A lightweight port-wrapper around IP. Unchanged since 1980: RFC 768.
For short request short response protocols like DNS, DHCP, NTP, SNMP.
where typically each request and response needs only one packet.
It's either uncritical if the response doesn't arrive (typical
for periodic protocols like SNMP, in which case just wait until the next
period happens) or send the request again (a few times, before giving up).
And for various streaming applications where the overhead of TCP would
slow down... packets that get lost or out-of-order are just ignored,
causing dropouts in the application.
latency: delay between transmission and reception.
Mouth-to-ear: <100ms OK conversation.
jitter: deviation from predictable periodic latency. Each packet can be different.
CD-quality audio: 44.1kHz (samples per second) @16b = 705Kbps mono
DS0: digital telephone: 8kHz@8b = 64Kbps
A.V. sync of separate audio and video streams. Timestamp each datagram: RTP.
Buffering, echo cancellation, and compression add latency.
Video: 60, 50, 25, 12 fps. Compression.
VPN typically over UDP.
NTP
Control Panel | Date and Time | Internet Time | Change settings | server to use, Update now.
client source port is 123.
stratum n: synchronized how many levels from an atomic clock
