Netopia R2020 - Manual (Page 104)

9-2 User’s Reference Guide
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 Router can use either one.
■ 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
“Dial-Up Networking for VPN” on page 9-10) utility built into Windows 95,
98, or NT, no additional client software is required.
■ 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 Router 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 Router is called a PPTP Network Ser ver (PNS, in PPTP language) or a home agent (in ATMP language).
In either case, the Netopia Router wraps, or encapsulates, information that one end of the tunnel exchanges
with the other, in a wrapper called General Routing Encapsulation (GRE), at one end of the tunnel, and unwraps,
or decapsulates, it at the other end.
Transit Internetwork
Logical
Equivalent
Virtual Private Network