Calculator inputs
Example data table
These sample scenarios show how packetization, encapsulation, and overhead choices change real wire bandwidth.
| Scenario | Calls | Packetization | Encapsulation | Headers | Per Call | Total |
|---|---|---|---|---|---|---|
| Branch voice link | 10 | 20 ms | Ethernet II + preamble | IPv4, no compression | 39.20 kbps | 392.00 kbps |
| Metro MPLS voice edge | 30 | 20 ms | VLAN + 2 MPLS labels + preamble | IPv4, no compression | 44.00 kbps | 1320.00 kbps |
| Compressed WAN tunnel | 25 | 30 ms | PPP | IPv6, 4-byte compressed header | 11.20 kbps | 280.00 kbps |
Formula used
Payload bytes = (G.729 codec rate in kbps × packetization in ms) ÷ 8
Packets per second = 1000 ÷ packetization in ms
Total packet bytes = payload bytes + RTP/UDP/IP bytes + Layer 2 bytes + MPLS bytes + extra overhead bytes
Per-call bandwidth = total packet bytes × 8 × packets per second ÷ 1000
Effective aggregate bandwidth = per-call bandwidth × simultaneous calls × activity factor
Engineered bandwidth = effective aggregate bandwidth + signaling allowance, then reserve margin
This model is useful for sizing links, estimating real wire usage, and comparing encapsulation choices before deploying voice traffic.
How to use this calculator
- Enter the number of simultaneous G.729 calls you expect during peak usage.
- Choose the packetization interval used by your voice gateway or IP PBX.
- Select IPv4 or IPv6, then match the Layer 2 profile to your access network.
- Add MPLS labels, compression, or extra bytes when your design includes those overheads.
- Set activity factor, signaling allowance, and reserve margin for engineering realism.
- Submit the form to view per-call usage, aggregate demand, engineered capacity, and link utilization above the form.
Frequently asked questions
1. Why does packetization change bandwidth?
Smaller packetization sends more packets each second. More packets mean headers and framing repeat more often, so the wire bandwidth rises even when codec bitrate stays fixed.
2. Does G.729 always use 8 kbps?
The codec payload rate is commonly treated as 8 kbps. Real network demand is higher because RTP, UDP, IP, Layer 2, and physical overhead are added.
3. What does voice activity factor mean?
It represents the percentage of time users are actively transmitting voice. Lower activity can reduce effective average bandwidth when silence suppression or similar behavior is present.
4. Should I include preamble and IFG?
Include them when you want true Ethernet wire-rate planning. Excluding them can still help when comparing logical packet overhead above the physical medium.
5. When should RTP header compression be used?
Use it for WAN designs where supported end to end. It can significantly reduce header overhead, especially on low-speed links with many small voice packets.
6. Why add MPLS labels separately?
Each MPLS label adds four bytes. Multi-label stacks can noticeably increase bandwidth, so separating them helps model transport networks more accurately.
7. What is the reserve margin for?
Reserve margin gives extra headroom for bursts, routing changes, measurement error, and future growth. It helps turn a raw estimate into a safer engineering target.
8. Can this calculator size a WAN circuit?
Yes. Enter the expected call count, transport details, and link speed. The utilization result shows whether the circuit can handle engineered voice demand comfortably.