Data Communications

Discussion in 'Royal Signals' started by toadinthehole, Nov 22, 2011.

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  1. I think this is the right forum...

    In non-techie laymans terms would someone be kind enough to explain to me in very simple terms the difference between a VPN, ADSL, IDSN and fibre optic channel ? Are they basically all the same thing, or does the VPN sit on top of the others as I suspect. If so, I'd be obliged if someone could tell me what the VPN does and its relationship with the ADSL/fibre optic etc. This would help me have a half-sensible discussion with an IT person at my part-time civvy job.
     
  2. I could explain all those acronyms but google/wikipedia is much better at it and quicker. However with regard to the VPN question, it stands for Virtual Private Network. It's a way of dividing an Ethernet network into sub networks which may be private and exclusive or may allow access to other networks.

    Using a building analogy, it's like having an office divided in to work areas where groups work together but may or may not shout over to other groups.
     
  3. They are different.

    ADSL and ISDN are long-distance communications systems. Fibre Channel is a special communications protocol for storage devices (which can run over copper as well as fibre!) A VPN is a "virtual private network" - it allows you to have segregated, normally encrypted comms, over long-distance shared networks.

    So, the VPN sits on top of ADSL or ISDN. You might be able to run Fibre Channel over the VPN (if it had very low latency) but ISDN wouldn't have the capacity.

    Also watch out for the "A" in ADSL. Upstream is much slower than downstream. Which is likely to affect the VPN quite significantly.
     
  4. Might you be confusing it slightly with a VLAN? A VPN is more like having a tunnel or corridor between different buildings. Ish, maybe.
     
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  5. Yep, looks like you've confused Virtual LAN with VPN. The VLAN is for splitting a local network into virtual networks, so traffic from one part won't reach the other unless forwarded by a router.

    The VPN, on the other hand, is basically just an encrypted link between two networks, and works just like a private line across the public Internet.

    I wouldn't worry too much about VLANs and VPNs at this point. The best place to start is learning to make the distinction between the local network and the external network, and focus on the router. If you get the chance, look at a router's setup/configuration and learn what all those acronyms and big words are about.
     
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  6. You are right, age has withered the few brain cells that remain sober these days
     
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  7. Don't worry. It took me ages to get that right as well :)
     
  8. I could manage not being sober shortly after starting basic!
     
  9. Don't agree that Fiber Channel is dead. I did the Cisco Nexus 5K course at Bedfont Lakes a couple of months back and FCoE is being pushed by Cisco for data centre infrastructure.
     
  10. meridian

    meridian LE Good Egg (charities)

    Roadster, are we sure the A in ADSL stands for asynchronous :|
     
  11. Fibre Channel is still used extensively in backups and disaster recovery centres, particularly online shadow systems. It had limitations of distance until the ability to push it over ethernet was established. Banking/Insurance companies use shedloads of Fiber Channel systems.

    Roadster, ISDN is mostly delivered in 128K units, using the 2B +D (2 Bearers + Data Channel) system. The normal presentation of ISDN to a consumer is usually 2 X 64Kb Channels and a 16Kb signalling channel. It is still used extensively for video conferencing applications, where the Bearer channels can be combined by the Terminal Equipment to form a 128Kb video/voice channel.

    I worked on something some years ago that would have made a major system for the Post Office, where payments of benefits would be via swipe card, and the terminals would be updated overnight. It would have used the Data channel (16Kb channel) for its normal transactions, only using the 2 bearer channels to provide short nightly system updates. It would have provided a low cost solution to implimenting an online system. Unfortunately it was 1996/97 and change of government put the kybosh on the project.

    ISDN2 is a subordinate system of ISDN30 (the 2Mb system)
     
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  12. You say Asymetric, I say asynchronous
    you say potato, I say neither

    skips off to a tune, tralala
     
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  13. meridian

    meridian LE Good Egg (charities)

    Scaleys eh, I don't know

    But

    I do know that asymmetric and asynchronous or definately not the same thing

    Bob, ISDN in the UK is delivered as either ISDN2e or BRI as 2x64k bearers plus a 16k signalling or 'data' channel. ISDN30e is multiple of 64k bearers (min 8 in the Uk usually delivered over fibre) plus a 64k signalling channel.

    ISDN2e is on its arse because it is expensive, video conferencing was a niche for it but with traffic control over ethernet, DSL and MPLS it is cheaper to deliver that bandwidth over a non nailed up WAN link. There is still a small bit of ISDN2 faxing about and I think it is also used a bit for broadcast and voice overs. The data over the signalling wheeze was interesting but given the tiny bandwidth and the fact that the Telcos said, of course you can do it but it will cost, kind of killed it off.
     
  14. ADSL and ISDN are not long distance links, they are limited in distance due to the ADSL frequency range and the ISDN by voltage. ISDN used to be the short link of choice of old where multiple ISDN 128K circuits could be aggregated together to support a much larger bandwidth supporting multiple applications. Nowadays bandwidth is either point to point TDM 2Meg+ or a more modern 10/40Gig link most likely over ATM or Ethernet stacked over a SDH payload on the national telephone network. VPN is just an IP solution using the above as the transport layer.
     
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  15. You're right, they don't. I don't know what I'm smoking, but I've had too much.