代写代考 SEHH2238: Computer Networking

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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WCB/McGraw-Hill  The McGraw-Hill Companies, Inc

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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􏰀 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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WCB/McGraw-Hill  The McGraw-Hill Companies, Inc.,

SEHH2238: Computer Networking
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

SEHH2238: Computer Networking
Bus Topology
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WCB/McGraw-Hill  The McGraw-Hill Companies, Inc.

SEHH2238: Computer Networking
􏰀 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

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Ring Topology
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WCB/McGraw-Hill  The McGraw-Hill Companies, Inc.,

SEHH2238: Computer Networking
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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WCB/McGraw-Hill  The McGraw-Hill Companies, Inc.,

SEHH2238: Computer Networking
Hybrid Topology
Figure 1.9 A hybrid topology: a star backbone with three bus networks SEHH2238 Lecture 1 23

SEHH2238: Computer Networking
WCB/McGraw-Hill
SEHH2238 Lecture 1
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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SEHH2238: Computer Networking
Internetwork
(Internet) is a network of networks
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WCB/McGraw-Hill  The McGraw-Hill Companies, Inc.,

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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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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WCB/McGraw-Hill  The McGraw-Hill Companies, Inc.,

SEHH2238: Computer Networking
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

SEHH2238: Computer Networking
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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