Contributors
What is network congestion?
Network congestion happens when more traffic tries to cross a network link than the link can carry. Data queues up, slows down or gets dropped, and your applications feel it.
Think of a motorway at rush hour. The road works well until too many vehicles arrive at once. A network behaves the same way. When demand outstrips capacity at any point on the path, everything behind that point waits. For your teams, that shows up as video calls that stutter, files that crawl and cloud applications that hang. For your customers, it can mean slow checkouts or failed transactions.
Congestion can be brief, like a software update landing on every laptop at once. Or it can be constant, when a link is simply too small for the work you ask of it. Either way, the cost is the same: lost time, frustrated users and applications that don't perform as they should.
What causes network congestion?
Congestion comes down to demand meeting a limit. These are the causes you'll meet most often:
- Too little bandwidth. The link was sized for last year's traffic, not today's
- Traffic spikes. Software updates, backups, large file transfers and company-wide video calls can fill a link in minutes
- More cloud traffic. As applications move to the cloud, more traffic crosses your wide area network (WAN) and heads out to the internet instead of staying inside one office
- Poor traffic management. Without prioritisation, a large backup can crowd out a voice call
- Overloaded equipment. Routers, switches and firewalls have processing limits too. An older device can become the bottleneck even when the link has spare capacity
- Shared connections. On shared services, other users' traffic can compete with yours at busy times
Most enterprises meet more than one of these at once. A link that's already close to full has no room for a spike, and poor prioritisation makes the spike hurt more.
How do you spot network congestion?
Congestion leaves clues. Look for these signs:
- Higher latency. The delay between a request and a response creeps up, especially at peak times
- Packet loss. Data packets get dropped when queues fill, so the network has to send them again
- Jitter. Delay varies from one packet to the next, which breaks up voice and video
- Slow applications. Cloud and file-sharing tools slow down at the same times each day
- Timeouts and dropped sessions. Connections fail or reset under load
Monitoring tools help you confirm the cause. Track link utilisation over time. If a link regularly runs close to full at busy periods, you have a capacity problem. If utilisation looks healthy but performance still suffers, look at equipment limits and routing next.
Network congestion, latency and bandwidth
These three terms often get mixed up. They're connected, but they're not the same thing.
Bandwidth is how much data a link can carry at once. Latency is how long data takes to travel from one point to another. Congestion is what happens when demand exceeds bandwidth.
Congestion pushes latency up, because packets sit in queues waiting their turn. That's why a link with plenty of headline bandwidth can still feel slow when traffic builds. Adding capacity is one way to fix it. Short, direct network paths help too, because they cut the delay that distance adds before congestion does any damage.
How do enterprises fix network congestion?
There's no single fix. Most enterprises combine several approaches:
- Add capacity. Upgrade links that run hot. Colt's Ethernet services give you high bandwidth connections between your sites and data centres
- Prioritise traffic. Quality of service (QoS) rules give voice, video and business-critical applications first call on capacity, so a backup can't crowd them out
- Route traffic intelligently. SD WAN (software-defined wide area network) steers traffic across your available links based on the application and current conditions
- Scale on demand. Traffic needs change through the year. Connectivity you can scale when you need it means you don't have to buy for your busiest day all year round
- Move heavy transfers. Schedule large backups and updates for quiet periods so they don't compete with people at work
- Monitor continuously. Watch utilisation and performance so you act before users complain
Read our guide to Network as a Service to see how on-demand connectivity works in practice.
How Colt helps you avoid congestion
Colt owns and operates its IQ Network, which connects 900+ data centres across 32,000+ km of metro fibre. That on-net reach gives your traffic short, direct paths to the data centres and cloud providers you rely on.
Colt's Network as a Service platform makes it straightforward to scale connectivity as your needs change. When traffic grows, you add capacity. You don't wait for a long upgrade cycle to catch up with demand.
Frequently asked questions
What causes network congestion?
Network congestion happens when traffic demand exceeds the capacity of a link or device. Common causes are too little bandwidth, sudden traffic spikes, poor traffic prioritisation and overloaded equipment.
What is the difference between network congestion and latency?
Latency is the time data takes to travel between two points. Congestion is one cause of higher latency. When links fill up, packets wait in queues, so delay rises.
Is network congestion the same as low bandwidth?
No. Bandwidth is the capacity of a link. Congestion is what happens when demand exceeds that capacity. A high bandwidth link can still become congested if traffic grows enough.
Does SD WAN fix network congestion?
SD WAN helps by steering traffic across the best available link and prioritising important applications. It doesn't add capacity by itself, so you may still need to upgrade or scale your bandwidth.
How do you prevent network congestion?
Monitor link utilisation, size capacity for peak demand, prioritise business-critical traffic and use connectivity you can scale as demand changes. Where you can, move large transfers to quiet periods.
