# SIP Inbound **Sending calls to Sinch platform from your SIP infrastructure** SIP Inbound calls are calls that are being routed from your SIP infrastructure to the Sinch platform through a SIP interconnection/trunk. ![Diagram showing SIP Inbound flow](/assets/spider_sip_inbound.bef339a3bc6c754d03bf4849b88ea3ecffe5acf7d8604e89240a7992b8200d53.c43d86dc.png) ### Sinch's SIP Inbound URIs Sinch operates voice services in multiple geographical regions. You can configure your SIP infrastructure to use any of the following Sinch geographical locations: > Europe: euc1.vp.sip.sinch.com North America: use1.vp.sip.sinch.com South America: sae1.vp.sip.sinch.com Southeast Asia: apse1.vp.sip.sinch.com Australia: apse2.vp.sip.sinch.com The above FQDNs provide redundancy. Use these as a Inbound SIP URI in your communications infrastructure to direct SIP traffic towards Sinch. For each region there are several IP addresses used for reliability purposes (see current IP address/CIDR block in allowlists section). Each of these IP addresses represents a unique public edge for our SIP Trunking services, distributed across multiple Availability Zones. Both UDP and TCP are supported for calls terminating to Sinch. * If you can't use FQDNs, reach out to support@sinch.com. Once the call arrives in the Sinch platform, your backend will get an Incoming Call Event callback, notifying of the incoming call. You can control how you would like the call to be connected by responding to this event. For details on how and what you can respond, check out [Callback API](/docs/voice/api-reference/voice/callbacks/). If no callback is specified in Sinch Build Portal, Sinch will try to terminate your call to PSTN using *To address* in your incoming SIP message as destination phone number. > Make sure that any phone number sent via SIP to Sinch is always E.164-formatted (e.g *+12345678900*). ### Authentication In order to use a trunk for Inbound it must have a Inbound SIP URI and at least one authentication scheme, see below. You need to authenticate your SIP infrastructure to make outbound calls via the Sinch SIP trunk: > Host: {region}.vp.sip.sinch.com Username/Authentication name: Your Sinch service Key Password: Your Sinch service Secret Realm: {region}.vp.sip.sinch.com ### Allowed caller ID number (CLI) for terminating calls You must specify a caller ID number that corresponds to a Sinch DID on your account or a phone number verified in your Sinch Build Portal. ### SIP Inbound example Example SIP INVITE sent to Sinch with SIP Inbound: ```shell > Request-Line: INVITE sip:+12345678900@euc1.vp.sip.sinch.com SIP/2.0 > > From: "+19876543210" ;tag=0c1e59a1af > > To: > > Contact: "+19876543210" ```