Routing IP packet data over GPRS wireless nets

GPRS technology is a standards-based packet overlay for existing Global System for Mobile (GSM) Communications networks that boosts data transfer rates to rates equivalent to the fastest analog wireline modems. GPRS thereby enables the deployment of next-generation mobile data applications, including wireless Internet access with customer-acceptable response times, always-on connectivity and enhanced voice and video communications. GPRS is based on GSM communication and will complement existing services such as circuit-switched cellular phone connections and the Short Message Service (SMS), which is limited to 160 characters per message, although messages can now be concatenated. Voice calls can be made simultaneously over GSM Communications - the world's mostly widely used wireless standard --while a data connection operates on GPRS depending on the phone class and type.

GPRS, known as 2.5G, is a significant step forward from 2G technology, which provides data transmission rates of roughly 9.6 kbits/second, far too slow for today's Internet-based, higher-bandwidth applications. GPRS uses the same technology foundation as Universal Mobile Telecommunications System (UMTS), also known as 3G, which will extend the bandwidth possible to 384 kbits/s for mobile and 2 Mbits/s for stationary endpoints. After sinking billions into 3G spectrum but having to wait several years before the infrastructure and handset technology is actually ready to use, operators worldwide are turning toward GPRS for several key benefits:

1) GPRS boosts data rates to up to 115 kbits/s, enabling new applications;

2) GPRS networks cost less than 3G networks;

3) GPRS moves the service providers and equipment manufacturers from circuit-switched to packet-switched technology (while 3G will just provide faster packet-switched performance);

4) GPRS enables operators to test-market which data applications customers will want and at what price, while offsetting ever-declining margins from commoditized wireless voice. GPRS indeed should serve as a testing ground for operators moving toward full 3G networks and services.

Given the impressive list of technical benefits, it is clear that the driving force behind GPRS's deployment is wireless operators' concerns for delivering a packet-switched wireless technology that can deliver the applications consumers want. Increasingly, these applications are tied to the Internet and hence to the delivery of IP packets — whether from e-mail, news services, instant messaging or Web browsing. Indeed, while GPRS services are just being rolled out, work is already under way to extend the usefulness of GPRS as a higher-speed packet delivery system by developing routing support to permit IP nodes using either IPv4 or IPv6 to seamlessly roam among IP subnetworks and media types. This new routing support is really a form of mobile IP and will bring transparency above the IP layer, ultimately allowing active TCP connections and UDP bindings across networks, including 802.11b, cellular and Bluetooth.

GPRS is a packet-based wireless communication service that promises two main advantages to mobile phone and computer users: data rates from 56 to 114 kbits/s and continuous (always-on) connection to the Internet. Theoretical maximum speeds of up to 171.2 kbits/s are achievable with GPRS using all eight time slots at the same time. This is about three times as fast as the data transmission speeds possible over today's fixed telecommunications networks (56-kbit/s analog modems) and 10 times as fast as current circuit-switched data services on GSM networks (9.6 kbits/s ). By allowing information to be transmitted more quickly, immediately and efficiently across the mobile network, GPRS may well be a relatively lower-cost mobile data service compared to SMS and circuit-switched data. Initial GPRS devices, however, are likely to support only four slots downstream (50 kbits/s) and one slot upstream (13 kbits/s). GPRS telephones will typically include Wireless Application Protocol (WAP) microbrowsers, but may also have connection options for external computers, using either cables or infrared connections. WAP to date has not lived up to its hype — the data rate is too slow for most users, the delay required to establish a dial-up connection is annoying and many handsets have inadequate display systems.

Immediacy is the second major advantage of GPRS and SMS when compared to circuit-switched data. The always-on feature is convenient for sending/receiving messages, e-mails, notifications and alerts, because there is no "dial up" waiting time to make a connection.

Enabling GPRS on a GSM network requires the addition of two core modules, the Gateway GPRS Service Node (GGSN) and the Serving GPRS Service Node (SGSN). A GGSN acts as a gateway between the GPRS network and public data networks such as IP and X.25. GGSNs also connect to other GPRS networks to facilitate GPRS roaming. The Serving GPRS Support Node (SGSN) provides packet routing to and from the SGSN service area for all users in that service area. In addition to adding multiple GPRS nodes and a GPRS backbone, some other technical changes need to be added to a GSM network to implement a GPRS service. These include

1) Packet control units often hosted in the basestation subsystems

2) Section mobility management to locate the GPRS Mobile Station,

3) A new air interface for packet traffic,

4) New security features such as ciphering

5) New GPRS-specific signaling.

Essentially, GPRS is a packet-switched overlay on the existing circuit-switched GSM network and therefore brings with it the efficiencies of a packet network. The design, however, was intentionally architected to make it easy for network operators to add packet technology to their existing infrastructure. Packet switching means that GPRS radio resources are used only when users are actually sending or receiving data. Rather than dedicating a radio channel to a mobile data user for a fixed period of time, the available radio resource can be concurrently shared between several users. Hence, large numbers of GPRS users can share the same bandwidth and be served from a single cell, analogous to the way many Ethernet users share a single network resource.

Because of the spectrum efficiency of GPRS, there is less need for operators to build in idle capacity used only in peak hours. GPRS therefore lets network operators maximize their network resources. GPRS also enables mobile Internet functionality by allowing interworking between the existing Internet and the new GPRS network. Any service used over the fixed Internet today will be available over the mobile network because of GPRS. Because it uses the same protocols, the GPRS network can be viewed as a subnetwork of the Internet with GPRS-capable mobile phones being viewed as mobile hosts. This means that each GPRS terminal can potentially have its own IP address and will be addressable as such.

The next stage for GPRS is even more interesting. Though GPRS was originally intended to be a data service operating parallel to voice services, standards groups are defining how it will be able to support voice services using Voice over IP (VoIP) protocols. Based on the Internet Session Initiation Protocol (SIP), the GPRS infrastructure could actually become the core network for 3G systems supporting a variety of multimedia services, including voice.

Many details must still be resolved before such networks are feasible, the biggest of which is quality of service (QoS). For multimedia services, a network with QoS will set and execute priorities of service levels to provide performance guarantees with respect to packet delay; jitter, which is related to the variation in packet delay; and packet loss.

While none of these parameters are crucial for normal data applications (file transfer and e-mail, for example), they are critical for IP voice and video. Just as with voice over the Internet, QoS standards and mechanisms are still evolving and will involve all handsets, servers, switches, and routers in the overall network system. Moreover, QoS mechanisms defined for wireless networks are different from those for wireline networks, due to the nature of the radio interface. And the two types of mechanisms must be reconciled. Nevertheless, an end-to-end QoS approach for multimedia over IP will enable many new kinds of applications and promises to reduce the cost of core networks for carriers. Concurrently, carriers must not lose sight of the fact that many customers will still see voice communications as the major reason for investing in wireless products and services at all.

A wide range of new, nonvoice corporate and consumer applications is enabled by nonvoice mobile services such as SMS and GPRS. Probably the most popular application will center on e-mail — both corporate-LAN-based as well as Internet-based. With GPRS, e-mail can arrive with a "beep" alert since the service is always on. A similar application could be receipt of information services such as stock quotes, weather and news and sports scores. These information services would be largely one-way data transmissions, with the user subscribing to a set list of services. Chat services, rather like instant messaging, will also be possible with GPRS-enabled networks and handsets, at least in a point-to-point configuration.

Web browsing via a mobile Internet appliance, PDA or cell phone is another application likely to be popular but it will require more than just GPRS-enabled high speed data. (Current Web browsing using circuit-switched data is too slow for most consumers.) Web browsing also requires Web sites and information configured appropriately for the receiving hardware and handsets with larger, brighter screens. Handsets with better imaging capabilities will also enable still and even moving image transfers. Forward-looking planners in the GPRS and wireless industries are also looking at other novel applications such as home automation, something that will be possible when many home devices are attached to the Internet. But no one seems to know yet what demand will be for these services, or whether consumers will pay an appropriate price.