Question

How to establish a GPRS connection using a Simcom sim300 module

Asked by: Subash_Iyer

Hi,
I am using a Simcom 300 module to connect my PC over the GPRS to a remote server to send data. The PC would later be replaced by microcontroller based equipment for remote a monitoring application.
I have tried using the data as a TCP pack thru IP and also by the APN but am facing the following problem.
My service provider is Airtel and their APN is airtelfun.com. The IP address of airtelfun.com is 100.1.200.99:8080
The IP address of my server is 192.168.1.18:2020. This is not actually a static IP but a virtual server that I have set up using a software called TCPIPECHO.
When I connect the module to the IP address of airtelfun.com. i.e. 100.1.200.99:8080, I am getting a CONNECT OK after the execution of the AT+CIPSTART command. However, when I connect to any other IP address, I get a TCP CONNECTING message and a CONNECT FAIL message following it.
As far as I can understand, the modem is successfully connecting to the network and is also being given an IP address. However, it is unable to establish a TCP connection to any IP apart from that of the service provider.
I have also tried using the SIM card in a mobile phone to verify whether there are any restrictions on access by the service provider. I am able to browse all sites over the mobile which confirms that there are no such access restrictions. I have also verified this with my service provider.
I do hope someone would be able to solve this problem.
Subash Iyer

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Asked On: 2009-03-18 at 10:59:23ID24242781
Tags: GPRS
,; Simcom
,; TCP
,; IP
,; server
Topics: General Packet Radio Service (GPRS)
,; TCP/IP
,; Microsoft Virtual Server
,; Miscellaneous Networking
,; Windows Networking
Participating Experts: 1
Points: 500
Comments: 16

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Answers

by: Subash_IyerPosted on 2009-03-20 at 12:13:29ID: 23942818

Hi,
I have moved further on this subject. I have come to understand that the IP 192.168.1.18 which I was using as a target was my local IP on my LAN. I have now taken a static IP from my service provider.
I have then tried to establish communication with this static IP at port 8080 from the GPRS modem but I am still getting the same message TCP CONNECTING and then CONNECT FAIL.
I think there is something wrong in the way I am expecting to connect to an IP address.
Hope someone can throw some light on this.

by: srujan1Posted on 2009-03-25 at 23:46:58ID: 23987809

Hi Subash_Iyer,

The IP address you are providing for your server is a local IP address. You can not connect to a local IP(static or dynamic) from outside your network. This is because 192.168.1.18 is simply an IP on your local network. it is not visible outside your network. you have to use the IP provided by your ISP or a VPN inoder to connect to your local IP.
I'm working on GPRS TCP connectin. If you can provide more info about your application (what you have to achieve) i may be more helpful.

Regards,
Srujan

by: Subash_IyerPosted on 2009-03-26 at 00:02:00ID: 23987862

Thanks srujan1 for your interest.
I am developing a remote monitoring application. There shall be several pieces of equipment (microcontroller based) located at varied locations across a wide area. Each of these would relay data to the server based on variations of parameters at site. Data would be about 150 bytes carrting information of temperature, humidity, status of equipment, etc.
The equipment at site must be able to send data to the sever over the GPRS network. We choose GPRS as the locations would not have wired Internet connections.
I am able to comprehend your comment on the local IP. I have also taken a static IP from my service provider which is now a real IP. But am not sure how to actually use this. I do hope you would be able to throw some light on this.
Thanks and Regards

by: srujan1Posted on 2009-03-26 at 00:29:52ID: 23987958

Hi Subash,
In my application I'm configuring the GPRS module as TCP server and the central server will be TCP client. Inorder to connect from my server I have to know the IP of my GPRS module. I'm using SMS for this purpose. After getting the IP and port number on which the GPRS module is listening a TCP client application can connect to the GPRS module. For this settting you dont require any special IP also. Even your local IP will work.
I'm using this setup for security reasons also. I think It is not wise to open port on your server connected to the internet directly.

From your answer i assume you are configuring GPRS module as TCP client. I have following questions
From where you are initiating TCP connection(GPRS module or PC)?
are you connecting to the correct port number?
are you sure your are using real IP. Please recheck once.
also take note that GPRS module`s IP is not a static one and is confined to a particular session. Once you start a TCP session you will get an IP and that IP will remain untill that session was closed.

Best regards,
Srujan

by: Subash_IyerPosted on 2009-03-26 at 01:15:25ID: 23988119

Thanks for the reply,
As you rightly said, I am using the GPRS module as a client. This is primarily because there would be several modules and only 1 PC (server).
The TCP communication is being initiated by the GPRS modules on field. However, there has to be a facility to allow the server (PC) also to intitiate communication to a specific module.
Your question on the port number is something that really has had me scratching my head for the last few days. I am really unable to know whether both the IP address and port number that I am using is correct. I have done the following:
1) As I said, I asked my ISP to allot me a static IP and configured this into the broadband modem which is our gateway to the internet in my office.
2) I downloaded a free webserver (Abyss Web Server). I understand that this by default occupies the port 80.
3) Then I tried to establish contact with my static IP address at port 80.
This attempt has not been successful.

Today I have also tried another approach:
1) I got the IP address of my company's website by pinging it from the Command Prompt.
2) I understand that the POP3 mail server of a website is generally at port 110 and the webserver at port 80. So I tried communicating to these 2 port numbers.
No success yet.
I then found out that the IP address that I got out by pinging hosts a lot of websites so I tried to locate the port of my wesite. I found that my webmail is at port 2015 and I tried to communication to it. Again no success.
I hope the long explanation above does not confuse you. But in short, I am not sure whether the IP and port numbers that I am communicating to are correct and am not sure how to locate / access them either.
Again, I would like to repeat that I have taken a static IP now and can use that. But I am not sure what application to run and how to configure the application to a specific port.

Thanks to your pointed questions, I now am able to have a clearer line of thought. I would be glad if you could throw some further light on the subject.

Regards
Subash

by: srujan1Posted on 2009-03-26 at 03:01:05ID: 23988584

I'm not an networking expert. But as per my understanding the IP provided by the ISP will be assigned to the modem. Your PC will be assigned a local network IP(something like 192.168.x.x) by the modem. you can get your ip using "ipconfig -all" command. If your IP is like what i said you will be only visible to local network and can not access your PC from outside without an VPN. I think that is the problem you are facing.
If you think that is not the case try using a TCP server program included(rename it to .exe) here to listen on a particular port(say 1000). This is a sample program developed for my application.

I'm sure your problem is regading IP address. I think configuring your GPRS modules as servers will work for even though there are multiple modules. you can distinguish the messages using some ID embedded into the messages. Only prob is you have to use some ethod like SMS to get the IP of your GPRS modules.

Best regards
Srujan

TAG-2388-Server.txt
- 28 KB
TCp server program

by: Subash_IyerPosted on 2009-03-26 at 09:07:47ID: 23991967

Yes, you have identified my problem correctly. I am not sure about the IP address and the port number that I need to communicate to. The problem I guess lies in properly addressing the server.
I shall do some work on the VPN. Please do keep in touch as I shall revert back with any developments.

by: srujan1Posted on 2009-04-05 at 21:54:01ID: 24074404

Hi Subash,
Have you identified any solution for the IP problem? Please let me know if you got any breakthrough.

Regards
Srujan

by: Subash_IyerPosted on 2009-04-07 at 06:01:28ID: 24086790

Hi Srujan,
Am still grappling with the issue. The latest that I got to know is that it would be better to install the static IP onto a PC directly instead of into the DSL modem as it is done now. I need a new broadband connection to do that so that I do not disturb my existing infrastructure. Am going to apply for a new connectiom and static IP. I guess, one I have a static IP that is loaded into a PC, it becomes a server sitting on the Internet. This would be accessible to a GPRS client. I hope I will have some feedback shortly.
Regards
Suabsh

by: srujan1Posted on 2009-04-08 at 06:16:26ID: 24096816

Hi Subash,

Small correction to the jargon. IP is static if the same IP is allocated to you every time you connect to the network. Dynamic IP means that you will not get the same IP every time you connect to the network. It may change with every session.

Public IP is the IP which is visible to the network(internet). Private IP is the IP which will be visible to only your private network(something like 192.168.1.1)

I think you intend to say that you will configure your pc with the public IP given by your ISP. If you configure your PC with the public IP then it is visible in th einter net and your application will work.

if you are connecting from your client susing the IP address make sure you that tha ISP provides a static IP not a dynamic IP. because if it is a dynamic IP it will change with every new session and your clients will not know.

by: Subash_IyerPosted on 2009-04-08 at 08:03:33ID: 24098044

Hi Srujan,
I understand what you are saying. The IP now alloted to me is both static and public. And I am now considering connecting a computer on the internet directly with this IP.
But yesterday, I tried connecting to an IP which is both static and publinc which has been provided to me by one of my friends who holds a server and hosts websites on this server. He also clarified that the IP he holds is both static and public. In fact, if I type this IP into a web browser, I am able to reach his website which proves that the IP is public.
He provided me a port too but I am till unable to establish a TCP connection.
By the way, I tried to make a UDP connection too. I could get a "CONNECT OK" but I realise that UDP does not involve handshaking the way TCP does so there is no way of ascertaining that a "connection" was actually made. After establishing UDP, I tried sending data to his IP and he was monitoring his PC using WireShark. I also provided him the dynamic IP which the GPRS network had provided to my modem. But he could not find any data coming in from my modem (dynamic IP).
I now think that the problem is in the way I am addressing the destination IP and port number. There could also be a problem in the TCP implementation in the modem. I wonder whether I need to do some configurations in the modem to activcate TCP connection in it. Do you have any ideas on this?
Subash

by: Subash_IyerPosted on 2009-04-20 at 08:43:50ID: 24185677

Hi Srujan,
Sorry I've been out of touch. I was on tour.
Anyway, I have now taken the following steps. I have taken a new Internet connection with a static IP and connected only 1 PC to is as the server. I have then NATted a test server application to one port on this "server". I tried to establish communication to this server thru the modem but got the same response.
I then tried to establish communication thru another PC (connected to the Internet by a seperate connection). I tried to send and receive data by another software (Putty) and was successful. That means that the static IP than I have is visible on the internet and the application I am running on the server is able to communicate with a client.
The problem therefore boils done to this: The modem is getting assigned a static IP. It is then able to establish communication with one particular IP (provided by the GPRS service provider) but is not able to communicate to any other IP. I guess the problem is in confguring the modem correctly for GPRS.
If you can advise on this, I would be very happy.
Regards
Subash

by: Subash_IyerPosted on 2009-04-22 at 22:15:16ID: 24211964

Hi Srujan,
I finally cracked the problem. It was too simple actually. My service provider requires a username for logging in to the APN. This is however specific for only our type of access applications and is not required for the general GPRS access by the moble phone.
The answer came to me from Excelpoint Systems who is the dealer of Simcom Modems in my country.
Thanks for all your help.
Do stay in touch.
Subash

20120131-EE-VQP-002

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How to establish a GPRS connection using a Simcom sim300 module

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