Content deleted Content added
Fixed typo Tags: canned edit summary Mobile edit Mobile app edit iOS app edit |
Fixed typo Tags: canned edit summary Mobile edit Mobile app edit iOS app edit |
||
Line 16:
==Overview of the Protocol==
Layer 1(CCITT) ITU-G703 defines the physical and electrical interface. G704 defines the Frame structure of the 2,048 Mbs sent across the link. G732 defines the allocation of that frame structure into the 32 discrete 64Kbit 'channels', of which 0 is used for alignment of the frames and 16 is (by convention only) allocated to common channel
Layer 2 Timeslot 16, 64Kbs operates as [[HDLC]] [[LAPB]], to support up to 60 PVCs or [[Data link connection identifier|DLC]]s (data link connections) (30 directly associated with the bearer channels and 30 for unrelated messages) as the specification describes them. Therefore, at maximum operation, each potential traffic channel can have two simultaneous data channels available for messages. Note that HDLC operates as a statistical [[multiplexing]] system. When traffic deltas are low, a single call establishment message will have access to the full 64Kbs (allowing for overheads).
DPNSS is a layer 3 protocol functioning as common channel signaling. The functionality is divided into Levels (confusingly nothing to do with OSI layers.) Levels 1-6 deal with simple call establishment (make call/break call) and are the minimum requirements by which a PBX can be said to be DPNSS compatible. The remaining levels are allocated to telephony features, supplementary services or to administrative features. Note that support of 'levels' by a PBX is not necessarily incremental. Some levels are interdependent but a PBX may omit support of some levels (above 6) and support others.
| |||