Network congestion occurs when the request for network resources overcomes the available capacity, managing to slower data transmission, packet loss, and delays. This situation is commonly observed in computer networks, such as internet, where multiple devices and applications resist for limited transmission capacity. As more users accessing the network concurrently, the network's performance to handle data traffic decreases, resulting in congestion.
What is Network Congestion?
Network Congestion occurs when the traffic moving through a network exceeds its highest capacity. In most cases, congestion is a short-term issue with the network caused due to a unexpected upsurge of traffic, however, sometimes, a network is continually congested, indicating a greater problem. End-users perceive network congestion as Network slowdown or a very large interruption in processing requests.
How to Identify Network Congestion?
Identifying network congestion consist of monitoring various indicators and metrics to determine if the network is experiencing issues related to high traffic loads. Here are some methods and tools to help identify network congestion:
1. Monitoring Network Performance Criteria
- Latency: Verify the time it takes for data to travel from origin to the destination place. Enhanced latency can indicate congestion.
- Throughput: Check the actual data transfer rate relative to the network’s expected capacity. Reduced bandwidth can be a sign of congestion.
- Packet Loss: Monitor the percentage of lost data packets. High packet loss can indicate congestion or network issues.
- Jitter: Measure the variability in packet arrival times. Increased jitter can affect real-time applications and indicate congestion.
2. Network Monitoring Tools
- Network Performance Monitors: Tools like SolarWinds, PRTG, and Nagios provide concurrent visibility into network effectiveness and can alert you to congestion issues.
- Traffic Analyzers: Tools such as Wireshark or NetFlow examiner can help identify heavy traffic origins and patterns.
- Bandwidth Usage Monitors: Tools that track data capacity usage can show if the network is being overworked.
3. Analyzing Network Traffic
- Traffic Patterns: Look for patterns in traffic that might indicate peak usage times or specific applications causing high traffic.
- Application Performance: Monitor performance issues in applications that rely on the network. Poor performance in applications like VoIP or video streaming can indicate congestion.
- Network Topology: Check if specific network segments or devices are experiencing higher traffic loads than others.
4. User Reports and Complaints
- Slow Network Speeds: Users may report lagging, which can indicate congestion.
- Connection Drops: Frequent timeouts reported by users can be a signal of network congestion.
5. Network Device Logs
- Router and Switch Logs: Review logs from network devices for error messages or warnings related to high traffic or congestion.
- Error Rates: High error rates in network devices can signal congestion or other issues affecting network performance.
6. Conducting Network Tests
- Ping Tests: Perform ping tests to measure latency and packet loss.
- Speed Tests: Use speed tests to measure actual throughput compared to expected performance.
7. Capacity Planning and Analysis
- Traffic Forecasting: Analyze historical traffic for future congestion and plan capacity updates.
- Network Capacity Assessment: Regularly evaluate if the network’s capacity matches with current and expected traffic loads. By using these methods and tools, you can efficiently analyze network congestion, analyze the underlying issues, and take steps to ease its impact on network performance. Network congestion is also a contributing element in the following underlying issues:
- High Latency: In a congested network, the time obtained by a packet to reach its destination rises significantly, hence a higher latency rate is noted.
- Connection timeouts: Ideally, the service should wait for the arrival of packets but in several cases, the connection terminates due to timeout.
- Packet loss: Many packets cannot reach their destination if the network is congested, and will be dropped eventually due to timeout.
Causes of Network Congestion
- Excessive bandwidth consumption: Particular users or devices on the network may occasionally use more bandwidth than the average user or device. This can put a pressure on the network and its routing equipment (routers, switches, and cables), causing network congestion.
 - Poor subnet management: For better resource management, a big network is divided into subnets. However, network congestion could arise if the subnets are not scaled according to usage patterns and resource requirements.
 - Broadcast Storms: A broadcast storm happens when there is a sudden rise in the number of demands to a network. As a result of this, a network may be unable to handle all of the requests at the same time.
 - Multi-casting: Multi-casting happens when a network allows multiple computers to interact with each other at the same time. In multi-casting, a collision can occur collisions may cause a network to be congested.
 - Border Gateway Protocol: All traffic is routed by BGP via the shortest possible path. However, while routing a packet, it doesn't consider the amount of traffic present in the route. In such scenarios, there is a possibility all the packets are being routed via the same route which may lead to network congestion.
 - Too many devices: Every network has a limit on the amount of data it can manage. This capacity establishes a limit on how much bandwidth and traffic your network can handle before performance degrades. If the network has too many devices linked to it, the network may become burdened with data requests.
 - Outdated Hardware: When data is transmitted over old switches, routers, servers, and Internet exchanges, bottlenecks can emerge. Data transmission can get hampered or slowed down due to outdated hardware. As a result, network congestion occurs.
 - Over-subscription: A cost-cutting tactic that can result in the network being compelled to accommodate far more traffic than it was designed to handle (at the same time).
Effects of Network Congestion
- Queueing delay
- Packet Loss
- Slow Network
- Blocking of new connections
- Low throughput
Test for Network Congestion
- Run Command Prompt as administrator.
- Type tracert google.com in the CMD window.
- Take note of how many hops it takes to get to the final server.
- For every hop, check out the value of ping.
Congestion at the Network Layer
Congestion at the network layer is related to two issues, throughput and delay:
Based on delay: When the load is much less than the capacity of the network, the delay is at a minimum. This minimum delay is composed of propagation delay and processing delay, both of which are negligible. However, when the load reaches the network capacity ,the delay increases sharply because we now need to add the queuing delay to the total delay. The delay becomes infinite when the load is greater than the capacity.
Based on Throughout: When the load is below the capacity of the network, the throughput increases proportionally with the load. We expect the throughput to remain constant after the load reaches the capacity, but instead the throughput declines sharply. The reason is the discarding of packets by the routers. When the load exceeds the capacity, the queues become full and the routers have to discard some packets.Discarding packets does not reduce the number of packets in the network because the sources re-transmit the packets, using time-out mechanisms, when the packets do not reach the destinations.
How to Fix Network Congestion?
- Divide your network into subnets that can be resized to meet traffic.
- TCP/IP settings should be adjusted to balance packet send/request speeds.
- Use a CDN (Content Delivery Network) to save time by directing more requests to edge servers.
- Choke packets are used to reduce the output of sender devices, which helps to avoid network congestion.
- In case the default route becomes congested, you can employ multi-hop routing so that traffic can be managed.
- Upgrade your Internet plan to allow for more devices and increased bandwidth. Check to see if your devices are up to date and not outdated (even the cables).
A good practice is to monitor your network for any abnormal changes in the traffic. This helps in identifying the issue in advance and planning out improvements.
Conclusion
Network congestion is a very serious issue that impacts the ability and reliability of computer networks. As the requirement for bandwidth-intensive applications continues to grow, maintaining congestion becomes more important. Successful congestion control mechanisms, such as traffic management, load balancing, and quality of service (QoS) protocols, are essential to manage perfect network performance. By handling the root issues of congestion and applying strong network management schemes, it is possible to reduce its impact and confirm a smoother, more effective data transmission across the network.