Data Link Layer and Higher
Asynchronous communication at the data link layer or higher protocol layers is known as statistical multiplexing or packet mode communication, for example asynchronous transfer mode (ATM). In this case the asynchronously transferred blocks are called data packets, for example ATM cells. The opposite is circuit switched communication, which provides constant bit rate, for example ISDN and SONET/SDH.
The packets may be encapsulated in a data frame, with a frame synchronization bit sequence indicating the start of the frame, and sometimes also a bit synchronization bit sequence, typically 01010101, for identification of the bit transition times. Note that at the physical layer, this is considered as synchronous serial communication. Examples of packet mode data link protocols that can be/are transferred using synchronous serial communication are the HDLC, Ethernet, PPP and USB protocols.
Read more about this topic: Asynchronous Communication
Famous quotes containing the words data, link, layer and/or higher:
“Mental health data from the 1950’s on middle-aged women showed them to be a particularly distressed group, vulnerable to depression and feelings of uselessness. This isn’t surprising. If society tells you that your main role is to be attractive to men and you are getting crow’s feet, and to be a mother to children and yours are leaving home, no wonder you are distressed.”
—Grace Baruch (20th century)
“We fight our way through the massed and leveled collective safe taste of the Top 40, just looking for a little something we can call our own. But when we find it and jam the radio to hear it again it isn’t just ours—it is a link to thousands of others who are sharing it with us. As a matter of a single song this might mean very little; as culture, as a way of life, you can’t beat it.”
—Greil Marcus (b. 1945)
“The writer in me can look as far as an African-American woman and stop. Often that writer looks through the African-American woman. Race is a layer of being, but not a culmination.”
—Thylias Moss, African American poet. As quoted in the Wall Street Journal (May 12, 1994)
“The higher the state of civilization, the more completely do the actions of one member of the social body influence all the rest, and the less possible is it for any one man to do a wrong thing without interfering, more or less, with the freedom of all his fellow-citizens.”
—Thomas Henry Huxley (1825–95)