3Com NBX VoIP Phone System

Requirements and Functionality of the 3Com NBX VoIP System

1. Based on the 3Com documentation, it appears that the following protocols/functionality must be supported for the network infrastructure in order to support the 3Com NBX VoIP Phone system:
   • IGMP Version 2
   • IPTOS QoS (Priority Bit 6).
2. The IGMP Version 2 protocol is necessary to support extended features of the NBX platform. Specifically, conference calls and transfer features require this protocol to minimize the bandwidth requirement to support this type of conversation. The IGMP protocol is an IP multicasting protocol that is used by the 3Com NBX platform to minimize the amount of data streams need to support a conference call. If the 3Com NBX had to transmit a single stream for each user during a conference call, the bandwidth requirement to support multiple users at the same remote location would quickly saturate the WAN. The operation of this protocol can be verified during network testing utilizing a network sniffer.
3. Currently, phone service via the remote 3Com IP phones and the corporate office is operational. But, voice quality service to these locations is described to be non-satisfactory from a user’s perspective. The VoIP call quality tends to be described as “choppy” and sporadic in frequency. This description clearly illustrates the effects of running VoIP over an IP infrastructure WITHOUT any quality of service mechanisms configured.
4. Bandwidth Requirements: (The 3Com NBX has two options for Layer 3 bandwidth options)
   
   Layer 3 Mulaw (G.711) Audio
   • 86Kbps per party in the conversation.
   • A point-to-point call requires this peak bandwidth in the each direction, while a 3 party conference requires a peak of 258kbit/serc in one of the direction.
   
   Layer 3 ADPCM Audio (Reduced Bandwidth Setting)
   • 54.7Kbps per party in the conversation.
   • A point-to-point call requires this peak bandwidth in each direction, while a 3 party conference requires a peak of 164kbit/second in one of the directions.

Note A: Silence suppression reduces this requirement on average by 30-40% but can not be assumed when determining the peak requirements.

Note B: The values provided do not include link overhead which may be added by the customer’s specific interconnection device. This overhead must be added based upon the device specification and is not under the control of the NBX 100 system.