Can someone clear up the WAN technologies for me?

hammiesink

How do these WAN protocols relate? I'm aware that PPP and HDLC are usually used for leased lines, and Frame Relay and ATM for packet switching, but...

1. Apparently, you can run PPP over Frame Relay. Why would you use two layer 2 protocols? Same with Frame Relay over ATM...?
2. Apparently, they are not tied to any particular physical layer, so you could use for example PPP and HDLC over...packet switched networks? Is that correct? Wouldn't they need addressing then?

In short, I'm just not clear on the taxonomies here, and how they relate to leased, circuit, and packet networks, as well as to each other.

Can you help make this clearer for me? Thanks!

theodoxa

My guess is to pass traffic between two similar networks over a dissimilar network. Sort of like how 6to4 passes data from one IPv6 Only network to another IPv6 Only network over an IPv4 Only network. Some ISPs might need to send data from one Frame Relay network to another over a portion of their network that only runs ATM.

iamme4eva

As far as my understanding goes, the main reason for using PPP over anything (PPPoE, PPPoA, PPPoFR) is because PPP brings a lot of features to the party that other layer two protocols don't, such as authentication, link quality monitoring, etc.

Most ADSL connections for home internet use some form of PPP, primarily so you have to use a username to connect to the internet so your ISP has accountability and tracking.