qos - Quality of Service specification
functions use the format described in
this man page. Because all standard ATM tools on Linux use those functions to
convert to or from the textual representation of QOS specifications, they
expect them in the same format too.
The most fundamental parameters are the traffic class
and the AAL (ATM
Adaption Layer) type
. If the connection is bi-directional, both directions
have the same traffic class and the same AAL type. The traffic class and the
AAL type are the first elements (in any order) in a QOS specification. The
traffic class is the only required element. If the AAL type is omitted, the
application will provide a default value. The following traffic classes are
- Unassigned Bit Rate
- Constant Bit Rate
- Available Bit Rate
The following AAL types are recognized:
- ("raw ATM")
If both, the traffic class and the AAL type are specified, they are separated by
If more parameters are supplied, the traffic class and AAL type must be followed
by a colon. Traffic parameters can be specified independently for the transmit
and the receive direction. Their parameter lists are prefixed with tx:
, respectively. If both parameter lists are present, the
list must precede the rx:
list. If a parameter is equal for
both directions, it can be placed in a common parameter list (without prefix).
The general format is as follows:
Each list consists of elements specifying a parameter. Elements can appear in
any order and they are separated with commas. The following elements are
- is a synonym for max_pcr=rate
- The upper limit for the peak cell rate to assign. If
omitted, any rate up to link speed may be chosen.
- The lower limit for the peak cell rate to assign. If
omitted, any rate above zero can be chosen.
- is a synonym for max_sdu=size
- The size of the largest packet that may be sent or
received. If omitted, a context-dependent default value is used.
Values are specified as follows:
- The (decimal) rate, optionally followed by a unit. The unit
may be prefixed with one of the multipliers k, M, or
G, meaning 1'000, 1'000'000, or 1'000'000'000, respectively. The
units cps (cells per second) and bps (bits per second) are
recognized. If multiplier and unit are omitted, cells per second are
assumed. Note that the rate is always converted to cells per second, so
rounding errors may occur when specifying the rate in bits per second.
Rates measured in bits per second are considered to be user data rates,
i.e. one cell corresponds to 384 bits. The rate can be a fractional value,
e.g. 1.3Mbps. It is an error to specify only a multiplier without a
unit. Link speed can be indicated by using the keyword max as the
- The (decimal) number of bytes.
lists may also just contain the single element
, which indicates that the corresponding direction is not used. It
is an error to specify none
for both direction.
Note that commas must never follow colons or other commas. Also, whitespace is
not allowed inside a QOS specification. QOS specifications are
Each of the following lines contains a valid QOS specification:
The following specificiations are equivalent:
Werner Almesberger, EPFL LRC/ICA <firstname.lastname@example.org>