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AMX closing IP port? How long to wait on IP connection?
Kari
Posts: 13
I?ve been playing w/wireshark >.< I have my PC, an extron device, and the controller connected to a dumb hub w/static IP addresses on the same subnet.
I?m watching communication w/extron devices. I know typically by default Extron has a 300 second (5minute) timeout on the IP connection.
I sent this command: SEND_STRING data.device,"$1B,'1*65000TC',$0D"
This sets the global extron timeout to 650,000 seconds (each increment = 10 seconds) ? that?s over 7 days.
SO?..
I open a connection on port 23. I send some data. After *60* seconds it looks like AMX is doing something to check the connection every 10 seconds.
111 65.530566 192.168.4.200 192.168.4.60 TCP [TCP Keep-Alive] cap > telnet [ACK] Seq=4 Ack=109 Win=17520 Len=0
124 75.555652 192.168.4.200 192.168.4.60 TCP [TCP Keep-Alive] cap > telnet [ACK] Seq=4 Ack=109 Win=17520 Len=0
137 85.580823 192.168.4.200 192.168.4.60 TCP [TCP Keep-Alive] cap > telnet [ACK] Seq=4 Ack=109 Win=17520 Len=0
150 95.605845 192.168.4.200 192.168.4.60 TCP cap > telnet [RST, ACK] Seq=5 Ack=109 Win=17520 Len=0
Then I get the message in diagnostics:
Exiting TCP read thread ? closing this socket for the local port 11.
cIPEvent::Offline 0:11:1
My connection definitely closes.
I decided to see how long port 23 will stay open if I just telnet into the extron device. I open a telnet session and wait, wait, wait?
It doesn?t seem to close (I?m not going to wait 7 days to verify ? it is definitely longer than 5 minutes).
So it seems like AMX is closing the port. Is this true? Is it new?
Last time I programmed an Extron switcher via IP was 2 years ago and I know it didn?t do this. I was able to hold a connection open for days.
It isn?t necessarily a problem. I wrote code to open a connection every time I need to send something, and queued up all the commands that are waiting for the connection to actually open. I?d rather the port stayed open longer. Maybe that is taboo for networking?
I did notice a nice thing about the IP connection though ? there is something really wants to ensure my strings get sent. If I open a connection, pull the plug, then send commands, there is a retransmission that occurs at 1s, 2s,4s,8s,16s,32s. Finally, something throws in the towel and the connection closes.
As an aside how do other programmers typically handle that little bit of lag between when you TELL the connection to open and it actually opening and the device being ready?
Naturally now that I?m trying this again, I haven?t gotten the errors and everything is behaving. Here is what I noticed though.
When I did this:
Open Client
Wait for client to open
Send String
Sometimes the connection opened, the device said ?hello, I?m here?, wait wait wait wait wait wait, some errors in diagnostics/spam in wireshark, strings sent
I was able to get rid of the errors/spam/waiting by doing this:
Open client
Wait till client open && device says ?hello, I?m here?
Wait a little more
Send String
I?m watching communication w/extron devices. I know typically by default Extron has a 300 second (5minute) timeout on the IP connection.
I sent this command: SEND_STRING data.device,"$1B,'1*65000TC',$0D"
This sets the global extron timeout to 650,000 seconds (each increment = 10 seconds) ? that?s over 7 days.
SO?..
I open a connection on port 23. I send some data. After *60* seconds it looks like AMX is doing something to check the connection every 10 seconds.
111 65.530566 192.168.4.200 192.168.4.60 TCP [TCP Keep-Alive] cap > telnet [ACK] Seq=4 Ack=109 Win=17520 Len=0
124 75.555652 192.168.4.200 192.168.4.60 TCP [TCP Keep-Alive] cap > telnet [ACK] Seq=4 Ack=109 Win=17520 Len=0
137 85.580823 192.168.4.200 192.168.4.60 TCP [TCP Keep-Alive] cap > telnet [ACK] Seq=4 Ack=109 Win=17520 Len=0
150 95.605845 192.168.4.200 192.168.4.60 TCP cap > telnet [RST, ACK] Seq=5 Ack=109 Win=17520 Len=0
Then I get the message in diagnostics:
Exiting TCP read thread ? closing this socket for the local port 11.
cIPEvent::Offline 0:11:1
My connection definitely closes.
I decided to see how long port 23 will stay open if I just telnet into the extron device. I open a telnet session and wait, wait, wait?
It doesn?t seem to close (I?m not going to wait 7 days to verify ? it is definitely longer than 5 minutes).
So it seems like AMX is closing the port. Is this true? Is it new?
Last time I programmed an Extron switcher via IP was 2 years ago and I know it didn?t do this. I was able to hold a connection open for days.
It isn?t necessarily a problem. I wrote code to open a connection every time I need to send something, and queued up all the commands that are waiting for the connection to actually open. I?d rather the port stayed open longer. Maybe that is taboo for networking?
I did notice a nice thing about the IP connection though ? there is something really wants to ensure my strings get sent. If I open a connection, pull the plug, then send commands, there is a retransmission that occurs at 1s, 2s,4s,8s,16s,32s. Finally, something throws in the towel and the connection closes.
As an aside how do other programmers typically handle that little bit of lag between when you TELL the connection to open and it actually opening and the device being ready?
Naturally now that I?m trying this again, I haven?t gotten the errors and everything is behaving. Here is what I noticed though.
When I did this:
Open Client
Wait for client to open
Send String
Sometimes the connection opened, the device said ?hello, I?m here?, wait wait wait wait wait wait, some errors in diagnostics/spam in wireshark, strings sent
I was able to get rid of the errors/spam/waiting by doing this:
Open client
Wait till client open && device says ?hello, I?m here?
Wait a little more
Send String
0
Comments
I don't generally worry about opening and closing TCP connections... just open them and leave them. If you need to worry about it for some reason, put commands in a buffer, then start sending from the buffer once you receive the "connected" response from the device.
I'm thinking jweather might be right, but I am not network savvy...
I can open up almost indefinite telnet sessions from my PC - Extron is not closing port 23.
Yes, with AMX I can hold the port open OR just open it when I need it and send buffered commands (this is what I'm doing)
What I'm wondering is - what changed? Or what could be affecting this differently than before?
I didn't used to have to ping the port OR continually reopen it.
Paul
Extron switchers will send unsolicited status change messages. If you close the connection, won't you miss these?
The port would still be listening for a passive open. If a port needed to already be open in order to communicate, you couldn't telnet to any server without advance knowledge of the imminent connection.
Paul
Well, yes, you need to have a connection in order to communicate. The Extron device has a built-in server -- I think of it as a telnet server, though I don't actually know if it technically meets the definition of a telnet server or not. In order for the Extron server to send information to a client, the client needs to connect to the server and that connection needs to be maintained and active. The server will not connect to a disconnected client and send information, that's not how servers work. Also, on the AMX side, there is a client which is set up to contact the Extron server, This client will not accept a connection -- it's not a server, it's a client. If you want the AMX to accept (not initiate) a connection from some device, there needs to be a server, not a client.
Some Extron devices may have telnet clients which will contact and connect to a telnet server and transfer information, but that's not the sort of connection we're discussing. Unless, of course, I've entirely missed the boat in this thread.
This confuses me too, if it works like a telnet port once the port is opened it should maintain the connection. So who's closing it? The Extron telnet server shouldn't be unless it just works unlike other telnet servers and AMX shouldn't be closing it unless there's a problem with the connection or it's being told to close via code. Is this a Duet mod? Is this a known to work correctly mod? Do you have another Extron device to test?
I've tested w/the DVS304 and the IPL T SFI244 Extron devices - both are behaving identically.
I'm not using a module. I'm just opening the port in Netlinx, then sending strings. I don't have anything that tells a port to close. Both devices stay infinitely open in telnet w/my PC. Both devices drop after ~60 seconds w/AMX. This happens after 3 StayAlive events I see in Wireshark.
DEFINE_FUNCTION Open_Client(INTEGER ip_index)
{
//if port is not open and not being opened, open it
IF(!_ipdev[ip_index].isconnected && !_ipdev[ip_index].inprocess)
{
IP_CLIENT_OPEN(_ipdev[ip_index].localport,_ipdev[ip_index].serveraddr,_ipdev[ip_index].serverport,_ipdev[ip_index].protocol)
_ipdev[ip_index].ACK=0
_ipdev[ip_index].inprocess=1
}
}
I don't *need* the port to stay open. This is more of a...hrm...I'm not timing out in Telnet, why am I timing out in AMX?
**edit**
I just tried this with the same results....
DEFINE_DEVICE
dvtp=10011:1:1
dvextron=0:5:0
DEFINE_EVENT
BUTTON_EVENT[dvtp,1]
{
PUSH:
{
ip_client_open(5,'192.168.4.72',23,IP_TCP)
}
}
Ok. Apparently the Netlinx TCP client implements an optional TCP feature called "keep alive". This doesn't actually keep the connection active, what it does is close the connection when a proper response is not received from the server. The Netlinx client appears to be hardwired to have this feature turned on. It seems to be set to send a probe after 60 seconds of inactivity and then, if no response is received from the server, to send two more probes at 10 second intervals and then close the connection if no response is received within 10 seconds of the last probe.
I checked this with the telnet server (using wireshark) that comes with XP Pro and the Netlinx TCP client sends this probe every 60 seconds and the XP server responds immediately. When connecting to an Extron IPL-T-S2, however, no response to the probe is generated by the Extron server and the Netlinx TCP client closes after 90 seconds.
So, the behavior you are seeing is a combination of the Netlinx client wanting a response and the Extron server not providing one.
I last experimented with the IPL-T-S2 a couple years ago and my recollection is that the Netlinx client did not shut down like it does now, but I can't recall for sure.
According to TCP documentation that I've looked at, a proper implementation of the "keep alive" feature should allow it to be turned on and off and should allow for setting the times and the number of repeat probes. If the Netlinx TCP client allows for this control, I can't see how -- there doesn't appear to be an "IP_SET_OPTION" applicable.
"The processor can send out unsolicited information (such as notice of a volume or input change or a change in some other setting). That is called verbose (wordy) relationship
between the processor and a connected device. For a direct RS-232/422 connection, the processor is set for Verbose mode by default. When the DVS 304 is connected via
Ethernet, Verbose mode is disabled by default in order to reduce the amount of communication traffic on the network. If you want to use the Verbose mode with a processor
connected via Ethernet, this mode must be set to On each time you reconnect to the processor.."
Paul
The new IP_SET_OPTION API was added to NetLinx recently to allow manipulation of particular socket options. To date the only options supported are IP_MULTICAST_TTL_OPTION and IP_TCP_NODELAY_OPTION. The TTL (time-to-live) option allows a multicast packet to be transmitted beyond the local subnet. The NODELAY option forces all outgoing TCP sends to be transmitted immediately rather than being buffered to ensure that all data is transmitted prior to a socket being closed.
The IP_SET_OPTION API was added recently to provide the ability to modify particular socket optional parameters. To date on two options are supported, IP_MULTICAST_TTL_OPTION and IP_TCP_NODELAY_OPTION. The TTL option is to allow a multicast socket to be transmitted beyond the local subnet and the NODELAY option is to ensure that all outbound socket communication is transmitted prior to the socket being closed.
I have the same issue with Lutron. I want to stay connected to catch any unsolicited data, but the connection keeps closing. I have written code to reconnect every few seconds. While this works, it has the unfortunate side effect of filling the log with online/offline events (not to mention all the unnecessary communication). The log is a great way to see how the program is running over the period of a few days - providing the opportunity to catch any programming errors in a live system.
It doesn't do much good, however, when every 7 hours the log is completely full of online/offline chatter:
Any thoughts?
Would it be safe to assume the AMX DUET module for Extron switchers would take care of all this IP connection keep alive / reconnect problems without us having to do anything?
Kurt Elfers - ACE
Ha! True, sad but true. Excellent advice.
You have an online, offline and error event for the socket so you always know whether its open or closed. If you want to stay connected to a socket on another device, the algorithm should be pretty simple. If your socket is open send your data with no worries. If your socket closes, open it so that asynchronous data can be received. I don't think its really any more complicated than that. In network code, you can't assume anything, so I don't bother with keep alive or pinging or any other workaround. Since I know whether the socket is connected or not at all times, I open it if I need it open and close it when I need to, and any errors that are generated I send to the console. This way you assume nothing, and it will always work if it can, otherwise an error is thrown. Are you looking for something beyond this functionality?
Paul
Thanks for the reply, I had forgotten about this thread (it was over a year ago when I posted the question).
If you'll reread my post you'll see I have everything working functionally (you explained exactly what I've been doing), my issue was the log file getting filled with all of the online/offline events.