ppp

[carl_townshend]

Hi all

Can anyone tell me with PPP, how does it know what the destination address is? like say with ethernet we have the sourceand dest mac address, how does ppp do this ?

[rohitrattan]

Hello Carl,

Addressing is not required in the PPP frame and thats because Link Layer addressing is not required on Point to Point link as such. Ethernet requires it because it is essentially "Multiaccess", which means that a number of nodes (PC's, Routers) can connect to a common segement. In HDLC which is also a Point to Point Network, the address field is present but as said earlier on point to point links the address field is not actually required so this field was kept because service providers used to sell a multidrop circut with a central site connecting spoke sites.

One More thing the address fiels on PPP frame always has a value of FF (Hex) and that is "Broadcast", and on HDLC Frames it is always 3 (Decimal).

HTH

Rohit

[YANGCCIE4]

Also , PPP have authentication and accounting function, which is ISP like to choose for counting the traffic.

Add my one cent..

Yang