We have problems when using a device on windows compact framework 2.0 (windows mobile) and a server with IIS (7) on windows server 2008 R2. We are on WIFI.
We encounter many problems of latency and freezing. Our app is pretty simple. It just send a very small request (a string of 10 chars) to the server which will respond with a string of the same length. There is a request from the device to the server every 3 or 4 seconds.
It works well for some times and suddenly it freeze. It does that with other clients environment : so the only things which vary is the network itself (not the device or the server they both were tested separately and together and they perform well on a wired network).
We are using TCP and we read that it does not work so well on WIFI where the packet loss are not always due to the same reason when on a wired network (congestion).
Does somebody had freezing problems like us on TCP over WIFI ? Do you think we pointed out the same problem as you (TCP over WIFI) ?
We would like to change the protocol used. The first thing we would like to try is TCP Westwood.
Is TCP Westwood not offered on windows server and windows mobile ? If yes, how do you activate it ?.
Our last solution is to build our own server and protocol using UDP. But it's a hard work.
Thank you for answering.
Try setting the TCP_NODELAY socket option as your sending small chunks less than 1500. This will improve performance in a lossy network.
Related
I am puzzled...
My project is a PC connected to multiple micro-controller boards in an isolated network. So far the protocol has been UDP which is easy to deal with, has no particular client/server but has its obvious shortcomings of lost messages when things get busy.
The micro-controllers have fixed IP-addresses (set by dip switches), the PC SW has a list of them, sends at present UDP messages to each of them and they reply to the address they came from (i.e. the PC) with status and/or data.
My question is now that I switch to TCP instead of UDP, should the PC be the listening server with many clients (could be anything from 1 - 50), or should the micro controllers be listening servers the PC can connect to as client? Note: controllers have fixed/known addresses - the PC does not.
An additional concern is re-connection. The micro-controllers are external and may lose connection, reset or otherwise need to connect again.
Thanks....
should the PC be the listening server with many clients (could be anything from 1 - 50), or should the micro controllers be listening servers the PC can connect to as client?
That is a basic design question that we cannot answer for you. Likely, it's more practical for arbitrary devices to connect to a central server but that's not a given.
controllers have fixed/known addresses - the PC does not.
That might turn the previous question around.
The micro-controllers are external and may lose connection, reset or otherwise need to connect again.
That's something you need to put into your design - have TCP connections time out and reconnect. Usually, a finite-state machine is useful here. You should also consider whether you use a one-shot connect-transmit-disconnect similar to UDP (easier to implement) or a longer TCP session with multiple data transmissions (more efficient).
I'm struggling to get an embedded platform with fairly standard IPV4 networking running. I have a working prototype which obtains an IP via DHCP without problem on a point to point connection (single cat5 cable) attached to a test laptop.
On my new hardware I get the link up but no DHCP request gets to the server (monitoring with wireshark). However what I do see, 100% repeatable, when those packets should be received, is a couple of ICMPv6 packets from the test laptop. This happens every time, there is no other activity on that link at any other time.
It seems to me that those packets are trying to tell me something, but what? Perhaps the DHCP request is going out but malformed for some reason?
(I can't post the actual packet from my phone, will make a copy and do so later.)
Seems to be something generated by the laptop when it sees the link comes up. Turned out to be unrelated to the issue I had (which was hardware related).
I have an RN-171 wifly module connected with a micro-controller.
I am using the UDP-protocol to communicate with the module. Also, I am using the firmware's UDP auto-pair feature to set the host ip. As soon as the module receives a UDP packet, it sets the host IP address to the ip from where it received the data. Now, this host ip cannot be changed without entering into the command mode.
I want the module to behave in the following way:
Every time it receives a UDP packet, it updates the host ip to the ip address from where that signal came from.
Also, I can use the TCP protocol but it only allows a single connection at a time. One more problem that I faced using the TCP protocol was that if I try to initiate a second TCP connection with the module, it not only refuses the second connection but also hangs the first stable connection. Even if the second connection initiation does not hang the module and it just gets refused, I will be ready to work with TCP.
I have been researching a lot on the web regarding this problem but since these modules are not widely used, they have a very limited support.
I've used RN-171 extensively and have many resolved tickets in their support system.
According to the WiFly Command Reference, Advanced Features and Applications User’s Guide, you cannot open more than one TCP port with the module. (the default number being 2000)
Unfortunately, regarding the UDP functionality, there's not much you can do. If you have a new host wishing to communicate over UDP, connect to the module over TCP, go into command mode and set the address using "$$$", "set ip host 0.0.0.0", "save", "exit" commands. Alternatively, instead of 0.0.0.0, you can enter the new host's own ip address: "$$$", "set ip host ###.###.###.###", "exit". Replace "###.###.###.###" with the ip address of the device.
This way, you won't get wrong host ip in case more than one device communicates over UDP at the same time. Also, by not using "save", the auto-pairing will still be saved to EEPROM memory. Also, you can send "ip flags 0x##" before "exit", this way you can also set bit[6] to 0 (UDP auto pairing disabled) temporarily by using the hex value that has this bit set to zero.
One of my problems that Microchip technical support tested around the summer of 2013 is that you cannot use RN-171 as an access point for other RN-171s since they have a firmware error preventing one from doing that and, as of firmware v4.41, released in January of 2014, there is no fix yet nor planned.
I myself do not recommend the latest firmware version v4.41, since it does not appear to work with most routers; however Soft AP mode on this works fine. On the other hand, v4.00.1 is much more compatible, however you should take care when cutting off the power since it has a potentially disastrous bricking problem if you cut the power when flash writing is in progress - the module may lock its memory forever.
I recommend registering and opening a Microchip ticket which usually will be answered within two business days and they're quite supportive. Their firmware update cycle is however quite long, and it usually takes a year or so for a new update.
I'm making a multiplayer game and I need to test it in simulated environment with packet loss, high latencies, packet reordering, etc. I'm using Network Emulator for Windows Toolkit for this purpose. However I can't get it to work for loopback packets. For instance when I do "ping google.com" I get increased latency but when I do "ping 127.0.0.1" - latency is under 1ms, so I think NEWT is not intercepting these packets. Do you have any idea how can I make it work?
If you install VMWare player you can create a "remote" server with its own network interface. You probably aren't going to be able to intercept the loopback address reliably on Windows, but more importantly what you are trying to do is not a good test: it doesn't tell you how the game will run in a realistic setting, with two computers and two OSs interacting. With a VM and network emulator you have something closer to reality.
Resolution, of sorts
The client computer that was showing this problem had Trend Micro Security installed. This security suite placed a service or driver on top of each network adapter in the system. I did not bother to debug further once this legacy app started working again.
Update 1
I disabled TCP window scale auto-tuning on Win7.
On Windows 7 if I unplug the ethernet cable directly connected to the server, the disconnection happens after about 5 seconds but the client process crashes. netstat on the server reports two TCP connections to the client that are no longer valid, because the client process did not gracefully shutdown and close the connections.
After putting the server in this strange state after the physical disconnect, If I restart the client process it hangs while connecting to the server (just as described in the original)
If I perform a physical disconnection on the XP side, the disconnect happens more quickly than on Win7. Some sort of keep alive value or behavior is different on XP. While ssh'd (via Putty) the ssh connection dies more quickly on XP than Win7 as well.
Original
I have a legacy TCP client/server app that appears to foul up the server only when the client is a Windows 7 machine.
The server is OpenEmbedded Linux running 2.6.11.
A Windows 7 client connects for a bit, and eventually gets to a state where the client disconnects after a second or two.
Once the server is in this state, If I immediately connect a Windows XP client, the XP client cannot connect either.
I cannot appear to get the server into the buggy state by connecting with an XP client alone.
I'd like to know what changes were made to the TCP/IP stack starting with Vista or Windows 7 so I can better debug the legacy code.
I'd also like to know what commands I can run on the Linux server that might better help me understand why the connections are failing.
Perhaps the best thing you can do is to fire up tcpdump or wireshark under linux and analyze the TCP SYN sent by both Windows XP and Windows 7. Wireshark allows you to break out bit-by-bit what TCP options are sent... for example, this is what you see from a debian lenny box making a TCP connection:
Transmission Control Protocol, Src Port: 58456 (58456), Dst Port: 23 (23), Seq: 0, Len: 0
Source port: 58456 (58456)
Destination port: 23 (23)
Sequence number: 0 (relative sequence number)
Header length: 40 bytes
Flags: 0x02 (SYN)
0... .... = Congestion Window Reduced (CWR): Not set
.0.. .... = ECN-Echo: Not set
..0. .... = Urgent: Not set
...0 .... = Acknowledgment: Not set
.... 0... = Push: Not set
.... .0.. = Reset: Not set
.... ..1. = Syn: Set
.... ...0 = Fin: Not set
Window size: 5840
Checksum: 0x8b77 [correct]
[Good Checksum: True]
[Bad Checksum: False]
Options: (20 bytes)
Maximum segment size: 1460 bytes
SACK permitted
Timestamps: TSval 136991740, TSecr 0
NOP
Window scale: 6 (multiply by 64)
My suspicion is that you'll see differences in RFC 1323 Window Scaling, but I don't have an XP machine handy to validate this.
I gave a detailed response of how to analyze TCP connections using tcptrace under linux in this answer...
How can I measure the performance and TCP RTT of my server code?
I also suspect a Window Scaling issue. I cannot find a link just at the moment, but there were complaints when Vista first came out reporting that that something was screwing with some routers (belkins If I recall). They traced it down to a problem with one of the window sizes that Vista (and thereby Windows 7) changes by default. The routers would get hung up and need to be reset every few minutes.
You can issue some commands to turn off window scaling, see if your problem goes away.
From Here:
netsh interface tcp set global autotuninglevel=disabled
Edit:
Try disabling IPv6 on windows 7. Link on how to do that. With IPv4, it should act the same as windows XP. Load up wireshark on the two systems and compare the differences