Справочник Пользователя для Netopia ISDN Router

Tunneling is a process of creating a private path between a remote user or private network and another private 
network over some intermediate network, such as the IP-based Internet. A VPN allows remote offices or 
employees access to your internal business LAN through means of encr yption allowing the use of the public 
Internet to look “vir tually” like a private secure network. When two networks communicate with each other 
through a network based on the Internet Protocol, they are said to be tunneling through the IP network.

Unlike the phone company, private and public computer networks can use more than one protocol to carr y your 
information over the wires. Two such protocols are in common use for tunnelling, Point-to-Point Tunnelling 
Protocol (PPTP) and Ascend Tunnel Management Protocol (ATMP). The Netopia R310 can use either one.

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Point-to-Point Tunneling Protocol (PPTP) is an extension of Point-to-Point Protocol (PPP) and uses a client 
and ser ver model. Netopia’s PPTP implementation is compatible with Microsoft’s and can function as 
either the client (PAC) or the ser ver (PNS). As a client, a Netopia R-series router can provide all users on a 
LAN with secure access over the Internet to the resources of another LAN by setting up a tunnel with a 
Windows NT ser ver running Remote Access Ser vices (RAS) or with another Netopia Router. As a ser ver, a 
Netopia R-series router can provide remote users a secure connection to the resources of the LAN over a 
dial-up, cable, DSL, or any other type of Internet access. Because PPTP can create a VPN tunnel using the 
Dial-Up Networking (DUN) (see 

 utility built into Windows 95, 

98, or NT, no additional client software is required.

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Ascend Tunnel Management Protocol (ATMP) is the protocol that is implemented in many Ascend routers. 
ATMP is a simple protocol for connecting nodes and/or networks together over the Internet via a tunnel. 
ATMP encapsulates IP or other user data without PPP headers within General Routing Encapsulation (GRE) 
protocol over IP. ATMP is more efficient than PPTP for network-to-network tunnels.

When used to initiate the tunnelled connection, the Netopia R310 is called a PPTP Access Concentrator (PAC, in 
PPTP language), or a foreign agent (in ATMP language). When used to answer the tunnelled connection, the 
Netopia R310 is called a PPTP Network Ser ver (PNS, in PPTP language) or a home agent (in ATMP language).

Transit Internetwork

Logical

Equivalent

Virtual Private Network