Solved

VoIP jitter

Posted on 2014-01-24
10
1,891 Views
Last Modified: 2014-04-08
Before I googel around. I know that from Cisco, an acceptable VoIP deplay is 150ms one-way. I'd like to get some feedback on what is an acceptable jitter time for VoIP. Is it depending on the codec? Is it depending on the network devices?

I have a Cisco switches infrastructure and I have NEC VoIP phone.

Thx
0
Comment
Question by:leblanc
  • 5
  • 3
  • 2
10 Comments
 
LVL 17

Assisted Solution

by:Spartan_1337
Spartan_1337 earned 125 total points
ID: 39806978
It is dependent on the codec. G711 and G729 cannot handle packet loss and delay needs to be less that 100ms.
On network devices, you configure them for QoS and mark the VOIP traffic and give it priority over the rest. It also depends where you are connecting to, over a WAN or internet?
Either way you need to prioritize your traffic and ensure that VOIP is always given greater priority.
0
 
LVL 1

Author Comment

by:leblanc
ID: 39807015
I am testing the jitter over the MPLS in preparation for the VoIP deployment. I am using iperf but I am not sure the paramaters I should use for UDP with the corresponding codec.

What is the recommended jitter for g711 or g729? is it 2ms? 10ms? 17ms?
 
How about the buffer for UDP for voice?

How big is the packet size for g711 and g729?

Thx
0
 
LVL 17

Expert Comment

by:Spartan_1337
ID: 39807162
OK. This is where you will have to ask you MPLS provider IF they are applying QoS to your circuit and what policy are they using. From there you will have to match those settings on your router. This needs to be an exact match for QoS to properly work.
0
Space-Age Communications Transitions to DevOps

ViaSat, a global provider of satellite and wireless communications, securely connects businesses, governments, and organizations to the Internet. Learn how ViaSat’s Network Solutions Engineer, drove the transition from a traditional network support to a DevOps-centric model.

 
LVL 1

Author Comment

by:leblanc
ID: 39807954
no I understand, They are applying QoS on their circuit.
I am injecting packets with iperf to test my jitter. My question is not about QoS. It is about jitter. What is a reasonable response time for VoIP jitter? and how big is the packet size for g711 and g729?
0
 
LVL 17

Assisted Solution

by:pergr
pergr earned 375 total points
ID: 39808629
Latency and jitter is different things.

There is really no problem with latency (more than 100ms its fine) - you will just have a delay when talking to each other.

Jitter is the difference in latency between different packets in the same flow (call). The limits depends on the phones. Basically the phone will not play the sound immediately when a packet is received - it waits a bit in case the next packet will be extra delayed.  That time is called jitter buffer. It is best to use dynamic jitter buffers,  if your phone supports it. It means that when the network is bad the phone automatically increases the jitter buffer a bit.

Any packet that arrives after the jitter buffer time is expired will not be played, and there is a gap in the call.
0
 
LVL 1

Author Comment

by:leblanc
ID: 39809391
So what is a reasonable response time for VoIP jitter? I am using iperf to get some stats and I have in average 6ms for the jitter. I am simulate UDP traffic with 64kbps packet size. But I am not sure if 6ms is a reasonable time for jitter.
0
 
LVL 17

Assisted Solution

by:pergr
pergr earned 375 total points
ID: 39809696
Anything under 30ms should be fine. Some phones might be able to handle up to 100ms jitter.

When you run the test, make sure that you set the TOS marking of the packets to the same as your phones TOS marking.
0
 
LVL 1

Author Comment

by:leblanc
ID: 39810645
"Anything under 30ms should be fine. " Where can I validate this statement? Thx
0
 
LVL 17

Accepted Solution

by:
pergr earned 375 total points
ID: 39810660
0
 
LVL 1

Author Comment

by:leblanc
ID: 39810667
That is exactly what I am looking for http://www.ciscopress.com/articles/article.asp?p=357102. Thank you very much.
0

Featured Post

Free Tool: Port Scanner

Check which ports are open to the outside world. Helps make sure that your firewall rules are working as intended.

One of a set of tools we are providing to everyone as a way of saying thank you for being a part of the community.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

Suggested Solutions

Title # Comments Views Activity
cti route point to unity issue 2 49
HP 2530 switch and routing 4 59
How do you restart a stacked switch? Hp Procurve 3 57
DFS replication issue 7 14
Even if you have implemented a Mobile Device Management solution company wide, it is a good idea to make sure you are taking into account all of the major risks to your electronic protected health information (ePHI).
I had an issue with InstallShield not being able to use Computer Browser service on Windows Server 2012. Here is the solution I found.
Viewers will learn how to connect to a wireless network using the network security key. They will also learn how to access the IP address and DNS server for connections that must be done manually. After setting up a router, find the network security…
After creating this article (http://www.experts-exchange.com/articles/23699/Setup-Mikrotik-routers-with-OSPF.html), I decided to make a video (no audio) to show you how to configure the routers and run some trace routes and pings between the 7 sites…

763 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question