The DECT protocol stack
How does it work? That is a simple question with a long answer.
If you consider the DECT standard specification (EN 300 175) being in
eight parts with an average size of a hundred pages, you can get an idea
of the size of the answer. And that leaves out the parts about the various
profiles, approval tests and additional applications of DECT.
But not to worry. Here is a selection of the most basic items which
should give you an idea of the technical sophistication of DECT. Also
this paper from the DECT forum
is an excellent source of information.
The DECT protocol stack is based on the lower three layers of
the OSI model.
The exception to this is the Medium Access Control (MAC) layer, which handles
the specifics of the ether and covers part of layer 1 and 2 of the OSI model.
Also a Lower Layer Management Entity (LLME) is defined which has management
interfaces to all the layers of the DECT protocol stack.
Click on any part of the stack to get more information on that particular
layer or interface, or read the book.
The DECT protocol stack presents a C(ontrol)-plane and a U(ser)-plane
interface onto the stack. The C-plane is the interface to the control entity
in the application, while the U-plane is designed for transport of data.
The Control Plane is the control interface for the application of the DECT
handset and base system. Through this interface the network layer
services can be used to eg. set-up calls and exchange end-to-end control
information. In a handset this interface is used by the Control entity
and User Interface entity in the handset which reads the keypad and
controls the handsets display. Based on the users actions services on the
C-plane are requested and indications from the C-plane are translated into
information on the display. In a base system the C-plane is most likely
used by an interworking unit to connect the DECT system to a
(telephone)network (eg. ISDN). Remember that DECT is an access technology,
it provides no network services like switching. The interworking unit will
translate the signalling back and forth between the DECT stacks' network
layer and the network protocol stack (eg. ISDN layer 3)
The User Plane is the data interface for the application of the DECT handset
and base system. In telephony applications this is used to transfer
ADPCM encoded speech
with a rate of 32 kbps.
In a handset this needs to be encoded/decoded and coupled to the audiosystem,
ie. speaker and microphone. Also echo cancellation plays an important role.
In a base system the coupling is to the network, which can either be
analog or digital. If, for instance, the coupling is to an ISDN the
speech data needs to be transcoded into PCM (64 kbps) also taking echo
cancellation into account.
Written by my own two hands and an ASCII editor.
Problems? write me
Last updated December 27, 2000
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