• 1. Enable multicast routing. Various names for this, including DVMRP, IP multicast routing, PIM Dense mode (Cisco term). Enabling DVMRP will allow NBX multicast traffic to be propagated over all WAN connections to remote sites, for both remote IP phones, or other NBX sites using VTL's. Without this feature enabled, the symptom of a remote IP phone would be no ability to conference, receive pages, no BLF lamp status for mapped lines, and no date/time synchronization with the NCP.

• 2. Set MTU to 1500. Router MTU determines the max size of each packet before the router will fragment the packet to smaller packets. NBX devices will NOT re-assemble audio packets that have been fragmented over a WAN link, thereby resulting in NO AUDIO heard. This is seen most where phone-to-phone calls over the WAN link are OK, but no audio is heard when connected to voicemail or an auto attendant menu over the WAN link. NBX hard disk audio (aa menus, voicemail system audio) has a very large packet size, that if fragmented by ANY router, will mean it will not be played back by the receiving NBX device.

NOTE for Frame Relay and Cisco Routers, affecting Conference Audio Quality only: the command is frame-relay broadcast-queue and must be set to allow 50 pps conference audio for each simultaneous device in a conference. By default, some Cisco routers are set to only 30 pps, not even enough for ONE conference call audio stream to pass

• 3. Support for ToS/DiffServe. Enable this service to properly prioritize voice over WAN connections. Critical if any other (non-nbx) traffic uses the same WAN connection.

Obviously it depends on each particular network, so this is a guideline.

• 1. Disable IGMP snooping, or, Enable IGMP snooping with IGMP Querying also enabled. This will allow multicast traffic for paging, conference calls and Music on Hold to flood all switch ports on all switches. This is required, as NBX devices do not make IGMP join requests, so all NBX multicast traffic must always flood the network for proper operation

• 2. Disable broadcast control. If your switch has such a setting, disable it, so that no broadcast traffic is limited. NBX uses broadcast traffic for adding new devices and initializing devices

• 3. Support 802.1p/q. Switches that support this protocol will prioritize NBX voice when this option is enabled in NetSet for improved performance. Strongly suggested, but not required

• 1. Open proper ports. TCP port 1040, and UDP ports 2093, 2094, 2095, and 2096. If you are running ConneXtions software (H.323), additional ports may need to be opened such as TCP 1720 (call setup), 1731 (audio control) and several others based on individual configuration.

• 2. Consider additional security for the NCP. To prevent DoS attacks to your phone system, you may wish to block popular port access to the NCP from the external network completely, or allow inbound connections from only selected IP addresses. These include FTP, HTTP, SMTP, TELNET, which are open for valid connections for administrative purposes.

— David Gonzalez 2021/04/10 11:21