Shaping can be applied only in the outbound direction and doesn’t discard the traffic exceeding the rate limit automatically. Shaping will bufferize the queue until the bandwidth become available or in last action will drop exceeding packets.
Compared to Policing , shaping preserves the bandwidth and is recommended on lower bandwidth links.
Qos Shaping is also considered as an Traffic Conditioner
Policing can be used in either the inbound or outbound direction and it discards packets which are exceeding a configured rate limit.
Pay attention to the fact that policing is dropping packets , it can result in retransmissions (TCP acknowledge), so it is better to use policing on higher bandwidth links !!!
Qos Policing is also considered as an Traffic Conditioner
The call load is referred to as Busy Hour Call Attempts ( BHCA) which is the maximum number of active calls during the busiest hour of the day .
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 .
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.
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.
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