Understanding of Delay in Computer Network | Types of Delay in Computer Network | Throughput and Loss

Different Types of Delay in Network

A packet during its travel from one node to the subsequent node it suffers from different types of delay at each node. Some important types of delays are: Processing Delay, Queuing Delay, Transmission Delay, Propagation Delay.

All delays accumulated together and result in a larger delay called total node delay.

Figure: Different types of delay in network

Processing Delay

Processing delay is a nodal delay and it is defined as the time required examining the packets header and determining where to direct the packet. The processing delay is denoted by d_proc.

Processing delay also include delay due to the time needed to check for bit-level errors in the packet that occurred in transmitting the packet’s bits from the upstream router to another router.

Queuing Delay

After processing delay, the router directs the packet to the queue that precedes the link to subsequent router. The queuing delay is denoted d_queue.

The queuing delay is observed at the queue, the packet experiences a queuing delay as it waits to be transmitted over the link. The queuing delay of a specific packet depends on earlier-arriving packets that are queued and waiting for transmission across the link.

The delay of a packet can vary from packet to packet. If the queue is empty and no other packet is currently being transmitted, then packet’s queuing delay zero. When the traffic is heavy and packets are waiting to be transmitted, the queuing delay will be high.

Transmission Delay

The transmission delay is defined as the amount of time required to transmit all of the packet bits over the link. The transmission delay is denoted by d_trans.

The transmission delay is also called as store-and forward delay. It is ration packet length(bits) to transmission rate (bits/sec).

Transmission delay = Packet length / Transmission rate = L/R

Propagation Delay

The propagation delay is defined as time required by a packet to propagate from transmitting node to the receiving node. The propagation delay is denoted d_prop.

The propagation speed of a packet depends on characteristic of physical medium of the link and the distance between the nodes.

Total Nodal Delay

The total node delay experienced by a packet is sum of processing delay, queuing delay, transmission delay and propagation delay within a network. The total delay is very significant parameter of a network.

Total nodal delay = d_proc + d_queue + d_trans + d_prop

Throughput

In data transmission, network throughput is the amount of data moved successfully from one place to another in a given time period, and typically measured in bits per second (bps), as in megabits per second (Mbps) or gigabits per second (Gbps).

Loss

Packet loss occurs when one or more packets of data travelling across a computer network fail to reach their destination. Packet loss is typically caused by network congestion. Packet loss is measured as a percentage of packets lost with respect to packets sent.

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