Plan Direct Routing
This is a preview release of Microsoft Phone System Direct Routing. Product functionality and documentation are subject to change.
Microsoft Phone System Direct Routing lets you connect a supported, customer-provided Session Border Controller (SBC) to Microsoft Phone System. With this capability, for example, you can configure on-premises PSTN connectivity with Microsoft Teams client, as shown in the following diagram:
Skype for Business Online also lets you pair a customer-provided SBC, but this requires an on-premises Skype for Business Server deployment or a special edition of Skype for Business, called Cloud Connector, in between the SBC and the Microsoft Cloud. This scenario is known as hybrid voice. In contrast, Direct Routing allows a direct connection between the supported SBC and the Microsoft Cloud.
With Direct Routing, you can connect your SBC to almost any telephony trunk or interconnect with third-party Public Switched Telephone Network (PSTN) equipment. Direct Routing enables you to:
- Use virtually any PSTN trunk with Microsoft Phone System.
- Configure interoperability between customer-owned telephony equipment, such as a third-party private branch exchange (PBX), analog devices, and Microsoft Phone System.
Microsoft also offers all-in-the-cloud voice solutions, such as Calling Plan. However, a hybrid voice solution might be best for your organization if:
- Microsoft Calling Plan is not available in your country.
- Your organization requires connection to third-party analog devices, call centers, and so on.
- Your organization has an existing contract with a PSTN carrier.
With Direct Routing, when users participate in a scheduled conference, the dial-in number is provided by Microsoft Audio Conferencing service, which requires proper licensing. When dialing out, the Microsoft Audio Conferencing service places the call using online calling capabilities, which requires proper licensing. (Note that dialing out does not route through Direct Routing.) For more information, see Online Meetings with Teams.
Planning your deployment of Direct Routing is key to a successful implementation. This article describes infrastructure and licensing requirements and provides information about SBC connectivity:
- Infrastructure requirements
- Licensing and other requirements
- SBC domain names
- Public trusted certificate for the SBC
- SIP Signaling: FQDNs and firewall ports
- Media traffic: IP addresses and port ranges
- Supported SBCs
For detailed information about configuring Direct Routing, see Configure Direct Routing.
The infrastructure requirements for the supported SBCs, domains, and other network connectivity requirements to deploy Direct Routing are listed in the following table:
|Infrastructure requirement||You need the following|
|Session Border Controller (SBC)||A supported SBC. For more information, see Supported SBCs.|
|Telephony trunks connected to the SBC||One or more telephony trunks connected to the SBC. On one end, the SBC connects to the Microsoft Phone System via Direct Routing. The SBC can also connect to third-party telephony entities, such as PBXs, Analog Telephony Adapters, and so on. Any PSTN connectivity option connected to the SBC will work. (Note: For configuration of the PSTN trunks to SBC, please refer to the SBC vendors or trunk providers.)|
|Office 365 tenant||An Office 365 tenant that you use to home your Microsoft Teams users, and the configuration and connection to the SBC.|
|User registrar||User must be homed in Office 365.
If your company has an on-premises Skype for Business or Lync environment with hybrid connectivity to Office 365, you cannot enable voice in Teams for a user homed on-premises.
To check the registrar of a user, use the following Skype for Business Online PowerShell cmdlet:
The output of the cmdlet should show:
|Domains||One or more domains added to your Office 365 tenants.
Note: You cannot use the default domain, *.onmicrosoft.com, that is automatically created for your tenant.
To view the domains, you can use the following Skype for Business Online PowerShell cmdlet:
For more information about domains and Office 365 tenants, see Domains FAQ.
|Public IP address for the SBC||A public IP address that can be used to connect to the SBC. Based on the type of SBC, the SBC can use NAT.|
|Fully Qualified Domain Name (FQDN) for the SBC||A FQDN for the SBC, where the domain portion of the FQDN is one of the registered domains in your Office 365 tenant. For more information, see SBC domain names.|
|Public DNS entry for the SBC||A public DNS entry mapping the SBC FQDN to the public IP Address.|
|Public trusted certificate for the SBC||A certificate for the SBC to be used for all communication with Direct Routing. For more information, see Public trusted certificate for the SBC.|
|Connection points for Direct Routing||The connection points for Direct Routing are the following three FQDNs:
For information on configuration requirements, see SIP Signaling: FQDNs and firewall ports.
|Firewall IP addresses and ports for Direct Routing media||The SBC communicates to the following services in the cloud:
SIP Proxy, which handles the signaling
Media Processor, which handles media -except when Media Bypass is on
These two services have separate IP addresses in Microsoft Cloud, described later in this document.
For more information, see the Microsoft Teams section in Office 365 URLs and IP address ranges.
|Media Transport Profile||TCP/RTP/SAVP
|Firewall IP addresses and ports for Microsoft Teams media||For more information, see Office 365 URLs and IP address ranges.|
Licensing and other requirements
Users of Direct Routing must have the following licenses assigned in Office 365:
- Skype for Business Online (Plan 2)
- Microsoft Phone System
- Microsoft Teams
- Microsoft Audio Conferencing
The Audio Conferencing license is required for adding external participants to scheduled meetings, either by dialing out to them or by providing the dial-in number.
The E5 license includes both Phone System and Audio Conferencing.
In addition, you must ensure the following:
- CsOnlineVoiceRoutingPolicy is assigned to the user.
- Allow Private Calling is enabled at the tenant level for Microsoft Teams.
Direct Routing also supports users who are licensed for Microsoft Calling Plan. Microsoft Phone System with Calling Plan can route some calls using the Direct Routing interface. However, the users' phone numbers must be either acquired online or ported to Microsoft.
Mixing Calling Plan and Direct Routing connectivity for the same user is optional, but could be useful, for example, when the user is assigned a Microsoft Calling Plan but wants to route some calls via SBC. One of the most common scenarios are calls to third-party PBXs. With third-party PBXs, all calls, except calls to the phones connected to that PBXs, are routed via Microsoft Calling Plan; but calls to the phones connected to third-party PBXs go to the SBC, therefore stay within the enterprise network and not to the PSTN.
For more information about Phone System licensing, see Skype for Business and Microsoft Teams add-on licensing.
SBC domain names
The SBC domain name must be from one of the names registered in “Domains” of the tenant. You cannot use the *.onmicrosoft.com tenant for the FQDN name of the SBC.
The following table shows examples of DNS names registered for the tenant, whether the name can be used as a FQDN for the SBC, and examples of valid FQDN names:
|DNS name||Can be used for SBC FQDN||Examples of FQDN names|
sbc1.europe.contoso.com (requires registering domain name europe.contoso.com in “Domains” first)
It is possible that a company might have several SIP address spaces in one tenant. For example, a company might have contoso.com as a SIP address space and fabrikam.com as the second SIP address space. Some users have address email@example.com and some users have address firstname.lastname@example.org.
The SBC only needs one FQDN and can service users from any address space in the paired tenant. For example, an SBC with the name sbc1.contoso.com can receive and send the PSTN traffic for users with addresses email@example.com and firstname.lastname@example.org as long as these SIP address spaces are registered in the same tenant.
Public trusted certificate for the SBC
Microsoft strongly recommends that you request the certificate for the SBC by generating a certification signing request (CSR). For specific instructions on generating a CSR for an SBC, refer to the interconnection instructions or documentation provided by your SBC vendors.
Most Certificate Authorities (CAs) require the private key size to be at least 2048. Keep this in mind when generating the CSR.
The certificate needs to have the SBC FQDN in the subject, common name, or subject alternate name fields.
Alternatively, Direct Routing supports a wildcard in the common name or SAN, and the wildcard needs to conform to standard RFC HTTP Over TLS. An example would be using *.contoso.com in the SAN, which would match the SBC FQDN sbc.contoso.com, but wouldn’t match with sbc.test.contoso.com.
The certificate needs to be generated by one of the following root certificate authorities:
- AddTrust External CA Root
- Baltimore CyberTrust Root
- Class 3 Public Primary Certification Authority
- DigiCert Global Root CA
- Go Daddy
- Verisign, Inc.
- Symantec Enterprise Mobile Root for Microsoft
- Thawte Timestamping CA
- T-Systems International GmbH (Deutsche Telekom)
Microsoft is working on adding additional certification authorities based on customer requests.
SIP Signaling: FQDNs and firewall ports
The connection point for Direct Routing are the following three FQDNs:
- sip.pstnhub.microsoft.com – Global FQDN – must be tried first. When the SBC sends a request to resolve this name, the Microsoft Azure DNS servers return an IP address pointing to the primary Azure datacenter assigned to the SBC. The assignment is based on performance metrics of the datacenters and geographical proximity to the SBC. The IP address returned corresponds to the primary FQDN.
- sip2.pstnhub.microsoft.com – Secondary FQDN – geographically maps to the second priority region.
- sip3.pstnhub.microsoft.com – Tertiary FQDN – geographically maps to the third priority region.
Placing these three FQDNs in order is required to:
- Provide optimal experience (less loaded and closest to the SBC datacenter assigned by querying the first FQDN).
- Provide failover when connection from an SBC is established to a datacenter that is experiencing a temporary issue. For more information, see Failover mechanism below.
The FQDNs – sip.pstnhub.microsoft.com, sip2.pstnhub.microsoft.com and sip3.pstnhub.microsoft.com – will be resolved to one of the following IP addresses:
You will need to open ports for all these IP addresses in your firewall to allow incoming and outgoing traffic to and from the addresses for signaling. If your firewall supports DNS names, the FQDN sip-all.pstnhub.microsoft.com resolves to all the IP addresses above. You must use the following ports:
|Traffic||From||To||Source port||Destination port|
|SIP/TLS||SIP Proxy||SBC||1024 – 65535||Defined on the SBC|
|SIP/TLS||SBC||SIP Proxy||Defined on the SBC||5061|
Failover mechanism for SIP Signaling
The SBC makes a DNS query to resolve sip.pstnhub.microsoft.com. Based on the SBC location and the datacenter performance metrics, the primary datacenter is selected. If the primary datacenter experiences an issue, the SBC will try the sip2.pstnhub.microsoft.com, which resolves to the second assigned datacenter, and, in the rare case that datacenters in two regions are not available, the SBC retries the last FQDN (sip3.pstnhub.microsoft.com), which provides the tertiary datacenter IP.
The table below summarizes the relationships between primary, secondary, and tertiary datacenters:
|If the primary datacenter is||EMEA||NOAM||ASIA|
|The secondary datacenter (sip2.pstnhub.microsoft.com)||US||EU||US|
|The tertiary datacenter (sip3.pstnhub.microsoft.com)||ASIA||ASIA||EU|
Media traffic: Port ranges
The media traffic flows to and from a separate service in the Microsoft Cloud. The port range of the Media Processors is shown in the following table:
|Traffic||From||To||Source port||Destination port|
|UDP/SRTP||Media Processor||SBC||49 152 – 53 247||Defined on the SBC|
|UDP/SRTP||SBC||Media Processor||Defined on the SBC||49 152 – 53 247|
Microsoft recommends at least two ports per concurrent call on the SBC.
Supported Session Border Controllers (SBCs)
Microsoft only supports the certified SBC to pair with Direct Routing. Because Enterprise Voice is critical for business, Microsoft runs intensive tests with the selected SBCs, and works with the SBC vendors to ensure the two systems are compatible.
Devices that have been validated are listed as Certified for Teams Direct Routing. The certified devices are guaranteed to work in all scenarios. There is also a joint support process between Microsoft and the SBC vendors established.
The following vendors are in the process of being certified:
- Ribbon (formerly Sonus):
- ThinkTel: ThinkTel does not sell the SBCs to the enterprises but their SBC is being certified.