mà không có sự hỗ trợ của một nhà điều hành hoặc cuộc gọi tự động viên. Dịch vụ này làm cho việc sử dụng của thân DID, mà phía trước chỉ 3-5 chữ số cuối cùng của một số điện thoại tổng đài, router, hoặc gateway. Ví dụ, một công ty có phần mở rộng điện thoại 555-1000 555-1999. Một người gọi quay số 555-1234, | 158 Authorized Self-Study Guide Cisco Voice over IP CVOICE Communications Manager and Cisco IOS routers and gateways without the assistance of an operator or automated call attendant. This service makes use of DID trunks which forward only the last three to five digits of a phone number to the PBX router or gateway. For example a company has phone extensions 555-1000 to 555-1999. A caller dials 555-1234 and the local CO forwards 234 to the PBX or VoIP system. The PBX or VoIP system then rings extension 234. This entire process is transparent to the caller. An FXS DID trunk can receive only inbound calls thus a combination of FXS DID and FXO ports is required for inbound and outbound calls. Two signaling types exist loopstart and groundstart with groundstart being the preferred method. Figure 3-22 shows an analog trunk using an FXS DID trunk for inbound calls and a standard FXO trunk for outbound calls. Figure 3-22 Configuring DID Trunks You could then complete the following steps to enable DID signaling on the FXS port Step 1. Configure the FXS port for DID and wink-start. Router config voice-port 0 0 0 Router config-voiceport signal did wink-start Step 2. Configure the FXO port for groundstart signaling. Router config voice-port 0 1 0 Router config-voiceport signal groundstart Step 3. Create an inbound dial peer using the FXS DID port. Note that direct inward dial is enabled. Router config dial-peer voice 1 pots Router config-dialpeer incoming called-number . Router config-dialpeer direct-inward-dial Router config-dialpeer port 0 0 0 Step 4. Create a standard outbound dial peer using the FXO port. Router config dial-peer voice 910 pots Router config-dialpeer destination-pattern 9 2-8 . Router config-dialpeer port 0 1 0 Chapter 3 Routing Calls over Analog Voice Ports 159 Example 3-5 shows the complete DID trunk configuration. Example 3-5 DID Trunk Configuration Router config voice-port 0 0 0 Router config-voiceport signal did wink-start Router config voice-port 0 1
