3Com® VCX V7111 VoIP Gateway User Guide 283CHAPTER 9: NETWORKING CAPABILITIESEthernet Interface ConfigurationUsing the parameter EthernetPhyConfiguration, users can control the Ethernet connectionmode.Either the manual modes (10 Base-T Half-Duplex, 10 Base-T Full-Duplex, 100 Base-TX Half-Duplex, 100 Base-TX Full-Duplex) or Auto-Negotiate mode can be used.Auto-Negotiation falls back to Half-Duplex mode when the opposite port is not Auto-Negotiate, but the speed (10 Base-T, 100 Base-TX) in this mode is always configuredcorrectly. Note that configuring the gateway to Auto-Negotiate mode while the opposite portis set manually to Full-Duplex (either 10 Base-T or 100 Base-TX) is invalid (as it causes thegateway to fall back to Half-Duplex mode while the opposite port is Full-Duplex). It is alsoinvalid to set the gateway to one of the manual modes while the opposite port is either Auto-Negotiate or not exactly matching (both in speed and in duplex mode). Users areencouraged to always prefer Full-Duplex connections to Half-Duplex ones and 100 Base-TXto 10 Base-T (due to the larger bandwidth). It is strongly recommended to use the samemode in both link partners. Any mismatch configuration can yield unexpected functioning ofthe Ethernet connection.Note that when remote configuration is performed, the gateway should be in the correctEthernet setting prior to the time this parameter takes effect. When, for example, thegateway is configured using BootP/TFTP, the gateway must perform many Ethernet-basedtransactions prior to reading the ini file containing this gateway configuration parameter.To work around this problem, the gateway always uses the last Ethernet setup modeconfigured. This way, if users want to configure the gateway to work in a new networkenvironment in which the current Ethernet setting of the gateway is invalid, they should firstmodify this parameter in the current network so that the new setting holds next time gatewayis restarted. After reconfiguration has completed, connect the gateway to the new networkand restart it. As a result, the remote configuration process that takes place in the newnetwork uses a valid Ethernet configuration.NAT (Network Address Translation) SupportNAT is a mechanism that maps a set of internal IP addresses used within a private networkto global IP addresses, providing transparent routing to end hosts. The primary advantagesof NAT are (1) Reduction in the number of global IP addresses required in a private network(global IP addresses are only used to connect to the Internet); (2) Better network security byhiding its internal architecture.Figure 105 illustrates the NAT architecture.
