Small Internet Protocol Stack using a standard serial port.

Dependencies:   mbed

PPP-Blinky - TCP/IP Networking Over a Serial Port

Note: The source code is at the bottom of this page.

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A Windows desktop showing PPP-Blinky in the network connections list.

Describe PPP-Blinky in Three Sentences

PPP-Blinky is a tiny library that enables Internet protocols (IPv4) to any mbed target hardware by using only a serial port.

The code runs on processors with as little as 8k RAM, for example the Nucleo-L053R8 board.

PPP-Blinky uses the industry-standard PPP (Point-to-Point) Protocol and a tiny "stateless" TCP/IP stack.

No Ethernet Port Required

No ethernet port is required - PPP-Blinky uses a serial port to send IP packets to your PC.

PPP-Blinky emulates a standard dial-up modem and therefore connects to Windows, Linux or Adroid machines.

The code runs on most ARM mbed platforms such as the LPC11U24 shown in the picture below:

/media/uploads/nixnax/blinky-to-laptop1.jpg mbed LPC11u24 acting as a webserver to a Windows laptop.

Webserver

The Webserver and WebSocket functions are ideal for building browser-based GUIs on mbed-enabled hardware.

PPP-Blinky's HTTP webserver works with most web clients such as Internet Explorer, Mozilla Firefox, Google Chrome, Safari, Curl, wget and Lynx as well as Microsoft Powershell Invoke-Webrequest command.

In the image below Firefox web browser displays the main web page embedded into PPP-Blinky's code:

/media/uploads/nixnax/ppp-blinky-firefox.jpg Firefox web browser displays a web page embedded into PPP-Blinky's code

WebSocket Service

WebSocket is the most popular protocol standard for real-time bidirectional TCP/IP communication between clients and servers.
In the image below a small Internet Explorer script has connected to PPP-Blinky's WebSocket Service.
A websocket message was then sent by the browser and was echoed back by the WebSocket, triggering the onmessage event in the script.
The WebSocket service enables bidirectional real-time interaction between PPP-Blinky and any element in the browser DOM via JavaScript.
If you already have PPP-Blinky up and running you can test your WebSocket service using this: http://jsfiddle.net/d26cyuh2/112/embedded/result
Websockets are ideal for building browser-based GUIs for mbed hardware.

/media/uploads/nixnax/ppp-blinky-websocke-2.gif

Trying PPP-Blinky on your mbed board

You will need an mbed-enabled hardware board: https://developer.mbed.org/platforms/

Establish a serial port connection between your host PC and your mbed board. The easiest way is to use mbed hardware with a USB serial debug port. I've tried the ST-Micro Nucleo-L476RG, Nucleo-L152RE, Nucleo-F401RE, Nucleo-L432KC, Nucleo-L053R8, mbed-LPC11U24 and mbed-LPC1768 boards and they all work out of the box. Use the mbed online compiler to compile the software for your target board. Save the compiled binary to your hardware.

Before establishing a network connection, you can verify the operation of the code by opening a terminal program such as Tera Term, and setting the baud rate of the COM port on your mbed board to 115200 baud. LED1 should toggle for every two 0x7E (~) (i.e. tilde) characters you type, as 0x7E is the PPP frame start/end marker. Don't forget to close the port when your'e done testing, or else Windows Dial-up Networking will report that the COM port is in use by another program when you try to connect.

Once you are certain that the serial port and firmware is working, proceed to creating a new network connection on your PC -see below.

Creating a Dial-up Connection in Windows

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Setting up Dial-Up Networking (DUN) on your Windows 7 or 8 PC is essentially a two-step process: First, you create a new modem device, because PPP-blinky partially emulates a standard Windows serial port modem device. Second, you create a new Internet connection (in practice, a new network adapter) which is associated with your new "modem".

Step-by-step description of how to configure Windows for PPP-Blinky here:

/users/nixnax/code/PPP-Blinky/wiki/Configuring-Windows-Dial-Up-Networking

There is also a screen on how to set up Linux dial-up networking near the bottom of this page.

Connecting to PPP-Blinky from your PC

Once Windows networking is configured you can establish a dial-up connection to your mbed board over the USB virtual com port.

The IP address you manually assigned to the new dial-up network adapter (172.10.10.1) functions as a gateway to any valid IP address on that subnet. In the screen capture below, I'm sending pings from the Windows 8 command line to my ST-Micro Nucleo-L476RG board over the USB virtual serial Port. I'm also using a second serial port and Tera Term to capture the debug output from a second serial port on the hardware. The optional debug output from the board prints out the IP source and destination address and the first few bytes of the data payload. Note that the source is the adapter IP address, (172.10.10.1 in this case) and the destination is some other address on that subnet - all packets to the subnet are sent to our mbed hardware. For example, you could also ping 172.10.10.123 or, if your PPP-Blinky is running, simply click on this link: http://172.10.10.123

/media/uploads/nixnax/ping-cap-3.gif

One Million Pings!

In the image below the ICMP ("ping") echo reply service was tested by sending one million pings to ppp-Blinky. This took over two hours.
The ping tool used on the Windows 8 PC was psping.exe from PsTools by Mark Russinovich - http://bit.ly/PingFast
The average reply time for a short ping (1 byte of payload data) was 11 milliseconds at 115200 baud on the $10 Nucleo-L053R8 board - barely enough time for 130 bytes to be sent over the port!

/media/uploads/nixnax/ppp-blinky-ping-results.jpg

Monitoring PPP-Blinky Packets

The image below is from a Microsoft Network Monitor 3.4 capture session.

Responses from PPP-Blinky are shown in blue.

Frame 2 - Internet Explorer at IP 172.10.10.1 (the Dial-Up Adapter IP) requests a TCP connection by sending an S (SYN) flag.
Frame 3 - PPP-Blinky at IP 172.10.10.2 responds with an ACK in frame 3. One direction of the link is now established.
Frame 4 - The PC acknowledges the SYN sent by PPP-Blinky in frame 3. The TCP link is now fully established.
Frame 5 - The browser "pushes" (P flag is set) an HTTP GET request to PPP-Blinky.
Frame 6 - PPP-Blinky responds with a standard HTTP response "pushes" (P flag set) back a small web page. It also sets the A (ACK) flag to acknowledge the message sent in frame 6.
Frame 7 - The PC acknowledges reception of the HTTP payload.
Frame 8 - The PC starts to shut down the TCP connection by sending a FIN flag.
Frame 9 - PPP-Blinky acknowledges the FIN request - the connection is now closed in one direction. It also sets a FIN flag in the response to request closure of the opposite direction of the connection.
Frame 10 - The PC acknowledges the FIN request. The closing of the TCP connection is now confirmed in both directions.

/media/uploads/nixnax/ms-network-monitor-http-get-1.gif

Debug Output

PPP-Blinky can output handy debug information to an optional second serial port.
The image below shows the debug output (Ident, Source, Destination, TCP Flags) for a complete HTTP conversation.
The PC messages are displayed in black. PPP-Blinky messages are blue.
Notice how PPP-blinky automatically inserts a blank line after each full HTTP conversation.

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Creating a Dial-Up Connection in Linux

The screen below shows the required pppd command to connect to PPP-Blinky from a Linux machine. This was much simpler than Windows! The USB serial port of the mbed LPC1768 board registered as /dev/ttyACM0 on my Linux box. Do a websearch on pppd if you want to learn more about pppd, the Linux PPP handler. Near the bottom of the screen below, two webpages are fetched (/ and /y) by using the curl command on the command line. Gnome Webkit and Firefox work fine, too. Also try echo GET / HTTP/1.1 | nc 172.10.10.2 which uses netcat, the "Swiss army knife" of networking tools. PPP-Blinky was also tested with ApacheBench, the Apache server benchmark software. After 100000 fetches, the mean page fetch rate was reported as 6 page fetches per second for a small page.

/media/uploads/nixnax/pppd-screen.png

Caveats

PPP Blinky is an extremely sparse implementation (1.5k lines) of HTTP,WebSocket,TCP, UDP, ICMP, IPCP and LCP over PPP, requiring around 8kB of RAM. The minimum functionality required to establish connectivity is implemented. These are often acceptable tradeoffs for embedded projects as well as a handy tool to learn the practical details of everyday networking implementations.

Revisions of main.cpp

Revision Date Message Actions
43:aa57db08995d 2017-01-17 Small Fiddles File  Diff  Annotate
42:4de44be70bfd 2017-01-10 Debug from (()) to () File  Diff  Annotate
41:e58a5a09f411 2017-01-09 HTML errors & changes File  Diff  Annotate
39:b90183d35f1e 2017-01-05 Comments File  Diff  Annotate
38:ab582987926e 2017-01-05 TCP State Machine changes; Comments File  Diff  Annotate
37:2e6689f8b181 2017-01-05 Cosmetic File  Diff  Annotate
36:2a9b457f8276 2017-01-05 Remove teardown File  Diff  Annotate
35:e7068df4d971 2017-01-05 TCP State Handler Fiddle File  Diff  Annotate
34:8a6fbc73a7f1 2017-01-05 Starting to fiddle with SEQ/ACK File  Diff  Annotate
33:b5a86ff03f3d 2017-01-05 Fixed Content-Length File  Diff  Annotate
32:512228c29209 2017-01-05 Send web page with ACK and FIN flags; Added 404 not found response File  Diff  Annotate
31:e000c1b9c565 2017-01-05 Made seq and ack UNSIGNED ints File  Diff  Annotate
30:273431bccb02 2017-01-05 Close Connection after delivering HTTP page File  Diff  Annotate
29:30de79d658f6 2017-01-04 HTTP now servers a good web page; Added verbosity debug options File  Diff  Annotate
28:1aa629be05e7 2017-01-04 HTTP, UDP and PING now working File  Diff  Annotate
27:78d194dd8799 2017-01-03 TCP printing data File  Diff  Annotate
26:11f4eb2663a7 2017-01-03 TCP starting to work - getting packets echoed File  Diff  Annotate
25:0b0450e1b08b 2017-01-02 Removed unneeded print size check File  Diff  Annotate
24:9f3db3bf7f9c 2017-01-02 Removed dumpFrame File  Diff  Annotate
23:af88d429bed1 2017-01-02 Fixed the bug for odd ICMP data block sizes File  Diff  Annotate
22:00df34cd4d7e 2017-01-02 Fiddled with IRQ again File  Diff  Annotate
21:66459cb32ce0 2017-01-02 More serial IRQ tweaks File  Diff  Annotate
20:5db9b77b38a6 2017-01-02 Serial port IRQ critical sections fixed File  Diff  Annotate
19:e53cdee9a33c 2017-01-02 Comments, made buffer larger File  Diff  Annotate
18:3e35de1bc877 2017-01-01 Made Ping more verbose File  Diff  Annotate
17:4918c893d802 2017-01-01 Fixed boundary issue in processFrame; moved interrupt disable in rxHandler File  Diff  Annotate
16:cb0b80c24ba2 2017-01-01 Fixed 7D bug in hdlcPut File  Diff  Annotate
15:b0154c910143 2017-01-01 Toggle LED in processFrame File  Diff  Annotate
14:c65831c25aaa 2017-01-01 removed wait in receive File  Diff  Annotate
13:d882b8a042b4 2017-01-01 Output formatting File  Diff  Annotate
12:db0dc91f0231 2017-01-01 UDP partially prints data; Clearer code File  Diff  Annotate
11:f58998c24f0b 2016-12-31 UDP and ICMP-ping working! File  Diff  Annotate
10:74f8233f72c0 2016-12-31 Can receive UDP packets. File  Diff  Annotate
9:0992486d4a30 2016-12-30 printing first incoming ip packets File  Diff  Annotate
8:48e40f1ff316 2016-12-29 Wow - the link is fully up. The code is a bit spaghetti but it's working for the first time. File  Diff  Annotate
7:ab147f5e97ac 2016-12-29 Fairly close on IP setup - one IPCP Conf Req is troublesome. PC won't Ack it. File  Diff  Annotate
6:fba4c2e817b8 2016-12-29 More IP progress File  Diff  Annotate
5:27624c02189f 2016-12-29 small changes File  Diff  Annotate
4:a469050d5b80 2016-12-29 PPP link is working; Receiving IPCP packet File  Diff  Annotate
3:bcc66de0bdcd 2016-12-27 Remove unneeded flag File  Diff  Annotate
2:b6ccdc962742 2016-12-27 Toggle LED on PPP frame found File  Diff  Annotate
1:9e03798d4367 2016-12-27 Toggle LED1 on PPP frame found File  Diff  Annotate
0:2cf4880c312a 2016-12-27 PPP-Blinky flash LED1 when a Dial-up Connection is made File  Diff  Annotate