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dumb terminal
An end−user station that can access another computer or switch but cannot provide any processing at
the local level.
Dynamic Host Configuration Protocol (DHCP)
A protocol that provides an IP address to requesting nodes on the network.
Dynamic ISL
A protocol that performs trunking negotiation. It also verifies that two connected ports can become
trunk links. A Dynamic ISL port can be configured in one of four modes: On, Off, Desirable, or Auto.
Dynamic VLAN port
A VLAN number assigned to a certain MAC address. The node attaching to any dynamic port on the
switch is a member of the VLAN assigned to the MAC address. Dynamically assigned VLANs are
configured using CiscoWorks 2000 or CiscoWorks for Switched Internetworks software.
dynamic window
A mechanism that prevents the sender of data from overwhelming the receiver. The amount of data
that can be buffered in a dynamic window can vary.
E−F
electromagnetic interference (EMI)
External interference from electromagnetic signals that causes reduction of data integrity and
increased error rates in a transmission medium.
Electronic Industries Association (EIA)
A group that specifies electrical transmission standards.
Embedded Control Unit (ECU)
A component of the ClearChannel Architecture that handles frame switching on the Cisco Catalyst
series 1900 and 2820 switches in software. The ECU is an Intel 486 processor, Flash memory module,
and 512K DRAM. It is also used in initializing the switch, using STP on a per−VLAN basis,
controlling the LEDs on the chassis, maintaining RMON statistics, and handling in−band and
out−of−band management of the switch.
emulated LAN (ELAN)
A feature used by ATM LANE to perform the basic functionality of a VLAN in Token Ring or
Ethernet environments. ELANs, like VLANs, require a route processor such as a router to route
frames between ELANs.
encapsulation
The technique used by layered protocols in which a layer adds header information to the Protocol
Data Unit (PDU) from the layer above.
Encoded Address Recognition Logic (EARL) ASIC
An ASIC located on the Catalyst 5000 family of switches that sees all the frames that cross the bus. It
performs a task similar to that of the CAM. The ASIC is responsible for making switching decisions
based on the MAC address and the source VLAN. It is also responsible for updating the address table.
encryption
The modification of data for security purposes prior to transmission so that it is not comprehensible
without the decoding method.
enterprise services
Services that involve crossing the backbone to achieve access. These services are typically located on
a separate subnet from the rest of the network devices.
EtherChannel
A connection used on the Catalyst 3000 family or Kalpana switches. It allows as many as seven
Ethernet links to be bundled and load−balanced frame by frame to provide up to 140Mbps of
bandwidth. It can utilize half−duplex or full−duplex links.
Extended Industry Standard Architecture (EISA)
The successor to the ISA standard. It provides a 32−bit bus interface used in PCs.
Fast EtherChannel (FEC)
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