When network vendors talk about bandwidth aggregation, the term often sounds magical multiple WAN connections pooled together to give you one fat pipe. But in reality, not all aggregation is created equal. Let’s peel back the layers and see what’s really happening.

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The Illusion of Aggregation: Weighted Round Robin Load Balancing

Most edge routers that advertise bandwidth aggregation are actually using load balancing, typically a Weighted Round Robin (WRR) mechanism. Here’s how it works:

• Multiple WAN connections (say two broadband links) are configured on the router.
• The router distributes outgoing TCP connections across these links based on assigned weights. For example, if WAN1 is 100 Mbps and WAN2 is 50 Mbps, the router might assign a 2:1 ratio, sending twice as many sessions over WAN1 as WAN2.
• During a speedtest or a file download manager with multiple threads, the application creates multiple TCP connections. Each of these connections is spread across the available WANs, making it appear that the total bandwidth is the sum of all links.

This is why a speedtest may show aggregated speeds, it’s leveraging multiple concurrent TCP sessions.

The Catch

If an application uses a single Layer-3 (L3) connection like a video stream, a Zoom call, or an SFTP transfer, it can only ride on one WAN link at a time. That means its throughput is capped by the speed of the single WAN it’s assigned to, regardless of how many WANs you’ve configured.

In short: load balancing creates the illusion of bandwidth aggregation, but it’s not true aggregation.

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True Aggregation: Packet-Level WAN Bonding

To actually combine bandwidth, you need packet-level aggregation, more accurately called WAN bonding.

WAN bonding works at a much lower level than session-based load balancing. Instead of distributing whole connections, the router splits individual packets of a single stream across multiple WAN links. On the other side (usually at a bonding server, VPN concentrator, or cloud aggregator), the packets are reassembled in order before being delivered to the destination.

This is similar to link-layer bonding in data centers, where multiple Ethernet links are combined to behave like one. The difference is that WAN bonding works across heterogeneous networks—fiber, broadband, 4G/5G each with its own latency and jitter.

Benefits of WAN Bonding

• Single-stream aggregation: A Zoom call, FTP upload, or single video stream can utilize the sum of all WAN bandwidth.
• Seamless failover: If one WAN link drops, packets continue flowing through the remaining links with minimal disruption.
• Higher efficiency: Real bonding squeezes out every bit of available bandwidth instead of just balancing sessions.

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Why the Distinction Matters

The term bandwidth aggregation is often misused in marketing because WRR-based load balancing is easy to implement on any edge router. True WAN bonding, however, requires sophisticated packet scheduling, reordering, and reassembly mechanisms usually involving a controller or cloud endpoint.

So when evaluating solutions:

• If your workload is multi-connection based (downloads, web browsing, speedtests), load balancing may be “good enough.”
• If your workload is single-connection based (video calls, live streams, large file transfers), only packet-level WAN bonding will give you real aggregated bandwidth.

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Final Word

Bandwidth aggregation is one of those terms that sounds universal, but the underlying mechanisms couldn’t be more different. Weighted Round Robin load balancing gives you a feel of aggregation, but it’s essentially session distribution. True packet-level WAN bonding, on the other hand, actually delivers the promise of merging multiple pipes into one.

The devil really is in the details, so the next time a vendor claims “bandwidth aggregation,” ask them: Do you mean load balancing, or true bonding?

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