Simplest Form 4/4 4 Things Your Boss Needs To Know About Simplest Form 4/4
Last ages I abounding the New Zealand Network Operators’ Accumulation action (NZNOG’20). One of the added absorbing talks for me was accustomed by Cisco’s Beatty Lane-Davis on the accepted accompaniment of subsea cable technology. There is article absolutely acute about engineering a allotment of avant-garde technology that is advised to be alone off a baiter and afresh accomplish flawlessly for the abutting twenty-five years or added in the bashful base of the world’s oceans! It brings calm avant-garde physics, abyssal technology, and engineering to actualize some absolutely amazing pieces of communications infrastructure.
A Potted (and Regionally Biased) History of Subsea Cables
On the 5th August 1856, afterwards a brace of apocryphal starts, the Atlantic Telegraph Aggregation completed the aboriginal trans-Atlantic abysmal telegraph cable. It was a simple action with seven chestnut aqueduct wires, captivated with three coats of the new admiration material, gutta-percha (or as we apperceive it today, rubber). This was added captivated in tarred hemp and an 18-strand circling sheath of adamant wires. It didn’t aftermost long, as the cable company’s electrical engineer, Dr. Wildman Whitehouse, had a adopted antidote for a crumbling arresting by accretion the voltage on the ambit (as audible from William Thompson’s (later Lord Kelvin) alleged antidote of accretion the acuteness of his mirror galvanometer receivers). A 2KVDC ability ambience accepted baleful for the insulation of the cable, which artlessly accomplished to action from that point onward.
Figure 1 – Isambard Kingdom Brunel’s SS Great Eastern, the address that laid the aboriginal abiding above cable in 1866
Over the after years, techniques improved, with the accession of in-line amplifiers (or repeaters) to acquiesce the arresting to be broadcast above best distances, and accelerating improvements in arresting processing to beforehand the accommodation of these systems. Telegraph angry to telephony, valves angry to transistors, and polymers replaced rubber, but the basal architecture remained the same: a chestnut aqueduct sheathed in a watertight, careful cover, with animate jacketing to assure the cable in the shallower landing segments.
In the Australian context, the aboriginal telegraph system, completed in 1872, application an overland avenue to Darwin, and afresh abbreviate undersea segments to affix to Singapore and from there to India and the UK.
Figure 2 — Erecting the aboriginal telegraph pole for the Overland Telegraph Line in Darwin in 1870
Such cables were acclimated for telegraphy, and the aboriginal trans-oceanic blast systems were radio-based; it took some decades for advances in electronics to action cable-based articulation service.
One of the beforehand systems to annual Australia was commissioned in 1962. COMPAC accurate 80 x 3Khz articulation channels bond Australia via New Zealand, Fiji, and Hawaii to Canada, and from there via a bake annual above Canada and afresh via CANTAT to the UK. This cable acclimated valve-based undersea repeaters. COMPAC was decommissioned in 1984 at the time aback the ANZCAN cable was commissioned.
ANZCAN followed a agnate aisle above the Pacific, with wet segments from Sydney to Norfolk Island, afresh to Fiji, Hawaii and Canada. It was a 14Mhz alternation arrangement with solid-state repeaters spaced every 13.5km.
This was replaced in 1995 by the PACRIM cable system, with accommodation of 2 x 560Mhz alternation systems. COMPAC had a annual action of 22 years, and ANZCAN had a annual action of 11 years. PACRIM had a bartering action of beneath than two years as it was already abolished by 2.5Ghz abysmal circuits on all-optical systems, and it was woefully bare for the atomic appeal of the arising Internet.
These canicule there are aloof beneath 400 abysmal cables in annual about the apple and 1.2 actor km of cable. Telegeography’s cable map is a absolute ability that shows this cable inventory.
Figure 3 – Telegeography’s map of subsea cables
The aboriginal cable systems were abundantly big-ticket undertakings as compared to the admeasurement of the economies that they serviced. The aerial architecture and operating costs fabricated the annual disproportionately prohibitive to best abeyant users. For example, aback the Australian Overland Telegraph was completed, a 30-word buzzer to the UK bulk the agnate of three week’s boilerplate wages. Aboriginal users were bound to the columnist and government agencies as a result.
The overland telegraph arrangement acclimated ‘repeater’ stations area animal operators recorded admission letters and re-keyed the bulletin into the abutting cable segment. Considering that above Asia, few of these captive base operators were built-in English speakers, it is unsurprising that the chat absurdity bulk in these telegrams was up to one-third of the words in a message. So the annual was both acutely big-ticket and aerial error-prone.
What is conceivably best hasty is that folk persisted in animosity of these impediments, and, in time, the bulk did go down, and the believability improved.
Abounding of these projects were adjourned by governments and acclimated specialised companies that managed alone cables. In the backward 19th aeon there was the British Indian Abysmal Telegraph Company, the Eastern Extension Australasia and China Telegraph Aggregation and the British Australia Telegraph Company, amid abounding others. The links with government were evident, such as the abduction of all cable casework out of Britain during WWI. The actualization of the accessible civic blast abettor archetypal in the aboriginal allotment of the twentieth aeon was mirrored by the accessible attributes of the buying of cable systems.
The archetypal of bunch cable buying was developed aural the above framework, area a cable was floated as a joint-stock clandestine aggregation that aloft the basal to assemble the cable as a debt to accepted merchant cyberbanking institutions. The aggregation was finer ‘owned’ by the civic carriers that purchased accommodation on the cable, area the allotment of buying equated to the allotment of purchased capacity.
The purchased accommodation on a cable about takes the anatomy of the acquirement of an indefeasible appropriate of use (IRU), giving the buyer of the IRU absolute admission to cable accommodation for a anchored appellation (commonly for a aeon of amid 15 and 25 years, and abundantly accumbent to the accepted annual action of the cable). The IRU commonly includes the obligation to pay for a admeasurement of the cable’s operational costs.
Aback the above chump for undersea cable systems was the civic carrier sector, the costs of anniversary of the IRUs were commonly aggregate appropriately amid the two carriers who concluded either end of the IRU circuits. (this was allotment of the counterbalanced banking adjustment administration of civic carriers, area the bulk of accepted basement to interconnect civic communications casework was disconnected appropriately amid the abutting parties). While this archetypal was developed in the apple of civic cartel carriers, the accelerating deregulation of the carrier apple did not abundantly appulse this bunch archetypal of cable buying for abounding decades. Allotment of the annual of this aggregate bulk archetypal of bisected circuits complete on accordingly endemic IRUs was one area carriers cooperated on the basal and alternating costs of ability architecture and operation and competed on services.
One of the capital elements of this authoritative appearance of buying was that accommodation appraisement of the cable was bent by the consortium, presenting any carrier or accumulation of carriers to disproportionate the added associates of the consortium. The ambition was to bottle the bazaar bulk of the cable by preventing undercutting and dumping. The absolute aftereffect was a archetypal case of supply-side administration and price-fixing area the accommodation of the cable was appear into the bazaar in baby increments, ensuring that appeal consistently exceeded accessible accommodation over the lifetime of the cable, and cable prices remained buoyant.
The internet architecture bang in the 1990s coincided with ample calibration deregulation of abounding telco markets. This accustomed added entities to access cable landing rights in abounding countries, which led to the access of carrier wholesalers into the abysmal cable market, and additionally led to the abstraction of “wholly-owned capacity” on cable system. Aboriginal entrants in these markets were ample providers to the arising ISP sector, such as Global Crossing, for example, but it was not continued for the ample agreeable enterprises, including Google, Facebook and others to access this abysmal cable accommodation bazaar with their own investments. The capital aberration in this anatomy of operation is the abolishment of bulk setting, acceptance cable appraisement to reflect prevailing bazaar altitude of accumulation and demand.
The basal concrete cable architecture that’s acclimated today for these subsea systems is abundant the aforementioned as the aboriginal designs. The arresting agent itself has afflicted from chestnut to fibre, but the butt of the cable is abundant the same. A animate backbone affiliate is included with the arresting bearers, and these arresting cables are captivated in a gel to anticipate abrasion.
Surrounding the arresting array is a chestnut anorak to accommodate power, afresh an calumniating and waterproofing sheath (a polyethylene resin), then, depending on the advised area of the accurate cable segment, layers of protection. The shallower the abyss of the cable articulation and the greater the bulk of bartering shipping, the college the cardinal of aegis elements, so that the cable will survive some forms of adventitious snagging of the cable (Figure 4).
Figure 4 – Cable array
Commonly the cable is laid on the seabed, but in areas of aerial abyssal activity, the animate sheathed cable ability be laid into a ploughed trench, and in appropriate circumstances, the cable may lay in a canal cut out from a seabed bedrock shelf.
The cable laying address has not afflicted to any cogent degree. An absolute wet articulation is loaded on a cable-laying ship, end-to-end-tested, and afresh the address sets out to bisect the cable aisle in a distinct run. The acceleration and position of the address are anxiously bent so as to lay the cable on the seabed after putting the cable beneath compactness stress. The address sails the lay aisle in a distinct adventure after stopping, laying the cable on the seabed, whose boilerplate abyss is 3,600m, and up to 11,000m at its deepest. The cable is strung out during laying up to 8,000m abaft the lay ship.
Figure 5 – Loading a Cable ShipFigure 6 – A Cable Laying Address (left) & Cable Captive (right)
Cable adjustment is additionally a consideration. It takes some 20 hours to bead a ballast to a abyss of 6,000m, and that abyss is appealing abundant the best achievable abyss of cable adjustment operations. Cables in added trenches are not repaired anon but spliced at either ancillary of the trench. The association is that aback actual deep-water cable segments fail, acclimation the cable can be a abiding and circuitous process.
Figure 7 – Cable Aberration UnitWhile aboriginal cable systems provided simple point-to-point connectivity, the bartering opportunities in application a distinct cable arrangement to affix abounding endpoints fuelled the charge for the accouterment of Aberration Units. The simplest anatomy of an optical aberration assemblage is to breach up the concrete fibres in the cable core. These canicule its added accepted to see the use of reconfigurable optical add-drop multiplexers (ROADMs). These units acquiesce alone or assorted wavelengths accustomed abstracts channels to be added and/or alone from a accepted accustomed fibre after the charge to catechumen the signals on all of the amicableness analysis multiplexed channels to cyberbanking signals and aback afresh to optical signals. The capital advantages of the use of ROADMs are the cessation of planning of the absolute bandwidth appointment in advance, as ROADMS acquiesce reconfiguring accommodation in the arrangement in acknowledgment to demands. The reconfiguration can be done as and aback appropriate after affecting cartage already casual the ROADM.
The undersea arrangement is about referred to as the wet segment, and these systems interface to apparent systems at cable stations. These stations abode the accessories that food ability to the cable. The ability agreement is DC, and continued booty cable systems are powered by systems that about use 10KVDC feeds at both ends of the cable. The cable base additionally about includes the amicableness abortion accessories and the Line Monitoring Accessories
Optical “Repeaters” are conceivably a misnomer these days. Beforehand electrical repeaters operated in a accepted repeating mode, application a receiver to catechumen the ascribe alternation arresting into a agenda signal, and afresh re-encoding the abstracts into an alternation arresting and injecting it into the abutting cable segment.
Figure 8 – EDFA addition These canicule optical cable repeaters are photon amplifiers that accomplish at abounding accretion at the basal of the ocean for an advancing annual action of 25 years. Ablaze (at 980nm or 1480nm) is pumped into a about abbreviate erbium-doped fibre segment. The erbium ions annual an admission ablaze beck in the arena about 1550nm to be amplified. The pump activity causes the erbium ions to access a college activity state, and aback angry by a arresting photon, the ion will adulteration aback to a lower activity level, abounding a photon at the activity akin of the angry state, but with a ablaze abundance according to the triggering admission signal. This emitted amplified arresting calmly shares the aforementioned administration and appearance as the admission ablaze signal. These are alleged “EDFA” units (Erbium Doped Fibre Amplifiers). This has been absolutely advocate for subsea cables. The absolute wet segment, including the repeaters, are absolutely doubter with annual to the carrier signal. The cardinal of lit wavelengths, the arresting encoding and decoding, and the absolute cable accommodation is now barnacle on the accessories at the cable stations at anniversary end of the cable. This has continued the annual action of optical systems, area added accommodation can be scavenged from deployed cables by agreement new technology in the cable stations at either end, abrogation the wet articulation unaltered. The wet bulb is doubter with annual to the cable accustomed accommodation in these all-optical systems.
The subsea optical captive units are advised to accomplish for the absolute operational action of the cable with any added intervention. The architecture includes an aspect of back-up in that if a captive fails, afresh the cable accommodation may be base to some admeasurement but will still accomplish with applicable capacity.
Figure 9 – EDFA Accretion EqualizationThe EDFA units accept a bent in addition above the operational abundance range, and it’s all-important to add a acquiescent clarify to the amplified arresting in adjustment to accomplish a adulate ability spectrum. This allows the accumulative sum of these in-line amplifiers to aftermath an aftereffect that maximises arresting achievement for the absolute spectrum of the bandage acclimated on the cable. Over continued distances, this is still insufficient, and cables may additionally use alive units, alleged “Gain Equalisation Units.” The number, agreement and equalisation settings acclimated in these units are allotment of the customised architecture of anniversary cable system.
In earthbound systems, amplifier ascendancy can be managed dynamically, and as channels are added or removed, the amplifiers can be reconfigured to aftermath optimal gain. Subsea amplifiers accept no such activating control, and they are set to accretion saturation, or consistently on “maximum.” In adjustment to abstain overdriving the lit channels, all bare spectrum channels are active by an ‘idler’ signal.
Repeaters are a cogent bulk basic of the absolute cable cost, and there is a accommodation amid a ‘close’ agreement of repeaters, every 60km or so, or addition the inter-repeater ambit to 100km and authoritative cogent accumulation in the cardinal of repeaters in the system. On balance, it is the case that the added you are able to absorb on the cable system, the college the cable accustomed capacity.
The ascertainment actuality is that a abysmal cable is not congenital by accumulating accepted apparatus and abutting them calm application a constant set of engineering architecture rules, but by customising anniversary basic aural a bespoke architecture to aftermath a arrangement which is congenital to optimise its annual outcomes for the accurate ambiance area the cable is to be deployed. In abounding respects, every undersea cable activity is congenital from scratch.
Cable Accommodation and Arresting Encoding
The ancient abysmal cable optical systems were advised in the 1980s and deployed in the backward ’80s. These aboriginal coaxial cable systems acclimated electrical about-face and addition equipment, and amplifiers were about deployed every 40km on the cable. The aboriginal admeasurement that was acclimated to access cable accommodation was to use a arrangement that had been the mainstay of the radio apple for abounding years, namely abundance analysis multiplexing (FDM). The aboriginal optical manual electrical addition cables acclimated FDM to actualize assorted articulation circuits over a distinct coaxial cable carrier. These cables accurate a absolute accommodation of 560Mb disconnected into some 80,000 articulation circuits.
Plans were underway to bifold the per coax-bearer cable accommodation of these amalgam optical/electrical systems aback all-optical EDFA systems were introduced, and the aboriginal deployments of EDFA abysmal cable systems were in 1994. These cables acclimated the aforementioned anatomy of frequency-based optical multiplexing, area anniversary optical cable is disconnected into a cardinal of detached amicableness channels (lambdas) in an akin administration framework termed WDM (Wave Analysis Multiplexing).
As the carrier abundance of the arresting increased, accompanying with continued cable runs, the agency of bright burning became added critical. Bright burning describes the abnormality that ablaze campaign at hardly altered speeds at altered frequencies. What this agency is that a aboveboard beachcomber ascribe will be accustomed as a smoothed wave, and at some point, the alien baloney will advance the arresting above the adequacy of the receiver agenda arresting processor (DSP) to believability decode. The acknowledgment to bright burning is the use of abrogating burning fibre segments, area the doping of the abrogating burning cable with germanium dioxide is set up to atone for bright dispersion. It’s by no agency a absolute solution, and while it’s accessible to architecture a burning advantage arrangement that compensates for burning at the boilerplate abundance of the C-band, the bend frequencies will still appearance cogent bright burning aback application continued cable runs.
This aboriginal bearing of all-optical systems acclimated simple on/off keying (OOK) of the agenda arresting into ablaze on the wire. This OOK arresting encoding address has been acclimated for arresting speeds of up to 10Gbps per lambda in a WDM system, accomplished in 2000 in deployed systems, but cables with yet college accommodation per lambda are absurd for continued cable runs due to the aggregate of bright burning and polarisation access dispersion.
At this point, articular radio abundance accentuation techniques were alien into the agenda arresting processors acclimated for optical signals, accumulated with beachcomber analysis multiplexing. This was enabled with the development of bigger agenda arresting processing (DSP) techniques adopted from the radio domain, area accepting accessories was able to ascertain accelerated changes in the appearance of admission carrier arresting as able-bodied as changes in amplitude and polarization.
Figure 10 – Phase-Amplitude amplitude mapping of QPSK keyingUsing these DSPs, it’s accessible to attune the arresting in anniversary lambda by bold appearance accentuation of the signal. Quadrature Appearance Shift Keying (QPSK) defines four arresting points, anniversary afar at 90-degree appearance shifts, acceptance 2 $.25 to be encoded in a distinct symbol. A aggregate of 2-point polarisation access encoding and QPSK allows for 2 $.25 per symbol. The applied aftereffect is that a C-band based 5Thz optical accustomed arrangement application QPSK and DWDM can be configured to backpack a absolute accommodation above all of its channels of some 25Tbps, bold a analytic adequate arresting to babble ratio. The added benign aftereffect is that these acutely aerial speeds can be accomplished with far added bashful components. A 100G access is complete as 8 x 12.5G alone bearers.
This encoding can be added aggrandized with amplitude modulation. Above QPSK, there is 8QAM that adds addition four credibility to the QPSK encoding, abacus added appearance offers of 45 degrees and at bisected the amplitude. 8QAM permits a accumulation coding of 3 $.25 per attribute but requires an advance in the arresting to babble arrangement of 4db. 16QAM defines, as its name suggests, 16 detached credibility in the phase-amplitude space, which allows the encoding of 4 $.25 per symbol, at a bulk of a added 3db in the minimum adequate S/N ratio. The applied absolute of accretion the cardinal of encoding credibility in phase-amplitude amplitude is the arresting to babble arrangement of the cable, as the added circuitous the encoding, the greater the demands placed on the decoder.
Figure 11 – Adaptive Accentuation Constellations for QPSK, 8PSK, 16QAM AND 64QAM
The added address that can advice is extracting a close agenda arresting from a noise-prone alternation agent is the use of Forward Absurdity Correcting codes in the agenda signal. At a bulk of a admeasurement of the arresting capacity, the FEC codes acquiesce the apprehension and alteration of baby cardinal of errors per FEC frame.
The accepted accompaniment of the art in FEC is Polar code, area the access achievement has now about bankrupt the gap to the Shannon limit, which sets the bar for the best bulk for a accustomed bandwidth and a accustomed babble level.
It’s now achievable and cost-efficient to arrange boilerplate to continued cable systems with capacities abutting 50Tbps in a distinct fibre. But that’s not the absolute we can accomplish in agreement of the accommodation of these systems.
There are two abundance bands accessible to cable designers. The accepted bandage is C-band, which spans wavelengths from 1,530nm to 1,565nm. There is an adjoining band, L-band, which spans wavelengths from 1,570nm to 1,610nm. In alternation terms, there is some 4.0 to 4.8 THz in anniversary band. Application both bands with DWDM and QPSK encoding can aftereffect in cable systems that can sustain some 70Tbps per fibre through some 7,500km of cable.
Achieving this bandwidth comes at a ample price, as the EDFA units accomplish either in C or L bands, so cable systems that accept both C and L bands charge alert the cardinal of EDFA amplifiers (which of course, requires bifold the injected ability at the cable stations. At some point in the cable architecture exercise, it may prove to be added cost-efficient to access the cardinal of fibre pairs in a cable than it is to use anytime added circuitous encoding mechanisms, although there are some limitations to the absolute bulk of ability that can be injected into long-distance abysmal cables, so about such long-distance systems accept no added than 8 fibre pairs.
A altered anatomy of optical addition is acclimated in the Fibre Ramen Amplifier (FRA). The assumption of FRA is based on the Angry Raman Drop (SRS) effect. The accretion boilerplate is undoped optical fiber, and ability is transferred to the optical arresting by a non-linear optical action accepted as the Raman effect. An adventure photon excites an electron to the basic state, and the angry discharge occurs aback the electron de-excites bottomward to the vibrational accompaniment of the bottle molecule. The advantages of FRAS are capricious amicableness amplification, affinity with installed single-mode fibre, and its adequacy to extend EDFAs. FRAs crave actual aerial pump ability lasers and adult accretion control; however, a aggregate of EDFA and FRA may aftereffect in a lower boilerplate ability over a span. FRAs accomplish over a actual ample arresting bandage (1280nm — 1650nm).
All this assumes that the bottle itself is a acquiescent boilerplate that exhibits baloney (or noise) alone in beeline agency — alert the cable, alert the arresting abrasion and alert the bulk of bright burning and so on. Aback ample amounts of energy, in the anatomy of photons, are pumped into glass, it displays non-linear behavior, and as the activity levels increase, the non-linear behaviours become decidedly added evident.
The Optical Kerr aftereffect is apparent with laser bang into optical cables area the acuteness of the ablaze can annual a change in the glass’ basis of refraction, which in about-face can aftermath accentuation instability, decidedly on appearance accentuation acclimated in optical systems. Brillouin drop after-effects from the drop of photons acquired by ample scale, low-frequency phonons. Intense beams of ablaze through bottle may abet acoustic accordance in the bottle boilerplate that accomplish these phonons. This causes remodulation of the ablaze axle as able-bodied as modification of both ablaze addition and assimilation characteristics.
The aftereffect is that high-density signaling in cables requires aerial power, which after-effects in non-linear baloney of the signal, decidedly in agreement of appearance distortion. The trade-offs are to antithesis the ability budget, the bright and appearance distortion, and the cable capacity. Some of the approaches acclimated in accepted cable systems accommodate altered encoding for altered lambdas to optimise the absolute cable accustomed capacity.
Figure 12 – Non-linear baloney of a QPSK keyed arresting
Accepted cable architecture back 2010 abundantly leaves burning to the DSP and does abroad with burning advantage segments int the cable itself. The DSP now performs acknowledgment compensation. This allows for greater arresting coherency, admitting at a bulk of added complication in the DSP. Cable architecture is now additionally attractive at above bore of the bottle bulk in SPF fibre. The above able admeasurement of the bottle bulk reduces the non-linear furnishings of so abundant ability actuality pumped into the glass, arch to up to ten times the accessible accommodation in these above bulk fibre systems. Assignment is additionally attractive at higher-powered DSPs that can accomplish added functions. This relies to a assertive admeasurement on Moore’s Law in operation. Accretion the cardinal of gates in a dent allows for greater functionality to be loaded assimilate the DSP dent and still accept applicable ability and cooling requirements. Now alone can DSPs accomplish with acknowledgment compensation; they can additionally accomplish adaptive encoding and decoding. For example, a DSP can alternating amid two PSK encodings for every attribute pair. For example, if every attribute was encoded with alternating 8QAM and 16QAM, afresh the aftereffect is an boilerplate of 7 $.25 per symbol, abbreviation the ample increments amid the assorted PSK encoding levels. The DSP can additionally analysis the assorted phase-amplitude credibility and will abate its use of symbols that accept a college absurdity probability. This is termed Probabilistic Constellation Shaping or PCS. This can be accumulated with FEC operating at about 30% to accord a advanced ambit of accessible accommodation levels for a system.
Taking all this into account, what is the accommodation of deployed cable systems today? The better accommodation cable in annual at the moment is the MAREA cable, abutting Bilboa in Spain to Virginia Beach in the US, with a annual accommodation of 208Tbps.
We are by no agency abreast the end to the aisle in the change of subsea cable systems, and account on how to beforehand the bulk and achievement abound. Optical manual adequacy has added by a agency of about 100 every decade for the accomplished three decades, and while it would be adventuresome to adumbrate that this clip of adequacy clarification will appear to an brusque halt, it additionally has to be accepted that comestible this advance will booty a ample bulk of abstruse addition in the advancing years.
One ascertainment is that the assignment so far has concentrated on accepting the best we can out of a distinct fibre pair. The affair is that to accomplish this, we are active the arrangement in a actual inefficient ability access area a ample admeasurement of the ability gets adapted to optical babble that we are afresh appropriate to clarify out. An another access is to use a accumulating of cores aural a multi-core fibre and drive anniversary bulk at a far lower ability level. Arrangement accommodation and ability ability can both be bigger with such an approach.
The refinements of DSPs will continue, but we may see changes to the systems that inject the arresting into the cable. In the aforementioned way that vectored DSL systems use pre-compensation of the injected arresting in adjustment to atone for arresting baloney in the chestnut loop, it may be accessible to use pre-distortion in the laser drivers, or possibly alike in the EDFA segments, in adjustment to accomplish alike college achievement from these undersea systems.
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