Ex­plor­ing satel­lite for de­ploy­ing real- time net­work O& G ser­vices

OffComm News - - CONTENTS - By Alexander Ben­itez, Se­nior Sci­en­tist for ComSource Inc., a Globecomm com­pany.

by Alexander Ben­itez, se­nior sci­en­tist, ComSource

In to­day’s hy­per- con­nected world, high band­width, low la­tency ter­res­trial net­works sup­port­ing Real- Time ( RT) or Near Real- Time ( NRT) ap­pli­ca­tions have be­come the ac­cepted norm by well­con­nected users. But, net­work ser­vices de­liv­ered over satel­lites in geo­sta­tion­ary or­bits ( GEOSATs) present a vi­able so­lu­tion for the ru­ral and off­shore en­vi­ron­ments in which the oil and gas in­dus­try op­er­ates.

The suit­abil­ity of satel­lite- based trans­port so­lu­tions for la­ten­cy­de­pen­dent ap­pli­ca­tions comes down to un­der­stand­ing the physics be­hind the la­tency, closed- loop op­er­a­tions and the ap­pli­ca­tions. First, let’s look at the physics. Due to the fi­nite speed of prop­a­ga­tion of an elec­tro­mag­netic wave in free space, the RoundTrip Time ( RTT) of an In­ter­net Con­trol Mes­sage Pro­to­col ( ICMP) echo re­quest and re­ply, also known as a ping, be­tween two ground ter­mi­nals over a GEOSAT ranges from 480 ms to 570 ms. When trans­fer­ring files over an In­ter­net Pro­to­col ( IP) based net­work, the im­pact of nearly 500 ms la­tency is felt in closed- loop op­er­a­tions as­so­ci­ated with ev­ery­thing from flow con­trol to file trans­fers. Within IP’s Trans­mis­sion Con­trol Pro­to­col ( TCP), flow con­trol is han­dled by a 16- bit Re­ceiver Win­dow Buf­fer. The buf­fer keeps track of the num­ber of bytes that can be sent, with­out ac­knowl­edge­ment, up to a max­i­mum value of ap­prox­i­mately 216 bytes, or 64 kB. For the com­mu­ni­ca­tions pro­to­col to be ef­fi­cient, the ether be­tween the ground sta­tions must be kept full of data over the pe­riod of time it takes for the re­ceiv­ing sta­tion to re­ceive and process the first tranche of data, then ac­knowl­edge re­ceipt of data back to the send­ing sta­tion.

Op­tions

A com­mon so­lu­tion to this band­width lim­it­ing ef­fect in­volves in­stalling a net­work ap­pli­ance, to re­move the con­straint im­posed by the small re­ceive win­dow buf­fer, by swap­ping out the TCP pro­to­col with a pro­pri­etary one. Th­ese ap­pli­ances are known as TCP Ac­cel­er­a­tors, WAN Optimizers, or Ap­pli­ca­tion Ac­cel­er­a­tors. They can also trans­form the se­quen­tial trans­fer of a set of small files into one where the files are trans­ferred in par­al­lel, to min­i­mize the im­pact of wait­ing for the in­di­vid­ual file open and close op­er­a­tions as data is writ­ten. En­cryp­tion pro­to­cols suites, such as IPsec, may re­quire a full 6- mes­sage hand­shake ( e. g. IKE Main Mode). Web based cryp­to­graphic pro­to­cols such as TLS will also re­quire mul­ti­ple hand­shakes that will also in­volve a X. 509 Cer­tifi­cate Server. The re­sult of the mul­ti­ple hand­shakes re­quired to setup an en­crypted link is an op­er­a­tional pause of ap­prox­i­mately 1.5 to 3.0 sec­onds be­fore any user data flows across a newly es­tab­lished en­crypted link. Re­mote drilling ap­pli­ca­tions in the oil and gas in­dus­try can be mod­eled as a Pro­por­tional- In­te­gral- Dif­fer­en­tial ( PID) con­troller, where the in­creased la­tency ap­pears as a phase shift in the er­ror value in the con­trol loop. Of course, an en­gi­neer­ing anal­y­sis must be per­formed to de­ter­mine its ul­ti­mate suit­abil­ity, but in many RT ap­pli­ca­tions, such as pi­lot­ing drones in avi­a­tion, the la­tency ex­pe­ri­enced over a GEOSAT can be ac­com­mo­dated by care­ful tun­ing of the PID pa­ram­e­ters, mak­ing the sys­tem re­spon­sive and sta­ble. In all but the most de­mand­ing RT ap­pli­ca­tion, net­work ser­vices de­liv­ered over GEOSATs can still meet user re­quire­ments with a care­fully en­gi­neered, end- to- end sys­tem. Satel­lite- based net­work ser­vices still pro­vide the de­sired band­width and ex­pected per­for­mance at a great value.

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