Endto End Delay
There are different types of delay from source to destination. End-to-end delay is the sum of those different delay types that affect the packets of a certain flow or application. Four of the important types of delay that make up end-to-end delay are as follows:
■ Processing delay
■ Queuing delay
■ Serialization delay
■ Propagation delay
Processing delay is the time it takes for a device such as a router or Layer 3 switch to perform all the tasks necessary to move a packet from the input (ingress) interface to the output (egress) interface. The CPU type, CPU utilization, switching mode, router architecture, and configured features on the device affect the processing delay. For example, packets that are distributed-CEF switched on a versatile interface processor (VIP) card cause no CPU interrupts.
Queuing delay is the amount of time that a packet spends in the output queue of a router interface. The busyness of the router, the number of packets waiting in the queue, the queuing discipline, and the interface bandwidth all affect the queuing delay.
Serialization delay is the time it takes to send all the bits of a frame to the physical medium for transmission across the physical layer. The time it takes for the bits of that frame to cross the physical link is called the propagation delay. Naturally, the propagation delay across different media can be significantly different. For instance, the propagation delay on a high-speed optical connection such as OC-192 is significantly lower than the propagation delay on a satellite-based link.
NOTE In best-effort networks, while serialization and propagation delays are fixed, the processing and queuing delays are variable and unpredictable.
Other types of delay exist, such as WAN delay, compression and decompression delay, and de-jitter delay.
Continue reading here: Definition of QoS and the Three Steps to Implementing It
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