tailieunhanh - CompTIA Network+ Certification Study Guide part 14

CompTIA’s Network+ certification Study Guide part 14 is a globally-recognized, vendor neutral exam that has helped over 235,000 IT professionals reach further and higher in their careers. The 2009 Network+ exam (N10-004) is a major update with more focus on security and wireless aspects of networking. Our new study guide has been updated accordingly with focus on network, systems, and WAN security and complete coverage of today’s wireless networking standards. | 116 CHAPTER 3 Network Devices In addition to speed ISDN supports multiple devices set up in one link. In an analog system a single line is required for each device attached. For example a separate phone line is needed for a normal phone a fax machine or a computer modem. Because ISDN supports multiple devices you can use each one of these items on a single line. It will also be clearer due to the fact that the data is being passed in a digital format. Because ISDN uses a separate channel the D channel for signaling it removes the administrative overhead required. This means that the data is not hindered by the session setups and the communications required by the devices. The D channel keeps all of this information off the data streams. Because of the separation the setup and takedown of each session is much faster. In addition ISDN equipment is able to handle calls more intelligently. CSU DSU The somewhat lengthy acronym CSU DSU is short for Channel Service Unit Data Service Unit. A CSU DSU is a device that takes a signal from a digital medium and multiplexes it. Although a CSU and a DSU can be separate components they are generally packaged as a single unit. The CSU is used to connect a terminal to a digital line while a DSU performs diagnostic and protective functions. A CSU DSU terminates the end of a leased T-carrier line which is a high-speed line that can be used to connect a LAN to a wide area network WAN . The CSU DSU is similar to a modem in that it connects to the media that will carry the data but because the T-carrier transmits the data digitally there is no need for device to modulate and demodulate between digital and analog formats. The CSU DSU can be a separate component that attaches to a router and provides an interface between the routers but many newer routers have more modular capabilities that allow you to purchase what are sometimes referred to as WAN interface cards or WICs for short. This is a card that incorporates the CSU DSU into the .