University of Kansas | School of Engineering Department of Electrical Engineering and Computer...

University of Kansas | School of Engineering

Department of Electrical Engineering and Computer Science

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IEEE 802.11r

Suyang Ju



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Outline

• Seamless Connectivity

• IEEE 802.11 Architecture

• IEEE 802.11i

• IEEE 802.11e

• IEEE 802.11r• Security Features• QoS Features• Performance• Proposals

• Summary

• Conclusion

• References



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Seamless Connectivity

•Motivation

• Customer interests Multiple applications (voice, video and data) Anywhere and Anytime

–WLAN (coffee shop or airport)

–WiMAX (Highway)

–GSM cellular networks (phone calls)

–GPRS

–“Wi-Fi plus cellular”

•Goals

• Supporting multiple heterogeneous radios

• Continuous and ubiquitous connectivity

•Requirements

• Homogenous handovers Involve transition across points of attachment (PoA– such as WLAN AP or WiMAX BS)

• Heterogeneous handovers Involve transition across different networks such as WLAN, WiMAX and Cellular networks



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Seamless Connectivity

• Issues

• Homogeneous environment Intelligently recognize the immediate wireless environment Automatically select the best available PoA Qos resources should be allocated Security association should be computed

• Heterogeneous environment Much more complicated than homogeneous environment

• Possible solutions

• Homogeneous environment (Focus on WLAN) IEEE 802.11k

–Provides the information to discover the best available AP IEEE 802.11r

–Defines the mechanisms for secure and fast transitions between APs

• Heterogeneous environment IEEE 802.21

–Defines a common media independent handover (MIH) function between layer 2 and layer 3

–Provides mechanisms for optimizing handovers across Wi-Fi, WiMax and cellular networks



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Media Independent Handover• Handover scenarios

• Scenario 1: Moving client Roams to a new AP with higher-receiving signal strength

• Scenario 2: Load balancing Increases the overall capacity of the wireless networks

• Scenario 3: Service availability Provides better QoS Signal quality issues include interference, noise and path loss

• Media independent handover (MIH)• Provides link layer intelligence • Supports handover for both mobile and stationary users

Mobile users: Scenario1 Stationary users: Scenario 2 or 3

• Supports multiple radio standards (multimode) or more than one interface simultaneously• Supports transparent service continuity when handover occurs• Offers a unified interface to the upper layers• Independent of the technology-specific protocol provided by the lower layers



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Media Independent Handover

Figure 1: IEEE 802.21 MIH functions in mobility management protocol stack

From: Kapil Sood, Emily H. Qi and Vivek G. Gupta “Seamless

Platform Mobility Across Wireless Networks”, 2005.



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Multi-radio Architecture

Figure 2: Multi-radio architecture in Intel mobile platform

From: Kapil Sood, Emily H. Qi and Vivek G. Gupta “Seamless

Platform Mobility Across Wireless Networks”, 2005.



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IEEE 802.11 Architecture

From: Pablo Brenner, “A Technical Tutorial on the IEEE 802.11 Protocol”

BSS: Basic Service Set

ESS: Extended Service Set

AP: Access Point

DS: Distributed System

Figure 3: IEEE 802.11 architecture



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IEEE 802.11 Architecture

•Based on Cellular architecture

• Subdivided into cells

• Each cell is controlled by a Base Station

• Base Station are connected through backbone

• The whole interconnected WLAN is called Extended Service Set (ESS)

•Portal

• A device interconnects between an 802.11 and another 802 LAN

IEEE 802.11 Cellular Networks

Basic Service Set (BSS) Cell

Access Point (AP) Base Station

Distributed System Backbone Network

Table 1: The name comparison between the IEEE 802.11 and cellular networks



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Roaming

• Definition• Roaming is the process of moving from one BSS to another without loosing connection.

• Differences between the IEEE 802.11 and cellular networks• Comparison #1

IEEE 802.11

– Packet based Cellular networks

– Circuit based Effect: Roaming in IEEE 802.11 is easier

• Comparison #2 IEEE 802.11

– Temporary disconnection significantly reduces the performance Cellular networks

– Temporary disconnection may not affect the conversation Effect: Roaming in IEEE 802.11 is more complicated



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IEEE 802.11 Extensions

From: www.tropos.com “802.11 Technologies: Past, Present and Future”, 2007.

Figure 4: 802.11 Extensions

•Goals:• Faster• Better performance• More secure• Broader applicability



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IEEE 802.11i

• Goal•Designed to correct the weakness of the Wired Equivalency Protocol (WEP)

• Features•Includes all the capabilities of WPA (Wi-Fi Protected Access)•Defines a new encryption standard using AEC-CCMP•Provides dynamic encryption-key techniques•Pairwise master key caching•Pre-authentication •Layered security method •Uses Remote Access Dial-In User Service (RADIUS)•Port-based network access control mechanism

• Methods:•EAP-TLS•EAP-FAST•EAP-SIM•PEAP

• Drawback:•Slow (Several hundred milliseconds)



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IEEE 802.11i

From: Sangeetha Bangolae, Carol Bell and Emily Qi, “Performance Study of Fast BS Transition using IEEE 802.11r”

Figure 5: Authentication and QoS exchange process during transition

•Transition process:• Discovery (Probe exchange)• 802.11 open authentication• Re-association• Authentication method• EAPOL key exchange• QoS re-negotiation



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IEEE 802.11e• Goal:

• Supports QoS in IEEE 802.11 MAC• Implements access control mechanism to regulate the traffic

• Features:• Introduces a new Hybrid Coordination Function (HCF)

Combines function from DCF and PCF• Hybrid coordinator (HC) at AP controls channel access

Contention periodContention free period

• HC can gain control of the channel with higher priority• Supports IntServ QoS• Maximum duration that an STA can use is controlled

• Method• Allocates TX opportunity (TXOP) to STA by polling

• Drawback• Complex



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IEEE 802.11e

From: Stefan Mangold, Sunghyun Choi, Peter May, Ole Klein, Guido, Hiertz and Lothar Stibor, “IEEE 802.11e Wireless LAN fro Quality of Service”

Figure 6: A typical superframe in IEEE 802.11e



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IEEE 802.11r: WLAN Fast Roaming

• Goal• Minimize BSS transition time while providing the service offered by 802.11i and 802.11e

• Issues• Provides both security and Qos features while fast roaming may be tricky• “Security is easy. Mobility is hard”

• Method• Performs the authentication processes before the station actually begins roaming• Eliminates much of the handshaking overhead

• Advantages:Security: Robust authentication and encryptionQoS: Fast roaming

–Authentication using 802.11i: several hundreds milliseconds–Authentication using 802.11r: about 50ms

• Possible application of IEEE 802.11r• Time-sensitive application: Vo-Fi



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IEEE 802.11r: Security Features

• New key-management hierarchy• Multi-level setup• Several security domain form a security mobility domain (SMD)• Rules:

The highest-level key holder has access to the original cryptographic materialHigher-level entity derive the keys for the next level downLower-level entity can not decipher the upper-level key

• Benefit:Securely cache and distribute encryption keysEliminates the needs to perform a full 802.1X authentication with each AP

• Key-derivation algorithm• Based on one-way hash function• Purpose:

Ensures lower-level key holder can not decipher the original master key



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Figure 7: IEEE 802.11r key hierarchy


MSK: Master session keyPSK: Pre-shared shared keyPMK: Pairwise master key



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• key-management hierarchy• Highest-level key will be same within the same SMD• SMD defines the boundary in which a station can perform fast hand-off

• Ideas• Authentication occurs only once, when entering the mobility domain• Subsequent cryptographic material derived from the initial authentication

• Procedures• Initialization:

Perform the key derivation for all layers in the key hierarchyAll APs in this SMD need to know the corresponding level key

• Roaming:No IEEE 802.1X authentication is required

• Benefits:Decreases roam timesReduces load on back-end authentication servers



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From: Dava Molta, “802.11r: Wireless LAN Fast Roaming”, 2007

Figure 8: A comparison between IEEE 802.11i and IEEE 802.11r



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IEEE 802.11r: QoS Features• Option #1

• Method:Requests QoS resources at the time of re-association

• TimeDuring re-association

• BenefitAvoids a separate message exchange to reserve the needed resource

• DrawbackTakes a long time if the QoS server is slow

• Option #2• Method:

Reserves QoS resources prior to committing to re-association• Time

Before re-association• Benefit

Faster if the QoS server is heavily loadedAvoids failed re-association attempts

• DrawbackMight waste some resources



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IEEE 802.11r: Performance

Figure 9: A comparison between the 802.11i and 802.11r




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Figure 10: IEEE 802.11r performance




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Table 2: A comparison between the 802.1X and 802.11r




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IEEE 802.11r: Summary

• Proposals• Fast BSS-Transition Tunnel• TAP (Transition Acceleration Protocols)• Fast Roaming Using Multiple Conhurrent Associations• Motorola TGr Fast Handover Proposal• PEKM (Post-EAP Key Management Protocol)• Proposal for Fast Inter-BBS Transitions • AP Scanning • Just-In-Time 2 Phase Association )

• The formal 802.11r standard is scheduled to be published in June 2008.

From: www.wikipedia.com



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IEEE 802.11r: Other proposals

Figure 11: Fast BSS-Transition Tunnel

From: Haixiang He and Darwin Engwer, “Fast BSS-Transition Tunnel”, 2004



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IEEE 802.11r: Other proposals

• Idea:• STA is allowed to be associated with multiple AP simultaneously

• Problems• Duplicated packets might be received by the STA• The bandwidth might be wasted

• Practically, wired infrastructure in IEEE 802.11 might prevent multiple APs receive the same packets

• Method:• Several APs need to maintain the information for the particular STA• The information might need to be coherent

• Change• APs might not be aware of roaming• The information for the STA will not be deleted from its database

• Drawback• More memory is needed in the AP



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IEEE 802.11r: Conclusion

• IEEE 802.11r is used to provide fast hand-off

• IEEE 802.11r considers both the security and QoS

• IEEE 802.11r reduces the transition time significantly



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References

[1] Kapil Sood, Emily H. Qi and Vivek G. Gupta “Seamless Platform Mobility Across Wireless Networks”, 2005.

[2] Pablo Brenner, “A Technical Tutorial on the IEEE 802.11 Protocol”

[3] www.tropos.com “802.11 Technologies: Past, Present and Future”, 2007.

[4] Sangeetha Bangolae, Carol Bell and Emily Qi, “Performance Study of Fast BS Transition using IEEE 802.11r”

[5] Stefan Mangold, Sunghyun Choi, Peter May, Ole Klein, Guido, Hiertz and Lothar Stibor, “IEEE 802.11e Wireless LAN fro Quality of Service”

[6] Dava Molta, “802.11r: Wireless LAN Fast Roaming”, 2007

[7] Haixiang He and Darwin Engwer, “Fast BSS-Transition Tunnel”, 2004

[8] www.wikipedia.com



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