152 CHAPTER 9: C ONFIGURING IP TELEPHONYIP TelephonyOverviewYou can integrate the NBX system into any network infrastructurebecause it can operate at either Layer 2 (Ethernet) or Layer 3 (IP).CAUTION: A qualified network design engineer should set up an IPnetwork for the first time.If all the telephones in your office connect to the same Local AreaNetwork (LAN) and you do not have your LAN segmented intosubnetworks, there is little reason to implement IP telephony. Even if yournetwork includes a few subnetworks, you can configure the routers topass NBX Ethernet frames and avoid the need for IP operation. In a morewidely distributed setting with several subnetworks or with a part of thenetwork distributed over a Wide Area Network (WAN), IP telephony maybe required.This section covers these topics:■ Implementing IP■ Standard IP Configuration■ IP On-the-Fly Configuration■ Providing the NCP IP Address to DevicesImplementing IP You can implement IP in one of two ways:■ Standard IPAll devices receive an IP address, either from a Dynamic HostConfiguration Protocol (DHCP) server or through manual assignment.■ IP On-the-FlyTelephones and other devices on the same subnet as the CallProcessor communicate with other devices on that subnet usingEthernet frames so they do not need IP addresses. Devices receive anIP address only when they need to communicate with a device on adifferent subnetwork. The system administrator specifies a list of IPaddresses using the NBX NetSet utility. When a local device needs anIP address, the system assigns one from the list. Remote devicesreceive their IP addresses either through a DHCP server or throughmanual assignment.
