How to troubleshoot signal drop/ low signal?

MobileSvc.SendOrder is like this:

[System.Web.Services.Protocols.SoapDocumentMethodAttribute("http://server.co.uk/SendOrder", RequestNamespace="http://server.co.uk/", ResponseNamespace="http://server.co.uk/", Use=System.Web.Services.Description.SoapBindingUse.Literal, ParameterStyle=System.Web.Services.Protocols.SoapParameterStyle.Wrapped)]
        public void SendOrder(string orderInfo, string guidString) {
            this.Invoke("SendOrder", new object[] {
                        orderInfo,
                        guidString});
        }

Thanks for your presence Bob

H

Bob,

My previous comment showed only the proxy code auto-generated by VS.  I have attached as a snippet the actual web service method that is called.

The LogExceptionToDatabase is not called when this error occurrs so I think the call doesn't make that far.  What is worse is that it seems that the order being sent sometimes goes through and sometimes doesn't!

[WebMethod]
public void SendOrder(string orderInfo, string guidString)
{
    string connStr = ConfigurationManager.ConnectionStrings["cvsConnectionString"].ConnectionString;
    SqlConnection con = new SqlConnection(connStr);
 
    try
    {
        using (TransactionScope scope = new TransactionScope(TransactionScopeOption.RequiresNew))
        {
            con.Open();
            SqlCommand cmd = new SqlCommand();
            cmd.Connection = con;
            cmd.CommandType = CommandType.StoredProcedure;
            cmd.CommandText = "mobile_order_transact";
            cmd.Parameters.Add(new SqlParameter("@orderDoc", orderInfo));
            cmd.Parameters.Add(new SqlParameter("@orderGUID", guidString));
            cmd.ExecuteNonQuery();
            con.Close();
            scope.Complete();
        }
    }
    catch (Exception ex)
    {
        if (con.State != ConnectionState.Closed)
            con.Close();
 
        this.LogExceptionToDatabase(this.GetExceptionXmlString(ex), this.ExtractUserId(orderInfo), "User name not available");
 
        throw;
    }
}

                                              

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I see where you are logging the exception to a database with LogExceptionToDatabase.  Are you getting any exceptions in the database for this web method?

No, I am not getting an exception from within this method BUT the client code calling the SendOrder method gets the exception I mentioned in my Q.  The client code then calls the LogExceptionToDatabase directly without going via SendOrder method.  I then get th exception in the DB and emailed to me as well.  

The problem is the ambigous error message so I can't tell what happened.  The error occurrs so randomly.  2 days ago it didn't accurr at all over 100 orders were made.  Yesterday it occurred 5 times with similar number of orders.  I am guessing it is dependent on the quality of the Orange and O2 network (we use) signal for the devices

Where is the web service running?  How are you connecting from the PDAs to the web service?

The web service is running on our web server (Windows 2003 server, IIS)
The PDA's are GPRS enabled (I am not fully conversant with these different device connection types, GSM, EDGE, GPRS) so I guyess we are connecting via GPRS.  Our main device is HTC TyTn 2 and shows H (capital H) when connected.  Not sure what that means.

I like to start with definitions:

GPRS (General Packet Radio Service)
The 2.5G data service enhancement for GSM host networks. GPRS is a packet-switched service that takes advantage of available GSM time slots for data communications and supports both X.25 and TCP/IP packet protocols, with quality of service (QoS) mechanisms. GPRS enables high-speed mobile datacom usage and is considered most useful for bursty data applications such as mobile Internet browsing, e-mail, and various push technologies. Through concatenating as many as eight GSM channels, GPRS yields a theoretical transmission rate as high as 171.2 kbps. GPRS maintains the same Gaussian minimum shift keying (GMSK) modulation scheme used by GSM and provides alwayson access. GPRS can run in either symmetric or asymmetric mode, with the speed in either direction sensitive to which of the 12 multislot service classes is selected. The multislot service class determines the number of time slots in each direction, with each time slot supporting a theoretical data rate of 21.4 kbps. The simplest is service class 1, which supports one time slot in each direction.The most capable is service class 12, which supports four time slots in each direction. GPRS specifications were developed in 1997 by the European Telecommunications Standards Institute (ETSI), which subsequently passed that responsibility to the 3rd Generation Partnership Project (3GPP). In Enhanced Data rates for GSM Evolution (EDGE) cellular radio networks, Enhanced GPRS (EGPRS) is a packet-switched transmission mode that supports transmission rates as high as 473.6 kbps.

EDGE (Enhanced Data rates for GSM Evolution)
Originally, Enhanced Data rates for Global Evolution.A 2.5G standard (1999) developed by the European Telecommunications Standards Institute (ETSI) as the final stage in the evolution of data communications within the Global System for Mobile Communications (GSM) standards. The only IMT-2000 specification based on time division multiple access (TDMA) rather than code division multiple access (CDMA), EDGE supports data transmission rates up to 473.6 kbps over GSM channels 200 kHz wide through an improved modulation technique known as 8-Phase Shift Keying (8-PSK), which involves eight levels of phase shift and, therefore, supports three bits per symbol. EDGE employs frequency division duplex (FDD) to support bidirectional communications over 124 channels, each of which supports 8 time slots. EDGE supports two modes of operation:

GSM (Global System for Mobile communications: originally from Groupe Spécial Mobile) is the most popular standard for mobile phones in the world. Its promoter, the GSM Association, estimates that 80% of the global mobile market uses the standard. GSM is used by over 3 billion people across more than 212 countries and territories.  Its ubiquity makes international roaming very common between mobile phone operators, enabling subscribers to use their phones in many parts of the world. GSM differs from its predecessors in that both signaling and speech channels are digital, and thus is considered a second generation (2G) mobile phone system. This has also meant that data communication was easy to build into the system.
The ubiquity of the GSM standard has been an advantage to both consumers (who benefit from the ability to roam and switch carriers without switching phones) and also to network operators (who can choose equipment from any of the many vendors implementing GSM). GSM also pioneered a low-cost (to the network carrier) alternative to voice calls, the Short message service (SMS, also called "text messaging"), which is now supported on other mobile standards as well. Another advantage is that the standard includes one worldwide Emergency telephone number, 112. This makes it easier for international travellers to connect to emergency services without knowing the local emergency number.
Newer versions of the standard were backward-compatible with the original GSM phones. For example, Release '97 of the standard added packet data capabilities, by means of General Packet Radio Service (GPRS). Release '99 introduced higher speed data transmission using Enhanced Data Rates for GSM Evolution (EDGE).

1) The PDA should have a signal strength indicator.

2) If you look in your Users Guide for the HTC TyTn 2 you would see H = HSDPA available, G = GPRS available, E = EDGE available.

3) What is the "normal" signal strength when you don't get an exception, and what is the "error" signal strength?

guys, that's very interesting discussion, but I've observed the same failures on the PDA connected to the PC via USB cable over ActiveSync, so I very much doubt it is ever related to GPRS et. al.

under the debugger there are some SocketExceptions while I try to execute simple HttpWebRequest, so that's the problems somewhere at Sockets level. Again, this happens only for some period of time, then works like a charm

I would be VERY interested in resolving this issue.

User manual:
http://member.america.htc.com/download/web_materials/Manual/HTC_TyTN_II/070820_TyTNII_HTC_English_Manual.pdf

Forgot:

High-Speed Downlink Packet Access (HSDPA) is a 3G (third generation) mobile telephony communications protocol in the High-Speed Packet Access (HSPA) family, which allows networks based on Universal Mobile Telecommunications System (UMTS) to have higher data transfer speeds and capacity. Current HSDPA deployments support down-link speeds of 1.8, 3.6, 7.2 and 14.4 Mbit/s. Further speed increases are available with HSPA+, which provides speeds of up to 42 Mbit/s downlink.

Cool.  Thanks Bob.

Answer to your question 3 above Bob,  it is difficult to determine exact signal strength as it changes often and error only ever occurred once for me but I have 100's of users so I get a few reporting almost on the daily basis.  What all user's agree is that prior to the error they get an error message telling them about low signal which is from my code as shown below

            catch (System.Net.Sockets.SocketException)
            {
                try { progress.Close(); }
                catch (Exception) { }

                ShowExceptionMessage("Your device does not currently have enough network signal to submit data");
            }

Now I am fully conversant with the all these acronyms.  I never get E.  Occassionally I get G but rest of the time I get H (which sounds good).

Alexey, it is interesting that you had the error while on a usb connection!!  Do you get the same error "An error message cannot be displayed because an optional resource assembly containing it cannot be found"  What devices are you using?  What operator?

It would be nice to get some M$ people on this one to clear the confusion.

Alexey, what have you tried as a solution?

It sounds like you are assuming that a SocketException is a low-signal exception, but you aren't specifically checking that.  I would get either the Message or the stack trace (ToString), and make sure.

Possible solution:

http://blogs.msdn.com/tolong/archive/2006/11/20/error-an-error-message-cannot-be-displayed-because-an-optional-resource-assembly-containing-it-cannot-be-found.aspx

Likely Solution:
Install SR CAB for NETCF V2.
By default the CAB should be
C:\Program Files\Microsoft Visual Studio 8\SmartDevices\SDK\CompactFramework\2.0\v2.0\WindowsCE\Diagnostics
If you've installed NETCF V2 to custom folder it might be in a different place, please search pc for actual location.

yes, I've got exactly the same error, with xxx_SR.cab installed of course :) I've seen it on Orange and O2 in UK, and even under the emulator (craddled and connected via ActiveSync). So I'm nearly 100% sure that's nothing to do with the bearer but with networking.

it seemed for me that it is somehow related to the server state, because after some delay the server comes back again as shiny new, like it releases some sessions or similar stuff

I agree Bob that I shouldn't be assuming low signal and I am just making changes to record the exception to DB and monitor that.

I have been through most System_SR suggesting solutions.  This doesn't seem to be my problem.  All other errors are displayed OK.

Alexey, I am in UK too and use Orange and O2.  How did you manage to get tech contact from them.  I am struggling to find anyone to contact from these providers.

Can you elaporate "server state" This issue may well be server issue.  I will dig around in that area and see what I come up with

I haven't contacted the operator, as I see that that happens even on the emulator, so the operator is out of the game unfortunately.

I do suspect that it is some unhandled exception happening when cf.net is trying to send HTTP request at sockets level, like the connection was refused by the server or something similar. Perhaps somewhere at IIS level

Did we look into the IIS log for any evidence of that?

Yep, if it is happening on the emulator and with usb I guess it will have to be either the OS or the .net cf.  What version are you using?  My devices are all WM 6.0 or WM 6.1 which comes with cf.net 2 but we never did any updates on them.  Perhaps there is a fix to this out?

Issues similar to ours

http://social.msdn.microsoft.com/Forums/en-US/vssmartdevicesvbcs/thread/6f5386af-9b57-4b79-85a4-2dde9eeb343d/

Bob,

I looked at my IIS logs and cannot see any errors at all.

yes, wm6.0 & wm6.1, cf.net v2.0

and above link looks promising, as it says about Conn Manager and RAS. I reckon OS gets into some wrong state and doesn't serve sockets correctly

Anyone of you know what one needs to get M$ to look at this?  I have MSDN subcription which I never seem to use.  Would that be enough?

Conn Manager and RAS?
How will that help?  doesn't it mean that it will happen again and then you will have to do the tweak again?

for ConnMgr & RAS - yes, the idea is to reset the Something once it's got into wrong state

re. Microsoft - don't know, try their tech support. I've also seen the forum somewhere on their site (perhaps make a post to the forum above)