Using GPRS & 3G for remote connectivity

Many distributed IP surveillance systems require data to be sent to a central server in real-time. The data could be a hot-list match from an ANPR system, snapshots from a DVR or time and attendance information from access control systems. Live video from an IP video surveillance system is also a common requirement. Whatever the data type, a connection to the internet is essential to gain access to a centralised server.

Many field-based applications do not have access to a wired connection to the internet and this is where GPRS and 3G cellular technology can solve major connectivity problems. Cellular routers also allow connections from moving vehicles thanks to the 'roaming' capability inherent in mobile networks.

A DSL (broadband) router connects Ethernet devices to the internet via telephone wires. In a conceptually similar way, a cellular router connects Ethernet devices (IP cameras / DVRs / NVRs / access control systems) to the internet using the mobile telephone networks.

The diagram below shows the basic concept of a cellular connection as it could be applied to an IP video surveillance system. The PC sends data to the internet, through the service provider's APN (Access Point Name) and into the network of the service provider (eg Vodafone). Data is routed to the appropriate cell tower and delivered wirelessly over the last few 100s of meters to a cellular router. The router forwards IP datagrams to specific devices as required.

Cellular connectivity is conceptually quite simple - it can provide a serial or Ethernet cable the length and breadth of the globe. However, there are some limitations that installers and integrators must consider when designing remote connections.

Bandwidth
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 strength
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 a way behind in the UK with OFCOM driving for 80% coverage on all networks by the end of 2007. 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.

Cost
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.

The Future
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.

With many years of cellular integration experience, Amplicon's application engineers can help with system design and hardware selection - no need for costly consultants.

If you would like more information relating to our IP video surveillance system and IP CCTV system solutions, please call sales on 01273 570 220 or email security@amplicon.co.uk.