WiMAX Forum Conference, January 2007 Seamless Mobility in WiMAX Nada Golmie and Richard Rouil...

WiMAX Forum Conference, January 2007

Seamless Mobility in WiMAX

Nada Golmie and Richard Rouil

Advanced Networking Technologies DivisionNational Institute of Standards and Technologies

Gaithersburg, MD 20899USA

www.antd.nist.gov/seamlessandsecure.shtml

2WiMAX Forum Conference, January 2007

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 Technologi

es

Seamless & Secure

Mobility Project

Edge Networks Ad-hoc Networks

PublicSafetyCommunications

Quantum Communications

Resilient AgileNetworking

Core Network Infrastructure

Internet Infrastructure Protection

Wireless Communication in Healthcare Environments

Advanced Networking Technologies Division


Seamless Future Networks

IP Based Core Networks

Media Access Systems

Services and Applications

Short RangeConnectivity

cellular

WirelineDSL/modem

WLAN

Interworking

Mobility Management

Roaming

Network of Networks


Everyday Usage Scenarios

Internet

EthernetWi-Fi

Cellular

Wi-Fi

Wi-Max

In the office

In the car

Out of Town

Wi-Fi

Wi-Fi

Wi-Fi

AP1AP2

AP3


Emergency Response Scenario

Satellite

Satellite3G

WiFi

3G


Military Usage Scenario

Satcom

Satcom

GPRS

3G

WiMax

Satcom

WiMax

WiMax

“Always Best Connected”


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.


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


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


Network entry evaluation

MN BSChannel 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 responseInitial ranging

Registration request

Registration responseRegistration

• 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.


Synchronization

0

2

4

6

8

10

12

0 2 4 6 8 10

Syn

chro

niz

atio

n la

ten

cy (

S)

DCD interval (s)

Effect of varying DCD and UCD interval on synchronization latency

UCD interval=1sUCD interval=2sUCD interval=5s

UCD interval=10s

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.


Initial Ranging

0

0.02

0.04

0.06

0.08

0.1

0.12

0 2 4 6 8 10 12

Ra

ng

ing

late

ncy

(s)

Number of initial ranging opportunities per frame

Effect of the number of initial ranging opportunities on the ranging latency

backoff window size=2backoff window size=4backoff window size=6


Registration

0

0.02

0.04

0.06

0.08

0.1

0 5 10 15 20

La

ten

cy (

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


Network Entry: summary

Network Entry step Layer 2 parameters Latency 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 reducedUse 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.


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


Channel Scanning in IEEE 802.16eMS Serving BS Target BS

Normal operationDecision to search possible BSs

Normal operation

Listen to channelsSynchronization 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


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.


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 level Association latency AttributesLevel 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 2 0

outfcs

B

ttn

12 exp

outt

expB

ft

outt

outt

csn


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


ACS algorithm: Example of scanning allocation

MN1scanning

MN1scanning

Period of no scanning

Iteration i Iteration i+1

Scanduration (ts)

Interleaved duration (td) Scanduration (ts)

Interleaved duration (td)

MN2scanning

MN2scanning

MN3scanning

MN3scanning


Evaluation results: simulation scenario

Base Station ls (ms) la (ms) tst (ms)

Parameter ValueBS1 8 110 118

Association levelBexp

Ncs (slot/frame)

Tf (ms)

0

4

1

4

BS2 8 50 58Association levelTf (ms)

1

4

BS3 16 306 314Association levelBexp

Ncs (slot/frame)

Tf (ms)

0

6

2

8

Total time required by MS to scan BSs (ms)

498

QoS Parameters Requirements

Video (MS1 and MS3)

Data rate (bytes/s)

Jitter (ms)

Delay (ms)

49600

100

200Audio (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


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

Pac

ket d

elay

(s)

Load

mean delaymax delay

Packet delay for MS supporting video traffic

scan duration ts

Breaking point

0

1

2

3

4

5

6

10 20 30 40 50 60 70 80 90 100

Tota

l sca

n t

ime

(s)

Load

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.


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

0 0.02 0.04 0.06 0.08

0.1

44 44.5 45 45.5 46

MS1: video

0 0.02 0.04 0.06 0.08

0.1

44 44.5 45 45.5 46

Pa

cke

t d

ela

y (s

)

MS2: audio

0 0.02 0.04 0.06 0.08

0.1

44 44.5 45 45.5 46

MS3: video

0 0.02 0.04 0.06 0.08

0.1

44 44.5 45 45.5 46

time (s)

background traffic

-0.1

-0.05

0

0.05

0.1

44 44.5 45 45.5 46

MS1: video

-0.1

-0.05

0

0.05

0.1

44 44.5 45 45.5 46

Jitt

er

(s)

MS2: audio

-0.1

-0.05

0

0.05

0.1

44 44.5 45 45.5 46

MS3: video

-0.1

-0.05

0

0.05

0.1

44 44.5 45 45.5 46

time (s)

background traffic

Pac

ket

del

ay

(s)

Pac

ket

jitte

r (s

)

Iteration 1 2 3 4 5 6 7 8 9 10 Iteration 1 2 3 4 5 6 7 8 9 10


Demos

Homogeneous handovers in IEEE 802.16 and 802.16e

Heterogeneous handovers between IEEE 802.11 and IEEE 802.16


Scenario: Handovers in IEEE 802.16 and 802.16e


Simulation Parameters

IEEE 802.16 parametersCell coverage radius (m) 500Frequency (GHz) 3.5Frequency bandwidth (MHz) 5Transmission power (W) 15Physical layer OFDMModulation 16QAM_3_4 Frame duration (ms) 4DCD/UCD interval (s) 5Min backoff window 2Max backoff window 6Number of contention slot per frame

5

IEEE 802.16e parametersLink going down factor 1.4Number of scan iteration 2Scan interval duration (frame) 50Interleaved 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) 30R0-R1, R1-R2, R2-R3 20

BSx-Rx (x=0..3) 10

Traffic specifications

Video rate (bytes/s) Variable rate ~40k

Audio rate (bytes/s) CBR 8000


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


Place for video


Scenario: Heterogeneous handovers


Simulation parameters

IEEE 802.16 parametersCell coverage radius (m) 400Frequency (GHz) 3.5Frequency bandwidth (MHz) 5Transmission power (W) 15Physical layer OFDMModulation 16QAM_3_4 Frame duration (ms) 4DCD/UCD interval (s) 5Min backoff window 2Max backoff window 6Number of contention slot per frame

5

IEEE 802.16e parametersLink going down factor 1.2Number of scan iteration 2Scan interval duration (frame) 50Interleaved time (frame) 40

Neighbor Discovery parametersRA interval (s) U [1:10]

Prefix lifetime (s) 5

Max RA delay (s) 0.5

Link Delays (ms)

R0-CN, R1-R2 30BSx-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 factor 1.2

Transmission power (W) 0.0134

Beacon Interval (ms) 100

Channel scanning (s) 3


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


Place for video


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


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.


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

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