Protocol: ISO 8073 / TP TP PCI / Überblick
PDU Part: Fixed Part
Field: class option
Length: 1 byte
Contents: indicates the used TP class.
The initiator shall propose a preferred class and may propose any number of alternative classes which permit a valid response. The initiator should assume when it sends the CR TPDU that its preferred class will be agreed to, and commence the procedures associated with that class, except that if class 0 or class 1 is an alternative class, multiplexing shall not commence until a CC TPDU selecting the use of classes 2, 3 or 4 has been received.
This means, for example, that when the preferred class includes resynchronization the resynchronization will occur if a reset is signalled during connection establishment.
The responder shall select one class as a valid response corresponding to the preferred class and to the class(es), if any, contained in the alternative class parameter in the CC TPDU and shall follow the procedures for the selected class.
If the preferred class is not selected, then on receipt of the CC TPDU the initiator shall adjust it's operation according to the procedures of the selected class.
Preferred Alternative
class class(es)
--------- -----------------------
0 none = class 0
0 = not valid
1 = not valid
2 = not valid
3 = not valid
4 = not valid
1 none = class 1 or 0
0 = class 1 or 0
1 = class 1 or 0
2 = not valid
3 = not valid
4 = not valid
2 none = class 2
0 = class 2 or 0
1 = not valid
2 = class 2
2 = class 2
3 = not valid
4 = not valid
3 none = class 3 or 2
0 = class 3, 2 or 0
1 = class 3, 2, 1 or 0
2 = class 3 or 2
3 = class 3 or 2
4 = not valid
4 none = class 4 or 2
0 = class 4, 2 or 0
1 = class 4, 2, 1 or 0
2 = class 4 or 2
3 = class 4, 3, or 2
4 = class 4 or 2