Getting online: DSL, cable and fibre to the home
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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.
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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.
المسرد
- 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.
الملاحظات والمصادر
- 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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