tailieunhanh - CCNA 1 and 2 Companion Guide, Revised (Cisco Networking Academy Program) part 41

Cisco Networking Academy Program CCNA 1 and 2 Companion Guide, Revised part 41 is the Cisco approved textbook to use alongside version of the Cisco Networking Academy Program CCNA 1 and CCNA 2 web-based courses. The topics covered provide you with the necessary knowledge to begin your preparation for the CCNA certification exam (640-801, or 640-821 and 640-811) and to enter the field of network administration. | Page 369 Tuesday May 20 2003 2 53 PM Key Terms 369 cut-through switching A packet-switching approach that streams data through a switch so that the leading edge of a packet exits the switch at the output port before the packet finishes entering the input port. A device using cut-through packet switching reads processes and forwards packets as soon as the destination address is looked up and the outgoing port is determined. See also store-and-forward switching. encoding Process by which bits are represented by voltages. fragment-free switching Switching that filters out collision fragments which are the majority of packet errors before forwarding begins. latency Delay between the time when a device receives a frame and the time when that frame is forwarded out the destination port. Manchester encoding Digital encoding scheme used by IEEE and Ethernet in which a mid-bit-time transition is used for clocking a 1 is denoted by a high level during the first half of the bit time. microsegmentation The division of a network into smaller segments usually with the intention of increasing aggregate bandwidth to network devices. NRZ nonreturn to zero Signals that maintain constant voltage levels with no signal transitions no return to a 0V level during a bit interval. NRZI nonreturn to zero inverted Signal that maintains constant voltage levels with no signal transitions no return to a 0V level . It interprets the presence of data at the beginning of a bit interval as a signal transition and interprets the absence of data as no transition. SNR signal-to-noise ratio The ratio of useable signal being transmitted to the undesired signal noise . It is a measure of transmission quality. The ratio of good data signal to bad noise on a line expressed in decibels dB . store-and-forward switching A packet-switching technique in which frames are processed completely before being forwarded out the appropriate port. This processing includes calculating the CRC and checking