The MAC protocol is specified by 3GPP in TS 25.321 5 for UMTS, TS 36.321 6 for LTE and TS 38.321 7 for 5G New Radio (NR).

The MAC sublayer and the logical link control (LLC) sublayer together make up the data link layer.

Within the data link layer, the LLC provides flow control and multiplexing for the logical link (i.e.

EtherType, 802.1Q VLAN tag etc), while the MAC provides flow control and multiplexing for the transmission medium.

For compatibility reasons, LLC is optional for implementations of IEEE 802.3 (the frames are then raw), but compulsory for implementations of other IEEE 802 physical layer standards.

Within the hierarchy of the OSI model and IEEE 802 standards, the MAC sublayer provides a control abstraction of the physical layer such that the complexities of physical link control are invisible to the LLC and upper layers of the network stack.

Thus any LLC sublayer (and higher layers) may be used with any MAC.

In turn, the medium access control block is formally connected to the PHY via a media-independent interface.

Although the MAC block is today typically integrated with the PHY within the same device package, historically any MAC could be used with any PHY, independent of the transmission medium.

For topologies with a collision domain (bus, ring, mesh, point-to-multipoint topologies), controlling when data is sent and when to wait is necessary to avoid collisions.

Additionally, the MAC is also responsible for compensating for collisions by initiating retransmission if a jam signal is detected.

When receiving data from the physical layer, the MAC block ensures data integrity by verifying the senders frame check sequences, and strips off the senders preamble and padding before passing the data up to the higher layers.

MAC addresses are typically assigned to network interface hardware at the time of manufacture.

The most significant part of the address identifies the manufacturer, who assigns the remainder of the address, thus provide a potentially unique address.

This makes it possible for frames to be delivered on a network link that interconnects hosts by some combination of repeaters, hubs, bridges and switches, but not by network layer routers.

Thus, for example, when an IP packet reaches its destination (sub)network, the destination IP address (a layer 3 or network layer concept) is resolved with the Address Resolution Protocol for IPv4, or by Neighbor Discovery Protocol (IPv6) into the MAC address (a layer 2 concept) of the destination host.

This makes it possible for several stations connected to the same physical medium to share it.

Examples of shared physical media are bus networks, ring networks, hub networks, wireless networks and half-duplex point-to-point links.

The multiple access method may detect or avoid data packet collisions if a packet mode contention based channel access method is used, or reserve resources to establish a logical channel if a circuit-switched or channelization-based channel access method is used.

The channel access control mechanism relies on a physical layer multiplex scheme.

This mechanism is only utilized within a network collision domain, for example an Ethernet bus network or a hub-based star topology network.

An Ethernet network may be divided into several collision domains, interconnected by bridges and switches.

However, the optimum scheduling of concurrent transmission is an NP-hard problem.

The MAC protocol in cellular networks is designed to maximize the utilization of the expensive licensed spectrum.

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.

The base station has absolute control over the air interface and schedules the downlink access as well as the uplink access of all devices.

Media Hub For Mac