Section: Miscellaneous (7)
Updated: April 20, 2000
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 recognized:
Unassigned Bit Rate
Constant Bit Rate
Available Bit Rate
The following AAL types are recognized:
If both, the traffic class and the AAL type are specified, they are separated
by a comma.
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: and rx:, respectively. If both parameter lists are
present, the tx: 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 recognized:
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 rate.
The (decimal) number of bytes.
The tx: or rx: lists may also just contain the single element
none, 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
Each of the following lines contains a valid QOS specification:
The following specificiations are equivalent:
Werner Almesberger, EPFL LRC/ICA <firstname.lastname@example.org