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Chapter 1 Part A
Data CommunicationsandNetworks Overview
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Chapter 1: Data Communications and NetworkingOverviewChapter 2: Data Communications Fundamental
Chapter 3: Characteristics of Data Communication
NetworksChapter 4: Reliable Data CommunicationsChapter 5: Multiple Access NetworksChapter 6: Internetworking Protocols
SyllabusSyllabus
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1-1 DATA COMMUNICATIONS1-1 DATA COMMUNICATIONS
The termThe term telecommunicationtelecommunication means communication at ameans communication at adistance. The worddistance. The worddatadata refers to information presented inrefers to information presented inwhatever form is agreed upon by the parties creating andwhatever form is agreed upon by the parties creating and
using the data.using the data. Data communicationsData communications are the exchange ofare the exchange of
data between two devices via some form of transmissiondata between two devices via some form of transmission
medium such as a wire cable.medium such as a wire cable.
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Figure 1.1 Five components of data communication
What is data communications?Exchange of data between two devices via a transmissionmediumAny transfer of data within a computer, between computer andany other devices
Exchange of digitally encoded information between two Sides
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Data Representation
Text represented as a bit pattern; codes oftenused: ASCII; Extended ASCII; Unicode; ISO
Numbers represented by binary equivalent
Images bit patterns representing pixels
Audio
Video
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Figure 1.2 Data flow (simplex, half-duplex, and full-duplex)
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1-2 NETWORKS1-2 NETWORKS
AA networknetwork is a set of devices (often referred to asis a set of devices (often referred to as nodesnodes))connected by communicationconnected by communication linkslinks. A node can be a. A node can be acomputer, printer, or any other device capable of sendingcomputer, printer, or any other device capable of sending
and/or receiving data generated by other nodes on theand/or receiving data generated by other nodes on the
network.network.
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Categories of Network
Based on size, ownership, distance covered, and
physical architecture:
Local Area Network (LAN) smaller
geographical area Metropolitan Area Network (MAN) network
extended over an entire city
Wide Area Network (WAN) largegeographical area
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Figure 1.3 Types of connections: point-to-point and multipoint
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Figure 1.4 Categories of topology
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Figure 1.5 A fully connected mesh topology (five devices)
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Figure 1.6 A star topology connecting four stations
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Figure 1.7 A bus topology connecting three stations
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Figure 1.8 A ring topology connecting six stations
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Figure 1.9 A hybrid topology: a star backbone with three bus networks
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Figure 1.10 An isolated LAN connecting 12 computers to a hub in a closet
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Figure 1.11 WANs: a switched WAN and a point-to-point WAN
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Figure 1.12 A heterogeneous network made of four WANs and two LANs
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1-3 THE INTERNET1-3 THE INTERNET
TheThe InternetInternet has revolutionized many aspects of our dailyhas revolutionized many aspects of our dailylives. It has affected the way we do business as well as thelives. It has affected the way we do business as well as the
way we spend our leisure time. The Internet is away we spend our leisure time. The Internet is acommunication system that has brought a wealth ofcommunication system that has brought a wealth of
information to our fingertips and organized it for our use.information to our fingertips and organized it for our use.
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Figure 1.13 Hierarchical organization of the Internet
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1-4 PROTOCOLS AND STANDARDS1-4 PROTOCOLS AND STANDARDS
In this section, we define two widely used terms:In this section, we define two widely used terms:protocolsprotocolsandand standardsstandards. First, we define protocol, which is. First, we define protocol, which is
synonymous with rule. Then we discuss standards, which synonymous with rule. Then we discuss standards, which
are agreed-upon rules.are agreed-upon rules.
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Protocols and Standards
Why do we need Protocol and Standard?
Protocol set of rules that govern data
communication; defines what, how, and when(Key elements syntax, semantics, timing)
Standard provides a model for development;allows for interoperability
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Protocols
When two computers across a network exchange data, procedures
involved can be quite complex.
These computers cannot simply send bit streams to each other and
expect to be understood.
There must be a high degree of cooperation between the two
computer systems.
For communication to occur, the entities must agree on a protocol,
what is communicated, how it is communicated, and when it is
communicated
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Key Elements of a Protocol
Syntax
Format of the data blocks
e.g. What are the fields, how many bits per field, etc.
Semantics
Control information for coordination & operation
Defines functions of the fields, what does each field do?
This include error handling information
Timing
Speed matching/synchronizing so that packets can be received properly
(especially to know where the protocol frame starts and ends)
Sequencing so that frames or packets can be received in order
(especially for packet-based switching)
f1 f2 f3
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Basic Protocol Architecture
Application Layer
Support for different user applications
e.g. e-mail, file transfer
Transport Layer
Reliable data exchange Independent of network being used
Independent of application
Network Access Layer
Exchange of data between the computer and the network
Sending computer provides address of destination so that data
can be routed
May invoke levels of service e.g. priority
Dependent on type of network used (Ethernet LAN, ATM, WLAN)
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Standards
A set of agreed-upon rules/protocols which are essential in creating
and maintaining an open and competitive market for equipmentmanufacturers and other service providers, also in guaranteeing
international interoperatibility of data and telecommunications
technology and processes
Standard Organization:
CCITT International Telegraph and Telephone Consultative
Committee in Europe [now ITU-T (International
Telecommunication Union Telecommunication standardization
sector)]
ISO International Standards Organization
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Standards
Advantages
Ensures a large market for equipment and software
Allows products from different vendors to communicate
Disadvantages
Freeze technology May be multiple standards for the same thing
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Chapter 1 Part B
Data Communications andNetworks Overview
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2-1 LAYERED TASKS2-1 LAYERED TASKS
We use the concept ofWe use the concept of layerslayers in our daily life.in our daily life.s an example, let us consider two friends whos an example, let us consider two friends who
communicate through postal mail. The processcommunicate through postal mail. The process
of sending a letter to a friend would beof sending a letter to a friend would becomplex if there were no services availablecomplex if there were no services available
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Fi ure 2.1 Tasks involved in
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2-2 THE OSI MODEL2-2 THE OSI MODEL
Established in 1947, the InternationalEstablished in 1947, the International
Standards Organization (Standards Organization (ISOISO) is a multinational) is a multinationalbody dedicated to worldwide agreement onbody dedicated to worldwide agreement oninternational standards. An ISO standard thainternational standards. An ISO standard thatcovers all aspects of network communicationscovers all aspects of network communications
is the Open Systems Interconnection (is the Open Systems Interconnection (OSIOSI))
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Motivation of OSI Model
Provides a common set of convention, to makecommunication among heterogeneous machinespossible.
If functions of each layer are well-defined,standards can be developed independently and
simultaneously for each layer that means fasterstandardization process.
If the boundaries between layers are well-defined,changes in standards in one layer need not affect
another layer easier to introduce new standards the task of communication between applications
on different computer is too complex to be handleas a unit. Problem can be decomposed intomanageable parts
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ISO is the organization.OSI is the model.
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Figure 2.2 Seven layers of the OSI
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Figure 2.3 The interaction between layers in the OSI
the same set of
layered functions must
exist in 2 systems(transmitting and
receiving sides)
communication is
achieved by having
The corresponding
(peer) layers in 2
Systems
communicate
telecom networksmainly concernthe lowest 3 layers
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Figure 2.4 An exchange using the OSI
2 3 A S OS O
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2-3 LAYERS IN THE OSI MODEL2-3 LAYERS IN THE OSI MODEL
In this section we briefly describe the functionsIn this section we briefly describe the functions
of each layer in the OSI model.of each layer in the OSI model.
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Figure 2.5 Physical
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The physical layer is responsible for movements ofindividual bits from one hop (node) to the next.
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Figure 2.6 Data link
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The data link layer is responsible for movingframes from one hop (node) to the next.
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Figure 2.7 Hop-to-hop
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Figure 2.8 Network
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The network layer is responsible for thedelivery of individual packets from
the source host to the destination host.
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Figure 2.9 Source-to-destination
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Figure 2.10 Transport
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The transport layer is responsible for the deliveryof a message from one process to another.
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Figure 2.11 Reliable process-to-process delivery of a
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Figure 2.12 Session
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The session layer is responsible for dialogcontrol and synchronization.
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Figure 2.13 Presentation
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The presentation layer is responsible fortranslation, compression, and encryption.
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Figure 2.14 Application
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The application layer is responsible forproviding services to the user.
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Fi 2 15 S f
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Figure 2.15 Summary of
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Th b i f ti f h l
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The basic functions of each layer aresummarized below:
1. Physical- Concerned with transmission of raw bit stream overphysical medium; deals with mechanical, electrical, functional andprocedural properties of interfaces and physical medium
2. Link- Responsible for node-to-node validity and integrity of thetransmissions; send blocks of data [frames] with synchronization
3. Network- Provide upper layers with data transmission andswitching technologies used to connect systems; establishes theroute between sender and receiver
4. Transport- Provide end-to-end error recovery and flow control
5. Session- Provide coordination for communication betweenapplications; establishes, manages and terminates connectionsbetween cooperating applications
6. Presentation- Manages the way data is represented to theapplication processes from difference in data representation
7. Application- Defines the rules for applications to gain entranceinto the communication system
2 4 TCP/IP PROTOCOL SUITE2-4 TCP/IP PROTOCOL SUITE
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2-4 TCP/IP PROTOCOL SUITE2-4 TCP/IP PROTOCOL SUITE
The layers in theThe layers in the TCP/IP protocol suiteTCP/IP protocol suite do nodo not
exactly match those in the OSI model. Theexactly match those in the OSI model. Theoriginal TCP/IP protocol suite was defined asoriginal TCP/IP protocol suite was defined ashaving four layers:having four layers: host-to-networkhost-to-network,, internetinternet,,transporttransport, and, and applicationapplication. However, when. However, when
TCP/IP is compared to OSI, we can say that theTCP/IP is compared to OSI, we can say that theTCP/IP protocol suite is made of five layers:TCP/IP protocol suite is made of five layers:
TCP/IP Model
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TCP/IP Model
Everyone believed that the OSI model would become the
ultimate standard for computer communication before1990, but this did not happen
TCP/IP protocol suite became the dominant commercialarchitecture because it was used and tested extensivelyin the Internet, while the OSI model was never fullyimplemented
As TCP/IP was developed concurrently with the OSImodel, it does not contain specific protocols relating toall the OSI layers
The TCP/IP suite is made of five layers
The three top-most layers in the OSI model arerepresented by the applications layer
The OSI model specifies functions associated with eachlayer, whereas TCP/IP layers contain relativelyindependent protocols that can be mixed and matched
Fi 2 16
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Figure 2.16 TCP/IP and OSI
TCP/IP M d l
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TCP/IP Model
TCP/IP M d l
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TCP/IP Model
TCP/IP Model
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TCP/IP Model
n Application Layer- contains a selection of application
protocols [e.g. FTP, SMTP, HTTP, SNMP and TELNET]
n Transport Layer- represented by 2 transport protocols:
i. TCP [Transmission Control Protocol]
ii. UDP [User Datagram Protocol]
- these are process-to-process protocols responsiblefor delivery of a message from a process [runningprogram] to another process
- TCP provides a reliable connection-oriented service- UDP provides an unrealiable connectionless service
by delivering the UDP datagrams on a best-effort basis[when error correction is not needed or for a single shortrequest/response message exchange between two
application protocols]
TCP/IP Model
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TCP/IP Model
n Network Layer
- The main protocol is IP [Internet Protocol] andother supporting protocols: ARP, ICMP and IGMP
- IP is an unreliable and connectionlessprotocol - a best-effort delivery service, it does itsbest to get a transmission through to itsdestination
- IP transport data in packets called datagrams[each=IP header + TCP or UDP packet] which
travel along different routes to destination- IP is a host-to-host protocol, meaning that it
can only deliver a packet from one device toanother by routing across multiple networks
TCP/IP Model
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TCP/IP Model
n Data Link Layer
- also known as network access layer, and isconcerned with the exchange of data between anend system and a network
- main functions are:
i. Framing IP datagrams into a stream ofbits
ii. Specifying the MAC [Medium AccessControl] methods to the networks
iii. Specifying MAC [hardware] and CRC inthe frame
- HDLC [High-level Data Link Control] and ARQ[Automatic Repeat Request] are the two
important protocols at this layer
TCP/IP Model
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TCP/IP Model
n Physical Layer
- defines the interface between devices andtransmission media [type of connectors], type ofmedia, transmission rate, type of encoding forrepresenting data bits in electrical or opticalsignals, network topology, communication mode
[e.g. fullduplex service] and etc
n There are no specific protocols defined for thelowest two layers
n
Hence, they support all of the standard andproprietary LAN or WAN protocols or technologies
2-5 ADDRESSING2-5 ADDRESSING
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2 5 ADDRESSING2 5 ADDRESSING
Four levels of addresses are used in an interneFour levels of addresses are used in an internet
employing the TCP/IP protocols:employing the TCP/IP protocols:physicalphysical,, logicallogical,,
Figure 2 17 Add i
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Figure 2.17 Addresses in
Figure 2 18 Relationship of layers and addresses in
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Figure 2.18 Relationship of layers and addresses in
Example
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In Figure 2.19 a node with physical address 10sends a frame to a node with physical address87. The two nodes are connected by a link(bus topology LAN). As the figure shows, the
computer with physical address 10 is thesender, and the computer with physical
Example
Figure 2 19 Physical
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Figure 2.19 Physical
Example
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Most local-area networks use a 48-bit(6-byte) physical address written as 12 hexadecimaldigits; every byte (2 hexadecimal digits) isseparated by a colon, as shown below:
Example
07:01:02:01:2C:4B
A 6-byte (12 hexadecimal digits) physical
Example
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Figure 2.20 shows a part of an internet withtwo routers connecting three LANs. Eachdevice (computer or router) has a pair oaddresses (logical and physical) for each
connection. In this case, each computer isconnected to only one link and therefore hasonly one pair of addresses. Each router,however, is connected to three networks (only
two are shown in the figure). So each route
p
Figure 2 20 IP
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Figure 2.20 IP
Example
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Figure 2.21 shows two computerscommunicating via the Internet. The sendingcomputer is running three processes at thistime with port addresses a, b, and c. The
receiving computer is running two processesat this time with port addresses j and k.Process a in the sending computer needs tocommunicate with process j in the receiving
computer. Note that although physicaladdresses change from hop to hop, logical
p
Figure 2 21 Port
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Figure 2.21 Port
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The physical addresses will change from hop tohop,
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Example
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p
port address is a 16-bit address representedby one decimal number as shown.
753
A 16-bit port address representedas one single number.
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The physical addresses change from hop to hop,but the logical and port addresses usually remain
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