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# S3_CAP, a modular framework for slotted transmission

This tutorial shows how to use the [S3_CAP framework](https://github.com/AmauryPARIS/gr-ephyl) inside the FIT/CorteXlab testbed and implement a access policy. The framework allows you to change the used PHY layer, as described [here](https://github.com/AmauryPARIS/gr-ephyl#phy-layer), but the tutorial will only show you how to implement the access policy.

First you need to retrieve this [docker image](https://hub.docker.com/repository/docker/amauryparis/s3cap):

you@yourpc:~$ docker pull amauryparis/s3cap:latest
you@yourpc:~$ docker run -dti --net=host --expose 2222 --privileged amauryparis/s3cap:latest

Access the docker container using ssh :

you@yourpc:~$ ssh -Xp 2222 root@localhost

In this environment, you have access to the S3CAP project with a LoRa PHY layer. By default, a dummy and random access policy is implemented in files `upper/sn_upper.py` and `upper/bs_upper.py`. You can change the two files as follow, to update the access policies of our system and make every node transmitting on a predefined slot. We will also update the content of control messages.

New `upper/sn_upper.py` :

while True:
    feedback_pmt = up.recv()
    feedback = up.extract(feedback_pmt)

    up.log(feedback["NODE"], "SN - Feedback received - source sensor : %s | frame : %s | dlcch : %s" % (feedback["NODE"], feedback["FRAME"], feedback["DLCCH"]))
    print("SN - Feedback received - source sensor : %s | frame : %s | dlcch : %s" % (feedback["NODE"], feedback["FRAME"], feedback["DLCCH"]))

    action = "True"
    frame = feedback["FRAME"] + 1
    
    if feedback["NODE"] == "A":
        sequence = [[0, "Y"], [1, False], [1, False], [1, False]]
        ulcch = str("poulet_basquaise")
    else:
        sequence = [[0, False], [1, "X"], [1, False], [1, False]]
        ulcch = str("boeuf_bourguignon")

    inst = up.create_SN_inst(feedback["NODE"], frame, action, sequence, ulcch)
    up.send(inst)
    
    up.log(frame, "Instruction send - %s" % (inst))
    print("SN - Instruction send - %s" % (inst))

New `upper/bs_upper.py`:

while True:
    feedback_pmt = up.recv()
    feedback = up.extract(feedback_pmt)

    up.log(feedback["FRAME"], "Feedback received - frame : %s | ulcch : %s | rx : %s" % (feedback["FRAME"], feedback["ULCCH"], feedback["RX"]))
    print("Feedback received - frame : %s | ulcch : %s | rx : %s" % (feedback["FRAME"], feedback["ULCCH"], feedback["RX"]))

    list_dlcch = []
    frame = feedback["FRAME"] + 1

    for sensor in up.list_sensors:
        dlcch = str("tarte_aux_pommes")
        list_dlcch.append([sensor, dlcch])
    
    inst = up.create_BS_inst(list_dlcch, frame)
    up.send(inst)

    up.log(frame, "Instruction send - %s" % (inst))
    print("Instruction send - %s" % (inst))

You can also set the number of slot on the uplink channel, with the `slot_count` parameter in the sensor and base station upper files, and with the `–S` option inside the GNU Radio flowgraph.

You can now exit the docker container, to commit and push the updated version on your account.

you@yourpc:~$ docker ps -a 
you@yourpc:~$ docker commit [CONTAINER ID] [NEW IMAGE NAME] 
you@yourpc:~$ docker tag [NEW IMAGE NAME] [DOCKER USERNAME]/[NEW IMAGE NAME] 
you@yourpc:~$ docker login 
you@yourpc:~$ docker push [DOCKER USERNAME]/[NEW IMAGE NAME] 

After booking the testbed with OAR, you can upload the image on three nodes of your choice with an SSH access, as follow :

  nodeX:
    container:
    - image: [DOCKER USERNAME]/[NEW IMAGE NAME]:latest
      command: /usr/sbin/sshd -p 2222 -D

Once connected to each of the three nodes, you can run the following commands. It will start the access policy and then the PHY layer of each node.

On `NODE_X` - the first sensor

python2 /root/cxlb_toolchain_build/gr-ephyl/upper/sn_upper.py --slot_count=4 &
python2 /root/cxlb_toolchain_build/gr-ephyl/examples/LoRa/sn_multislot_dyn_ephyl_lora.py --sn-id=A --ip-bs-addr=NODE_Z --S=4

On `NODE_Y` - the second sensor

python2 /root/cxlb_toolchain_build/gr-ephyl/upper/sn_upper.py --slot_count=4 &
python2 /root/cxlb_toolchain_build/gr-ephyl/examples/LoRa/sn_multislot_dyn_ephyl_lora.py --sn-id=B --ip-bs-addr=NODE_Z --S=4

On `NODE_Z` - the base station

python2 /root/cxlb_toolchain_build/gr-ephyl/upper/bs_upper.py --slot_count=4 &
python2 /root/cxlb_toolchain_build/gr-ephyl/examples/LoRa/bs_multisn_multislot_dyn_ephyl_lora.py --sn-1-ip-addr=NODE_X --sn-2-ip-addr=NODE_Y --S=4

You will then observe the newly updated access policy.