Some small office/home office (SOHO) environments lack sufficient IP phones to justify the purchase of CCM servers. Although these smaller offices might be able to register with a centralized CCM cluster using the IP WAN, some IP telephony designers instead recommend (for redundancy and scalability) the purchase of Cisco CallManager Express (CME) routers for these locations. The CME feature supports CCM-like functions on a router, as opposed to a dedicated server platform, thus reducing a customer's investment.
Network Module (NM) The NM-CUE or NM-CUE-EC network modules each occupy a network module slot in a router and support up to 100 user mailboxes.
Advanced Integration Module (AIM) The AIM-CUE card mounts on a router's motherboard and supports up to 50 user mailboxes.
CUE hardware and software fully integrates into 2600XM, 2691, 2800, and 3800 Series routers. Although you can use CUE in conjunction with CME, you might also use CUE as your voice mail/auto attendant solution in a CCM server environment. Like the CCM server, administrators can configure both the CME and CUE via a web interface, as shown in Figure 4-30.
CUE's automated attendant function allows the router to answer incoming calls. Callers can then interact with CUE by, for example, entering extension numbers using their telephony keypad. Companies can create custom greetings and provide recorded answers to commonly asked questions (for example, directions and hours of operation). Also, administrators can configure CUE with a company's holiday and hours of operation information, giving callers different call treatment for times when the business is closed.
Similar to a CCM server environment, IP phones register with a CME router using SCCP. However, recall that before an IP phone registers, it typically gets an IP address from a DHCP server and downloads a configuration file from a TFTP server. In the CME environment, the CME router can function as both a DHCP server and a TFTP server, eliminating the need for an external server. Once the CME router establishes a call between a couple of IP phones, the IP phones communicate directly between themselves using the RTP, as shown in Figure 4-31.
The CME router might also contain analog or digital interfaces (for example, FXO, Foreign Exchange Station (FXS), Integrated Services Digital Network (ISDN), or T1 interfaces) to send calls originating from an IP phone out to a PBX or to the PSTN.