IPv4 Stack, Web Server, WebSocket Server, UDP Server.

Dependencies:   mbed

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

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

/media/uploads/nixnax/blinky-connected.gif
A Windows desktop showing PPP-Blinky in the network connections list.

Describe PPP-Blinky in Three Sentences

PPP-Blinky enables Internet protocols 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

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

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.

/media/uploads/nixnax/tcp-data-3.gif

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.

Changes

RevisionDateWhoCommit message
264:71c191a24d30 5 weeks ago nixnax Stream vs RawSerial comment default tip
263:83a6d767c349 2 months ago nixnax Toggle LED for every received frame
262:c044fed611aa 3 months ago nixnax Change ping counter to ppp packet counter
261:272ec8e2a7d4 3 months ago nixnax Make mbed-code field in websocket response optional.
260:2c9a01c9d03e 4 months ago nixnax Don't count empty PPP frames.
259:f694046fc06f 4 months ago nixnax Simplified TCP responder.
258:1eb9abd66922 5 months ago nixnax small changes to PPP handler
257:1990a41a1e31 7 months ago nixnax Fixed comments, new jsfiddle URL
256:16543c8dd55c 8 months ago nixnax License update
255:14e83e1e2b40 9 months ago nixnax new mbed library revision 172
254:7345c9a6f4c2 9 months ago nixnax Display SystemCoreClock on main HTTP page
253:ee1044976b2c 10 months ago nixnax PPP frames were double-counted.
252:b3c8c5699153 11 months ago nixnax Count all PPP frames in ping count.
251:ae27cf9ec58d 11 months ago nixnax Added LCP packets to ping counter
250:35a3a19dc184 11 months ago nixnax Remove Connection: Close from http header
249:9ff0e20325f7 11 months ago nixnax More favicon work
248:5aca1c98fc24 11 months ago nixnax Use Data URI for fake favicon image
247:7b0a8e6fbb86 11 months ago nixnax Restore the escaping of characters >127
246:68a38a3bfdbe 12 months ago nixnax Revert the escaping (using 0x7d) of characters >127
245:544cea761769 12 months ago nixnax HTML comment example
244:f062ca9b6e06 12 months ago nixnax Increase RXBUFLEN to 4000
243:24f899297799 12 months ago nixnax Trap buffer full event with LED flashing
242:1e9215c09da5 12 months ago nixnax Escape characters > 0x7f
241:dece92cb7296 12 months ago nixnax Display ICMP ping count in webpage using strstr()
240:d7a01533397d 12 months ago nixnax Show number of pings in webpage.
239:426e50519204 12 months ago nixnax Added a counter for ICMP pings
238:f39289ed5a2e 12 months ago nixnax Remove unneeded define
237:796851817c26 12 months ago nixnax Toggle LED1 for each HTTP GET
236:b931c4909ee1 12 months ago nixnax new mbed library revision 171
235:43004d18b130 12 months ago nixnax mbed version 171 has issues, reverting
234:c581abc0feeb 12 months ago nixnax New mbed library rev 171
233:1b590d78ec9c 13 months ago nixnax restoring RXBUFLEN to 1500
232:db31d91f71d2 13 months ago nixnax Reduce rxbuflen to 500
231:6bd4523833a2 13 months ago nixnax Remove more debugPrintf
230:ee097c486e45 13 months ago nixnax Change debugPrintf to debugPuts where possible
229:a81c37376187 14 months ago nixnax Consistency in server header
228:7fb878500862 14 months ago nixnax removed LCPConfigurationRequest()
227:f87156f9ef11 14 months ago nixnax consolidate LCP handler
226:4898247048c7 15 months ago nixnax Removed delay in sendPPPbuf; Edits in webpages
225:4c9994e3becb 15 months ago nixnax mbed library revision 170 and updated jsfiddle revision 112
224:28a12be8d52d 15 months ago nixnax Updated jsfiddle
223:917b554cb8a5 15 months ago nixnax make ppp.rx.buf volatile
222:0ec93b1ff979 15 months ago nixnax Updated jsfiddle version
221:1d7c32d8256b 15 months ago nixnax Removed putcwhilechecking and putswhilechecking.; Added ppp.xx.bufferfull
220:54f45f924707 15 months ago nixnax Unrolled the CRC calculation.
219:cbf6a235d1f2 16 months ago nixnax New jsfiddle for WebSocket demo
218:651241ad5928 16 months ago nixnax Reduce RXBUFLEN to 1800
217:86498f9ab967 16 months ago nixnax Enable MAXBUFLEVEL in the TCP/IP headers for testing
216:e3c5a5b47295 16 months ago nixnax RXBUFLEN can now be any value
215:a489170c3c57 17 months ago nixnax New mbed library Revision 169
214:4d832a4877ed 18 months ago nixnax Change SHOWMAXBUFLEVEL_YES to SHOWMAXBUFLEVEL_NO
213:8555b6a3355a 18 months ago nixnax Removed printf in receive interrupt handler
212:a9646f0a8c46 18 months ago nixnax receive buffer size back to 2048
211:a40c58b34560 18 months ago nixnax Reduced serial receive buffer to 1024 bytes (from 2048)
210:a2a651249a9a 18 months ago nixnax Fixed 404 not found error for web page /w
209:aa514cd631ee 18 months ago nixnax Removed checkPC() and other small changes.
208:73086736610a 18 months ago nixnax Back to this copy
207:28cd834b785d 18 months ago nixnax Test comment
206:7537ce2620c1 18 months ago nixnax Test comment
205:c730866cb598 18 months ago nixnax Removed checkPC(); Other small changes, comments.