Technotes contradicts Cramsession

p0et

Cramsession and ExamForce say PPP is on the data-link layer whereas the technotes on this site say that PPP is on the network layer. Which one is it? Is there a way to find out what "CompTIA" says?

keatron

I would have to say PPP is a layer 2 protocol, as it performs linking for several layer 3 protocols including IP, IPX, appletalk and many others.

georgemc

Hi,
I don't know what Comptia says but Microsoftsays:

"The Point-to-Point Protocol (PPP) is a data link layer protocol which encapsulates other network layer protocols for transmission on synchronous and asynchronous communication lines."
found in this link www.microsoft.com/technet/archive/winntas/plan/pppras.mspx

RFC 1661 (http://www.faqs.org/rfcs/rfc1661.html)(which is about as clear as mud) says:

"The PPP encapsulation provides for multiplexing of different
network-layer protocols simultaneously over the same link. The
PPP encapsulation has been carefully designed to retain
compatibility with most commonly used supporting hardware."

This implies data-link layer, since it is encapsulating network layer protocols.

RFC 1661 also says:

"packet The basic unit of encapsulation, which is passed across the
interface between the network layer and the data link
layer. A packet is usually mapped to a frame; the
exceptions are when data link layer fragmentation is being
performed, or when multiple packets are incorporated into a
single frame."

AND

"The PPP encapsulation is used to disambiguate multiprotocol
datagrams. This encapsulation requires framing to indicate the
beginning and end of the encapsulation. Methods of providing framing
are specified in companion documents."

This also implies Data-Link layer, since it's framing higher level protocols.

but later in the same document it says:

"In order to establish communications over a point-to-point link, each
end of the PPP link MUST first send LCP packets to configure and test
the data link. After the link has been established, the peer MAY be
authenticated.

Then, PPP MUST send NCP packets to choose and configure one or more
network-layer protocols. Once each of the chosen network-layer
protocols has been configured, datagrams from each network-layer
protocol can be sent over the link.

The link will remain configured for communications until explicit LCP
or NCP packets close the link down, or until some external event
occurs (an inactivity timer expires or network administrator
intervention)."

This implies Network-Layer since this is where packets/datagrams are normally found.

If I had to choose, I'd say Data-Link layer, just because it's a lower level protocol than the ones(IP, IPX, etc.) that it carries.

kenny504

PPP protocol is a data-link layer protocol...meaning it operates at layer 2. But it also mediates between the network layer with its embedded LCP protocol. PPP has two parts NCP and LCP...the link control protocol basically grabs information from the network layer to prepare the FRAME format on the sending end. PPP then prepares the frames to be transffered to the network layer on the recieving end.

Webmaster

Yup, PPP is layer 2, I have no idea how I messed that one up. I updated the TechNotes and apologize for any confusion caused.