Network Class 3

1.  Four sources of packet delay

 

 

1) nodal processing

       • check bit errors

       • determine output link

       • typically < msec

 

2) queueing delay (variable)

       • time waiting at output link for transmission

       • depends on congestion level of router

 

       • L * a : 단위시간당 유입되는 traffic의 양

       • L * a / R : traffic intensity

 

       • L : packet length

       • a : average packet arrival rate

       • R : link bandwidth

 

3) transmission delay

       • L/R

       • L : packet length

       • R : link bandwidth

 

4) propagation delay

       • d/s

       • d : length of physical link

       • s : propagation speed in medium

 

 

2.  Packet loss

 

• Packet arriving to full queue dropped

 

 

3.  Throughput

 

• rate at which bits transferred between sender/receiver

 

‣ bottleneck link : link on end-end path that constrains end-end throughput

 

 

4.  Why layering? (protocol)

 

Dealing with complex systems:

• explicit structure allows identification, relationship of complex system's pieces
• modularization eases maintenance, updating of system

 

‣ Layering considered harmful?

        - One layer may duplicate lower-layer functionality

        - functionality of one layer may require information available in another layer

 

5.  Internet protocol stack

 

• application : supporting network applications (HTTP, FTP)

 

• transport : process-process data transfer (TCP)

 

• network : routing of datagrams from source to destination (IP)

 

• link : data transfer between neighboring network elements

 

• physical : bits 'on the wire'