A trunk moves phone calls in and out of your workspace. A trunk is a named SIP/RTP profile. It tells the voice gateway where your carrier is, how to authenticate, which codecs to offer, and what to do with an inbound call. Set up a trunk once per carrier. Calls then flow to your AI agents, IVR flows, and human queues. You have two ways to connect:

Bring your own trunk

Point your existing carrier’s SBC at your workspace. You keep your numbers, your contract, and your rates. You only re-home the signalling.

Managed trunk

Provision a number and carrier connectivity from inside ClutchCall. You configure nothing on your side. The number lands in your inventory, ready to bind.

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Your inbound SIP endpoint

Every workspace gets its own SIP endpoint. ClutchCall provisions it automatically at onboarding:
Carriers send calls to you at this endpoint. The gateway reads the leftmost DNS label of each inbound INVITE and resolves it to your tenant. This isolates calls per workspace, with no cross-tenant extension collisions. Find your <workspace-id> under Admin → Trunks on agent.clutchcall.dev.
Browser and app callers use a separate per-workspace WebRTC endpoint, <workspace-id>.webrtc.clutchcall.dev — see Transport to Web & Apps. This page covers the phone-network (PSTN/SIP) side.

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Bring your own SIP trunk

Use this option when you already have a carrier or on-prem PBX and want to keep it. You tell the gateway where the far end is. The gateway acts as a back-to-back user agent (B2BUA) between your carrier and the runtime. The gateway has a built-in registrar, so you do not need a separate registration server.
1

Name the trunk and set a channel limit

Give the trunk a stable Trunk ID and a friendly Display Name. The Trunk ID is a short handle that you reference everywhere, for example INT-KA-SBC09. Set the Channel Limit — the maximum concurrent calls that this trunk carries (default 50). Match the limit to your carrier contract. The gateway rejects calls above the limit, so a limit that is too low silently drops traffic at peak.
2

Point at the carrier or SBC

Enter the location of your carrier’s session border controller:
  • The SBC IP, or the Gateway IP for a direct peer.
  • The SIP Domain used in the From header and registration (often the SBC host).
  • The local Source Port (default 5060).
  • The far-end Destination Port that your carrier assigned.
  • An Outbound Proxy (host:port), if the carrier routes through one.
Inbound INVITEs from a configured trunk peer bypass the workspace’s registrar ACL. The gateway matches the trunk by source IP (and by the dialed DID). Your carrier does not need to register or digest-authenticate to reach you, unless you require it below.
3

Add credentials (only if your carrier requires registration)

Some carriers expect you to register before you place calls. If yours does, enable Require SIP REGISTER. Set a SIP Username, a SIP Password, and Register Expires in seconds (default 3600). When you save, the trunk registers immediately. Its status chip turns connected, or error if the carrier rejects the credentials.
SIP passwords are sealed at rest. The system never returns them when you read a trunk back. To rotate a credential, save the trunk again with the new value.
4

Fill in your own network addresses and realm

Enter your side of the connection: Internal SIP IP / External SIP IP and Internal RTP IP / External RTP IP. The carrier sees the external (public) addresses in your SIP and SDP. The internal addresses are the bind addresses for traffic that stays inside your network. This split makes the trunk work behind NAT.Set the Realm to describe the far end. Use Internal for your own PBX or extensions. Use External for a PSTN/SIP carrier (per-minute billing applies). Use AI Vendor when the trunk is an AI-agent leg.
5

Choose codecs and media mode

List Codec Preferences in priority order (default PCMU, PCMA, OPUS). The first codec that both sides support wins. On the wire, phone legs are almost always G.711 (µ-law PCMU / A-law PCMA). The gateway transcodes to the internal audio format for the runtime. See Codecs for the full matrix.Leave Media Mode on Proxy (the default) unless you have a specific reason to change it. Proxy anchors media at the gateway. This is the safe, NAT-friendly choice.
Direct media is a preview. Even when you select it, the runtime currently anchors (proxies) the RTP media. Keep new trunks on Proxy.
6

Pick your SIP compliance headers

Choose an outbound identity mode. Full adds the caller-identity headers that carriers expect from a regulated edge: Remote-Party-ID, P-Asserted-Identity, and P-Access-Network-Info. Full is the recommended default. Minimal suppresses all three.
A few carriers silently drop calls when the customer edge asserts identity. If your outbound calls only return 100 Trying and then time out, switch to Minimal.
7

Save and confirm

Save the trunk. It appears in the list with a live status chip: connected, error, or disconnected. The list also shows live health: answer ratio, average call duration, and an estimated MOS from the media plane. Click a trunk to edit any section or to remove it. In-flight calls keep running until they hang up naturally.
After the trunk is up, register the numbers (DIDs) that callers dial. Bind each number to this trunk — see Number Provisioning.

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Managed trunk

If you do not want to run a carrier relationship, provision a number and its connectivity from inside ClutchCall. Under Admin → Trunks, choose the managed option. Pick a number from the catalog. The number lands in your inventory, ready to bind. You do not fill in an SBC, credentials, or network addresses.
The self-serve number catalog is currently an early-access demo with limited inventory. Production carrier coverage (multi-region DID search across Twilio, Telnyx, and Bandwidth) is rolling out. The number-allocation and inbound-routing paths behind the catalog are fully live. If the catalog does not list a number that you need, bring it in as a bring-your-own DID and route it over a BYO trunk.

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Inbound routing

inbound_rule decides what happens when a call arrives on the trunk. New trunks default to reject until you set one of the handlers: You can also route the trunk into an IVR/ACD program. To do this, bind the trunk to a skill or a VDN instead of a single agent — see Inbound Calls and PBX & ACD.

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Field reference & raw RPC

The console form maps 1:1 onto the trunk record. The key fields:
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uint32
default:"50"
The maximum concurrent calls on the trunk.
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string
Your private bind address, and the public address advertised in SIP (NAT).
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string
The same split, for the RTP media plane.
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string
Registrar credentials, used when registration is required. Sealed at rest.
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uint32
default:"3600"
The REGISTER Expires value when the trunk registers with the carrier.
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string
default:"proxy"
proxy anchors media at the gateway. direct is a preview.
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string
internal, external, or ai_vendor.
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string
The outbound identity mode: full (asserts identity) or minimal.
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int32
Reject / play & hangup / notify & hangup / handle with AI.
Do you want to automate trunk provisioning? The full DTO — AddTrunk, UpdateTrunk, GetTrunk, RemoveTrunk — and its raw over-QUIC RPC envelope are documented in Trunks.

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Next steps

Number provisioning

Register DIDs and bind each to a trunk, agent, or flow.

Inbound calls

Route incoming calls to AI agents, IVR flows, and queues.

Codecs

G.711 on the wire, Opus for apps, and how transcoding works.

Outbound calls

Originate calls and run paced campaigns over your trunks.