In context of networking I keep running into statements such as "east-west traffic is larger than north-south traffic". I have tried a bit of googling but have not been able to locate an authoritative answer to understand the origin of these terms.
The terms are usually used in the context of data centers.
Generally speaking, "east-west" traffic refers to traffic within a data center -- i.e. server to server traffic. "North-south" traffic is client to server traffic, between the data center and the rest of the network (anything outside the data center).
I believe the terms have come into use from the way network diagrams are typically drawn, with servers or access switches spread out horizontally, and external connections at the top or bottom.
East-West – East-West refers to traffic flows that occur between
devices within a datacenter. During convergence for example, routers
exchange table information to ensure they have the same information
about the internetwork in which they operate. Another example are
switches, which can exchange spanning-tree information to prevent
North | South – North- South refers to traffic flows into and out of
the datacenter. Traffic entering the datacenter through perimeter
network devices is said to be southbound. Traffic exiting via the
perimeter network devices is said to be northbound.
North South traffic is usually considered from end users to the internet, where traditionally organizations used to have fat links to end user and thin links to the external connectivity. In the recent times, the traffic patterns have changed drastically and more traffic is generated inside the data center in a server to server communication which is referred as east west traffic.
I have also seen it used in an NFV context where the traffic entering/leaving a NFV stack. North/South (entering and leaving a virtual router) and traffic between modules at the same layer in the same physical infrastructure is referred to as East/West, i.e. Routing within the same physical box.