Metrodata ATM CBR DSU, User Manual

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CONFIGURING THE ATM CBR DSU
37 76-02-031E
5 . 4. 1 ATM definitions
Brief definitions of the ATM set-up options are included below:
FORWARD IDLE CELLS: This option permits idle cells, which contain no payload to be
forwarded. In practise, they are usually deleted, and therefore the option is usually set to NO.
HCS COSET: This parameter is derived as follows: the HEC (Header Error Checksum) in
the 5 byte ATM Header, is X-OR’ed with 55
HEX
so that the idle cell HEC is non-zero.
PAYLOAD SCRAMBLING: This is usually enabled, and ensures that bit patterns in the
payload do not ghost Frame Alignment Patterns, thus causing false ATM framing errors.
IDLE CELL PAYLOAD: This option allows the User to specify a bit pattern for use in the
payload of idle ATM cells instead of all zeros. This provides some transmission traffic in
situations where this is desirable for system reasons.
5 . 4. 2 ATM masks
Header masks for filtering ATM traffic are set up with the ATM MASKS menu, which is
selected from the MAIN SET-UP menu.
The masks are set up to permit firstly deletion of idle cell traffic, and then to filter out good
cells so that only these are forwarded.
Figure 5.21 ATM Masks set-up
SDH/SONET ATM
MASKS
1- idle cell GFC 0000
2- idle cell VPI 00000000
3- idle cell VCI 0000000000000000
4- idle cell PT 000
5- idle cell CLP X
6- good cell GFC XXXX
7- good cell VPI XXXXXXXX
8- good cell VCI XXXXXXXXXXXXXXXX
9- good cell PT XXX
0- good cell CLP X
HIGHLIGHTED letter - select item
<escape> - exit menu