Licklider Transmission Protocol (CCSDS 734.1-B) for reliable DTN links
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README.md
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README.md
···
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minutes to hours. It provides selective acknowledgment and retransmission
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with support for both reliable and unreliable data segments.
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## Packages
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- **ltp** -- Core protocol: segment types, SDNV codecs, session management
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- **ltp-eio** -- Eio-based LTP segment transport
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## Installation
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Install with opam:
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```shell
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$ opam install ltp ltp-eio
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```
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If opam cannot find the packages, they may not yet be released in the public
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`opam-repository`. Add the overlay repository, then install them:
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```shell
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$ opam repo add samoht https://tangled.org/gazagnaire.org/opam-overlay.git
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$ opam update
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$ opam install ltp ltp-eio
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```
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## Usage
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### Send a block
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A block is delivered as a chain of data segments on a shared session, ending
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with `is_eob:true`:
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```ocaml
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let send_block ~host ~port ~block =
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Eio_main.run @@ fun env ->
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Eio.Switch.run @@ fun sw ->
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let net = (env#net :> [`Generic] Eio.Net.ty Eio.Resource.t) in
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let conn = Ltp_eio.connect ~sw ~net ~host ~port in
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let session = { Ltp.originator = 1L; number = 42L } in
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let chunk_size = 1024 in
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let len = String.length block in
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let rec send offset =
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if offset >= len then ()
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else
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let size = min chunk_size (len - offset) in
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let data = String.sub block offset size in
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let last = offset + size = len in
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let seg =
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Ltp.data_segment
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~session_id:session
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~client_service_id:1L
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~block_offset:(Int64.of_int offset)
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~is_eob:last
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data
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in
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Ltp_eio.send conn seg;
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send (offset + size)
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in
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send 0;
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Ltp_eio.close conn
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```
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### Receive a block
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Read segments until one with `is_eob seg` and concatenate their payloads:
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```ocaml
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let recv_block ~host ~port =
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Eio_main.run @@ fun env ->
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Eio.Switch.run @@ fun sw ->
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let net = (env#net :> [`Generic] Eio.Net.ty Eio.Resource.t) in
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let conn = Ltp_eio.connect ~sw ~net ~host ~port in
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let buf = Buffer.create 4096 in
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let rec loop () =
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match Ltp_eio.recv conn with
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| Ok seg ->
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(match seg.Ltp.content with
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| Ltp.Data d -> Buffer.add_string buf d.Ltp.data
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| _ -> ());
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if Ltp.is_eob seg then () else loop ()
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| Error msg -> Fmt.epr "Error: %s@." msg
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in
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loop ();
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Ltp_eio.close conn;
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Fmt.pr "received %d bytes@." (Buffer.length buf)
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```
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## Features
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- SDNV (Self-Delimiting Numeric Value) encoding/decoding
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- Cancel segments
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- Checkpoint and report-based flow control
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## Packages
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## Segment-level API
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For protocol-level work (checkpoints, reports, cancel flow), construct and
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inspect segments directly.
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### Build and encode
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```ocaml
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open Ltp
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- **ltp** -- Core protocol: segment types, SDNV codecs, session management
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- **ltp-eio** -- Eio-based LTP segment transport
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let session = { originator = 1L; number = 42L }
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## Installation
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let segment =
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data_segment
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~session_id:session
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~client_service_id:1L
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~block_offset:0L
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"hello"
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```
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opam install ltp ltp-eio
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let wire = encode_segment segment
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```
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## Usage
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### SDNV
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```ocaml
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open Ltp
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let encoded = Ltp.encode_sdnv 127L
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let () =
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match Ltp.decode_sdnv encoded 0 with
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| Ok (value, _offset) -> Fmt.pr "Value: %Ld@." value
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| Error msg -> Fmt.pr "Error: %s@." msg
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```
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### Predicates
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(* Create a session ID *)
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let session = { originator = 1L; number = 42L }
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- `is_data_segment`, `is_red_segment`, `is_green_segment`
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- `is_checkpoint`, `is_eorp`, `is_eob`
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(* Encode an SDNV value *)
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let encoded = encode_sdnv 127L
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### Report and cancel
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(* Decode an SDNV value *)
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match decode_sdnv encoded 0 with
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| Ok (value, _offset) -> Printf.printf "Value: %Ld\n" value
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| Error msg -> Printf.printf "Error: %s\n" msg
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```
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- `Ltp.report_segment ~session_id ~report_serial ~checkpoint_serial ~upper_bound claims`
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- `Ltp.report_ack ~session_id ~report_serial`
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- `Ltp.cancel ~session_id ~from_sender reason`
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- `Ltp.cancel_ack ~session_id ~to_sender`
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## Related Work
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+4
dune
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dune
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dune-project
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dune-project
···
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(lang dune 3.21)
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(using mdx 0.4)
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(name ltp)
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···
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(fmt (>= 0.9))
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wire
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(alcotest :with-test)
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(mdx :with-test)
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(alcobar :with-test)))
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(package
···
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(ltp (= :version))
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(eio (>= 1.0))
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(fmt (>= 0.9))
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(mdx :with-test)
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(logs (>= 0.7))))
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ltp-eio.opam
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ltp-eio.opam