GPRS / 3G is the bottleneck of any IP based connection. Whilst a wired Ethernet connection will happily transfer raw data at 100Mbps, GPRS connections can offer as little as 20kbps. The theoretical limit of 171kbps is never realised on modern networks - 50kbps download and 25kbps upload is the typical data transfer rate available.
If your application needs greater throughput 3G (UMTS) networks offer a high bandwidth solution - 384kbps download and 64kbps upload. A symmetric 384kbps down and 384kbps up has recently become available, contact Amplicon's sales team for details.
Mobile terminated connections
Most software that is supplied with Ethernet devices operates as a client application. The Ethernet device acts as a server listening for an incoming connection. This means that the PC must have a route to the target IP address of the device. As standard, GPRS / 3G cannot provide this. Mobile devices lease a private DHCP IP address from the mobile network to enable communications. Because the IP address is private, the device is not visible on the public internet and end-to-end communications cannot take place from your office / home PC to the device.
There are a number of workarounds to this problem and the most popular is to obtain a SIM card with a static public IP address. This effectively means that your Ethernet device is visible on the internet and can be accessed from anywhere in the world. Firewall and authentication measures provide network security. Amplicon can provide advice on solutions for mobile terminated applications including static IP SIMS and NAT-traversal capable VPN connections.
Signal coverage provided by mobile networks is now well established all over the world. In the UK, operators claim up to 99% GSM/GPRS coverage. The figure quoted is always the 'population' coverage and not the 'geographical' coverage - clearly the marketing department had some influence in the figures we see! 3G is some way behind in the UK with coverage of nearly 80% increasing year on year. City centres are the first to benefit from 3G coverage and, fortunately for the security market, this is where there is the most requirement for an IPCCTV system.
It is easy to forget that every SIM card in a system will generate some degree of cost. In 'always-on' applications, just keeping the network connection alive (idle TCP connections are terminated by network operators after a set period) will cost money. Specialist network operators can offer multiple SIMs on a single contract making system management easier and airtime subscriptions more cost-effective. 'All you can eat' tariffs on 3G networks are the most popular option but keep an eye out for reasonable usage policies.
Despite the handful of stumbling-blocks associated with GPRS, 3G and other IP based cellular connectivity solutions, the M2M market is expected to enter a substantial growth phase between 2006 and 2011. This will be driven by the new generation of high-bandwidth cellular protocols such as 3G (UMTS) and HSDPA (Super 3G).
IP-based cellular routers follow the same basic principles regardless of which wireless technology is used. To invest time now understanding the principles of GPRS/3G would not be wasted, as the concepts for remote cellular access are the same. Get your wireless scheme up and running now, gain the competitive advantage that it brings to your business and seamlessly upgrade to high-speed networks once the coverage is in place.