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Terminology

A computer network interconnects computers with each other. Cables or radio waves (wireless) are used. In between, there are switches and routers … to lead the traffic to the right destinations.

  • The computers are called HOSTs
  • The cables or radio waves are called MEDIA
  • The network devices are called NETWORK DEVICES

Hosts / End Devices

A host is a computer connected to the IP network.
Each host has at least one IP address:

  • all desktops and laptops
  • all servers
  • all smartphones on WiFi or on G2/G3/G4
  • many network printers are currently connected via a network cable or WiFi.
    These are network printers and therefore also hosts.
  • NAS storage devices via Ethernet are also hosts.

Peripherals

Peripherals are devices connected to a computer via USB (or a serial or parallel port). Peripherals cannot operate independently and are not directly connected to the network. Examples include USB printers, scanners, keyboards and mice, USB storage, etc.

A smartphone tethered via USB to a laptop or PC acts as a network card. The network card(s) are part of the hosts.

Media

  • all network cables (usually Cat5e or Cat6a)
  • the “ether” used for WiFi

Network Devices / Intermediary Devices

On the work floor today we mainly encounter switches, routers, and wireless access points.
Some devices, such as cable routers from Telenet and DSL routers from Proximus, contain a router, a switch, and a W.A.P.

  • Switches connect hosts at the Ethernet MAC layer
  • Wireless Access Points (W.A.P.) facilitate communication
    between hosts at the wireless MAC layer
  • Routers connect networks at the IP layer
  • Hubs and repeaters belong to history,
    and used to connect hosts at the physical layer

Bandwidth

In internet applications, the term bandwidth is used to indicate the instantaneous transfer limit (kilobit per second = kbps, Megabit per second = Mbps, Gigabit per second = Gbps, Terabit per second = Tbps).
The units are expressed as bit/s or bps.

For a file transfer, we usually measure in BYTES.

1 byte = 8 bits, but because bandwidth has a large margin of error of about ±20% (always rounded downward), we simplify:

1 kilobyte per second = 1 kBps ≈ 10 kbps (note the capital B for byte).

1 terabit = 1,000,000,000,000 bits (10¹² bits)

Why

Bandwidth is important for estimating how long a backup or any other network transfer will take.
Often, we derive the instantaneous bandwidth by checking how much data has been transferred over 10 or 100 seconds, and by applying the rule of three we get an idea of the total transfer duration.
Many copy tools also display the average speed of a transfer.

Examples

Some examples of maximum theoretical bandwidth:

  • 10Gbit cat6A cable: 10Gbit/s -- https://en.wikipedia.org/wiki/Category_6_cable
  • Gigabit Ethernet cat5e and cat6: 1 Gbps = 1000 Mbps
  • Fast Ethernet cat5: 100 Mbps
  • Internet via TV cable: 5 Mbit/s, 30 Mbit/s, 90 Mbit/s, 160 Mbps, 250 Mbps up to 1000 Mbps
  • VDSL: up to 52 Mbit/s / ADSL2+: up to 24 Mbit/s
  • Coax Ethernet: 10 Mbps
  • Standard ADSL (Asymmetric Digital Subscriber Line): 1 Mbit/s, 2 Mbit/s, 4 Mbit/s, 8 Mbit/s
  • integrated Services Digital Network (ISDN): 64 kbit/s, 128 kbit/s
  • “Analog” modem: 14.4 kbit/s, 28.8 kbit/s, 56 kbit/s  

wikipedia: Wikipedia – Data rate units

Exercise

How long does a transfer of 11 Gbyte take at 3 Mbyte/s?

Answer:

11 Gbyte = 11000 Mbyte;
11000 Mbyte aan 3 Mbyte per seconde duurt 11000 / 3 = 3667 seconden ~~ 1 uur