Logical link control

August 22, 2016 by zafer mehmood95

Filed under Ethernet Performance

Last modified August 22, 2016

Logical link control

In the IEEE 802 reference model Computer networks, the logical link control (LLC) data communication protocol layer, the upper sublayer of the data link layer (Layer 2) of the seven layers of OSI model. The LLC sublayer providence multiplexing mechanisms dying to allow for multiple network protocols (IP, IPX, DECnet and AppleTalk) side by side within a multipoint network, and transported through the same network medium. It can also flow control and automatic Repeat Request (ARQ) error mechanisms for the management.
The LLC sublayer acts as an interface between the Media Access Control (MAC) sub-layer and the network layer.
Operation
The LLC sublayer is principally engaged in:
Multiplexing Protocols coming from the MAC layer (Zenden) and decoding them (with receipt).
Providing the junction to flow and error control
In the dialog Networks, Will flow control and error management generally provided door-including a transport layer protocol TCP, the door an application layer protocol, in an end-to-end fashion, ie, transmission is done from source to destination. This means that the need of LLC sublayer flow control and error management Has reduced. LLC is usefull only a multiplexing function in the dialog link layer protocols. An LLC header tells the data link layer what to DO met a packet once a frame is received. It works as Follows: A host will receive a frame and look in the LLC header to go after in Which protocol stack package will Destined – for example, the IP protocol on the network layer of IPX. However, today Abandoned Most Non-IP network protocols.
Application examples
X.25 and LAPB
An LLC sublayer was an important component in the beginning of packet-switched networks-including X.25 networks met the LAPB data link layer protocol, where the flow control and error management Executed In a junction to fashion Were Executed, which means that if an error was detected in a frame, it is the framework Resent one switch to the Next Post. This Extended hand shake between the nodes made the Slow Networks.
Local Area Network (LAN) and metropolitan area network (MAN) Protocols
The IEEE 802.2 standard specifies the LLC sublayer for IEEE 802 Local Networks, goals IEEE 802.3 / Ethernet (Ether as the Field Type Not Being Used), IEEE 802.5 and IEEE 802.11. IEEE 802.2 Is ook used in some non-IEEE 802 networks-including FDDI.
Ethernet
Since bit errors are very rare in wired networks, HAS Ethernet No flow control of automatic repeat request (ARQ) What does THAT incorrect Packages Are detected, but canceled only, not broadcast (except door detected in the case of collisions, the CSMA / CD MAC layer protocol). Instead thereof, depending retransmissions Higher Protocols.
Ether type as an Ethernet frame via Ethernet II framing HAS several at multiplexing protocols on top of the Ethernet MAC header Can Be seen as an LLC identifier. However, Ethernet frames Lacking an Ether type No LLC identifier in the Ethernet header, and instead use an IEEE 802.2 LLC header after the Ethernet header to give OM protocol multiplexing function.
wireless LAN
In wireless communications, bit errors are very common. Wireless networks-including IEEE 802.11, flow control and error handling is Himself in the CSMA / CAMAC protocol and not the LLC layer. The LLC sublayer Following the IEEE 802.2 standard.
HDLC
Some non-IEEE 802 Protocols can be considered as being divided into MAC and LLC layers. For example, while HDLC specifies both MAC FEATURES (framing packages) and LLC FUNCTIONS (protocol multiplexing, flow control, detection, and error checking through a rebroadcast of Fall Packages as indicated), Can some protocols-including Cisco HDLC use HDLC-like packet framing and their own LLC protocol.
PPP and modems
Over telephone modems, PPP link layer protocols can be considered as an LLC protocol, providing multiplexing, But best No flow control and error management. In a telephone network, bit errors can are common, meaning THAT error handling is crucial, but THAT Nowadays door modern protocols. Today’s modem Protocols LLC FUNCTIONS taken from the Elder LAPM link layer protocol made for modem communications at old X.25 networks.
Cellular Systems
The GPRS LLC layer does ook ciphering and deciphering of SN-PDU (SNDCP) packages.
power cables
Another example of a data link layer die is Divided Between LLC (for flow and error control) and MAC (for multiple access) is the ITU-T G.hn standard, die high-speed local area networking best compared Existing home wiring (power lines, phone lines and coaxial cables)

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