Packet loss

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Packet loss occurs when one or more packets of data traveling across a computer network fail to reach their destination. Packet loss is distinguished as one of the three main error types encountered in digital communications; the other two being bit error and spurious packets caused due to noise.

1 Causes
2 Effects
3 Packet recovery
4 Acceptable packet loss
5 See also
6 References and notes
- 6.1 Footnotes
7 References

[edit] Causes

Packet loss can be caused by a number of factors, including signal degradation over the network medium, oversaturated network links, corrupted packets rejected in-transit, faulty networking hardware, maligned system drivers or network applications, or normal routing routines.

[edit] Effects

When caused by network problems, lost or dropped packets can result in highly noticeable performance issues or jitter with streaming technologies, voice over IP, online gaming and videoconferencing, and will affect all other network applications to a degree. However, it is important to note that packet loss does not always indicate a problem. If the latency and the packet loss at the destination hop are acceptable then the hops prior to that one don't matter. ^[1]

[edit] Packet recovery

Some network transport protocols such as TCP provide for reliable delivery of packets. In the event of packet loss, the receiver asks for retransmission or the sender automatically resends any segments that have not been acknowledged. Although TCP can recover from packet loss, retransmitting missing packets causes the throughput of the connection to decrease. This drop in throughput is due to the sliding window protocols used for acknowledgment of received packets. In certain variants of TCP, if a transmitted packet is lost, it will be re-sent along with every packet that had been sent after it. This retransmission causes the overall throughput of the connection to drop.

Protocols such as UDP provide no recovery for lost packets. Applications that use UDP are designed to handle this type of packet loss.

[edit] Acceptable packet loss

Perhaps the way to garner this number and still maintain a semblance of objectivity is to offer target numbers for different classes of service or types of architectures

For example, certain routers allow you to "prioritize" your traffic according to content [putting the different types into different queues]. For such an architecture, you might specify that the highest priority for a critical service, packet types should pass with less than 1% packet loss. Lower priority packet types might pass with less than 5% and then 10% for the lowest of priority of services.

Packet loss is closely associated with quality of service considerations, and is related to the erlang unit of measure.