5.1.1.5.1. Broken
or missing packets
SPEAD can handle broken or missing data packages but has no mechanism to
request resending missing data [AD3].
The SDP shall be capable of accepting all valid data, including
out-of-order data, from CSP that arrives no later than the travel-time
from CSP-SDP + 100ms from the time it is sent.
5.1.1.5.2.
Recovery from receiver failure
How to recover when a receiver (SDP node) fails or loses sync with the
stream is TBD-001.
This section shows the variability than can be expected and any
constraints on specific use cases of the interface or particular aspects
of the interface.
Note that parameter values for modes shown in this section are
expected or typical values and are provided for information only. This
interface does not constrain parameter values unless explicitly stated
as a constraint. Actual parameter values will be chosen by Telescope
Manager (for each scheduling block and its scans) according to the
requirements of the observation and any constraints imposed by
components of the telescope [AD6].
5.1.1.6.1.
Maximum supported data rate
The maximum data rates calculated here is based on the following
parameters (as specified for this interface):
-
MTU of 9000 bytes
-
Layer 1 and Layer 2 (ethernet) overheads of 38 bytes
-
Layer 3 and Layer 4 (IPv4 and UDP) overheads of 28 bytes
-
SPEAD packet (layer 5 & 6) overhead of 48 bytes
-
SPEAD packet header of 8 bytes
-
5 ItemPointers (8 bytes each) for each SPEAD packet
-
64 links (100GbE) as per I.S1M.SADT_SDP.003 with maximum link
occupancy over time of 80%
-
Mbaseline = (2 + (8 x Npol)) = 34
bytes. Size (in bytes) of TCI + FD + 4 polarisation products per
baseline.
Additional overheads are included to account for heap header packets and
for packets that are only partially filled with payload data (the last
packet from each CSP Node in the heap).
The maximum allowed correlator output data rate summed over all
simultaneous scheduling blocks11Reference is made here to
simultaneous scheduling blocks instead of subarrays since
SKA1-SYS_REQ-3026 (Mid) constrains the total number of simultaneous
scheduling blocks. Subarrays that are not allocated a scheduling block
(like a maintenance subarray) do not produce data and therefore should
not constrain the data rate. is shown in the table below. Refer to
the [RD7] for the detailed calculations.
5: Maximum Allowed