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Home > Support > FAQs > GPRS FAQs
GPRS Technology, Benefits and Devices
I'm not clear on GSM and GPRS technologies. Can you explain the difference? 
(open topic page)

GSM (Global System for Mobile Communication) is the underlying digital cellular technology, including radio interfaces and network architecture. GPRS (General Packet Radio Service) is a packet data service that uses the same radio link, but adds new infrastructure elements to provide data capabilities. All GSM networks deployed today include GPRS and are software upgradeable to EDGE (Enhanced Data rate for Global Evolution).

Updated: 10/11/2011 | Created: 04/14/2010
There seem to be so many different platforms. How do I choose the best one for my application?
(open topic page)

The beauty of GPRS is that so many vendors have developed multiple types of devices. Based on your application, a PC card modem, GPRS capable mobile telephone, or PDA device will make the most sense. Once you have narrowed it down to one of these, you can compare the features of the various products, such as number of radio bands they support, number of time slots they use, tethering options, and so forth.

Updated: 10/11/2011 | Created: 04/14/2010
Applications Software, Communications Protocols
What documentation do you have available to guide developers on wireless application development?
(open topic page)

Plenty. Browse the AT&T Developer Program Web site to find a wide range of available information. We've gathered information, documentation, and/or tools on all of the following topics: GSM/GPRS network information and performance, application development considerations, IP addressing, security, Java, messaging, WAP, mark-up languages, billing platforms, and devices such as phones, modems, and BlackBerry handhelds and more.

Updated: 10/11/2011 | Created: 04/14/2010
How do I figure out whether my application is sufficiently optimized for wireless networking or not?
(open topic page)

The easiest way is to test it over a dial-up modem connection as a baseline. If your application works OK, chances are good that it will work fine with GPRS. Next, for general throughput and responsiveness, try the application in a stable environment with a good radio signal. Finally, for reliability, test your application in the representative environment in which it will be used. If mobile, try it while riding in a car or train, as this is a true stress test.

Updated: 10/11/2011 | Created: 04/14/2010
Can I push data to my mobile device?
(open topic page)

Yes. However, there is one item to consider, which is that AT&T's wireless network (not GPRS technology itself) protects against unwanted packets being directed at a mobile device. So all communications must be initiated by the mobile device, and any packets that come back must be associated with outgoing communications. With a custom Access Point Name(APN) and a Fixed-End Connection, however, this restriction can be lifted, to enable mobile terminated communications. You will want to learn more about custom APNs.

Updated: 10/11/2011 | Created: 04/14/2010
Can you expand on the pros/cons of TCP versus UDP?
(open topic page)

Both work with GPRS. The thing to keep in mind is that TCP (Transmission Control Protocol) provides services such as reliability, reordering of out-of-sequence packets, and congestion avoidance that UDP (User Datagram Protocol) does not. With UDP, if your data is critical, some higher level must take care of these items. The problem with TCP, however, is that it is not optimized for wireless. It's not bad, but it's not optimal.

That's why protocols such as WAP have their own wireless transport. Many middleware companies that specialize in wireless develop their own transports. But a reliable transport is not a trivial undertaking. In general, TCP makes most sense if you need compatibility with existing applications, have a smaller-size deployment, or want to get up and running as quickly as possible. In contrast, if you have a major deployment that must be robust over all wireless operating conditions, than a UDP approach may make more sense. Just realize you'll either need to use middleware or develop your own transport protocols.

Updated: 10/11/2011 | Created: 04/14/2010
Networking and Security
What resources do you have that explain networking and security?
(open topic page)

The AT&T Developer program webside provides a wide range of information on networking and security . Topics include IP Address Management , Packet Data Protocol Contexts, Access Point Names , Roaming , and Fixed-End Connections , among others. The GPRS overview discusses GPRS network security provisions, including encryption, which most developers need to know.

Updated: 10/11/2011 | Created: 04/14/2010
How long does a PDP context last?
(open topic page)

A Packet Data Protocol (PDP) context is the data session that assigns an IP address to a mobile device and allows it to send and receive IP packets. Learn more about PDP contexts.

Updated: 10/11/2011 | Created: 04/14/2010
When does my IP address change?
(open topic page)

The IP address stays the same for the period of the PDP context. With a new PDP context, the IP address is likely to change. Learn more about PDP contexts and IP Address Management.

Updated: 10/11/2011 | Created: 04/14/2010
How do I send a packet to a mobile device or a specific IP address?
(open topic page)

Easy. GPRS is a seamless extension of the Internet once the mobile device has activated a context, it is reachable from any Internet host in the world. GSM/GPRS uses dynamic IP addressing. Learn more about IP Address Management.

Updated: 10/11/2011 | Created: 04/14/2010
If a device is not powered on, how long will messages & packets be stored before they're discarded?
(open topic page)

This depends on the type of data traffic. IP packets are not stored, so if the mobile device is off or out of range, the packets are discarded. Short Messaging Service (SMS) is called a reliable service because the network makes sure that messages are delivered reliably, which includes correcting any errors during transmission, and storing the messages in the network for a limited time if the device is unable to receive them. This can occur if the device is off, or if it has used up all its available message memory.

Updated: 10/11/2011 | Created: 04/15/2010
When do I use IPv6 and when do I use IPv4?
(open topic page)

Current GPRS networks are all based on IP version 4. Work has begun within AT&T and 3G Americas to add support for IPv6. As the number of devices capable of IPv6 increases, developers should strongly consider including support for IPv6 within their applications.

Updated: 10/11/2011 | Created: 04/15/2010
I've heard that wireless networks are not secure. What's up with that?
(open topic page)

There has been a lot of press about the security weaknesses of wireless local area networks (LANs). This is indeed a problem, though there are remedies in process, such as signed certificates for mobile applications. GPRS, however, uses completely different security mechanisms that do not have the same vulnerabilities as wireless LANs, and overall GPRS is much more secure.

Updated: 09/02/2011 | Created: 04/15/2010
GPRS security is encrypted at 64 bits. How can we implement a higher level of security?
(open topic page)

The GPRS airlink is encrypted at 64 bits. This 64-bit encryption is part of the GPRS specification as mandated by the Third Generation Partnership Project (3GPP). It would take equipment that is extremely sophisticated and not commercially available to eavesdrop on a GPRS session. That said, Content Providers transmitting very sensitive data should consider employing application level security such as a VPN, Secure Socket Layer (SSL), or another option. There are a number of third party middleware solutions available that can help achieve this level of security.

Updated: 09/02/2011 | Created: 04/15/2010
Are public, fixed IP addresses available?
(open topic page)

A range of public addresses are available from AT&T. Learn more in IP Address Management.

Updated: 09/02/2011 | Created: 04/15/2010
How do I ensure that the IP address I'm using will pass my company firewall?
(open topic page)

You can use a custom APN to specify a range of IP addresses to be used. If you need to use public IP addresses, you have two options:

  • Provide the public IP addresses yourself. You would provide AT&T a range from your pool of Public IP addresses.
  • Use the AT&T public IP address pool. AT&T would provide a range based on the number of IP addresses needed. Learn more about IP Address Management.
Updated: 09/02/2011 | Created: 04/15/2010
Are static IP addresses available for GPRS?
(open topic page)

Static IP addresses in the truest form are not offered in GPRS; instead, AT&T utilizes a persistent IP methodology where the IP address does not change from data session to data session. To summarize the distinction between static and persistent IP addresses:

  • Static. Places a hard-coded IP address in the device.
  • Persistent. Uses a network-driven solution in which the same IP is assigned to the device for each session.
Updated: 10/11/2011 | Created: 06/02/2010
Value-Added Services, Evolution
How do I send an SMS message to my device?
(open topic page)

AT&T's wireless network provides a number of messaging approaches. Which one you should use depends on the type of message you are sending and the business intent (i.e., consumer or enterprise messaging).

Updated: 09/02/2011 | Created: 04/15/2010
How does my device know when an SMS message arrives?
(open topic page)

The device (for example, a modem) knows when it has received an SMS message because it is engaged in the transfer of the message. The real question is how it notifies users or applications. With a phone, this might be a beep. With a modem, this might be a message sent to an application, or the application can query the modem for the SMS information.

Updated: 09/02/2011 | Created: 04/15/2010
What differences and changes need to be made to applications to upgrade from GPRS and EDGE to UMTS?
(open topic page)

From an application point of view, EDGE is almost identical to GPRS, and nearly any application developed for GPRS will work with EDGE. Universal Mobile Telecommunications System (UMTS) also uses the GPRS framework for providing data service, so migration of applications should be very straightforward.

Updated: 09/02/2011 | Created: 04/19/2010