Technical introduction to GSM modem technology

FACTS AND APPLICATIONS OF GSM/GPRS MODEM

The GSM/GPRS Modem comes with a serial interface through which the modem can be controlled using AT command interface. An antenna and a power adapter are provided.
The basic segregation of working of the modem is as under:
� Voice calls
� SMS
� GSM Data calls
� GPRS

Voice calls:Voice calls are not an application area to be targeted. In future if interfaces like a microphone and speaker are provided for some applications then this can be considered.

短信:SMS is an area where the modem can be used to provide features like:
� Pre-stored SMS transmission
� These SMS can be transmitted on certain trigger events in an automation system
� SMS can also be used in areas where small text information has to be sent. The transmitter can be an automation system or machines like vending machines, collection machines or applications like positioning systems where the navigator keeps on sending SMS at particular time intervals
SMS可以是GSM数据调用或GPRS服务的解决方案

GSM Data Calls:可以使用此调制解调器进行数据调用。可以将数据调用转到普通的PSTN调制解调器/电话线(甚至接收)。基本上,数据调用是在两个单元之间发送/接收数据流的PC或嵌入式设备。数据调用比SMS的优点是,双方都能够通过其终端发送/接收数据。

Applications of GSM GPRS Modems GSM Guwahati GSM Gurgaon GSM Haridwar GSM Hyderabad GSM Indore GSM Jaisalmer GSM Jodhpur GSM Kanyakumari GSM Kashmir GSM Khajuraho GSM Kodaikanal GSM Kolkata GSM Lonavala GSM Lucknow GSM Ludhiana GSM Madurai GSM Manali GSM Mumbai GSM Mussoorie GSM Munnar GSM Mysore GSM Nainital GSM Ooty GSM Patna GSM Pune GSM Pushkar GSM Rajkot GSM Shimla GSM Udaipur GSM Varanasi GPRS INDIA GLOBAL POSITIONING SYSTEM INDIA GPS (AVL) Automatic Vehicle Location(AVM)Automatic Vehicle Monitoring with Google yahoo MSN Mps.

Some points to be remembered in case of data calls:
� The data call service doesn�t come with a normal SIM which is purchased but has to be requested with the service provider (say Airtel).
�在激活数据/传真服务你的箴言ided with two separate numbers i.e. the Data call number and the Fax service number.
�使用电路交换数据连接建立数据调用。
� Right now the speed at which data can be transmitted is 9.6 kbps.
� The modem supports speeds up to 14.4 kbps but the provider give a maximum data rate of 9.6 kbps during GSM data call.
� Technologies like HSCSD (high Speed Circuit Switched Data) will improve drastically the data rates, but still in pipeline.

有关GSM数据调用的应用程序和事实:

�在PC上或嵌入式环境中具有串行端口通信的设备
� Devices that want to communicate with a remote server for data transfer
�数据传输的能力可以帮助减少设备的处理要求
� The basic aim is to provide a wireless solution keeping the existing firmware intact
� The clients firmware continues to work without any modifications (no changes in the existing software required)
�GSM数据调用可以是一个很好的解决方案,必须将数据从手持设备传输到中央服务器
� The interface on two sides can be between PC�s as well as embedded devices

Calls can be established by the terminals at either side to start data calls
�在建立呼叫后,调制解调器在数据传输期间保持透明。
� Call establishment utility to be provided in case PC terminals
� Call establishment to be automated in case of embedded terminals. GSM converter can be an option where intelligence of establishing calls has to be put in case of embedded devices. Concept of GSM converter is discussed later in this document

使用GSM数据调用拨号网络:Dial up networking is a utility available with Windows through a person can dial the Data call number of this modem from any PC and share the file system on either PC�s. This can be a good utility where both terminals are PC based. Sharing the file system remotely enables monitoring of devices remotely. Thus the modem can act as a piece of device which acts as a spy in the system. Can be a good debugging utility wherein a person can configure/monitor a remote PC based system and even rectify it. Some companies do sell their products with a GSM modem inside it just for this handy feature which allows them to configure the machines sitting anywhere in the world. Since the connection can have upper layer protocols like TCP/IP in this connection it becomes more reliable and useful.

GSM Converter:GSM converter will be an add-on device to be attached between a terminal which wants data transfer and the GSM modem. This GSM converter will take care of call establishment where the embedded device cannot make a call. The converter will remain transparent through-out the call once call is established. The GSM converter will be a very small piece of hardware possibly embedded inside the cable itself.

GPRS:该调制解调器可用于建立GPRS连接。连接后,调制解调器可用于设备的Internet连接。

Key-Points in GPRS:

� The PC/Embedded device dials the Service Provider (say Airtel)
� Data is routed through the ISP (Internet Service Provider)
面向�GPRS基本上是包的服务
� Protocols like TCP/IP are inherent characteristics in GPRS
�必须在此处就IP地址进行交谈,而不是电话号码
� The implementation is more useful where PC�s want to communicate over GPRS
� Although data transfer is done from embedded devices too but with reduced features
� Since you are charged either on monthly flat rates or amount of data transfer taking place GPRS is anyday a cheaper option as compared to GSM data call. But GPRS services are not available everywhere.
� The data rate rates in GPRS can go upto 40 kbps

Application areas in GPRS using this Modem:

� Applications where mobile devices want to upload data to a central server
� Monitoring devices that are continuously logged on to the server. Since you are charged for the amount of data transfer hence a continuous connection can be maintained.
�虚拟专用网络
� Radius servers

虚拟专用网络

虚拟专用网络(VPN)是一个专用网络的扩展,该网络涵盖了跨越Internet等共享或公共网络的链接。VPN使您能够以模拟点对点私有链接的属性的方式在共享或公共互联网工作的两台计算机之间发送数据。配置和创建虚拟专用网络的行为称为虚拟专用网络。
To emulate a point-to-point link, data is encapsulated, or wrapped, with a header that provides routing information allowing it to traverse the shared or public transit internet work to reach its endpoint. To emulate a private link, the data being sent is encrypted for confidentiality. Packets that are intercepted on the shared or public network are indecipherable without the encryption keys. The portion of the connection in which the private data is encapsulated is known as the tunnel. The portion of the connection in which the private data is encrypted is known as the virtual private network (VPN) connection.

Figure 1: Virtual private network connection

VPN connections allow users working at home or on the road to connect in a secure fashion to a remote organization server using the routing infrastructure provided by a public internet work (such as the Internet). From the user�s perspective, the VPN connection is a point-to-point connection between the user�s computer and an organization server. The nature of the intermediate internet work is irrelevant to the user because it appears as if the data is being sent over a dedicated private link.
VPN技术还允许公司通过公共互联网工作(例如互联网)连接到分支机构或其他公司,同时保持安全的通信。逻辑上,Internet上的VPN连接作为大型网络(WAN)链接在网站之间运行。
在这两种情况下,用户出现在互联网工作中的安全连接,作为一种私人网络通信。
VPN technology is designed to address issues surrounding the current business trend toward increased telecommuting and widely distributed global operations, where workers must be able to connect to central resources and must be able to communicate with one another.
为了使员工能够连接到组织计算资源,无论其位置如何,公司都必须部署可扩展的远程访问解决方案。通常,公司选择部门解决方案,其中内部信息系统部门负责购买,安装和维护组织调制解调器池和专用网络基础架构;或者他们选择一个增值网络(VAN)解决方案,在那里他们向外包公司支付购买,安装和维护调制解调器池和电信基础架构。
Neither of these solutions provides the necessary scalability, in terms of cost, flexible administration, and demand for connections. Therefore, it makes sense to replace the modem pools and private network infrastructure with a less expensive solution based on Internet technology so that the business can focus on its core competencies. With an Internet solution, a few Internet connections through Internet service providers (ISPs) and VPN server computers can serve the remote networking needs of hundreds or thousands of remote clients and branch offices.
Common Uses of VPNs
接下来的几节更详细地描述了更常见的VPN配置。
Remote Access Over the Internet
VPNs provide remote access to organization resources over the public Internet, while maintaining privacy of information. Figure 2 shows a VPN connection used to connect a remote access client to an organization intranet. This is known as a remote access VPN connection.

图2:使用VPN连接将远程访问客户端连接到组织Intranet

用户拨打本地ISP,而不是向组织或外包网络访问服务器(NAS)拨打组织或外包网络访问服务器(NAS)。使用与本地ISP的连接,VPN客户端在远程访问计算机与组织VPN服务器之间创建VPN连接。
Connecting Networks Over the Internet
There are two methods for using VPNs to connect local area networks at remote sites:
� Using dedicated lines to connect a branch office to an organization LAN.
例如,分支机构和公司中心路由器都可以使用本地专用电路和本地ISP连接到Internet,而不是使用分支机构和公司中心之间的昂贵长距离专用电路。VPN软件使用本地ISP连接和Internet在分支机构路由器和公司中心路由器之间创建虚拟专用网络。
�使用拨号线将分支机构连接到Internet。
分支机构的路由器可以打电话给当地的ISP,而不是在分支机构设有路由器在分支机构或向公司或外包的NAS打电话。VPN客户端使用与本地ISP的连接来在分支机构路由器和公司中心路由器之间创建VPN连接。这被称为站点对站点的VPN连接。

图3:使用VPN连接连接两个远程站点

在这两种情况下,将分支机构和公司办公室连接到互联网的设施都是本地的。充当VPN服务器的公司中心路由器必须连接到具有专用行的本地ISP。该VPN服务器必须每天24小时收听传入的VPN流量。
Connecting Computers Over an Intranet
In some organization internet works, the departmental data is so sensitive that the department�s LAN is physically disconnected from the rest of the organization internet work. Although this protects the department�s confidential information, it creates information accessibility problems for those users not physically connected to the separate LAN.

Indian cities GPRS Agra, GPRS Ahmedabad, GPRS Ajmer, GPRS Allahabad, GPRS Amritsar, GPRS Aurangabad, GPRS Bangalore, GPRS Bharatpur, GPRS Bhopal, GPRS Bikaner, GPRS Calicut, GPRS Chandigarh, GPRS Chennai Madras, GPRS Cochin-Kochi, GPRS Coimbatore, GPRS Darjeeling, GPRS Dehradun, GPRS Gangtok, GPRS Guwahati, GPRS Gurgaon, GPRS Haridwar, GPRS Hyderabad, GPRS Indore, GPRS Jaisalmer, GPRS Jodhpur, GPRS Kanyakumari, GPRS Kashmir, GPRS Khajuraho, GPRS Kodaikanal, GPRS Kolkata, GPRS Lonavala, GPRS Lucknow, GPRS Ludhiana, GPRS Madurai, GPRS Manali, GPRS Mumbai, GPRS Mussoorie, GPRS Munnar, GPRS Mysore, GPRS Nainital, GPRS Ooty, GPRS Patna, GPRS Pune, GPRS Pushkar, GPRS Rajkot, GPRS Shimla, GPRS Udaipur, GPRS Varanasi,GSM and USA states GSM Alabama, GSM Alaska, GSM Arizona, GSM Arkansas, GSM California, GSM Colorado, GSM Connecticut, GSM Delaware, GSM Columbia, GSM Florida, GSM Georgia, GSM

Figure 4: Using a VPN connection to connect to a secured or hidden network

vpn允许部门�年代局域网物理connected to the organization internet work but separated by a VPN server. The VPN server is not acting as a router between the organization internet work and the department LAN. A router would connect the two networks, allowing everyone access to the sensitive LAN. By using a VPN server, the network administrator can ensure that only those users on the organization internet work who have appropriate credentials (based on a need-to-know policy within the company) can establish a VPN connection with the VPN server and gain access to the protected resources of the department. Additionally, all communication across the VPN can be encrypted for data confidentiality. Those users who do not have the proper credentials cannot view the department LAN.

RADIUS:
The Remote Authentication Dial-in User Service (RADIUS) protocol is a popular method for managing remote user authentication and authorization. RADIUS is a lightweight, UDP-based protocol. RADIUS servers can be located anywhere on the Internet and provide authentication (including PPP PAP, CHAP, MS-CHAP, MS-CHAP v2, and EAP) and authorization for access servers such as NASes and VPN servers.
In addition, RADIUS servers can provide a proxy service to forward authentication requests to distant RADIUS servers. For example, many ISPs have agreements to allow roaming subscribers to use local services from the nearest ISP for dial-up access to the Internet. These roaming alliances take advantage of the RADIUS proxy service. If an ISP recognizes a user name as being a subscriber to a remote network, the ISP uses a RADIUS proxy to forward the access request to the appropriate network.
Windows Server 2003 includes a RADIUS server and proxy with the Internet Authentication Service (IAS); an optional Windows networking component installed using Control Panel-Network.

NOTE:

1.使用VPN和Radius Technologies等GPR的领域的可能性很丰富,必须被发现。
Future documents will try to keep you updated about these trends.
2. Similarly other areas of applications will be documented as early as possible
3.请在此文档上提出您的建议。

Send SMS using AT commands

Some advanced GSM modems like WaveCom and Multitech, support the SMS text mode. This mode allows you to send SMS messages using AT commands, without the need to encode the binairy PDU field of the SMS first. This is done by the GSM modem

Check if your GSM phone or modem supports SMS text mode

To check if your modem supports this text mode, you can try the following command:

at+cmgf = 1

If the modem responds with "OK" this mode is supported. Please note that using this mode it is only possible to send simple text messages. It is not possible to send multipart, Unicode, data and other types of messages.

Hawaii, GSM Idaho, GSM Illinois, GSM Indiana, GSM Iowa, GSM Kansas, GSM Kentucky, GSM Louisiana, GSM Maine, GSM Maryland, GSM Massachusetts, GSM Michigan, GSM Minnesota, GSM Mississippi, GSM Missouri, GSM Montana, GSM Nebraska, GSM Nevada, GSM New Hampshire, GSM New Jersey, GSM New Mexico, GSM New York, GSM North Carolina, GSM North Dakota, GSM Ohio, GSM Oklahoma, GSM Oregon, GSM Pennsylvania, GSM Rhode Island, GSM South Carolina, GSM South Dakota, GSM Tennessee, GSM Texas, GSM Utah, GSM Vermont, GSM Virginia, GSM Washington, GSM West Virginia, GSM Wisconsin, GSM Wyoming,GPRS and USA states GPRS Alabama, GPRS Alaska, GPRS Arizona, GPRS Arkansas, GPRS California, GPRS Colorado, GPRS Connecticut, GPRS Delaware, GPRS Columbia, GPRS Florida, GPRS Georgia, GPRS Hawaii, GPRS Idaho, GPRS Illinois, GPRS Indiana, GPRS Iowa, GPRS Kansas, GPRS Kentucky, GPRS Louisiana, GPRS Maine, GPRS Maryland, GPRS Massachusetts, GPRS Michigan, GPRS Minnesota, GPRS Mississippi, GPRS Missouri, GPRS Montana, GPRS Nebraska, GPRS Nevada, GPRS New Hampshire, GPRS New Jersey, GPRS New Mexico, GPRS New York, GPRS North Carolina, GPRS North Dakota, GPRS Ohio, GPRS Oklahoma, GPRS Oregon, GPRS

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