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  1. Junior Member
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    #1

    Default ISDN PRI Question

    Are ISDN PRI and T1 terms that can be used interchangeably? My understanding is that T1 is a term for PRI in the US. Am I wrong?
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  3. Johan Hiemstra Forum Admin Webmaster's Avatar
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    #2
    Well yes and no it's not actually the term that is interchangable, the speed is however... I'm working on an ISDN TechNote for the CCNA exam which will cover it in more detail, but here are two excerpts from the TechNotes I've written for the Network+ exam:

    **********
    T1/T3
    T1 is a digital leased line made up of 24 channels (called DS0, 1 DS0 is 64K), providing rates up to 1.544 Mbps, often used to connect corporate networks and ISPs to the Internet. The European version E1 is made up of 30 channels providing rates up to 2.048 Mbps.
    T1 uses the DS1 signaling standard and that's why they are sometimes also referred to as DS1 lines.

    A T3 is an even faster digital leased line providing rates up to 44.736 Mbps (672 DS0s), often used for high-speed internet backbones. The European version E3 provides rates up to 34.064 Mbps (480 DS0s).
    Uses the DS3 sin galling standard.

    ISDN PRI
    ISDN PRI (Primary-Rate Interface) is made up of 23 B-channels and 1 D-channel (The European version supports 30 B-channels).
    **********

    (1 B-channel is 64K.)

    It's sometimes said that ISDN PRI (the US version) operates at T1 speed. But this goes for Frame Relay as well, the CIR is fractional T1 (x amount of DS0s) to T1.

    I hope this helps!

    Johan
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  4. Junior Member
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    #3
    Thanks! That clears it up.
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  5. Junior Member
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    #4
    Ok,

    I was watching Keystone Learning video by Todd Lammle last night and he mentions that T1 is another name for PRI in the US. Now Im really confused. HELP.
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  6. Junior Member
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    #5
    What is the difference between the two?
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  7. Junior Member
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    #6

    Default ..

    Feel free to correct me if i'm wrong, i'm still working on passing this exam (taking it in 20 hours actually...been aceing all the transcender stuff for a week and a half now so i'm hopeful)

    last i checked T1's / T3's is a constant leased line connection..aka your always connected?

    ISDN runs through regular phone lines and you dialup when you want to send information out. In other words ISDN is DDR (dial on demand routing) and that's why i think you shouldn't consider T1 and ISDN PRI swappable terms to use because you are always having your T1 line up, your ISDN line however is used as a backup to your dedicated leased line when it goes down (it's not always in use).

    Yes, ISDN PRI and T1 have the same speed, but they are very different types connections if i'm thinking clearly.
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  8. Member
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    #7
    Quote Originally Posted by SoCo4Fun
    Ok,

    I was watching Keystone Learning video by Todd Lammle last night and he mentions that T1 is another name for PRI in the US. Now Im really confused. HELP.
    I agree with Dokudorf, Todd Lammle is also correct. It is true that some people call a PRI a T1, but for the record no one ever calls a T1 a PRI. The terms T1 and PRI are not interchangeable.
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  9. Junior Member
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    #8
    Thanks guys. I think I get it now.

    T-1 = Leased Line
    PRI = DDR

    Thanks!
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