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Optimizing Converged Cisco Networks (ONT). Module 6: Implement Wireless Scalability. Module 6: Implement Wireless Scalability. Lesson 6.1: Implementing WLAN QoS. Objectives. Describe why WLANs need to support QoS policies in enterprise networks.

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Optimizing converged cisco networks ont

Optimizing Converged Cisco Networks (ONT)

Module 6: Implement Wireless Scalability


Module 6 implement wireless scalability

Module 6: Implement Wireless Scalability

Lesson 6.1: Implementing WLAN QoS


Objectives
Objectives

  • Describe why WLANs need to support QoS policies in enterprise networks.

  • Explain the issues with implementing QoS in a WLAN.

  • Describe the technologies used to support QoS in the WLAN.

  • Describe the configuration parameters available in the Cisco Wireless Control System (WCS) to support QoS in the WLAN.


The need for qos in wireless lans
The Need for QoS in Wireless LANs

  • WLANs use collision avoidance rather than collision detection, which is used by Ethernet LANs.

  • Wired LANs use DSCP or 802.1p to provide QoS. These do not work in a WLAN.

  • 802.11e is an extension of 802.11 that provides more consistent, quality RF transmission for voice and video.





Qos wlan deployment challenges
QoS WLAN Deployment Challenges

  • Facts:

    • Wireless RF (802.11e or WMM) uses Layer 2 marking.

    • End-to-end QoS uses Layer 3 DSCP packet marking.

    • Traffic destined for access points does not contain 802.1p QoS tag information because the access points connect to Cisco Catalyst switches via access ports rather than trunks.

  • Consequence:

    • Layer 2 marking and QoS information is lost in end-to-end transit.

  • The Challenge:

    • The goal is to use the Layer 3 DSCP information to preserve end-to-end QoS in the absence of Layer 2 QoS information.


Overcoming the challenge
Overcoming the Challenge

  • WLAN data is tunneled between the access point and WLAN controller via LWAPP.

  • QoS settings of the encapsulated data packet are mapped to the Layer 2 (802.1p) and Layer 3 (IP DSCP) fields of the outer tunnel packet.


Qos implementation overview

2

1

LWAPP Tunnels

Si

Si

4

3

QoS Implementation Overview


Wlan qos implementation step 1 ethernet switch to controller and into the lwapp tunnel

Si

Si

WLAN QoS Implementation Step 1: Ethernet Switch to Controller and Into the LWAPP Tunnel

1

Create the outer header of the LWAPP packet with a copy of the DSCP value of the incoming packet, and a translation of the DSCP value into a 802.1p value.

LWAPP Tunnels



2

Map the DSCP value of the incoming LWAPP packet to the 802.11e priority value. Place in the 802.11 tX queue appropriate for that 802.11e/WMM value.

Si

Si

LWAPP Tunnels

WLAN QoS Implementation Step 2: Out of the Tunnel and Through the Access Point to the Wireless Client

The original DSCP value is preserved.


Wlan qos implementation step 3 from client to access point and into the tunnel

LWAPP Tunnels

Police the 802.11e priority value, then map the value to the DSCP value.

Si

Si

3

WLAN QoS Implementation Step 3: From Client to Access Point and Into the Tunnel


Mapping traffic from access point to controller
Mapping Traffic from Access Point to Controller

  • The access point will not send tagged packets on a nontrunk port destined for the controller; therefore, the access point will not copy the 802.11e client incoming priority value to the 802.1p (outer) that is destined for the switch.


Wlan qos implementation step 4 out of the tunnel though the controller to the ethernet switch

LWAPP Tunnels

Map the DSCP value of the original packet to the 802.1p value.

The original DSCP value is preserved.

Si

Si

4

WLAN QoS Implementation Step 4: Out of the Tunnel Though the Controller to the Ethernet Switch


802 1p and dscp packet tagging
802.1p and DSCP Packet Tagging

  • 802.1p or DSCP-tagged packets received from LAN:

    • Tag is propagated to LWAPP frame.

    • WLAN ID-configured QoS takes priority for assigned access category; if tag is lower than configured QoS, access point will queue packet at lower access category.

    • AAA override can be applied to Cisco IBNS WLAN clients.

  • Untagged packets received from LAN:

    • WLAN ID-configured QoS will be applied for access category.

    • AAA override can be applied to Cisco IBNS WLAN clients.


802 11e packet tagging
802.11e Packet Tagging

  • 802.11e QoS packets received from WLAN:

    • Tag is propagated to LWAPP frame.

    • WLAN ID-configured QoS takes priority for assigned 802.1p tag; if 802.11e access category is lower than configured QoS, lower 802.1p tag will be applied.

    • 802.11e QoS packets received from WLAN will be802.1p-tagged when transmitted on the LAN by the controller.

  • Non-QoS packets received from WLAN will be best effort (default silver) when transmitted on the LAN by the controller.


Cisco unified wireless network solution

Cisco WLAN Controller

Network

CLI Console

Cisco WCS GUI or CLI

Location Appliance (Optional)

Access Points

Cisco Unified Wireless Network Solution


Qos configuration per user bandwidth contracts
QoS Configuration: Per User bandwidth Contracts

  • Each level has a configurable per-bandwidth contract rate:

    • Per-user data bandwidth contract—Configurable peak and average data rate enforcement for non-UDP traffic

    • Per-user real-time bandwidth contract—Configurable peak and average data rate enforcement for UDP traffic


Qos configuration over the air qos
QoS Configuration: Over the Air QoS

  • Each level has configurable “over the air” QoS rates:

    • Maximum RF usage per access point (%)—Defined maximum percentage of air bandwidth given to an access category

    • Queue depth—Defined depth of queue for a particular user level that will cause packets in excess of the defined value to be dropped


Qos configuration editing qos profiles
QoS Configuration: Editing QoS Profiles

  • The 802.1p tag is applied to the wired side to allow proper precedence to be applied to traffic across the entire network infrastructure.



Self check
Self Check

  • What kind of access technology do WLANs use and why?

  • What are the four access categories or classes of traffic used for QoS in WLANs?

  • How is Enhanced DCF (EDCF) used to implement QoS policies in WLANs?

  • How are non-QoS packets handled by the controller when trasmitted on the LAN?


Summary
Summary

  • With the expansion of WLANs into enterprise and vertical (retail, finance, education) markets, WLANs are now used to transport high-bandwidth, intensive data applications in conjunction with time-sensitive multimedia applications. This requirement has led to the necessity for wireless QoS.

  • The lightweight access point WLAN solution enhances the way access points use Layer 3 information to ensure that packets receive the correct over-the-air prioritization when the packets are transmitted from the access point to the wireless client.

  • QoS protocols used on the WLAN and wired network media must be mapped to one another while traffic transits the boundary between the two media.



Resources
Resources

  • Is Your WLAN Ready for Voice?

    • http://www.cisco.com/en/US/netsol/ns340/ns394/ns348/networking_solutions_white_paper0900aecd80472e80.shtml

  • Design Principles for Voice Over WLAN,

    • http://www.cisco.com/en/US/netsol/ns340/ns394/ns348/networking_solutions_white_paper0900aecd804f1a46.shtml

  • The Benefits of Centralization in Wireless LANs

    • http://www.cisco.com/en/US/products/ps6108/products_white_paper0900aecd8040f7b2.shtml


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