资料计算机网络考核内容computer networks2.pptxVIP

CH2 Key Network Technology:multiplexing/switching /transmission ;3.1 Multiplexing 复用;Introduction;;;;;;;;;;T1 Frame;;;;;;;;;;;;FDM — 模拟信号传输;复用的时域图;复用的频域图;解复用的时域图;解复用的频域图;;;;;;;ADSL;;;;;;;3.2 switching;;;;Circuit-Switched Network;Switch;Folded Switch;Crossbar Switch;Multistage Switch;Switching Path;Switching Path;In modern circuit-switched networks, electronic signals pass through several switches before a connection is established. During a call no other network traffic can use those switches. The resources remain dedicated to the circuit during the entire data transfer and the entire message follows the same path. Circuit switching can be analog or digital. ;With the expanded use of the Internet for voice and video, analysts predict a gradual shift away from circuit-switched networks. A circuit-switched network is excellent for data that needs a constant link from end-to-end, for example, real-time video.;Advantages Circuit is dedicated to the call – no interference, no sharing Guaranteed the full bandwidth for the duration of the call Guaranteed quality of service ;Disadvantages Inefficient – the equipment may be unused for a lot of the call; if no data is being sent, the dedicated line still remains open. It takes a relatively long time to set up the circuit. During a crisis or disaster, the network may become unstable or unavailable. It was primarily developed for voice traffic rather than data traffic.;Packet Switching;;;Advantages Security Bandwidth used to full potential Devices of different speeds can communicate Not affected by line failure (redirects signal) Availability – no waiting for a direct connection to become available During a crisis or disaster, when the public telephone network might stop working, e-mails and texts can still be sent via packet switching;Disadvantages Under heavy use there can be a delay Data packets can get lost or become corrupted Protocols are needed for a reliable transfer Not so good for some types data streams