Multitech PROXYSERVER MTPSR1-120 Guía de usuario descargar pdf (Pagina 70)

Firewall User Guide

Encapsulation: A technique used by network-layer protocols in which a layer adds header information to the protocol

data unit from the preceding layer. Also used in “enveloping” one protocol inside another for transmission. For

example, IP inside IPX.

Errored Seconds (ES): Any second of operation that all 1.544M bits are not received exactly as transmitted. Contrast

“Error Free Seconds”.

Error Free Seconds (EFS): Any second of operation that all 1.544M bits are received exactly as transmitted. Contrast

“Errored Seconds”.

ESF Error Event: A T1 error condition that is logged when a CRC-6 error or an Out-Of-Frame (OOF) error occurs.

Ethernet: A 10-megabit baseband local area network that allows multiple stations to access the transmission medium

at will without prior coordination, avoids contention by using carrier sense and deference, and resolves contention by

using collision detection and transmission. Ethernet uses carrier sense multiple access with collision detection (CSMA/

CD).

Excess Zeros: A T1 error condition that is logged when more than 15 consecutive 0s or fewer than one 1 bit in 16 bits

occurs.

Exchange: A unit (public or private) that can consist of one or more central offices established to serve a specified

area. An exchange typically has a single rate of charges (tariffs) that has previously been approved by a regulatory

group.

Exchange Area: A geographical area with a single uniform set of charges (tariffs), approved by a regulatory group, for

telephone services. Calls between any two points within an exchange area are local calls. See also “Digital PBX”,

“PBX”.

Exchange Termination (ET): The carrier’s local exchange switch. Contrast with “Loop Termination - LT”.

Explicit Congestion Management: The method used in frame relay to notify the terminal equipment that the network

is overly busy. The use of FECN and BECN is called explicit congestion management. Some end-to-end protocols use

FECN or BECN, but usually not both options together. With this method, a congestion condition is identified and fixed

before it becomes critical. Contrast with “implicit congesion”.

Extended Super Frame (ESF): One of two popular formats for framing bits on a T1 line. ESF framing has a 24-frame

super-frame, where robbed bit signaling is inserted in the LSB (bit 8 of the DS-0 byte) of frames 6, 12, 18 and 24. ESF

has more T1 error measurement capabilities than D4 framing. Both ESF and B8ZS are typically offered to provide clear

channel service.

Failed Seconds: A test parameter where the circuit is unavailable for one full second.

Failed Signal: A T1 test parameter logged when there are more than 9 SES (Severely Errored Seconds).

Fax (facsimile): Refers to the bit-mapped rendition of a graphics-oriented document (fax) or to the electronic

transmission of the image over telephone lines (faxing). Fax transmission differs from data transmission in that the

former is a bit-mapped approximation of a graphical document and, therefore, cannot be accurately interpreted

according to any character code.

Firmware: A category of memory chips that hold their content without electrical power, they include ROM, PROM,

EPROM and EEPROM technologies. Firmware becomes “hard software” when holding program code.

Foreground: The application program currently running on and in control of the PC screen and keyboard. The area of

the screen that occupies the active window. Compare with “background”.

Fractional T1 (FT1): A digital data transmission rate between 56K bps (DS0 rate) and 1.544M bps (the full T1 rate - in

North America). FT1 is typically provided on 4-wire (two copper pairs) UTP. Often used for video conferencing, imaging

and LAN interconnection due to its low cost and relatively high speed. FT1 rates are offered in 64K bps multiples,

usually up to 768K bps.

Frequency: A characteristic of an electrical or electronic signal which describes the periodic recurrence of cycles.

Frequency is inversely proportional to the wavelength or pulse width of the signal (i.e., long wavelength signals have

low frequencies and short wavelength signals yield high frequencies).

Foreign Exchange (FX): A CO trunk with access to a distant CO, allowing ease of access and flat-rate calls anywhere

in the foreign exchange area.

Foreign Exchange Office (FXO): provides local telephone service from a CO outside of (“foreign” to) the subscriber’s

exchange area. In simple form, a user can pick up the phone in one city and receive a tone in the foreign city.

Connecting a POTS telephone to a computer telephony system via a T1 link requires a channel bank configured for the

FX connection. To generate a call from the POTS set to the computer telephony system, a FXO connection must be

configured.

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