Information about Channel Access Method
In telecommunications and computer networks, a channel access method or multiple access method allows several terminals connected to the same physical medium to transmit over it and to share its capacity. Examples of shared physical media are bus networks, ring networks, hub networks, wireless networks and half-duplex point-to-point links.
Multiple access protocols and control mechanisms are called media access control (MAC), which is provided by the data link protocol layer in the OSI seven layer model as well as in the TCP/IP five layer model.
A multiple access method is based on a multiplex method, that allows several data streams or signals to share the same communication channel or physical media. Multiplexing is provided by the physical layer. Note that multiplexing also may be used in full-duplex point-to-point communication between nodes in a switched network, which should not be considered as multiple access.
Multiple access protocols and control mechanisms are called media access control (MAC), which is provided by the data link protocol layer in the OSI seven layer model as well as in the TCP/IP five layer model.
| Multiplex techniques |
| Circuit mode — for constant bandwidth |
| TDM | FDM | WDM | Polarization multiplexing | Spatial multiplexing (MIMO) |
| Statistical multiplexing — for variable bandwidth |
| Packet mode | Dynamic TDM | FHSS | DSSS | OFDMA |
| Related topics |
| Channel access methods | Media Access Control
|
List of channel access methods
Circuit mode and channelization methods
The following are common circuit mode and channelization channel access methods:- Frequency division multiple access (FDMA)
- Orthogonal frequency division multiple access (OFDMA)
- Time-division multiple access (TDMA)
- Spread spectrum multiple access (SSMA)
- Direct-sequence spread spectrum (DSSS)
- Frequency-hopping spread spectrum (FHSS)
- Orthogonal Frequency-Hopping Multiple Access (OFHMA)
- Code division multiple access (CDMA) - the overarching form of DS-SS and FH-SS
- Multi-carrier code division multiple access (MC-CDMA)
- Space division multiple access (SDMA)
- Multi-Frequency Time Division Multiple Access (MF-TDMA)
- Wavelength division multiple access (WDMA)
Packet mode methods
The following are examples of packet mode channel access methods:- Contention based random multiple access methods:
- Aloha
- Slotted Aloha
- Multiple Access with Collision Avoidance (MACA)
- Multiple Access with Collision Avoidance for Wireless (MACAW)
- Carrier sense multiple access (CSMA)
- Carrier sense multiple access with collision detection (CSMA/CD)
- Carrier sense multiple access with collision avoidance (CSMA/CA)
- Distributed Coordination Function (DCF)
- Point Coordination Function (PCF)
- Carrier sense multiple access with collision avoidance and Resolution using Priorities (CSMA/CARP)
- Token passing:
- Token ring
- Token bus
- Polling
- Resource reservation (scheduled) packet-mode protocols:
- Dynamic Time Division Multiple Access (Dynamic TDMA)
- Packet reservation multiple access (PRMA)
- Reservation ALOHA (R-ALOHA)
Duplexing methods
Where these methods are used for dividing forward and reverse communication channels, they are known as duplexing methods, such as:- Time division duplex (TDD)
- Frequency division duplex (FDD)
Hybrid channel access scheme application examples
Note that hybrids of these techniques can be - and frequently are - used. Some examples:- The GSM cellular system combines the use of frequency division duplex (FDD) to prevent interference between outward and return signals, with FDMA and TDMA to allow multiple handsets to work in a single cell.
- GSM with the GPRS packet switched service combines FDD and FDMA with slotted Aloha for reservation inquiries, and a Dynamic TDMA scheme for transferring the actual data.
- Bluetooth packet mode communication combines frequency hopping (for shared channel access among several private area networks in the same room) with CSMA/CA (for shared channel access inside a medium).
- IEEE 802.11b wireless local area networks (WLANs) are based on FDMA and DS-CDMA for avoiding interference among adjacent WLAN cells or access points. This is combined with CSMA/CA for multiple access within the cell.
- HIPERLAN/2 wireless networks combine FDMA with dynamic TDMA, meaning that resource reservation is achieved by packet scheduling.
Definition within certain application areas
Local and metropolitan area networks
In local area networks (LANs) and metropolitan area networks (MANs), multiple access methods enable bus networks, ring networks, hubbed networks, wireless networks and half duplex point-to-point communication, but are not required in full duplex point-to-point serial lines between network switches and routers, or in switched networks (logical star topology). The most common multiple access method is CSMA/CD, which is used in Ethernet. Although today's Ethernet installations typically are switched, CSMA/CD is utilized anyway to achieve compatibility with hubs.Satellite communications
In satellite communications, multiple access is the capability of a communications satellite to function as a portion of a communications link between more than one pair of satellite terminals concurrently. Three types of multiple access presently used with communications satellites are code-division, frequency-division, and time-division multiple access.Switching centers
In telecommunication switching centers, multiple access is the connection of a user to two or more switching centers by separate access lines using a single message routing indicator or telephone number. This article contains material from the Federal Standard 1037C (in support of MIL-STD-188), which, as a work of the United States Government, is in the public domain.
See also
- Media access control
- Multiplex
- Statistical multiplexing
- Dynamic bandwidth allocation
- Diversity scheme
Telecommunication is the transmission of signals over a distance for the purpose of communication. In modern times, this process typically involves the sending of electromagnetic waves by electronic transmitters, but in earlier times telecommunication may have involved the use of
..... Click the link for more information.
..... Click the link for more information.
as a college campus, industrial complex, or a military base. A CAN, may be considered a type of MAN (metropolitan area network), but is generally limited to an area that is smaller than a typical MAN.
..... Click the link for more information.
..... Click the link for more information.
terminal is a device which is capable of communicating over a line. Examples of terminals are telephones, fax machines, and network devices - printers, work stations, routers in a VoIP network.
..... Click the link for more information.
..... Click the link for more information.
A transmission medium (plural transmission media) is a material substance (solid, liquid or gas) which can propagate energy waves. For example, the transmission medium for sound received by the ears is usually air, but solids and liquids may also act as transmission media
..... Click the link for more information.
..... Click the link for more information.
A bus network topology is a network architecture in which a set of clients are connected via a shared communications line, called a bus. There are several common instances of the bus architecture, including one in the motherboard of most computers, and those in some versions of
..... Click the link for more information.
..... Click the link for more information.
A ring network is a network topology in which each node connects to exactly two other nodes, forming a circular pathway for signals: a ring. Data travels from node to node, with each node handling every packet.
..... Click the link for more information.
..... Click the link for more information.
An Ethernet hub or concentrator is a device for connecting multiple twisted pair or fiber optic Ethernet devices together, making them act as a single segment. Hubs work at the physical layer (layer 1) of the OSI model. The device is thus a form of multiport repeater.
..... Click the link for more information.
..... Click the link for more information.
While the term wireless network may technically be used to refer to any type of network that is wireless, the term is most commonly used to refer to a telecommunications network whose interconnections between nodes is implemented without the use of wires, such as a
..... Click the link for more information.
..... Click the link for more information.
A duplex communication system is a system composed of two connected parties or devices which can communicate with one another in both directions. (The term duplex is not used when describing communication between more than two parties or devices.
..... Click the link for more information.
..... Click the link for more information.
Media Access Control (MAC) data communication protocol sub-layer, also known as the Medium Access Control, is a part of the data link layer specified in the seven-layer OSI model (layer 2).
..... Click the link for more information.
..... Click the link for more information.
data link is the means of connecting one location to another for the purpose of transmitting and receiving data. It can also be an assembly, consisting of parts of two data terminal equipments (DTEs) and the interconnecting data circuit, that is controlled by a link protocol
..... Click the link for more information.
..... Click the link for more information.
Open Systems Interconnection Basic Reference Model (OSI Reference Model or OSI Model for short) is a layered, abstract description for communications and computer network protocol design, developed as part of the Open Systems Interconnection (OSI) initiative.
..... Click the link for more information.
..... Click the link for more information.
The Internet protocol suite is the set of communications protocols that implement the protocol stack on which the Internet and most commercial networks run. It has also been referred to as the TCP/IP protocol suite, which is named after two of the most important protocols in it:
..... Click the link for more information.
..... Click the link for more information.
In electronics, telecommunications and computer networks, multiplexing (short muxing) is a term used to refer to a process where multiple analog message signals or digital data streams are combined into one signal. The aim is to share an expensive resource.
..... Click the link for more information.
..... Click the link for more information.
In telecommunications, a circuit switching network is one that establishes a dedicated circuit (or channel) between nodes and terminals before the users may communicate. Each circuit that is dedicated cannot be used by other callers until the circuit is released and a new
..... Click the link for more information.
..... Click the link for more information.
Time-Division Multiplexing (TDM) is a type of digital or (rarely) analog multiplexing in which two or more signals or bit streams are transferred apparently simultaneously as sub-channels in one communication channel, but physically are taking turns on the channel.
..... Click the link for more information.
..... Click the link for more information.
In fibre-optic communications, wavelength-division multiplexing (WDM) is a technology which multiplexes multiple optical carrier signals on a single optical fibre by using different wavelengths (colours) of laser light to carry different signals.
..... Click the link for more information.
..... Click the link for more information.
Statistical multiplexing is a type of communication link sharing. In statistical multiplexing, a communication channel is divided into an arbitrary number of variable bit-rate digital channels or data streams.
..... Click the link for more information.
..... Click the link for more information.
Packet switching is a communications paradigm in which packets (discrete blocks of data) are routed between nodes over data links shared with other traffic. In each network node, packets are queued or buffered, resulting in variable delay.
..... Click the link for more information.
..... Click the link for more information.
Frequency-hopping spread spectrum (FHSS) is a method of transmitting radio signals by rapidly switching a carrier among many frequency channels, using a pseudorandom sequence known to both transmitter and receiver.
..... Click the link for more information.
..... Click the link for more information.
In telecommunications, direct-sequence spread spectrum (DSSS) 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.
..... Click the link for more information.
..... Click the link for more information.
Orthogonal Frequency Division Multiple Access (OFDMA) is a multi-user version of the popular OFDM digital modulation scheme. Multiple access is achieved in OFDMA by assigning subsets of subcarriers to individual users as shown in the figure below.
..... Click the link for more information.
..... Click the link for more information.
Media Access Control (MAC) data communication protocol sub-layer, also known as the Medium Access Control, is a part of the data link layer specified in the seven-layer OSI model (layer 2).
..... Click the link for more information.
..... Click the link for more information.
In electronics, telecommunications and computer networks, multiplexing (short muxing) is a term used to refer to a process where multiple analog message signals or digital data streams are combined into one signal. The aim is to share an expensive resource.
..... Click the link for more information.
..... Click the link for more information.
Channel, in communications (sometimes called communications channel), refers to the used to convey information from a sender (or transmitter) to a receiver.
..... Click the link for more information.
Overview
A Channel can take many forms...... Click the link for more information.
A transmission medium (plural transmission media) is a material substance (solid, liquid or gas) which can propagate energy waves. For example, the transmission medium for sound received by the ears is usually air, but solids and liquids may also act as transmission media
..... Click the link for more information.
..... Click the link for more information.
physical layer is level one in the seven-level OSI model of computer networking as well as in the five-layer TCP/IP reference model. It performs services requested by the data link layer.
..... Click the link for more information.
..... Click the link for more information.
A duplex communication system is a system composed of two connected parties or devices which can communicate with one another in both directions. (The term duplex is not used when describing communication between more than two parties or devices.
..... Click the link for more information.
..... Click the link for more information.
Point-to-point may refer to:
..... Click the link for more information.
- Point-to-point (telecommunications)
- Point-to-point construction, an electronics assembly technique
- SAN Point-to-Point, a topology used in Fibre Channel
- Point to point racing, a form of horse race
..... Click the link for more information.
In telecommunications, a circuit switching network is one that establishes a dedicated circuit (or channel) between nodes and terminals before the users may communicate. Each circuit that is dedicated cannot be used by other callers until the circuit is released and a new
..... Click the link for more information.
..... Click the link for more information.
This article is copied from an article on Wikipedia.org - the free encyclopedia created and edited by online user community. The text was not checked or edited by anyone on our staff. Although the vast majority of the wikipedia encyclopedia articles provide accurate and timely information please do not assume the accuracy of any particular article. This article is distributed under the terms of GNU Free Documentation License.
Herod_Archelaus
