Basic components III (06.523) Basic components of communication networks III Lecture 3

Reminder - network layers Application layer Network layer Data link layer Physical layer

Standards Role of standards IEEE ANSI ISO Character encoding

Types of standards Formal Defacto

Forms of communication Basics of a protocol UART, ADB, USB Serial vs. Parallel Synchronous vs. Asynchronous Duplex

Synchronous transmission Packet/Frame at a time (fixed length) Fixed length block Checksum or CRC rather than parity

Asynchronous transmission Character at a time Start, stop and parity bits

Duplex Simplex –One way, No control structure needed –Example: Television Half duplex –RTS/CTS (Clear/Request to Send) or XON/XOFF (Transmission On/Off) –Example: Walkie talkie, Older modem protocols Full duplex –Send and receive simultaneously –Example: Telephones

UART Like a miniature FEP Parallel -> serial at the right rate Start, stop, and parity bits Handshaking (which level?)

ADB Only used by Apple and NeXT, now dead No conversion or control bits Standard bit rate Dynamic device ID, no handshaking

USB Hubs Guaranteed transfer rates Master/slave protocol

Serial Slow Example: Modems, Ethernet Mainly used between computers

Parallel Fast Example: Printers, Fiber optics, Internal bus Rarely used externally due to timing problems (5m limit).