Page 22 - Overview of Secure VPN Implementation
Example 2
The following example uses the formula below to determine the total bandwidth
required for a 14400 baud fax call using PPP encapsulated in Frame Relay. See page
21 for details of the variables.
(L2_ Fax_ Payload) X Payload_per_sec
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:
8
For PPP encapsulated in Frame Relay the “L2_
header” value is 2 + 6 = 8 bytes.
Step 2
Choose the Fax_header type:
46
Step 3
Choose the PAYLOAD type:
72
For 14400 Fax this value is 72.
Step 4
Choose the sample rate:
200
For 14400 Fax this value is 200.
For example, total bandwidth for a 14400 fax call using PPP over Frame Relay is:
25200 = (8 + 46 + 72) * 200 = 25.2Kbps
(in the direction of the fax traffic)
Guidelines
1. IP Office running 3.0+ has been limited to 1Mbps of throughput for all traffic types.
2. IP Office running 3.0+ does not support IPHC for VPN networking.
3. IPSec performs IP fragmentation in order to avoid illegal VPN frame sizes. IP Office
does not perform IP fragmentation in support of QoS.
4. Although IP Office is able to perform fragmentation, IP Office will not respond to
fragmented ICMP ping requests directed to its system interface address
5. The IPSec QoS feature is only available to IPSec. If it is a requirement to run L2TP
with a mix of VoIP and non-VoIP traffic, then L2TP traffic must be encapsulated in
IPSec.
6. When running IPSec over a WAN link and using PPP, the normal QoS mechanism
(multilink and IPHC) should not be used. Under IP Office 3.0+ implementation
IPSec uses a separate QoS mechanism which is not configurable. The DSCP
values that are specified on the Manager application System/Gatekeeper form are
however used in the normal way to distinguish VoIP traffic types.
Page 22 - Overview of Secure VPN Implementation
IP Office (R3.0)
Typical VPN Deployment
40DHB0002UKER Issue 3 (4th February 2005)
