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Bufferbloat is the undesirable latency that comes from a router or other network equipment buffering too many data Network packet. Bufferbloat can also cause packet delay variation (also known as jitter), as well as reduce the overall network throughput. When a router or Network switch is configured to use excessively large buffers, even very high-speed networks can become practically unusable for many interactive applications like voice over IP (VoIP), audio streaming, Online game, and even ordinary web browsing.
Some communications equipment manufacturers designed unnecessarily large buffers into some of their network products. In such equipment, bufferbloat occurs when a network link becomes congested, causing packets to become queued for long periods in these oversized buffers. In a first-in first-out queuing system, overly large buffers result in longer queues and higher latency, and do not improve network throughput. It can also be induced by specific slow-speed connections hindering the on-time delivery of other packets.
The bufferbloat phenomenon was described as early as 1985. It gained more widespread attention starting in 2009.
According to some sources the most frequent cause of high latency ("lag") in online video games is local home network bufferbloat. High latency can render modern online gaming impossible.
A bloated buffer has an effect only when this buffer is actually used. In other words, oversized buffers have a damaging effect only when the link they buffer becomes a bottleneck. The size of the buffer serving a bottleneck can be measured using the ping utility provided by most operating systems. First, the other host should be pinged continuously; then, a several-seconds-long download from it should be started and stopped a few times. By design, the TCP congestion avoidance algorithm will rapidly fill up the bottleneck on the route. If downloading (and uploading, respectively) correlates with a direct and important increase of the round trip time reported by ping, then it demonstrates that the buffer of the current bottleneck in the download (and upload, respectively) direction is bloated. Since the increase of the round trip time is caused by the buffer on the bottleneck, the maximum increase gives a rough estimation of its size in milliseconds.
In the previous example, using an advanced traceroute tool instead of the simple pinging (for example, MTR) will not only demonstrate the existence of a bloated buffer on the bottleneck, but will also pinpoint its location in the network. Traceroute achieves this by displaying the route (path) and measuring transit delays of packets across the network. The history of the route is recorded as round-trip times of the packets received from each successive host (remote node) in the route (path).
Packets are queued within a network buffer before being transmitted; in problematic situations, packets are dropped only if the buffer is full. On older routers, buffers were fairly small so they filled quickly and therefore packets began to drop shortly after the link became saturated, so the TCP protocol could adjust and the issue would not become apparent. On newer routers, buffers have become large enough to hold several seconds of buffered data. To TCP, a congested link can appear to be operating normally as the buffer fills. The TCP algorithm is unaware the link is congested and does not start to take corrective action until the buffer finally overflows and packets are dropped.
All packets passing through a simple buffer implemented as a single queue will experience similar delay, so the latency of any connection that passes through a filled buffer will be affected. Available channel bandwidth can also end up being unused, as some fast destinations may not be promptly reached due to buffers clogged with data awaiting delivery to slow destinations. These effects impair interactivity of applications using other , including UDP used in latency-sensitive applications like VoIP and online gaming.
When the bufferbloat phenomenon is present and the network is under load, even normal web page loads can take many seconds to complete, or simple DNS queries can fail due to timeouts. Actually any TCP connection can timeout and disconnect, and UDP packets can get discarded. Since the continuation of a TCP download stream depends on acknowledgement (ACK) packets in the upload stream, a bufferbloat problem in the upload can cause failure of other non-related download applications, because the client ACK packets do not timely reach the internet server.
Network solutions generally take the form of queue management algorithms. This type of solution has been the focus of the IETF AQM working group. Notable examples include:
Notable examples of solutions targeting the endpoints are:
The problem may also be mitigated by reducing the buffer size on the OS and network hardware; however, this is often not configurable and optimal buffer size is dependent on line rate which may differ for different destinations.
Utilizing DiffServ (and employing multiple priority-based queues) helps in prioritizing transmission of low-latency traffic (such as VoIP, videoconferencing, gaming), relegating dealing with congestion and bufferbloat onto non-prioritized traffic.
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