3Com OfficeConnect 3CR100A97, Руководство пользователя

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including PPP over Ethernet (PPPoE), PPP over ATM (PPPoA), and
multi-protocol encapsulation over ATM.
Virtual Private
Networks (VPNs)
The full-featured virtual private networking (VPN) functionality of the
OfficeConnect Gateway gives remote offices and telecommuters secure
access to corporate LANs. VPN support is provided through the initiation
and termination of IPSec, PPTP, and L2TP tunnels. The OfficeConnect
Gateway supports up to 16 simultaneous VPN tunnels. Dedicated
hardware acceleration provides high-performance IPSec tunnels.
VPN technology is based on a tunneling strategy. Tunneling involves
encapsulating packets constructed in a base protocol format within some
other protocol. For VPNs that are run over the Internet, packets in one of
several VPN protocol formats are encapsulated within IP packets.
Voice over DSL VoDSL combines asynchronous transfer mode (ATM) with DSL service to
deliver voice and data services over a single copper line. The different
attributes of DSL technology and ATM functionality work well together.
DSL links are ideally suited for voice and data integration. ATM can
simultaneously carry voice and data traffic.
VoDSL is usually provisioned as an overlay to a DSL broadband access
network. A VoDSL implementation requires several additional
components. A voice gateway resides at the service provider’s central
office near a PSTN (Public Switched Telephone Network) telephone switch
(Class 5 Switch) and serves as the bridge between the circuit-based voice
switch and the packet-based DSL network. An IAD, located at each
customer premises, is connected to the DSL circuit. The device manages
voice services via analog POTS ports and Internet service through an
Ethernet port. Existing telephone and LAN equipment interconnect with
the IAD.
The IAD converts LAN and voice data to ATM cells and transmits the data
over the DSL link to the service provider’s network. The DSLAM
aggregates traffic coming from individual lines; encapsulated voice traffic
is sent to the voice gateway and the data traffic is carried as packet or cell
to its final destination, an ISP or corporate network. The voice gateway
converts the voice traffic to conventional voice signals and sends it to a
Class 5 voice switch.
An example of a typical VoDSL implementation is shown in the following
illustration.