Contact Graph Routing for time-varying satellite networks
cgr: Fix arrival time calculation for query time
The arrival_time function was using departure_time (contact start) as the
initial time, but should use start_time (query time when we were at the
source). This caused incorrect arrival times when the query time was after
a contact's start time.
Found by fuzz testing.
+20
-4
+17
-4
lib/cgr.ml
+17
-4
lib/cgr.ml
···
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103
(* Routes *)
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module Route = struct
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-
type t = { hops : Contact.t list; src : Node.t; dst : Node.t }
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+
type t = {
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+
hops : Contact.t list;
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+
src : Node.t;
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+
dst : Node.t;
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+
start_time : float;
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+
}
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let hops t = t.hops
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let src t = t.src
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let dst t = t.dst
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+
let start_time t = t.start_time
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let departure_time t =
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-
match t.hops with [] -> 0. | c :: _ -> Contact.start c
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+
match t.hops with [] -> t.start_time | c :: _ -> Contact.start c
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let arrival_time t =
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let rec last_arrival time = function
···
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let arrival = tx_start +. Contact.owlt c in
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last_arrival arrival rest
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in
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-
last_arrival (departure_time t) t.hops
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+
(* Start with the time we arrive at source (the query time) *)
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last_arrival t.start_time t.hops
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let capacity t =
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match t.hops with
···
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| Some contact -> build_path (Contact.from contact) (contact :: acc)
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in
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let path = build_path dst [] in
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-
Some { Route.hops = path; src = state.src; dst }
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+
Some
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+
{
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+
Route.hops = path;
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src = state.src;
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+
dst;
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start_time = state.start_time;
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}
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end
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(* High-level routing *)
+3
lib/cgr.mli
+3
lib/cgr.mli
···
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val dst : t -> Node.t
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(** [dst route] is the destination node. *)
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+
val start_time : t -> float
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+
(** [start_time route] is the query time (when we were at the source). *)
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+
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val departure_time : t -> float
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(** [departure_time route] is when transmission should begin. *)
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