Chapter 1. Introduce

Internet ?: a.specific construction of handware and software

                b.communication services provied for applications

Protocal ?: it define format, order of msgs sent and received among network entities, and actions taken on msg transmission, receipt(语法&语义||格式&次序+动作）

Network edge
 end systems, access networks, links

Network core
 circuit switching, packet switching, network structure

circuit vs packet switch：

great for bursty data
resource sharing
simpler, no call setup
excessive congestion: packet delay and loss
protocols needed for reliable data transfer, congestion control

 

Four sources of packet delay

1. nodal processing:
 check bit errors
 determine output link

2. queueing
 time waiting at output
link for transmission
 depends on congestion
level of router

3. Transmission delay:
 R=link bandwidth (bps)
 L=packet length (bits)
 time to send bits into
link = L/R

4. Propagation delay:

 

Internet protocol stack

1.application: supporting network applications
FTP, SMTP, HTTP
  2.transport: process-process data transfer
TCP, UDP
  3.network: routing of datagrams from source to destination
IP, routing protocols
  4.link: data transfer between neighboring network elements
PPP, Ethernet
  5.physical: bits “on the wire