design-docs: timetable: unify arrival times and margin types

Co-Authored-By: Younes Khoudli <[email protected]>

Author: multun

content/docs/reference/design-docs/timetable/index.en.md

@@ -98,6 +98,12 @@ What we can do about outdated trains:
     - We can not check what changed between the old and new version
     - We can not know the cause of this change (RS, Infra, Algorithms...)
 
+### Separating stops and arrival times
+
+This is a side effect of unifying the margins model: as arrival times now
+are just another way to specify margin values. It makes little sense to have
+stops be part of the margin subsystem.
+
 ## Creation fields
 
 These fields are required at creation time, but cannot be changed afterwards.
@@ -129,19 +135,30 @@ path:
  - {id: c, deleted: true, waypoint: true, trigram: ABC}
  - {id: d, waypoint: true, track: toto, offset: 42}
 
-# the algorithm used for computing the standard margins AND scheduled points
-distribution_margins: MARECO
-
-standard_margins:
-  # the begin and end waypoints are always implicitly added
-  intermediate_waypoints: [b]
-  values: ["5%", "2%"]
-
-# all durations and times are specified using ISO 8601
-scheduled_points:
- - {at: a, arrival: PT0M, stop_for: PT5M}
- - {at: b, arrival: PT10M}
- - {at: c, arrival: PT25M}
+stops:
+ - {at: a, for: PT5M}
+
+# there are two mutually exclusive ways to add time constraints:
+# margins and arrival times. Both methods share parameters, such
+# as the distribution, intermediate waypoints, and transitions.
+time_constraints:
+  # algorithm used to distribute time over space
+  distribution: MARECO
+
+  # time constraints apply on the entire path. intermediate
+  # waypoints delimit zones which can be configured with distinct
+  # time constraints.
+  intermediate_waypoints: [b, c]
+
+  #   method 1: fixed arrival times
+  # arrival times to intermediate_waypoints and the destination waypoint,
+  # expressed as ISO 8601 durations since departure.
+  arrival_times: [PT10M, PT25M, PT30M]
+
+  #   method 2: margins
+  # margins values are given for each zone, delimited by the
+  # departure, intermediate, and arrival waypoints.
+  margins: ["5%", "30s/km", "1min"]
 
 
 # train speed at departure, in meters per second