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| reply to aryoba
Re: [Info] Why is PPP necessary for "dedicated connection"?
PPP is not necessary for a dedicated connection. But some kind of layer 2 protocol is. Are you referring to PPPoE or just plain old PPP? OF course, every ISP builds their networks differently. But, typically, you can't compare DSL service with T-1 service. They are each terminated in a different fashion to the ISP's router and use different layer 2 protocols because of that. PPP itself is not a secure protocol, but it provides access to authentication methods which are like CHAP.
On a point to point T-1 circuit you have to run either PPP, HDLC, Frame-Relay, X.25 or some other kind of layer 2 encapsulation to get your data to and from the other end. You usally have dedicated ports on either end to support these circuits as well. Authentication is mutually exclusive of these protocols but can be facilitated by the protocol, in the case of PPP. When you have dedicated hardware to support the circuit at each end, there is no need for authentication. However, you can still use PPP as your layer 2 protocol, just configured to not force the authentication.
DSL is usually backhauled to the ISP's router over an ATM circuit coming out of the telco DSLAM. This comes into a shared interface on the ISP's router that all or a portion of the ISP's DSL connections will terminate on. If you don't control access to this interface with some kind of authentication, then you have no way of accounting for who is connected to which virtual circuit and/or assigning the correct static routes for those customers with blocks of static IP addresses. So even though DSL is a dedicated connection it uses a shared head-end infrastructure which needs to be controlled with authentication.
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