Carrier sense multiple access with collision avoidance

Carrier sense multiple access with collision avoidance

In computer networking, CSMA/CA belongs to a class of protocols called multiple access methods. CSMA/CA stands for: Carrier Sense Multiple Access With Collision Avoidance.In CSMA, a station wishing to transmit has to first listen to the channel for a predetermined amount of time so as to check for any activity on the channel. If the channel is sensed "idle" then the station is permitted to transmit. If the channel is sensed as "busy" the station has to defer its transmission. This is the essence of both CSMA/CA and CSMA/CD. In CSMA/CA (LocalTalk), once the channel is clear, a station sends a signal telling all other stations not to transmit, and then sends its packet. In Ethernet 802.3, the station continues to wait for a time, and checks to see if the channel is still free. If it is free, the station transmits, and waits for an acknowledgment signal that the packet was received.

Details

CSMA/CA is a modification of pure Carrier Sense Multiple Access (CSMA). Collision avoidance is used to improve the performance of CSMA by attempting to be less "greedy" on the channel. If the channel is sensed busy before transmission then the transmission is deferred for a "random" interval. This reduces the probability of collisions on the channel.

CSMA/CA is used where CSMA/CD cannot be implemented due to the nature of the channel. CSMA/CA is used in 802.11 based wireless LANs. One of the problems of wireless LANs is that it is not possible to listen while sending, therefore collision detection is not possible. Another reason is the hidden terminal problem, whereby a node A, in range of the receiver R, is not in range of the sender S, and therefore cannot know that S is transmitting to R.

CSMA/CA can optionally be supplemented by the exchange of a Request to Send (RTS) packet sent by the sender S, and a Clear to Send (CTS) packet sent by the intended receiver R, alerting all nodes within range of the sender, the receiver, or both, to keep quiet for the duration of the main packet. This is known as the IEEE 802.11 RTS/CTS exchange......

Usage

*GNET - an early proprietary LAN protocol
*Apple's LocalTalk implemented CSMA/CA on an electrical bus using a three-byte jamming signal.
*802.11 RTS/CTS implements virtual carrier sensing using short Request to Send and Clear to Send messages for WLANs (802.11 mainly relies on physical carrier sensing though).
* IEEE 802.15 (Wireless PAN) uses CSMA/CA
* NCR WaveLAN - an early proprietary wireless network protocol
* HomePNA
* Bus networks

ee also

* Carrier sense multiple access with collision detection (CSMA/CD): - a different approach to the same problem; used for Ethernet

References

* [http://www.atis.org/tg2k/ American National Standard T1.523-2001, Telecom Glossary 2000]
* [http://www.securitytube.net/CSMA-CA-video.aspx CSMA/CA Tutorial on www.SecurityTube.net]


Wikimedia Foundation. 2010.

Игры ⚽ Нужно сделать НИР?

Look at other dictionaries:

  • Carrier sense multiple access with collision avoidance — Saltar a navegación, búsqueda Contenido 1 Detalles 2 Usos 3 Problemas que resuelve CSMA/CA (con respecto a CSMA/CD) …   Wikipedia Español

  • Carrier Sense Multiple Access with Collision Avoidance — Pile de protocoles 7.  Application 6.  Présentation 5.  Session 4.  Tr …   Wikipédia en Français

  • Carrier sense multiple access with collision avoidance — En redes informáticas, Carrier Sense Multiple Access With Collission Avoidance (CSMA/CA) es un protocolo de control de redes utilizado para evitar colisiones entre los paquetes de datos (comúnmente en redes inalámbricas, ya que estas no cuenta… …   Enciclopedia Universal

  • Carrier sense multiple access with collision detection — (CSMA/CD), in computer networking, is a network control protocol in which *a carrier sensing scheme is used. *a transmitting data station that detects another signal while transmitting a frame, stops transmitting that frame, transmits a jam… …   Wikipedia

  • Carrier sense multiple access with collision detection — CSMA/CD, siglas que corresponden a Carrier Sense Multiple Access with Collision Detection (en español, Acceso Múltiple por Detección de Portadora con Detección de Colisiones ), es una técnica usada en redes Ethernet para mejorar sus prestaciones …   Wikipedia Español

  • Carrier-Sense Multiple Access with Collision Avoidance —    The network access method used by Apple s LocalTalk networks, among others. In a CSMA/CA environment, a primary workstation attempting to transmit data sends a request to transmit signal to a secondary workstation. When the sending workstation …   IT glossary of terms, acronyms and abbreviations

  • Carrier sense multiple access with collision avoidance — …   Википедия

  • Multiple Access with Collision Avoidance for Wireless — (MACAW)[1] is a slotted Medium Access Control (MAC) protocol widely used in Ad hoc networks.[2] Furthermore, it is foundation of many other MAC protocols used in Wireless Sensor Networks (WSN).[2] The IEEE 802.11 RTS/CTS mechanism is adopted from …   Wikipedia

  • Multiple Access with Collision Avoidance — (MACA) is a slotted media access control protocol used in wireless LAN data transmission to avoid collisions caused by the hidden station problem and to simplify exposed station problem. The basic idea of MACA is a wireless network node makes an… …   Wikipedia

  • Carrier sense multiple access — (CSMA) is a probabilistic Media Access Control (MAC) protocol in which a node verifies the absence of other traffic before transmitting on a shared physical medium, such as an electrical bus, or a band of electromagnetic spectrum. Carrier Sense… …   Wikipedia

Share the article and excerpts

Direct link
… Do a right-click on the link above
and select “Copy Link”