IP fundamentals

Almost every AV device made today has a network port: displays, projectors, DSPs, microphones, cameras, codecs, touch panels, control processors. Some only use it for control and monitoring; others send their audio and video over it. Either way, an AV technician now spends a surprising share of the job on network questions: what address does this have, why can't I reach it, and who do I ask? This lesson covers the essentials.

Two addresses for every device

Every network interface has a MAC address, a hardware identifier set at the factory and written as six pairs of hex digits, like 00:1A:2B:3C:4D:5E. Switches use it to deliver traffic within a local network.

On top of that sits the IP address, which is assigned to the device on site and tells the network where it lives. This course uses IPv4, still the norm on AV networks: four numbers from 0 to 255 separated by dots, such as 10.20.30.41. Each number is 8 bits, so the whole address is 32 bits.

Subnets: who is a neighbour?

An IP address has two parts: a network part, shared by every device on the same subnet, and a host part, unique to each device. The subnet mask says where the split falls. It is written either in dotted form (255.255.255.0) or as a prefix length — the number of network bits — after a slash: /24.

Two addresses in every subnet are reserved: the first is the network address itself, and the last is the broadcast address, which reaches every device on the subnet. A /24 therefore has 256 addresses and 254 usable hosts.

Devices on the same subnet talk directly. To reach anything on a different subnet, a device sends the traffic to its default gateway — a router or layer-3 switch on its own subnet — which forwards it on. The gateway must be inside the device's own subnet, or the device has no way to reach it.

Private addresses

Three ranges are reserved for private networks by RFC 1918 and are never routed on the public internet. Almost every building's internal network uses one of them:

Getting an address: static, DHCP or reserved

• Static — typed into the device by hand. Predictable, but every address must be tracked, and a typo or duplicate causes faults that are hard to spot.
• DHCP — the device asks a DHCP server and is handed an address, mask, gateway and DNS server automatically. Easy, but the address can change, which breaks a control system that expects to find the display at a fixed address.
• DHCP reservation — the DHCP server always gives a particular MAC address the same IP. Many IT teams prefer this for AV: central management with predictable addresses.

DNS: names instead of numbers

The Domain Name System turns names into IP addresses, so a control system can find boardroom-display.example.com even if the address behind it changes. Cloud-managed AV devices and conferencing systems rely on DNS to find their services; if a device can reach IP addresses but not names, check the DNS server it was given.

Ports and protocols, briefly

An IP address gets traffic to a device; a port number gets it to the right service on that device. Web interfaces use TCP port 80 (HTTP) or 443 (HTTPS), and many control protocols have their own port. TCP confirms delivery and resends lost data — right for control commands and file transfers. UDP just sends — right for live audio and video, where a late packet is as useless as a lost one. When IT asks which ports a system needs opened through a firewall, the answer is in the manufacturer's network documentation.