I couldn't say it shorter and more clearly than Vint : PPP does NOT belong to
the TCP/IP protocol suite.
It's a Layer 2(*) protocol, intended to carry multiple Layer 3 protocols (like
IP, IPX,...) over a point-to-point connection (like PSTN, ISDN,...).
PPP succeeded SLIP by bringing extended features : SLIP could only encapsulate
IP while PPP can encapsulate several protocols, PPP supports authentication
while SLIP didn't, etc.
Remember that TCP/IP only covers Layer 3 up to Layer 7 : it's designed to be
implemented on existing lower layers (1 and 2) : LAN (Ethernet, Token Ring,
Wireless Lans,...) or WAN (ISDN, ATM, Frame Relay,...).
(*) Those layers always refer to the OSI model. Think of a Layer 2 or 3 or 4
Switch : it doesn't depend on the protocol suite above, so we always refer to
the vendor- technology- protocol-independent OSI reference model.
--- The basic answer ends here ---
Now a small yet technical recall : when data comes from an application to be
transported on a physical medium (copper cable, fiber optics, radio waves,
infra-red,...), on its way from Layer 7 to Layer 1 it reaches IP (Layer 3) that
encapsulates it in a datagram/packet and specifies the destination network+host
address. Then it's forwarded to PPP (Layer 2) that encapsulates it in a frame
and specifies the way bits are organized to travel through the physical medium.
Then it's forwarded to some Layer 1 technology that converts the bits into a
specific signal using a specific encoding scheme (V.90 on PSTN, I.430 on ISDN
BRI,...) and finally reaches the physical medium to be physically transported
through the network.
--- The extended answer ends here ---
From: vint cerf [mailto:vinton(_dot_)g(_dot_)cerf(_at_)wcom(_dot_)com]
IP is encapsulated in PPP for all practical purposes. PPP can support
multiple protocols on a single point to point link in the same way
ethernet can support multiple protocols
At 08:01 AM 3/1/2002 -0500, Bill Cunningham wrote:
Is IP actually encapsulated in PPP, or is PPP and IP sent out at the same
time at different protocol layers? Kinda holding hands in a sense to each