Pydtnsim

Added
- Added requirements.txt to allow for an easy dependency installation.

Changed
- First public release version. Renamed project from `simpy-dtn` to `pydtnsim`.
- Adapted changelog and readme
- Switched to Travis CI .yml file (and removed gitlab CI file). The checks
performed during the CI runs are the same.
- Updated `setup.py` to load long description from `README.md` with common
function call

Fixed
- Corrected and cleaned up dependencies, deleted requirements.txt, added
version value ranges for dependencies

Added
- The `ContactPlan` object now allows for the loading of topology information
from Strings and not just only files. This allows for a loading of data
embedded in other file types than simple json files.
- The `SimpleCGRNode` is now provided with a list of the hotspots in the
topology (this change is scenario-specific, i.e. for the ring road scenario,
and might be removed in future versions).
- The `Simulator` in combination with the `Contacts` now keeps track of the
contact utilization.

Changed
- Improved monitoring interface: The monitoring interface now allows for a
more fine-grained evaluation of occurring events. In particular, more
detailed parameters about routing decisions are provided to the registered
monitors.
- The internal forwarding handling of the `Packet` object, the implemented
routing mechanisms and the unit tests were modified to accommodate the
changes to the monitoring interface as well.

Fixed
- Removed cyclic imports in `monitors` and `packet_generators` submodules.
- Additional style issues were removed that arose due to the update of pylint
to version 2.2.2
- The `qsim` backend was updated to assure that insertion of events in the
past are caught. Also, the backend now allows for the insertion of two
concurrent events scheduled for the same time by the same runner.

Added
- Allowing naming of simulation runs for an better overview if multiple
simulations are running at the same time. Also provide 3 types of output:
`NONE`, `TQDM` and `TEXTUAL`.

Changed
- Removed delay calculations from the simulation environment.
- Order successor list in `ContactGraph` object both after to_time and hash
value of the to_node.

Fixed
- Fixed bug in the calculation of route capacities in all Dijkstra flavours.
- Create nominal nodes for otherwise unconnected contacts.

Added
- Allow handover of a list of the hotspots to the routing algorithms. This
list is used to prevent loops inbetween the hotspots due to congestion to
the satellites. Whenever a packet is received at a hotspot from another
hotspot with the `Return-To-Sender`-Flag set to False, the packet can not
only be returned to the sender, but to no other hotspot as well. It has to
be scheduled on the local node for a later contact.
- If the JSON source file contains the information regarding the hotspots, this
information is automatically extracted during the generation of the
`ContactPlan`. It can be accessed through both the `ContactPlan` and the
`ContactGraph` object.

Changed
- Sort successor and predecessor lists by the to_time. Instead of having to
remove nodes from the `ContactGraph` over time to gain a performance boost,
we can simply exit the loop in the neighbor function if we encounter the
first value that is <= the current distance.
- Moved commonly used CGR functionality to a shared module `cgr_utils`.

Fixed
- Fixed bug in routing algorithms where the delay of a contact was not
considered when deciding on the feasible neighbors.
- Removed unnecessary search operations by setting the start value of the
Dijkstra search to the current time. A search run for values below that
value is never needed.

Added
- Consider the delay provided with the ContactPlan information both for the
simulation forwarding as well as the routing approaches. A delay has to be
provided (as default delay) that is used when no delay is provided or the
delay is zero. The delay (propagation + processing etc.) must never be zero
as (in combination with the restricted simulation resolution) this could
cause infinite forwarding loops and would prevent the simulation from
terminating.

Changed
- Improved the decision consistency of CGR_Basic, CGR_Anchor and SCGR. By
using the forwarding time to the next hop instead of the hash as third
characteristic value, the overall performance in the face of network
congestion is improved. The hash values are used as tie-break as fourth
characteristic.

Fixed
- Fixed problem where the successor list was altered (items were removed)
while iterating over it. This led to undefined behaviour where randomly
subsequent values were not considered.

Added
- Added lookahead window in SCGR: Instead of looking for routes of the entire
period that the contact graph holds information, the algorithm makes an
educated guess as of in which timespan a route could be expected. This is
based on a static value for the first run and the previously observed mean
route EDT times 1.2 in subsequent runs. If no route can be found within the
window, the Dijkstra run is repeated without the window to ensure that a
route is found if there is one. With this approach, in Simulations usually
more than 90% of the found routes were within the window, thus reducing the
overall route finding time significantly while returning the same results.
- Added option to ignore contacts that lie beyond the simulation window. I.e.
if the scenario source file contains more topology information, that
information is discarded during the ContactPlan generation and thus not used
for the contact ContactGraph generation.
- Implemented new custom backend (called qsim) that handles the event-based
simulation procedure much faster than simpy. Changed contact and packet
generators to use the new backend.
- Added rich comparison methods for packet object (based on packet identifier).
- Contact Utilization Analysis. The average value for all contacts is provided
in the standard post-simulation summary and the function
`get_utilization_list` returns a list of the utilizations per individual
contact.

Changed
- Switched to python 3.7.0 to make use of the integrated dataclasses ("mutable
namedtuple"). Updated docker image in CI.
- Removed redundant code in SCGR.
- Refactoring of the Dijkstra implementation to improve the performance.
Previously, many variables for the search were initialized for all nodes. By
rewriting Dijkstra, this could be mitigated. Instead, the variables are
considered to be in a certain stage if they are not initialized. They are
instead create on-demand if needed.
- Switched visited data structure in Dijkstra from list to set, which hashes
the values and thus yields in better performance.
- Changed removal of past contacts from contact graph to on-demand. Instead of
iterating over the entire graph all the time, the approaches are now
removing the old contact only if they encounter them again in the neighbor function. Improves performance by getting rid of another iteration over all
elements of the graph.
- Removed profiling script from CI. It takes way too long on the CI runner
while having only very limited CI testing significance.
- Changed time steps/unit to milliseconds and removed round() where possible.
Also switched to int instead of float wherever possible to improve
performance. With the new approach, round is only used in places where the
performance impact is not that severe, but e.g. in is_capacity_sufficient()
which is called very often, an approximation is used that slightly
deteriorates the overall routing efficiency (because it underestimates the
remaining capacity of contacts due to it's conservative estimation). After a
routing decision has been made, the precise time is calculated using round().
- Reduced computational complexity of the ContactGraph generation procedure.
Moved edge generation into a separate internal static function.
- Changed CI scripts to new ms time unit.
- Adapted documentation to new ms time unit and int type.

Fixed
- Fixed static selection of SCGR as profiling algorithm in profiler script.
- Fixed bug where due to missing parentheses the datarate during the contact
graph generation was computed incorrectly (much higher).
- Fixed division-by-zero bug in profiler script.