FRAMES applies to any Data Link (Layer 2) PDU : in WANs (PPP, HDLC, LAP-xxx, etc.) but also in LANs (Ethernet II, Token Ring, etc.). Now, things are not THAT simple. There are always exceptions to confirm the rule. Look at LAN technologies, now (= since IEEE 802) using 2 sub-layers instead of one Data Link layer : MAC and LLC. FRAMES doesn't apply to both sub-layers : we usually speak of a MAC frame containing an LLC header. Look at ATM, using 2 sub-layers instead of one Data Link layer : ATM and AAL. For ATM, we use the word CELL instead of FRAME. Now, depending on the context (HTTP over TCP over IP over PPP over PSTN), FRAMES will actually apply to PPP - neither to PSTN nor to IP. -----Original Message----- From: Lloyd Wood [mailto:l.wood@eim.surrey.ac.uk] On Wed, 12 Jun 2002, Bill Cunningham wrote: > When you say FRAMES I guess you mean PPP frames. or HDLC. (PPP's HDLC-like.) Or frames specific to the MAC or data-link protocol being used, be it Ethernet or whatever. L. <http://www.ee.surrey.ac.uk/Personal/L.Wood/><L.Wood@surrey.ac.uk>