BT SD-WAN runs over multiple underlay circuit types. The circuit you choose at each site determines the bandwidth, SLA targets, lead time and monthly cost. Most real-world deployments use a mix of circuit types across locations. A headquarters might run on a BTnet leased line while smaller branches use FTTP or SoGEA with 4G/5G failover. Understanding the technical differences between each circuit type is essential for designing a cost-effective and resilient SD-WAN network.
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Available Underlay Circuit Types
| Circuit Type | Bandwidth Range | Contention | Symmetric | Typical Use Case |
|---|---|---|---|---|
| BTnet Leased Line (EAD) | 100Mbps to 10Gbps | Uncontended (1:1) | Yes | HQ, data centres, high-traffic branches |
| FTTP (Fibre to the Premises) | Up to 1Gbps download | Contended | No (asymmetric) | Medium offices with Openreach FTTP coverage |
| SoGEA (Single Order Generic Ethernet Access) | Up to 80Mbps download | Contended | No (asymmetric) | Small branches, retail sites, low-bandwidth locations |
| 4G/5G Cellular | Variable (10-300Mbps typical) | Contended (shared spectrum) | Varies | Backup/failover, temporary sites, pop-up locations |
BTnet Leased Lines in Detail
BTnet leased lines use Ethernet Access Direct (EAD) bearer circuits delivered over the Openreach network. They provide a dedicated uncontended connection between your site and the BT network. This is the highest-performing underlay option and the only circuit type that guarantees symmetric bandwidth.
| Specification | Detail |
|---|---|
| Bearer speeds | 100Mbps, 1Gbps, 10Gbps |
| Bandwidth increments | 100Mbps steps on 1G bearer; 1Gbps steps on 10G bearer |
| Availability SLA | 99.95% |
| Fix time (standard) | 7 hours |
| Fix time (enhanced) | 5 hours |
| Typical lead time | 60-90 working days (new install) |
| Indicative monthly cost | From approximately £250/month (100Mbps) to £600+/month (1Gbps) |
FTTP in Detail
FTTP delivers broadband over Openreach full-fibre infrastructure. It provides high download speeds at a lower cost than leased lines but is asymmetric and contended. FTTP works well as a primary circuit for medium-sized offices or as a secondary resilience circuit alongside a leased line.
| Specification | Detail |
|---|---|
| Download speeds | Up to 1Gbps (900Mbps on some packages) |
| Upload speeds | Up to 220Mbps (varies by package) |
| Availability SLA | 99.9% |
| Fix time | Next business day |
| Typical lead time | 10-20 working days |
| Indicative monthly cost | £30-£60/month |
SoGEA in Detail
SoGEA is a broadband product that does not require a traditional phone line. It uses the existing copper/fibre-to-the-cabinet infrastructure and is available at most UK postcodes. Bandwidth is lower than FTTP but it is the cheapest fixed-line underlay option.
| Specification | Detail |
|---|---|
| Download speeds | Up to 80Mbps (FTTC dependent) |
| Upload speeds | Up to 20Mbps |
| Availability SLA | 99.5% |
| Fix time | Next business day |
| Typical lead time | 5-10 working days |
| Indicative monthly cost | £20-£40/month |
4G/5G Cellular
Cellular connectivity is primarily used as a failover circuit or for temporary/pop-up sites. Performance depends on signal strength and local cell capacity. BT can supply managed 4G/5G routers as part of the SD-WAN service or integrate with existing cellular hardware.
- No fixed availability SLA (best-effort service)
- Throughput varies significantly by location and time of day
- Works well for failover when paired with a fixed-line primary circuit
- Not recommended as the sole circuit for sites running real-time voice or video
- Data usage may be capped depending on the tariff selected
Leased Line vs Broadband: Full Comparison
| Factor | BTnet Leased Line | FTTP | SoGEA |
|---|---|---|---|
| Contention | Uncontended (1:1) | Contended | Contended |
| Symmetric | Yes | No | No |
| Lead time | 60-90 working days | 10-20 working days | 5-10 working days |
| Fix time SLA | 5-7 hours | Next business day | Next business day |
| Availability SLA | 99.95% | 99.9% | 99.5% |
| Monthly cost | £250-£600+ | £30-£60 | £20-£40 |
Dual-Circuit Resilience Options
BT SD-WAN supports active-active and active-standby failover configurations across two or more circuits. The SD-WAN appliance handles path selection and failover automatically based on link health metrics (latency, jitter, packet loss). Common pairings used in BT deployments:
| Pairing | Use Case | Cost Level |
|---|---|---|
| Leased line + FTTP | High-priority sites needing guaranteed failover bandwidth | High |
| FTTP + 4G/5G | Cost-effective resilience for medium offices | Medium |
| SoGEA + 4G/5G | Budget resilience for small branches | Low |
| Dual leased line | Mission-critical sites (data centres, trading floors) | Very high |
| Leased line + 4G/5G | Primary performance with cellular backup | Medium-high |
Planning Tips
- Order leased lines early in the project. The 60-90 day lead time is the most common cause of SD-WAN deployment delays.
- Check Openreach FTTP coverage at each site before assuming it is available. Coverage is expanding but still not universal.
- SoGEA performance depends on distance from the cabinet. Sites more than 1km from the DSLAM may see significantly lower speeds.
- For dual-circuit sites use circuits from different physical paths where possible. Two broadband circuits on the same Openreach infrastructure do not provide true resilience against a cable cut.
- Factor in the cost of the SD-WAN appliance port count. Dual-circuit sites need appliances with at least two WAN interfaces.
Bandwidth Sizing by Site Type
Selecting the right circuit bandwidth depends on the number of users at the site, the applications in use and whether the site uses local internet breakout or backhauled traffic. The table below provides general guidance for common site profiles.
| Site Profile | Users | Recommended Primary Circuit | Recommended Backup |
|---|---|---|---|
| Small retail / branch | 1-10 | SoGEA (40-80Mbps) | 4G/5G |
| Medium office | 10-50 | FTTP (100-300Mbps) | 4G/5G or SoGEA |
| Large office | 50-200 | FTTP (500Mbps-1Gbps) or Leased Line (100Mbps) | FTTP or 4G/5G |
| Headquarters | 200+ | Leased line (1Gbps+) | Second leased line or FTTP |
| Data centre | N/A | Leased line (1-10Gbps) | Dual leased line (diverse routes) |
| Temporary / pop-up | 1-20 | 4G/5G | Second 4G/5G (different carrier) |
Circuit Availability by Postcode
Not all circuit types are available at every UK location. Before finalising your SD-WAN design check availability at each site postcode.
- BTnet leased lines are available at most commercial premises in the UK. Availability depends on proximity to an Openreach exchange with EAD capability. Rural locations may require excess construction charges.
- FTTP coverage is expanding rapidly but is not universal. Check the Openreach network availability checker for each site. Approximately 60-70% of UK premises had FTTP availability as of early 2025.
- SoGEA has the widest coverage and is available at almost all UK postcodes served by Openreach. Performance depends on distance from the street cabinet.
- 4G/5G availability depends on mobile network coverage at the specific site location. 5G coverage is concentrated in urban areas. Indoor signal strength should be tested before relying on cellular as a primary or backup circuit.
