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136 lines
5.3 KiB
136 lines
5.3 KiB
\subsubsection{Introduction}
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Asterisk support different QoS settings on application level on various protocol
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on any of signaling and media. Type of Service (TOS) byte can be set on
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outgoing IP packets for various protocols. The TOS byte is used by the network
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to provide some level of Quality of Service (QoS) even if the network is
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congested with other traffic.
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Also asterisk running on Linux can set 802.1p CoS marks in VLAN packets for all
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used VoIP protocols. It is useful when you are working in switched environment.
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In fact asterisk only set priority for Linux socket. For mapping this priority
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and VLAN CoS mark you need to use this command:
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\begin{verbatim}
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vconfig set_egress_map [vlan-device] [skb-priority] [vlan-qos]
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\end{verbatim}
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In table behind shown all voice channels and other modules of asterisk, that
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support QoS settings for network traffic and type of traffic which can have
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QoS settings.
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\begin{verbatim}
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Channel Drivers
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+==============+===========+=====+=====+=====+
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| | Signaling |Audio|Video| Text|
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+==============+===========+=====+=====+=====+
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|chan_sip | + | + | + | + |
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|--------------+-----------+-----+-----+-----+
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|chan_skinny | + | + | + | |
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|--------------+-----------+-----+-----+-----+
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|chan_mgcp | + | + | | |
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|--------------+-----------+-----+-----+-----+
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|chan_unistim | + | + | | |
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|--------------+-----------+-----+-----+-----+
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|chan_h323 | | + | | |
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|--------------+-----------+-----+-----+-----+
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|chan_iax2 | + |
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+==============+=============================+
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Other
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+==============+=============================+
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| dundi.conf | + (tos setting) |
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|--------------+-----------------------------+
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| iaxprov.conf | + (tos setting) |
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+==============+=============================+
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\end{verbatim}
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\subsubsection{IP TOS values}
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The allowable values for any of the tos* parameters are:
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CS0, CS1, CS2, CS3, CS4, CS5, CS6, CS7, AF11, AF12, AF13, AF21, AF22, AF23,
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AF31, AF32, AF33, AF41, AF42, AF43 and ef (expedited forwarding),
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The tos* parameters also take numeric values.
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Note, that on Linux system you can use ef value in case your asterisk is running
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from a user other then root only when you have compiled asterisk with libcap.
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The lowdelay, throughput, reliability, mincost, and none values are removed
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in current releases.
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\subsubsection{802.1p CoS values}
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As far as 802.1p uses 3 bites from VLAN header, there are parameter can take
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integer values from 0 to 7.
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\subsubsection{Recommended values}
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Recommended values shown above and also included in sample configuration files:
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\begin{verbatim}
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+============+=========+======+
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| | tos | cos |
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+============+=========+======+
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|Signaling | cs3 | 3 |
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|Audio | ef | 5 |
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|Video | af41 | 4 |
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|Text | af41 | 3 |
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|Other | ef | |
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+============+=========+======+
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\end{verbatim}
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\subsubsection{IAX2}
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In iax.conf, there is a "tos" parameter that sets the global default TOS
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for IAX packets generated by chan\_iax2. Since IAX connections combine
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signalling, audio, and video into one UDP stream, it is not possible
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to set the TOS separately for the different types of traffic.
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In iaxprov.conf, there is a "tos" parameter that tells the IAXy what TOS
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to set on packets it generates. As with the parameter in iax.conf,
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IAX packets generated by an IAXy cannot have different TOS settings
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based upon the type of packet. However different IAXy devices can
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have different TOS settings.
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\subsubsection{SIP}
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In sip.conf, there are three parameters that control the TOS settings:
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"tos\_sip", "tos\_audio", "tos\_video" and "tos\_text". tos\_sip controls
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what TOS SIP call signaling packets are set to. tos\_audio, tos\_video
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and tos\_text controls what TOS RTP audio, video or text accordingly
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packets are set to.
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There are four parameters to control 802.1p CoS: "cos\_sip", "cos\_audio",
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"cos\_video" and "cos\_text". It behavior the same as written above.
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\subsubsection{Other RTP channels}
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chan\_mgcp, chan\_h323, chan\_skinny and chan\_unistim also support TOS and
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CoS via setting tos and cos parameters in correspond to module config
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files. Naming style and behavior same as for chan\_sip.
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\subsubsection{Reference}
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IEEE 802.1Q Standard:
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\url{http://standards.ieee.org/getieee802/download/802.1Q-1998.pdf}
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Related protocols: IEEE 802.3, 802.2, 802.1D, 802.1Q
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RFC 2474 - "Definition of the Differentiated Services Field
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(DS field) in the IPv4 and IPv6 Headers", Nichols, K., et al,
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December 1998.
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IANA Assignments, DSCP registry
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Differentiated Services Field Codepoints
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\url{http://www.iana.org/assignments/dscp-registry}
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To get the most out of setting the TOS on packets generated by
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Asterisk, you will need to ensure that your network handles packets
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with a TOS properly. For Cisco devices, see the previously mentioned
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"Enterprise QoS Solution Reference Network Design Guide". For Linux
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systems see the "Linux Advanced Routing \& Traffic Control HOWTO" at
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\url{http://www.lartc.org/}.
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For more information on Quality of
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Service for VoIP networks see the "Enterprise QoS Solution Reference
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Network Design Guide" version 3.3 from Cisco at:
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\url{http://www.cisco.com/application/pdf/en/us/guest/netsol/ns432/c649/ccmigration\_09186a008049b062.pdf}
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