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| In [[Telecommunications network|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 (networking)|node]]. The packet transmission time in seconds can be obtained from the ''packet size'' in bit and the [[bit rate]] in [[bit/s]] as:
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| :Packet transmission time = Packet size / Bit rate
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| Example: Assuming 100 Mbit/s Ethernet, and the maximum packet size of 1526 bytes, results in
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| :Maximum packet transmission time = 1526*8 bit / (100 000 000 bit/s) ≈ 122 μs
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| ==Propagation delay==
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| The transmission time should not be confused with the [[propagation delay]], which is the time it takes for the first bit to travel from the sender to the receiver (During this time the receiver is unaware that a message is being transmitted). The [[Velocity of propagation|propagation speed]] depends on the [[Transmission medium|physical medium]] of the link (that is, [[fiber optics]], [[twisted-pair]] copper wire, etc.) and is in the range of <math>2*10^8</math> meters/sec for copper wires and <math>3*10^8</math> 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]].
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| :Propagation time = Distance / propagation speed
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| Example: Ethernet communicaiton over a UTP copper cable with maximum distance of 100 meter between computer and switching node results in:
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| :Maximum link propagation delay ≈ 100 m / (200 000 000 m/s) = 0.5 μs
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| ==Packet delivery time==
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| The ''packet delivery time'' or [[latency (engineering)|latency]] 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:
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| :Packet delivery time = Transmission time + Propagation delay
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| 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 network|wide-area networks]], the delivery time is in the order of [[milliseconds]].
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| ==Roundtrip time==
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| The [[round-trip time]] or [[ping 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:
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| :Roundtrip time = 2 * Packet delivery time + processing delay
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| In case of only one physical link, the above expression corresponds to:
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| :Link roundtrip time = 2 * packet transmission time + 2 * propagation delay + processing delay
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| If the response packet is very short, the link roundtrip time can be expressed as close to:
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| :Link roundtrip time ≈ packet transmission time + 2 * propagation delay + processing delay
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| ==Throughput==
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| The [[network throughput]] of a connection with [[flow control (data)|flow control]], for example a [[Transmission Control Protocol|TCP]] connection, with a certain [[TCP window|window size]] (buffer size), can be expressed as:
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| :Network throughput ≈ Window size / roundtrip time | |
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| In case of only one physical link between the sending and transmitting nodes, this corresponds to:
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| :Link throughput ≈ Bitrate * Transmission time / roundtrip time
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| 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:
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| :Message delivery time = Message size / Network throughput
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| ==References==
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| *Behrouz A. Forouzan, Sophia Chung Fegan, ''Data communications and networking''.
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| *McGraw-Hill Higher Education, 2007 - 1134 pages
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| *Kurose, J.F. & Ross, K.W. (2005) ''Computer Networking—A top-down approach featuring the internet.'' Pearson Education Inc. ISBN 0-321-26976-4
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| [[Category:Data transmission]]
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Thoracic Medication Specialist Lezcano from Listuguj Mi'gmaq First Nation, likes to spend some time parachuting, ganhando dinheiro na internet and writing songs. Has enrolled in a world contiki journey. Is incredibly ecstatic specifically about taking a trip to Kenya Lake System in the Great Rift Valley.
My web page: como ganhar dinheiro na internet