Comtech EF Data SDM-300A - Manual (Page 234)

SDM-300A Satellite Modem Revision 6
Buffering SDM300A.IOM
8–6
8.5 Frame/Multiframe Length
The depth of the receive buffer required has been discussed in Section 8.4, and is
applicable to all unframed data.
When the data is framed (such as 2048 kbps G732 or 1544 kbps G733), it is
desirable to provide slips in predefined locations. The advantage of organized slip
locations (in relation to the frame) is that multiplexing equipment does not lose
sync and outages on any channel are kept to a minimum.
A 2048 kbps frame structure commonly used is G732. This has a frame length of
256 bits with 16 frames per multiframe (4096 bits total, or 2 ms).
8.5.1 Multiples of the Frame Length
If this setting is set to NONE, the user can choose any buffer depth.
8.5.2 Total Buffer Length
T1 and E1 framing structure under G.704 is available. When this is selected, the
buffer length is restricted to the size of the buffer. Using the examples from the
three previous sections, the total buffer depth (end to end) will be:
Doppler + Plesiochronous (rounded up to the nearest multiframe)
1.15 ms + 6.98 ms = 8.13 ms
If the frame length is 2 ms, then the nearest multiframe will be 10 ms, or 20,480
bits.
8.6 Converting Between Bits and Seconds
8.6.1 Bits to Seconds
1/Data Rate x Bits = Seconds.
8.6.2 Seconds to Bits
Data Rate x Seconds = Bit.