In
computer networkingComputer networking is the engineering discipline concerned with communication between computer systems or devices. Networking, routers, routing protocols, and networking over the public Internet have their specifications defined in documents called RFCs...
, 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.
In
computer networkingComputer networking is the engineering discipline concerned with communication between computer systems or devices. Networking, routers, routing protocols, and networking over the public Internet have their specifications defined in documents called RFCs...
, 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 AccessCarrier Sense Multiple Access is a probabilistic Media Access Control protocol in which a node verifies the absence of other traffic before transmitting on a shared transmission medium, such as an electrical bus, or a band of the electromagnetic spectrum."Carrier Sense" describes the fact that a...
(
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/CDCarrier Sense Multiple Access With Collision Detection , in computer networking, is a network access method in which*a carrier sensing scheme is used....
cannot be implemented due to the nature of the channel. CSMA/CA is used in 802.11 based
wireless LANA wireless local area network links two or more devices using some wireless distribution method , and usually providing a connection through an access point to the wider internet...
s. One of the problems of
wireless LANA wireless local area network links two or more devices using some wireless distribution method , and usually providing a connection through an access point to the wider internet...
s 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/CTSRTS/CTS is the optional mechanism used by the 802.11 wireless networking protocol to reduce frame collisions introduced by the hidden terminal problem...
exchange.
Usage
- GNET
GNet is a simple network library. It is written in C, object-oriented, and built upon GLib. It is intended to be small, fast, easy-to-use,and easy to port. The interface is similar to the interface for Java's network library....
- an early proprietary LANLän are the Swedish and lääni Finnish language terms, respectively, for the administrative divisions used in Sweden and Finland.They are also sometimes used in other countries, especially as a translation of the Russian word oblast...
protocol
- Apple's
Apple Inc. is an American multinational corporation that designs and manufactures consumer electronics and computer software products. The company's best-known hardware products include Macintosh computers, the iPod and the iPhone...
LocalTalkLocalTalk is a particular implementation of the physical layer of the AppleTalk networking system from Apple Computer. LocalTalk specifies a system of shielded twisted pair cabling, plugged into self-terminating transceivers, running at a rate of 230.4 kbit/s....
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 WLAN
A wireless local area network links two or more devices using some wireless distribution method , and usually providing a connection through an access point to the wider internet...
s (802.11 mainly relies on physical carrier sensing though).
- IEEE 802.15
IEEE 802.15 is the 15th working group of the IEEE 802 and specializes in Wireless PAN standards. It includes seven task groups :-Task group 1 :...
(Wireless PAN) uses CSMA/CA
- NCR WaveLAN
WaveLAN is a trade name that describes two completely different families of wireless network solutions:* Pre-IEEE 802.11 WaveLAN, also called Classic WaveLAN* IEEE 802.11-compliant WaveLAN, also known as WaveLAN IEEE or ORiNOCO-History:...
- an early proprietary wireless network protocol
- HomePNA
The HomePNA Alliance is an incorporated non-profit industry association of companies that develops and standardizes technology for home networking over the existing coaxial cables and phone wires within the home.The HomePNA promoter companies that set the course for the organization are AT&T, 2Wire,...
- Bus networks
- The ITU-T
The Telecommunication Standardization Sector coordinates standards for telecommunications on behalf of the International Telecommunication Union and is based in Geneva, Switzerland....
G.hnG.hn is the common name for the "next generation" home network technology standard being developed under the International Telecommunication Union and promoted by the and many other organizations....
standard, which provides a way to create a high-speed (up to 1 Gigabit/s) Local area networkA local area network is a computer network covering a small physical area, like a home, office, or small group of buildings, such as a school, or an airport...
using existing home wiring (power linesPower line communication or power line carrier , also known as Power line Digital Subscriber Line , mains communication, power line telecom , or power line networking , is a system for carrying data on a conductor also used for electric power transmission...
, phone lines and coaxial cablesEthernet over Coax is a family of technologies that supports the transmission of Ethernet frames over co-axial or coax cable.- History :The first Ethernet standard, IEEE 802.3, specified baseband operation over coaxial cable...
), uses CSMA/CA as a Channel access methodIn telecommunications and computer networks, a channel access method or multiple access method allows several terminals connected to the same multi-point transmission medium to transmit over it and to share its capacity...
for flows that don't require guaranteed Quality of serviceIn the field of computer networking and other packet-switched telecommunication networks, the traffic engineering term quality of service refers to resource reservation control mechanisms rather than the achieved service quality...
, specifically the CSMA/CARPIn computer networking, Carrier Sense Multiple Access With Collision Avoidance and Resolution using Priorities is Channel access method. CSMA/CARP is similar in nature to the CSMA/CD Channel access method used in Ethernet networks, but CSMA/CARP provides no detection of network collisions...
variant.
See also
- Carrier sense multiple access with collision detection
Carrier Sense Multiple Access With Collision Detection , in computer networking, is a network access method in which*a carrier sensing scheme is used....
(CSMA/CD): - a different approach to the same problem; used for EthernetEthernet is a family of frame-based computer networking technologies for local area networks . The name comes from the physical concept of the ether...
- CSMA/CARP
In computer networking, Carrier Sense Multiple Access With Collision Avoidance and Resolution using Priorities is Channel access method. CSMA/CARP is similar in nature to the CSMA/CD Channel access method used in Ethernet networks, but CSMA/CARP provides no detection of network collisions...