Distributed switching
Encyclopedia
Distributed switching is an architecture in which multiple processor
-controlled switching units are distributed. There is often a hierarchy of switching elements, with a centralized host
switch
and with remote switches located close to concentrations of users.
s, though it is often called host-remote switching.
In rural areas, population centers tend to be too small for economical deployment of a full-featured dedicated telephone exchange
, and distances between these centers make transmission
costs relatively high. Normal telephone traffic patterns show that most calling is done between people in a community of interest
, in this case a geographical one: the population center. Use of distributed switching allows for the majority of calls that are local to that population center to be switched there without needing to be transported to and from the host switch.
The host switch provides connectivity between the remote switches and to the larger network, and the host may also directly handle some rare and complex call types (conference call
ing, for example) that the remote itself is not equipped to handle. Host switches also perform OAM&P (Operation, Administration, Maintenance, and Provisioning) functions, including billing, for the entire cluster of the host and its remote switches.
A key capability of a remote switch is the ability to act in emergency standalone (ESA) mode, wherein local calls can still be placed even in the event that the connection between that remote and the host has been lost. In this mode, only local calling is available anyway, so the billing capability of the host switch is not required. ESA is increasingly available on digital loop carrier
platforms as well as on purpose-built remote switches in order to improve the scope of their utility.
switches utilize distributed switching on separate cards within an equipment chassis
. Even when this is used, it is common to have a centralized switching fabric to interconnect the distributed switches. This architecture has become less common as backplane
bus
speeds and centralized switch fabric capacities have increased.
Central processing unit
The central processing unit is the portion of a computer system that carries out the instructions of a computer program, to perform the basic arithmetical, logical, and input/output operations of the system. The CPU plays a role somewhat analogous to the brain in the computer. The term has been in...
-controlled switching units are distributed. There is often a hierarchy of switching elements, with a centralized host
Server (computing)
In the context of client-server architecture, a server is a computer program running to serve the requests of other programs, the "clients". Thus, the "server" performs some computational task on behalf of "clients"...
switch
Stored Program Control exchange
Stored Program Control exchange is the technical name used for telephone exchanges controlled by a computer program stored in the memory of the system. Early exchanges such as Strowger, panel, rotary, and crossbar switches were electromechanical and had no software control...
and with remote switches located close to concentrations of users.
Use in telephony networks
Distributed switching is often used in telephone networkTelephone network
A telephone network is a telecommunications network used for telephone calls between two or more parties.There are a number of different types of telephone network:...
s, though it is often called host-remote switching.
In rural areas, population centers tend to be too small for economical deployment of a full-featured dedicated telephone exchange
Telephone exchange
In the field of telecommunications, a telephone exchange or telephone switch is a system of electronic components that connects telephone calls...
, and distances between these centers make transmission
Transmission (telecommunications)
Transmission, in telecommunications, is the process of sending, propagating and receiving an analogue or digital information signal over a physical point-to-point or point-to-multipoint transmission medium, either wired, optical fiber or wireless...
costs relatively high. Normal telephone traffic patterns show that most calling is done between people in a community of interest
Community of interest
A community of interest is a community of people who share a common interest or passion. These people exchange ideas and thoughts about the given passion, but may know little about each other outside of this area...
, in this case a geographical one: the population center. Use of distributed switching allows for the majority of calls that are local to that population center to be switched there without needing to be transported to and from the host switch.
The host switch provides connectivity between the remote switches and to the larger network, and the host may also directly handle some rare and complex call types (conference call
Conference call
A conference call is a telephone call in which the calling party wishes to have more than one called party listen in to the audio portion of the call. The conference calls may be designed to allow the called party to participate during the call, or the call may be set up so that the called party...
ing, for example) that the remote itself is not equipped to handle. Host switches also perform OAM&P (Operation, Administration, Maintenance, and Provisioning) functions, including billing, for the entire cluster of the host and its remote switches.
A key capability of a remote switch is the ability to act in emergency standalone (ESA) mode, wherein local calls can still be placed even in the event that the connection between that remote and the host has been lost. In this mode, only local calling is available anyway, so the billing capability of the host switch is not required. ESA is increasingly available on digital loop carrier
Digital loop carrier
A digital loop carrier is a system which uses digital transmission to extend the range of the local loop farther than would be possible using only twisted pair copper wires...
platforms as well as on purpose-built remote switches in order to improve the scope of their utility.
Use within telecommunications equipment platforms
Many data-centric telecommunications platforms such as routers and EthernetEthernet
Ethernet is a family of computer networking technologies for local area networks commercially introduced in 1980. Standardized in IEEE 802.3, Ethernet has largely replaced competing wired LAN technologies....
switches utilize distributed switching on separate cards within an equipment chassis
Chassis
A chassis consists of an internal framework that supports a man-made object. It is analogous to an animal's skeleton. An example of a chassis is the underpart of a motor vehicle, consisting of the frame with the wheels and machinery.- Vehicles :In the case of vehicles, the term chassis means the...
. Even when this is used, it is common to have a centralized switching fabric to interconnect the distributed switches. This architecture has become less common as backplane
Backplane
A backplane is a group of connectors connected in parallel with each other, so that each pin of each connector is linked to the same relative pin of all the other connectors forming a computer bus. It is used as a backbone to connect several printed circuit boards together to make up a complete...
bus
Computer bus
In computer architecture, a bus is a subsystem that transfers data between components inside a computer, or between computers.Early computer buses were literally parallel electrical wires with multiple connections, but the term is now used for any physical arrangement that provides the same...
speeds and centralized switch fabric capacities have increased.