(SDH) An international digital telecommunications network hierarchy which standardises transmission around the bit rate of 51.84 megabits per second, which is also called STS-1. Multiples of this bit rate comprise higher bit rate streams. Thus STS-3 is 3 times STS-1, STS-12 is 12 times STS-1, and so on. STS-3 is the lowest bit rate expected to carry ATM traffic, and is also referred to as STM-1 (Synchronous Transport Module-Level 1).
The SDH specifies how payload data is framed and transported synchronously across optical fibre transmission links without requiring all the links and nodes to have the same synchronized clock for data transmission and recovery (i.e. both the clock frequency and phase are allowed to have variations, or be plesiochronous).
SDH offers several advantages over the current multiplexing technology, which is known as Plesiochronous Digital Hierarchy. Where PDH lacks built-in facilities for automatic management and routing, and locks users into proprietary methods, SDH can improve network reliability and performance, offers much greater flexibility and lower operating and maintenance costs, and provides for a faster provision of new services.
Under SDH, incoming traffic is synchronized and enhanced with network management bits before being multiplexed into the STM-1 fixed rate frame.
The fundamental clock frequency around which the SDH or SONET framing is done is 8 KHz or 125 microseconds.
SONET (Synchronous Optical Network) is the American version of SDH.
- Synchronous dram
Synchronous Dynamic Random Access Memory
- Synchronous idle
character (SYN) The mnemonic for ASCII character 22. [Why?] (1996-06-28)
- Synchronous key encryption
algorithm, cryptography Data encryption using two interlocking keys where enything encoded using one key may be decoded using the other key. This means if someone makes one of the two keys publicly available (as in public-key encryption) and keeps the other private, then anyone may send them a message or data that only they can […]
adjective 1. occurring at the same time; coinciding in time; contemporaneous; simultaneous. 2. going on at the same rate and exactly together; recurring together. 3. Physics, Electricity. having the same frequency and zero phase difference. 4. Computers, Telecommunications. of, relating to, or operating using fixed-time intervals controlled by a clock (opposed to asynchronous). 5. Aerospace. […]