Requested revision
| Standard: | 802.1Q-2011 | Clause: | I.5 |
| Clause title: | Supporting the credit-based shaper algorithm | ||
Rationale for revision
Table 8-4 does not show "a set of recommended priority to traffic class
mappings where the credit-based shaper algorithm (8.6.8.1) is supported
by one or two of the available traffic classes". As correctly stated in
8.6.6 "Table 8-4 shows the recommended mapping for the number of classes
implemented, in implementations that do not support the credit-based
shaper transmission selection algorithm (8.6.8.2)".
The mappings which support the credit-based shaper are shown in 34.5.
"the recommended mappings shown are intended for use where priority 5
is used to support SR class A and priority 4 is used to support SR
class B"
The recommended priorities are 3 (SR class A) and 2 (SR class B).
The reference to table G-3 is wrong. (Such a table does not exist.)
In the tables I-4 and I-5 the acronyms VO ("voice") and VI ("video")
are used for the traffic types of the two SR classes. In table I-2 the
traffic type "voice" is associated with priority 5 and "video" is
associated with priority 4. This does not correspond with the
recommended priorities for the SR classes.
Table I-4 "Credit-based shaper support of one SR class" shows the
traffic types in the case that only SR class A is supported. "SR class B
only" seems to be the more common case. (According to IEEE 802.1BA "All
Bridges shall support SR class B".) Table I-4 should show the
"SR class B only" case instead (in order to be consistent with table 34-2).Proposed text
Change "Table 8-4 defines a set of recommended priority to traffic class mappings where the credit-based shaper algorithm (8.6.8.1) is supported by one or two of the available traffic classes; the recommended mappings shown are intended for use where priority 5 is used to support SR class A and priority 4 is used to support SR class B." to "The tables 34-1 and 34-2 define a set of recommended priority to traffic class mappings where the credit-based shaper algorithm (8.6.8.1) is supported by one or two of the available traffic classes; the recommended mappings shown are intended for use where priority 3 is used to support SR class A and priority 2 is used to support SR class B." Change "table G-3" to "table I-3" Change the traffic type - priority mapping concept so that it fits to AVB. Change table I-4 to "SR class B only".
Impact on existing networks
None, assuming every implementation is based on the normative text.
A bridge or an end station using the wrong priority would not be able to
send a stream over a network or to an end station which uses the correct
one.
Using the shaper with the wrong priority - traffic class mapping would
lead to a higher and completely unpredictable latency for AVB streams.
Originator
| Name: | Christian Boiger | Email: | christian.boiger@fh-deggendorf.de |
| Affiliation: | Hochschule Deggendorf - University, Hirschmann | ||
| Submitted: | 2011-09-14 | ||