ECMA - European Computer Manufacturers Association
· Close coordination with ISO
IEEE - Institute of Electrical and Electronic Engineers
· Addresses many standards including LANs. Established the IIEE 802 set of standards.
ISO - International Standards Organization
· The ISO creates the sets of rules and standards for graphics, document exchange, and
related technologies.
· Also responsible for endorsing and coordinating the work of the other standards
organizations.
· Originated OSI MODEL
· Principal activity: manufacturers and user committees.
· Technical committee 97 TC deals with Information Technology.
ITU - International Telecommunications Union
· Treaty union for UN
NBS - National Bureau Of Standards
· Working on upper layers of OSI standard
Digital Communications Systems
Transmission Impairments
- Electrical Noise
- Echoes
- Crosstalk
- Transients
- Delay Distortion
- Thermal Noise
- Phase and timing jitter
- Intermodulation noise
- Space and mark distortion
- Harmonic Distortion
Note : jitter- very short-term variations in the arrival times of digital signals in a communication system. It is the major cause of errors in synchronous systems, especially data loss at the higher data rates and over longer distances.