One-way delay (OWD) refers to the time it takes for a packet to travel from the source to the destination across a network. It is an important metric in many real-time applications, such as VoIP (Voice over Internet Protocol), video conferencing, and online gaming, where timely delivery of data packets is crucial to maintain quality of service.
Components of One-way delay:
Propagation Delay:
- The time taken for a packet to travel from the sender to the receiver through the medium. It’s determined mainly by the distance between the two ends and the speed of the medium (e.g., speed of light in fiber optic cables).
Transmission Delay:
- The time it takes to push the packet’s bits onto the link. This delay depends on the packet size and the bandwidth of the link.
Processing Delay:
- Time taken by devices (like routers or switches) to process the packet, check for errors, determine the outgoing interface, etc.
Queuing Delay:
- Time a packet waits in a queue before it can be transmitted, especially when there’s congestion or when the outgoing interface is busy.
When measuring OWD, it’s important to ensure synchronized clocks between the source and destination, especially if accurate measurements are crucial. Asymmetries in routing paths (i.e., the path from source to destination is different from the path from destination back to source) can also influence OWD.
Two-way delay or Round Trip Time (RTT) is another related metric. It measures the time taken for a packet to travel from the source to the destination and back again. RTT is essentially the sum of two OWDs (from source to destination and then from destination back to source).
For many real-time services, keeping the one-way delay low is essential. For example, in VoIP services, a one-way delay of more than 150 milliseconds can start to degrade call quality significantly.
Key terms in plain language
Open a term for a concise explanation of language used on this page.
Fiber Internet
Internet delivered through strands of glass using light. Fiber commonly supports high capacity, low latency, and strong upload performance, but availability must be confirmed for the exact address.
Bandwidth
The amount of data a connection can carry in a given time, usually measured in Mbps or Gbps. More bandwidth supports more users, devices, and simultaneous applications.
VoIP
Voice over Internet Protocol carries phone calls over an IP network instead of a traditional analog phone line. Call quality depends on network stability, latency, and traffic management.
Unified Communications (UCaaS)
A cloud-based combination of business calling, messaging, meetings, presence, and collaboration tools managed as one communications service.
SIP Trunking
A service that connects a business phone system to the public telephone network using Internet Protocol, replacing or supplementing traditional phone lines.
Latency
The time it takes data to travel between two points. Lower latency improves voice, video meetings, cloud applications, gaming, and other real-time services.