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An overview of the Call User Data formats used in X25 calls is provided in this section. It shows how to format user data for X25 call clearing.
The format for Call User Data consists of four protocol identifier octets followed by a maximum of 12 octets of the call user data. Octets consist of bits numbered 7 to 0, where bit 0 is the low order bit and is transmitted first. Octets are consecutively numbered starting from 1 and are transmitted in this order.
See below for information on how bit 0 relates to bits 6 &7 of octet 1
Protocol Identifier octet 1 details are shown below:
When bits 7 and 6 are 00, bits 5 to 0 are 000001 to indicate PAD messages relating to the PAD facility for the start-stop mode DTE. Other coding of bits 5 to 0 is reserved for future standardization by the CCITT, subject to the rules of Recommendation X.244.
All bits of octets 2, 3, and 4 are set to 0. These octets are reserved for future use to provide the called PAD or packet mode DTE with additional information pertinent to the calling party.
Octets of the call data field will contain the user characters received by the PAD from the start-stop mode DTE during the call establishment phase. The coding of these octets is similar to that of user sequences. The call data field is limited to 12 octets.
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Copyright (c) 2001 Eicon Networks