DHCP 6-27caller identity (and finds, then connects to, the recipient’s IP address). The IPaddress of the intended recipient is their (SIP) phone number.By creating and storing a caller identity, a proxy server enables party A to callparty B (and vice-versa), even if the recipient’s IP address (SIP phone number) isnot specifically known to the caller. Additionally, through the implementationof a user name and password scheme, the proxy server provides a simple yeteffective security mechanism for SIP phone callers and call recipients alike.When a SIP phone user places a call to a conventional telephone connected tothe PSTN (Public Switched Telephone Network), the call is passed to theconventional telephone via a voice gateway. Voice GatewayAs the last major link in the SIP phone network infrastructure, the voicegateway forwards the IP address (SIP phone number) received from the proxyserver to the telephone company’s Central Office (CO). Once received by theCO, the IP address is mapped to a conventional (non-SIP) phone number. Fromthis point on, the phone call is processed through the telephone companynetwork like any other non-SIP phone call originating from a conventionaltelephone.For more information about 3Com SIP phone products, please see our web site athttp://www.3com.com/products/sip.DHCP Dynamic Host Configuration Protocol (DHCP) is designed to provide a centralizedapproach for configuration of IP addresses and parameters.When a workstation is configured for automatic assignment of IP addresses, itbroadcasts a request out on the LAN. The DHCP Server responds with an IPaddress for the workstation, the domain name, and the IP addresses of the defaultrouter, two DNS Servers, and two WINS Servers.The assignment of an IP address to the workstation is for a specified period oftime, referred to as the lease period. Before the lease is set to expire, theworkstation will send a request to the server to extend the lease period. The servermaintains a list of assigned IP addresses and the duration period of the leases.When a lease expires, the IP address can be reassigned to another workstation.The OCR 812 can be configured to support up to 40 workstations on the localLAN. In addition, the OCR 812 can be configured to be a DHCP Relay. Whenenabled, the Relay will process the broadcast request from the local workstationand send it to one or two remote DHCP servers. The response from the remoteDHCP servers is processed and forwarded to the local workstation.Remember to save your configuration using the save all command beforerebooting your OCR 812 so that your changes will be written to permanent FLASHmemory.Configuring the DHCPModeThe OCR 812 has three DHCP modes: Server, Relay and Disable. To configure the mode, use the following command:set dhcp mode [SERVER | RELAY | DISABLE]
