added dependencies section for PTF NN agent, and updated diagram

ptf_nn/README.md

@@ -8,11 +8,33 @@ the host running PTF).
 
 ---
 
+## Dependencies
+
+We rely on [nanomsg](http://nanomsg.org/) (a messaging library) to forward
+packets between the PTF agent and the PTF test runner. You will therefore need
+to install the following:
+
+  - [nanomsg](https://github.com/nanomsg/nanomsg/releases): we recommend
+    installing the `1.0.0` production release.
+  - [nnpy](https://github.com/nanomsg/nnpy): these are the Python bindings for
+    nanomsg. You may use the provided [install_nnpy.sh](install_nnpy.sh) script
+    to install nnpy. It will install a version of nnpy that we have tested.
+
+We provide a [check_deps.py](check_deps.py) script that you can run to check
+that nanomsg and nnpy are running properly.
+
 ## Overview
 
 ![PTF nanomsg overview](resources/ptf_nn.png)
 
----
+In the above setup, we are able to capture and send packets on two different
+machines (the PTF host and a remote host). Each agent acts as an intermediary
+between a set of interfaces (connected to the switch) and the PTF
+tester. Packets received on an interface (from the switch) will be tagged with
+the port number and forwarded to the PTF tester. Packets received from the PTF
+tester will be forwarded to the switch using the appropriate
+interface. Communications between the PTF tester and each agent is done over TCP
+using the nanomsg messaging library.
 
 ## Demo
 

ptf_nn/check_deps.py

@@ -0,0 +1,17 @@
+#!/usr/bin/env python
+
+import nnpy
+import sys
+
+pub = nnpy.Socket(nnpy.AF_SP, nnpy.PUB)
+pub.bind('inproc://foo')
+
+sub = nnpy.Socket(nnpy.AF_SP, nnpy.SUB)
+sub.connect('inproc://foo')
+sub.setsockopt(nnpy.SUB, nnpy.SUB_SUBSCRIBE, '')
+
+pub.send('hello, world')
+recv = sub.recv()
+
+if recv != 'hello, world':
+    sys.exit(1)

ptf_nn/install_nnpy.sh

@@ -0,0 +1,9 @@
+#!/bin/sh
+set -e
+git clone https://github.com/nanomsg/nnpy.git
+# top of tree won't install
+cd nnpy
+git checkout c7e718a5173447c85182dc45f99e2abcf9cd4065
+sudo pip install cffi
+sudo pip install .
+cd ..