CAPWAP Taxonomy Recommendations

Pat R. Calhoun, Cisco Systems

Bob O’Hara, Cisco Systems

Inderpreet Singh, Chantry Networks

Problem

• The taxonomy document did a great job of providing a survey of architectures

• It did not provide an unambiguous definition of Split and Local MAC

• As a consequence, all protocols assume different meaning to the terms– This became obvious in discussions between the LWAPP and

CTP teams

• The protocol evaluation team cannot successfully compare all protocols without a clear set of definitions– When a protocol claims support for Local MAC, what does it

mean?

Architecture Table

CAPWAP Functions

802.11 MAC

CAPWAP Functions

802.11 Non Real-Time MAC

802.11 Real-Time MAC

802.11 PHY802.11 PHY

AC

AC

WTP

WTP

Local AP Split AP

CAPWAP Functions (overview)

• As listed in taxonomy document– RF monitoring, such as Radar detection, noise and interference

detection and measurement.– RF configuration, e.g., for retransmission, channel

selection, transmission power adjustment, etc.– WTP configuration, e.g., for SSID, etc.– WTP firmware loading, e.g., automatic loading and

upgrading of WTP firmware for network wide consistency.– Network-wide STA state information database, including the

information needed to support value-added services, such as mobility, load balancing etc.

– Mutual authentication between network entities, e.g., for AC and WTP authentication in a Centralized WLAN Architecture.

Contradicting Text

• Following taxonomy text comes to a different conclusion:– The commonalities and differences between Local MAC and

Split MAC are most clearly seen by comparing Figure 7 and Figure 10. The commonality between the two is that 802.11 control frames are terminated at WTPs in both cases. The main difference between Local MAC and Split MAC is that in the latter the WTP terminates only the 802.11 control frames, while in the former the WTP may terminate all 802.11 frames. An interesting consequence of this difference is that the Integration Service, which essentially refers to bridging between 802.11 and 802.3 frames, is implemented by the AC in the Split MAC, but can be part of either the AC or WTP in the Local MAC.

So what is the difference then?

• Split MAC– Access Point Function (APF) resides in AC– 802.11 MAC management frames are sent to the AC– User frames are tunneled

• Local MAC– APF resides in the WTP– SME event notifications are sent to the AC– User frames MAY be tunneled

• Local MAC did not split the MAC due to latency issues between the STA and the AP for MAC Management packets

Two modes of operation

• We believe the crux of the problem is the terms chosen by the CAPWAP WG, split and local MAC

• The WG should focus on where functionality resides, instead of how the MAC is divided.– The draft proposes the use of the terms Split

and Local AP

Proposed Split vs. Local* APFunction Location• Distribution Service WTP• Integration Service WTP• Beacon Generation WTP• Probe Response WTP• Power Mgmt/Packet Buffering WTP• Fragmentation/Defrag WTP• Assoc/Disassoc/Reassoc WTP

802.11e• Classifying WTP• Scheduling WTP• Queuing WTP

802.11i• 802.1X/EAP AC• Key Management AC• 802.11 Encryption/Decryption WTP

Function Location• Distribution Service AC• Integration Service AC• Beacon Generation WTP• Probe Response WTP• Power Mgmt/Packet Buffering WTP• Fragmentation/Defrag WTP• Assoc/Disassoc/Reassoc AC

802.11e• Classifying AC• Scheduling WTP/AC• Queuing WTP

802.11i• 802.1X/EAP AC• Key Management AC• 802.11 Encryption/Decryption WTP

Given the vast differences between architectures reviewed, this table uses themost common functionality split

What about Local AP latency issues?

• Introduce Proxy MAC– Proposal is to allow the WTP to process

802.11 MAC management frames, but forward the frame to the AC

– The end solution is exactly the same, but allows for a single simpler CAPWAP protocol

SME vs. 802.11 MAC management?

CAPWAP AC Function

802.11 MAC Management

AC

WTP

Local AP Split AP

SME Layer

CAPWAP Protocol

CAPWAP Protocol

802.11 Real-Time MAC Management

CAPWAP Protocol

CAPWAP Protocol

(Local AP)Non real-timeMAC mgmt

(Split AP)non real-timeMAC mgmt

CAPWAP AC Function

Options, capabilities and negotiations

• There is a desire to provide a large number of modes of operation

• We contend that allowing for a complex matrix of modes of operation will harm interoperability

• Proposal:– Limit number of options– Clearly define the mandatory to implement

mode

Proposed modes of operation

• Support the following optional features:– User Frame Tunneling: mandatory is local

bridge– Local vs. Split: mandatory is Local– 802.11 Encryption: mandatory is WTP

Conclusion

• The authors of the CAPWAP Taxonomy Recommendation strongly urge the WG to adopt this document

• And of course…. Comments are more than welcomed!