Internet DRAFT - draft-shao-capwap-plus-ps
draft-shao-capwap-plus-ps
Network Working Group CJ. Shao
Internet-Draft H. Deng
Intended status: Informational China Mobile
Expires: April 25, 2013 R. Zhang
China Telecom
F. Bari
AT&T Services
October 22, 2012
Enhancement of CAPWAP Problem Statement
draft-shao-capwap-plus-ps-01
Abstract
In recent widescale deployments of large public Wi-Fi networks, and
in their integration with cellular networks EAP based authentication
has been considered as a good candidate to making Wi-Fi user
experience seamless similar to what it has been for cellular users.
A few new functions which could enhance CAPWAP protocol have been
identified in such deployments that can help improve the large scale
carrier grade Wi-Fi networks.
Status of this Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on April 25, 2013.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Conventions used in this document . . . . . . . . . . . . . . . 3
3. Supporting EAP authencation in Wi-Fi network . . . . . . . . . 3
3.1. Scenario Description . . . . . . . . . . . . . . . . . . . 3
4. The Scope of Split and Local MAC mode . . . . . . . . . . . . . 4
5. 802.11n support . . . . . . . . . . . . . . . . . . . . . . . . 4
6. Channel auto reconfiguration . . . . . . . . . . . . . . . . . 5
7. Power auto reconfiguration . . . . . . . . . . . . . . . . . . 6
8. Security Considerations . . . . . . . . . . . . . . . . . . . . 6
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6
10. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 6
11. Normative References . . . . . . . . . . . . . . . . . . . . . 6
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 7
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1. Introduction
Mobile devices such as smartphones and tablets continue to lead
growth in internet traffic. It is predicted that such growth will
continue even with the deployment of LTE network. Almost all mobile
devices today are Wi-Fi enabled. Public Wi-Fi services have lately
been paid more attention for that reason to help bring this growth of
cellular data traffic to a sustainable level. Wi-Fi spectrum is free
and globally available. Because of capacity and coverage issues, LTE
networks will continue to need public Wi-Fi network as a
complementary technology.
Recently industry efforts have been made to make Wi-Fi roaming as
seamless as it is for cellular GSM networks by deploying EAP based
authentication mechanism; Toward this end current CAPWAP protocol
could be enhanced to help ease such deployments.
There have been a number of proprietary implementations of the
interface between Access Point (AP) and Access Controller (AC) and
some of them provide capabilities which could be used to improve the
Wi-Fi performance. Once a standard interface is specified, the
benefits for operators of standards based deployment will outweigh
any benefits of past proprietary solutions.
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 Wi-Fi network
Current EAP message is designed to be transmitted in CAPWAP data
Plane. AC which is in the data path will act as the authenticator to
transmit this EAP message to AAA server. An operator may however
prefer to bypass the AC for the user plane in order to improve the
performance of AC and allow it to manage more APs when the network is
growing. In order to allow ACs to be bypassed for EAP messages, 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 networks. 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
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(AR). In this scenario, the CAPWAP-CTL tunnel and CAPWAP-DATA tunnel
are separated from each other.
Because there are no explicit 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
deliver 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 Split and Local MAC mode
There are 3 major categories has been specified by CAPWAP, the first
is about Functions: such as "Distribution Service", "Integration
Service", "Beacon Generation", "Probe Response Generation" "Power
Mgmt/Packet Buffering", "Fragmentation/Defragmentation", and "Assoc/
Disassoc/Reassoc"; the second is about QoS, such as, "Classifying",
"Scheduling", and "Queuing"; the third is about RSN (WPA2) such as
"IEEE 802.1X/EAP", "RSNA Key Management", and "IEEE 802.11
Encryption/Decryption". Even Split and Local MAC model has optional
implementation, either at AP or AC, this lead to serious issue about
Interoperation
Proposing a specific mode about all this implementation will help
interoperation among different vendors.
5. 802.11n support
There are a couple of capabilities of 802.11n that need to be
supported by CAPWAP control message such as radio capability, radio
configuration and station information.
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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 achieve the high
throughput. 802.11n use multiple antennas to form antenna array which
can be dynamically adjusted to improve the signal strength and extend
the coverage.
802.11n support two modes of channel usage: 20MHz mode and 40Mhz
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 different 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 Wi-Fi 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.
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7. Power auto reconfiguration
Power auto reconfiguration could improve the Wi-Fi 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.
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
Satoru Matsushima satoru.matsushima@tm.softbank.co.jp
11. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
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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.
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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Farooq Bari
AT&T Services
7277 164th Avenue NE
Redmond
US
Email: farooq.bari@att.com
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