| x.25.a | A Bit | Boolean | Address Bit |
| x.25.d | D Bit | Boolean | Delivery Confirmation Bit |
| x.25.gfi | GFI | Unsigned 16-bit integer | General format identifier |
| x.25.lcn | Logical Channel | Unsigned 16-bit integer | Logical Channel Number |
| x.25.m | M Bit | Boolean | More Bit |
| x.25.mod | Modulo | Unsigned 16-bit integer | Specifies whether the frame is modulo 8 or 128 |
| x.25.p_r | P(R) | Unsigned 8-bit integer | Packet Receive Sequence Number |
| x.25.p_s | P(S) | Unsigned 8-bit integer | Packet Send Sequence Number |
| x.25.q | Q Bit | Boolean | Qualifier Bit |
| x.25.type | Packet Type | Unsigned 8-bit integer | Packet Type |