Transmission time
Encyclopedia
In telecommunication networks
, the transmission time, is the amount of time from the beginning until the end of a message transmission. In the case of a digital message, it is the time from the first bit until the last bit of a message has left the transmitting node
. The packet transmission time in seconds can be obtained from the packet size in bit and the bit rate
in bit/s as:
Example: Assuming 100 Mbps Ethernet, and the maximum packet size of 1526 bytes, results in
, which is the time to from the full message has been sent until it has reached the receiving node. The propagation speed
depends on the physical medium
of the link (that is, fiber optics, twisted-pair copper wire, etc.) and is in the range of
meters/sec for copper wires and 
for wireless communication, which is equal to the speed of light
. The propagation delay of a physical link can be calculated by dividing the distance (the length of the medium) in meter by its propagation speed in m/s.
Example: Ethernet communicaiton over a UTP copper cable with maximum distance of 100 meter between computer and switching node results in:
is the time from the first bit leaves the transmitter until the last is received. In the case of a physical link, it can be expressed as:
In case of a network connection mediated by several physical links and forwarding nodes, the network delivery time depends on the sum of the delivery times of each link, and also on the packet queueing time (which is varying and depends on the traffic load from other connections) and the processing delay of the forwarding nodes. In wide-area networks
, the delivery time is in the order of milliseconds.
In case of only one physical link, the above expression corresponds to:
If the response packet is very short, the link roundtrip time can be expressed as close to:
, for example a TCP
connection, with a certain window size (buffer size), can be expressed as:
In case of only one physical link between the sending and transmitting nodes, this corresponds to:
The message delivery time or latency over a network depends on the message size in bit, and the network throughput or effective data rate in bit/s, as:
Telecommunications network
A telecommunications network is a collection of terminals, links and nodes which connect together to enable telecommunication between users of the terminals. Networks may use circuit switching or message switching. Each terminal in the network must have a unique address so messages or connections...
, the transmission time, is the amount of time from the beginning until the end of a message transmission. In the case of a digital message, it is the time from the first bit until the last bit of a message has left the transmitting node
Node (networking)
In communication networks, a node is a connection point, either a redistribution point or a communication endpoint . The definition of a node depends on the network and protocol layer referred to...
. The packet transmission time in seconds can be obtained from the packet size in bit and the bit rate
Bit rate
In telecommunications and computing, bit rate is the number of bits that are conveyed or processed per unit of time....
in bit/s as:
- Packet transmission time = Packet size / Bit rate
Example: Assuming 100 Mbps Ethernet, and the maximum packet size of 1526 bytes, results in
- Maximum packet transmission time = 1526*8 bit / (100 000 000 bit/s) ≈ 122 μs
Propagation delay
The transmission time should not be confused with the propagation delayPropagation delay
Propagation delay is a technical term that can have a different meaning depending on the context. It can relate to networking, electronics or physics...
, which is the time to from the full message has been sent until it has reached the receiving node. The propagation speed
Velocity of propagation
The velocity factor , also called wave propagation speed or velocity of propagation , of a transmission medium is the speed at which a wavefront passes through the medium, relative to the...
depends on the physical medium
Transmission medium
A transmission medium is a material substance that can propagate energy waves...
of the link (that is, fiber optics, twisted-pair copper wire, etc.) and is in the range of
meters/sec for copper wires and for wireless communication, which is equal to the speed of lightSpeed of light
The speed of light in vacuum, usually denoted by c, is a physical constant important in many areas of physics. Its value is 299,792,458 metres per second, a figure that is exact since the length of the metre is defined from this constant and the international standard for time...
. The propagation delay of a physical link can be calculated by dividing the distance (the length of the medium) in meter by its propagation speed in m/s.
- Propagation time = Distance / propagation speed
Example: Ethernet communicaiton over a UTP copper cable with maximum distance of 100 meter between computer and switching node results in:
- Maximum link propagation delay ≈ 100 m / (200 000 000 m/s) = 0.5 μs
Packet delivery time
The packet delivery time or latencyLatency (engineering)
Latency is a measure of time delay experienced in a system, the precise definition of which depends on the system and the time being measured. Latencies may have different meaning in different contexts.-Packet-switched networks:...
is the time from the first bit leaves the transmitter until the last is received. In the case of a physical link, it can be expressed as:
- Packet delivery time = Transmission time + Propagation delay
In case of a network connection mediated by several physical links and forwarding nodes, the network delivery time depends on the sum of the delivery times of each link, and also on the packet queueing time (which is varying and depends on the traffic load from other connections) and the processing delay of the forwarding nodes. In wide-area networks
Wide area network
A wide area network is a telecommunication network that covers a broad area . Business and government entities utilize WANs to relay data among employees, clients, buyers, and suppliers from various geographical locations...
, the delivery time is in the order of milliseconds.
Roundtrip time
The roundtrip time or ing time] is the time from the start of the transmission from the sending node until a response (for example an ACK packet or ping ICMP response) is received at the same computer. It is affected by packet delivery time as well as the data processing delay, which depends on the load on the responding node. If the sent data packet as well as the response packet have the same length, the roundtrip time can be expressed as:- Roundtrip time = 2 * Packet delivery time + processing delay
In case of only one physical link, the above expression corresponds to:
- Link roundtrip time = 2 * packet transmission time + 2 * propagation delay + processing delay
If the response packet is very short, the link roundtrip time can be expressed as close to:
- Link roundtrip time ≈ packet transmission time + 2 * propagation delay + processing delay
Throughput
The network throughput of a connection with flow controlFlow control
In data communications, flow control is the process of managing the pacing of data transmission between two nodes to prevent a fast sender from outrunning a slow receiver. It provides a mechanism for the receiver to control the transmission speed, so that the receiving node is not overwhelmed with...
, for example a TCP
Transmission Control Protocol
The Transmission Control Protocol is one of the core protocols of the Internet Protocol Suite. TCP is one of the two original components of the suite, complementing the Internet Protocol , and therefore the entire suite is commonly referred to as TCP/IP...
connection, with a certain window size (buffer size), can be expressed as:
- Network throughput ≈ Window size / roundtrip time
In case of only one physical link between the sending and transmitting nodes, this corresponds to:
- Link throughput ≈ Bitrate * Transmission time / roundtrip time
The message delivery time or latency over a network depends on the message size in bit, and the network throughput or effective data rate in bit/s, as:
- Message delivery time = Message size / Network throughput