Token passing
Encyclopedia
In telecommunication
, token passing is a channel access method
where a signal called a token is passed between nodes that authorizes the node to communicate. The most well-known examples are token ring and ARCNET
.
Token passing schemes provide round-robin scheduling
, and if the packets are equally sized, the scheduling is max-min fair. The advantage over contention
based channel access is that collisions are eliminated, and that the channel bandwidth
can be fully utilized without idle time when demand is heavy. The disadvantage is that even when demand is light, a station wishing to transmit must wait for the token, increasing latency
.
Some types of token passing schemes do not need to explicitly send a token between systems because the process of "passing the token" is implicit. An example is the channel access method used during "Contention Free Time Slots" in the ITU-T
G.hn
standard for high-speed local area network
ing using existing home wires (power lines, phone lines and coaxial cable).
Telecommunication
Telecommunication is the transmission of information over significant distances to communicate. In earlier times, telecommunications involved the use of visual signals, such as beacons, smoke signals, semaphore telegraphs, signal flags, and optical heliographs, or audio messages via coded...
, token passing is a channel access method
Channel access method
In 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...
where a signal called a token is passed between nodes that authorizes the node to communicate. The most well-known examples are token ring and ARCNET
ARCNET
ARCNET is a local area network protocol, similar in purpose to Ethernet or Token Ring. ARCNET was the first widely available networking system for microcomputers and became popular in the 1980s for office automation tasks...
.
Token passing schemes provide round-robin scheduling
Round-robin scheduling
Round-robin is one of the simplest scheduling algorithms for processes in an operating system. As the term is generally used, time slices are assigned to each process in equal portions and in circular order, handling all processes without priority . Round-robin scheduling is simple, easy to...
, and if the packets are equally sized, the scheduling is max-min fair. The advantage over contention
Contention (telecommunications)
In packet mode communication networks, contention is a media access method that is used to share a broadcast medium.-Collision detection and recovery:...
based channel access is that collisions are eliminated, and that the channel bandwidth
Bandwidth (computing)
In computer networking and computer science, bandwidth, network bandwidth, data bandwidth, or digital bandwidth is a measure of available or consumed data communication resources expressed in bits/second or multiples of it .Note that in textbooks on wireless communications, modem data transmission,...
can be fully utilized without idle time when demand is heavy. The disadvantage is that even when demand is light, a station wishing to transmit must wait for the token, increasing latency
Latency (engineering)
Latency is a measure of time delay experienced in a system, the precise definition of which depends on the system and the time being measured. Latencies may have different meaning in different contexts.-Packet-switched networks:...
.
Some types of token passing schemes do not need to explicitly send a token between systems because the process of "passing the token" is implicit. An example is the channel access method used during "Contention Free Time Slots" in the ITU-T
ITU-T
The ITU Telecommunication Standardization Sector is one of the three sectors of the International Telecommunication Union ; it coordinates standards for telecommunications....
G.hn
G.hn
G.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 for high-speed local area network
Local area network
A local area network is a computer network that interconnects computers in a limited area such as a home, school, computer laboratory, or office building...
ing using existing home wires (power lines, phone lines and coaxial cable).
See also
- Token ringIBM token ringthumb|Two examples of token ring networks: a) Using a single [[Media Access Unit|MAU]] b) Using several MAUs connected to each otherthumb|Token ring networkthumb|IBM hermaphroditic connector with locking clipthumb|An IBM 8228 MAU...
- ARCNETARCNETARCNET is a local area network protocol, similar in purpose to Ethernet or Token Ring. ARCNET was the first widely available networking system for microcomputers and became popular in the 1980s for office automation tasks...
- Cambridge RingCambridge RingThe Cambridge Ring was an experimental local area network architecture developed at the Cambridge University Computer Laboratory in the mid-late 1970s and early 1980s. It used a ring topology with a theoretical limit of 255 nodes , around which cycled a fixed number of packets...