Optional fields may always be present in requests, even when not needed. In such case, they will be ignored. Requests received missing a mandatory field will be 904 - Format Error.

The third party host must ignore unknown fields included in the response messages.

When no usage notes are given in the field description, the field should be used as described in IFSF [1].

The “Format”-column can contain following info:

• LL: Variable length field, max 99 bytes as data. The field contains 2 bytes holding the length of the data. Example: 303101 a one byte field with LL = 3031 and the data is 01.
• LLL: Variable length field, max 999 bytes as data. The field contains 3 bytes holding the length of the data. Example: 30303101 a one byte field with LLL = 303031 and the data is 01.
• Date/time field formats, YYMMDDhhmmss (or variations), where:
  • YY : Last 2 digits of the year, 00 through 99
  • MM: Month, 01 through 12.
  • DD: Day, 01 through 31
  • hh: Hour, 00 through 23
  • mm: Minutes, 00 through 59
  • ss: Seconds, 00 through 59

The “Type”-column can contain:

• a : Alphabetic character [a..z,A..Z]
• n : Numeric BCD-digit. [0..9]
• ans: alphabetic, numeric and special characters
• an : alphabetic and numeric.
• s : Special characters.
• b : Binary
• p: pad character, space
• x: “C” for credit, “D” for debit and shall always be associated with a numerical amount data element.

The “Size”-column can contain:

• Variable length fields have a size that looks like “..nn”, where nn is the maximum number of characters or bytes.
• A fixed length field has “n” as size content, with n the number of characters or bytes.

All fixed length “n” data elements are assumed to be right justified with leading zeroes. All other fixed length data elements are left justified with trailing spaces. In all “b” data elements, blocks of 8 bits are assumed to be left justified with trailing zeroes.

Message protocol

All messages are transferred using TCP/IP sockets.

The message will be encapsulated in a transmission frame as follows:

• The first 4 digits contain the length of the message in ASCII (decimal value, most significant digit first). The length field includes all bytes from the first byte of the message ID up to the last byte of the last field.
• This 4-digit length field is immediately followed by the message ID, also in ASCII (decimal value, most significant digit first).
• An 8 byte message bitmap, which is a binary field (so not ASCII encoded).
• Message fields, which could be ASCII or binary encoded. The fields with format ‘n, ns, an, ans, anp or x’ are ASCII encoded, while the fields with format ‘b’ are binary encoded. The following conventions shall be applied to all data elements:
  • All fixed length numeric data element values shall be right justified with leading zeroes.
  • All fixed length data elements with alphabetic or special characters shall be left justified with trailing blanks.
  • All fixed length binary data elements shall be right justified with leading zeroes.
  • The position of a character or a bit in a data element shall be counted from the left beginning with one (1).(See also section 5.1 Attribute specification in [01])
  • No trailer is included.

Example: An imaginary message which consists only of a message ID “0300” and an empty bitmap (all zeros) will be transmitted as follows:
 

Example: An 1820 message, without MAC, will be transmitted as follows: Message bytes (hex):
303035303138323002300101000000003039313031353238343133383239313030393039313031353238343138333130353130303331

The PayEx response timeout is set to XX seconds. If after xx+1 seconds, no response has been received, the third party host needs to take the appropriate action based on the message type. (E.g. send a reversal)

The third party host has the possibility to perform offline stand-in, thought this needs to be agreed with the indididual card issuers. Otherwise the station might not be reimbursed.