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.

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:



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:


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.


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


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:


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 ( 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, ( 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 or, if your PPP-Blinky is running, simply click on this link:


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!


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 (the Dial-Up Adapter IP) requests a TCP connection by sending an S (SYN) flag.
Frame 3 - PPP-Blinky at IP 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.


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.


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 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.



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
201:9fcf92e9f427 18 months ago Moved comment. File  Diff  Annotate
199:074061f85f1a 19 months ago typo File  Diff  Annotate
198:e604d26281ab 19 months ago Nucleo-L432KC target now working after target board firmware upgrade using latest http://www.st.com/en/development-tools/stsw-link007.html File  Diff  Annotate
189:9fc4ae041974 21 months ago Latest mbed library - Revision 152. File  Diff  Annotate
187:e2cea223dd85 21 months ago Test comment. File  Diff  Annotate
179:ba2b2ddd0da5 22 months ago Changed BufferedSerial to RawSerial. File  Diff  Annotate
177:dab9e685af53 22 months ago sendUdpData() changes. File  Diff  Annotate
174:e5a3f16421a5 22 months ago sendUdpData() File  Diff  Annotate
153:7993def8663f 22 months ago Merge, small changes, comments. File  Diff  Annotate
150:3366bf3d294e 22 months ago changed connected() to connectedPPP() File  Diff  Annotate
147:0f40005cbc5f 22 months ago Added swapIpAddresses() File  Diff  Annotate
144:01d98cf7738e 22 months ago If UDP message starts with "echo" send it back. File  Diff  Annotate
142:54d1543e23e5 23 months ago Documentation, restructure, comments. File  Diff  Annotate
141:4cc1518ee06f 23 months ago Comments, removed Dial-up Error 777 reference. File  Diff  Annotate
140:f526e9ecfebb 23 months ago Toggle LED only every second PPP packet. File  Diff  Annotate
139:1f87c6bc8db3 23 months ago Moved text-align in root web page to center everything. File  Diff  Annotate
137:eda0cfcf4d3c 23 months ago Changed TCP sending delay from 70 to 45 ms. File  Diff  Annotate
136:28a838086979 23 months ago Link to JSFiddle demo. File  Diff  Annotate
135:6c3eec2fa634 23 months ago Added menu to root page File  Diff  Annotate
134:af9d1f8d451d 23 months ago serial port monitor = no. File  Diff  Annotate
133:0f5b4085b6d3 23 months ago Fixed length of root web page (sizeof -1).; Added 1-character delay in send_pppframe.; Added websocket demo page /ws.; Added benchmark demo page /xb.; File  Diff  Annotate
132:09b66cc5cf4a 23 months ago Reduced buffer size so NUCLEO-L053R8 (8k RAM) can work too. File  Diff  Annotate
131:134b6d0c11e9 23 months ago Graceful WebSocket close. File  Diff  Annotate
130:45ee0d648a72 23 months ago Imported Sam Grove's BufferedSerial library. Eliminated all FCS errors due to dropped characters. File  Diff  Annotate
129:b8a0b0e8cff1 23 months ago Fixed debug print. Added a space to number in GET /x so there is number separation when using curl. File  Diff  Annotate
128:e5958d143e9d 23 months ago Added WebSocket Service.; TCP-header checksum bug on odd lfixed.; Comments.; File  Diff  Annotate
127:3ea6f776e287 23 months ago FRDM-KL46Z board added & tested. File  Diff  Annotate
126:4e1058fa2128 23 months ago Rxbuflen back to 1<<11 File  Diff  Annotate
125:ea88200b1df6 23 months ago Enable ICMP reporting. File  Diff  Annotate
124:18ef53f1d8b7 23 months ago Added input checking to more functions. File  Diff  Annotate
123:fc64fc6caae0 23 months ago Comment fix File  Diff  Annotate
122:963abcbff21e 23 months ago Renamed to PPP_max_size File  Diff  Annotate
121:705679672685 23 months ago Reduced TCP_MAX_SIZE to get Nucleo-L053R8 board working. File  Diff  Annotate
120:bef89e4c906e 23 months ago Fixed dropping characters when dumping debug data on second serial port File  Diff  Annotate
119:e14dd2bf0ea3 23 months ago Fix dropping of input characters, first packet error. File  Diff  Annotate
118:54d1936e3768 23 months ago More compact debug dump format, check for input characters while dumping headers, removed 20ms wait before sending, added PUSH flag to outgoing TCP data. File  Diff  Annotate
117:c819ae068336 23 months ago Shortened IP debug dump. TCP send delay 20ms. File  Diff  Annotate
116:1272e9f7ad70 23 months ago Add FIN flag to FIN ACK response. File  Diff  Annotate
115:b8ddff0e782f 23 months ago Removed spaces in HTTP response File  Diff  Annotate
114:8a5d70bbc1b2 23 months ago Latest mbed library; Added 10ms delay before sending; Changed IP & TCP header dump format File  Diff  Annotate
113:d9666fe4d0ed 23 months ago TCP flags display order same as MS Network Monitor File  Diff  Annotate
112:30172f36bd33 23 months ago Removed unneeded led toggles. File  Diff  Annotate
111:6a3b77c065c0 23 months ago Comments File  Diff  Annotate
110:baec959e1915 23 months ago Added/tested LPC11U24 and 3 Nucleo Boards. File  Diff  Annotate
109:644a59ebb5b1 23 months ago Remove fillbuf() from sendFrame() File  Diff  Annotate
108:f77ec4605945 23 months ago Added link to Windows Dial-up Configuration. File  Diff  Annotate
107:5fe806713d49 23 months ago Replace memchr scan for 0x7E with a per-character check. File  Diff  Annotate
106:d14e6b597ca3 23 months ago Shortened Connect string. IPCP uses suggested IP. Removed framefound. File  Diff  Annotate
105:45001195b325 23 months ago Reduced requirements (without stack) to 6.3kB File  Diff  Annotate
104:b1280b084f75 23 months ago Reduced receive buffer size File  Diff  Annotate
103:4f5512dd11cf 23 months ago Improved IPCP response. File  Diff  Annotate
102:a89c55672170 23 months ago Removed 1 line File  Diff  Annotate
101:0a15de2ca623 23 months ago Removed unused lines File  Diff  Annotate
100:3f3a017684c5 24 months ago Remove unused ppp.seq File  Diff  Annotate
99:3f56162e703e 24 months ago Shorten HTTP check to GET /x for fast benchmarking. File  Diff  Annotate
98:3babad0d1bd4 24 months ago TCP response handler.; TCP flag handling improved.; HTTP/1.0 response. File  Diff  Annotate
97:bdf885e146dc 24 months ago Window Size 700 File  Diff  Annotate
96:e14f42ecff66 24 months ago TCP Window size of 3*256 File  Diff  Annotate
95:40af49390daf 24 months ago Don't report FCS errors - they are common. File  Diff  Annotate
94:8ee3eec2a2bb 24 months ago Debug serial port off; Display frame count for /x File  Diff  Annotate