网络工程专业英语课件ch1 Introduction.ppt

* * * * * * * * * * * * * * * * * * * * * 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 * * * * * * * * * * * * * * * * * * * * * * * * * * * * * Introduction 1-* Caravan analogy Cars “propagate” at 100 km/hr Toll booth takes 12 sec to service a car (transmission time) car~bit; caravan ~ packet Q: How long until caravan is lined up before 2nd toll booth? Time to “push” entire caravan through toll booth onto highway = 12*10 = 120 sec Time for last car to propagate from 1st to 2nd toll both: 100km/(100km/hr)= 1 hr A: 62 minutes toll booth toll booth ten-car caravan 100 km 100 km Introduction 1-* Caravan analogy (more) Cars now “propagate” at 1000 km/hr Toll booth now takes 1 min to service a car Q: Will cars arrive to 2nd booth before all cars serviced at 1st booth? Yes! After 7 min, 1st car at 2nd booth and 3 cars still at 1st booth. 1st bit of packet can arrive at 2nd router before packet is fully transmitted at 1st router! See Ethernet applet at AWL Web site toll booth toll booth ten-car caravan 100 km 100 km Introduction 1-* Packet loss queue preceding link in buffer has finite capacity when packet arrives to full queue, packet is dropped lost packet may be retransmitted by previous node, by source end system, or not retransmitted at all Introduction 1-* Chapter 1: roadmap 1.1 What is the Internet? 1.2 Network edge 1.3 Network core 1.4 Network access and physical media 1.5 Internet structure and ISPs 1.6 Delay loss in packet-switched networks 1.7 Protocol layers, service models 1.8 History Introduction 1-* Protocol “Layers” Networks are complex! many “pieces”: hosts routers links of various media applications protocols hardware, software Question: Is there any hope of organizing structure of network? Or at least our discussion of networks? Introduction 1-* Organiza