Transmission Effect and Wired Digital Communication Professor: Dr. Miguel Alonso Jr.

Outline Effects of Noise on the pulse Impedance Effects Frequency Effects Coding efficiency Code Noise Immunity Communication Links and Protocols Computer Communication

Noise Effects on the Pulse

Impedance Effects

Frequency Effects

Coding Efficiency Coding is defined as the process of transforming messages or signals in accordance with a definite set of rules. Normally use some type of binary coding High and Low are referred to as mark and space n=log 2 M relates the number of levels to the number of required bits coding efficiency u=# of bits used / (# of bits required)‏

Example Determine the number of bits required for a binary code to represent 110 different possibilities, and compare its efficiency with a decimal system to accomplish the same goal.

Code Noise Immunity Errors in digital communication occur as a result of noise The error probability (P e ) in a digital system is the number of total errors per total number of bits received. Example: 1 error bit per 100,000 bits, P e = 1/100,000 = 10 -5

Communication Links and Protocols Transmission in communication links are defined by three basic protocol techniques Simplex – one direction Half-Duplex – both directions, but only one at a time Full-Duplex – both parties can talk at the same time Also, recall asynchronous (no timing information needs to be added) and synchronous (timing information is required in addition to the signal)‏

Protocols Equipment must talk to each other There must exist a set of rules to control the process Handshaking – procedures allowing for orderly exchange of information between a central computer and remote sites Protocol – set of rules to make devices sharing a channel observe orderly communication procedures Protocols have four major functions

Functions of a protocol Data are normally transmitted in blocks or chunks at a time Framing – separation of blocks into the information (text) and control sections Control information includes address and error detection mechanism/procedure Line Control – procedure used to decide which device has permission to transmit at any given time Flow Control- protocol process used to monitor and control the data rate ( speed may vary between devices)‏ Sequence Control- necessary for when a message must pass through numerous links before it reaches its final destination. keeps the message from being lost or duplicated

protocols also handle control character insertion but, these characters can also occur in the data stream itself character insertion takes care of this. protocol should insert a bit or character so that a data stream is not mistake for a control character Protocols are classified according to their framing technique character oriented (COP)‏ bit oriented (BOP)‏

Example of a BOP protocol SDLC – synchronous data link control protocol developed by IBM Start and stop bit (0x7E), six consecutive ones If there are five consecutive ones in the stream, the protocol will insert a zero so as to avoid confusion

USB, Firewire (IEEE 1394) and RS serial buses HW: USB, FIRE-WIRE, RS-232 protocol handout next time