RTP Ports
Hi ,
RTP ports are used on top of UDP to carry on the voice payload/traffic.
The common range of ports are 16384 and 32767 .
Header
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.
VPN Overhead
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.
QOS – MQC
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
DSP Complexity
The higher is the codec complexity , the fewer number of calls that the DSP can process
PSTN Emulator
Hi ,
Just thinking how can we make a pstn emulator in a lab …. First thought is to use a CME router with several T1/E1 , BRI cards to distribute PSTN connection back-to-back to all locations …..
Need to think about it !!!
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