
DS34S132 DATA SHEET
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the Fragment byte depth (e.g. 24 bytes for T1). Pn.PRCR1.BFD and Pn.PTCR1.BFD specify how many Fragments
are used by each Staging Buffer (4 Fragments will store data for a 4 x 125 us = 500 us period).
BPF should be set to the number of bytes exchanged on the TDAT/RDAT interface in a 125 us period (e.g. for T1:
17 hex for “24 bytes”; for E1: 1F hex for “32 bytes”). For applications where TDAT and RDAT are used to support a
slower, non-T1/E1 interface, the BPF can be set to any integer value to represent the TDM Port data rate (data
received in a 125 us period; e.g. BPF = 1 for 64 Kb/s).
The BFD setting enables a compromise between the processing latency and the total number of Bundles supported
by an S132. Smaller BFD settings enable a smaller processing latency (smaller wait period to fill the Staging
Buffer), but with a smaller maximum number of Bundles. To function properly, the BFD value must also be set so
that the data stored in the Staging Buffer cannot exceed the smallest Bundle payload size associated with that TDM
Port (i.e. the number of bytes represented by BPF * BFD must be ≤ the number of bytes represented by
B.BCDR1.PMS for all Bundles assigned to that TDM Port). Table 9-3 describes the BFD settings. Table 9-3. TDM Port BFD Settings
BFD value Staging Buffer Depth
Staging Buffer Latency
Maximum # of Bundles
0
TDM Port data path disabled
-
1
1 Fragment
125 us
64
2
2 Fragment
250 us
128
3
4 Fragment
500 us
256
For CES applications, the BFD and PMS settings can be directly compared since both are essentially specified in
frames (BFD ≤ PMS; for CES applications the number of bytes stored by the Staging Buffer Fragment is equal to
the number of bytes in one CES Frame, or 1 Fragment = 1 Frame). As an example, if PMS = 3 (3 frames per
packet payload), then BFD should be set to 10b or 01b (1 or 2 fragments). For SAT applications the PMS setting is
specified in bytes (instead of frames) and the TXP/RXP Bundle packets are programmed to carry a payload size
that is not related to a frame size (“frames” are not applicable to the SAT/Unstructured application). For SAT
applications the following “BFD to PMS” comparison can be used:
BFD (in Fragments) x BPF (in bytes per Fragment) ≤ PMS (in bytes)
In SAT applications, the S132 supports T1/E1 line rates and slower, non-T1/E1 rates. For all SAT applications, the
Pn.PRCR1.SPL register be programmed to indicate how many bytes are included in each RXP/TXP Bundle
payload. The TDM Port SPL value should be set to the same value as the Bundle PMS.
For SAT (Unstructured), non-T1/E1 applications (e.g. V.35), the TDM Port should use a line rate that is
approximately equal to an integer multiple of 64 Kb/s. This might be referred to as an “Unstructured Nx64” signal. In
this document it is called a “non-T1/E1” signal. Unstructured (SAT) signals usually are asynchronous signals. The
term “Nx64” can also refer to a “Structured Nx64” signal that is synchronized to the public network and can be
carried by a T1/E1 for transporting and switching in the public network (e.g. “Fractional T1/E1” and ISDN signals). A
“Structured Nx64” signal is carried by a CES PW (the S132 only supports “Structured Nx64” with T1/E1 line rate
TDM Ports).
For the best latency performance, each TDM Port BFD should be set to the lowest possible value allowed for the
maximum number of Bundles that will be supported by the S132. With a selected BFD value, all Bundle PMS
values associated with that TDM Port cannot be smaller than BFD. As an example, if it is necessary to support a
Bundle with a PMS = 1 (1 frame per packet or one packet every 125 us) then no more than 64 Bundles can be
supported by the S132 (the standards only require a maximum packet rate of one packet every 1 ms).
9.2.4 Timeslot Assignment Block
For T1/E1 applications, the S132 includes a Timeslot Assignment Block with the ability to monitor outgoing CAS
and control outgoing SW CAS Conditioning, Data Conditioning, and Loopback functions (depicted i
n Figure 9-13).