AudioCodes Mediapack mp-11x, Руководство пользователя

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Version 5.2 369 August 2007
SIP User's Manual 8. Networking Capabilities
The CHAP is a more sophisticated method of authentication. The two hosts share a
‘secret’. The authenticator sends a ‘challenge’ to the host requesting authentication. The
host performs a calculation (one-way hash) using the challenge received from the
authenticator and the shared ‘secret’, and sends the result to the authenticator. The
authenticator verifies the host if the result of the calculation is correct; otherwise it is
rejected.
The last configuration phase, immediately after the authentication phase (or after the Link
Configuration) is the Network Control Protocol. There is a family of control protocols for
establishing and configuring different network-layer protocols, for example, IPCP (PPP
Internet Protocol Control Protocol), IPv6CP (PPP IP v6 Control Protocol), and BCP (PPP
Bridging Control Protocol). Each of them handles and manages the specific needs required
by their respective network-layer protocol.
When working in an IP network, IPCP is used as the Network Configuration Protocol. The
IPCP is used to configure the network layer of the hosts, requesting/declaring on IP
Addresses.
Further information on PPP Protocol is available on the IETF Web site
(
http://www.ietf.org/rfc/rfc1661.txt ). Further information on Password Authentication
Protocol is available on the IETF Web site ( http://www.ietf.org/rfc/rfc1334.txt ). Further
information on Challenge Handshake Authentication Protocol is available on the IETF Web
site (
http://www.ietf.org/rfc/rfc1994.txt ). Further information on PPP Internet Protocol
Control Protocol (IPCP) is available on the IETF Web site
(
http://www.ietf.org/rfc/rfc1332.txt ).
8.3.2 PPPoE Overview
PPPoE is a method of sending the Point-to-Point Protocol over Ethernet network. PPPoE
provides the ability to connect a network of hosts over a simple bridging access device to a
remote Access Concentrator. Access control, billing and type of service can be done on a
per-user, rather than a per-site, basis.
A common use of the PPPoE is in the ADSL market: The home PC is connected to a
modem via Ethernet, and the PC uses the PPPoE to ‘simulate’ as if it was directly
connected to the remote host on a point-to-point connection.
Since PPPoE frames are sent over Ethernet, each PPP session must learn the Ethernet
address of the remote peer, as well as establish a unique session identifier. The PPPoE
standard describes a discovery protocol that provides this. A PPPoE session begins with a
discovery phase. Only after this discovery is completed can the PPP state machine start
(with LCP, Authentication etc, as described above).
Each of the Ethernet frames carrying PPP session has a standard Ethernet header
followed by PPPoE header, and is sent with the remote host Ethernet MAC address
(except for the very first one, in the discovery phase, which is broadcasted to all hosts).
Further information on the transmission of PPPoE is available on the IETF website
(http://www.ietf.org/rfc/rfc2516.txt ).
8.3.3 PPPoE in AudioCodes Gateway
The AudioCodes gateway contains a PPPoE client embedded in its software. When
configured, the gateway can try to connect to a remote PPPoE Access Concentrator.
When resetting the gateway after several BootP attempts and if PPPoE is enabled (see
ini
file parameter EnablePPPoE), the gateway tries to initiate a PPP session.