• Status: Solved
  • Priority: Medium
  • Security: Public
  • Views: 888
  • Last Modified:

Weighted Fair Queue vs FIFO at serial interface.

I have a test setup. At two ends are Cisco2501(IOS 12.05) and Cisco2611(IOS 12.07). The serial link(64kbps) between the two routers has ftp and netmeeting(VoIP) traffic to simulate congestion conditions. According to my test I start the ftp and let it run for about 2 minutes. Then I start VoIP. I have noticed that with WFQ(Weighted Fair Queueing) at the serial interfaces , the VoIP call never gets established(I think the VoIP packets are simply dropped!!!!!!!!). However , with FIFO(First In First Out policy) at the same interface , the VoIP works fine. Could someone explain the observation?  
0
Siddhartha_s
Asked:
Siddhartha_s
1 Solution
 
scraig84Commented:
To know for sure what is going on, one would need to view a trace of the traffic to see exactly what is getting across and what is not.  Remember that WFQ is just a simple auto-queuing method and has really never done much in my opinion.

However, I have done extensive testing with Class-Based WFQ (CBWFQ) and that works well.  With this you can manually define traffic classes and play with them in all sorts of different ways.

I will also say that if you are concerned with QoS, it is likely that finding an acceptable queuing method won't be enough.  When dealing with latency-sensitive protocols such as H.323 and ICA, problems come in when competing with heartier protocols such as FTP, HTTP, etc.  The average voice packet is fairly small, whereas the average file transfer packet is as large as possible.  Even when little priority is given to the transfer protocols, some packets get through and wind up interleaved into the data stream, causing jitter.  In order to deal with this, you need to chop up the larger protocols to come down to size with the sensitive protocol.  Cisco employs a method called LFI, or you can use simple IP fragmentation by reducing MTU size.  Take a look at the following for more info:

http://www.cisco.com/warp/public/732/Tech/link/

Hope that helps!
0
 
lrmooreCommented:
No comment has been added lately, so it's time to clean up this TA.
I will leave a recommendation in the Cleanup topic area for this question:

I recommend: points to scraig84

If you would like to keep this question open for more expert input, this cleanup effort will get it closer to the top of the list where it will get more visibility for the experts.

if there is any objection or other expert commentary to this recommendation then please post in here within 7 days.
If you feel that your question was not properly addressed, or that none of the comments received were appropriate answers, please post a request in Community support (with a link to this page) to refund your points. http://www.experts-exchange.com/Community_Support/

PLEASE DO NOT ACCEPT THIS COMMENT AS AN ANSWER!

thanks,
lrmoore
EE Cleanup Volunteer
---------------------
0
 
SpideyModCommented:
per recommendation

SpideyMod
Community Support Moderator @Experts Exchange
0
Question has a verified solution.

Are you are experiencing a similar issue? Get a personalized answer when you ask a related question.

Have a better answer? Share it in a comment.

Join & Write a Comment

Featured Post

Cloud Class® Course: Certified Penetration Testing

This CPTE Certified Penetration Testing Engineer course covers everything you need to know about becoming a Certified Penetration Testing Engineer. Career Path: Professional roles include Ethical Hackers, Security Consultants, System Administrators, and Chief Security Officers.

Tackle projects and never again get stuck behind a technical roadblock.
Join Now