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Guidelines for
DiffServ to IEEE 802.11 Mapping
draft-szigeti-tsvwg-ieee-802-11e-01
Tim Szigeti
[email protected]
July 23, 2015
Fred Baker
[email protected]
IEEE 802.11 User Priority (UP)
3 Bit Field allows for UP values 0-7
IEEE 802.11 UP Values and Access
Categories
802.11
UP Value
802.11
Access Category
WMM
Designation
7
AC_VO
Voice
AC_VI
Video
AC_BE
Best Effort
AC_BK
Background
6
5
4
3
0
2
1
IEEE 802.11 Arbitration Inter-Frame Space
(AIFS) and Contention Windows (CW)
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•
•
•
due to the nature of wireless as a shared media, a Congestion Avoidance algorithm (CSMA/CA) must be utilized
wireless senders have to wait a fixed amount of time (the AIFS)
wireless senders also have to wait a random amount of time (bounded by the Contention Window)
AIFS and Contention Window timers vary by Access Category
Access
Category
AIFS
(Slot Times)
CWmin
(Slot Times)
3
CWmax
(Slot Times)
7
Voice
2
Access Category
Voice
Video
2
Video
7
15
Best Effort
3
Best-Effort
15
1023
Background
7
Background
15
1023
EDCF Operation
Round 1
Voice
2+1=3
Round 2
2+3=5
Video
2+1=3
2+7=9
2+1=3
Best Effort
3+1=4
3+15=3
3+15=18
Background
7+1=8
7+15=22
7+15=22
Voice
Video
Collision
Round 3
2+2=4
Downstream DSCP-to-UP Default Mapping
3-Bit UP 6-Bit DSCP
802.11 Frame
UP
DSCP
CAPWAP Packet
DSCP
DSCP
IP Packet
DSCP
Default DSCP-to-UP Mapping
IETF PHB for VoIP: EF
Per RFC 4594 & 3246
DSCP
802.11
User Priority
56-63
7
48-55
6
40-47 46
5
32-39
4
24-31
3
0-7
0
16-23
2
8-15
1
802.11
Access Category
Voice (AC_VO)
Video (AC_VI)
Best Effort (AC_BE)
Background (AC_BK)
Downstream DSCP-to-UP Mapping Model
Proposal
RFC 4594-Based Model
Pros
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•
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Endeavors to align RFC
4594 recommendations
into the IEEE 802.11
model
Provides distinction
between elastic and
inelastic video classes
Plugs potential security
vulnerabilities
Cons
•
Requires several custom
DSCP-to-UP mappings
DSCP
Network Control
(CS7)
Internetwork Control
CS6
Voice + DSCP-Admit
EF + 44
Broadcast Video
CS5
Multimedia Conferencing
AF4
Realtime Interactive
CS4
Multimedia Streaming
AF3
Signaling
CS3
Transactional Data
AF2
OAM
CS2
Bulk Data
AF1
Scavenger
CS1
Best Effort
DF
Remark /
Drop
if not in use
IEEE 802.11 Model
UP 7
UP 6
UP 5
UP 4
UP 3
UP 0
Voice
Access
Category
Video
Access
Category
Best Effort
Access
Category
UP 2 Background
Access
UP 1
Category
Upstream UP-to-DSCP Default Mapping
802.11 Frame
DSCP
CAPWAP Packet
UP
3-Bit UP
DSCP
IP Packet
6-Bit DSCP
Last 3 Bits are zeroed-out
DSCP
DSCP
First 3 Bits are copied
Upstream DSCP Trust Model
802.11 Frame
DSCP
CAPWAP Packet
UP
6-Bit DSCP
DSCP
IP Packet
DSCP
DSCP
6-Bit DSCP
Inner DSCP becomes
outer (e.g. CAPWAP) DSCP
Appendix A:
WLAN QoS Considerations
and Implementation Models
Why Consider Wireless QoS?
• QoS is like a chain
• It’s only as strong as its weakest link
• the WLAN is one of the weakest links in enterprise QoS
designs for three primary reasons:
1) Typical downshift in speed
2) Shift from full-duplex to half-duplex media
3) Shift from a dedicated media to a shared media
• WLAN QoS policies control both jitter and packet loss
Wireless QoS-Specific Limitations
• No EF PHB
• No AF PHB
• Non-deterministic media access
• Only 4 levels of service
IP QoS
WLAN QoS
WLAN QoS Improvements Quantified
Application
Original Metric
Improved Metric
Percentage
Improvement
Voice
15 ms max jitter
5 ms max jitter
300%
3.92 MOS
(Cellular Quality)
4.2 MOS
(Toll Quality)
9 fps
14 fps
Visual MOS:
Good
Visual MOS:
Excellent
14 ms latency
2 ms latency
Video
Transactional Data
55%
700%
http://www.cisco.com/en/US/prod/collateral/wireless/cisco_avc_application_improvement.pdf
IEEE 802.11-Figure 9-19
Practical Implementation Models
• Per User-Priority Queues
• Per Client Queues
• Per-Radio Queues
Appendix B:
Related Mapping Models
IEEE 802.11-2012
Annex V.3.3—Table V-2
Example Enterprise
DSCP to UP/AC Mapping
•
These are examples;
not recommendations
•
Several examples seem
out-of-alignment with
RFC 4594 intent
•
802.1d UP is different
from 802.11 UP
•
802.11 UP determines
access-category
IEEE 802.11-2012
Annex V.3.3—Table V-3
Notable PHB Inclusions
UP to DSCP Range Mapping
Example
DF
•
•
These are examples;
not recommendations
Several examples seem
out-of-alignment with
RFC 4594 intent
CS1
AF1-CS2
AF2
CS3-AF3
CS4-AF4-CS5
EF
CS6-CS7
DiffServ Interconnection Classes and Practice
SP Interconnection Approach Summary
(Includes Recommendations from RFC 5127—shown as dotted lines)
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•
•
•
•
Proposes a simplified
model for interconnecting
SPs
“Draws heavily” on RFC
5127
Is intended for MPLS, but
“is applicable to other
technologies”
This approach “is not
intended for use within
the interconnected (or
other) networks”
DSCPs may be remarked
at the interconnection
Traffic Class
SP Interconnect Model
DSCP
Network Control
CS6
Voice
EF
Voice-Admit (RFC 5685)
44
Broadcast Video
CS5
Multimedia Conferencing
AF4
Realtime Interactive
CS4
Multimedia Streaming
AF3
Signaling
CS3
Transactional Data
AF2
Network Management
CS2
Bulk Data
AF1
Scavenger
CS1
Best Effort
DF
Special
Case
Section 3.2
EF
https://tools.ietf.org/pdf/draft-ietf-tsvwg-diffserv-intercon-01.pdf
44
AF41
Telephony Service
Treatment Aggregate
Bulk Real-Time
Treatment Aggregate
AF31 Assured
Forwarding
Treatment Aggregate
DF
Default / Elastic
Treatment Aggregate