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

OffComm News - - CONTENTS -

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.

An­other op­tion

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

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