Section 5 Codec And Bandwidth; Figure 6-2 Virtual Private Network (Vpn) Example - NEC Sl2100 Networking Manual

ISSUE 1.0
ADSL
Router
Firewall /
Chassis
SL2100
Head Office LAN
When IP address translation is applied to a VoIP packet, the application fails and the communication
path is broken. VoIP packets contain the IP address information and the ports used as part of its
payload. When NAT is applied, only the header parameter is changed, not the payload data that
affects the process of data packets within the VoIP switch and terminal.
The common scenario for remote IP deployment is:
• Implementation of an IP Phone with a public IP address talking with an NEC SL2100 behind NAT.
An example would be a telecommuter.
Implementation of an IP Phone behind a NAT, which connects to the Internet, terminates in a NEC
SL2100 behind a different NAT.
When selecting VPN equipment it is important to consider Quality of Service. Generally, VPN
hardware is connected to Internet connections which are unreliable and out of the control of the
customer. However, it is possible to set prioritization on some VPN units for voice traffic. This does
not solve the unreliability of the Internet, but helps to ensure that the data traffic to and from the LAN
do not impair the quality of the voice traffic. (Refer to
NEC strongly recommends that any VPN hardware used for VoIP has the facility to prioritize voice
traffic.
S 5 CODEC AND BANDWIDTH
ECTION
This section describes CODEC and bandwidth and their application with the NEC SL2100 system.
Networking Manual
VPN
Mobile Workers
(Software VPN Client)

Figure 6-2 Virtual Private Network (VPN) Example

Internet
QoS on page 6-1).
SL2100
ADSL
Router
Firewall /
VPN
Home Office LAN
6-7