determining how many PRI connections will be needed for a site

Posted on 2007-10-11
Last Modified: 2008-03-06
We are setting up a site in Japan with about 55 to 60 user's.  all will be utilizing standard network resources (database access, email access, document access).  There will also be a cisco VioP solution in place for about 10 of those users.  How would I determine how many PRI lines are needed for this.  I'm know to this so please let me know if you need additional info so you can better help me.  Thanks.
Question by:tonymopar440
    LVL 36

    Expert Comment

    Are you just going to use the PRI for voip and general internet access?
    Or are you going to use it for standard telephone services aswell?
    LVL 36

    Expert Comment

    A full bandwidth VoIP connection uses 80kbps of bandwidth per call. You can reduce this a little.
    PRI (E1) has 30 channels of 64kbps bandwidth each.
    A single PRI will therefore give you approx 2Mbps of bandwidth. Even if you have 10 active VoIP calls that will still leave you with 1.2Mbps of bandwidth which should be sufficient for the users.

    It really depends on how heavily you will make use of the internet connection.

    Author Comment

    well, the servers (email, database, ext.) will be at a colocation so I would gather internet use will be pretty steady. so you think 50 to 60 users plus 10 active viop calls would be ok for 2mbps? whould two PRI lines be over kill?
    LVL 36

    Accepted Solution

    I would think that it would be pretty reasonable. You will need some QOS (Quality of service) on the internet connection at both ends. Or you could have the PRI split into two banks so you have two internet connections effectivly. One for normal internet and once for VoIP only so it cannot be interfered with. Worst case you will need 13 channels (PRI has 30 available) for VoIP. Each channel is 64k so 10* 80kbps needs 13. You can use other VoIP codecs other than G711 which will reduce the bandwidth requirement and therefore the number of channels required.

    Even if you use 13 channels for VoIP it will still leave 1Mbps of bandwidth for the normal internet connection.
    It is reasonable for the number of people you have. If you are going to be using email a lot (large files) or downloading off the internet you might want a faster connection. A 2nd PRI is certenly not overkill when you consider it is only 2Mbps and therefore slower than most broadband home connections.
    It really depends on the cost.

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