automatic and self-recovery connections on smartpack, smartpack ii
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1. Enabled Disabled X Keep alive Autoping Buffer delay 2 Packet max size Autoping delay Save GPRS Settings Figure 3 3 1 Configuring the TCP and UDP parameters with the Maestro configuration tool 3 4 Testing the automatic connection Before going further it is a good idea to test the setup now It can be easily done with a PC and some virtual serial port software For testing purpose the tool VSPE from Eterlogic has shown pretty effective If the modem is a server create a new TCP client serial port and have it point to the modem s IP address If the modem is a client create a new TCP server serial port and make sure that it is available to the modem that you have the IP that is entered in the modem and that your company router is correctly setup Then open two terminal windows one connected to your virtual serial port and one connected to your modem trough the physical serial port Twenty seconds after the modem startup the connection should be estab lished Send some characters into one terminal the same data should appear after a short delay on the other terminal Figure 3 4 1 Basic test setup Note that if your terminal software directly supports TCP connections you may not require a virtual serial port to test your configuration Confidential the whole document is the sole property of Maestro Wireless Solutions Itd 15 3603 9 36 F 118 Connaught Road West Sheung Wan Hong Kong contact maestro wire2. set to 0 initiates the sending of a TCP frame as soon as possible after the reception of a single character value from the host If it is set to 1 initiate a delay will be introduced before the sending of a TCP frame Modem as client If the modem is a server the parameters are Port is the server port The modem establish connection on the server to this specific port only Mode must be set as C for client Address is the IP address of your server If you are hosting the server on your company s network this should be the Internet IP address of your company router not the IP ofthe server on the LAN TxDelay determines if there is time delay introduced before sending a TCP frame that has not been entirely filled with user data If it is set to 0 initiates the sending of a TCP frame as soon as possible after the reception of a single character value from the host If it is set to 1 initiate a delay will be introduced before the sending of a TCP frame Choosing whether the modem is a client or a server will only make a difference during the connection initial ization once the connection is established the modem will try to maintain it all the time making it is a real bi directional data link Data transfer can be initiated by both the server and the client once they are connected 3 3 2 Activating the automatic connection Once all the parameters are setup it is time to actually activate the automatic connection Th
3. this stage the function pack may not be installed in your modem Please contact your Maestro Wireless Solutions sales contact FAE or local distributor for more details and application loading instructions Please note that function packs are not installed by default on all Maestro modems and may have to be purchased separately Using the configuration software you can set the GPRS from the GPRS amp TCP IP tab figure 3 2 1 The configuration software will not start if the function pack is not installed on the modem Confidential the whole document is the sole property of Maestro Wireless Solutions Itd 12 3603 9 36 F 118 Connaught Road West Sheung Wan Hong Kong contact maestro wireless com Modem Status IP Ping Username Password Packets settings IP buffer size Keep alive Packet max size Command String corpf net Network Serial Port TMODE Add on board DOTA TCP settings Tx Delay TTL Autoping Autoping delay GPRS amp TCP IP Send SMS Call Screening UDP settings Port IP Tx Delay Connection type Auto connection Type Enabled Buffer delay Dynamic DNS maestro y 0 2 Remote Configuration empowering wireless Save GPRS Settings Figure 3 2 1 Configuring APN with the Maestro configuration tool 3 3 Configuring the IP connection In this third step you will have to enter the TCP UDP parameters in the modem We will show here how to config
4. application since both will think they are still connected to serial ports While this is an extremely convenient tool virtual serial ports are not a very scalable solution since operating systems limit the number of serial ports Windows XP has a limit of 255 ports it is not possible to do larger deployments using virtual serial ports For large deployments direct TCP UDP connection is a much better solution 1 3 PSTN modem replacement The use of PSTN modems in SCADA and AMR applications is very common but due to the growing difference in price between voice communications and GPRS plans it is tempting to upgrade deployments from switched circuits to packets communications Just like it is possible to use virtual serial ports to retrofit existing applications it is possible to create virtual modems on the back end server that will react to AT commands the same way a regular modem would do but which will dial IP addresses instead of phone numbers These modems provided by third party companies are a drop in retrofits and will work with the existing back end software 2 Any virtual modem that supports raw TCP connections should work with the Maestro modems Confidential the whole document is the sole property of Maestro Wireless Solutions Itd 5 3603 9 36 F 118 Connaught Road West Sheung Wan Hong Kong contact maestro wireless com ast empowering wireless Chapter 2 Practical considerations and limitati
5. ation induces delay which may cause timing issues If will be necessary whenever possible to change the sofware settings and extend any serial timeout to better fit values for example two to four seconds 2 3 TCP and UDP The TCP and UDP protocol are different in their implementation We will not enter in the very technical details here but you need to know that TCP includes an integrated acknowledgement mechanism Every packet sent will have to be acknowl edged by the recipient or it will be considered lost and re sent UDP does not include this acknowledgement mechanism If packets are lost on their way to the recipient they will not be re sent automatically Both protocols have their pros and cons While TCP is safer it is also slower and has a higher data payload if your operator charges you by the kilobyte of data TCP will cost you much more than UDP On the other hand UDP offers reduced latency and lower data payload but packets have more chances to be lost in the network As a general rule UDP is often prefered for streaming or very granular applications where the loss of some data is not critical sensors of slow varying signals etc or when acknlowedgement re sending can be handled at the application layer instead of the transport layer If data integrity is very important or if the acknowledgement can not be handled at higher communication layers then TCP will be preferred Confidential the whole docume
6. aught Road West Sheung Wan Hong Kong contact maestro wireless com maestro empowering wireless References More technical informations about the commands and functions mentionned in this application note can be found in these documents AT commands interface guide from Sierra Wireless M100 SmartPack User Manual from Maestro Wireless Solutions M100evo SmartPackil User Manual from Maestro Wireless Solutions Maestro Heritage Software Tools User Manual from Maestro Wireless Solutions For any assistance please consult your Maestro Wireless Solutions local distributor Maestro sales person or FAE Confidential the whole document is the sole property of Maestro Wireless Solutions Itd 18 3603 9 36 F 118 Connaught Road West Sheung Wan Hong Kong contact maestro wireless com
7. cess to a serial device 2 2 mn 4 1 2 Serial port replacement aoaaa 4 1 3 PSTN modem replacement aoaaa aa ee 5 2 Practical considerations and limitations 6 2 1 IP address consideration aoaaa aaa en 6 2 1 1 Public IP for back end application 2 2 nn nn nn 6 2 1 2 Public IP for cellular modems s ss sarasa nn nn nn 7 2 1 3 Servers with Dynamic IP anaa non 7 2 2 Timing and delay issues 2 2 22 Coon ce 8 2 3 TCPandUDP ss p asa koaa saa onma a aa a a i a aaa aa aoaia aaa a aaoi i 9 3 Configuring the modem 11 3 1 Configuring the serial Port 2 2 2 aa 11 3 2 Configuring the GPRS connection a aoaaa a 12 3 3 Configuring the IP connection aosa aa 13 3 3 1 Entering the TCP UDP parameters aoa aa eee ee 13 3 3 2 Activating the automatic connection 2 2 2 2 nn 14 3 4 Testing the automatic connection 22 22 m nn 15 4 Configuring the back end application 16 4 1 Timing anddelay su ee aaa a nn a a a a ee ee ee 16 4 2 Virtual Serial ports s s se u zoo aa u ann na ar ee eee ren 16 4 3 Virtualmodems aaau aaa a 16 Confidential the whole document is the sole property of Maestro Wireless Solutions Itd 2 3603 9 36 F 118 Connaught Road West Sheung Wan Hong Kong contact maestro wireless com maest empowering wireless Introduction This application notes covers the process of using the Maestro modems to setup automatic TCP or UDP connections This is applicable to the Maestro 100 Mae
8. in non volatile memory AT amp W For details about the syntax of these commands please refer to the AT commands interface guide document Do not forget to change the settings of your terminal software as you reconfigure the modem If you do not like AT commands you can use the modem s configuration software provided by Maestro Wireless Solutions The serial port parameters are in the Network Serial Port tab figure 3 1 1 The fourth point will determine which kind of serial cable you will have to use A GSM modem is a DCE meaning that Tx pin is an input and Rx pin is an ouptput If your serial equipment is also a DCE you have to use an RS 232 crossed cable also known as null modem cable to connect it to the modem If your serial equipment is a DTE you need to use a straight cable An easy way to identify your equipment is to remember that a PC is a DTE If you use a straight cable to connect the PC to the serial equipment then you will use a crossed cable to connect the modem to the serial equipment and vice versa Confidential the whole document is the sole property of Maestro Wireless Solutions Itd 11 3603 9 36 F 118 Connaught Road West Sheung Wan Hong Kong contact maestro wireless com maestro y empowering wireless Modem Status Network Serial Port Add on board GPRS amp TCP IP Call Screening Dynamic DNS Remote Configuration IP Ping Command String TMODE DOTA Send SMS Serial Port Band Selec
9. is is simply done by sending the command AT AUTOTCP 1 After this you can reboot the modem The automatic connection function actually starts twenty seconds after the modem is switched on or reset During the first twenty seconds the modem works in normal AT commands mode In this mode it is possible to deactivate the automatic connection function with AT AUTOTCP 0 Using the Maestro configuration software these settings are entered on the GPRS amp TCP IP tab On figure 3 3 1 the green box is equivalent of the informations entered with the AT IPTCP command The blue box is for the AT IPUDP command you only have to fill one of these two groups and finally the red box is to select whether the automatic connection is done in TCP mode UDP mode or is disabled equivalent to AT AUTOTCP 1 AT AUTOUDP 1 or AT AUTOTCP 0 and AT AUTOUDP 0 Buffer delay refers to the AT AUFCM command Confidential the whole document is the sole property of Maestro Wireless Solutions Itd 14 3603 9 36 F 118 Connaught Road West Sheung Wan Hong Kong contact maestro wireless com maestro X empowering wireless Modem Status Network Serial Port Add on board GPRS amp TCP IP Call Screening Dynamic DNS Remote Configuration IP Ping Command String TMODE DOTA Send SMS GPRS settings TCP settings UDP settings APN corpf net Username Tx Delay EJ Tx Delay a Password Packets settings Auto connection IP buffer size Type
10. less com t empowering wireless Chapter 4 Configuring the back end application 4 1 Timing and delay As explained in section 2 2 the cellular modem has a non negligible transmission delay due to the nature of the cellular network A lot of back end applications usually have a timeout delay to detect errors in the communication chain which is often tuned to very short times It is recommended to increase this timeout delay to a value of several seconds two to four so that the application s behavior is not affected by the new setup 4 2 Virtual serial ports If your back end application was relying on serial ports it will now have to work with TCP or UDP sockets instead Many older applications can not support such mode It is tnen necessary to use virtual serial ports devices A virtual serial port is a piece of software designed by a third party company that runs on your PC and will create any number of emulated serial ports on it These virtual devices will be seen as real serial ports by your applications but instead sending data to a physical port at the back on the computer they will send it to TCP or UDP sockets accross the Internet This allows your serial port only application to connect with TCP UDP sockets The automatic connection feature of Maestro modems has been successfully tested with virtual serial ports solutions from Eltima and Eterlogic Please refer to the documentation of these solutions to setup inst
11. nt is the sole property of Maestro Wireless Solutions Itd 9 3603 9 36 F 118 Connaught Road West Sheung Wan Hong Kong contact maestro wireless com maestro NY empowering wireless It is not possible to use both UDP and TCP at the same time Confidential the whole document is the sole property of Maestro Wireless Solutions Itd 10 3603 9 36 F 118 Connaught Road West Sheung Wan Hong Kong contact maestro wireless com t empowering wireless Chapter 3 Configuring the modem 3 1 Configuring the serial port The very first thing to do is to gather vital information about your serial equipment and especially its serial port You need to know 1 What is the baudrate of the equipment 9600bps 19200bps 115200bps another value 2 What is the character framing and parity of the equipment 8 data bits 1 stop bit no parity 7 data bits 1 stop bit even parity another value 3 Does the equipment uses hardware flow control or no flow control 4 Is the equipment a DTE or a DCE i e is the Tx pin of the equipment an input or an output The first three points cover the software serial port configuration You then have to configure your modem to match exactly the same parameters as your serial equipment using the following AT commands Configure the baudrate 0 0 ee eee eee AT IPR Configure the character framing AT ICF Configure the flow control 0085 AT IFC Save these parameters
12. o modem s automatic connection feature for this The automatic connection features works by creating a logical bridge between the modem serial port and its cellular interface Once the modem has activated its data mode it will get an IP address and assign this IP address to your serial device or will connect to a determined IP address i e the IP address of the server on which your back end application is running Figure 1 1 1 Data communication chain remote access to a serial device Once this is done every byte of data received on the Internet side is forwared to the serial port and vice versa This is a transparent process for your device and it is usually not required to change its settings 1 2 Serial port replacement Since many legacy back end applications can not work with TCP or UDP sockets it is possible to translate back the TCP UDP data into serial port format using virtual serial ports Virtual serial ports solutions are provided and supported by third party companies Confidential the whole document is the sole property of Maestro Wireless Solutions Itd 4 3603 9 36 F 118 Connaught Road West Sheung Wan Hong Kong contact maestro wireless com empowering wireless RS232 TCP Figure 1 2 1 Data communication chain remote access to a serial device using virtual serial ports Using such ports the serial port replacement will be completely transparent to both the serial devices and the back end
13. ommunication will assume a null transmission delay This is a major issue when moving to cellular Because of the very nature of the GSM network GPRS communications have a long transmission delay that can be more than one second This means that every protocols and software that base some of their features on the transmission time may behave in unexpected ways The typical example is the one of a SCADA software that has a request timeout function Everytime this software sends a request to a serial device it will expect to receive an immediate answer with a short timeout of 100ms If no reply is received after 100ms the software will interpretate this as a communication error While this works fine in a pure serial environment if the information is relayed over the GPRS network where 250ms is a typical transmission delay then the software will see a lot of errors as shown on figure 2 2 2 Confidential the whole document is the sole property of Maestro Wireless Solutions Itd 8 3603 9 36 F 118 Connaught Road West Sheung Wan Hong Kong contact maestro wireless com empowering wireless Sends a request with a 100ms timeout Sonvaidatieisaues transmission time 250ms Receives the request transmission time Oms Processes the request processing time 15ms Sends a reply transmission time Oms Forwards the request transmission time 250ms Total reply time 515ms TIMEOUT Figure 2 2 2 Cellular communic
14. ons 2 1 IP address consideration When establishing an automatic connection with a Maestro modem it is necessary that at least one of the connection end points i e either the modem or the back end application can be reached by the other end point Typically this consists of verifying that at least one of the connection end points has a public and ideally fixed IP address and that a TCP port can be opened on this address Any end point with a public IP address can be a TCP UDP server The other end point will be the TCP UDP client 2 1 1 Public IP for back end application Most back end applications do not have a direct access to Internet They are often installed on a computer connected to a company local network which will have Internet access through this company s router and firewall Assuming that this company has a public IP address which is often the case it will be necessary that the company router is setup to make the communication port of the back end application available from Internet using NAT for example as shown on figure2 1 1 192 168 0 56 Figure 2 1 1 By using port forwarding it is possible to host a TCP UDP server on a machine on the local network 1A public IP address also called true IP is an IP address that is directly accessible from the Internet and that is not hidden on customer s or carrier s private network Confidential the whole document is the sole property of Maestro Wi
15. pecially if the server gets a different IP address each time it connects to Internet If your ISP can only give you a dynamic IP address it will be necessary to rely on a dynamic DNS service such as DynDNS or No IP These are third party companies that will help to turn your dynamic IP address of the TCP UDP server into a fixed hostname which can be addressed by the client cf figure 2 1 4 Confidential the whole document is the sole property of Maestro Wireless Solutions Itd 7 3603 9 36 F 118 Connaught Road West Sheung Wan Hong Kong contact maestro wireless com maestro empowering wireless Ea zz Ea Figure 2 1 4 Dynamic DNS service providers help you resolve dynamic IP problem You still need a public IP 2 2 Timing and delay issues A serial cable has negligible transmission delays Every bit of information that is generated at one end of the cable is immediatly received at the other end and the communication has no transmission problem Most serial communication protocols and software that used serial port took this zero transmission delay for granted and some even used this as integral parts of their communication methods see figure 2 2 1 Se Sends a request with a 100ms timeout aes Receives the request transmission time Oms Processes the request processing time 15ms Sends a reply pee time Oms Receives a reply in 15ms before the 100ms timeout Figure 2 2 1 Serial c
16. reless Solutions Itd 6 3603 9 36 F 118 Connaught Road West Sheung Wan Hong Kong contact maestro wireless com maestro X empowering wireless If the back end application does not support TCP UDP ports and you want to use serial port emulation soft ware then it will be necessary to open one port for each virtual serial port 2 1 2 Public IP for cellular modems There is a trend within network operator to assign mobile devices with private IP addresses see figure 2 1 3 instead of public addresses figure 2 1 2 Since these operators will ask their customer to pay some premium for public IP addresses many customers prefer to let the back end application be the TCP UDP server 110 4 1 155 110 4 1 155 110 4 1 156 110 4 1 157 110 4 1 156 110 4 1 157 Figure 2 1 2 Cellular modems with public IP addresses These modems can be used at TCP UDP servers mopem 1 10 10 25 201 10 10 25 202 monems 10 10 25 203 Figure 2 1 3 Cellular modems with private IP addresses These modems can not be used at TCP UDP servers 110 4 1 155 However if for some reasons you can not do this and you need the modem to be the TCP UDP server please contact your network provider to update your data plan 2 1 3 Servers with Dynamic IP Having a public IP is one good thing as it allows the client to see the server and connect to it But the client also needs a fixed identification for this IP address es
17. ructions and support Note that you can not add more virtual serial ports than the maximum limit of your PC operating system Under Windows XP for example you can not have more than 255 serial ports 4 3 Virtual modems Virtual modems work in a similar manner as virtual serial ports except that they will offer an AT command interface to your application so that it can tell the modem which end point to reach It will be necessary Confidential the whole document is the sole property of Maestro Wireless Solutions Itd 16 3603 9 36 F 118 Connaught Road West Sheung Wan Hong Kong contact maestro wireless com maestro empowering wireless to replace the phone numbers list in your application with the IP addresses and port numbers of your new modems Using a virtual modem you will mostly need to use the Maestro modem in TCP server mode so that it can be called by the virtual modem If the Maestro modem is a TCP client it will establish the connection Make sure that your virtual modem application can support incoming connections in that case Virtual modems solution COM IP from Tactical software has been successfully tested with Maestro modems however any solution that support raw TCP connection should work as well Please refer to the documentation from the virtual modem supplier for setup instructions and support Confidential the whole document is the sole property of Maestro Wireless Solutions Itd 17 3603 9 36 F 118 Conn
18. stro 100evo and Maestro Heritage Maestro 100 CDMA and Maestro 100 TD do not support this function The Maestro Industrial can also establish such automatic connections but is not convered in this document When used in automatic connection mode the modem will automatically register on the GPRS or UMTS at startup and create a TCP or UDP socket As long as this socket is connecte to another end point usually a back end application the modem creates a bridge between the socket and its physical serial port every received byte is forwarded from the socket to the serial port and vice versa Automatic connection is a very popular feature of the Maestro modems that can give cellular Internet connec tivity to virtually any serial device even to those which have not been designed to work with modems Maestro Heritage 3G only Confidential the whole document is the sole property of Maestro Wireless Solutions Itd 3 3603 9 36 F 118 Connaught Road West Sheung Wan Hong Kong contact maestro wireless com ast empowering wireless Chapter 1 Use cases of automatic connection 1 1 Remote access to a serial device Few serial devices are designed to drive a modem and even fewer have the necessary PPP stack to establish a cellular data connection Nevertheless you may need a remote access to the device Be it an environmental sensor a industrial controller an I O unit or the console interface of a network router you can use the Maestr
19. t empowering wireless AUTOMATIC AND SELF RECOVERY CONNECTIONS ON SMARTPACK SMARTPACK Il AND SOFTOOLS TECHNICAL APPLICATION NOTE REVO 3 WWW MAESTRO WIRELESS COM EMAIL CONTACT MAESTRO WIRELESS COM TEL 852 2869 0688 FAx 852 2525 4701 ADDRESS ROOM 3603 3609 36 F 118 CONNAUGHT ROAD WEST SHEUNG WAN HONG KONG II IAS Sti C empowering wireless Revision history Rev Date Details Originated by 0 1 28 March 2011 First issue Pierre Emmanuel Surga 0 2 30 March 2011 Proof reading Wallace Lee 0 8 8 April 2011 Added notes on virtual modems Pierre Emmanuel Surga This manual is written without any warranty Maestro Wireless Solutions Ltd reserves the right to modify or improve the product and its accessories which can also be withdrawn without prior notice Besides our company stresses the fact that the performance of the product as well as accessories depends not only on the proper conditions of use but also on the environment around the places of use Maestro Wireless Solutions Ltd assumes no liability for damage incurred directly or indirectly from errors omissions or discrepancies between the modem and the manual Confidential the whole document is the sole property of Maestro Wireless Solutions Itd 1 3603 9 36 F 118 Connaught Road West Sheung Wan Hong Kong contact maestro wireless com empowering wireless Contents 1 Use cases of automatic connection 4 1 1 Remote ac
20. tor Baudrate 115200 Z dual band mode 900E extended 1800 MHz Format 8 data 1 stop k Save Band Selection P anty Please restart the modem to switch band Save Serial Port Be sure to keep this configuration in mind This will be required to reconnect to the modem after restart Figure 3 1 1 Configuring the serial port with the Maestro configuration tool 3 2 Configuring the GPRS connection It is then necessary to instruct the cellular modem how to connect to the GPRS network This is done by entering the APN APN username and APN password given by our service provider with the AT IPGPRS command Command Syntax AT IPGPRS 1 lt APN gt lt UserName gt lt Password gt Response Syntax IPGPRS 1 lt APN gt lt UserName gt lt Password gt Examples AT IPGPRS 1 ra internet a a AT IPGPRS 1 mySpecialAPN johnDoe 12345 Note that depending of the network operator and the subscription type APN username and password may be blank If you get an ERROR message when configuring the APN it may be because the value added function pack is not activated in your device You can check this with the following command AT VAFV This command will return the version of the Smartpack Smartpackll or Softools that is installed on your modem If this command returns an ERROR the function pack may not be activated Enter this command to reactivate it AT WOPEN 1 If you still can not configure the APN at
21. ure a TCP socket using AT IPTCP and AT AUTOTCP but if you are working in UDP mode you can follow the same guidelines only replacing these two commands by AT IPUDP and AT AUTOUDP 3 3 1 Entering the TCP UDP parameters The first command to type is AT IPTCP resp AT IPUDP Command Syntax AT IPTCP lt port gt lt mode gt lt address gt lt TxDelay gt Response Syntax IPTCP lt port gt lt mode gt lt address gt lt TxDelay gt Exemple Server AT IPTCP 6000 S 255 255 255 255 0 Client AT IPTCP 6000 C 110 4 1 221 0 Modem as server If the modem is a server the parameters are Port is the listening port The modem will accept incoming connections on this port only and once a client is connected it will establish a logical bridge between this port and its RS232 interface Mode must be set as S for server Confidential the whole document is the sole property of Maestro Wireless Solutions Itd 13 3603 9 36 F 118 Connaught Road West Sheung Wan Hong Kong contact maestro wireless com t empowering wireless Address is an IP address that can be used to filter incoming connections If it is set to 255 255 255 255 it will accept connections from any client If it is set to a specific IP address only this IP address can access the serial port TxDelay determines if there is time delay introduced before sending a TCP frame that has not been entirely filled with user data If it is
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