Network Switches

The network switch is like a powerboard for the network.  Each device is plugged in and it facilitates communication.  Devices might be

  • workstations
  • printers
  • network attached storage
  • OCT machine

and so on

They are essentially layer 2 devices – they work on Ethernet frames and MAC addresses.  The physical interface (the part where the network cables is plugged in) has a speed rating – now almost always 1Gb/s .  Thus the device is called a Gigabit Switch.  The number of ports can vary from 4 up to 48

An ethernet frame has within it the source address (where the frame comes from) and the destination address (where it is going ) Fundamentally, when a frame arrives on an interface on a switch it needs to very quickly decide whether to do one of 3 things to the frame based on the source and destination address

  • Flood it.  If the switch does not know which interface to send it to it will send it out all interfaces except for the one on which it arrived
  • Forward it.  If the switch knows (based on previous frames) which interface the destination is connected to, it will send the frame out only that interface
  • Drop it.  Under certain circumstances the switch will drop the frame.  It will then be up to higher layers of the network to detect this and ask for retransmission (or not)

A typical medical business might need up to 24 devices on the network.  There are a wide range of switch models available that are gigabit and 24 ports.  For example

a very economical switch $129 new
a much more expensive switch – up to $2000

The difference is not obvious at first – both switches are “Gigabit”.  There are significant differences though

  • Higher end switches are “managed” that is they have an interface at layer 3 so the user can log in and configure the switch.  They often have layer 3 (IP) functions as well such as performing some of the tasks of a router
  • Higher end switches have faster dedicated memory and hardware.  Although the interfaces may be rated at 1Gb, it does not mean that the switch can switch the frames at that speed.  That is dependent on other hardware within the switch
  • Higher end switches will have more reliability when connected to other devices

For a medical business, there is often just one core switch.  It is a false economy to use a cheap unmanaged switch for this task