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User Manual - Configuration Guide (Volume 3)
Versatile Routing Platform
Chapter 1
VPN Overview
1-2
5) With VPN, users can make mobile access at any time and place, meeting the
increasing mobile service requirements.
6) VPN with service quality guarantee, e.g. MPLS VPN, can provide different levels
of service quality guarantees for users in exchange for different service charges,
harvesting surplus profit. In addition, in terms of implementing the same functions,
the networks can be used more effectively when these services are provided by
specialized public networks rather than the networks established by the
enterprises themselves.
Take an enterprise for example. The Intranet established with VPN is shown in the
following figure.
POP
POP
POP
PC
PSTN / ISDN
Partner
Remote users
Internal server
Internet
Headquarter
Figure VPN-1-1 Schematic diagram of VPN networking
It can be found in the above figure that the users of internal resources of enterprises
access the POP (Point of Presence) server of local ISP via PSTN network, and thus
they can communicate with each other. Conventional WAN construction technique can
only score the same goal with the aid of leased line between them. After 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 of local
ISP. This means a lot to clerks who travel a lot and geographically widely distributed
clients.
VPN services of enterprises only require a server supporting VPN at resource sharing
location (a Windows NT server or a router supporting VPN). After accessing local POP
server via PSTN, resource users directly call the remoter servers of enterprises (VPN
servers). The call mode is the same as that with PSTN connection, with the rest of work
completed by Access Server of ISP.
1.2 Classification of IP VPN
IP VPN means the simulation of leased line services of private WAN equipment
performed with IP facilities (including public Internet or private IP backbone network).
IP VPN has the following classification methods:
I. According to operation mode
1) CPE-based VPN
The users not only install expensive equipment and private authentication tools, but
also are engaged in multifarious VPN maintenance (e.g. channel maintenance and
bandwidth management). The networking is complicated, but its service scalability is
weak.
2) Network-based VPN
NBIP-VPN