Getting online: DSL, cable and fibre to the home
Your home router still needs a line to the internet service provider. Walk down one street where three homes get online three ways (a copper phone line, the shared TV coax, and fibre through a passive splitter) and see why distance, sharing and upload speed differ between them.
5 quick questions
Pick an answer to see why. Your score saves with your progress.
01Your friend's DSL is much slower than yours, on the same plan. What is the most likely reason?
The DSL copper pair is not shared, but its high-frequency tones fade with distance: VDSL2 gives about 100 Mb/s at 0.5 km and only about 50 Mb/s at 1 km.
02Why can cable internet feel slower on a busy evening?
DOCSIS 3.1 can carry up to about 10 Gb/s down per coax segment, but that is for everyone on the line together.
03What does the passive splitter in a GPON fibre network do?
The splitter is just glass: each home fibre gets a share of the light's power. Up to 64 homes share 2.488 Gb/s down and 1.244 Gb/s up; each ONT keeps only its own (encrypted) data, and the ONT is the box that turns light into Ethernet.
04A plan says "80/20 Mb/s". What does the second number mean?
Plans are usually written download/upload. Most access links give far more speed down than up because homes mostly download; uploads, backups and video calls feel the smaller number.
05A home has no phone line, coax or fibre. How can it still get online?
Fixed wireless access uses radio to a base station that is wired back to the ISP. Its speed depends on signal strength and on how many people share the mast.
Glossary
- Last mile
- The access link between a home and its ISP: a phone line, coax, fibre or radio.
- DSL / VDSL2
- Digital subscriber line: data sent as high-pitched tones on the copper phone pair (ITU-T G.993.2). Ends at a DSLAM.
- DOCSIS
- The cable data standard. A cable modem talks DOCSIS over the shared TV coax to a CMTS at the ISP.
- FTTH
- Fibre to the home: a glass fibre runs all the way into the house.
- GPON
- Gigabit passive optical network (ITU-T G.984): one fibre from the OLT, split passively to up to 64 homes.
- ONT / OLT
- Optical network terminal (the box in your home) and optical line terminal (the ISP's end of the fibre).
- Mb/s, Gb/s
- Megabits and gigabits per second: how many million or billion bits a link moves each second.
- Fixed wireless
- Home internet over 4G or 5G radio from a nearby mast instead of a cable.
Notes and sources
- VDSL2 rates by distance are typical planning figures for profile 17a; real lines vary. 80/20 Mb/s is a common retail plan. DOCSIS 3.1 and GPON figures are the shared capacity of one line, not one home's speed.
- 203.0.113.21 is an RFC 5737 documentation address, 192.168.1.0/24 an RFC 1918 private range, and 00:00:5e:00:53:21 a MAC from the RFC 7042 documentation block.
- Most cable networks are hybrid fibre-coax: fibre runs to a node in the neighbourhood and coax covers the last few hundred metres.
- Many DSL lines today are fibre to the cabinet (FTTC): the DSLAM sits in a street cabinet, so the copper part is short.
- Fixed wireless and 4G/5G speeds depend on signal strength and on how busy the radio cell is, so no single figure is given.
- ITU-T G.993.2: Very high speed digital subscriber line transceivers 2 (VDSL2)
- ITU-T G.984.1: Gigabit-capable passive optical networks (GPON): General characteristics
- ITU-T G.984.2: GPON physical media dependent layer
- ITU-T G.9807.1: 10-Gigabit-capable symmetric passive optical network (XGS-PON)
- CableLabs: DOCSIS 3.1 technology
- 3GPP: 5G system overview
- RFC 5737: IPv4 Address Blocks Reserved for Documentation
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