0/chapter2/quizzes.html SEHH2238 Lecture 1 41
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