For VOIP What is sufficient connection to 62 users with an existing 2 T1 lines, and how do you know if the lines are enough for the site

Thank you for creating the site. I'm pretty sure the readers are finding out more of the technology by sharing.

Ok so I am assuming that you have 2 T1 lines on traditional Voice... I will assume PRI, which means you would have had 46 call paths to your location.  I am also assuming from your question the you want to migrate to a SIP connection and they are talking about bringing in a data T1 (which really seems low nowadays) to handle the calls.  If you compress the calls with G.729 you can fit a significant amount of calls on that T1 that is dedicated to your SIP trunk.  So if you take your calculations and come up with 42 calls, you need to leave some bandwidth available for routing on the SIP trunk as there is still some overhead.  But lets say you have have 40 call paths as an estimate.

The question then becomes is 40 call paths enough for 62 users.  The answer is it depends.  If this is just a normal office  - as in no call center, then you can probably safely do an oversubscriton of 8 people to every call path which means you have plenty.  If this is a call center, and you have 50 agents, and 12 office staff, then you stand a chance of not having enough if the call center is extremely busy.

If it is not a call center, and you just have normal office phone usage you will have plenty.

A couple rules of thumb here but it will eventually depend on your exact provider's bandwidth per call, your company's calling patterns, & what other Internet applications you're using, in addition to VoIP.

The average employee-to-simultaneous-call ratio is approx. 4:1... which means with 64 employees, you probably will only have 16 people on the phone at your busiest time.

16 x 38k = 608k.

Each T1 line is approx. 1,500k. 2 T1 lines will thus, give you 3,000k of bandwidth.

So yes, 2 T1 lines is plenty of bandwidth for your VoIP calls... but I highly doubt it's enough bandwidth for anything else you're going to be doing on the Internet, like sending files, downloading anything, etc.

A rough guestimate from being a business ISP & VoIP broker for 15 years: A company with 64 employees (with normal Internet use), will typically need a 100M fiber Internet connection... although more is never bad, right?

Add VoIP to the mix and I'd highly recommend a 100M Fiber circuit and a secondary business class cable circuit (approx. 100M/20M), load balanced with a cloud-enabled SD-WAN service. The SD-WAN service will allow you to prioritize Internet applications for both inbound and outbound Internet traffic... a huge help with call quality. Feel free to PM me if you'd like to chat and get more info. I also have a ton of vendor agnostic content I'd be happy to share.

Much is missing in the question.
VOIP is merely a protocol over which Voice calls will be transmitted, but the important part where the bandwidth comes into play is where is the PBX.
If this is an internal PBX being fed by a PRI, the calls between extensions does not impact/affect the bandwidth of outside calls.
a T1 only has 23 channels over which to carry calls, thus you can only have 23 simultaneous calls at any one time (outgoing+incoming can not exceed the 23 T1 limit or the limit set by your provider if less). 64k sip channel..

If however, you are using a Cloud based PBX with VOIP calls, any call between extensions and inside/outisde will impact the bandwidth. with calls between extensions consuming double the normal call bandwidth.


The number of users is important but not so much, how many incoming and outgoing calls do you need your users to be able to handle at one time.
i.e. if this is a Customer Support call center a T1 would likely not be adequate during peak demand. if this is a regular office, a t1 with these many users might be sufficient. I.e. some offices may have 5-6 active simultenous calls ......


Do you also have Data demands such that the T1 or 2T1 provide both Voice and data services, with the voice gateway handling the bandwidth management by prioritizing resource (bandwidth) allocation to the Voice calls versus the Internet Data .......