Overview

Yealink has introduced “Router Phones” in their T4 and T5 series. These models include special firmware that enables them to operate across NAT internet connections without requiring a VPN or a dedicated Session Border Controller (SBC). This makes them ideal for remote workers or small branch offices connecting back to Webvault’s hosted PBX services.  Additionally, router phones can sometimes act as a mini-SBC, allowing other non-router phones on the same LAN to register through them.

Supported Router Phone Models

Yealink T4 Series (Reference)

• T42U

• T43U

• T44U

• T44W

• T46U

• T48U

Yealink T5 Series (Reference)

• T53

• T53C

• T53W

• T54W

• T57W

• T58W

If you have one of these models, it can connect directly to Webvault’s PBX over standard internet connections, even behind NAT.

What is SBC (Session Border Controller) Functionality?

An SBC is a service that sits between VoIP phones and a hosted PBX. Traditionally, this runs as dedicated software or hardware (e.g., the 3CX SBC service on a Windows PC or Raspberry Pi). It ensures:

• NAT Traversal: Phones behind routers/firewalls can register reliably.

• Traffic Security: SIP and RTP streams are encapsulated and encrypted.

• Stability: Consolidates multiple SIP connections into one secure tunnel.

• Scalability: Allows multiple phones to connect through one point.

Router phones replicate much of this function inside the handset itself:

• A router phone can self-register directly across NAT.

• Some router models can act as a gateway for other local phones.

What Happens Without an SBC?

If a non-router phone (e.g., a Yealink model not listed above) attempts to connect directly over NAT internet without an SBC or VPN:

• The phone may register intermittently or fail entirely.

• Incoming calls may not reach the phone (one-way or no audio issues are common).

• RTP streams (voice packets) may get blocked or misrouted by NAT, leading to no audio or call drops.

• Overall, reliability is poor because SIP signalling was never designed to handle NAT directly.

This is why SBCs (or router phone firmware) are so critical for remote VoIP deployments.

Webvault Direct Route Option for Non-SBC Phones

For customers using non-router Yealink phones, Webvault offers a solution that avoids the need for an SBC: dedicated private IP route networks. These use internal IP ranges delivered directly over Webvault internet services.

With this configuration:

• Phones are assigned addresses on the private IP range.

• NAT translation is not applied, ensuring SIP and RTP packets reach the PBX reliably.

⚠️ Important: This setup is only possible when using Webvault internet connections that are directly connected to our network. Standard third-party ISPs cannot provide this capability.

Example Diagram

[Phones VLAN 2] ---> [Router on VLAN2]
                            |
   (Selective NAT Applied)  |---> [Internet]  (NAT APPLIED)
                            |
                            |---> [3CX PBX Host IP] (NAT NOT APPLIED)

Direct Route Router Configuration Guidance

Please refer to our direct routing guide for 3CX for assistance configuring a privately routed subnet.

https://cloudhelpdesk.com.au/KB/View/121348-webvault-direct-routing-for-3cx-configuring-a-no-nat-routed-subnet

Key Takeaways for Customers

• For remote or home use, choose one of the router-enabled models listed above.

• Router phones reduce complexity by eliminating the need for separate SBCs or VPNs.

• Non-router phones cannot reliably connect over NAT internet without SBC support, unless using Webvault’s private routed subnet service.

• For office deployments with several or more phones Webvault recommends directly routing a subnet so there is not a single point of failure as when using an SBC or router phone.