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Computer Networks Lecture: Kholoud .A.E Contents .… • IEEE 802 / Communication channel access method IEEE 802.3 CSMA/CD (Ethernet) IEEE 802.5 Token Ring • IEEE 802 references model Logical Link Control (LLC) Media Access Control (MAC) • Ethernet • Servers • Workstations

Computer Networks Lecture: Kholoud.A.E Contents…. IEEE 802 / Communication channel access method IEEE 802.3 CSMA/CD (Ethernet) IEEE 802.5 Token Ring IEEE

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Computer Networks Lecture: Kholoud.A.E IEEE CSMA/CD (Ethernet) Ethernet is the most well-known example of the IEEE CSMA/CD standard The original CSMA/CD standard – Defines a bus topology network that uses a 50 ohm coaxial baseband cable – Carries transmissions at 10Mbps Currently, the standard has been amended to include speeds up to 10Gbps 3

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Page 1: Computer Networks Lecture: Kholoud.A.E Contents…. IEEE 802 / Communication channel access method IEEE 802.3 CSMA/CD (Ethernet) IEEE 802.5 Token Ring IEEE

Computer Networks

Lecture: Kholoud .A.E

Contents.…• IEEE 802 / Communication channel access methodIEEE 802.3 CSMA/CD (Ethernet)IEEE 802.5 Token Ring• IEEE 802 references model Logical Link Control (LLC)Media Access Control (MAC)• Ethernet• Servers• Workstations

Page 2: Computer Networks Lecture: Kholoud.A.E Contents…. IEEE 802 / Communication channel access method IEEE 802.3 CSMA/CD (Ethernet) IEEE 802.5 Token Ring IEEE

Computer Networks

Lecture: Kholoud .A.E

IEEE 802 Standards

• Designed primarily for enhancements “ تحسينات ” to the bottom three layers of the OSI model

• Breaks the Data Link layer into two sublayers– The LLC sublayer manages data link

communications – The MAC sublayer watches out for data collisions

and assigns physical addresses .

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Page 3: Computer Networks Lecture: Kholoud.A.E Contents…. IEEE 802 / Communication channel access method IEEE 802.3 CSMA/CD (Ethernet) IEEE 802.5 Token Ring IEEE

Computer Networks

Lecture: Kholoud .A.E

IEEE 802.3 CSMA/CD (Ethernet)• Ethernet is the most well-known example of the IEEE

802.3 CSMA/CD standard• The original 802.3 CSMA/CD standard

– Defines a bus topology network that uses a 50 ohm coaxial baseband cable

– Carries transmissions at 10Mbps• Currently, the 802.3 standard has been amended to

include speeds up to 10Gbps

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IEEE 802.3 CSMA/CD (Ethernet)• The CSMA/CD acronym illustrates how it works

– Carrier Sense (CS) means that computers on the network are listening to the wire at all times

– Multiple Access (MA) means that multiple computers have access to the line at the same time

– Collision Detection (CD) detects collisions and senders send again

• CSMA/CD technology is considered a contention-based access method

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Page 5: Computer Networks Lecture: Kholoud.A.E Contents…. IEEE 802 / Communication channel access method IEEE 802.3 CSMA/CD (Ethernet) IEEE 802.5 Token Ring IEEE

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Lecture: Kholoud .A.E

IEEE 802.3 CSMA/CD (Ethernet)• The only major downside to 802.3 is that with

large networks (more than 100 computers on the same cable), the number of collisions

increases to the point where more collisions than transmissions are taking place .

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IEEE 802.5 Token Ring• Specifies a physical star, logical ring topology

that uses a token-passing technology to put the data on the cable

• A computer with data to transmit takes a free token off the ring, modifies it, places the token (along with the data) back on the ring

• When the original sender receives the token back, it modifies the token to make it free for use and sends the token back on the ring

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Page 7: Computer Networks Lecture: Kholoud.A.E Contents…. IEEE 802 / Communication channel access method IEEE 802.3 CSMA/CD (Ethernet) IEEE 802.5 Token Ring IEEE

Computer Networks

Lecture: Kholoud .A.E

IEEE 802.5 Token Ring

• Main advantage of the token-passing access method is that it eliminates collisions

• Whole procedure takes place in a few milliseconds

• Scales very well– Not uncommon for Token Ring networks based on

the IEEE 802.5 standard to reach hundreds of workstations on a single ring

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Lecture: Kholoud .A.E

Token Ring

• Exactly like the IEEE 802.5 specification • Uses a physical star, logical ring topology• Workstations are cabled to a central device

called a multi station access unit (MAU)• Can use shielded or unshielded cable and can

transmit data at either 4Mbps or 16Mbps

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Lecture: Kholoud .A.E

Ethernet• Original definition of the IEEE 802.3 model

included a bus topology using coaxial cable and baseband signaling

• From this model came the first Ethernet architecture

• Has several specifications, each one specifying the speed, communication method, and cable

• Original Ethernet was given a designation of 10Base5

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Lecture: Kholoud .A.E

Servers

• Core component of the network– Provide a link to the resources needed to perform

tasks– Direct client computers – Centralize the control of resources and security– Balance the load on computers– Compartmentalize files

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Workstations• The computers on which the network users do their

work• Connected to a network that offers additional

resources• Also known as client computers• Items needed to make a workstation into a network

client– Network interface card (NIC)– Special expansion card – Cabling system – Client software

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Workstations• To users, being on a network changes a few

things:– They can store more information– They can share and receive information from

other users– They can use programs that would be too large or

complex for their computer– They can use hardware not attached directly to

their computer

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Computer Networks

Lecture: Kholoud .A.E

Contents.…

Objective :-

• Advantages of Network

• Type of Network

• Comparison between LAN,MAN &WAN

• What is Interanet , Extranet , and Internet

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Advantages of NetworkComputer network provides several important advantages to company and individuals.1.Organization today are widely desired over in the world. The sites need to exchange information and data. A network provides the means to exchanges data among these computer and to make data available to the people of the company .

2.The networking of computers permit the sharing of resources.

3.It allows a very flexible working environment Employee can work at home by using terminal tied networks into the computer at the office.

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Lecture: Kholoud .A.E

Type of Network

Local Area Network (LAN)

Wide Area Network (WAN)

Metropolitan Area Network ( MAN)

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Lecture: Kholoud .A.E

LAN LAN can provide users

Flexibility

Speed

Reliability

Adaptability

Security

Transparent Interface

Access to the other LAN & WAN.

Hardware & Software sharing.

Centralized Management.

Private ownership of the LAN.

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Computer Networks

Lecture: Kholoud .A.E

LAN Attributes of LAN

1. The LAN transmits data among user stations.

2. The LAN transmission capacity is more than 1 Mbps.

3. The LAN channel is typically privately owned by the organization

using the facility .

4. The geographical coverage of LANs is limited to areas less than 5

square kilometers.

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Computer Networks

Lecture: Kholoud .A.E

LAN LANs are typically identified by the following properties :

1. High total bandwidth ( -10 Mbps) . 2. Low delay. 3. Low error rate.4. Broadcast / Multicast capability. 5. Limited geography ( 1-2 Km) . 6. Peer relationship between stations. 7. Confined to private property.

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Lecture: Kholoud .A.E

LAN • The low level protocols used in such environment are different from

those used in wide area network .• The common forms of LAN are those described by the IEEE

standard 802. This standard describes operation up to and including OSI layer 2. Individuals may build what they like on top of these basic protocols.

• A commonly set oh higher level protocols is called TCP/IP which provides OSI layer 3 and 4 functionality, on top of this may be found a set of protocols commonly called Talent protocols.

• LANs are capable of transmission data at very fast rates, mush faster than data can be transmitted over a telephone line; but the distances are limited, and there is also a limited on the number of computer that can be attached to a single LAN .

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Lecture: Kholoud .A.E

LAN The following characterizes differentiate one LAN from another :

• Topology : the geometric arrangement of devices on the network .For example :devices can be arranged in a ring or in a straight line.

• Protocols : The rules and encoding specifications for sending data. The protocol also determine whether the network uses a peer- to –peer or client/server architecture .

• Media: Devices can be connected by twisted-pair wire, coaxial cable, or fiber optic cable . Some networks do without connecting media altogether, communicating instead via radio waves.

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MAN • A MAN ,while larger than LAN is limited to city or group of nearby

corporate offices. It uses similar technology of LAN.

• The Metropolitan Area Network standards are sponsored by the

IEEE,ANSI and the Regional Bell operating companies.

• MAN is provides the transfer rates from 34 to 150 Mbps.

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MAN • MAN is designed with two unidirectional buses. Each bus is

independent of the other in the transfer of traffic.

• MANs are based on fiber optic transmission technology and provide

high speed interconnection between sites. It can support both data

and voice.

• MAN as special category is that a standard has been adopted for

them and this standard is now begin implemented. It is called IEEE

802.6.

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Computer Networks

Lecture: Kholoud .A.E

WAN • A WAN provides long distance transmission of data and voice.

• A Network that covers a large area such as a city , state, country or the world is called

wide area network.

• The WAN contains host and collection of machines. User program is installed on the

host and machines. All the host are connected by each other through communication

subnet. Subnet carries messages from host.

• Subnet consists of transmission lines and switching element. The transmission line is

used for data between two machines. Switching elements are used for connecting two

transmission lines. Switching elements are specialized computers. It selects the proper

outgoing line for incoming data and forward the data on that line.

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Comparison between LAN,MAN &WAN

Parameterمؤشر

LANWANMAN

Area covered Covers small areaWithin the building

Covers larger geographical area

Converse larger than LAN& smaller than WAN

Error rates LowestHighestModerate

Transmission speedHigh speedLow speedModerate speed

Equipment cost Uses inexpensive equipment

Uses most expensive equipment

Uses moderately expensive equipment

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Computer Networks

Lecture: Kholoud .A.E

Comparison between MAN &WAN NoWANMAN

1It Converse small areaWAN covers large geographical area

2LAN operates on the principle of broadcastingWAN operates on the principle of point to point

3Uses for time critical applicationNot used for time critical application

4Transmission speed is highTransmission speed is low

5Easy to design 7 maintainDesign& maintenance is not easy

6LAN is broadcasting in natureWAN is point to point in nature

7Transmission medium is coaxial or UTP cableTransmission or communication medium is PSTN or satellite link

8LAN does not suffer form propagation delayWAN suffer from propagation delay

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Lecture: Kholoud .A.E

Internet• Definition:- The Internet is the worldwide, publicly accessible network of

interconnected computer networks that transmit data by packet switching using the standard Internet Protocol (IP). It is a "network of networks" that consists of millions of smaller domestic, academic, business, and government networks, which together carry various information and services, such as electronic mail, online chat, file transfer, and the interlinked Web pages and other documents of the World Wide Web.

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Intranet• Definition:- An intranet is a private computer network that uses Internet

protocols, network connectivity, and possibly the public telecommunication system to securely share part of an organization's information or operations with its employees. The same concepts and technologies of the Internet such as clients and servers running on the Internet protocol suite are used to build an intranet. HTTP and other Internet protocols are commonly used as well, especially FTP and e-mail

• Briefly, an intranet can be understood as "a private version of the Internet", or as a version of the internet confined to an organization.

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Extranet• Definition:- An Extranet is a private network that uses Internet protocols,

network connectivity, and possibly the public telecommunication system to securely share part of an organization's information or operations with suppliers, vendors, partners, customers or other businesses. An extranet can be viewed as part of a company's Intranet that is extended to users outside the company (eg: normally over the Internet).

• It has also been described as a "state of mind" in which the Internet is perceived as a way to do business with other companies as well as to sell products to customers. Briefly, an extranet can be understood as "a private internet over the Internet“.

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FTP & HTTP

FTPHTTP

File Transfer ProtocolHyper Text Transfer Protocol

Supports remote file transferSupport web pages transfer & display

Relies on services offered by TCPBased on client (Browse)