Teams Direct Routing local media optimisation
How Local Media Optimisation reduces latency and bandwidth on Direct Routing deployments by keeping media on the local network.
For organisations running Teams Phone with Direct Routing, Local Media Optimisation (LMO) is the configuration that reduces latency and bandwidth consumption by keeping voice media on the local network instead of routing it through the Microsoft cloud. For international deployments specifically, LMO is the difference between acceptable and noticeably-bad call quality.
The problem LMO solves
In a default Direct Routing configuration, voice media flows:
[User A in Sydney office]
│ (audio)
▼
[Microsoft Teams media service] (likely in Australia East datacentre)
│
▼
[User B in same Sydney office, sitting 5 metres away]
Even though both users are on the same LAN, the media routes through Microsoft's datacentre. For local-to-local calls, this is wasteful: latency, bandwidth, datacentre cost.
For international deployments — Sydney office calling Sydney office, but the SBC is in a different region — the routing through Microsoft's network plus through the SBC can produce dramatic latency increases.
What LMO does
With LMO configured:
[User A in Sydney office]
│ (audio direct on LAN)
▼
[User B in same Sydney office]
Teams clients detect that both endpoints are on the same network site (same office), and route media directly between them — never through Microsoft, never through the SBC. Latency drops to LAN latency (microseconds), bandwidth stays on the local network.
For inter-site calls within the same region, LMO routes media to the nearest SBC rather than the user's home SBC, reducing latency.
Configuration
LMO requires:
Network sites
Define network sites in the Teams admin centre — corporate networks identified by IP subnet, region, country. Each site has:
- Site name and location.
- Subnets belonging to the site.
- Region (the Microsoft datacentre region for the site).
- SBC associations (which SBCs are local to this site).
Voice routing policies
User-level voice routing policies specify which SBCs the user can use. Combined with site detection, the right SBC is chosen at call time.
SBC media bypass
The SBC must support media bypass — capable of receiving the SDP from Teams clients telling it to negotiate media directly. Most modern SBCs (AudioCodes, Ribbon, Oracle, Cisco) support this.
Trusted IPs
Configure trusted IPs for the corporate network so Teams clients know they're "at the office" vs roaming.
When LMO matters most
- International offices with central SBCs in another region — media that previously went around the world stays local.
- High call volume within a single site — bandwidth and latency improvements compound.
- Branch offices with limited WAN bandwidth — keeping media off the WAN preserves bandwidth for other traffic.
For organisations with a single office and a local SBC, LMO is a smaller optimisation but still worth doing.
Combined with other Teams network optimisations
LMO is one of several Teams networking patterns:
- Local egress for Teams traffic to Microsoft.
- QoS marking for Teams media (DSCP EF).
- Network protection bypass for Teams media endpoints.
- LMO for Direct Routing media.
Each is independently configurable; combine for best results.
Operational considerations
- Subnet inventory has to be accurate — wrong subnets in network sites = wrong site detection = LMO doesn't apply.
- VPN clients can confuse site detection — endpoints think they're at the office when actually they're remote (or vice versa).
- Diagnostic tools — Teams Call Quality Dashboard shows whether LMO is engaging for specific calls. Verify after configuration.
- SBC firmware matters — older firmware may not support all LMO scenarios; keep current.
When LMO isn't enough
Some scenarios still don't optimise well:
- Microsoft Calling Plans — LMO doesn't apply; Microsoft is the carrier.
- Operator Connect — LMO is operator-dependent.
- Highly mobile users — LMO works best for office-bound users; roaming users skip in and out of network sites.
For these, normal Teams media path with proper network connectivity is the answer.
For Teams Phone Direct Routing deployments at scale, LMO is one of the higher-leverage networking investments. The configuration effort is moderate; the call-quality improvement is significant — especially for international and branch-office scenarios.