IEEE 802.11 Medium Access Control (MAC) Profile for Control and Provisioning of Wireless Access Points (CAPWAP)

The CAPWAP protocol supports two MAC modes of operation: Split and Local MAC, as described in and . However, there are MAC functions that have not been clearly defined. For example, IEEE 802.11 encryption is specified as located in either the AC or the WTP with no clear way to negotiate where it should be located. Because different vendors have different definitions of the MAC mode, many MAC-layer functions are mapped differently to either the WTP or the AC by different vendors. Therefore, depending upon the vendor, the operators in their deployments have to perform different configurations based on implementation of the two modes by their vendor. If there is no clear specification, then operators will experience interoperability issues with WTPs and ACs from different vendors. from illustrates how some functions are processed in different places in the Local MAC and Split MAC mode. Specifically, note that in the Split MAC mode, the IEEE 802.11 encryption/decryption is specified as WTP/AC, implying that it could be at either location. This is not an issue with Local MAC because encryption is always at the WTP.

To solve this problem, this specification introduces the IEEE 802.11 MAC Profile. The IEEE 802.11 MAC Profile unambiguously specifies where the various MAC functionalities should be located.

A IEEE 802.11 MAC Profile refers to a description of how the MAC functionality is split between the WTP and AC shown in .

The functional split for the Split MAC with WTP encryption is provided in . This profile is similar to the Split MAC description in , except that IEEE 802.11 encryption/decryption is at the WTP. Note that fragmentation is always done at the same entity as the encryption. Consequently, in this profile fragmentation/defragmentation is also done only at the WTP. Note that scheduling functionality is denoted as WTP/AC. As explained in , this means that the admission control component of IEEE 802.11 resides on the AC; the real-time scheduling and queuing functions are on the WTP.

The functional split for the Split MAC with AC encryption is provided in . This profile is similar to the Split MAC in , except that IEEE 802.11 encryption/decryption is at the AC. Since fragmentation is always done at the same entity as the encryption, in this profile, AC does fragmentation/defragmentation.

An example of message exchange using the IEEE 802.11 MAC Profile message element is shown in . The WTP informs the AC of the various MAC Profiles it supports. This happens in either a Discovery Request message or the Join Request message. The AC determines the appropriate profile and configures the WTP with the profile while configuring the WLAN.

| | | |Join Response | |<----------------------------------------| | | |IEEE 802.11 WLAN Config. Request [ | | IEEE 802.11 Add WLAN, | | IEEE 802.11 MAC Profile | | ] | |<----------------------------------------| | | |IEEE 802.11 WLAN Config. Response | |---------------------------------------->| ]]>

The IEEE 802.11 Supported MAC Profile message element allows the WTP to communicate the profiles it supports. The Discovery Request message, Primary Discovery Request message, and Join Request message may include one such message element.

Type: 1060 for IEEE 802.11 Supported MAC Profiles Num_Profiles >=1: This refers to the number of profiles present in this message element. There must be at least one profile. Profile: Each profile is identified by a value specified in .

The IEEE 802.11 MAC Profile message element allows the AC to select a profile. This message element may be provided along with the IEEE 802.11 ADD WLAN message element while configuring a WLAN on the WTP.

Type: 1061 for IEEE 802.11 MAC Profile Profile: The profile is identified by a value as given below 0: This refers to the IEEE 802.11 Split MAC Profile with WTP encryption 1: This refers to the IEEE 802.11 Split MAC Profile with AC encryption

This document does not introduce any new security risks compared to . The negotiation messages between the WTP and AC have origin authentication and data integrity. As a result, an attacker cannot interfere with the messages to force a less-secure mode choice. The security considerations described in apply here as well.

The following IANA actions have been completed. This specification defines two new message elements: IEEE 802.11 Supported MAC Profiles (described in ) and the IEEE 802.11 MAC Profile (described in ). These elements have been registered in the existing "CAPWAP Message Element Type" registry, defined in .

The IEEE 802.11 Supported MAC Profiles message element and IEEE 802.11 MAC Profile message element include a Profile field (as defined in ). The Profile field in the IEEE 802.11 Supported MAC Profiles denotes the MAC Profiles supported by the WTP. The Profile field in the IEEE 802.11 MAC Profile denotes the MAC Profile assigned to the WTP. The namespace for the field is 8 bits (0-255). This specification defines two values: zero (0) and one (1) as described below. The remaining values (2-255) are controlled and maintained by IANA, and the registration procedure is Expert Review . IANA has created a new subregistry called "IEEE 802.11 Split MAC Profile" under the existing registry "Control And Provisioning of Wireless Access Points (CAPWAP) Parameters". The registry format is given below.

&rfc5415; &rfc5416; IEEE Standard for Information Technology - Telecommunications and information exchange between systems - Local and metropolitan area networks - Specific requirements Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications IEEE &rfc5226;

The authors are grateful for extremely valuable suggestions from Dorothy Stanley in developing this specification. Guidance from the management team -- Melinda Shore, Scott Bradner, Chris Liljenstolpe, Benoit Claise, Joel Jaeggli, and Dan Romascanu -- is highly appreciated.

Yifan Chen <chenyifan@chinamobile.com> Naibao Zhou <zhounaibao@chinamobile.com>