This invention relates to media control in a communication network.
Use of shared communication media for network communication typically requires control of those shared media. For example, the media may provide a limited communication capacity and media control, including media allocation and management, provides mechanisms for controlling access by stations on the network to the media in order to provide fair and efficient communication over the network.
Coupling of multiple stations using a wireless local area network (WLAN) can provide the benefits of a wired local area network (LAN) without requiring the stations to be physically coupled using transmission "wires" such as coaxial conductors, twisted pairs of wires, or optical fibers. Data is transferred using radio frequency (RF) or optical frequency (e.g., infra-red (IR)) transmission through space. Radio-based wireless networks, in general, have several characteristics that differ from wired networks. These characteristics include lower achievable data capacity due to factors including bandwidth and power limitation, time-varying communication capacity that may depend on the particular source and destination of a transmission, and higher error rates, for example, due to interfering signals.
Wireless networks typically use a similar software architecture as wired networks. A multi-layer communication protocol "stack," such as the OSI reference model, is used to implement communication over the WLAN. In current LANs, as in WLANs, the media access control (MAC) layer is responsible for access control of the communication medium. It is the MAC layer, between the communication protocols above the physical layer, that differs most between wired and wireless networks.
Various MAC approaches for WLANs have been proposed. These approaches use techniques including random access and time-, frequency-, or code-division multiple access (TDMA, FDMA, CDMA) in which each wireless station is allocated a portion of the total available communication capacity. For example, the IEEE 802.11 media access control standard is a random access technique which uses a carrier sense with a collision avoidance (CSMA/CA) scheme.
Polling techniques have been used to control access to shared communication resources, such as to a shared communication medium in a communication network. In such polling techniques, stations transmit in response to being polled by a master station in the network. In this way, multiple stations are prevented from transmitting concurrently. Concurrent transmission would, in general corrupt the data being transmitted. A polled station must respond in some way to a polling message before the master station can poll another station. Stations are typically polled in a round-robin manner. In such a round-robin approach, polling messages are sent to all other stations, and responses are sent from those stations, before a station is polled again.
Local area networks are increasingly used to transfer data, including multimedia data streams, that have various quality-of-service requirements. Examples of such requirements include a guaranteed minimum data rate and maximum delay. Applications that have such quality-of-service requirements include audio or video telephony and conferencing, multimedia collaboration, and multimedia distribution.