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    Networking 2 min read

    Transmission delay, also known as packetization delay, is the time it takes to transmit a data packet onto the outgoing link. The delay is determined by the size of the packet and the capacity of the outgoing link. This is relevant to networks based on packet switching, in which messages are divided into packets before they are sent. Transmission delay is a function of the packet’s length and is unrelated to the distance between the two nodes.

    Transmission delay causes

    Transmission delay can depend on multiple factors, including:

    • Number of active sessions: With packet switching, the physical layer processes the packets in First-In, First-Out (FIFO) order. Because of this, if there are several active sessions, the delay can become substantial. It becomes even more substantial if the operating system (OS) doesn’t support real-time scheduling algorithms to support multimedia traffic.
    • Transmission capacity of the link: An increase in transmission capacity reduces the transmission delay. Upgrading a 10 Mbps ethernet to 100 Mbps Ethernet will reduce the transmission delay by a factor of 10.
    • Medium access control (MAC) access delay: If the transmission link is shared, a MAC protocol must be used to access the link. The MAC layer is responsible for moving data packets to and from one Network Interface Card to another across a shared channel. The choice of MAC protocol plays a large role in influencing the delay.
    • Context switch in the OS: Sending or receiving a packet involves a context switch in the OS, taking a finite time. Because of this, there is a theoretical maximum at which a computer can transmit packets. For a 10 Mbps LAN, this delay will seem insignificant. For a gigabit network, however, the delay becomes substantial.

    Transmission delay formula

    Transmission delay is given in the following formula:

    TD = L/R

    • TD is the Transmission Delay
    • L is the length of the data packet
    • R is the bit rate (Bits per second)