Local Area Network

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A Local Area Network (English pronunciation [ ləʊkl ˈɛəɹɪə ˈnɛtwɜːk ], in German local or local network ), LAN for short , is a computer network that exceeds the size of Personal Area Networks , the size of Metropolitan Area Networks , Wide Area Networks and Global Area Networks but not reached. A LAN is e.g. B. used in home networks or companies.

General technology variants

Infrastructure cabling

LAN cabling

A local network can be set up in different ways. Typically, a LAN is cabled from a certain size as structured cabling . Ethernet is the most widely used standard. The transmission takes place either electrically via twisted pair ( CAT5 or higher) or optically via optical fiber from fiberglass or plastic .


Current Ethernet covers data transfer rates from 10 Mbit / s to 400 Gbit / s (corresponds to a maximum of 50 GByte / s data throughput ). With the copper-based twisted pair (TP) cabling that is most frequently used today, the network radius is usually a maximum of one hundred meters, with multimode fiber a few hundred meters and with single mode fiber, standardized up to forty kilometers. Fast Ethernet 100BASE-TX and Gigabit Ethernet 1000BASE-T are the most widely used variants within the Ethernet family. 100 Gigabit Ethernet is mainly available for data centers and fast interconnections; apart from short interconnections, it practically always requires fiber optics. 40 Gigabit Ethernet for twisted pair cables as well as 2.5, 5 and 25 Gigabit Ethernet for slightly lower cable qualities have also been developed.

Hub / multiport repeater

A hub is a distribution node on a network that is a multi-port repeater . If more than two computers are connected in a network, this can be implemented via a hub. Several network cables can be routed to a hub, which is why one speaks of a star-shaped structure at the physical level . In the logical sense, each participant is connected to all others, it is a bus topology . Multiple hubs can be used in a LAN to increase the number of components that can be connected, but rules must be observed .

The hub works on a fairly simple principle: it forwards bits or symbols received from one port to all other ports. If the hub receives data from two ports at the same time, a collision occurs . The hub can neither forward nor save two data streams at the same time, colliding data transmissions are disrupted and have to be interrupted. A hub basically works in half-duplex mode . Since no data processing takes place in the hubs themselves and the signal amplification is purely physical, they only work in OSI layer 1 (bit transmission layer).

As of Gigabit Ethernet, hubs are no longer used, and they can hardly be found for Fast Ethernet either.

Switch / multiport bridge

A switch is a multi-port bridge in one component. In contrast to a hub, it has logic functions to temporarily store and filter data. A bridge only forwards each received packet to the port assigned to the respective recipient address ( MAC address ), so that physical communication is limited to the sender and recipient (“packet switching”). The lines of the other participants are not loaded and can transport other packets. If there are only switched ports in a network and no repeaters, this is referred to as a “fully switched network” (microsegmentation) in technician jargon. Such a network works collision-free and all channels reach the maximum data transmission rate . In today's networks, therefore, hubs are rarely used, but switches.


A router makes it possible to connect several networks with different protocols or media. Among other things, a router connects WAN to LAN. In contrast to a switch, it can evaluate network addresses from layer 3 , for example the network portion of IP addresses from the TCP / IP model . A router is often found at the outer borders of a network in order to connect it to the Internet or another network.

LAN over radio

Wireless local networks are called wireless LANs (WLAN); they are usually implemented using a standard from the IEEE 802.11 group , which is largely compatible with wired Ethernet. Since wireless networks do not stop at building or plant boundaries, there is a special feature here, the encryption technology. Initially, the standards according to WEP (WEP-64 or WEP-128) and WPA , which are now classified as unsafe , were used, which should therefore no longer be used. The newer WPA2 standard is currently still considered secure, although security gaps have already been identified in this too . However, this is also referred to as poor man's security , because WLAN access points and routers are marketed under enormous cost pressure. WPA2 uses a much better encryption mechanism than WPA, namely AES (Advanced Encryption Standard). The combination of any WLAN technology (WEP or WPA or WPA2 ( AES or TKIP )) with professional VPN technology via IPsec is considered to be much more secure . The only downer here are the costs for the additional VPN gateway systems such as B. Cisco PIX , Checkpoint VPN or the freely available OpenVPN solution. In Windows (from Windows XP) and macOS, a VPN client is now standard.

LAN over the power or telephone line network

Both technologies have to contend with comparatively high radiation rates, which can lead to disruption of radio services in the vicinity. Various PowerLAN variants are common for power lines, while VDSL is often used for telephone lines .

Outdated technology

LAN technology such as Token Ring , Fiber Distributed Data Interface (FDDI) and ARCNET , but also Ethernet according to 10BASE2 , 10BASE5 and 100BASE-FX are becoming less important, as are practically all other less common technology variants.

Active LAN components

In the past , the key elements of a local network were repeaters and hubs , and in some cases also routers and bridges . In newer installations, on the other hand, you can practically only find switches and routers. Since conventional routers are rarely arranged within a LAN today and Internet gateway routers are mostly used instead, a local network often represents exactly one common broadcast domain , i.e. the area of ​​a computer network in which all connected devices with their hardware Address ( MAC address ) on layer 2 of the ISO / OSI reference model ( data link layer ) can communicate directly with one another. A broadcast is a message to all domain participants that is not forwarded through a router and therefore usually does not leave the LAN.

Different segments - LANs or WLANs and VLANs

A local area network can, however, also be divided into several LANs or Virtual LANs (VLAN) in order to divide the network communication of a single physical local area network physically or logically over two or more VLANs. The end systems of one VLAN can neither see the end systems of the other VLAN, nor can they communicate with them. A router or a switch with routing functionality is usually used to connect several separate LANs or VLANs.

Collision domains are divided into smaller domains by switches (also known as bridges). In this way, collisions can be avoided and the risk of slowing down or even failure of a network due to overload can be reduced. Since repeater hubs are rarely used and there are only full duplex connections from Gigabit Ethernet , the CSMA / CD access method for half-duplex operation is rarely used.

A network subscriber can use a router (OSI reference model: layer 3, network layer) to gain access to other networks, such as other local networks or the Internet , beyond the broadcast domain .

If there is an Internet router in the network, it usually has a public IP address that is unique in the Internet , while the hosts in the local network are assigned private IP addresses . Masquerading , a special case of NAT , is used on the router so that the hosts can communicate with the Internet .

Above all in larger networks, routers are also used within a local network, among other things in order not to have too many participants within a broadcast domain .

Other devices in the network

In addition to normal computers, a LAN can also integrate other devices such as printers. Printers that do not have a LAN interface can either be integrated via special routers or via intermediate devices that take over the network communication.

See also

Web links

Commons : Local Area Network  - Album with pictures, videos and audio files

Individual evidence

  1. ^ BJ Hauser, Textbook of Communication Technology, 2010, p. 70f.
  2. ^ BJ Hauser, Textbook of Communication Technology, 2010, p. 72ff.
  3. ^ BJ Hauser, Textbook of Communication Technology, 2010, pp. 74f.
  4. Half-duplex transmission was originally intended for Gigabit Ethernet, but devices actually do not support this. For all faster variants, only full duplex is defined.