INTELLIGENT WORK FORUMS
FOR COMPUTER PROFESSIONALS

Log In

Come Join Us!

Are you a
Computer / IT professional?
Join Tek-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!

*Tek-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Jobs

VOIP bandwidth calculation

VOIP bandwidth calculation

(OP)
Hi guys,

I ´m a little confused with bandwidth concept for VoIP.

Ok, I´m trying to figure out why we have troubles with cutted-voice on our IP Phones. We have a Siemens Hipath 2036, and according to configuration, the branch is configured with G.711.

Theory says that codec G.711 requires 64kbps, so if have 4 IP Phones, should we require a total bandwidth of 4 x 64 kbps = 256 kbps ?  Ok it could be a little more adding overhead and other headers, so the total could be less than 512 kbps.

I also tried to configure G.729, and have activated the VAD (voice activity for silence suppression) but the problem is still appearing.

Am I wrong with this concept ?

Please any advice.....

RE: VOIP bandwidth calculation

"cutted voice" sounds like the sort of thing you can get if you have a duplex mis-match on one of your network interfaces. Check all your relevant network interfaces for errors. Especially the ones connecting your voice servers/gateways/etc... to the network.

RE: VOIP bandwidth calculation

does the issue with choppy voice happen on internal calls or calls to the outside?
A g711 call requires 128kbps per call total not 64. Overhead is also added to that, but that depends on the connection.

RE: VOIP bandwidth calculation

Do you have a voice VLAN and QoS on the network?  You do not calculate by device, you calculate by call volume, how many active calls are on the network.  And if you have Music on hold, there are additional calculations for the media stream for hold music.  What kind of Total Network traffic is going on?  Have you done a traffic study?

RE: VOIP bandwidth calculation

(OP)
Ok, first thank you guys for your responses.

We have several branches pointing to main office. Each branch has a Hipath 2036 while the main site has a Hipath 3800 system.

The cutted voice problem arise when calls are establishes between sites. Our carrier provides us point-to-point links between each branch and main site.

We have 3 subnets (Data, voice and video) for each branch. Those subnets are delivered using 1 fiber optic cable. I use internal vlans on our LAN switches and I suppose that our carrier use trunking through the fiber. I calculated the voice bandwidth considering just 64 kbps per call.

So, should I consider more bandwidth for the voice subnet ?  

RE: VOIP bandwidth calculation

You are not telling us what kind of bandwidth you have between sites or the volume of call expected between them. Regardless, your issue is a qos issue between sites. Voice has to be tagged on your edge devices with high priority (dscp ef). Of course that has to be honored by your provider as well otherwise it will not work.

RE: VOIP bandwidth calculation

(OP)
We have different bandwidth configurations, all same for each branch:
  - Data link ( 1 Mbps )
  - Voice Link ( 512 kbps)
  - Video link (just 1 camera for each branch) ( 256 kbps )

We don´t have QoS configured by our carrier.  

RE: VOIP bandwidth calculation

Ok so at g711 you can have a maximum of 4 simultaneous calls per branch. That is without counting any overhead. Truly I would say anything over 3 calls you will have voice quality degradation.
You can do g729 and get many more calls across the 512 link though. Are these bandwidth constrictions one single link to each site? if so what is the speed and what type? P2P, MPLS etc.

 

RE: VOIP bandwidth calculation

Try this...

http://www.voip-calculator.com/calculator/

Of top of my hard G711 = 80k (inc overheads) / direction, so bi-directional = about 160k

However choppyness is often dropped or out of order packets.

 

Robert Wilensky:
We've all heard that a million monkeys banging on a million typewriters will eventually reproduce the entire works of Shakespeare. Now, thanks to the Internet, we know this is not true.

http://alvechurchlounge.org.uk

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Tek-Tips Forums free from inappropriate posts.
The Tek-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Tek-Tips forums is a member-only feature.

Click Here to join Tek-Tips and talk with other members!

Resources

Close Box

Join Tek-Tips® Today!

Join your peers on the Internet's largest technical computer professional community.
It's easy to join and it's free.

Here's Why Members Love Tek-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close