Network Working Group CJ. Shao
Internet-Draft H. Deng
Intended status: Informational China Mobile
Expires: April 18, 2013 R. Zhang
China Telecom
October 15, 2012
Enhancement of CAPWAP Problem Statement
draft-shao-capwap-plus-ps-00
Abstract
With the recent widely deployment of large public Wifi network, and
the integration with cellular network. EAP based authentication has
been considered as the good candidate to improve the Wifi user
experience similarly to the extend of GSM network. Couple of new
functions which could enhance CAPWAP protocol have been raised to
improve the large carrier grade Wifi network.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Conventions used in this document . . . . . . . . . . . . . . . 3
3. Supporting EAP authencation in Wifi network . . . . . . . . . . 3
3.1. Scenario Description . . . . . . . . . . . . . . . . . . . 3
4. The scope of definition of split MAC mode . . . . . . . . . . . 4
5. 802.11n support . . . . . . . . . . . . . . . . . . . . . . . . 4
6. Channel auto reconfiguration . . . . . . . . . . . . . . . . . 5
7. Power auto reconfiguration . . . . . . . . . . . . . . . . . . 5
8. Security Considerations . . . . . . . . . . . . . . . . . . . . 6
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6
10. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 6
11. Normative References . . . . . . . . . . . . . . . . . . . . . 6
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 6
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1. Introduction
Public Wifi service has been paid more attention due to the growth of
cellular data traffic, this is mainly originated from faster mobile
network and more smart terminals. It is predcited that such growth
will continue even with the deployment of LTE network. The capacity
and coverage of LTE network still needs the complementation of public
wifi network because Wifi spectrum is free, limited and globally
available. and almost all smart terminal has the Wifi equiped.
Recent efforts have been made to let Wifi roaming similar to as easy
as legacy cellular GSM network by deploying EAP based authentication
mechanism, and to let mobile to Wifi integration is seamless and
transparent to the customer; Toward this two directions, current
CAPWAP protocol could be enhanced to improve better user experiences.
There have been lots of propritary implementations between AP and AC
interfaces, some of them have very strong capability which could be
used to improve the wifi performance. Once Standard interface is
specified, such merits may be not exist, but it benefit for operators
deployment with such sacrifice.
2. Conventions used in this document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL","SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
3. Supporting EAP authencation in Wifi network
Current EAP message is designed to be transmited in CAPWAP data
plane, AC in the middle of data path will act as the authenticator to
transmit this EAP message to AAA server, but sometime, operator would
like to let AC to be in the bypass of the data plane which could help
to improve the performance of AC, allow it can manage more APs once
the network is growing. In order to allow AC be bypassed, the capwap
control message could be extended to support EAP messages.
3.1. Scenario Description
The following figure shows where and how the problem arises. In many
operators' network, the Access Controller is placed remotely at the
central data center. In order to avoid the traffic aggregation at
the AC, the data plane out of the AP is directed to the Access Router
(AR). In this scenario, the CAPWAP-CTL tunnel and CAPWAP-DATA tunnel
are separated from each other.
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Because there are no explict message types to support the
encapsulation of EAP packets in the CAPWAP-CTL tunnel, the EAP
messages are tunneled via the CAPWAP-DATA plane to the AR. AR acts
as authenticator in the EAP framework. After authentication, the AR
receives the keying message for the session. But AC is supposed to
delieve these keying messages to the AP, and AR has no standard
interface to ship them to the AP or the AC. This is unacceptable in
the scenario of EAP-based auto-authentication.
CAPWAP-CTL +--------+
++========+ AC |
// +--------+
//
+-----+// CAPWAP-DATA +--------------+
| AP |===========================| Access Router|
+-----+ +--------------+
Figure 1: Split between CAPWAP-CTL and CAPWAP-DATA Plane
So it is desirable to encapsulate EAP messages in the CAPWAP-CTL
plane, to avoid data aggregation and improve WLAN system scalability.
4. The scope of definition of split MAC mode
There are many functions hasn't been clearly defined whether they
belong to either AP and AC in the split mode. Operation needs to
configure differently handle the various implementation of split MAC
mode. if there is no clear scope definition of split MAC and local
MAC, then operator has the diffculty to interoperate different
vendors.
5. 802.11n support
There are couple of capabilities of 802.11n need to be supported by
CAPWAP control message such as radio capability, radio configuration
and station information.
IEEE 802.11n standard was published in 2009 and it is an amendment to
the IEEE 802.11-2007 standard to improve network throughput. The
maximum data rate increases to 600Mbit/s physical throughput rate.
In the physical layer, 802.11n use OFDM and MIMO to achive the high
throughput. 802.11n use multiple antennas to form antenna array which
can be dynamically adjusted to imporve the signal strength and extend
the coverage.
802.11n support two modes of channel usage: 20MHz mode and 40Mhz
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mode.802.11n has a new feature called channel binding. It can bind
two adjacent 20MHz channel to one 40MHz channel to improve the
throughput.If using 40Mhz channel configuration there will be only
one non-overlapping channel in 2.4GHz. In the large scale deployment
scenario, operator need to use 20MHz channel configuration in 2.4GHz
to allow more non-overlapping channels.
In MAC layer, a new feature of 802.11n is Short Guard Interval(GI).
802.11a/g use 800ns guard interval between the adjacent information
symbols. In 802.11n, the GI can be configured to 400nm under good
wireless condition.
Another feature in 802.11 MAC layer is Block ACK. 802.11n can use one
ACK frame to acknowledge several MPDU receiving event.
CAPWAP need to be extended to support the above new 802.11n features.
For example, CAPWAP should allow the access controller to know the
supported 802.11n features and the access controller should be able
to configure the differe channel binding modes. One possible
solution is to extend the CAPWAP information element for 802.11n.
6. Channel auto reconfiguration
Channel auto reconfiguration could imporve the Wifi performance,
CAPWAP message could be extended to support this function.
Each channel may provide different quality of service, when WTP
works. WTP can be active or passive scanning and monitoring each
channel, form the report of measurement results to the Access
Controller. WTP can periodically send configure status request to
the AC. According to the current channel quality and other channel
quality scanning report, ACs decide whether modify the channel to be
used, send the configure status response packet to set up a new
channel for the WTP.
7. Power auto reconfiguration
Power auto reconfiguration could imporve the Wifi performance.
CAPWAP message could be extended to achieve following outcome.
o Maximize Spectrum Usage: Real-world Wi-Fi deployments are
depending on the features of shared media. Three channels
available in the 2.4GHz band and 23 channels in the 5GHz band.
Power auto reconfiguration could help these channels be fully
utilized. As the results, clients could be distributed across all
available channels.
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o Reduce Interference: when multiple devices attempt to
simutaneously access the same channel at the same time, a co-
channel interference likely happned. It reduces overall
performance of the channel. The reconfiguration via CAPWAP could
efficiently mitigate the interference. That is essential to
proper network operation
o Optimize Coverage: Simply increasing AP power may not help to
maximize converage because it creates an unbalanced condition in
which more distantly located clients may perforIm poorly due to
their lower transmit output power. The power reconfiguration
could achieve a balanced environment, where configuration could
ensure that coverage is uniform and adequate throughout the
service area.
8. Security Considerations
BD
9. IANA Considerations
None
10. Contributors
Yifan Chen chenyifan@chinamobile.com
Bocun Deng 13316090701@189.cn
11. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC4564] Govindan, S., Cheng, H., Yao, ZH., Zhou, WH., and L. Yang,
"Objectives for Control and Provisioning of Wireless
Access Points (CAPWAP)", RFC 4564, July 2006.
[RFC5415] Calhoun, P., Montemurro, M., and D. Stanley, "Control And
Provisioning of Wireless Access Points (CAPWAP) Protocol
Specification", RFC 5415, March 2009.
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Authors' Addresses
Chunju Shao
China Mobile
No.32 Xuanwumen West Street
Beijing 100053
China
Email: shaochunju@chinamobile.com
Hui Deng
China Mobile
No.32 Xuanwumen West Street
Beijing 100053
China
Email: denghui@chinamobile.com
Rong Zhang
China Telecom
No.109 Zhongshandadao avenue
Tianhe District,
Guangzhou 510630
China
Email: zhangr@gsta.com
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