Wireshark Lua postdissector that converts frame.time_delta_displayed to distance values.

delta_distance.lua

-- delta_distance.lua
-- Add delta_distance.{copper,fiber}.{km,mi} fields
-- By Gerald Combs <gerald@wireshark.org>
-- Modified from https://wiki.wireshark.org/Lua/Examples/PostDissector
-- My Wireshark Lua skills were getting rusty so I wrote this. There are
-- probably mistakes.

-- To use this script, place it in your personal Lua plugin directory.
-- You can find that by going to "About → Folders".

-- Links:

-- Fractional speed of light in copper and fiber
-- https://en.wikipedia.org/wiki/Velocity_factor

-- The Lua programming language
-- https://www.lua.org/

-- The Wireshark Developer's Guide Lua reference
-- https://www.wireshark.org/docs/wsdg_html_chunked/wsluarm.html

-- Wireshark Q&A
-- https://ask.wireshark.org/

-- The Wireshark development mailing list
-- wireshark-dev@wireshark.org

--
-- Setup.
-- The following code is run once during program startup
--

-- Extract frame.time_delta_displayed. This will be added by the Frame
-- dissector before delta_distance_p.dissector is called below.
local delta_t_f = Field.new("frame.time_delta_displayed")

-- Define the delta_distance protocol.
-- This will show up at the bottom of the packet details in square brackets.
local delta_distance_p = Proto("delta_distance", "Frame displayed delta distance")

-- Define our fields. These will show up under delta_distance.
local dd_cat6_km_field = ProtoField.float("delta_distance.cat6.km", "Cat 6 km")
local dd_cat6_mi_field = ProtoField.float("delta_distance.cat6.mi", "Cat 6 mi")
local dd_fiber_km_field = ProtoField.float("delta_distance.fiber.km", "Fiber km")
local dd_fiber_mi_field = ProtoField.float("delta_distance.fiber.mi", "Fiber mi")

-- Add our fields to delta_distance_p.
delta_distance_p.fields = { dd_cat6_km_field, dd_cat6_mi_field, dd_fiber_km_field, dd_fiber_mi_field }

-- Register delta_distance_p as a postdissector.
register_postdissector(delta_distance_p)

--
-- Post-dissection.
-- The following code is run after each packet has been dissected.
--

-- This is where we add items to the tree.
function delta_distance_p.dissector(tvb, pinfo, tree)
    local delta_fld = delta_t_f()
    if delta_fld == nil then
        return
    end

    -- Speed of light in a vacuum.
    local c_vacuum_km_s = 299792
    local c_vacuum_mi_s = 186282
    -- Cat 6a velocity factor
    local cat_6a_vf = .65
    -- Fiber velocity factor
    local fiber_vf = .67

    -- Do some arithmetic and add our items to the tree.
    local distance_tree = tree:add(delta_distance_p)
    distance_tree:set_generated()
    local delta_t = delta_fld.value:tonumber()
    local dd_cat6_km  = delta_t * c_vacuum_km_s * cat_6a_vf
    local dd_cat6_mi  = delta_t * c_vacuum_mi_s * cat_6a_vf
    local dd_fiber_km = delta_t * c_vacuum_km_s * fiber_vf
    local dd_fiber_mi = delta_t * c_vacuum_mi_s * fiber_vf

    distance_tree:add(dd_cat6_km_field, dd_cat6_km):set_generated()
    distance_tree:add(dd_cat6_mi_field, dd_cat6_mi):set_generated()
    distance_tree:add(dd_fiber_km_field, dd_fiber_km):set_generated()
    distance_tree:add(dd_fiber_mi_field, dd_fiber_mi):set_generated()
end

https://gitlab.com/-/snippets/2156053 is probably more up to date.