Vocality V100 Technical Manual page 161

timeslot allocation map when transferring to TDM operation; if the configurations are different, the units
will remain in V100 mode until the discrepancy is resolved. Once agreed, both units will enable their
respective TSA and adopt the multiplexed frame structure. If the units fail to resynchronise within their
new frame sub-structures, they will revert to V100-only mode, re-establish communications and try
again. This process will repeat indefinitely.
Control and management continues to be maintained through the V100 timeslots once the
framer/deframers are synchronised. Any subsequent configuration changes are managed using the same
technique but the first attempt is made from within the V100 frame sub-structure. On failure, the units
again revert to V100-only mode and retry:
Initial slot assignment – V100 only:
S O O O V V V V V V V V V V V V V V V V V V V V V V V V V V V V
Final slot assignment – 25% slots allocated to TDM bandwidth:
S O O O T T T T T T T T V V V V V V V V V V V V V V V V V V V V
Byte-interleaved TDM subframes are constructed as a function of link rate and tributary channel rate with
padding bytes as necessary. Tributary channel data rates from 50 to 1600bps may be configured at 25bps
intervals and in 100bps intervals from 1600bps up to the practical maximum of 448Kbps. By default, the
granularity of the TDM submultiplex is 100bps; the 25bps granularity is used only when a rate is
configured with this as the highest common factor.
The presence of the TDM card does not preclude tributary operation at low speeds such as 50, 300, 600,
1200 baud since the V100 creates a framed submultiplex beneath the physical 32-timeslot frame. So,
despite the fact that, at 128Kbps link rate each primary slot represents 4Kbps, the eventual superframe
contains as many 32-byte frames as required to represent all of the TDM octets in the submultiplex (in the
above example, the TDM submultiplex occupies 32Kbps out of 128Kbps).
The TDM submultiplex frame is constructed according to an algorithm which allocates 100bps to each slot
by default. Thus with 64Kbps available, the framelength would be 640 octets, yielding a frame duration of
80mS. The algorithm then allocates timeslots to tributary channels in a manner proportional to bit rate,
with any spare or surplus bandwidth allocated to a "spare" or unused pool. In this way, it is not necessary
to transmit length bytes since each member of the submultiplex is allocated its precise bit rate.
Within the TDM bandwidth a submultiplex allocates 100bps to each octet. In this example, channel 1 is
configured to 100bps, channel 2 to 9600bps, channel 3 to 16Kbps and channel 4 to 4800bps:
V100 Versatile Multiplexer Technical Manual Version 2.2
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