SIP Channel Calculator
Calculate the number of concurrent SIP trunk channels a given bandwidth can support, including SIP signaling overhead.
Inputs
Effective per-call media bandwidth, e.g. ~87.2 kbps for G.711 with RTP/IP overhead
Amortized SIP INVITE/ACK/BYE signaling bandwidth per active channel
Max Concurrent SIP Channels
11
Bandwidth per Channel (media + signaling)
89.70kbps
Bandwidth Utilization at Max Channels
98.7%
Step by step
Values used
Available Bandwidth = 1,000 kbps; Codec Media Rate (incl. RTP/IP overhead) = 87.20 kbps; SIP Signaling Overhead per Channel = 2.50 kbps
Max concurrent channels
channels = bandwidth_kbps / (codec_rate_kbps + sip_overhead_kbps)
Max Concurrent SIP Channels
= 11
Bandwidth per Channel (media + signaling)
= 89.70 kbps
Bandwidth Utilization at Max Channels
= 98.7
How it works
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)
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.