What Lan stands for?
Local area network
Local area network (LAN), any communications network that connects computers in a building or small group of buildings. A LAN can be configured to be (1) a bus, main node or secondary channel connected to a structure, (2) a ring, in which each computer is connected to two neighboring computers to make a circular circuit. star, or (3), in which each computer is directly connected to a central computer and indirectly connected to each other. All of these have advantages, although bus design is now the most LAN design.
Even if only two computers are connected, they must follow rules or protocols when communicating. For example, you can say "ready to throw" and wait for the other to appear "ready to launch. When “multiple computers share a network, the protocol can have the rule“ speak only when you think it is ”or“ speak when someone else is talking ”.
The most common design for LANs until the mid-1970s was bus-connected Ethernet, originally made for Xerox PARC. Each computer or device has its own 48-bit address on Ethernet. Every computer that wants to transmit listens to the carrier device that indicates that the transmission is in progress. If it finds out, it will initiate the referral, sending it to the recipient 's address at the beginning of the referral. Each network system receives all messages but ignores those that are not addressed. While the system is transmitting, it listens, and if it detects a transmission, it stops, waits indefinitely, and tries. Delaying the transition period before you try again reduces the likelihood of them hitting again. This scheme is called a high risk fluid detection system (CSMA / CD). It works very well until a network is moderately loaded, and then slows down as conflicts become repetitive.
The first Ethernet had a capacity of about 2 megabits (millions of bits) per second (mbps), and 10 and 100 mbps Ethernet is common today, and Gigabit Ethernet per second is also used. bits per second; gbps). Ethernet transceivers for personal computers are inexpensive and easy to install.
A standard for wireless Ethernet networks, known as Wi-Fi, has become commonplace for home and small office networks. With frequencies of 2.4 to 5 gigahertz (GHz), these networks can transfer data at speeds of up to 600 mbps. In early 2002 another standard similar to Ethernet was released. Known as HomePlug, the first version could transmit data at approximately 8 Mbps through a building’s existing electrical infrastructure. A later version could reach rates of 1 gbps. Another standard, WiMax, covers the gap between LANs and wide area networks (WANs).
The installed base is another facet of profitability. The chances of creating a new network from scratch are slim. In most cases, there are existing equipment, applications, servers, and a cable plant. There may be much cheaper alternative network technology. And you are a migrant so that means that you have to absorb a high cost in changing your installed base, then simply staying with the existing technology may be more cost-effective.
For example, a large company can make extensive use of native Token Ring protocols to connect to legacy mainframe computers. Token Ring computers are more expensive than Ethernet computers, but after considering the cost of replacing the main computer, rewriting the applications to use TCP / IP, and changing all the end devices to use this new application, they probably won't want to. change.
Here it is useful to have a long-term strategic vision of information technology for the entire organization. If you have a long-term goal of eliminating these older applications, you need to build a network that can accommodate incremental migration to the target technology. You can migrate the core network from Token Ring to Fast and Gigabit Ethernet using TCP / IP routing and use DLSw to tunnel native Token Ring protocols. As new servers and applications become available, user devices can be migrated in relatively small groups.
An installed base does not need to shut down a network, but it can temporarily limit design options.
One of the biggest potential hidden costs of a network is maintenance. I mentioned that using unmanageable workgroup devices at the network access level can make troubleshooting difficult. I mentioned earlier that the principle of simplicity of design makes it easy to maintain the network. Remember, these are not just annoying factors for the engineer who is stuck with the ultimate responsibility for managing the network. There are costs associated with these problems.
The problem is that quantifying these costs can be extremely difficult. For example, how do you know that cutting out a specific corner will lead to the need for another employee to keep the network up and running? In general, because your design goals focus on reliability, the more corners you cut, the less reliable your results will be. Lower reliability generally translates into higher maintenance costs.
And this topic leads us to think about performance. You always want to build the best and fastest possible network for money. By "better", of course, I think the network better meets the requirements of enterprise applications. A brilliant network with incredible performance and low latency is useless if it is not compatible with the applications for which it was created.