D-Link Unified Access Point Administrator’s Guide
156 © 2001-2008 D-Link Corporation. All Rights Reserved.
Variations on EAP include EAP Cisco Wireless
(LEAP), Protected EAP (PEAP), EAP-TLS, and
EAP Tunnelled TLS (EAP-TTLS).
EDCF
Enhanced Distribution Control Function is an
extension of
DCF
. EDCF, a component of the IEEE
Wireless Multimedia (WMM) standard, provides
prioritized access to the wireless medium.
ESS
An extended service set (ESS) is an
Infrastructure
Mode
Wireless Networking Framework
with
multiple access points, forming a single subnetwork
that can support more clients than a basic service set
(
BSS
). Each access point supports a number of
wireless stations, providing broader wireless
coverage for a large space, for example, an office.
Ethernet
Ethernet is a local-area network (
LAN
) architecture
supporting data transfer rates of 10 Mbps to 1 Gbps.
The Ethernet specification is the basis for the
IEEE
802.3
standard, which specifies the physical and
lower software layers. It uses the
CSMA/CA
access
method to handle simultaneous demands.
Ethernet supports data rates of 10 Mbps, Fast
Ethernet supports 100 Mbps, and Gigabit Ethernet
supports 1 Gbps. Its cables are classified as
“XbaseY”, where X is the data rate in Mbps and Y is
the category of cabling. The original cable was
10base5 (Thicknet or “Yellow Cable”). Some others
are 10base2 (Cheapernet), 10baseT (Twisted Pair),
and 100baseT (Fast Ethernet). The latter two are
commonly supplied using CAT5 cabling with RJ-45
connectors. There is also 1000baseT (Gigabit
Ethernet).
ERP
The Extended Rate Protocol refers to the protocol
used by
IEEE
802.11g
stations (over 20 Mbps
transmission rates at 2.4GHz) when paired with
Orthogonal Frequency Division Multiplexing
(OFDM). Built into ERP and the IEEE
802.11g
standard is a scheme for effective interoperability of
IEEE 802.11g stations with IEEE 802.11b nodes on
the same channel.
Legacy IEEE 802.11b devices cannot detect the
ERP-OFDM signals used by IEEE 802.11g stations,
and this can result in collisions between data frames
from IEEE 802.11b and IEEE 802.11g stations.
If there is a mix of 802.11b and 802.11g nodes on the
same channel, the IEEE 802.11g stations detect this
via an ERP flag on the access point and enable
request to send (
RTS
) and clear to send (
CTS
)
protection before sending data.
See also
CSMA/CA
protocol.
F
Frame
A Frame consists of a discrete portion of data along
with some descriptive meta-information packaged
for transmission on a wireless network. Each frame
includes a source and destination
MAC
address, a
control field with protocol version, frame type, frame
sequence number, frame body (with the actual
information to be transmitted) and frame check
sequence for error detection. A Frame is similar in
concept to a
Packet
, the difference being that a
packet operates on the Network layer (layer 3 in the
OSI model) whereas a frame operates on the Data-
Link layer (layer 2 in the OSI model).
G
Gateway
A gateway is a network node that serves as an
entrance to another network. A gateway also often
provides a proxy server and a firewall. It is
associated with both a router, which use headers and
forwarding tables to determine where packets are
sent, and a switch or bridge, which provides the
actual path for the packet in and out of the gateway.
Before a host on a
LAN
can access the Internet, it
needs to know the address of its default gateway.