Jitter in a network can be caused by various factors including network congestion, the physical distance between the source and destination, the processing speed of networking hardware, and the routing protocols used. Network congestion can cause packets to queue, leading to varying packet arrival times. Similarly, if a router on the network is slow to process packets, this can introduce additional delay. Dynamic routing protocols can also lead to an uneven packet delay, as some routes may be longer or more congested than others.