Direct Routing


I often see posts on here asking for assistance configuring or troubleshooting Direct Routing. This makes me wonder what benefits organisations are seeing and why they choose to use their own SBC (on prem or vSBC)?

There are a growing number of SIP trunk providers who will host the SBC and will take care of all the SBC configuration, SIP trunk configuration, management/monitoring of SBC etc. Therefore, I'm interested to hear why an organisation would still choose to use their own SBC rather than carrier hosted? Or whether you weren't aware of carriers offering this?

Look forward to hearing everyone's thoughts.



3 Replies


It can entirely depend on the organizations involved.  Several I've worked with have a lot of analog equipment that they still need to support on premises. Taking these to third party SBC providers isn't always easy compared to hosting your own SBC.


Third party integrations, such as call center, that might have dedicated hardware that the hosting provider won't/cannot connect to.


Number portability, and retaining the control over their number pools.


One of the bigger ones I've seen has been cost.  The cost to host the infrastructure and SIP trunks, has been less than having somebody else host it.  That doesn't include things like the cost built into the number of users that the provider may charger by as well.

Thanks for your feedback, I really appreciate it. It seems there is quite a misconception around carrier hosted direct routing. We are a sip trunk provider who offers carrier hosted model and I have seen other vendors are charging per user but we only charge per sip channel/concurrent call which is much more cost effective. That is good to know as maybe sometimes customers aren't knocking on our door as they assume it will be cost prohibitive before they make the enquiry.

Not sure what the concern is over number portability? As the numbers will be hosted by the sip trunk provider either way?

We've done quite a few deployments, particularly universities in the UK where they needed to retain legacy analogue equipment or sip endpoints. All done successfully.

We haven't done many deployments which required third party integrations i.e. call centre (if customer requires call centre solution we have partnered with Mida and deploy their solution) but I'm not sure why this would be solved by an organisation using their own on prem or vSBC? If it can be done using their own SBC it can also be done carrier hosted.


Interesting to hear.  I suspect that there may not be enough talk or details being provided that might lead to confusion over what is capable. I agree that if you provide SIP, anything you can probably do on-premises can be done with a service provider as well.


A couple I've seen previously only did SIP to specific providers, which would be Teams/Skype, but that'd be it, so you could not get the integrations you'd possibly need for third parties.


I guess the number portability thing comes up because the few folks that I've seen that offer hosted PBX services are not usually the carriers, such as AT&T, BT, etc, so there is hesitation on porting the numbers to somebody else. It becomes an issue between "I'm paying my carrier and they're my numbers" to "I'm paying vendor A, to whom I transferred my numbers, and now they own them under their contract". Granted, most situations like that probably have clauses that say the numbers are still yours, but folks get antsy about losing that control.


Other caveats could be directory lookups for call routing decisions, for example user exists in AD with phone number, then route to MS Teams, otherwise route to old PBX. I'm sure there are ways around that such as VPN, or LDAP servers with firewall restrictions.


It might also be regional, you mentioned UK so the offerings might be different compared to the US where I've been dealing with folks. It would be a curious survey, calling plan vs direct routing vs 3rd party direct routing, and broken down by countries.