.. _session-protocol:

Session Protocol
****************

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Traffic Server supports some session level protocols in place of, or on top of.
 HTTP. These can be provided by a plugin (see :ref:`new-protocol-plugins`) or
be one that is supported directly by Traffic Server. The
`SPDY <http://www.chromium.org/spdy>`_ protocol is the only one currently
supported, but it is planned to support HTTP 2 when that is finalized.

Session protocols are specified by explicit names, based on the
`NPN <https://technotes.googlecode.com/git/nextprotoneg.html>`_ names. The
core supported names are:

*  ``http/0.9``
*  ``http/1.0``
*  ``http/1.1``
*  ``http/2``
*  ``spdy/1``
*  ``spdy/2``
*  ``spdy/3``
*  ``spdy/3.1``

The ``http/2`` value is not currently functional, but is included for future
use. Both ``spdy/1`` and ``spdy/2`` are obsolete, but are include for
completeness.

The session protocols supported on a proxy port are a subset of these values.
For convenience some pseudo-values are defined in terms of these fundamental
protocols:

*  ``http`` means ``http/0.9``, ``http/1.0``, and ``http/1.1``
*  ``spdy`` means ``spdy/3`` and ``spdy/3.1``.
*  ``http2`` means ``http/2``

Each proxy port can be configured in :ts:cv:`proxy.config.http.server_ports`
to support a subset of these session protocols. For TLS enabled connections this
configuration controls which protocols are offered by NPN. Protocol sniffing is
use for non-TLS proxy ports to determine which protocol is being used by the
client. If the detected protocol is not supported for that proxy port the
connection is dropped.
