The here listed additional information should help you with a problem solution. However, an assurance for the correctness or wholeness of the statements doesn´t exist.

The feature of a Calls as well as within a Registration consists from the Facility-Length (1 byte) and the Facility-Field (0 ..63 bytes). By means of these statements, specific parameters can be arranged in term.
Here a short overview: (Numbers in HEX)

LengthCodePara 1Para 2Para xFacility
00 without Facility
020101 Reverse charging
0201x0 Fast select
0201x1 Reverse charging and Fast select
0202xy Throughput class
0203xx Closed User Group selection
020401 Charging information request
02080x Called line address modification
0209xx Closed User Group outgoing selection
0341xxxx Bilateral Closed User Group selection
0342sprp Paket size negotiation
0343swrw Window size negotiation
0344xxxx RPOA selection
0347xxxx Closed User Group selection (ext.)
0348xxxx Closed User Group outgoing selection (ext.)
0349xxxx Transitdelay selection and indication
034Cstrt Throughput class (ext.)
xxC1......Charging indication call duration
xxC2......Charging indication segment count
xxC30x....Call redirection/deflection notification
xxC4......RPOA selection (ext.)
xxC5......Charging indication monetary unit
xxC6......NUI selection
xxD1Cx....Call deflection to X25 number
xxFF reserved

Protocol Identifier:
Broadly ale has User-data-field a length of 0 ..16 bytes the option and serves the transmission of beforehand information at the goal system.
If the bits are 7 and 6 of the first byte ZERO, the only 4 bytes serve as Protocol-Identifier for higher protocol layers, for example 01-00-00-00 for the PAD - followed from 12 bytes of User-Data as Logon-ID or Routing-Information for the PAD. (Numbers in HEX)

Byte 0Byte 1Byte 2Byte 3Protocol
01000000Async. CCITT
C2000000SNA LLC2 (PSH)
C3000000SNA QLLC

Clearing Causes:

Code in HEXReason
00DTE originated
01Number Busy
03Invalid Facilty Request
05Network Congestion
09Out of Order
0BAccess Barred
0DNot Obtainable
11Remote Procedure Error
13Local Procedure Error
15RPOA Out of Order
19Collect Call Refuse
21Incomptible Destination
29Fast Select not Subscribed
39Ship absend
41Buffer Overrun

Reset Causes:

Code in HEXReason
00DTE originated
01Out of Order (PVC)
03Remote Procedure Error
05Local Procedure Error
07Network Congestion
09Remote DTE Operational (PVC)
0FNetwork Operational (PVC)
11Incompatible Destination
1DNetwork Out of Order (PVC)

Restart Causes:

Code in HEXReason
00DTE originated
01Local Procedure Error
03Network Congestion
07Network Operational
7FRegistration/Cancellation Confirmed

Diagnostic Codes:

Code in HEXReason
00No additional Infos
01Invalid P(S)
02Invalid P(R)
10Paket-Type Invalid for (this State)
11- for paket level ready (r1)
12- for DTE restart request (r2)
13- for DCE restart indication (r3)
14- for DCE ready (p1)
15- for DTE waiting (p2)
16- for DCE waiting (p3)
17- for data transfer (p4)
18- for call collision (p5)
19- for DTE clear request (p6)
1A- for DCE clear indication (p7)
1B- for flow-control ready (d1)
1C- for DTE reset request (d2)
1D- for DCE reset indication (d3)
20Paket not allowed
21Unidentifiable paket
22CALL on One-way logical channel
23Invalid Paket type on PVC
24Paket on unassigned logical channel
25REJECT not allowed
26Paket too short
27Paket too long
28Invalid GFI
29RESTART on channel unequal 00
2APaket type not compatible with facility
2BUnauthorized Interrupt Confirmation
2CUnauthorized Interrupt
2DUnauthorized Reject
30Timer expired
31- on incomming call
32- on clear indication
33- on reset indication
34- on restart indication
35- on call deflection
40CALL setup, clear or registration problem
41Facility Code not allowed
42Facility Parameter not allowed
43Invalid called DTE address
44Invalid calling DTE address
45Invalid facility/registation length
46Incomming Call barred
47No logical channel avaible
48Call collision
49Dublicate Facility request
4AAddress length is not zero
4BFacility length is not zero
4CExpected Facility is not provided
4DInvalid CCITT spezified DTE facility
4EMaximum of call redirections exceeded
50Miscellaneous / QLLC error (SNA)
51Improper Cause code from DTE / Undefined C field (SNA)
52Not aligned Byte / Unexpected C field (SNA)
53Inconsistent Q-bit setting / Missing I field (SNA)
54NUI problem / Undefined I field (SNA)
55I-field too long (SNA)
56QFRMR received (SNA)
57Invalid QLLC header (SNA)
58Data received in none-data state (SNA)
59Timeout condition (SNA)
5AInvalid number (number received) (SNA)
5BRecovery rejected or terminated (SNA)
5CXID negotiation in wrong state (SNA)
5DELLC timeout condition (SNA)
5EQ-bit discrepancy (SNA)
60Not assigned
61DNIC not available
62Incorrect transit DNIC
64Facility used incorrectly
67Incorrect M-bit
70International Problem / PAD error (SNA)
71Remote network problem / PAD access facility failure (SNA)
72International protocol problem / SDLC FCS error (SNA)
73International link out of order / SDLC timeout (SNA)
74International link busy / SDLC frame invalid (SNA)
75Transit network facility problem / I-field too long (SNA)
76Remote network facility problem / SDLC sequence error (SNA)
77International routing problem / SDLC frame aborted (SNA)
78Temporary routing problem / SDLC FRMR received (SNA)
79Unknown called DNIC / SDLC responce invalid (SNA)
7AMaintenance action
7BInvalid paket type
7FPAD inoperable (SNA)
80Q-bit error or network not avaible
81Fast select not substribed / 8100 DPPX-specific (SNA)
82Cause byte unequal to zero / INN QLLC-specific (SNA)
83Incompatible paket length
84Missing M-bit
85NUI not allowed
86PVC configuration error
87CLEAR / RESET by network
88DNIC not obtainable
89Reverse changing not subscribed
8ANot subscribed
8BCalling address missing
8CInvalid calling address
8DTemporary network link problem
8ENetwork link out of order
8FTimer expired in state p1 / INN QLLC-specific (SNA)
90Invalid cause code
91Invalid direct call / DDX-P RNR paket received (SNA)
92Byte not aligned
93Unexpected facility (X75)
94Facility not allowed (X75)
95Invalid address in call accept paket (X75)
96Interrupt paket not allowed in subnetwork
97Unexpected reset confirmation
98Fast select type 2 not allowed
99Incompatible PVC
9AInvalid window size negotiated
9BIncomplete call paket
9CInvalid address length
9DInvalid length of facility
9EIncomplete field
9FInvalid throughput class
A0Hunt group out of order
A1Hunt group not obtainable / Invalid M-bit paket sequence (SNA)
A2Hunt group temporary out of order / Invalid paket type received (SNA)
A3Missing address / Invalid paket on PVC (SNA)
A4Missing subaddress / Unassigned logical channel number (SNA)
A5Invalid facility format / Diagnostic paket received (SNA)
A6Facility length unequal to zero / Paket too short (SNA)
A7Missing user-data / Paket too long (SNA)
A8Missing national facility / Invalid GFI (SNA)
A9Access barred / Not identifiable (SNA)
AANumber temporarily not obtainable / Not supported (SNA)
ABNUI required in call / Invalid paket send sequence number (SNA)
ACFast select not subscribed / Invalid paket receive sequence number (SNA)
ADNetwork received download request / Invalid D-bit received (SNA)
AENetwork component failure / Invalid Q-bit received (SNA)
AFNetwork internal connection lost
B0Network internal restart
B1Invalid adress in call accept / No LU-LU session (SNA)
B2Unknown facility / Abend 703 in progress (SNA)
B3Cancel chain command (SNA)
B5X32 port not available
B6X32 port not available
C0X32 port service data error / X25 dial access invalid service data field
C1X32/X25 port service data error / Termination pending (SNA)
C2X32/X25 port user data error / Channel inoperative (SNA)
C3X32/X25 port procedure error / Unauthorized interrupt confirmation (SNA)
C4X32/X25 port modem error / Unauthorized interrupt request (SNA)
C5X32/X25 port modem error / PU resource not available (SNA)
C6Inactivity time-out (SNA)
C7Incompatible line configuration (SNA)
C8X32/X25 port connected / Reset indication to PAD (SNA)
C9X32/X25 port dialing / DTE not operational (SNA)
D0Resources - general (SNA)
D1Buffer depleted (SNA)
D2PIU too long (SNA)
E0Local procedure error - general (SNA)
E1Paket received with LC not equal to zero (SNA)
E2Restart/Diagnostic paket on LC not equal zero (SNA)
E3Incoming call received on wrong LC (SNA)
E4Facility not subscribed (SNA)
E5Invalid paket for LC equal zero (SNA)
E6Facility parameters not supported (SNA)
E7Facility not supported (SNA)
E8Unexpected calling DTE (SNA)
E9Invalid D-bit received (SNA)
EAReset indication on virtual Call (SNA)
EBInvalid protocol identifier (SNA)
ECConnection identifier mismatch (SNA)
EDMissing cause/diagnostic code (SNA)
F0Remote procedure error - general (SNA)
FALink reset (SNA)

Other Diagnostic-Codes often are used for own mistake codes by communication-device manufacturers.