|
E
EBCDIC
EBCDIC stands for
Extended Binary Coded Decimal Interchange Code. It is the IBM standard for
binary encoding of characters.
EDI
EDI stands for
Electronic Data Interchange. The EDI standards document how to exchange
data electronically between individual corporations using the public
telephone network or a public packet-switching network.
AH
The IP Authentication Header seeks to provide security
by adding
authentication information to an IP datagram. This authentication
information is calculated using all of the fields in the IP datagram
(including not only the IP Header but also other headers and the user
data) which do not change in transit. Fields or options which need
to change in transit (e.g., hop count, time to live, ident, fragment
offset, or routing pointer, such as audio and video. Sources of data can
include both live data feeds and stored clips. This protocol is intended to
control multiple data delivery sessions, provide a means for choosing
delivery channels such as UDP, multicast UDP and TCP, and provide a means
for choosing delivery mechanisms bases upon RTP. ) are considered to be
zero
for the calculation of the authentication data. This provides
significantly more security than is currently present in IPv4 and
might be sufficient for the needs of many users.
When used with IPv6, the Authentication Header normally appears after the
IPv6 Hop-by-Hop Header and before the IPv6 Destination Options. When used
with IPv4, the Authentication Header normally follows the main IPv4 header.
EGP
The Exterior Gateway Protocol
(EGP) exists in order to convey net-reachability information between
neighboring gateways, possibly in different autonomous systems. The
protocol includes mechanisms to acquire neighbors, monitor neighbor
reachability and exchange net-reachability information in the form of
Update messages. The protocol is based on periodic polling using
Hello/I-Heard-You (I-H-U) message exchanges to monitor neighbor
reachability and Poll commands to solicit Update responses.
EIGRP
EIGRP Enhanced Interior Gateway
Routing Protocol (EIGRP) is an enhanced version of IGRP. IGRP is Cisco's
Interior Gateway Routing Protocol used in TCP/IP and OSI internets. It is
regarded as an interior gateway protocol (IGP) but has also been used
extensively as an exterior gateway protocol for inter-domain routing. IGRP
uses distance vector routing technology. The same distance vector
technology found in IGRP is also used in EIGRP, and the underlying distance
information remains unchanged. The convergence properties and the operating
efficiency of this protocol have improved significantly.
Electronic Industry Association
The
Electronic Industries Association, EIA, is a national trade organization
that publishes hardware-oriented standards for data communications.
EIA-232-D is an example.
Emulate
To emulate is to
imitate. Emulation refers to the process of one device imitating another
device. An example of an emulator would be a 3270-emulator board used in a
PC that emulates an IBM 3270 coax device. This type of emulator allows a PC
to connect directly to a cluster controller via a coax connection. PCs also
run DEC terminal emulation modes such as DEC VT100 and VT220.
Encapsulation
Data
communications programs accept data from the layer above them and pass
data, after possibly having transformed them in some way, to the layer
below. They must usually communicate with their peer program in some way,
using the protocol established for their level, in order to perform their
functions. For example, suppose a program divides a long message into
shorter segments. It must somehow tell the receiving program how many
segments it is sending and in what order they should be re-assembled. One
possible alternative is to modify the message, but that would require that
the sender provide some portion of the message for the use of lower levels.
That would make even the highest levels sensitive to the operation of the
lower levels — not a good solution.
Virtually
all modern communications systems solve the problem this way: the
intermediate levels simply add prefixes, called headers, and sometimes
postfixes, called trailers, to the messages. This is called encapsulation.
Encoding
Encoding refers
to the process of translating binary data (1s and 0s) into signals to be
transmitted across a physical link such as a twisted pair cable. The
signals used to represent the binary data can take many forms. The two most
common forms are electrical signals and light signals. The most commonly
used physical layer encoding scheme found in LANs is Manchester Encoding.
End Office
A
central office (CO) is a telephone company facility where local loops are
terminated. The function of a CO is to connect individual telephones
together through a series of switches. COs are tied together in a hierarchy
for efficiency in switching. Other terms for a central office are local
exchange, wiring center, end office and public exchange.
Error Control
Error
control is the ability to automatically recover when an error occurs during
the transmission of data. Error control protocols (such as ITU-T V.42) are
protocols within most modems which guarantee error free transmission of
data. Devices that have this type of capability automatically retransmit
corrupted data. This type of error control is done at the physical layer.
Other means of correcting errors take place at other levels of the protocol
stack such as the Data Link Layer.
Error Recovery
Error
recovery is a procedure that allows a user to recover from certain errors
such as failure of either host system or transfer process. In FTP, error
recovery may involve restarting a file transfer at a given checkpoint.
ESCON
ESCON stands for
Enterprise System Connections. It is IBM's latest channel technology that provides
dynamic connection of devices to a host over fiber optic links of up to 60 kilometers.
ESF
ESF stands for
extended super frame. It is a term used in reference to the T1 data stream
where the 193rd bit is used as a framing bit.
ESP
The IP Encapsulating Security Payload (ESP) seeks to
provide confidentiality and integrity by encrypting data to be protected
and placing the encrypted data in the data portion of the IP ESP. Depending
on the user's security requirements, this mechanism may be used to encrypt
either a transport-layer segment (e.g., TCP, UDP, ICMP, IGMP) or an entire
IP datagram. Encapsulating the protected data is necessary to provide
confidentiality for the entire original datagram.
ESP
may appear anywhere after the IP header and before the final
transport-layer protocol. The Internet Assigned Numbers Authority has
assigned Protocol Number 50 to ESP. The header immediately preceding an ESP
header will always contain the value 50 in its Next Header (IPv6) or Protocol
(IPv4) field. ESP consists of an unencrypted header followed by encrypted
data. The encrypted data includes both the protected ESP header fields and
the protected user data, which is either an entire IP datagram or an
upper-layer protocol frame (e.g., TCP or UDP).
Ethernet
Ethernet
technology, originally developed in the 1970s by Xerox Corporation in
conjunction with Intel and Digital Equipment Corporation, is now the
primary medium for local area networks. The original Ethernet has 10Mbps
throughput and uses the CSMA/CD method to access the physical media.
100Mbps Ethernet is also used.
Extended Binary Coded Decimal
Interchange
EBCDIC
stands for Extended Binary Coded Decimal Interchange Code. It is the IBM
standard for binary encoding of characters.
|
