Anatomy of a HFC network

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Anne Mills
5 years ago
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1 Anatomy of a HFC network 1 Everything you wanted to know and were afraid to ask about how HFC networks work and deliver data services.

2 Outside plant primer 2 What the heck are those things on the pole and what do they do?

3 Coax plant: frequency assignments 3 If a cable network offers internet, it is a bi-directional system. Most cable systems are capable of passing signals roughly below 100 MHz upstream and frequencies from MHz downstream. Contrary to popular belief, this is neither easy to reconfigure nor consistent across various plants (often not even within the same company) Fun fact: did you know most cable systems don t use the frequencies that overlap with the FM band as most used to carry a FM simulcast of local radio stations as well.

Splitters are just like the ones you have at home, but they split the backbone cable itself into two, this is used

4 Coax plant: splitters and taps Taps are what your house or apartment connects to, they drop a low level signal out of the backbone cable, they typically divert a few percent of the power on the cable to each port. Splitters are just like the ones you have at home, but they split the backbone cable itself into two, this is used mostly for going different directions, depending on design requirements these could split 50% of the power or be an unequal split 4

5 Coax plant: amplifiers Amplifiers in a modern HFC network amplify the downstream signal as it moves away from the node. N+X is used as the definition of how many amplifiers are cascaded between all the homes in the node and the node itself. These amps also amplify the upstream channel in the opposite direction. They run on DC power that is riding the backbone coax cable, injected by the power supply DOCSIS 3.1 does higher speeds with lower sized cascades as the noise floor is lower. 5 amplifier

Coax plant: power supplies Each node and the associated mininetwork requires its own power supply, the biggest vendor in this space is Alpha power systems their equipment says Alpha on it typically

6 Coax plant: power supplies Each node and the associated mininetwork requires its own power supply, the biggest vendor in this space is Alpha power systems their equipment says Alpha on it typically and is easily identifiable Modern units typically have four hours or so of batteries in them, older units have no batteries Old style, no batteries. TWC did not like batteries, hoping they fix this. These output DC power via a coax cable to a special type of splitter that passes only DC into the backbone cable for the system, in most plants they are located a pole or two away from the node Typically fed by 120v unmetered power services (MECO in this case requires a meter) This is why your cable does not work in a power outage even if you have a generator 6

7 Nodes: fiber meets coax 7 Typically services between customer passings Counter to popular belief nodes are analog devices Dual direction, typically upstream bandwidth (IE 6 mhz to 100 mhz) mapped onto one wavelength or fiber and downstream 100 mhz to 750 mhz (in a modern system) mapped onto another. Fiber is always APC connectors (reflectance = noise in analog)

8 Inside a cable headend 8 From fiber back to copper, in fact multiple copper cables

9 Head end / hub: Node lasers 9 Coax in, fiber out. Typically DWDM light out, but passive systems without EDFAs are most common (at least in our systems) Strict distance limits on fiber distance are in place, most providers have many more hubs than you might expect

10 Head end / hub: combining network 10

11 Head end / hub: combining network Mixes upstream and downstream signals from CMTS, video gear, cable voice and other signals onto coax The output from this network is a pair of coax cables per node (one upstream and one downstream) A typical head end may have many racks of these 11

Head end / hub: video added Video used to come from satellite receivers, now it mostly is delivered to headend via multicast IP Channel line up is produced and output on a single coax cable that

12 Head end / hub: video added Video used to come from satellite receivers, now it mostly is delivered to headend via multicast IP Channel line up is produced and output on a single coax cable that generally feeds all nodes in the entire head end (often via a bunch of amplifiers and splitters in the HE) Our network uses edgequam modulators, multicast IP in, video in digital format output via coax In a modern hub it only takes a few RU to produce a full cable lineup 12

utilizing 48 6 MHz TV channels downstream on every port to supply 3.0 and 3.

13 Head end / hub: CMTS aggregation (IP) CMTSes have downstream and upstream ports, any given port is either downstream or upstream Most modern CMTS versions can produce both OFDM and normal QAM carriers from the same ports, in our case we are utilizing 48 6 MHz TV channels downstream on every port to supply 3.0 and 3.1 DOCSIS Cisco CBR 8 A single chassis often has a /20 or more of IP space on it, thus serving users These things have so many coax ports they use these annoying high density connectors 13

14 Head end / hub: routers After the CMTS, we head back to 10G and 100G ethernet using normal routers that everyone is used to. Within wave all CMTS units are connected to a pair of routers, all connect using 4X 10G to each member of the pair Normal, dual stack ebgp peer (in Wave s case), some providers join them to their IGP like a normal edge router, we decided against that for scale and support reasons. 14

15 Enough of all that, I just want a faster connection at my house 15

16 Optimizing customer CPE 16 Get a modem that can do DOCSIS 3.1 If you have a DOCSIS 3.0 modem, get one that can bond 32 downstream channels. If you want more upload speed, honestly use something else, this is really hard to fix, it requires replacing every amp, tap and node in the system to add more upstream frequency space. The above should be able to provide up to 2.5 gbit/sec down (yes there are 3.1 modems with 2.5g copper ethernet ports, we have tested several)

17 Can I improve roundtrip latency? 17 Nope, not usually, but here are some tips. RRT on cable modems is driven by FEC spreading the data over a little bit of time to overcome plant ingress noise. If your cable company has noise issues latency will be really bad, but if it is in the 5-10 ms range it likely can t be improved Be sure and remove unused splitters and jacks at your place, if possible plug cable modem right into demarcation jack and run ethernet to router (this is the opposite of what most cable company installers do)

18 Thanks and Questions 18

Passive Optical Neworks Optical Distribution Network. White Paper. Northforge Innovations Inc.

Passive Optical Neworks Optical Distribution Network White Paper Northforge Innovations Inc. February 2018 1 Introduction Passive Optical Networks (PON) are broadly deployed to provide high-bandwidth Fiber