by Roland Schaller
We have experienced it all, as far as Internet access is concerned hotels, airports, train stations, cars with cellular modems, even in planes Internet access has become a crucial commodity. We cannot live without the Internet anymore, even for just a few hours. For business professionals, travelling without online access is simply unacceptable .
A last challenge for Internet access was obtaining connectivity in a high-speed train running at 200 Miles per Hour just for informational purposes, thats 320 km/h, which is a common cruising speed for bullet trains in Europe these days. Such posed unique technical challenges. Enabling Internet access to train users offered the following options:
Cellular Wireless high-speed Internet access via 3G or CDMA technologies this technology is mostly available in countries where high-speed trains are deployed. However, the amount of work required to cover hundreds of kilometers of railway networks, often located in remote rural areas where Internet access is not much needed, does not make it economically feasible for the cellular providers to invest in such infrastructure. Bandwidth obtained using this technology is poor and as unsuitable as a backbone for the hundreds of users in a train attempting to access the Internet. Furthermore the high travel speeds pose some severe constraints on cellular infrastructure in terms of Doppler Effect and Cell Handover. Another commercial problem for cellular access is that data subscriptions are usually quite expensive when used outside of the home operators coverage, such as when crossing borders, which is very frequent in Europe where a train can easily travel through as many as three or four countries during the course of its journey.
Wi-Fi access is potentially interesting. Experiments are underway to cover lengthy track segments with dedicated Wi-Fi access, leaky cable technology (designed to radiate a portion of a signal along its entire length the longer the cable, the less uniform the connection due to signal dispersal), and also WiMAX. These technologies are too immature for robust, daily service and use. Additionally, Wi-Fi does not behave well at high speeds.
Of course, satellite access has the major advantage of providing high bitrates (up to a few Mbit/s per train) while being relatively immune to the high speed of the train, but does require a clear view of the sky.
Combining these three technologies enables seamless access to the Internet and takes advantage of the strengths of each technology:
- Satellite access when satellite is visible, i.e., no tunnels or buildings blocking the link
- Wi-Fi access when the train is approaching, standing in, or leaving the train station
- Cellular access while in dense urban environments or in tunnels
Wi-Fi access will always be favored over everything else when Wi-Fi is not available, satellite Internet will be used when satellite access is not available, the system will fall back on cellular access. For cell access, there are multiple modems installed, with subscriptions from providers in the different countries traveled through in order to access the best available data tariff for each country.
This diagram illustrates the communication principles:
All seems quite obvious from a principle point of view. However, there are some serious implementation challenges that need to be solved:
- When switching from one technology to the other, the IP addressing space changes, as other operators are brought into the mix There can be a short interruptions in traffic flow
- Open data connections will reset due to changed IP addressing
- Different links have very different characteristics in terms of bandwidth, delay, packet loss, and so on
The number of simultaneous users per train, when high enough, can saturate the link with the total user traffic
- Some users will attempt to consume more bandwidth, either consciously (watching video, downloading, peer-to-peer, etc), or unconsciously (viruses, Trojans and other Malware)
First, the extreme data compression, named WANcompress®, is used to reduce the amount of data sent over the data link, independently of which link is currently in use. WANcompress stores all IP data streams at the sending and receiving end, while at the sending end, the data is indexed and searched in real-time. This allows data to be found that has been already transmitted between a particular train and the ground (and vice-versa) to prevent retransmission a pointer to the data is sent instead. This particular technology offers a bandwidth savings of 30 to 40 percent.
Protocol and application enhancements such as TCP acceleration, HTTP Caching and Prefetching, DNS caching, further enhance the user experience and decrease data volume. For example, UDcasts TCP ACK suppression technology reduces the bandwidth on the return channel, allowing the use of freed up bandwidth for more valuable data.
The UDcast Virtual Private Network (VPN) function performs two functions in this train context:
In a train environment, like any other vehicular environment, there are specific environmental concerns such as temperature, shocks and vibrations, as well as regulatory and safety constraints, which have an impact on the hardware that can be used in the train.
The UDcast software has been ported on an existing train-qualified hardware with the required Railway Certifications, and it could as well be easily integrated on any other hardware on different form factors for marine, road, or aeronautical transport use.
Further advantages of the UDcast open service platform are modular, meaning that specific features can be implemented to accommodate user needs. In example, hardware with very limited processing power. The UDcast technology can also be extended with additional features that could include, but are not limited to, GPS fleet tracking, video surveillance, telemetry, remote maintenance, least-cost routing, and so on.
This photo illustrates the complete equipment rack, mounted in one of the wagons, and feeding the entire train, allowing Wi-Fi coverage through all of the wagons.
Internet access in trains is currently deployed on some routes where there is a long travel time, typically a few hours the technology is gradually being extended to shorter routes and commuter trains.
In addition to the service for the railway passenger, the railway operators themselves are starting to use the same Internet access for their internal use. This would include non-vital train communication, on-board passenger information, video surveillance, and digital signage systems, just to name a few.
All these technologies make Internet access truly mobile and covers one of the few last white spots, much to the enjoyment of the traveller, or to the sadness of the business traveller who sees there is no excuse anymore for being unproductive on a train if you are on an Internet-enabled train right now, get back to work and stop gazing through the window to watch the cows watching you zip by at 200 Miles per Hour.