Some networks may choose to provide a service of mapping some or all of the information from the incoming call packet into the SETUP message (see 3.2.3/X.31). Table 6-4 shows the mapping of the X.25 incoming call elements to Q.931 information elements. The incoming call packet will still contain these fields when it is delivered. See 3.2.3/X.31 for mapping requirements.
Table 6-4/Q.931 – Mapping of X.25 information elements to corresponding Q.931 SETUP message information elements in packet-mode incoming call a)
Information elements in X.25 incoming call packet |
Corresponding information element in Q.931 SETUP message |
|
Calling DTE address |
Calling party number (Note 6) |
|
Called DTE address |
Called party number |
|
User data (UD) |
User-user information (Note 1) |
|
A-bit (Note 2) |
For further study |
|
D-bit |
Packet layer binary parameters |
|
Modulus |
Packet layer binary parameters |
|
X.25 user |
Flow control parameter negotiation |
Packet size, |
Throughput class negotiation |
Information rate (Note 4) |
|
Fast select |
Packet layer binary parameters |
|
Reverse charging |
Reverse charging indication |
|
Closed user group selection |
Closed user group |
|
Closed user group with outgoing access selection |
Closed user group |
|
Bilateral closed user group |
For further study |
|
Transit delay selection and indication |
Transit delay selection and indication |
|
Call redirection and deflection notification |
Redirecting number |
|
DTE facility |
Calling address extension |
Calling party subaddress |
Called address extension |
Called party subaddress (Note 5) |
|
End-to-end transit delay |
End-to-end transit delay |
|
Minimum throughput class |
Information rate (Note 3) |
|
Expedited data negotiation |
Packet layer binary parameters |
|
Priority |
For further study |
|
Protection |
For further study |
|
a) Mapping is optional or required as indicated in 8.2.3/X.31. NOTE 1 – The maximum length of the user data within the User-user informatione element is network dependent and is either 32 or 128 octets. NOTE 2 – The need and procedures for A-bit mapping is for further study. NOTE 3 – This information is not always present even when the "Information rate" is provided in the Q.931 SETUP message. NOTE 4 – When the "Throughput class negotiation" is not set in the X.25 incoming call packet, this information shall be provided as the default throughput values applying to the virtual call. NOTE 5 – The network will map bits 8 and 7 of the first octet of the called address extension facility parameter field in X.25 incoming call packet to type of subaddress field in octet 3 of the Called party subaddress information element in the Q.931 SETUP message, assuming that the X.25 incoming call packet is coded based on the 1988 version of X.25. Therefore, the called user should notice that the received type of subaddress may not be correct when the X.25 incoming call packet is coded based on the 1984 version of X.25. NOTE 6 – This mapping is mandatory and octet 3a shall be set with Presentation indicator set to presentation allowed and Screening indicator set to network provided. |
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