by olivier | Feb 20, 2010 | QOS, Written Theory
Depending the Layer 2 technology that you use , the header can change :
- Ethernet Frame => 18 bytes
- Frame Relay/FRF.12 => 6 bytes
- MLP => 6 bytes 13 bytes
- ATM => 5 bytes
- MLP over Frame Relay => 14 bytes
For Layer 3 , you can use the following values
- IP Header = 20 bytes
- UDP Header = 8 bytes
- RTP Header = 12 bytes
So it gives you the following amount
- IP+TCP+UDP Header => 40 bytes
With CRTP enabled, you can then benefit of a huge saving of compression of this payload.
Indeed , from 40 bytes , you can decrease this payload from 2 up 4 bytes.
(more…)
by olivier | Feb 20, 2010 | QOS, Written Theory
Please , don’t forget also that VPN mechanisms add a lot of overhead to your voice packets and it depends also of the technology that you deploy (L2TP for Layer 2 or IPSEC for Layer 3).
So as rule , we can add 30 to 60 bytes of overhead per voip packet when you transmit the packet over the VPN paths.
by olivier | Feb 20, 2010 | IOS, QOS, Written Theory
Here is as short recap/representation of the MQC ( Modular QoS CLI)
Step #1 : Classify Traffic => CLASS-MAP
Step #2 : Assisgn Policies to the traffic classes => POLICY-MAP
Step #3 : Apply the policy to an interface => SERVICE-POLICY
