Applications of Local Area Networks

Content:

LAN APPLICATIONS

Some of the most important general application areas of this type of networks:

PC LAN.

Some administrators frequently purchase PCs for applications such as spreadsheets, project management tools, and Internet access due to the low cost of the system.

This set of PCs does not cover all the needs of an organization because the programs are too large for a PC, requiring a centralized process and, in turn, should be accessible to different users.

The members of a project team need to share work and information, digitally being the best way to do it.

Expensive resources like a laser printer can be shared on a LAN, this can be at the building level.

A communication server can give controlled access to these resources.

The best example of using a PC is the implementation of client / server applications.

The cost of connecting to the network will be less than that of the connected device.

This suggests that the speed of the network may be limited as the cost is higher the higher the speed.

BACKUP AND STORAGE NETWORKS.

Backend networks (<<backend>>) connect large systems such as mainframe computers, supercomputers, and mass storage devices in a small space with high data throughput on a limited number of devices.

Features:

  • High speed.
  • High speed interface.
  • Distributed access.
  • Limited distance.
  • Limited number of devices. These networks are in large companies with high budgets due to their high cost.
  • It can be seen that some of the main requirements for computer room networks are the opposite of those of PC LANs. High speeds are required to work properly, which generally implies the transfer of large data blocks.
  • Although the cost of equipment to achieve high speeds is high, it is reasonable due to the much higher cost of connected devices.

HIGH-SPEED OFFICE NETWORKS.

Generally this environment includes a wide variety of devices with low-medium speed data transfer requirements. However, new applications are appearing in the office environment for which the limited speeds (up to 10 Mbps) of traditional LANs are inadequate. So the fax, graphics programs on PCs and workstations.

Even making use of compression techniques, this will generate a tremendous load. In addition, the technology and price of disks have evolved in ways that storage capacities in excess of 1 Gbyte are common. These new demands necessitate high-speed LAN networks that can support the large number and greater geographic spread of office systems compared to existing systems in computer rooms.

THE TRUNKS.

The increasing use of distributed processing applications and PCs has led to the need for a flexible LAN strategy. The support of data communications between offices requires a network service capable of covering the distances (which can be great) in large buildings or several of them. Although it is possible to develop a single LAN, it is not an acceptable alternative in most cases. There are several drawbacks to a single LAN strategy:

  • Reliability: a service outage, even of short duration, on a simple LAN could cause significant disruption to users.
  • Capacity: a single LAN could become saturated as the number of devices connected to a network grows over time.
  • Cost: a simple LAN technology is not optimal for the various interconnection and switching requirements. The existence of a large number of low-cost PCs means that network support for these devices is also low. LANs that support very low-cost connections are not adequate to meet global requirements.

A more attractive alternative is to use lower-cost, lower-capacity LANs in buildings or departments and interconnect these networks through a higher-capacity LAN. This latter network is called a backbone or backbone LAN.

LAN ARCHITECTURE

It is a hierarchy of protocols which organize the operation of it.

PROTOCOL ARCHITECTURE

Protocols with network transmission deal with issues related to the transmission of data blocks over the network. These functions are associated at OSI Layer 2. There are functions that are grouped into the LOGICAL LINK CONTROL (LLC) layer as well as the MEDIUM ACCESS CONTROL (MAC) layer. The higher level data is passed down to the LLC level, which adds a control information header giving rise to a:

  • PROTOCOL DATA UNIT (PDU) LLC. This information is used for the operation of the LLC protocol. The LLC PDU is passed to the MAC layer, which adds information to the beginning and end of each packet, forming a MAC frame. Therefore, the stored information is used for the operation of the MAC protocol.
  • TOPOLOGY.- It is a structure that consists of paths and that provides the means of interconnection between the nodes of the network. There are several types of topologies among which there are:
  • BUS.-It is characterized by the use of a multipoint medium.

All stations are directly connected, through physical interfaces called sockets, to a transmission medium. Through the operation of the FULL DUPLEX, between the station and the connection socket, it allows the transmission of data through the bus and the reception of these from it. The transmission propagates through the medium in both directions and is received by the rest of the stations. At each end there is a terminator that absorbs the signal removing it from the bus.

  • TREE.-It is a generalization of the bus topology. The transmission medium is a branched cable without closed loops. It starts at a point called
  • ROOT.-The cables begin at that point and each one has branches. The transmission propagates through the medium and reaches the rest of the stations.
  • RING.-It consists of a set of repeaters linked by point-to-point links forming a closed loop. The repeater is a device capable of receiving data through the link and transmitting it bit by bit through another link. The links are unidirectional, the data is transmitted in one direction, so that it circulates around the ring. Each station is connected to the network through a repeater, transmitting data to the network through it.
  • STAR.- Each station is directly connected to a central node, usually two point-to-point links, one for transmission and one for reception. The mode of operation is diffusion; that is, when an information frame is transmitted by a station, it is retransmitted on all the output links of the central node. Only one station can be broadcast at a given time. Also the central node works as frame switching device

PROTOCOL

Medium access control.- All LAN handheld networks consist of a set of devices that must share the transmission capacity of the network. This is why Medium Access Control (MAC) is used.

PARAMETERS: They are the where and the how refers to whether the control is distributed or centralized, that is, giving authority for access to the network.

Advantages:

- Improve access control giving priorities.

- Allows simple logic

- Solve coordination problems between joint entities

- Facility to stop the entire network when there is a failure.

How: It is imposed by the topology of the networks.

CLASSIFICATION

They are classified in:

- synchronous

- asynchronous:

  • Circular rotation.-Each station is given the opportunity when the station ends to give up the turn to the next logical station. It is used when several stations have to transmit data for a long period of time.

  • Booking.-Reservation techniques are suitable for continuous traffic, generally in these techniques the slot time is divided.

  • Containment.-They are suitable for bursty traffic, with this technique there is no control to determine whose turn it is, their advantage is that they are simple to implement and efficient for low loads.

classification_redeslan

MAC Frame Format

The MAC layer receives a data block from the LLC layer and must perform functions related to media access and data transmission like the other layers of the protocol architecture.

Media Access Control Techniques

The exact format of the MAC frame differs slightly for the various MAC protocols in use.

-MAC Control: this field contains protocol control information necessary for the operation of the MAC protocol

- DESTINATION MAC ADDRESS: Physical MAC connection point on the LAN of the destination of the frame.

- SOURCE MAC ADDRESS: Physical MAC connection point on the LAN of the source of the frame.

-LLC: LLC data of the layer immediately above.

-CRC: physical redundancy check field. It is an error detection field.

LOGICAL LINK CONTROL

The LLc layer in LANs is similar in many respects to other common list layers. Like all link layers, the LLc is associated with a PDU (data protocol unit) LLC has two characteristics:

- Must support multiple access

- The MAC layer downloads it from some link access details.

Services LLC

It specifies addressing mechanisms and controls the exchange of data between users.

Unacknowledged connectionless services

It is very simple since it does not include a mechanism to control errors and the logic is very simple.

It is useful in two situations.

1) Avoid duplication of large mechanisms.

2) the cost is very low.

Connection mode service

It is the logical connection between two users for data exchange.

It is used in very simple devices such as terminal devices for these cases the system provides flow control mechanisms and reliability.

Service NOT connection oriented without acknowledgment

It is a mixture of the previous two.

It is useful in several situations to have a logical link in tables for each active connection, but for connections that have too many tables it is impractical to make this connection.

LLC PROTOCOL (logical access control)

Advantages:

- It makes use of the operation called asynchronous balancing.

- Provides a connection-oriented service without confirmation.

- Offers a confirmed connectionless service.

-Allows multiplexing through the use of access points to the LLC service.