Adding figures to ECN and MRI exercises (#84)

* adding a figure of the network setup to ecn

* adding a figure of the network setup for MRI

P4D2_2017_Fall/exercises/ecn/README.md

@@ -41,12 +41,15 @@ network in Mininet to test its behavior.
      (`10.0.<Switchid>.<hostID>`).
    * The control plane programs the P4 tables in each switch based on
      `sx-commands.txt`
+
 2. We want to send a low rate traffic from `h1` to `h2` and a high
 rate iperf traffic from `h11` to `h22`.  The link between `s1` and
 `s2` is common between the flows and is a bottleneck because we
 reduced its bandwidth to 512kbps in topology.json.  Therefore, if we
 capture packets at `h2`, we should see the right ECN value.
 
+![Setup](setup.png)
+
 3. You should now see a Mininet command prompt. Open four terminals
 for `h1`, `h11`, `h2`, `h22`, respectively:
    ```bash

P4D2_2017_Fall/exercises/mri/README.md

@@ -50,6 +50,8 @@ switch in Mininet to test its behavior.
    capture packets at `h2`, we should see high queue size for that
    link.
 
+![Setup](setup.png)
+
 3. You should now see a Mininet command prompt. Open four terminals
    for `h1`, `h11`, `h2`, `h22`, respectively:
    ```bash