SIP Channel
Calculate the number of concurrent SIP channels supported by available bandwidth.
About SIP Channel
A SIP trunk channel's total bandwidth footprint is the RTP media stream (governed by the chosen codec plus RTP/UDP/IP overhead) plus the SIP signaling traffic needed to set up, maintain, and tear down the call (INVITE, ACK, re-INVITEs for hold/transfer, BYE). While signaling is a small fraction of a call's total bandwidth compared to media, it still counts against the link's total capacity and should be included when sizing exactly how many concurrent channels a SIP trunk's bandwidth allocation can support.
Formula
Max concurrent channels
channels = bandwidth_kbps / (codec_rate_kbps + sip_overhead_kbps)
Worked example
With the default values below, SIP Channel returns Max Concurrent SIP Channels of 11. Change any input above and every figure here is recalculated in your browser.
Inputs used
- Available Bandwidthminimum 1 kbps
- 1,000 kbps
- Codec Media Rate (incl. RTP/IP overhead)minimum 1 kbps
- 87.2 kbps
- SIP Signaling Overhead per Channelminimum 0 kbps
- 2.5 kbps
Results
- Max Concurrent SIP Channels
- 11
- Bandwidth per Channel (media + signaling)
- 89.70 kbps
- Bandwidth Utilization at Max Channels
- 98.7%
Step by step
- 1Values used
- 2Max concurrent channels
- 3Max Concurrent SIP Channels= 11
- 4Bandwidth per Channel (media + signaling)= 89.70 kbps
- 5Bandwidth Utilization at Max Channels= 98.7
Assumptions and limits
- The result is derived only from the 3 inputs listed above. Anything not among them is not part of the calculation.
- In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
- Figures are rounded for display to 2 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.
Frequently Asked Questions
Why is SIP signaling overhead amortized per channel rather than counted once for the whole trunk?
Each active call generates its own independent stream of SIP signaling messages (its own INVITE/ACK/BYE and any mid-call re-INVITEs), so signaling bandwidth scales with the number of concurrent calls, not as a single fixed cost for the trunk — amortizing it per channel gives an accurate total bandwidth estimate at any given channel count.
Does SIP registration and OPTIONS keepalive traffic count against channel capacity?
Typically these are negligible and not counted per-channel since they occur at a fixed, low frequency (e.g. every 30-60 seconds) regardless of call volume — this calculator focuses on per-call signaling overhead (INVITE through BYE) which is the dominant, volume-scaling component.
How many SIP channels should I provision versus my actual concurrent call needs?
Provision for your busy-hour peak concurrent call count (derived from Erlang B/C analysis) plus a safety margin — many SIP trunk providers also sell channels in fixed increments, so round up to the provider's next available tier rather than provisioning the exact calculated minimum.