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598 CHAPTER 42: CONFIGURING VPN
The VPN with service quality guarantee can provide different levels of service
quality guarantees for users by charging for different services.
Basic Networking
Applications of VPN
An enterprise that has an intranet established with VPN is shown in the following
figure.
Figure 178 Schematic diagram of VPN networking
In this configuration, the users who need the internal resources of enterprises, can
access the POP (Point of Presence) server of local ISP via PSTN or ISDN, and further
access the internal resources of the enterprises. Traditional WAN construction
techniques only supply the service with the aid of leased line between them. After
a VPN is established, the remote users and the clients in other places can access
internal resources of enterprises even if they do not have the Internet access
authority given by local ISP.
VPN services of enterprises only require a server supporting VPN (a Windows NT
server or a router). After connecting the local POP server via PSTN or ISDN, the
users who want a resource directly call the remote servers of enterprises (VPN
servers). The access server of ISP along with the VPN server accomplishes the call
process.
Classification of IP
VPN
IP VPN is the emulation of leased line services (remote dial-up and DDN) of WAN
equipment using IP facilities (including public Internet or private IP backbone
network). IP VPN classification is based on:
■ Operation Mode
■ Tunnel Protocols
■ Service Purpose
■ Networking Model
Operation Mode VPNs can be CPE- or network-based. CPE-based VPN's require installation of
networking and authentication equipment to support establishment of the VPN. It
requires configuration and administration of WAN resources and bandwidth
management.
In a network-based VPN, the maintenance of VPN is allocated to the ISP, although
users are allowed to manage and control services to some extent. VPN functions
are mainly fulfilled on the equipment at the network side. This type of service
reduces the investments of the users, increases the flexibility and scalability of
services, bringing profits to the service providers.
POP
POP
POP
PC
PSTN/ISDN
Partner
Remote user
Internal server
Internet
Headquarters