Note that this data rate is the maximum pulsar timing data rate that the
SaDT links can support (given the maximum link occupancy SDP
can support) and is therefore a constraint on the pulsar timing output
data rate and not the actual pulsar timing data rate at any point in
time. This data rate takes into account all Layer 1 to 7 protocol and
file format overheads.
The total pulsar timing output data rate is calculated as the sum of the
data rate of each beam11The parameters (and mode) for each
pulsar timing beam could be different.: ∑RPT:BEAM +
∑RDS:BEAM + ∑RFT:BEAM bytes/s.
The maximum allowed pulsar timing data rate (as calculated above)
constrains the parameters of the pulsar timing modes, summed
over all simultaneous scheduling blocks to:
∑RPT:BEAM + ∑RDS:BEAM +
∑RFT:BEAM ≤ 8.26 GB/s
5.3.1.7.
Quality attribute
characteristics
5.3.1.8.
Rationale and design issues
TCP: Data transfer must be reliable. TCP provides the required reliable
data delivery. Using UDP would require retransmission by the application
layer which would simply duplicate the functionality of TCP to no
obvious advantage.
FTP: Transfers are periodic and independent (for each beam, each block
of data is self contained and is processed independently). Note
that FTP (in spite of the name) does not imply that real files have to
exist at either end of the link - the protocol is a mechanism for
transferring a block of data with a name.
FTP is a mature protocol with many high quality implementations in a
wide range of languages.
5.3.2. Presentation
layer
(OSI layer 6) N/A
5.3.3. Session
Layer
5.3.4. Transport
Layer
(OSI layer 4). TCP RFC 793, as specified in [RD2]
5.3.5. Network
Layer
(OSI layer 3). IPv4 RFC 791, as specified in [RD2]
5.3.6. Data Link
Layer
Refer to [RD1] and [RD2]
5.3.7. Physical
Layer
Refer to [RD1] and
[RD2]
5.4.
SDP - CSP Transient Buffer Data Interface: I.S1M.SDP_CSP.004
The SDP shall receive Transient Buffer data from the CSP for the purpose
of archiving the transient buffer data, based on the results of single
pulse searches (independently for each subarray). CSP will interleave
the buffer data in the same physical interface as the visibilities
(I.S1M.SDP_CSP.001).
This interface will carry real-time streaming transient buffer data
unidirectionally from the CSP to the SDP instances.
5.4.1. Application
Layer
SPEAD will be used for this interface since the data transmission will
be on the visibility interface (I.S1M.SADT_SDP.003). This interface
will use the SPEAD implementation as defined for the visibility
interface (section 5.1.1.), therefore the description of this interface
implementation will only show differences or additions to the
description in section 5.1.1.
5.4.1.1. Interface
identity
Refer to paragraph 5.1.1.1
5.4.1.2.1.
Data organisation (SPEAD Heaps and
Streams)
Data is organised per receptor. Each heap will contain the following set
of transient buffer data: all voltage data samples from one receptor for
a duration of 1s to 10s (TBC-006).
Subsequent SPEAD heaps of a particular transient buffer dump of the same
receptor will be grouped as a stream of transient buffer data (SPEAD
stream) and routed to a specific IP and port combination. Multiple
concurrent streams are created by directing the transmission of SPEAD
heaps to different ports or hosts. Each individual transient buffer dump
will be transferred as a separate SPEAD stream.
5.4.1.2.2. Data routing
SDP will supply the routing information to CSP (via TM) [RD4] for a
particular scheduling block and this routing will remain static for the
duration of the scheduling block. The routing information will be
supplied to CSP prior to the start of the scheduling block. Since
routing is done receptor the routing information will contain
the following for each receptor (TBC-007 ):
-
Receptor ID
-
SDP destination node IP address & MAC address
-
SDP destination node port
5.4.1.2.3. Sending
data
Each individual transient buffer dump will be transferred as a separate
SPEAD stream and therefore a session is started and terminated for each
individual transient buffer dump data transfer.
5.4.1.2.4. Receiving
data
Refer to par 5.1.1.2.4
5.4.1.3. Data
pre-conditions
Not applicable.
5.4.1.4. Data types
and constants
Each data Item that can be communicated over SPEAD is described by an
ItemDescriptor (refer to [AD3]). The following table list the SKA1
specific SPEAD items (and their ItemDescriptor items).
22: SKA1 SPEAD items