Medium access control
OSI model by layer |
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Internet protocol suite |
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Application layer |
Transport layer |
Internet layer |
Link layer |
In
These two sublayers together correspond to layer 2 of the
When sending data to another device on the network, the MAC sublayer encapsulates higher-level frames into frames appropriate for the transmission medium (i.e. the MAC adds a
Multiplexing |
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Analog modulation |
Statistical multiplexing (variable bandwidth) |
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Related topics |
Functions performed in the MAC sublayer
According to IEEE Std 802-2001 section 6.2.3 "MAC sublayer", the primary functions performed by the MAC layer are:[2]
- Frame delimiting and recognition
- Addressing of destination stations (both as individual stations and as groups of stations)
- Conveyance of source-station addressing information
- Transparent data transfer of LLC PDUs, or of equivalent information in the Ethernet sublayer
- Protection against errors, generally by means of generating and checking frame check sequences
- Control of access to the physical transmission medium
In the case of Ethernet, the functions required of a MAC are:[3]
- receive/transmit normal frames
- half-duplex retransmission and backoff functions
- append/check FCS (frame check sequence)
- interframe gap enforcement
- discard malformed frames
- prepend(tx)/remove(rx) preamble, SFD (start frame delimiter), and padding
- half-duplex compatibility: append(tx)/remove(rx) MAC address
Addressing mechanism
The local network addresses used in
Examples of physical networks are Ethernet networks and Wi-Fi networks, both of which are IEEE 802 networks and use IEEE 802 48-bit MAC addresses.
A MAC layer is not required in
Channel access control mechanism
The channel access control mechanisms provided by the MAC layer are also known as a
The most widespread multiple access method is the contention-based
A multiple access method is not required in a switched
Channel access control mechanism for concurrent transmission
Use of directional antennas and
Cellular networks
Cellular networks, such as GSM, UMTS or LTE networks, also use a MAC layer. The MAC protocol in cellular networks is designed to maximize the utilization of the expensive licensed spectrum.[5] The air interface of a cellular network is at layers 1 and 2 of the OSI model; at layer 2, it is divided into multiple protocol layers. In UMTS and LTE, those protocols are the Packet Data Convergence Protocol (PDCP), the Radio Link Control (RLC) protocol, and the MAC protocol. The base station has absolute control over the air interface and schedules the downlink access as well as the uplink access of all devices. The MAC protocol is specified by 3GPP in TS 25.321[6] for UMTS, TS 36.321[7] for LTE and TS 38.321[8] for 5G.
See also
- Isochronous media access controller
- List of channel access methods
- MAC-Forced Forwarding
- MACsec(IEEE 802.1AE)
References
- ^ "X.225 : Information technology – Open Systems Interconnection – Connection-oriented Session protocol: Protocol specification". Archived from the original on 1 February 2021. Retrieved 10 March 2023.
- ^ "IEEE 802-2001 (R2007) IEEE Standard for Local and Metropolitan Area Networks: Overview and Architecture" (PDF). IEEE.
- ^ "4.1.4", IEEE 802.3-2002, IEEE
- .
- ISBN 978-1107143210.
- ^ 3GPP TS 25.321 Medium Access Control (MAC) protocol specification
- ^ 3GPP TS 36.321 Evolved Universal Terrestrial Radio Access (E-UTRA); Medium Access Control (MAC) protocol specification
- ^ 3GPP TS 38.321 NR; Medium Access Control (MAC) protocol specification