| MTP
functions |
| Physical transmission
(e.g. 64 kbit/s PCM time slot) |
|
|
|
| HDLC-type
frame-based protocol for flow control, |
||
| error control
(using ARQ), and signalling network |
||
| supervision and
maintenance functions. |
||
|
|
| Routing in the signalling
network (using OPC, DPC) |
|
| between SPs
with level 4 users (see SIO at level 2). |
|