Point one:
HSCDS has always been the technology which bridges the gap
between single slot, switched ciruit GSM data and GPRS.
That is, HSCDS introduces multislot circuit switched
data in the network, but can also be single slot.
This means that lesser changes to the basestations,
network, billing,etc,etc is needed than for GPRS.
The reason HSCSD is now beeing touted by somebody is
probably that they finally have upgraded most of
their network to it.
Very simple???
The speed, as I have tried to explain, is variable, dynamic,
depending on the air channel controlled by the base station.
options are at least
- full raw speed (the 21.4kbps),
- 2/3 rate coder for 14.4kbps
- 1/2 rate coder for 9.6kbps
for every slot. (if I remember the basic coders right, but
it is more complicated than that, more variations, above
numbers are not exact, 21.4 would probably be called 19.2)
For multislot operation the speeds are 2x,3x,4x above
numbers.
Very simple??
"error correction" is based on (at least) two mechanisms
- channel coding, as above, to achieve a good enough
error rate for the air interface, good enough for
- end-to-end error correction by resending frames detected
to have an error
it is after this end-to-end error correction where
there must be no errors, not inbetween.
Channel coding is _NOT_ an error correction, except that
it is/was called forward error correction long time
ago, forward meaning that no messages had to be sent
in the opposite direction, while the "whaddyasay"
is exactly that.
Circuit switched means that the data flows with the same
speed all the time, while packets can be stored, buffered,
resent almost anywhere in the path, reordered, lost or
whatever.
Finally, operators have basestations, networks,etc which
support all HSCSD feature or just the basic one, this
includes how all of above is taken care of.
Additionally they have to decide on what speeds their
cell and user structure can support.
===
Handoffs have nothing to do with channel coding, the
data speed over the airinterface.
If data is lost during the handoff it is the task of
the end-to-end error correction to ask for that data to
be resent.
For the last stuff, you seem to forgotten that HSCDS is
multislot, like
9.6+ 9.6+ 9.6 or
14.4+14.4+14.4 or even
21.4+21.4+21.4
or whatever the exact speeds are for all coder variations.
Just to give a further hint, GPRS introduces more coders,
CS-1,2,3,4 or whatever they are called.
Ilmarinen |
