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The Media Access Control Layer is one of two sublayers that make up the Data Link Layer of the OSI model. The MAC layer is responsible for moving data packets to and from one Network Interface Card (NIC) to another across a shared channel.
The MAC sublayer uses MAC protocols to ensure that signals sent from different stations across the same channel don't collide.
In the Open Systems Interconnection (OSI) model of communication, the Media Access Control layer is one of two sublayers of the Data Link Control layer and is concerned with sharing the physical connection to the network among several computers. Each computer has its own unique MAC address. Ethernet is an example of a protocol that works at the Media Access Control layer level.
WiMAX MEDIA ACCESS CONTROL, MAC (data link) layer
The WiMAX MAC uses a scheduling algorithm for which the subscriber station needs to compete only once for initial entry into the network. After network entry is allowed, the subscriber station is allocated an access slot by the base station. The time slot can enlarge and contract, but remains assigned to the subscriber station, which means that other subscribers cannot use it. In addition to being stable under overload and over-subscription, the scheduling algorithm can also be more bandwidth efficient. The scheduling algorithm also allows the base station to control Quality of Service (QoS) parameters by balancing the time-slot assignments among the application needs of the subscriber station.
A MAC layer or Media Access Control data communication protocol sub-layer may also be known as a Medium Access Control layer.
A MAC layer is a sub-layer of the Data Link Layer. This is defined in the standard seven-layer OSI model as layer 2. The MAC layer provides addressing and channel access control mechanisms that make it possible for several terminals or network nodes to communicate within a multi-point network, typically a local area network (LAN) or metropolitan area network (MAN).
The WiMAX MAC has been designed and optimised to enable point to multipoint wireless applications and the WiMAX MAC layer provides an interface between the physical layer and the higher application layers within the stack.
The WiMAX MAC layer has to meet a number of requirements:
The WiMAX MAC layer is primarily an adaptation layer between the physical layer and the upper layers within the overall stack.
One of the main tasks of the WiMAX MAC layer is to transfer data between the various layers.
For the different formats: IEEE 802.16-2004 and IEEE 802.16e-2005, the WiMAX MAC design includes a convergence sublayer. This is used to interface with a variety of higher-layer protocols, such as ATM, Ethernet, IP, TDM Voice, and other future protocols that may arise.
WiMAX defines a concept of a service flow and has an accompanying Service Flow Identifier, SFID. The service flow is a unidirectional flow of packets with a particular set of QoS parameters, and the identifier is used to identify the flow to enable operation.
There is an additional layer between the WiMAX MAC itself and the upper layers. This is called the Convergence Sublayer. For the upper protocol layers, the convergence sublayer acts as an interface to the WiMAX MAC. Currently the convergence sublayer only supports IP and Ethernet, although other protocols can be supported by encapsulating the data.
The WiMAX MAC layer provides for a flexible allocation of capacity to different users. It is possible to use variably sized MPDUs from different flows - these can be included into one data burst before being handed over to the PHY layer for transmission. Also, multiple small MSDUs can be aggregated into one larger MPDU. Conversely, one big MSDU can be fragmented into multiple small ones in order to further enhance system performance. This level of flexibility gives significant improvements in overall efficiency.
Before any data is transferred over a WiMAX link, the user equipment or mobile station and the base station must create a connection between the WiMAX MAC layers of the two stations. To achieve this, an identifier known as a Connection Identifier, CID, is generated and assigned to each uplink / downlink connection. The CID serves as an intermediate address for the data packets transmitted over the WiMAX link.
There is another identifier used within the WiMAX MAC layer. Known as the Service Flow Identifier, SFID, this is assigned to unidirectional packet data traffic by the base station. It is worth noting that the base station WiMAX MAC layer also handles the mapping of the SFIDs to CIDs to provide the required quality of service.
The WiMAX MAC layer also incorporates a number of other features including power-management techniques and security features.
The WiMAX MAC layer has been developed to provide the functionality required for a point to multipoint system. The WiMAX MAC layer is also able to provide support for the different physical layers needed for the different flavours of WiMAX that are in use.
WiMAX QoS or WiMAX Quality of Service is a key element in the delivery of service over the WimAX medium. WiMAX QoS.
With techniques such as Internet Protocol being used, delays or latency and jitter can be introduced into the data transmission arena. While IP techniques provide improved levels of efficiency, this comes at a cost.
To overcome the effects of latency and jitter, the concept of quality of service is used. For WiMAX QoS several techniques and definitions are at the core of the implementation.
In an ideal world it would be possible to send data over a network and gain the same performance as that achieved by a circuit switched network. However the nature of packet data means that the same channels are sued for data travelling to and from a variety of different sources and end points.
Within a packet data network, there are three main parameters that are key to the performance of the network, and the WiMAX QoS. These three parameters are:
In order to categorise the different types of quality of service, there are five WiMAX QoS classes that have been defined.
These WiMAX QoS classes are defined in the table below:
The basic WiMAX standard does not define the WiMAX network for end to end connectivity. However the need for a standard WiMAX network architecture is realised and the WiMAX Forum Network Working Group have developed a standard for defining the WiMAX network architecture.
The standard now used is available from the WiMAX Forum as WiMAX Forum Network Architecture, document: WMF - T32-002-R010v04 and it is dated February 03, 2009.
The WiMAX architecture developed by the WiMAX form supports is a unified network architecture to support fixed, nomadic and mobile operation. The WiMAX network architecture is based upon an all-IP model.
The WiMAX network architecture comprises three major elements or areas.
The overall WiMAX network comprises a number of different entities that make up the different major areas described above. These include the following entities