 remote site to the SP. Figure 12-6 shows the overall SIP trunking architecture of the bank. 276 SIP Trunking Switch Service Provider CUCM Cluster 6.1 Data Center Branch Office CUBE/SRST Switch 8 FXO Figure 12-6 Distributed SIP Trunking Connectivity Bank Requirements The bank had the following requirements: PSTN Access: The bank was asking for the following PSTN services from the SP: Emergency services Local numbers Long distance International calling Codec Default codec of G.729 on both call legs, that is, CUCM and SP: The bank wanted to use threshold values of CPU, memory, and total call for the CAC on the remote gateway. Chapter 12: Case Studies 277 Multiple protocols on single remote site gateway: CUBE, SRST, and MGCP in a single router. SP Requirements The SP had the following requirements: SIP Signaling: SP requires the usage of Early Offer over SIP trunk. SIP trunk registration: No credentials required for SIP trunk registration from the SP. CAC: The SP's requirement is to send it a 486 Busy Here SIP error code when the threshold is reached SO that the SP issues a standard busy indication back to the caller. Calling number: The SP is to allow calls only into the SP's network that have the allo- cated Direct Inward Dial (DID)-numbers either in the Remote Party ID or Diversion header of the SIP INVITE message. Configurations You need to configure two components to enable the SIP trunk at the enterprise side: CUCM configuration CUBE configuration In the following sections, we show you the step-by-step configurations of CUCM and CUBE. But, we do not cover the configuration of the SP side. CUCM Configuration You need to log in into the CUCM administrative interface and configure the following things to enable the SIP trunking with CUBE. Step 1. Configure a SIP Trunk Security Profile: The SIP Trunk Nonsecurity Profile is defined. Step 2. Create a new SIP Profile. The Standard Profile is created. Step 3. Configure a Region and Device Pool: To accommodate the G.729 codec and MTP requirement, you must configure the