Not all networks are connected with cabling, some networks are wireless. Wireless LANs use high frequency radio signals, infrared light beams or laser to communicate between the workstations and the file server or hubs. Each workstation and file server on a wireless network has some sort of transceiver/antenna to send and receive the data. Information is relayed between transceivers as if they were physically connected. For longer distance, wireless communications can also take place through cellular telephone technology, microwave transmission or by satellite.
Wireless networks are great for allowing laptop computers or remote computers to connect to the LAN. Wireless networks are also beneficial in older buildings where it may be difficult or impossible to install cables.
The two most common type of infrared communications used in schools are Line-of-sight and Scattered broadcast.
Line-of-sight communication means that there must be an unblocked direct line between the workstation and the transceiver. If a person walks within the line-of-sight while there is a transmission, the information would need to be sent again. This kind of obstruction can slow down the wireless network.
Scattered infrared communication is a broadcast of infrared transmissions sent out in multiple directions that bounces of walls and ceilings until it eventually hits the receiver. Networking communications with laser are virtually the same as line-of-sight infrared networks.
Wireless LANs have several disadvantages. They are very expensive, provide poor security and are susceptible to interference from lights and electronic devices. They are also slower than LANs using cabling.
Showing posts with label Local Area Network (LAN). Show all posts
Showing posts with label Local Area Network (LAN). Show all posts
LAN Transmission Methods
LAN data transmission fall into three classifications
In each type of transmission, a single packet is sent to one or more nodes.
In a Unicast transmission, a single packet is sent from the source to a destination on a network. First, the source node addresses the packet by using the address of the destination node. The package is then sent onto the network and finally,the network passes the packet to its destination.
A Multicast transmission consists of a single data packet that is copied and sent to a specific subset of nodes on the network. First, the source node addresses the packet by using a multicast address. The packet is then sent into the network, which makes copies of the packet and sends a copy to each node that is a part of the multicast address.
A Broadcast transmission consists of a single data packet that is copied and sent to all nodes on the network. In these types of transmissions, the source node addresses the packet by using the broadcast address. The packet is then sent on the network, which makes copies of the packet and send.
LAN Media-Access Methods
Media contention occurs when two or more network devices have data to send at the same time. Because multiple devices cannot talk on the network simultaneously, some type of method must be used to allow one device access to the network media at a time. This is done in two main ways:
- Carrier Sense Multiple Access Collision Detect (CSMA/CD) - In networks using CSMA/CD technology such as Ethernet, network devices contend for the network media. When a device has data to send, it first listens to see if any other device is currently using the network. If not, it starts sending its data. After finishing its transmission, it listens again to see if a collision occurred. A collision occurs when two devices send data simultaneously. When a collision happens, each device waits a random length of time before resending its data. In most cases, a collision will not occur again between the two devices. Because of this type of network contention, the busier a network becomes, the more collisions occur. This is why performance of Ethernet degrades rapidly as the umber of devices on a single network increases.
- Token Passing - In Token Passing networks such as Token Ring and FDDI, a special network packet called a token is passed around the network from device to device. When a device has data to send, it must wait until it has the token and then sends its data. When the data transmission is complete, the token is released so that other devices may use the network media. The main advantage of token is released so that other devices may use the network media. The main advantage of token-passing networks is that they are deterministic. In other words, it is easy to calculate the maximum time that will pass before networks in some real-time environments such as factories, where machinery must be capable to communicating at a determinable interval.
LAN Topologies
LAN topologies define the manner in which network devices are organized. Four common LAN topologies exist:bus, ring, star and tree.
- Bus topology is a linear LAN architecture in which transmissions from network stations propagate the length of medium and are received by all other stations.
- Ring topology is a LAN architecture that consists of a series of devices connected to one another by unidirectional transmission links to form a single closed loop. Both Token Ring/IEEE 802.5 and FDDI networks implement a ring topology.
- Star topology is a LAN architecture in which the endpoints on a network are connected to a common central hub or switch, by dedicated links. Logical bus and ring topologies are often implemented physically in a star topology.
- Tree topology is a LAN architecture that is identical to the bus topology, except that branches with multiple nodes are possible in this case.
LAN as a Management tool
Management
As a management tool, a LAN can:
Increase system performance through the distribution of tasks and equipments, improve the availability of computer resources. Tasks can be assigned to several machines; increase system reliability. Crucial processes can be duplicated and/or divided so that, on the failure of one machine, other machine can quickly take up the load. Minimize the adverse effects of loss of any one system. Help regain administrative control of equipment, LAN improves the efficiency with more information accessible at workstation which can be used for taking better and timely decision. LAN can have dramatic impact on efficiency where the data is dynamic. The LAN server concept allows efficient centralization of information by allowing control over who uses the network and for what purpose. A LAN has extensive security system. A LAN has configuration flexibility. PCs and other resources can be added as and when needed.
The advantages of local area networks can be enumerated:
As a management tool, a LAN can:
Increase system performance through the distribution of tasks and equipments, improve the availability of computer resources. Tasks can be assigned to several machines; increase system reliability. Crucial processes can be duplicated and/or divided so that, on the failure of one machine, other machine can quickly take up the load. Minimize the adverse effects of loss of any one system. Help regain administrative control of equipment, LAN improves the efficiency with more information accessible at workstation which can be used for taking better and timely decision. LAN can have dramatic impact on efficiency where the data is dynamic. The LAN server concept allows efficient centralization of information by allowing control over who uses the network and for what purpose. A LAN has extensive security system. A LAN has configuration flexibility. PCs and other resources can be added as and when needed.
The advantages of local area networks can be enumerated:
- Local area networks are the best means to provide a cost-effective multiuser computer environment.
- A LAN can fit any site requirements.
- It can be tailored to suit any type of application.
- Any number of users can be accommodated.
- It is flexible and growth-oriented.
- It offers existing single users a familiar Disk Operating System (DOS) environment.
- It can use existing software if the original language supports multi-user environment.
- It offers electronic mail as an in-built facility.
- It allows sharing of mass central storage and printers.
- Data transfer rates are above 10 Mbps.
- It allows file/record locking.
- It provides foolproof security system against illegal access to data.
- It provides data integrity.
More characterisctic of LAN
LAN as a Communication Resource
Communication
LAN facilitates communication through its powerful Electronic Mail System (EMS) among authorized network users across time boundaries and distance. Network provides fast responses and transmits urgent notes, messages and circulars.
As a communication resources, a LAN can:
LAN facilitates communication through its powerful Electronic Mail System (EMS) among authorized network users across time boundaries and distance. Network provides fast responses and transmits urgent notes, messages and circulars.
As a communication resources, a LAN can:
- Facilitate communication within the organization by supplying an additional channel for coordinating the work of various groups, exchanging data, sending messages and sharing information.
- Provide in-house, computer-to-computer communication at high speed.
- Provide a method of accessing remote resources, thereby facilitating communication with the world outside the immediate organization.
More characteristic of LAN
LAN as a Productivity tool
Productivity
Productivity depends on ensuring that people have timely access to the equipment and information required to perform their job. LAN increases productivity because key individuals in the organization will be able to get access to and share database, documents and expensive peripherals.
As a productivity tool, a LAN can:
Productivity depends on ensuring that people have timely access to the equipment and information required to perform their job. LAN increases productivity because key individuals in the organization will be able to get access to and share database, documents and expensive peripherals.
As a productivity tool, a LAN can:
- Enable wider distribution of information and the technologies needed to deal with it.
- Improve information retrieval, processing, storage and dissemination through a distributed database.
- Minimize or even if possible, eliminate redundant and repetitive tasks.
- Improve efficiency by facilitating the unification of systems and procedures.
- Provide graphic capabilities and other specialized application that are not cost-effective on stand-alone micros.
More characteristic of LAN
LAN as a Resource Sharing Tool
Resource Sharing
LAN eliminates the possibility of overspending by allowing workstations to share peripherals like printers, plotters, digitizers, tape drives and hard disks. The lowers the overall cost of data processing. Provides for efficient and flexible communication. By providing a facility through which a wide variety of computer equipment can shared by many people, the local area network presents a cost-effective solution. In a LAN the shared resources need not be just hardware, software and information also may be shared.
As a resource sharing tool, a LAN can:
LAN eliminates the possibility of overspending by allowing workstations to share peripherals like printers, plotters, digitizers, tape drives and hard disks. The lowers the overall cost of data processing. Provides for efficient and flexible communication. By providing a facility through which a wide variety of computer equipment can shared by many people, the local area network presents a cost-effective solution. In a LAN the shared resources need not be just hardware, software and information also may be shared.
As a resource sharing tool, a LAN can:
- Permit sharing of expensive hardware.
- Facilitate sharing of complex programs and the information that they generate and manage.
Aid in the integration of all aspects of information processing, particularly transforming a group of individual, not very powerful microcomputers into a powerful distributed processing system.
More characteristics of LAN:
Characteristics of LAN
A common communication medium over which all user devices can share information, programs and equipment without regard to the physical location of the user or the resource. A high transmission rate intended to accommodate the needs of both people and equipment. The system normally is able to support transmission between workstations at the maximum speed at which they can communicate, a limited geographic range: generally defined as less than 10 miles or 16 kilometers. To minimize the error rate, a built-in method of detecting and compensating for system errors is implied.
A LAN is characterized by the following:
A LAN is characterized by the following:
LAN Cable
LAN Cable as a comp0nent of LAN
LAN uses coaxial cable RG-62. This is a relatively superior cable that allows for base band transmission. The cable is capable of transferring up to 10 Mbps. Special end connectors are used to interface with network interface card or hubs.
The advantage of the coaxial cable are:
LAN uses coaxial cable RG-62. This is a relatively superior cable that allows for base band transmission. The cable is capable of transferring up to 10 Mbps. Special end connectors are used to interface with network interface card or hubs.
The advantage of the coaxial cable are:
- Wider band width
- Interference resistance
- High conductivity without distortion
- Longer distance covered.
Active Hub and Passive Hub
Active and Passive Hub as a component of LAN
Active Hub
An active hub is a powered distribution point with active devices which drive distant nodes up to 1 kilometer away. Active hubs can be cascaded to connect 8 connections to which passive hubs, file servers or another active hubs can be connected Maximum distance covered by an active hub is about 2000 ft.
Passive Hub
It is passive distribution point which dies not use power or active devices in a network to connect up to 4 nodes within a very short distance. Maximum distance covered by a passive hub is about 300 ft.
Active Hub
An active hub is a powered distribution point with active devices which drive distant nodes up to 1 kilometer away. Active hubs can be cascaded to connect 8 connections to which passive hubs, file servers or another active hubs can be connected Maximum distance covered by an active hub is about 2000 ft.
Passive Hub
It is passive distribution point which dies not use power or active devices in a network to connect up to 4 nodes within a very short distance. Maximum distance covered by a passive hub is about 300 ft.
Network Interface Unit (NIU)
Network Interface Unit (NIU) as a component of LAN
The network interface unit is a microprocessor-based device containing hardware and software which supply the intelligence to control access and communication across the network and to perform all communication processing. It is the means by which the workstations are connected functionally and physically to the network.
On most microcomputer, the network interface is a printed circuit board installed in the microcomputer. On some networks, the network interface may be implemented as a stand-alone box, termed a wiring center, or hub, attached between the main network cable and the workstation.
Network interface functions are realized through chips on the interface unit: Network bus drivers, communication controller chips, specialized microprocessors, RAM buffers and ROM code are executed by the workstation itself. For most LANs, the network interface unit for all user workstations is identical. Server interface units may include additional ROM code to implement additional functions. Physical connection to the network is provided through a standard communication or input/output interface.
Through the network interface, data on the medium is available to all attached workstations and peripherals. System users never need to know what it takes to get from one point to another; they simply indicate the desired destination. The network interface unit provides transmission and data control, formats the data into manageable units, translates the data rate and protocols of the attached workstation to the network communication medium and vice versa, and supplies address recognition capabilities. Details of network operation are hidden from users of the attached workstations.
Network Interface can be classified in to the communication interface, containing network oriented functions and the host interface, containing computer specific functions.
The communication interface is the unit which logically interfaces to the network. It performs all transmission related functions. It accepts data from the attached workstations, buffers the data until the communication channel is available and then transmits the data. The communications interface also monitors the channel for messages addressed to its workstation, stores the data and transfers the data to the device.
The host interface supplies the connection between a specific workstation's internal circuitry and the communication interface unit. It fits into the input/output structure of a particular computer and governs all data exchange between the workstation and the communication-oriented portion of the network interface.
The network interface unit is a microprocessor-based device containing hardware and software which supply the intelligence to control access and communication across the network and to perform all communication processing. It is the means by which the workstations are connected functionally and physically to the network.
On most microcomputer, the network interface is a printed circuit board installed in the microcomputer. On some networks, the network interface may be implemented as a stand-alone box, termed a wiring center, or hub, attached between the main network cable and the workstation.
Network interface functions are realized through chips on the interface unit: Network bus drivers, communication controller chips, specialized microprocessors, RAM buffers and ROM code are executed by the workstation itself. For most LANs, the network interface unit for all user workstations is identical. Server interface units may include additional ROM code to implement additional functions. Physical connection to the network is provided through a standard communication or input/output interface.
Through the network interface, data on the medium is available to all attached workstations and peripherals. System users never need to know what it takes to get from one point to another; they simply indicate the desired destination. The network interface unit provides transmission and data control, formats the data into manageable units, translates the data rate and protocols of the attached workstation to the network communication medium and vice versa, and supplies address recognition capabilities. Details of network operation are hidden from users of the attached workstations.
Network Interface can be classified in to the communication interface, containing network oriented functions and the host interface, containing computer specific functions.
The communication interface is the unit which logically interfaces to the network. It performs all transmission related functions. It accepts data from the attached workstations, buffers the data until the communication channel is available and then transmits the data. The communications interface also monitors the channel for messages addressed to its workstation, stores the data and transfers the data to the device.
The host interface supplies the connection between a specific workstation's internal circuitry and the communication interface unit. It fits into the input/output structure of a particular computer and governs all data exchange between the workstation and the communication-oriented portion of the network interface.
Gateway
Gateway as a component of LAN
This component is used to connect two different LANs which are having dissimilar components. The gateway assists in transferring bits from one LAN to the other. A workstation is dedicated to act as the gateway. Network adapter cards for both types of LANs are inserted in the machine, and a special set of Novell program transfers the bits from one LAN to the other. Similarly a LAN can also be connected to another mainframe computer by a gateway.
This component is used to connect two different LANs which are having dissimilar components. The gateway assists in transferring bits from one LAN to the other. A workstation is dedicated to act as the gateway. Network adapter cards for both types of LANs are inserted in the machine, and a special set of Novell program transfers the bits from one LAN to the other. Similarly a LAN can also be connected to another mainframe computer by a gateway.
File Server
File Server as a powerful component of LAN
The file server is a powerful computer which runs a special software to act as a file server. As the name suggests, it serves to networked computers which share and use these files. The files can be programs, text or data. The file server is a completely enclosed logical structure, which is secure against accidental or malicious abuse as it can be accessed only through Network Operating System (NOS).
The activity of each file server can be monitored from the file server's screen. The system supervisor monitors and control operation of each individual network through the file server and uses it to control the print spooling, send/broadcast messages and perform many other system functions. The file server has a large volume of memory which is used for caching directories, files and directory hashing. File servers also support backup facilities, print serving and so on.
Novell Net Ware, for example, requires on a workstation to log on to a file server to enter the LAN. Under Novell Net Ware, specifically designed machines are converted to file servers. Under the PC network Program, any workstation can perform the function of file serving on any files that have been designated as public.
A file server is a resource that should be available to all workstations. If the file server is forced to operate as a workstation at the same time, it then must divide its processing time and memory between two tasks, with the performance of both suffering.
The file server is a powerful computer which runs a special software to act as a file server. As the name suggests, it serves to networked computers which share and use these files. The files can be programs, text or data. The file server is a completely enclosed logical structure, which is secure against accidental or malicious abuse as it can be accessed only through Network Operating System (NOS).
The activity of each file server can be monitored from the file server's screen. The system supervisor monitors and control operation of each individual network through the file server and uses it to control the print spooling, send/broadcast messages and perform many other system functions. The file server has a large volume of memory which is used for caching directories, files and directory hashing. File servers also support backup facilities, print serving and so on.
Novell Net Ware, for example, requires on a workstation to log on to a file server to enter the LAN. Under Novell Net Ware, specifically designed machines are converted to file servers. Under the PC network Program, any workstation can perform the function of file serving on any files that have been designated as public.
A file server is a resource that should be available to all workstations. If the file server is forced to operate as a workstation at the same time, it then must divide its processing time and memory between two tasks, with the performance of both suffering.
Workstation
Workstation as a component of a LAN
As the most common component, a workstation is an individual single-user microcomputer with communications capabilities added. The term includes in the microcomputer itself as well as all its attached bits and pieces-memory cards, CRT, floppy disk drives, hard disks and printers. A workstation is distinguished from a personal computer by the network operating system software that controls what the workstations can and cannot do and by a network interface unit that supplies the communications capabilities.
Every workstation will run memory resident software, called Workstation Shell, which is the software interface between file server and workstation. This will filter local and network requests/commands.
A workstation can send or receive messages to or from other workstation or file server. For some LANs, the connection to a workstation can be made with a serial port. In that case, the LAN interface-unit is not a plug-in board internal to the computer but an external component.
Workstations may have one to several floppy-disk drives and hard-disk drives. Workstations may be divided into two classes: users and servers, User Work stations are microcomputers on the network which have a primary responsibility to an individual user. Server workstations perform a service to other workstation on the network. All workstations on the network communicate and cooperate with one another. The primary difference between server and user workstations is directly attached resources and programs which they run.
User workstations normally do not and cannot fulfill request from other workstations.
Resources attached to a user workstation, such as floppy disk drives, can only be accessed by the user of that workstation.
More than one server may be attached to a network, with each server providing a different function or one server fulfilling several roles.
Server workstations are of two kinds:
As the most common component, a workstation is an individual single-user microcomputer with communications capabilities added. The term includes in the microcomputer itself as well as all its attached bits and pieces-memory cards, CRT, floppy disk drives, hard disks and printers. A workstation is distinguished from a personal computer by the network operating system software that controls what the workstations can and cannot do and by a network interface unit that supplies the communications capabilities.
Every workstation will run memory resident software, called Workstation Shell, which is the software interface between file server and workstation. This will filter local and network requests/commands.
A workstation can send or receive messages to or from other workstation or file server. For some LANs, the connection to a workstation can be made with a serial port. In that case, the LAN interface-unit is not a plug-in board internal to the computer but an external component.
Workstations may have one to several floppy-disk drives and hard-disk drives. Workstations may be divided into two classes: users and servers, User Work stations are microcomputers on the network which have a primary responsibility to an individual user. Server workstations perform a service to other workstation on the network. All workstations on the network communicate and cooperate with one another. The primary difference between server and user workstations is directly attached resources and programs which they run.
User workstations normally do not and cannot fulfill request from other workstations.
Resources attached to a user workstation, such as floppy disk drives, can only be accessed by the user of that workstation.
More than one server may be attached to a network, with each server providing a different function or one server fulfilling several roles.
Server workstations are of two kinds:
- Dedicated: The microcomputer is restricted to network function and often incorporates more powerful capabilities than user workstations do. It can support more features, such as electronic mail service or multiple hard disks and provides faster system response. Larger networks usually require dedicated servers.
- Non-dedicated: The microcomputer can act as an individual workstation even while it controls the network. Additional memory is required for all but the simplest tasks. Under light load, performance of a non-dedicated server may be slightly less than that of a workstation; under heavy processing demand, the individual user of the server may find work impossible.
Some network servers are capable of operating in both dedicated and non-dedicated mode, depending on the user's selection.
Components of a LAN
Local Area Network (LAN) has several distinct components like work-station, file-server, gateway, Network interface card, active hub, passive hub, LAN cables etc.
LAN (Local Area Network)
LAN is computer network that spans a relatively small area. Most LAN's are confined to a single building or group of buildings. However, one LAN can be connected to other LANs over any distance via telephone lines and radio waves. A system of LANs connected in this way is called a Wide Area Network (WAN).
Most LANs connect workstations and personal computers. Each node (individual computer) in a LAN has its own CPU with which it executes programs, but it also is able to access data and devices anywhere on the LAN. This means that many users can share expensive devices, such as laser printers, as well as data. Users can also use the LAN to communicate with each other, by sending e-mail or engaging in chat sessions.
Related Topics:
Most LANs connect workstations and personal computers. Each node (individual computer) in a LAN has its own CPU with which it executes programs, but it also is able to access data and devices anywhere on the LAN. This means that many users can share expensive devices, such as laser printers, as well as data. Users can also use the LAN to communicate with each other, by sending e-mail or engaging in chat sessions.
Related Topics:
- Components of a LAN
- Characteristics of LAN
- LAN Topologies
- LAN Media-Access Methods
- LAN Transmission Methods
- Wireless LANs
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