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Cisco Networking Academy Program CCNA 1 and 2 Companion Guide, Revised part 104 is the Cisco approved textbook to use alongside version 3.1 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. | 1102.book Page 999 Tuesday May 20 2003 2 53 PM Glossary of Key Terms 999 plenum An open ceiling that acts as an air-return duct for heating ventilation and air-conditioning systems. plug-in Software or a program that can easily be installed and used as part of a web browser. PM phase modulation Modulates the polarity phase of the wave. poison reverse updates Updates that are necessary to defeat larger routing loops. Generally speaking increases in routing metrics indicate routing loops. Poison reverse updates are then sent to remove the route and place it in holddown. port In IP terminology an upper-layer process that receives information from lower layers. Ports are numbered and many are associated with a specific process. For example SMTP is associated with port 25. A port number of this type is called a well-known port or address. power cord Connects an electrical device to an electrical outlet to provide power to the device. power supply Supplies power to a computer. power-on self-test POST Set of hardware diagnostics that runs on a hardware device when that device is powered up. presentation layer Layer 6 of the OSI reference model. This layer ensures that information sent by the application layer of one system can be read by the application layer of another. printed circuit board PCB A thin plate on which chips integrated circuits and other electronic components are placed. privileged mode Used for copying and managing entire configuration files. propagation delay A simple measurement of how long it takes for a signal to travel along the cable being tested. protocol stack A set of related communications protocols that operate together and as a group address communication at some or all of the seven layers of the OSI reference model. Not every protocol stack covers each layer of the model and often a single protocol in the stack addresses a number of layers at once. TCP IP is a typical protocol stack. protocol suite A set of related communications protocols .
