Your guide to broad­band tech

FTTP, FTTN, HFC, GPON? THE AUS­TRALIAN BROAD­BAND SCENE CAN BE CON­FUS­ING, SO WE’VE PUT TO­GETHER THIS QUICK GUIDE TO HELP YOU COM­PRE­HEND THE MOST IM­POR­TANT BITS.

TechLife Australia - - WELCOME -

[ NATHAN TAY­LOR ]

OUR MULTI-TECH­NOL­OGY MIX NBN sure has cre­ated some con­fu­sion. With at least five dif­fer­ent tech­nolo­gies in use, on top of the four ma­jor broad­band techs al­ready avail­able, it’s no won­der that there’s a lot of mis­un­der­stand­ing about how things work and what the dif­fer­ent tech­nolo­gies are ca­pa­ble of. So this month, we thought we’d break it down for you.

CON­TENTION

Be­fore we start talk­ing about the dif­fer­ent tech­nolo­gies, we should touch on an in­cred­i­bly im­por­tant con­cept in net­work­ing — con­tention. We’d say that the mis­un­der­stand­ing (or lack of un­der­stand­ing) of con­tention is the rea­son for roughly 90% of false claims about broad­band. It’s why peo­ple, in­clud­ing politi­cians that should know bet­ter, still make claims like 4G be­ing as good as fi­bre (“It can do gi­ga­bit!”), even when it’s ac­tu­ally not even a con­test.

Con­tention, in short, is com­pe­ti­tion for the net­work. When two de­vices on the same net­work try to trans­mit at the same time, they have to share net­work re­sources. If you have two Wi-Fi de­vices, both have to share the air­waves, so the band­width for each is halved. Pretty sim­ple, re­ally.

When it comes to broad­band, you may have heard the term ‘con­tention ra­tio’. Your ISP doesn’t have enough back­haul (that’s the links that carry data from your lo­cal ex­change or hub back to the ISP) and in­ter­net band­width to sup­port all users go­ing at max speed all the time. In­stead, it un­der-pro­vi­sions, ex­pect­ing that, at any given time, only a cer­tain num­ber of users are ac­cess­ing the in­ter­net at once.

The higher the con­tention ra­tio is, the worse the ISP will be at peak times.

But con­tention also plays a part in what’s called the lo­cal loop — that’s the ‘last mile’, the link between your home or wire­less de­vice and the hub/node/ex­change/cell where your sig­nal is joined with that of your neigh­bours and sent on to the ISP for de­liv­ery onto the in­ter­net. This is a huge part of what sep­a­rates dif­fer­ent ser­vices. For ex­am­ple, with 4G, ev­ery user con­nected to a given cell is com­pet­ing for band­width, and that could be sev­eral thou­sand users at once so the ‘gi­ga­bit’ speed is di­vided amongst all those users. With ADSL, on the other hand, there is no con­tention between you and the ex­change. The link is yours alone.

Now with an un­der­stand­ing of that in mind, let’s look at how the dif­fer­ent techs stack up.

FI­BRE TO THE HOME (FTTH)

FTTH is, as many have noted, the Rolls Royce of Aus­tralian broad­band. If you have FTTN (fi­bre to the node), you’ve pretty much won the broad­band lot­tery.

In Aus­tralia, the NBN is us­ing what is called GPON: gi­ga­bit pas­sive op­ti­cal net­work. The ‘pas­sive’ part means that, un­like FTTN, the fi­bre distri­bu­tion hubs (FDH) — the street-side cab­i­nets that con­nect to your home — re­quire no power.

Each FDH node has a to­tal band­width of 2.488Gbps down­stream and 1.244 gi­ga­bit up­stream. That is ef­fec­tively di­vided amongst the homes con­nected to that FDH — nom­i­nally 32 homes per FDH ac­cord­ing to the ini­tial roll­out plans. Tech­ni­cally, any home could con­nect at the full 2.488Gbps, but to pre­vent a sin­gle home from suck­ing up all the band­width they’re throt­tled to 25, 50, 100 or 1000Mbps, de­pend­ing on the type of ser­vice you’re sub­scribed to.

The con­tention ra­tio with fi­bre is, thus, in­cred­i­bly good. A sin­gle GPON is enough to de­liver around 77Mbps to ev­ery user, all at once. So, at least in the lo­cal loop, you’ll be pretty much guar­an­teed to al­ways get the full 100mbps bar­ring some freak oc­cur­rence where ev­ery user is typ­ing to max out their con­nec­tion at once. In the fu­ture, an up­grade to XG-PON (also known as 10G-PON), which pro­vides four times as much down­stream band­width, would be pos­si­ble, eas­ily al­low­ing 1Gbps sub­scriber ser­vices with very lit­tle

con­tention. Of course, there can still be con­tention deeper in the net­work, de­pend­ing on how much in­ter­net band­width your ISP has pro­vi­sioned, but lo­cally fi­bre is the bee’s knees.

HFC CA­BLE

Ca­ble in­ter­net looks good on pa­per. Tech­ni­cally, sub­scriber speeds of 1Gbps down­stream are pos­si­ble. But it’s the very high con­tention ra­tios that make it less ca­pa­ble than it might ap­pear.

With ca­ble, a coax­ial ca­ble is run from a node along the street sides. To con­nect to the net­work, you es­sen­tially splice into this ca­ble. The band­width on this ca­ble is shared amongst all the homes it passes, which is typ­i­cally sev­eral hun­dred. The node it­self is con­nected back to the par­ent net­work via a fi­bre ca­ble (thus hy­brid fi­bre-coax, or HFC).

With the cur­rent setup, a sin­gle ca­ble seg­ment can pass sev­eral hun­dred homes. With DOCSIS 3.0 (which we’re cur­rently us­ing) a to­tal band­width of just over 1.2Gbps is pos­si­ble, shared amongst all the users on a given seg­ment (as with fi­bre, in­di­vid­ual users are throt­tled to 30Mbps or 100Mbps to pre­vent one per­son tak­ing over the net­work). Thanks to the rel­a­tively low cur­rent sub­scriber base, that ac­tu­ally works out pretty well – but if ev­ery­body whose house was passed by ca­ble ac­tu­ally used it, it would be a dif­fer­ent story.

When DOCSIS 3.1 is im­ple­mented on the NBN, the shared speed can ac­tu­ally go up to 10Gbps, though with the plan to put ev­ery­one in the ca­ble foot­print onto ca­ble, the sub­scriber base will also likely go up (bar­ring the build­ing of more nodes).

DSL, FTTN AND FTTDP

Al­though they don’t pro­vide nearly as much to­tal band­width, the cop­per cables used in ADSL, VDSL (used in fi­bre to the node) and G.Fast (po­ten­tially used in FttDP) have one ad­van­tage — they’re non-con­tend­ing. The link between your house and the ex­change (for ADSL), lo­cal node (for FTTN) or mi­cro-node (FttDP) is yours alone, though, of course, there’s still con­tention deeper in the net­work. (With FTTN, the up­link from the street-side node to the ex­change varies — cur­rently, the de­sign doc­u­ment lists up to 4Gbps — and each node will ser­vice between 48 and 384 users.)

So, in gen­eral, DSL speeds in the lo­cal loop are de­ter­mined by the qual­ity of the sig­nal your home re­ceives, which is, in turn, a prod­uct of your dis­tance from the ex­change/ node and line noise. There’s a the­o­ret­i­cal max, and you’ll get some frac­tion of that de­pend­ing on your sig­nal qual­ity. ADSL2 can go up 24Mbps. VDSL2 (in the NBN im­ple­men­ta­tion) can max 100Mbps. G.Fast can the­o­ret­i­cally hit 500Mbps.

3G/4G, SATEL­LITE AND FIXED WIRE­LESS

Wire­less tech­nolo­gies all share one Achilles’ heel: they’re a shared medium. So when some­one says “Why do we need land­lines when 4G will be able to do 1Gbps?” this is your an­swer. There is a rea­son that data vol­umes on mo­bile ser­vices are so tight: if ev­ery­body started to use 4G for ev­ery­thing, the whole sys­tem would col­lapse.

The to­tal amount of data that an LTEAd­vanced net­work can carry largely de­pends on how much spec­trum the tele­coms provider has pur­chased, and the con­tention ra­tio de­pends on the den­sity and range of cell tow­ers. What’s more, fi­nal speeds are heav­ily af­fected by sig­nal in­ter­fer­ence and sig­nal power loss — with­out a ca­ble to shield a sig­nal and hold it to­gether, wire­less sig­nals de­grade eas­ily, re­duc­ing the ef­fec­tive band­width. The end re­sult is speeds that vary pretty wildly from place to place and time to time. In a per­fect sit­u­a­tion, with no­body else us­ing a cell, speeds of up to 100Mbps and even 1,000Mbps (for fixed po­si­tion in­stal­la­tions) are pos­si­ble, but in prac­tice they’re likely to be much, much lower.

Like 3G, satel­lite and fixed wire­less are also de­pen­dent on a shared medium. Direc­tional an­ten­nae and mul­ti­ple ac­cess sig­nalling can and do limit con­tention, but where sig­nals over­lap, there will be per­for­mance trade-offs. Nom­i­nally fixed wire­less speeds go up to 50Mbps/20Mbps and satel­lite to 25Mbps/5Mbps, but they’re subject to the same rules of wire­less con­tention as 3G.

With HFC, a sin­gle ca­ble seg­ment can ser­vice hun­dreds of homes.

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