I have a device which connects via serial port. I communicate with it via Windows Hyper Terminal. I'm just wondering, what protocol does it use? As you probably, know hyper terminal can display and accept input as well. It's a two way communication.
Thank you for any help.
HyperTerminal uses the following communication protocols according to TechNet:
Transmission protocol and port: The protocols used are Kermit, Xmodem, Xmodem-1K, Ymodem, Ymodem-G and Zmodem transmissions protocols on port 23
There is actually no protocol. Serial sends and recieve bits. You specify them in your serial setting when you want to communicate with a device. Typically 8 bits are specified which is equivalent to an ASCII character. Both communicating parties send and receive ASCII data any time they want
Related
This is a more constrained version of this question:
I have an embedded ARM device running a custom image with a Linux 3.10.0 kernel.
The only physical interface (no, USB, no Ethernet) is the default Linux shell which is connected one of the serial interfaces.
My question is: Is there any built-in or external tool that opens an IP tunnel over this connection?
I see some general issues:
The device is already use by Linux, so it must use stdin/out to communicate instead of accessing the device directly.
After starting the tunneling application, the application must wait for a tunnel client to connect because I need to close the serial connection on my computer and then start the tunnel client.
There should be a way to close the connection and go back to the normal shell
The actual requirement is, that I can access a REST interface that is running on the embedded device from a computer connected to the embedded device via serial cable.
This already works on devices with a physical Ethernet or Ethernet-over-USB but this device does not offer that.
[UPDATE]
As explained, socat is currently not available on our embedded device so as a first attempt, I used the following:
A Linux (Ubuntu) laptop with a physical serial interface
A Windows Laptop with a physical serial interface and cygwin+socat installed
Both connected via Null-modem cable
Note: I'm using a Windows laptop on one side because we will have the socat client running on Linux (unfortunately).
Direct STDIO Connection
Server
socat stdio file:/dev/ttyS0,b115200
Client
socat file:/dev/ttyS4,b115200 stdio
In cygwin, ttyS0 is COM1, ttyS4 in this case is COM5.
Using these, socat works like a little chat program. Why I type on one side is output on the other and vice-versa.
TCP Connection
The next step is to use a TCP connection.
Server
socat /dev/ttyS0,b115200,crtscts=1,raw,echo=0 tcp-connect:localhost:80
Client
socat -T2 file:/dev/ttyS4,b115200,crtscts=1,raw,echo=0 tcp-l:7777,reuseaddr
I specified the baud rate (115200), used raw transmission, no echo (The HTTP request would otherwise be sent back to the requester) using hardware flow control. Pus I had to use a timeout -T2 wich terminates the connection after 2s. Otherwise, curl does not terminate either and waits for more data.
When I use curl on the windows computer, it successfully transmits the request over serial connection and returns the complete HTTP response of the HTTP server on the Linux computer:
curl localhost:7777/index.html
However, it works only once. After the request is completed, both socatclient and server terminates.
Moreover, when I use a browser (Chorme), it uses g-zip encoding which most probably sends binary characters. And one of these characters will be a EOF character which again terminates socat before completing the request/response.
Then I tried to add fork to the server:
socat /dev/ttyS0,b115200,crtscts=1,raw,echo=0 tcp-connect:localhost:80,fork
This keeps the server alive, but curl returns a 400 Bad Request. So it seems as if the socat server initiated a request for each line or chunk since it does not understand HTTP.
IP Connection
Then I thought about going a layer below and using a TUN connection. However, this is not implemented on the Windows version of socat.
HTTP connection
Correct me if I'm wrong, but as far as I understand, socatdoes not provide a connection type that actually understands HTTP and is able to serialize it properly over a serial connection.
So, I couldn't find any stable way to start both client and server and run multiple HTTP requests over the serial connection.
On a normal linux, you could use socat.
This program allows you to connect several stream types (file, socket, tcp, udp, ...). In your case it would be tcp to file or more precisely a tcp socket at port xx to /dev/ttyUSB1. You should launch socat on both sides to build a tunnel.
Edit 1:
Sorry I got also disappointed by socat. I can't find a solution that keeps my TCP listener active for multiple successive connections, but handles only one connection at a time.
My solution is a simple C# program that uses 4 threads:
1. wait for input on stdin e.g. exit command
2. the TCP listener
3. the TCP worker thread for a active connection
4. if TCP is open, it opens another thread for COM
Thread 3 reads from TCP and writes to COM and Tread 4 reads from COM and writes to TCP. If thread gets a TCP close event, it stops thread 4, which closes COMx, and exits it self. Now thread 2 can accept a new connection. If thread 1 reads exit on stdin, it passes a message to all threads to stop and shutdown.
Maybe you can implement such a short program in C with pthreads on your embedded system, which has no socat.
The EOF problem:
I tried to google for a program that escapes a special character or reencodes a data stream from ASCII to ANSI or base64 or whatever.... If you can find such a program or write it also in C you can pipe it in between
Server <=> reencode <=> socat <--serial--> socat <=> reencode <=> client
We've now solved the problem halfway using pppd. As it turns out, even Windows supports ppp. In contrast to socat, pppd actually uses a protocol that will have error detection included and it automatically creates network devices on the Linux and Windows system.
The only problem is, that pppd requires to have access to the serial device. There is no direct mode like the ppp tool provides.
We are now disabling the shell on demand, rebooting into IP-over-serial mode. When we are done, we reboot the system which automatically switch back to getty using the serial line.
The is not the prettiest solution but right now, it seems to work.
Can anyone tell me which Communication Protocol is used by hyperterminal connecting via Tcp/Ip ?
Protocol here means UDP, Socket/Server, other(If any).
Actually, I need to design an application (in QT, Linux as OS) to communicate to a machine (basically a printer) via Ethernet. I need to send request to the printer as well as receive response, if any, from the printer.
It can be communicated via Hyperterminal using Tcp/IP.
So I wonder which protocol should i use for the communication. As Printer simply supports ethernet therefore I have no idea, if I can use Socket/Server for communication.
Need suggestion over this. All idea/suggestion are welcome.
Thanks in Advance
You need to get your terminology right. TCP/IP and UDP are transport layers. A protocol refers to the application data that is transmitted over a transport. A socket is a programming API that allows an application to gain access to a transport so it can send/receive protocol data.
Now, to answer your question - HyperTerminal typically uses the Telnet protocol over TCP/IP. Many protocols in existence are text-based, and Telnet is largely compatible with simple ASCII text, which makes it convenient for allowing users to use Telnet UI clients, like HyperTerminal, to manually send text commands to network-connected devices. However, most devices/protocols do not use the actual Telnet protocol. But if you can communicate with a device using HyperTerminal, you can code your app to send/receive the same text commands.
I have an interesting problem. I am working on an embedded box with multiple instances of Linux running each on an ARM processor. They are connected over internal 1GBps network. I have a serial port device node attached to processor A (Lets say Linux-A running on it). I have a program running on processor B (Lets say on Linux-B) access the serial port device as if it is attached to Linux-B locally.
My program invokes term i/o type api calls on device node to control tty echo, character mode input. What I am wondering is if there is a way to create a virtual serial device that is available on Linux-B somehow talking to real serial device on Linux-A over internal network.
I am thinking something along the lines of:
Linux-B has /dev/ttyvirtual. Anything that gets written to it gets transported over network socket to Linux-A serialserver. The serial server exrcises the api calls on real device lets say /dev/ttys0.
Any data waiting on ttys0 gets transported back to /dev/ttyvirtual.
What are all the things involved to get this done fast?
Thanks
Videoguy
Update:
I found a discussion at
http://fixunix.com/bsd/261068-network-socket-serial-port-question.html with great pointers.
Another useful link is http://blog.philippklaus.de/2011/08/make-rs232-serial-devices-accessible-via-ethernet/
Take a look at openpty(3). This lets you create a pseudo-TTY (like /dev/pts/0, the sort that ssh connections use), which will respond as a normal TTY would, but give you direct programmatic control over the connections.
This way you can host a serial device (eg. /dev/pts/5) that you forward data between a network connection, and then other apps can perform serial operations on it without knowing about the underlying network bridge.
I ended up using socat
Examples can be found here: socat examples
You socat back to back on both the machines. One listens on a tcp port and forwards data to local virtual port or pty. The socat on other box uses real device as input and forwards any data to tcp port.
Assuming that you have determined that for a given niche case, neither TCP or UDP are ideal, how would you go about writing your own IP based protocol?
For example, if you're developing on Linux, where would you look in the kernel to "hook" your protocol in?
Where would you start?
You can do this through a kernel module. I would start by reading how arp works for example. That is a simpler protocol since userspace doesn't send packets out with it directly.
The entry point for creating a new network protocol is dev_add_pack, and the code for arp can be found here.
If your protocol can be implemented directly on top of IP, then it can also be implemented wrapped in UDP packets - and the latter has the advantage that it'll pass through existing NAT devices and firewalls that would simply drop your custom protocol.
Read up on UNIX sockets and networking. It's not so much 'hooking' into the kernel, as it is opening a socket and sending your binary data over that.
I have a black-box device with a modem attached (which I can send commands to), and would like to be able to connect to send data to a server from it. What connectivity options do I have, is PPP the protocol I need to use or is there a better option?
ppp is certainly the most common solution for getting an IP connection over a modem. There are other solutions, but there's no reason not to use PPP if what you need is an IP connection.
If you don't need an IP connection and you're writing both the client and the server, you could also do a straight serial connection from one modem to another, but that's kind of old-school.
PPP is probably your best option, if you also want an IP gateway and routing. If you only need terminal access to the device, and it runs some form of *nix, you probably have getty+serial communication as an option. You can use any number of modem terminal clients on the other side.