Overview of Secure VPN Implementation - Page 21
Bandwidth Requirement Calculation
Example 1
The following example uses the formula below to determine the total bandwidth
required for a G729 call using IPSec encryption (3DES) over Ethernet. See page 20 for
details of the variables.
(L2_ Tunneling _ VoIP_ Payload) X Payload_per_sec X Bit__conversion
Use the calculation above to determine total bandwidth requirement then set the
appropriate values (in terms of the allowed number of calls) by using IP Line
parameters.
Task Description
Step 1
Chose the layer 2 media type: 14
For Ethernet the “L2_ header” value is 14 bytes.
Step 2
Choose the tunnel type: 52
For IPSec this value must be chosen with
respect to the VoIP compression type that is to
be used, for G729 this value is = 52.
For L2TP the value is fixed for all compression
types.
For the case where IPSec and L2TP are used in
conjunction e.g. L2TP protected IPSec both
tunneling headers must be added.
Step 3
Choose the VoIP_header header type:
40
Without IPHC the VoIP header is = 40.
Step 4
Choose the PAYLOAD type:
20
This choice must be consistent with tunnel type
(see step 2 above). For G729 this value is 20.
Step 5
Choose the sample rate:
50
This choice must be consistent with tunnel type
(see step 2 above). For G729 this value is 50.
For example, total bandwidth for a G729 call using IPSec over Ethernet is:
50400 = (14 + 52 + 40 + 20) * 50* 8 = 50.4Kbps
(in each direction)
Note:
The Ethernet header is generally stripped by the DSL.
IP Office (R3.0) Virtual Private Networking
Overview of Secure VPN Implementation - Page 21
40DHB0002UKER Issue 3 (4th February 2005)
Typical VPN Deployment
