IntroductionWhen electronic devices transfer information to another electronic device, the devices must know when the data flow begins and ends. This is done with timing signals.iThis report will describe the two forms of data communications in terms of physical interfaces and modes of operation. It will describe the characteristics of data communications equipment as it relates to synchronous and asynchronous communication, including modems, network terminating units, and sending and receiving equipment. Define synchronous and asynchronous timing: The receiver is able to determine when a signal starts arriving and when it is finished. . He must also know the duration of each signal. Asynchronous transmission: Asynchronous signaling methods use only a single signal. The receiver uses changes to this signal to determine the transmitter's rate and timing, then synchronizes a clock at the appropriate timing with the transmission rate. A pulse of the local clock indicates when another bit is ready. Asynchronous transmission is slower but less expensive and efficient for low-speed data communication. Synchronous transmission: Synchronous signaling methods use 2 different signals. A pulse on one signal indicates when another bit of information is ready on the other signal. This is high-speed data communication. ASYNCHRONOUS/SYNCHRONOUS TRANSMISSION COMPARISONAsynchronousSynchronousSuitable for low speed serial transmission.Can achieve higher speeds than asynchronous.Does not include error checking function.Error checking function.One (or more) character is contained in a start and stop bit envelope. Groups characters into blocks. Less efficient than synchronization...... middle of paper ......r line, United States NEC Corporation (Tokyo, JP) 4999836 http://www.freepatentsonline. com/4999836.htmlUK Yahoo.com (2009) Is an NTU a modem...why is it connected to the Cisco router? what is the function? http://uk.answers.yahoo.com/question/index?qid=20091118020312AAjeaKkContent-Wire (2001) Deutsche Telekom deploys ATM network access solution http://www.content-wire.com/deutsche-telekom -deploys-atm -network-access-solutionVoxTechnologies Corp (2010) MainStreet 2902 Network Termination Unit http://www.voxtechnologies.com/2902_mainstreet_network_termination_unit.htmRAD Data Communications, Ltd. (2010) ACE-201 Multiservice Network Termination Unit http://uk.precisionnews.com/article_ACE-201-multiservice-network_5505.htmlErrealMedia (2010) OSI Reference Model of Networking Standards; History of the OSI model; OSI layers in action http://www.erealmedia.com/cms125/