Network class 2

1.  Host : sends packets of data

 

host sending function:

     • takes application message

     • breaks into smaller chunks, known as packets, of length L bits

     • transmits packet into access network at transmission rate R

                           ‣ link transmission rate = link capacity = link bandwidth

 

     • packet transmission delay = L / R sec

 

 

2.  Physical media

 

• Type of links

 

       1. guided media

 

                • twisted pair (copper) : e.g) Ethernet

 

                • coaxial cable : broadband, e.g) HFC

 

                • fiber optic cable : low error rate, High transmisstion rate, high-speed, e.g) HFC

 

 

       2. unguided media

 

                • radio : wireness, reflection, obstruction by objects, interference

                               

                          - types : terrestrial microwave

                                          LAN : e.g) WiFi

                                          wide-area : e.g) cellular

                                          satellite

 

 

3.  Delivery method

 

1) Circuit switching

• end-end resources allocated to, reserved for 'call' between source & destination:

 

• circuit segment idle

 

• commonly used in traditional telephone networks

 

 

 

✓  Split method : FDM, TDM

 

- FDM

 

 

- TDM

 

 

2) Packet Switching

• mesh of interconnected routers

 

• packet-switching : hosts break application-layer messages into packets

    - forward packets from one router to the next, across links on path from source to destination

    - each packet transmitted at full link capacity

 

 

 

✓  Store-and-forward

 

- store and forward : entire packet must arrive at router before it can be transmitted on next link

 

- takes L/R seconds to transmit L-bit packet into link at R bps

 

- end-end delay = 2L/R (assuming zero propagation delay)

 

 

✓  Queueing delay, loss

 

• If arrival rate to link exceeds transmission rate of link for a period of time:

         - packets will queue, wait to be transmitted on link

         - packets can be dropped (lost) if memory (buffer) fills up

 

 

 

 

4.  Internet structure : network of networks

 

 

• peer : When two ISPs peer, settlement-free

• multi-home : can have a lot of provider ISPs