eVLBI with Mark5C

1. eVLBI with Mark5C Chester Ruszczyk MIT Haystack Observatory chester@haystack.mit.edu

2. Outline • Mark5C basics • Data sources for Mark 5C • Mark 5C data-packet format • e-VLBI with Mark 5C • Whither VSI-E? 7th International e-VLBI Workshop, Shanghai China, June 2008

3. Mark 5C basics • Mark 5C is basically a ‘dumb’ asynchronous Ethernet packet recorder that simply records the payload of each Ethernet packet which it receives • Will work with a ‘transmit only’ data source (i.e. no handshaking required • Data source is responsible for creating Ethernet packet, including time-tagging and data-formatting • A Mark 5C data-format specification has been developed (but Mk5C itself doesn’t really care): • One freq channel per Ethernet packet • Ethernet frame size allowable range: 64 to 9000 bytes • For each freq channel: integral number of packets per second • For each channel: must be a packet starting on second boundary • Arbitrary # of channels(i.e. not constrained to 2**n channels, unlike Mk5A/B/B+) 7th International e-VLBI Workshop, Shanghai China, June 2008

4. Data Sources for Mark 5C • Digital Data Sources (DDS) • Any device that can generate OSI Layer 2 or higher Ethernet packets • DDSs currently being designed for VLBI • DBE : Haystack • VDBE: NRAO • dBBC: EVN • Others? 7th International e-VLBI Workshop, Shanghai China, June 2008

5. Example Configuration 7th International e-VLBI Workshop, Shanghai China, June 2008

6. Ethernet Packet Structure Rule: All packets must have same length within a single scan. 7th International e-VLBI Workshop, Shanghai China, June 2008

7. Mark 5C VLBI Data Payload Composed of (optional) Data Frame Header followed by Data Frame Data Frame may be of arbitrary length, but must be multiple of 8 bytes All data in Data Frame are recorded Optional – not recorded 7th International e-VLBI Workshop, Shanghai China, June 2008

8. Managing out-of-order packets • Sending source inserts monotonically increasing 32-bit PSN into Data Frame • Mark 5C user option (executed in hardware) • On record: • Mark 5C checks the PSN for each Data Frame • Re-orders packets to be sequential within buffer limits (up to 16 packets buffered) • On playback • Software can re-order as necessary 7th International e-VLBI Workshop, Shanghai China, June 2008

9. Mark 5C Data Frame Header format Followed immediately by sampled data for specified channel Must be integral number of Data Frames per second First sample in Data Frame number zero must correspond to second tick Mark 5C data may be discontinuous in time, but must be monotonic in time; useful for pulsars, burst-mode mm-VLBI, etc 00UT 1 Jan 1990 is standard reference time for RTP data ‘Unassigned’ may be used for any purpose (e.g. PSN) ‘I’ indicates data in Data Frame is ‘invalid’ 7th International e-VLBI Workshop, Shanghai China, June 2008

10. e-VLBI with Mark5C • Important Mark 5C recording characteristics for e-VLBI • Receive only; no handshaking capability • Accepts data from user-specified list of MAC addresses (or all MAC addresses) • Supports recording of any OSI Layer 2 or higher Ethernet frames, including UDP/IP data streams 7th International e-VLBI Workshop, Shanghai China, June 2008

11. Long-haul e-VLBI Capabilities • Long haul connectivity • Standard transport layer • UDP • Dedicated light path • OK with OSI Layer 2 or higher connection • Configuration suggestion for long-haul • Place switch before 10G interface • Reason is convenience • IP to MAC Address resolution capability presently does not exist on Mark 5C I/O daughtercard 7th International e-VLBI Workshop, Shanghai China, June 2008

12. Whither VSI-E? • Is VSI-E still a good idea? • VSI-E strengths • Standardized on-the-wire data format over the network • Strong statistical transmission-channels information available to users • Completeness of user information about scan • VSI-E weaknesses • 2n channel requirement embedded in current VSI-E definition • Varying opinions of RTP/RTCP • Very complete and general; too much overhead? • Replace VSI-E simply with standard on-the-wire packet format (Mark 5C data format)? 7th International e-VLBI Workshop, Shanghai China, June 2008

13. Thank you!

14. Mark 5C Data-Frame data format Each Data Frame contains samples from one freq channel Multi-bit sampling is supported Bits within each sample are adjacent in Data Frame word;LSB in lower bit number 0 1-bit/sample data word format 2 bits/sample data word format 3 bits/sample data word format. ‘xx’ indicates unused bits 4 bits/sample data word format 7th International e-VLBI Workshop, Shanghai China, June 2008

15. Mark 5B emulation mode Goal is to create disk in format which can be played back on Mark 5B DOM (but will not play back on Mark 5A+) Mark 5B disk frame is 10016 bytes, too long for single Ethernet packet, so data source must create Mark 5B disk frame as two adjacent packets, each 5008 bytes long Sample coding same as Mark 5B (VLBA coding) Mark 5B emulation Disk Frame Header format(shaded parameters are created by Mark 5B, but not needed for Mk5B emulation mode) 7th International e-VLBI Workshop, Shanghai China, June 2008

16. Mark 5C Sample coding Fixed-point two’s-complement of desired number of bits 2-bit/sample example 7th International e-VLBI Workshop, Shanghai China, June 2008

17. Mark 5C setup parameters • List of valid MAC source addresses (to filter out spurious packets) • Length of MAC Client Data; option to ignore packets of wrong length • Byte offset to beginning VLBI Data Payload • PSN monitoring mode • 0 - off • 1 - write replacement fill pattern for missing or bad packets; primarily for Mark 5B emulation mode • 2 - do not write packets tagged as ‘Invalid’ • Byte offset to PSN (if PSN monitoring is enabled) 7th International e-VLBI Workshop, Shanghai China, June 2008