Carrier sense multiple access with collision avoidance
Encyclopedia
Carrier sense multiple access with collision avoidance (CSMA/CA), in computer network
ing, is a wireless network multiple access method in which:
CSMA/CA is a modification of carrier sense multiple access
.
Collision avoidance is used to improve CSMA performance by not allowing wireless transmission of a node if another node is transmitting, thus reducing the probability of collision due to the use of a random truncated binary exponential backoff time.
Optionally, but almost always implemented, an IEEE 802.11 RTS/CTS
exchange can be required to better handle situations such as the hidden node problem
in wireless networking.
CSMA/CA is a layer 2 access method, not a protocol of the OSI model.
spectrum. Collisions cannot be detected while occurring at the sending node, thus it is vital for CSMA/CA or another access method to be implemented.
CSMA/CA is used in 802.11 based wireless LAN
s and other wired and wireless communication systems. One of the problems of wireless data communications 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.
exchange. Implementation of RTS/CTS helps to solve the hidden node problem
that is often found in wireless networking.
(DSSS) provides the highest throughput for all nodes on a network when used in conjunction with CSMA/CA and the IEEE 802.11 RTS/CTS exchange under light network load conditions. Frequency Hopping Spread Spectrum (FHSS) follows distantly behind DSSS with regard to throughput with a greater throughput once network load becomes substantially heavy. However, the throughput is generally the same under real world conditions due to radio propagation factors.
Computer network
A computer network, often simply referred to as a network, is a collection of hardware components and computers interconnected by communication channels that allow sharing of resources and information....
ing, is a wireless network multiple access method in which:
- a carrierCarrier waveIn telecommunications, a carrier wave or carrier is a waveform that is modulated with an input signal for the purpose of conveying information. This carrier wave is usually a much higher frequency than the input signal...
sensing scheme is used. - a nodeNode (networking)In communication networks, a node is a connection point, either a redistribution point or a communication endpoint . The definition of a node depends on the network and protocol layer referred to...
wishing to transmit data has to first listen to the channel for a predetermined amount of time to determine whether or not another node is transmitting on the channel within the wireless range. If the channel is sensed "idle," then the node is permitted to begin the transmission process. If the channel is sensed as "busy," the node defers its transmission for a random period of time. Once the transmission process begins, it is still possible for the actual transmission of application data to not occur.
CSMA/CA is a modification of carrier sense multiple access
Carrier Sense Multiple Access
Carrier 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...
.
Collision avoidance is used to improve CSMA performance by not allowing wireless transmission of a node if another node is transmitting, thus reducing the probability of collision due to the use of a random truncated binary exponential backoff time.
Optionally, but almost always implemented, an IEEE 802.11 RTS/CTS
IEEE 802.11 RTS/CTS
RTS/CTS is the optional mechanism used by the 802.11 wireless networking protocol to reduce frame collisions introduced by the hidden node problem...
exchange can be required to better handle situations such as the hidden node problem
Hidden node problem
In wireless networking, the hidden node problem or hidden terminal problem occurs when a node is visible from a wireless access point , but not from other nodes communicating with said AP. This leads to difficulties in media access control....
in wireless networking.
CSMA/CA is a layer 2 access method, not a protocol of the OSI model.
Details
The use of collision avoidance is used to improve the performance of CSMA by attempting to divide the wireless channel somewhat equally among all transmitting nodes within the collision domain. CSMA/CA differs from CSMA/CD due to the nature of the medium, the radio frequencyRadio frequency
Radio frequency is a rate of oscillation in the range of about 3 kHz to 300 GHz, which corresponds to the frequency of radio waves, and the alternating currents which carry radio signals...
spectrum. Collisions cannot be detected while occurring at the sending node, thus it is vital for CSMA/CA or another access method to be implemented.
CSMA/CA is used in 802.11 based wireless LAN
Wireless LAN
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. This gives users the mobility to move around within a local coverage area and still be connected to the network...
s and other wired and wireless communication systems. One of the problems of wireless data communications 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.
IEEE 802.11 RTS/CTS Exchange
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. Thus alerting all nodes within range of the sender, receiver or both, to not transmit for the duration of the main transmission. This is known as the IEEE 802.11 RTS/CTSIEEE 802.11 RTS/CTS
RTS/CTS is the optional mechanism used by the 802.11 wireless networking protocol to reduce frame collisions introduced by the hidden node problem...
exchange. Implementation of RTS/CTS helps to solve the hidden node problem
Hidden node problem
In wireless networking, the hidden node problem or hidden terminal problem occurs when a node is visible from a wireless access point , but not from other nodes communicating with said AP. This leads to difficulties in media access control....
that is often found in wireless networking.
Performance
CSMA/CA performance is based largely upon the modulation technique used to transmit the data between nodes. Studies show that under ideal propagation conditions (simulations), Direct Sequence Spread SpectrumDirect-sequence spread spectrum
In telecommunications, direct-sequence spread spectrum is a modulation technique. As with other spread spectrum technologies, the transmitted signal takes up more bandwidth than the information signal that is being modulated. The name 'spread spectrum' comes from the fact that the carrier signals...
(DSSS) provides the highest throughput for all nodes on a network when used in conjunction with CSMA/CA and the IEEE 802.11 RTS/CTS exchange under light network load conditions. Frequency Hopping Spread Spectrum (FHSS) follows distantly behind DSSS with regard to throughput with a greater throughput once network load becomes substantially heavy. However, the throughput is generally the same under real world conditions due to radio propagation factors.
Usage
- GNET - an early proprietary LANLänLän and lääni refer to the administrative divisions used in Sweden and previously in Finland. The provinces of Finland were abolished on January 1, 2010....
protocol - Apple'sApple ComputerApple Inc. is an American multinational corporation that designs and markets consumer electronics, computer software, and personal computers. The company's best-known hardware products include the Macintosh line of computers, the iPod, the iPhone and the iPad...
LocalTalkLocalTalkLocalTalk 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 WLANWireless 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. This gives users the mobility to move around within a local coverage area and still be connected to the network...
s (802.11 mainly relies on physical carrier sensing though). - IEEE 802.15.4IEEE 802.15.4IEEE 802.15.4 is a standard which specifies the physical layer and media access control for low-rate wireless personal area networks . It is maintained by the IEEE 802.15 working group....
(Wireless PAN) uses CSMA/CA - NCR WaveLANWaveLANWaveLAN is a brand 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 - HomePNAHomePNAThe 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 telephone wiring within homes.-Overview:HomePNA does not manufacture products, although its members do...
- Bus networks
- The ITU-TITU-TThe ITU Telecommunication Standardization Sector is one of the three sectors of the International Telecommunication Union ; it coordinates standards for telecommunications....
G.hnG.hnG.hn is the common name for a home network technology family of standards developed under the International Telecommunication Union's Standardization arm and promoted by the HomeGrid Forum...
standard, which provides a way to create a high-speed (up to 1 Gigabit/s) local area networkLocal area networkA local area network is a computer network that interconnects computers in a limited area such as a home, school, computer laboratory, or office building...
using existing home wiring (power linesPower line communicationPower line communication or power line carrier , also known as power line digital subscriber line , mains communication, power line telecom , power line networking , or broadband over power lines are systems for carrying data on a conductor also used for electric power transmission.A wide range...
, phone lines and coaxial cablesEthernet over coaxEthernet over Coax is a family of technologies that supports the transmission of Ethernet frames over coaxial cable.- History :The first Ethernet standard, known as 10BASE5 in the family of IEEE 802.3, specified baseband operation over coaxial cable...
), uses CSMA/CA as a channel access methodChannel 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 serviceQuality of serviceThe quality of service refers to several related aspects of telephony and computer networks that allow the transport of traffic with special requirements...
, specifically the CSMA/CARPCSMA/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 accessCarrier 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...
- Carrier sense multiple access with collision detectionCarrier sense multiple access with collision detectionCarrier sense multiple access with collision detection is a Media Access Control method in which:*a carrier sensing scheme is used....
- CSMA/CARPCSMA/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...
- IEEE 802.11 RTS/CTSIEEE 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 node problem...
- Truncated binary exponential backoff
- Network Allocation VectorNetwork Allocation VectorThe Network Allocation Vector is virtual carrier sensing mechanism used with wireless network protocols such as IEEE 802.11 and IEEE 802.16 . The virtual carrier sensing is a logical abstraction which limits the need for physical carrier sensing at the air interface in order to save power...