I am learning netwroking and would like to ask about how exactly we (as a casual user) get connected to internet and how a datacenter would do the same thing. i bet they dont use a regular modem which hangs on wall right ?

A fiber goes in to building and then modem translates it is signal to standart 802 ?

2 Answers 2


Larger datacenters mostly use fiber lines, predominantly running Ethernet already. The fibers uplink to an ISP, carrier or directly to an IX.

ISP uplinks are often terminated by an ISP router, very similar to domestic Internet connections. On the WAN line they use various protocols including xDSL, WLL, (Metro) Ethernet. What they use is of little consequence; the customer usually gets a routed Ethernet connection (handover port). This variant is very similar to a domestic Internet access, just using more professional hardware.

Carrier and IX uplinks are mostly Ethernet and you supply your own router. The handover is direct on the WAN fiber, esp. 1000BASE-LX, -BX, 10GBASE-LR and so on, that runs into your router (or switch) using an appropriate SFP transceiver.

  • Just adding that there are also very great differences in internet addressing and routing between domestic, medium-scale commercial and large commercial internet links.
    – jonathanjo
    Jul 8, 2019 at 14:26

A fiber goes in to building and then modem translates it is signal to standart 802 ?

The modem might be anything. A SFP is at heart a modem; it modulates and demodulates signals.

What interface you get depends on the ISP and service your order. It may be a fiber handoff at an agreed wavelength, or it may be copper based ethernet. If it's copper based ethernet, the ISP will provide CPE which translates from whatever the ISP uses to Ethernet.

Commonly, the ISP's line will be connected to a router. If multihoming is used, multiple links will terminate to the same router(s).

The point of handover is commonly known as demarcation point. It marks the border between ISP's responsibility and customer responsibility.

TL;DR: The exact interface is agreedupon by ISP and customer.

  • the reason i asked is i have a fiber coming to my office and i would like to put a storage unit (file storage server) there so it becomes accessible from home.ISP provides 1gbit connection but it goes in to router/modem ubit which is pretty bad as in it is cheap chinese router with no english interface basically. so i thought it would be ok if i just plug this fiber in SFP and plug that into my own router Jul 6, 2019 at 4:58
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    Then, by the love of god, ask that question, not a general one. The answer is probably that you'll have to talk to your ISP.
    – vidarlo
    Jul 6, 2019 at 5:01
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    Sorry mate, thought that would be better to ask general one since i didnt know anything about how isp provides on their side Jul 6, 2019 at 5:02
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    When you wonder about a specific problem, it's never wise to ask a general question. In case of handovers it's wildly variable how it's handled. It may be anything from a docsis modem to a specific wavelength on fiber.
    – vidarlo
    Jul 6, 2019 at 5:03
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    A (SFP) transceiver doesn't modulate and it's not a modem. It's 'just' a media interface with a transmitter and a receiver. Modulation (mostly PCS) happens in the switch/router itself.
    – Zac67
    Jul 6, 2019 at 7:06

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