On a
local area network
A local area network (LAN) is a computer network that interconnects computers within a limited area such as a residence, campus, or building, and has its network equipment and interconnects locally managed. LANs facilitate the distribution of da ...
, token passing is a
channel access method
In telecommunications and computer networks, a channel access method or multiple access method allows more than two terminals connected to the same transmission medium to transmit over it and to share its capacity. Examples of shared physical ...
where a packet called a ''token'' is passed between nodes to authorize that node to communicate. In contrast to
polling access methods, there is no pre-defined "master" node. The most well-known examples are
IBM Token Ring and
ARCNET, but there were a range of others, including
FDDI
Fiber Distributed Data Interface (FDDI) is a standard for data transmission in a local area network.
It uses optical fiber as its standard underlying physical medium.
It was also later specified to use copper cable, in which case it may be c ...
(Fiber Distributed Data Interface), which was popular in the early to mid 1990s.
Token passing schemes degrade deterministically under load, which is a key reason why they were popular for industrial control LANs such as
MAP, (Manufacturing Automation Protocol). The advantage over
contention based channel access (such as the
CSMA/CD of early Ethernet), 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
The International Telecommunication Union Telecommunication Standardization Sector (ITU-T) is one of the three Sectors (branches) of the International Telecommunication Union (ITU). It is responsible for coordinating Standardization, standards fo ...
G.hn
Gigabit Home Networking (G.hn) is a specification for wired home networking that supports speeds up to 2 Gbit/s and operates over four types of legacy wires: telephone wiring, Coaxial cable, coaxial cables, Power line, power lines and pla ...
standard for high-speed
local area network
A local area network (LAN) is a computer network that interconnects computers within a limited area such as a residence, campus, or building, and has its network equipment and interconnects locally managed. LANs facilitate the distribution of da ...
ing using existing home wires (power lines, phone lines and coaxial cable).
See also
*
Cambridge Ring
*
HP Interface Loop (HP-IL)
*
Ring network
References
Channel access methods
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