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.
5.3.1.9. Usage guide

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. Resources

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 ):

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