1. WiMAX Forum Conference, January 2007 Seamless Mobility in WiMAX Nada Golmie and Richard Rouil Advanced Networking Technologies Division National Institute of Standards and Technologies Gaithersburg, MD 20899 USA www.antd.nist.gov/seamlessandsecure.shtml

2. WiMAX Forum Conference, January 2007 2 Innovative IT Services and Applications Internet Telephony Programmable Networks Knowledge Management for Global Information Systems Bridging the Gap Between Advanced Network Technology and IT Innovation Complex Systems Trustworthy Networking Disruptive Technologies Seamless & Secure Mobility Project Edge Networks Ad-hoc Networks Public Safety Communications Quantum Communications Resilient Agile Networking Core Network Infrastructure Internet Infrastructure Protection Wireless Communication in Healthcare Environments Advanced Networking Technologies Division

3. WiMAX Forum Conference, January 2007 3 Seamless Future Networks IP Based Core Networks Media Access Systems Services and Applications Short Range Connectivity cellular Wireline DSL/modem WLAN Interworking Mobility Management Roaming Network of Networks

4. WiMAX Forum Conference, January 2007 4 Everyday Usage Scenarios Internet Ethernet Wi-Fi Cellular Wi-Fi Wi-Max In the office In the car Out of Town Wi-Fi AP1 AP2 AP3

5. WiMAX Forum Conference, January 2007 5 Emergency Response Scenario Satellite 3G WiFi 3G

6. WiMAX Forum Conference, January 2007 6 Military Usage Scenario Satcom GPRS 3G WiMax Satcom WiMax “Always Best Connected”

7. WiMAX Forum Conference, January 2007 7 Key Challenges Scalability – roaming from any access network to any other access network (2G, 3G, 4G, Wi-Fi, Wi-Max, Bluetooth, Satellite, Ethernet) Standard handover interfaces – interoperability between different vendor equipment. Cross-layer solutions - extensions to layer 1 & layer 2 functionalities in order to optimize higher layer mobility architectures (MIPv4, MIPv6, SIP). QOS guarantees during handover – no disruption to user traffic: extreme low latency, signaling messages overhead and processing time, resources and routes setup delay, near-zero handover failures and packet loss rate Security – user maintains the same level of security when roaming across different access networks.

8. WiMAX Forum Conference, January 2007 8 Seamless & Secure Mobility Project Technical Plan Develop plug-and-play mobility simulation platform: - Assess state of the art & availability of tools available in the public domain. - Build model extensions and abstractions to accurately characterize protocol interactions Derive analytical models for evaluating handover latency, and transition blocking probability. Devise benchmarks and realistic usage scenarios. Devise metrics for quantifying handover performance. Devise and evaluate handover protocol optimizations and decision algorithms. Devise access link security profiles and mappings across access link technologies. Technical Approach Investigate mobility protocols and methods that characterize & improve their performance. Bridging the interconnection gap between heterogeneous and “stovepipe” access network technologies Deliverables Contribute to standard group activities such as IETF and IEEE 802.21: conduct comparative performance evaluation of handover mechanisms being considered in IEEE 802 Create and maintain a repository of tools, benchmarks and performance metrics on NIST Web site. Publish performance analysis results in conference / journal articles: characterize implications on handover performance including mobility management, QOS, and security. Key Questions How to support seamless mobility across different access network technologies? How to maintain security when handing over a connection from one access link to another access link? Internet

9. WiMAX Forum Conference, January 2007 9 Our results on mobility in IEEE 802.16 Network entry in IEEE 802.16 Network entry evaluation results Mobility support in IEEE 802.16e Channel scanning algorithm

10. WiMAX Forum Conference, January 2007 10 Network entry evaluation MN BS Channel Selection Normal operation DL_MAP (Downlink map) Link Detected DCD (Downlink Channel Descriptor) Ranging request Link UP UCD (Uplink Channel Descriptor) UL_MAP (Uplink map) Downlink synchronization Uplink synchronization Ranging response Initial ranging Registration request Registration response Registration The DL_MAP and UL_MAP messages contain the burst allocation decided by the BS. The DCD and UCD messages contain burst profiles. They are periodically generated by the BS. The standard defines the maximum interval between two messages to 10 seconds.

11. WiMAX Forum Conference, January 2007 11 Synchronization DCD and UCD messages synchronized (i.e located in the same frame) The delay contributed by the synchronization component is the most significant (order of magnitude is in seconds!!!) When both UCD and DCD are synchronized, the delay between the downlink and the uplink synchronization is minimized.

12. WiMAX Forum Conference, January 2007 12 Initial Ranging

13. WiMAX Forum Conference, January 2007 13 Registration 0 0.02 0.04 0.06 0.08 0.1 0 5 10 15 20 Latency (s) Number of SS in the cell Effect of the number of SS on the registration latency (using a FIFO Round Robin Scheduling) Frame duration = 4ms

14. WiMAX Forum Conference, January 2007 14 Network Entry: summary Network Entry stepLayer 2 parametersLatency range (s) Downlink and uplink synchronization - DCD interval - UCD interval 0.2-10 Initial ranging - Backoff window size - Number of ranging opportunities per frame 0.005-0.110 Registration - Transmission opportunity allocation 0.005-0.080 To speed up network entry, the time to acquire the downlink and complete the uplink synchronization must be reduced Use IEEE 802.16e mobility extensions R. Rouil, N. Golmie, “Effects of IEEE 802.16 link parameters and handover performance for select scenarios, ” IEEE 802.21 Media Independent Handover Working Group Contribution #21-06-0524, March 2006.

15. WiMAX Forum Conference, January 2007 15 Mobility support in IEEE 802.16e In IEEE 802.16e, a MS can scan for potential target BSs while maintaining connection with current BS. There are 4 possible scanning modes: Scan without association: no ranging during scanning Association level 0: contention based ranging Association level 1: dedicated ranging slot Association level 2: level 1 with ranging responses sent over the backbone Exchange of information with neighboring BSs such as DCD and UCD messages Broadcast of neighboring information (DCD and UCD messages) to connected MSs Synchronization between scanning MS and serving BS to reduce packet loss Messages exchange Negotiation of scanning time

16. WiMAX Forum Conference, January 2007 16 Channel Scanning in IEEE 802.16e MSServing BSTarget BS Normal operation Decision to search possible BSs Normal operation Listen to channels Synchronization messages (DL_MAP,DCD, UCD, UL_MAP) MOB-SCN_REQ MOB-SCN_RSP Scanning Normal mode Repeat scanning and normal mode intervals MOB-SCN_REP MOB-MSHO_REQ MOB-MSHO_RSP Switch channel and network entry MOB-MSHO_IND

17. WiMAX Forum Conference, January 2007 17 Proposed solution Objectives of the Adaptive Channel Scanning (ACS) algorithm: minimize the disruptive effects of scanning on the application traffic by using the QoS traffic requirements. Assumptions: Neighboring BSs exchange information over the backbone The messages are extended to fit the information required by the algorithm Stage 1: estimate the time needed by a MS to scan the possible neighboring stations Stage 2: compute the interleaving of channel scanning and data transmission intervals R. Rouil, N. Golmie, “Adaptive channel scanning for IEEE 802.16e” in the Proceedings of Military Communications, MILCOM 2006, October 2006.

18. WiMAX Forum Conference, January 2007 18 ACS stage 1: scanning time estimation The scanning time consists of two elements: Synchronization latency: DCD and UCD messages are provided by the serving BS. The MS only waits for DL_MAP and UL_MAP messages, generally located in each frame. Association latency: depends on the association level provided by the neighbor BS. Association levelAssociation latencyAttributes Level 0 is the backoff exponent number of slots per frame the frame duration the timeout value for receiving a ranging response (default: 50ms) Level 1 the timeout value for receiving a ranging response (default: 50ms) Level 20

19. WiMAX Forum Conference, January 2007 19 ACS stage 2: Interleaving of channel scanning and data transmission intervals The information used is: Quality of Service of the applications Available bandwidth Number of concurrent scanning stations The algorithm computes the following information: Channel scanning duration Duration between scanning iterations Number of scanning iterations

20. WiMAX Forum Conference, January 2007 20 ACS algorithm: Example of scanning allocation MN1 scanning MN1 scanning Period of no scanning Iteration iIteration i+1 Scan duration (t s ) Interleaved duration (t d ) Scan duration (t s ) Interleaved duration (t d ) MN2 scanning MN2 scanning MN3 scanning MN3 scanning

21. WiMAX Forum Conference, January 2007 21 Evaluation results: simulation scenario Base Stationl s (ms)l a (ms)t st (ms) ParameterValue BS18110118 Association level B exp N cs (slot/frame) T f (ms) 04140414 BS285058 Association level T f (ms) 1414 BS316306314 Association level B exp N cs (slot/frame) T f (ms) 06280628 Total time required by MS to scan BSs (ms) 498 QoS ParametersRequirements Video (MS1 and MS3) Data rate (bytes/s) Jitter (ms) Delay (ms) 49600 100 200 Audio (MS2) Data rate (bytes/s) Jitter (ms) Delay (ms) 8000 50 75 Zone of Link Going Down and generation of scan requests for all MSs

22. WiMAX Forum Conference, January 2007 22 Simulation results for 1 MS 0 0.05 0.1 0.15 0.2 0.25 0.3 10 20 30 40 50 60 70 80 90 100 Packet delay (s) Load mean delay max delay Packet delay for MS supporting video traffic scan duration t s Breaking point Algorithm gradually increases the interleaved time to compensate the smaller available bandwidth Total scanning time for MS supporting video traffic As the load increases, there is less bandwidth available to flush the buffered data therefore the delay increases.

23. WiMAX Forum Conference, January 2007 23 Simulation results for 3 MS Packet delay and jitter are kept within the required bounds. We can identify each iteration and the scattering of the scanning stations Peak values occur when the MS sends the first packet after scanning. Background traffic is minimally impacted Packet delay (s) Packet jitter (s) Iteration12345678910Iteration12345678910

24. WiMAX Forum Conference, January 2007 24 Demos Homogeneous handovers in IEEE 802.16 and 802.16e Heterogeneous handovers between IEEE 802.11 and IEEE 802.16

25. WiMAX Forum Conference, January 2007 25 Scenario: Handovers in IEEE 802.16 and 802.16e

26. WiMAX Forum Conference, January 2007 26 Simulation Parameters IEEE 802.16 parameters Cell coverage radius (m)500 Frequency (GHz)3.5 Frequency bandwidth (MHz)5 Transmission power (W)15 Physical layerOFDM Modulation 16QAM_3_4 Frame duration (ms)4 DCD/UCD interval (s)5 Min backoff window2 Max backoff window6 Number of contention slot per frame 5 IEEE 802.16e parameters Link going down factor1.4 Number of scan iteration2 Scan interval duration (frame)50 Interleaved time (frame)40 Neighbor Discovery parameters RA interval (s)U [10:30] Prefix lifetime (s)5 Max RA delay (s)0.5 Link Delays (ms) Rx-CN (x=0..3) 30 R0-R1, R1-R2, R2-R320 BSx-Rx (x=0..3)10 Traffic specifications Video rate (bytes/s)Variable rate ~40k Audio rate (bytes/s) CBR 8000

27. WiMAX Forum Conference, January 2007 27 Handover configuration parameters No Triggers: The movement detection is based on Layer 3 Neighbor Discovery The reception of a RA indicates the new network. Since the node is not aware of the new link, no RS is sent. Simulation parameters: RA interval for the simulation U[1s,10s] Prefix lifetime 18s Link Triggers: Device is MIH enabled and receives Link Detected/UP/Down triggers. The triggers are generated by the media to indicate new network or loss of connection Link Detected upon reception of DL_MAP message; UCD=DCD= 5s Link Up upon successful registration Link Down when the synchronization messages are not received within the Lost_UL_Map=Lost_DL_Map= 600ms (Max value in spec) Link Going Down when the power received is below the Link Going Down Threshold: 3.559572e-9W

28. WiMAX Forum Conference, January 2007 Place for video

29. WiMAX Forum Conference, January 2007 29 Scenario: Heterogeneous handovers

30. WiMAX Forum Conference, January 2007 30 Simulation parameters IEEE 802.16 parameters Cell coverage radius (m)400 Frequency (GHz)3.5 Frequency bandwidth (MHz)5 Transmission power (W)15 Physical layerOFDM Modulation 16QAM_3_4 Frame duration (ms)4 DCD/UCD interval (s)5 Min backoff window2 Max backoff window6 Number of contention slot per frame 5 IEEE 802.16e parameters Link going down factor1.2 Number of scan iteration2 Scan interval duration (frame)50 Interleaved time (frame)40 Neighbor Discovery parameters RA interval (s)U [1:10] Prefix lifetime (s)5 Max RA delay (s)0.5 Link Delays (ms) R0-CN, R1-R2 30 BSx-Rx (x=1,2)15 Traffic specifications Video rate (bytes/s)Variable rate ~40k Audio rate (bytes/s) CBR 8000 IEEE 802.11 parameters Cell coverage radius (m)50 Link going down factor1.2 Transmission power (W)0.0134 Beacon Interval (ms)100 Channel scanning (s)3

31. WiMAX Forum Conference, January 2007 31 Link Going Down trigger parameters Device is MIH enabled and receives Link Detected/UP/Down/Going Down triggers Link Going Down triggers are based on the received power (relative to the receiver sensitivity) Timeline: Handover 802.11-802.16: 17s, due to Link Going Down 802.11: Pt=0.0134W, RxThreshold: 5.25089e-10 W, Going Down Threshold: 6.301068e-10 W, F= 2.4Ghz Handover 802.16-802.16: 53s, due to Link Going Down 802.16: RxThreshold: 2.96631e-09W, Going Down Threshold: 3.559572We- 9, Pt = 15W, F=3.5 GHz Handover 802.16-802.11: 98s, due to detection of new AP, Link UP

32. WiMAX Forum Conference, January 2007 Place for video

33. WiMAX Forum Conference, January 2007 33 Contributions to IEEE 802.21 N. Golmie, S. Woon, “Performance measurements for Link Going Down Trigger,” IEEE 802.21 Media Independent Handover Working Group Contribution #21-05-419, January 2006. R. Rouil, N. Golmie, “Effects of IEEE 802.16 link parameters and handover performance for select scenarios,” IEEE 802.21 Media Independent Handover Working Group Contribution #21-06-0524, March 2006. N. Golmie, U. Olvera, R. Salminen, “Media Independent Handover QOS Framework and parameters,” IEEE 802.21 Media Independent Handover Working Group Contribution #21-06-0493, March 2006. N. Golmie, U. Olvera, R. Salminen, “QOS Proposal,” IEEE 802.21 Media Independent Handover Working Group Contribution #21-06-0598, May 2006. R. Rouil, N. Golmie, “MIH primitives and scenarios,” IEEE 802.21 Media Independent Handover Working Group Contribution #21-06-0614, May 2006. N. Golmie, U. Olvera, R. Salminen, R. Rouil, S. Woon, “Implementing Quality of Service based handovers using the IEEE 802.21 framework,” IEEE 802.21 Media Independent Handover Working Group Contribution #21-06-0687, July 2006 N. Golmie, R. Rouil, “QOS Updates,” IEEE 802.21 Media Independent Handover Working Group Contribution #21-07-011, January 2007

34. WiMAX Forum Conference, January 2007 34 Conference papers S. Lee and N. Golmie, ‘’Power Efficient Interface selection scheme using paging for WLAN in Heterogenous wireless networks,” to appear in the Proceedings of the International Conference on Communications,” ICC 2006, June 2006. S. Woon, N. Golmie, and A. Sekercioglu, “Effective Link Triggers to Improve Handover Performance,” to appear in the Proceedings of the International symposium on Personal Indoor and Mobile Radio Communications, PIMRC 2006, September 2006. R. Rouil, N. Golmie, “Adaptive channel scanning for IEEE 802.16e” to appear in the Proceedings of Military Communications, MILCOM 2006, October 2006.

35. WiMAX Forum Conference, January 2007 35 Tools for Public Download IEEE 802.16 NS-2 model IEEE 802.21 mobility package Some documentation Available on: http://www.antd.nist.gov/seamlessandsecure/download.html