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Table Of Contents  The TCP/IP Guide
 9  TCP/IP Application Layer Protocols, Services and Applications (OSI Layers 5, 6 and 7)
      9  TCP/IP Key Applications and Application Protocols
           9  TCP/IP Interactive and Remote Application Protocols
                9  Telnet Protocol

Previous Topic/Section
Telnet Connections and Client/Server Operation
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Pages in Current Topic/Section
12
3
4
Next Page
Telnet Protocol Commands
Next Topic/Section

Telnet Communications Model and the Network Virtual Terminal (NVT)
(Page 3 of 4)

NVT ASCII Control Codes

Regular ASCII consists of 95 regular, “printable” characters (codes 32 through 126) and 33 control codes (0 through 31 and 127). The Telnet standard specifies that the output device must be able to handle all the printable characters, and it mandates how several of the other common ASCII control codes should be interpreted. Of these codes, three (0, 10 and 13) are required to be accepted by all Telnet software; five others are optional, but if supported, must be interpreted in a manner consistent with the Telnet specification. They are all described in Table 280.


Table 280: Interpretation of Standard Telnet NVT ASCII Control Codes

ASCII Value (Decimal)

ASCII
Character Code

ASCII Character

Description

Support Optional / Mandatory

0

NUL

Null

No operation (no effect on output).

Mandatory

7

BEL

Bell

Produces an audible or visible signal on the output without moving the print head. This notification may be used to get the user’s attention, as in the case of an error.

Optional

8

BS

Back Space

Moves the print position one character to the left.

Optional

9

HT

Horizontal Tab

Moves the printer to the next horizontal tab stop. The standard does not specify how devices agree on tab stop positions; this can be negotiated using Telnet options.

Optional

10

LF

Line Feed

Moves the printer to the next line, keeping the print position the same.

Mandatory

11

VT

Vertical Tab

Moves the print line to the next vertical tab stop. As with the “HT” character, devices must use an option to come to an agreement on vertical tab stop positions.

Optional

12

FF

Form Feed

Moves the printer to the top of the next page (or on a display, clears the screen and positions the cursor at the top.)

Optional

13

CR

Carriage Return

Moves the printer to the left margin of the current print line.

Mandatory


Previous Topic/Section
Telnet Connections and Client/Server Operation
Previous Page
Pages in Current Topic/Section
12
3
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Next Page
Telnet Protocol Commands
Next Topic/Section

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Version 3.0 - Version Date: September 20, 2005

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