Computer Networks
• 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
Lecture: Kholoud .A.E

Computer Networks
• Designed primarily for enhancements
” تانيسحت “ 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 .
2 Lecture: Kholoud .A.E

Computer Networks
• 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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Computer Networks
• 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
4 Lecture: Kholoud .A.E

Computer Networks
• 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 .
5 Lecture: Kholoud .A.E

Computer Networks
• 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
6 Lecture: Kholoud .A.E

Computer Networks
• 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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Computer Networks
• 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
8 Lecture: Kholoud .A.E

Computer Networks
• 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
9 Lecture: Kholoud .A.E

Computer Networks
• 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
10 Lecture: Kholoud .A.E

Computer Networks
• 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
11 Lecture: Kholoud .A.E

Computer Networks
• 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
12 Lecture: Kholoud .A.E

Computer Networks
• Advantages of Network
• Type of Network
• Comparison between LAN,MAN &WAN
• What is Interanet , Extranet , and Internet
Lecture: Kholoud .A.E

Computer Networks
Computer 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.
Lecture: Kholoud .A.E

Computer Networks
 Local Area Network (LAN)
 Wide Area Network (WAN)
 Metropolitan Area Network ( MAN)
Lecture: Kholoud .A.E

Computer Networks
 LAN can provide users
LAN
 Flexibility
 Speed
 Reliability
 Adaptability
 Security
 Transparent Interface
 Access to the other LAN & WAN.
 Hardware & Software sharing.
 Centralized Management.
 Private ownership of the LAN
.
Lecture: Kholoud .A.E

Computer Networks
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.
Lecture: Kholoud .A.E

Computer Networks
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.
Lecture: Kholoud .A.E

Computer Networks
• 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 .
Lecture: Kholoud .A.E

Computer Networks
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.
Lecture: Kholoud .A.E

Computer Networks
• 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.
Lecture: Kholoud .A.E

Computer Networks
• 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.
Lecture: Kholoud .A.E

Computer Networks
• 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 .
Lecture: Kholoud .A.E

Computer Networks
Comparison between LAN,MAN &WAN
Parameter
رشؤم
LAN WAN MAN
Area covered
Error rates
Transmission speed
Equipment cost
Covers small area
Within the building
Lowest
High speed
Uses inexpensive equipment
Covers larger geographical area
Highest
Converse larger than
LAN& smaller than WAN
Moderate
Low speed Moderate speed
Uses most expensive equipment
Uses moderately expensive equipment
Lecture: Kholoud .A.E

Computer Networks
3
4
5
6
7
1
No
2
WAN
It Converse small area
MAN
WAN covers large geographical area
LAN operates on the principle of broadcasting WAN operates on the principle of point to point
8
Uses for time critical application
Transmission speed is high
Easy to design 7 maintain
LAN is broadcasting in nature
Transmission medium is coaxial or UTP cable
LAN does not suffer form propagation delay
Not used for time critical application
Transmission speed is low
Design& maintenance is not easy
WAN is point to point in nature
Transmission or communication medium is PSTN or satellite link
WAN suffer from propagation delay
Lecture: Kholoud .A.E

Computer Networks
• 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.
Lecture: Kholoud .A.E

Computer Networks
• 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.
Lecture: Kholoud .A.E

Computer Networks
• 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“.
Lecture: Kholoud .A.E

Computer Networks
FTP
File Transfer Protocol
Supports remote file transfer
Relies on services offered by TCP
HTTP
Hyper Text Transfer Protocol
Support web pages transfer & display
Based on client (Browse)
Lecture: Kholoud .A.E