การส่�งข้อมู�ลผ่�าน PSTN

DTE : Data Terminal Equipment is any device that is a source of or destination for binary digital data (PC)

DCE : Data Circuit-terminating Equipment is any device that transmits or receives data in the form of an analog or digital signal through a network (Modem)

DTE DCE PSTN DTEDCE

Data communication interfacing DTE -DCE InterfacingRequirement : Use the same encoding

scheme and have common standards Mechanical characteristics : plugs,

circuits Electrical characteristics : voltage-level,

timing Functional characteristics : meaning of

each interchange circuits เช่�นขา 7 คือ Ground

V.24/EIA-232 (RS 232)

Electronic Industries Association (EIA)

(ISO 2110) 25-pin connector (but can be substituted by 9-pin (DB-9) : 8, 3, 2, 20, 7, 6, 4, 5, 22)

Mechanical characteristics

Electrical characteristics -3 to -15 V=binary 1 or OFF condition +3 to 15 V =binary 0 or ON condition Maximum bit rate 20 kbps

0

1 1

Functional specification

Control SignalName To Function

Request to send

DCE DTE wishes to transmit

Clear to send DTE DCE is ready to receive

DCE ready DTE DCE is ready to operate

DTE ready DCE DTE is ready to operate

Ring indicator DTE DCE is receiving a ringing signal

Received line signal detector

DTE DCE is receiving a signal(carrier)

Null modem

MODEMS MOdulator/DEModulator

Bandwidth 600 Hz to 3000 Hz

PSTN

Dial-up operation

20

DTE