Switch56
Encyclopedia
Nortel
's Switch56 was a networking protocol built on top of the telephone cabling hardware of their Digital Multiplex System
and other telephone switches.
The name comes from the fact that Switch56 carried 56 kbit/s of data on its 64 kbit/s lines, as opposed to most systems, including ISDN, where the entire 64 kbit/s bandwidth was available for data. The speed was a side effect of Nortel using a 2-wire cable to carry both voice and switching commands, as opposed to other systems where the command data was carried on a separate set of low-speed lines. Switch56 "folded" the two sources of data into one, placing a single bit from the command channel onto the end of every 7 bits of data, similar to the original T-carrier
supervision scheme. This data was split out at the "far end" as 56 kbit/s and 8 kbit/s subchannels.
Switch56 was built on top of the basic Nortel hardware to allow computers to put data into the existing telephony network. Although slow compared to even contemporary systems, Switch56 allowed network traffic to flow not only within an office like other LAN
systems, but between any branch offices that were connected using a Nortel PBX like the Meridian Norstar
. This was a much easier option to install than ISDN for most offices, requiring nothing more than a Switch56 bridge to their existing network. For the LAN role new telephone terminals were produced with a RS-232C port on the back, which were then plugged into the user's computer and used with custom software. Although interesting in theory, it appears Switch56 saw little use in this role.
Nortel
Nortel Networks Corporation, formerly known as Northern Telecom Limited and sometimes known simply as Nortel, was a multinational telecommunications equipment manufacturer headquartered in Mississauga, Ontario, Canada...
's Switch56 was a networking protocol built on top of the telephone cabling hardware of their Digital Multiplex System
Digital Multiplex System
Digital Multiplex System is the name shared among several different telephony product lines from Nortel Networks for wireline and wireless operators...
and other telephone switches.
The name comes from the fact that Switch56 carried 56 kbit/s of data on its 64 kbit/s lines, as opposed to most systems, including ISDN, where the entire 64 kbit/s bandwidth was available for data. The speed was a side effect of Nortel using a 2-wire cable to carry both voice and switching commands, as opposed to other systems where the command data was carried on a separate set of low-speed lines. Switch56 "folded" the two sources of data into one, placing a single bit from the command channel onto the end of every 7 bits of data, similar to the original T-carrier
T-carrier
In telecommunications, T-carrier, sometimes abbreviated as T-CXR, is the generic designator for any of several digitally multiplexed telecommunications carrier systems originally developed by Bell Labs and used in North America, Japan, and South Korea....
supervision scheme. This data was split out at the "far end" as 56 kbit/s and 8 kbit/s subchannels.
Switch56 was built on top of the basic Nortel hardware to allow computers to put data into the existing telephony network. Although slow compared to even contemporary systems, Switch56 allowed network traffic to flow not only within an office like other LAN
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...
systems, but between any branch offices that were connected using a Nortel PBX like the Meridian Norstar
Meridian Norstar
The Meridian Norstar, later called Nortel Norstar was a small-office digital PBX introduced by Northern Telecom . It is based on the same internal design and instruction set as Nortel's earlier SL-1 and DMS systems, allowing it to support features such as integrated voice messaging, automatic call...
. This was a much easier option to install than ISDN for most offices, requiring nothing more than a Switch56 bridge to their existing network. For the LAN role new telephone terminals were produced with a RS-232C port on the back, which were then plugged into the user's computer and used with custom software. Although interesting in theory, it appears Switch56 saw little use in this role.