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.

/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 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

/media/uploads/nixnax/modem.jpg

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.

Revisions of main.cpp

Revision Date Message Actions
87:9f5ac1fabd95 2017-07-21 Changed TCP flag handling.; All TCP headers to 20 bytes. File  Diff  Annotate
85:53e57ff1cf05 2017-07-20 Removed receive interrupt handler & replaced with fillbuf(); Modified TCP flag handling File  Diff  Annotate
84:456e73151f11 2017-07-18 html changes File  Diff  Annotate
83:cdcb81d1910f 2017-07-18 Increment TCP ident; Code consolidation; File  Diff  Annotate
82:051f77f7dd72 2017-07-16 Ignore all TCP options File  Diff  Annotate
81:9ede60e9a2c8 2017-07-15 wait_for_HDLC logic change; only scan for connect string when offline File  Diff  Annotate
80:753f5dd2e84e 2017-07-12 Improved tcp seq number usage File  Diff  Annotate
79:f0fc1c19a550 2017-07-09 TCP seq handling change File  Diff  Annotate
78:809c2631a5eb 2017-07-09 Bettter managing of TCP ack and seq File  Diff  Annotate
77:abf92baebb42 2017-07-08 New mbed library; Compile errors when serial debug is on; Seq and Ack number handling File  Diff  Annotate
76:00e208cceb8b 2017-07-05 TCP checksum bug fix File  Diff  Annotate
75:0d513869231f 2017-07-04 PPP packet handler updated; CRC to unsigned int File  Diff  Annotate
74:7409fbeabb2e 2017-06-28 Added HTTP header - Connection: close File  Diff  Annotate
73:2f56ec87dbe9 2017-06-26 Fixed destination IP debug print.; Latest mbed library. File  Diff  Annotate
72:ad3d12753acf 2017-06-17 Moved globals into ppp structure; Latest mbed lib; Comments File  Diff  Annotate
71:965619fedb3a 2017-06-08 Debug/Comments File  Diff  Annotate
70:713f86229288 2017-06-07 flagInfo File  Diff  Annotate
69:23f560087c16 2017-06-07 Simpler TCP Flags; Remove 200ms wait; TCP length multiple of four File  Diff  Annotate
68:0b74763ae67f 2017-06-05 Removed 200ms delay for faster response; Calculation of Content-Length File  Diff  Annotate
67:a63e3486bcda 2017-06-05 Separated HTTP response; Comments; File  Diff  Annotate
66:f005b9fdf4d1 2017-06-05 Separated HTML; Comments File  Diff  Annotate
65:23b17c43aa0f 2017-06-04 Shorter swap File  Diff  Annotate
64:677b9713a120 2017-06-04 Comments File  Diff  Annotate
63:9253b0e1b7d8 2017-06-04 Remove unneeded file; Light reformatting File  Diff  Annotate
62:f192926e42f1 2017-06-04 Merge, comments, small changes in TCPhandler() File  Diff  Annotate
61:b3c1a04efd0a 2017-06-04 Buffer use in TCPhandler; Latest mbed library File  Diff  Annotate
60:2b770949c911 2017-06-04 Buffer consolidation File  Diff  Annotate
58:8f39f28f9b14 2017-04-24 Latest mbed library V140 File  Diff  Annotate
57:8deab70fef2e 2017-01-31 Remove unneeded rxbufNotEmpty File  Diff  Annotate
56:b5b2e1c09f42 2017-01-29 Moved buffer read into critical section File  Diff  Annotate
55:43faae812be3 2017-01-29 Removed compile warnings with #IFNDEF File  Diff  Annotate
54:13f83621db80 2017-01-29 Merge - small changes File  Diff  Annotate
53:3a8a37fda757 2017-01-29 Removed unneeded test before waitForConnectString File  Diff  Annotate
52:accc3026b2b0 2017-01-29 Removed redundant check before waitForConnectString File  Diff  Annotate
51:a86d56844324 2017-01-29 Successful Test of 1 Million Pings File  Diff  Annotate
50:ad4e7c3c88e5 2017-01-29 Fixed HDLC frameEndIndex wraparound bug; Moved wait_for_HDLC_Frame code to a function File  Diff  Annotate
49:2213f9c132b2 2017-01-24 rxbuf clashing with other libs - renamed to rxbufppp File  Diff  Annotate
48:6352c1411c5f 2017-01-19 SERIAL_PORT_MONITOR_NO so we don't need second serial port File  Diff  Annotate
47:00a5ca075f8f 2017-01-19 Fixed & added notes re HTTP response header size File  Diff  Annotate
46:d73a565eaf7c 2017-01-18 Default to SERIAL_PORT_MONITOR_NO File  Diff  Annotate
45:ed9112b1734c 2017-01-18 font-family added File  Diff  Annotate
44:d0c61ae49ea5 2017-01-18 Automatic Content-Length; Avoid sending Null at the end of sprintf string File  Diff  Annotate
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