THE FORGOTTEN OPTION
When energy companies are putting together IT solutions for their offshore operations, the network choice typically comes down to desire to be on a dedicated versus shared network, writes Andrew Lucas, chief technology officer at Harris CapRock Communicat
Harris CapRock’s CTO, Andy Lucas presents a case for TDMA.
Offshore communications have historically been split over two types of networks, each with their own perceived benefits and disadvantages. A time division multiple access ( TDMA) network is a channel access method that allows several users to share the same frequency channel by dividing the signal into different time slots. In a single channel per carrier ( SCPC) system, users are assigned a single signal at a given frequency and bandwidth. Traditionally, TDMA solutions were deployed as contended services with guaranteed committed information rates ( CIRs) and viewed as shared networks. A contended service offers users of the network in remote, offshore environments a minimum statistically guaranteed contention ratio. The contention ratio is the ratio of the potential maximum demand to the actual bandwidth. The higher the contention ratio, the greater the number of users that may try to use the actual bandwidth at any one time, and therefore lower the effective bandwidth offered - especially at peak times. With a service level agreement ( SLA) that includes contended CIRs, offshore operators can expect a contention ratio of four to one with peaks of usage of up to the maximum bandwidth, while uncontended services deliver a one- to- one ratio. As an example, an offshore site receiving 1 Megabit per second ( Mbps) of traffic, over a contended TDMA network, may have access to only 250 Kilobits per second at a given time due to a four- to- one contention rate. However if that same site were receiving 1 Mbps of traffic over an uncontended TDMA network, it would have access to the full 1 Mbps at all times because it has a one- to- one contention rate. Over time SCPC’s reputation as a private network developed into the preferred choice within the offshore community as it is natively uncontended - despite the fact that it is not as flexible for burst transmissions, such as satellite internet access which is needed with more and more frequency.
Today, investing in satellite communications technology enables companies who operate offshore to access the maximum amount of resources available to meet their daily, hourly and even by- the- minute needs.
However, offshore operators may have forgotten that they have another choice in quality of communications delivery in the form of uncontended TDMA network services. In fact, TDMA is capable of changing requirements in remote- to- hub direction much faster than can be done on an SCPC network. Consequently it performs better for burst transmissions that temporarily allocate more bandwidth when needed. With more networks around the world, TDMA also provides the necessary flexibility and worldwide coverage to support migrations between regions which is a key factor given the complexity of offshore communications. The way scenarios change as a drillship, for example, moves around the world or even just a few hundred miles makes the reliability of mobile connectivity a must. In some situations, the need for an SCPC network solution may be unavoidable due to very high- bandwidth demands combined with lower latency at offshore sites where criticality is elevated. Yet the majority of offshore operators’ needs are compatible with TDMA’s capability of supporting up to 20 Mbps up and 10 Mbps down. Today, investing in satellite communications technology enables companies who operate offshore to access the maximum amount of resources available to meet their daily, hourly and even by- the- minute needs. Satellite technology has grown tremendously in the last 50 years; and with the continued advancements, tasks that were once unthinkable and improbable, such as video conferencing with individuals thousands of miles out at sea, can occur every day.
At the end of the contract, what’s most important is that IT decision- makers for oil and gas exploration and production companies are informed about all of their communications options; further that they are prepared to hold their service providers accountable. Fully- managed service providers should be able to guarantee an uncontended CIR based on an operator’s unique needs whether they choose SCPC or TDMA. What matters most is a communications partner’s commitment to the SLA and Quality of Service, not the network.
Andy Lucas, CTO at Harris CapRock Communications