Network interfaces | Code | Description |
| A1 | Type A Tie Trunk type I signalling |
| A2 | Type A Tie Trunk type II signalling |
| B1 | Type B Tie Trunk type II signalling |
| B2 | Type B Tie Trunk type II signalling |
| CT | Type C Tie Trunk |
| DI1 | Digital Interface |
| DI2 | Digital Interface with signalling bits |
| DI3 | Digital Interface containing encode analogue |
| DSC | Digital Subrate Channels |
| GS | Ground Start |
| HEI | Handset with CS-03 Exempted Interface (HAC / ROLR) |
| IST | ISDN S/T Reference |
| ISTA | ISDN S/T reference with encoded analogue |
| IUB | ISDN U reference Basic Rate Access |
| IUP | ISDN U reference Primary Rate Access |
| LS | Loop Start |
| MC | Metallic Channels |
| OPP | Off Premises Station Proprietary |
| OPS | Off Premises Station |
| PL | Private Line (lease line) |
| RB | Reverse Battery |
| RL | Release Link Trunk |
| WH | Wireless Handset only (HAC / ROLR) |
