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Delay

bandwidth

  • Number of bits that can be transmitted over the network.
  • Can be used to specify the range of frequencies served.

Transmission-Delay

  • time to put the data from device to wire
  • $TD = \frac{message size}{band width}$
  • Maximum size of message is 1514B or 1522B based on header

Propagation-Delay

  • time taken to send the message through the wire
  • $PD = \frac{distance}{speed}$
  • $speed$ is ideally the speed of light

Latency

  • Time for the message to travel from one end of a network to other.
  • $L = TD + PD + QD$

Throughput

  • Throughput = TransferSize/TransferTime
  • TransferTime = RTT + 1 / Bandwidth * TransferSize

Latency and Bandwidth go hand in hand.

  • Latency dominates for small objects
  • Bandwidth dominates for large objects

Variation in latency is called jitter

Loss

!!! where loss can happen "Where loss can happen" - generation - transmission - transit

Reasons

  • internet disconnection
  • physical tampering
  • Conjuction when multiple nodes are connected to a router
  • Transport layer will check the loss of data
  • Loss can be identified from the headers of the message

Types

  • Guided -> No possibility of loss
  • Unguided

Relation b/w Bandwidth, Throughput and Input Traffic

Throughput <= Bandwidth (ideally) but it can temporarily exceed, resulting in congestion or packet loss

Practically Throughput < Bandwidth Throughput can reduce drastically when collisions occur

Delay x Bandwidth Product

Volume of the pipe - the maximum number of bits that could be in transit through the pipe at any given instant.

eg, a transcontinental channel with a one way latency 50ms and a bandwidth of 45 Mbps is able to hold

50 * 10e-3 * 45 * 10e6 bits/sec = 2.25 * 10e6

It represents the amount of data that can be in flight in the network.

Because the propagation delay, the first bit won't the receiver until after the one way delay. So the sender must be keep transmitting up to one RTT * Bandwidth worth of data before it even hears back.

TCP window

TCP uses a sliding window mechanism, sender can only send data up to the window size before waiting for an ACK If the window is too small, underutilized Window Size >= RTT * Bandwidth