When talking about speed in computer networks, we usually talk about the RTT (Round Trip Time) of a packet. This is the time it takes for a packet to go from host A to another host through a series of links to host B and return to host A using the same or a different path.
This path between 2 hosts is a bunch of routers and switches linked together using a physical medium such as copper wires.
There are two important concepts here:
Latency:
The time it takes for one packet to move from one host (i.e. A Client) to another host (i.e. A Server).
A packet needs to be forwarded through a series of physical routers & switches as it moves between them through physical links.
Latency = Propagation Delay + Queuing Delay + Processing Delay + Transmission Delay
Unit of measurement: ms (Milliseconds)
ping google.com
PING google.com (142.250.69.78): 56 data bytes
64 bytes from 142.250.69.78: icmp_seq=0 ttl=117 time=26.966 msIn the example, it takes 26.966 ms to get an ICMP (Internet Control Message Protocol) packet to Google’s servers and back.
1. Propagation Delay:
The time it takes for a packet to travel through a physical medium.
Propagation delay is influenced by the type of physical medium used for transmission. For instance, fibre optic cables (400 Gbps) have significantly lower propagation delay as compared to copper cables (10 Gbps).
2. Queuing Delay
Routers can only forward one packet at a time. So, they mention a forwarding queue to keep packets there until they can be forwarded. The length of the queue determines how long it takes for a packet to be forwarded. This can cause delays in forwarding packets, known as queuing delay.
3. Processing Delay
Routers need to read L2 and L3 Headers to determine where to forward the packet. This is known as processing delay.
4. Transmission Delay
Time taken to push all the bits to a link (i.e. copper cable).
Bandwidth
The amount of packets (or bytes — just a different unit of measurement) that can travel on a link at a time. This is again influenced by the physical medium. For example, Copper cables only allow for multiplexing up to 10 Gbps, but Fiber Optic cables allow for multiplexing up to 100 Tbps using a technology called Dense Wavelength Division Multiplexing. Due to this property of Fiber Optic cables, they are used as a primary medium for connecting major networks due the sheer amount of network traffic sometimes known as backbone links.
Unit of measurement: bps (bits per second)
speedtest-cli // brew install speedtest-cli
Retrieving speedtest.net configuration...
Testing from Bell DSL Internet (65.95.196.204)...
Retrieving speedtest.net server list...
Selecting best server based on ping...
Hosted by Primus (Toronto, ON) [20.93 km]: 19.999 ms
Testing download speed..........................................
Download: 33.40 Mbit/s
Testing upload speed ...........................................
Upload: 10.27 Mbit/s