title: T.50 (standard)
text: # T.50 (standard)
  
  ITU-T recommendation T.50 specifies the International Reference Alphabet (IRA), formerly International Alphabet No. 5 (IA5), a character encoding. ASCII is the U.S. variant of that character set.
  
  The original version from November 1988 corresponds to ISO 646. The current version is from September 1992.
  
  ## History
  
  At the beginning was the International Telegraph Alphabet No. 2 (ITA2), a five bits code. IA5 is an improvement based on seven bits bytes.
  
  * Recommendation V.3 IA5 (1968) Initial version, superseded
  * Recommendation V.3 IA5 (1972) Superseded
  * Recommendation V.3 IA5 (1976-10) Superseded
  * Recommendation V.3 IA5 (1980-11) Superseded
  * Recommendation T.50 IA5 (1984-10) Superseded
  * Recommendation T.50 IA5 (1988-11-25) Superseded
  * Recommendation T.50 IRA (1992-09-18) In force
  
  ## Use
  
  This standard is referenced by other standards such as RFC 3966. It is also used by some analog modems such as Cisco ones.
  
  This standard is referenced by other standards such as RFC 3939 - Calling Line Identification for Voice Mail Messages.
  
  ## Character set
  
  The following table shows the IA5 character set. Each character is shown with the hex code of its Unicode equivalent.
  
  IA5 character set :
  
  | | 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | A | B | C | D | E | F |
  | - | - | - | - | - | - | - | - | - | - | - | - | - | - | - | - | - |
  | 0x | NUL | SOH | STX | ETX | EOT | ENQ | ACK | BEL | BS | HT | LF | VT | FF | CR | SO | SI |
  | 1x | DLE | DC1 | DC2 | DC3 | DC4 | NAK | SYN | ETB | CAN | EM | SUB | ESC | FS | GS | RS | US |
  | 2x | SP | ! | " | # | $ | % | & | ' | ( | ) | * | + | , | - | . | / |
  | 3x | 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | : | ; | < | = | > | ? |
  | 4x | @ | A | B | C | D | E | F | G | H | I | J | K | L | M | N | O |
  | 5x | P | Q | R | S | T | U | V | W | X | Y | Z | [ | \ | ] | ^ | _ |
  | 6x | ` | a | b | c | d | e | f | g | h | i | j | k | l | m | n | o |
  | 7x | p | q | r | s | t | u | v | w | x | y | z | { | | | } | ~ | DEL |
  
  ## Standardisation
  
  * Identical standard: ISO/IEC 646:1991 (Twinned)
  