Cisco Aironet Access Point Quality of Service Feature
Cisco.corn
Same Class of Service (CoS) as Cisco routers
Only downstream Quality of Service (QoS)
With future 802.11e, QoS upstream and downstream
Cisco.corn
Email:
Lowest data priority
Email:
Lowest data priority
- Video traffic: Second data priority
Voice traffic: Highest data priority
© 2003, Cisco Systems, Inc. All rights re
QoS Feature
Time critical data like voice and video benefit from Quality of Service (QoS) because the QoS feature can be configured to give voice and video higher priority. This allows for smooth voice communication, jitter free video and reliable delivery of E-Mail configured with a lower priority.
Cisco uses the same Class of Service (CoS) used on Cisco Routers. At this time Cisco can only support downstream (Access Point to Client) QoS. When 802.11e QoS becomes ratified, Cisco will also support upstream (Client to Access Point) QoS as well by simply upgrading the firmware.
|
Ethernet 802.1P Class of Service |
|||
|
Illllllllllllllllllllll CoS |
lllll;. Cisco.com Application |
||
|
802.1P User Priority field also called Class of Service (CoS) Different types of traffic are assigned different CoS value © 2003, Cisco Systems, Inc. All rights reserved. |
7 |
Reserved |
|
|
6 |
Reserved |
||
|
5 |
Voice Bearer |
||
|
4 |
Video Conferencing |
||
|
3 |
Call Signaling |
||
|
2 |
High Priority Data |
||
|
1 |
Medium Priority Data |
||
|
0 Best Effort Data Example of Typical Values AWLF v3.1—3-38 |
|||
Class of Service (CoS) uses the 802.1P standard to set priority field to network traffic. There are eight different types of CoS traffic values that can be assigned different network traffic.
Priority Level of these Values:
■ 7 and 6 are reserved for network traffic
■ 5 is used for most time sensitive traffic. (e.g.) Voice/IP
■ 4 is used for the second most time sensitive traffic. (e.g.) Video
■ 3 is used for call signaling
■ 2 is used for high priority data. (e.g.) Enterprise Application
■ 1 is used for medium priority data. (e.g.) Email
■ 0 is used for best effort data. (e.g.) Web Browsing
WLAN QoS
^Vhat is 802.11e?
• Pre-standard
• Supplement to 802.11 MAC layer
Managed levels of QoS for data, voice and video applications
802.11e has two components:
• Prioritization: eDCF (Enhanced Distributed Coordination Function)
• Transmission control: TXOP (Transmission Opportunity)
© 2003, Cisco Systems, Inc. All rights reserved. AWLF v3.1—3-39
802.11e is supplementary to the MAC layer to provide QoS support for LAN applications. It will apply to 802.11 physical standards a, b and g. The purpose is to provide classes of service with managed levels of QoS for data, voice and video applications.
802.11e has two components:
■ Enhanced Distributed Coordination Function (eDCF) which is responsible for prioritization.
■ Transmission Opportunity (TXOP) which is responsible for transmission control.
Cisco.com
A(0) Backoff eDCF
A(n) Backoff
What is eDCF?
• eDCF allows high priority traffic first access to the media
• Cisco Aironet Access Points supports eDCF from the access point
There is bound to be network collisions when sharing the WLAN. Clients communicating on the WLAN at the exact same time cause these collisions. This causes both packets to back off for a random period of time before sending the packets again. Collisions cannot be entirely eliminated but keeping them to a minimum will help to preserve your WLAN bandwidth.
To help maintain the bandwidth QoS uses eDCF to allow higher priority traffic first access to the WLAN media. With QoS, instead of backing off for a random period of time they will back of for variable amount of time depending on the packets priority. eDCF allows the higher priority traffic to pass through the access points interfaces before lower priority traffic.
In the example above you we see that A (0) IFS (Inter-Frame Space) has a shorter back off time (e.g.) voice packet. A (n) IFS has a longer back off time (e.g.) email packet.
© 2003, Cisco Systems, Inc. All rights
TXOP = Transmission Opportunity
• Send at regular protected intervals
• Send during a protected interval Uses eDCF
© 2003, Cisco Systems, Inc. All rights reserved. AWLF v3.1—3-41
TXOP is for environments that have a large amount of WLAN traffic going through the access point. High priority packets will only wait a few second to retransmit and if the traffic volume is still high the high priority packet will continue to resend and resend. TXOP will always reserve a place in line for the high priority packets by reserving the first couple seconds for high priority packets. This will guarantee higher priority packet handling and if there is not a high priority packet in the queue that access point addresses the next packet in line. eDCF is also used to assist the process of handling high priority packets.
Continue reading here: Cisco Aironet Access Point Proxy Mobile IP
Was this article helpful?