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Common VOIP Problems
Deze tekst is alleen in het Engels beschikbaar. Omdat vrijwel alle termen ook engels zijn zou een vertaling een warboel opleveren.
Door: Peter Buijsman
By using voice communication, near-perfect audio is the #1 goal. After all, the end-users do not care how things are done. They just want to be able to have a good sound. By using VoIP there are 4 common problems that can, and at some point in time will, affect voice quality:
- Delay
- Jitter
- Packet loss
- Sequence order problems
Delay
Excessive end-to-end delay makes conversation inconvenient and unnatural. Each component in the transmission path - sender, network, and receiver - adds delay. ITU-T G.114 (One-Way Transmission Time) recommends 150 mSec as the maximum desired one-way latency to achieve high-quality voice.
Delay exceeding 1/4 second will have a severe impact on normal communication and will be considered 'a bad line' by end users.
Jitter
Quantifies the effects of network delays on packet arrivals at the receiver. Packets transmitted at equal intervals from the left gateway arrive at the right gateway at irregular intervals. Excessive jitter makes speech choppy and difficult to understand. Jitter is calculated based on the inter-arrival time of successive packets. For high-quality voice, the average inter-arrival time at the receiver should be nearly equal to the inter-packet gaps at the transmitter and the standard deviation should be low. Jitter buffers (packet buffers that hold incoming packets for a specified amount of time) are used to counteract the effects of network fluctuations and create a smooth packet flow at the receiving end.
Packet loss
Typically occurs either in bursts or periodically due to a consistently congested network. Periodic loss in
excess of 5-10% of all voice packets transmitted can degrade voice quality significantly. Occasional bursts of packet loss can also make conversation difficult.
Sequence Errors
Congestion in packet switched networks can cause packets to take different routes to reach the same
destination. Packets may arrive out of order resulting in garbled speech.
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