Software Architecture
=====================

The fd.io vpp implementation is a third-generation vector packet
processing implementation specifically related to US Patent 7,961,636,
as well as earlier work. Note that the Apache-2 license specifically
grants non-exclusive patent licenses; we mention this patent as a point
of historical interest.

For performance, the vpp dataplane consists of a directed graph of
forwarding nodes which process multiple packets per invocation. This
schema enables a variety of micro-processor optimizations: pipelining
and prefetching to cover dependent read latency, inherent I-cache phase
behavior, vector instructions. Aside from hardware input and hardware
output nodes, the entire forwarding graph is portable code.

Depending on the scenario at hand, we often spin up multiple worker
threads which process ingress-hashes packets from multiple queues using
identical forwarding graph replicas.

VPP Layers - Implementation Taxonomy
------------------------------------

.. figure:: /_images/VPP_Layering.png
   :alt: image

   image

-  VPP Infra - the VPP infrastructure layer, which contains the core
   library source code. This layer performs memory functions, works with
   vectors and rings, performs key lookups in hash tables, and works
   with timers for dispatching graph nodes.
-  VLIB - the vector processing library. The vlib layer also handles
   various application management functions: buffer, memory and graph
   node management, maintaining and exporting counters, thread
   management, packet tracing. Vlib implements the debug CLI (command
   line interface).
-  VNET - works with VPP's networking interface (layers 2, 3, and 4)
   performs session and traffic management, and works with devices and
   the data control plane.
-  Plugins - Contains an increasingly rich set of data-plane plugins, as
   noted in the above diagram.
-  VPP - the container application linked against all of the above.

It’s important to understand each of these layers in a certain amount of
detail. Much of the implementation is best dealt with at the API level
and otherwise left alone.
