  We study synchronization in the context of network traffic on a $2-d$
communication network with local clustering and geographic separations. The
network consists of nodes and randomly distributed hubs where the top five hubs
ranked according to their coefficient of betweenness centrality (CBC) are
connected by random assortative and gradient mechanisms. For multiple message
traffic, messages can trap at the high CBC hubs, and congestion can build up on
the network with long queues at the congested hubs. The queue lengths are seen
to synchronize in the congested phase. Both complete and phase synchronization
is seen, between pairs of hubs. In the decongested phase, the pairs start
clearing, and synchronization is lost. A cascading master-slave relation is
seen between the hubs, with the slower hubs (which are slow to decongest)
driving the faster ones. These are usually the hubs of high CBC. Similar
results are seen for traffic of constant density. Total synchronization between
the hubs of high CBC is also seen in the congested regime. Similar behavior is
seen for traffic on a network constructed using the Waxman random topology
generator. We also demonstrate the existence of phase synchronization in real
Internet traffic data.
