Computer communication and network
Click Here to download or preview Computer communication and network book by Forouzan
11-12/8/2015 By: AD Khan Lecture 5 -6
The switched WAN connects the end systems, which usually comprise a router (internetworking connecting device) that connects to another LAN or WAN. The point-to-point WAN is normally a line leased from a telephone or cable TV provider that connects a home computer or a small LAN to an Internet service provider (lSP). This type of WANis often used to provide Internet access.
the inter network: Toady is very rare to see a LAN, a MAN or LAN in isolation they are connected to one another so when two are more networks are connect they become and inter network or internet eg a company has tow offices one in the east the another is west the east company has a bus topology lan; the the onother has a star topology lan. and the president of the company live in the middle the administrator have to control over the company to connect these three entities a switch wan has been leased to connect lans to this switched wan so three point to point wans are required so these are provided by a telephone company..
Internet
The internet has come along way since the 1960s The internet today is not a simple It is made up many wide and local area nerowrks jioned by connecting devices and switching stationstoday most end users who want Internet connection use the sevices of internet sevice providers ISPS there are international serivece provides national services providers regional seveces providers and local serveces providrs The internet today is run by private companies not the goveernamentInternational Internet Service ProvidersAt the top of the hierarchy are the international service providers that connect nations together
National Internet Service ProvidersThe national Internet service providers are backbone networks created and maintainedby specialized companies. There are many national ISPs operating in North America; some of the most well known are SprintLink, PSINet, UUNet Technology, AGIS, and internet Mel. To provide connectivity between the end users, these backbone networks
Regional Internet Service Providers
Regional internet service providers or regional ISPs are smaller ISPs that are connected to one or more national ISPs. They are at the third level of the hierarchy with a smallerdata rate. Local Internet Service Providers Local Internet service providers provide direct service to the end users. The local ISPs can be connected to regional ISPs or directly to national ISPs. Most end users are connected to the local ISPs
Switching
WAN is a switch network . switch is the device that connect the different device
there are tow types
circut switching the telephone is a a circut switching in wich for the the communication the dedicated line is created then thats become of
pecket switching. internet is a pecket switch netowrk here the data is converted to pecket ype data when the cables is if free so itwill send the data and if the line is busy so the data is store it in a queue and when the cable become free so it send data.
Internet Standards
An Internet standard is a thoroughly tested specification that is useful to and adhered to by those who work with the Internet. It is a formalized regulation that must be followed.There is a strict procedure by which a specification attains Internet standard status. A specification begins as an Internet draft. An Internet draft is a working document(a work in progress) with no official status and a 6-month lifetime. Upon recommendation from the Internet authorities, a draft may be published as a Request for Comment (RFC). Each RFC is edited, assigned a number, and made available to all interested parties. RFCs go through maturity levels and are categorized according to their requirement level.
how to access network or network access/
there are different ways of to access the network
dial up it is the old method which is very slow and here id the possibility of one either we have to use the phone network or we have to use the internet.
DSL stands for digital subscriber line in this type the internet speed improved and we can use the phone netowrk and internet at a same time
the wire less netowrk
cable network in which the another option we can use the cable for tow purpases we can also use it for the network access and we also recive the data signals by which we can watch diffrent tv channles with out a reciver.
Computer communication and network
Click Here to download or preview Computer communication and network book by Forouzan
10/8/2015 By: AD Khan Lecture 4
Star topology:
In a star topology, each device has a dedicated point to point link only to a central controller
usually called a hub the devices not linked each other directly like a mesh topology
in this first the data is send to the controller then the data is sanded to another device. this
topology is less expensive because in this each device require one link
in this the one link is fail so the other links are not disturb bay that so they are active
but here the all topology is depend one a single point that is hub if the hub fail all network
will be fail in this more cables will be required because each node must be linked to the
hub so more cable than other topology..
Ring topology:
In this topology the devices are connected to both side with each other and has a dedicated
point to point. it may be like a ring or logically like a ring not necessary that it will
like a ring shape. the signal is passed in one direction form device to device to reach its
target.it is easy to install because each device linked to only its next neighbors.
in this one device is not working its start alarm to the network operator and there location
here the problem is traffic is unidirectional if the ring break so it can disable the entire
network .. so to solve this problem the doul ring was used in witch the traffic signal goes
both side clock wise and anti clock wise if the one link is break so it will use the next link anti clock
wise. this topology was implemented by IBM by token name and the token is called token ring.
Mesh topology:
in this topology every device has a dedicated point to point connected to every each other the traffic goes only the two links that connect. so no other device will be able to read the signals.
if there one link is break so no problem it will use another link and never effect all the
network ..to find the link n(n-1) here the more cable will be required because every device
is connected to each other by cable so the more cable will be use so it is expensive
so if there the link use both direction so n(n-1)/2
Types of network :
the criteria for network is size geographical area and owner of the network
types of network are
local area network (WAN), metropolitan area network (MAN), Wide area network (WAN)
local area network:
local area networks (LANs) are used to connect networking devices that are in a very close geographical area, such as a floor of
building ,building itself, home , shop or campus environment.
Wide Area Network: Wide area Networks (WANs) are use to connect LANs together typically wan are used when the LANs that must be connected are separated by a large distance.
Metropolitan Area Network:
A metropolitan area network (MAN) is a hybrid between a LAN and WAN
A metropolitan area network (MAN) is a computer network larger than a local
area network, covering an area of a few city blocks to
the area of an entire city, possibly also including the surrounding areas
Computer communication and network
Click Here to download or preview Computer communication and network book by Forouzan
5/8/2015 By: AD Khan Lecture 3
Network.
A network is a group of two or more computer systems devices linked together is called network.The connective devices are router modems switches .
Criteria for network.
A network must be able to meet a certain number of criteria. The most important of these are performance, reliability, and security.
Performance Performance can be measured in many ways, including transit time and response time. Transit time is the amount of time required for a message to travel from one device to another.The performance of a network depends on a number of factors, including the number of users, the type of transmission medium, and the efficiency of sofware
Reliability In addition to accuracy of delivery, network reliability is measured by the frequency of failure, the time it takes a link to recover from a failure, and the network's robustness in a catastrophe
Security Network security issues include protecting data from unauthorized access, protecting data from damage and development, and implementing policies and procedures for recovery from breaches and data losses.
Physical structure of a network
Before discussing networks, we need to define some network attributes.
Type of Connection A network is two or more devices connected through links. A link is a communications pathway that transfers data from one device to another. For visualization purposes, it is simplest to imagine any link as a line drawn between two points. For communication , two devices must be connected in some way to the same link at the same time. There are two possible types of connections: point-to-point and multipoint.
1 Point-to-Point A point-to-point connection provides a dedicated link between two devices. the link is reserved for transmission between those two devices. Most point-to-point connections use an actual length of wire or cable to connect the two ends.
2 A multipoint (also called multidrop) connection is one in which more than two specific devices share a single link . In a multipoint environment, the capacity of the channel is shared, either spatially or temporally. Ifseveral devices can use the link simultaneously, so it is a spatially shared connection. If users use the link turn by turn so, it is a timeshared connection
Physical Topology. The physical laid outs Structure of a network .
and 1 or more devices connect to a link; two or more links form a topology network. There are four basic topologies possible: mesh, star, bus, and ring
Bus Topology.A bus network is a network topology in which nodes are directly connected to a common linear (or branched) half-duplex link called a bus This network is like a bus in in the center way for walking and their link are with the different sets. the installation of the bus topology is easy. in this if the link is break every where so all the network will be disable to the both side of the break area
more about bus.(Nodes are connected to the bus cable by drop lines and taps. A drop line is a connection running between the device and the main cable. A tap is a connector that either splices into the main cable or punctures the sheathing of a cable to create a contact with the metallic core. As a signal travels along the backbone, some ofits energy is transformed into heat. Therefore, it becomes weaker and weaker as it travels farther and farther. For this reason there is a limit on the number of taps a bus can support and on the distance between those taps. Advantages of a bus topology include ease of installation. Backbone cable can be laid along the most efficient path, then connected to the nodes by drop lines of various lengths. In this way, a bus uses less cabling than mesh or star topologies. In a star, for example, four network devices in the same room require four lengths of cable reaching 12 CHAPTER 1 INTRODUCTION all the way to the hub. In a bus, this redundancy is eliminated. Only the backbone cable stretches through the entire facility. Each drop line has to reach only as far as the nearest point on the backbone. Disadvantages include difficult reconnection and fault isolation. A bus is usually designed to be optimally efficient at installation. It can therefore be difficult to add new devices. Signal reflection at the taps can cause degradation in quality. This degradation can be controlled by limiting the number and spacing of devices connected to a given length of cable. Adding new devices may therefore require modification or replacement of the backbone. In addition, a fault or break in the bus cable stops all transmission, even between devices on the same side of the problem. The damaged area reflects signals back in the direction of origin, creating noise in both directions. Bus topology was the one of the first topologies used in the design of early localarea networks
Notes written By Imdadullah
Physical Topology. The physical laid outs Structure of a network .
and 1 or more devices connect to a link; two or more links form a topology network. There are four basic topologies possible: mesh, star, bus, and ring
Bus Topology.A bus network is a network topology in which nodes are directly connected to a common linear (or branched) half-duplex link called a bus This network is like a bus in in the center way for walking and their link are with the different sets. the installation of the bus topology is easy. in this if the link is break every where so all the network will be disable to the both side of the break area
more about bus.(Nodes are connected to the bus cable by drop lines and taps. A drop line is a connection running between the device and the main cable. A tap is a connector that either splices into the main cable or punctures the sheathing of a cable to create a contact with the metallic core. As a signal travels along the backbone, some ofits energy is transformed into heat. Therefore, it becomes weaker and weaker as it travels farther and farther. For this reason there is a limit on the number of taps a bus can support and on the distance between those taps. Advantages of a bus topology include ease of installation. Backbone cable can be laid along the most efficient path, then connected to the nodes by drop lines of various lengths. In this way, a bus uses less cabling than mesh or star topologies. In a star, for example, four network devices in the same room require four lengths of cable reaching 12 CHAPTER 1 INTRODUCTION all the way to the hub. In a bus, this redundancy is eliminated. Only the backbone cable stretches through the entire facility. Each drop line has to reach only as far as the nearest point on the backbone. Disadvantages include difficult reconnection and fault isolation. A bus is usually designed to be optimally efficient at installation. It can therefore be difficult to add new devices. Signal reflection at the taps can cause degradation in quality. This degradation can be controlled by limiting the number and spacing of devices connected to a given length of cable. Adding new devices may therefore require modification or replacement of the backbone. In addition, a fault or break in the bus cable stops all transmission, even between devices on the same side of the problem. The damaged area reflects signals back in the direction of origin, creating noise in both directions. Bus topology was the one of the first topologies used in the design of early localarea networks
Notes written By Imdadullah
Computer communication and network
Click Here to download or preview Computer communication and network book by Forouzan
4/8/2015 By: AD Khan Lecture 1-2
Data Representation.
Data Representation refers to the methods used internally to represent information stored in a computer. Computers store lots of different types of information:
- numbers
- text
- graphics of many varieties (stills, video, animation)
- sound
Memory Structure in Computer
- Memory consists of bits (0 or 1)
- a single bit can represent two pieces of information
- bytes (=8 bits)
- a single byte can represent 256 = 2x2x2x2x2x2x2x2 = 28 pieces of information
- words (=2,4, or 8 bytes)
- a 2 byte word can represent 2562 pieces of information (approximately 65 thousand).
- Byte addressable - each byte has its own address.
- For more information click here.
- a single bit can represent two pieces of information
- a single byte can represent 256 = 2x2x2x2x2x2x2x2 = 28 pieces of information
- a 2 byte word can represent 2562 pieces of information (approximately 65 thousand).
Data transmission modes.
Transmission modes
A given transmission on a communications channel between two machines can occur in several different ways. The transmission is characterised by:
- the direction of the exchanges
- the transmission mode: the number of bits sent simultaneously
- synchronization between the transmitter and receiver
Simplex, half-duplex and full-duplex connections
There are 3 different transmission modes characterised according to the direction of the exchanges:
- A simplex connection is a connection in which the data flows in only one direction, from the transmitter to the receiver. This type of connection is useful if the data do not need to flow in both directions (for example, from your computer to the printer or from the mouse to your computer...).
- A half-duplex connection (sometimes called an alternating connection or semi-duplex) is a connection in which the data flows in one direction or the other, but not both at the same time. With this type of connection, each end of the connection transmits in turn. This type of connection makes it possible to have bidirectional communications using the full capacity of the line.
- A full-duplex connection is a connection in which the data flow in both directions simultaneously. Each end of the line can thus transmit and receive at the same time, which means that the bandwidth is divided in two for each direction of data transmission if the same transmission medium is used for both directions of transmission.
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