Latency and Jitter
Latency
In the context of system engineering, the term latency is used to describe the amount of time something takes to complete. For example..
- the time to transmit a packet across a network
- the time to complete an IO operation
- the time to complete a database transaction
Latency diagram
The diagram below illustrates two alternative network routes between two endpoints, Host W and Host E.
If network packets being sent between Host W and Host E take 2 milliseconds to transmit across network Route A, and 8 milliseconds to transmit across network Route B, then we conclude that Route A has lower latency than Route B.
In this context, latency refers to the time delay experienced when transmitting data between two points on a network. A higher latency indicates a longer delay in data transmission, while a lower latency indicates a shorter delay."
Latency charts
The 3 charts A1, and A2 illustrate 2 different levels of consistent latency.
High Latency and Zero Jitter
Chart A1, shows a consistent level of 8ms latency for each of the packets a ~ l.
Chart A1
High Latency and Zero Jitter
_
| |
L| 8| * * * * * * * * * * * *
a| |
t| 6|
e| |
n| 4|
c| |
y| 2|
_| |
0|-------------------------
a b c d e f g h i j k l
__________
| Packet |
Medium Latency and Zero Jitter
Chart A2, shows a consistent level of 2ms latency for each of the packets a ~ l.
Chart A2
Low Latency and Zero Jitter
_
| |
L| 8|
a| |
t| 6|
e| |
n| 4|
c| |
y| 2| * * * * * * * * * * * *
_| |
0|-------------------------
a b c d e f g h
Jitter
In the context of latency, the term jitter is used to describe the variance of the latency.
Low-High Latency and High Jitter
Chart B1, illustrates the latency levels experienced for each packet sent from Host W to Host E while alternating between Route A and Route B for each packet.
- The first packet (a) was sent via Route A,
- the second packet (b) was sent via Route B,
- the third packet (c) was sent via Route A,
- the fourth packet (d) was sent via Route B, etc....
Chart B1
Jitter
_
| |
L| 8| * * * * * *
a| |
t| 6|
e| |
n| 4|
c| |
y| 2| * * * * * *
_| |
0|-------------------------
a b c d e f g h i j k l
__________
| Packet |