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2622 Views 4 Replies Latest reply: Mar 3, 2011 1:06 AM by Sey RSS

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E1 & T1

Feb 11, 2011 3:39 AM

achilleus 4 posts since
Jan 12, 2010

Hey Guys,


I am really confused between E1s & T1s, CAS & CCS signalling & PRI. Following are my questions,


Q1) Are E1s & T1s type of PRI?




Q2) Is E1 different than a PRI? (The reason I ask this is because this was one of the questions I was asked in an interview,  i.e. What is the difference between PRI & E1)



Q3) Is ISDN E1 different than a normal E1?


Q4) Does CAS signalling depend upon the type of PRI being used, i.e. Is it different (with respect to channels used for signalling) in case of E1, than that of T1?





  • Conwyn 9,681 posts since
    Sep 10, 2008
    Currently Being Moderated
    1. Feb 11, 2011 4:04 AM (in response to achilleus)
    Re: E1 & T1

    Hi Acilleus


    T1 and E1 are speed definition and but we normally refer to channelized T1 and E1 which consists of 24 or 32 channels.


    These channels can be used in different ways.


    For E1  PRI the first and sixteenth channel have special control function and for T1 the final channel is used.


    I believe channel signal is different between Europe E1 and the Americans T1.


    Regards Conwyn

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  • Bill James 29 posts since
    Aug 19, 2008
    Currently Being Moderated
    2. Feb 11, 2011 4:14 AM (in response to achilleus)
    Re: E1 & T1

    Q1) E1 and T1 are a type of 'Pipe' E1 is used mainly in Europe and T1 in the U.S.A. Both can be configured as an ISDN PRI, which changes the the signaling from CAS to CCS.


    Q2) E1 is different. Think of E1 or T1 as a stripped down version of a truck, no radio, no AC, no frills. When you add ISDN services it becomes a PRI, and now you can pass all the caller info, as well as networking info between sites.


    Q3) yes and no. ISDN is additional services added to the E1 pipe, and changes signaling to CCS


    Q4) With PRI there is no CAS, (or robbed bit signaling), the signaling is sent in a special channel. In the case of T1 ISDN PRI channel 24 becomes the D-Channel, (or Data-Channel). All info is sent on this channel. Including call setup and teardown, caller and calling party info, which B-channel to use, as well as other signaling info. The remaining 23 channels are now B-Channels, (Bearer-Channel), which carries the voice. With E1 ISDN PRI there is 1 D-Channel and 30 B-Channels.


    Hope this helps.

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  • Sey 1,393 posts since
    May 4, 2010
    Currently Being Moderated
    4. Mar 3, 2011 1:06 AM (in response to achilleus)
    Re: E1 & T1


    30 are bearer channels

    1 D channel


    then what is the 1 remaining channel used for?

    One timeslot (TS0) is reserved for framing purposes, and alternately transmits a fixed pattern. This allows the receiver to lock onto the start of each frame and match up each channel in turn. The standards allow for a full Cyclic Redundancy Check to be performed across all bits transmitted in each frame, to detect if the circuit is losing bits (information), but this is not always used.


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