计算机网络学习入门(自顶向下).ppt

* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * /osmhome/allochrt.pdf * * * * * Two simple multiple access control techniques. Each mobile’s share of the bandwidth is divided into portions for the uplink and the downlink. Also, possibly, out of band signaling. As we will see, used in AMPS, GSM, IS-54/136 * * * * * Breaking message into packets allows parallel transmission across all links, reducing network latency. In summary the benefits that of packet switched networks can be summarized as follows: They use the bandwidth efficiently, meaning that a trunk link uses less resources than the sum of its tributaries, as they multiplex and conserve bandwidth They have little state in the intermediate nodes They are robust, some claim that they were designed to withstand a nuclear attack They do not have a central authority from whom we need permission to run experiments * * * Statistical multiplexing Important if traffic is bursty Less expensive Contention requires buffering Variable delay = no QoS guarantees * Statistical multiplexing Important if traffic is bursty Less expensive Contention requires buffering Variable delay = no QoS guarantees * * * * * * * * * * * * Introduction 1-* Internet History Early 1990’s: ARPAnet decommissioned 1991: NSF lifts restrictions on commercial use of NSFnet (decommissioned, 1995) early 1990s: Web hypertext [Bush 1945, Nelson 1960’s] HTML, HTTP: Berners-Lee 1994: Mosaic, later Netscape late 1990’s: commercialization of the Web Late 1990’s – 2000’s: more killer apps: instant messaging, P2P file sharing network security to forefront est. 50 million host, 100 million+ users backbone links running at Gbps 1990, 2000’s: commercialization, the Web, new apps Introduction 1-* Internet History 2007: ~500 million hosts Voice, Video over IP P2P applications: BitTorrent (file sharing) Skype (VoIP), PPLive (video) more applications: YouTube, gaming wireless, mobility Introduction 1-* Introduction: Summary Covered a “ton” o