嘿，我竟然从字典上能查到它们的解释：(www.dictionary.com)
E1:
A European framing specification for the
transmission of 32 DS0 (64 kb/s) data streams. By
extension, it can also denote the transmission rate required
(2.048 Mb/s = 2048 kb/s). Unlike DS1 it is free of
bit-robbing.
Frame Relay:
A DTE-DCE interface specification based
on LAPD (Q.921), the Integrated Services Digital Network
version of LAPB (X.25 data link layer). A common
specification was produced by a consortium of StrataCom,
Cisco, Digital, and Northern Telecom.
Frame Relay is the result of wide area networking
requirements for speed; LAN-WAN and LAN-LAN
internetworking; "bursty" data communications; multiplicity
of protocols and protocol transparency. These
requirements can be met with technology such as optical
fibre lines, allowing higher speeds and fewer transmission
errors; intelligent network end devices (personal computers,
workstations, and servers); standardisation and adoption
of ISDN protocols. Frame Relay could connect dedicated lines
and X.25 to ATM, SMDS, BISDN and other "fast packet"
technologies.
Frame Relay uses the same basic data link layer framing and
Frame Check Sequence so current X.25 hardware still works.
It adds addressing (a 10-bit Data Link Connection Identifier
(DLCI)) and a few control bits but does not include
retransmissions, link establishment, windows or error
recovery. It has none of X.25's session layer but adds some
simple interface management. Any network layer protocol can
be used over the data link layer Frames.
