All about Network Delays

Delay and Loss in Packet-Switched Networks

As a packet travels from one node (host or router) to the

subsequent node (host or router) along this path, the packet

suffers from several different types of delays at each node

along the path.

The most important of these delays are:

- Nodal processing delay

- Queuing delay

- Transmission delay

- Propagation delay

As a packet travels from one node (host or router) to the

subsequent node (host or router) along this path, the packet

suffers from several different types of delays at each node

along the path.

The most important of these delays are:

- Nodal processing delay

- Queuing delay

- Transmission delay

- Propagation delay

Nodal processing delay

The time required to examine the packet's header and determine

where to direct the packet is part of the processing delay. The

processing delay can also include other factors, such as the time

Nodal processing delay

needed to check for bit-level errors in the packet that occurred

in transmitting the packet's bits from

the upstream router to router A.

Queuing Delay

After this nodal processing, the router directs the packet to the queue that

precedes the link to router B. At the queue, the packet experiences a

Queuing Delay

queuing delay as it waits to be transmitted onto the link.

The queuing delay of a specific packet will depend on the number

of other, earlier-arriving packets that are queued and waiting for

transmission across the link.

Eg: Queue is empty and we receive 10 packets!

Transmission Delay

Transmission Delay

The transmission delay (also called the store-and-forward

delay) is the amount of time required to transmit all of the

packet's bits into the link.

Propagation Delay

Propagation Delay

Once a bit is pushed onto the link, it needs to propagate to router B.

The time required to propagate from the beginning of the link to route

B is the propagation delay.

The bit propagates at the propagation speed of the link.

The propagation speed depends on the physical medium of the link

(i.e., multimode fiber, twisted-pair copper wire,i etc.)

Total Nodal Delay

Together, these delays accumulate to give a total nodal delay.

Total Nodal Delay

If we let dproc, dqueue, dtrans and dprop be the processing,

Queuing, transmission and propagation delays, then the total nodal

delay is given by:

dnodal = dproc + dqueue + dtrans + dprop