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L U N D U N I V E R S I T Y

QoS Provisioning in Wireless Mesh Networks

Ali Hamidian and Ulf Körner

Fourth EuroNGI/FGI Workshop on Wireless and MobilityJanuary 16-18 2008, Barcelona, Spain

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L U N D U N I V E R S I T Y

Outline

• Overview of IEEE 802.11e• EDCA with Resource Reservation

(EDCA/RR)• Multi-hop resource reservation in EDCA/RR• Summary

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L U N D U N I V E R S I T Y

IEEE 802.11e and HCF

• 802.11e introduces hybrid coordination function (HCF), which has 2 medium access methods:– enhanced distributed channel access (EDCA)– HCF controlled channel access (HCCA)

• HCF introduces 2 new concepts:– transmission opportunity (TXOP): A bounded

time interval during which a station may transmit multiple frames

– traffic specification (TSPEC): Contains information about the QoS expectation of a traffic stream (frame size, service interval, data rate, burst size, delay bound, etc.)

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L U N D U N I V E R S I T Y

EDCA HCCA

• Contention-based

• “Enhanced DCF”

• Distributed

• Service differentiation

• Contention-free

• “Enhanced PCF”

• Centralized

• Resource reservation

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L U N D U N I V E R S I T Y

Motivation of EDCA/RR: QoS Limitations in 802.11e

• Problem with EDCA– Contention-based medium access & no distributed

admission control ==> not possible to guarantee QoS

• Problem with HCCA– Centralized infrastructure requirement ==> HCCA

not useful in ad hoc/mesh networks

• We need a solution which is– Contention-free (unlike EDCA)

• Remove the random medium access delays– Distributed (unlike HCCA)

• Remove the need of an access point

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L U N D U N I V E R S I T Y

Outline

• Overview of IEEE 802.11e• EDCA with Resource Reservation

(EDCA/RR)• Multi-hop resource reservation in EDCA/RR• Summary

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L U N D U N I V E R S I T Y

EDCA/RR Operation

EDCA/RR is similar to EDCA as long as the stations are sending LP-frames (which do not need resource reservation).

source

destination

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L U N D U N I V E R S I T Y

EDCA/RR Operation

When an HP-stream needs to reserve resources, EDCA/RR in the source checks whether its own new stream can be admitted.

source

destination

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L U N D U N I V E R S I T Y

EDCA/RR Operation

If admission control OK:

• schedule the new stream

• broadcast ADDTS request containing TSPEC

• wait for ADDTS response

ADDTS request

source

destination

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L U N D U N I V E R S I T Y

EDCA/RR Operation

Once all ADDTS responses are received by the source, it waits until its first reserved TXOP at service start time & starts transmitting.

ADDTS response

source

destination

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L U N D U N I V E R S I T Y

EDCA/RR Operation

Now the source has periodic and contention-free access to the medium.

HP data frames

source

destination

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L U N D U N I V E R S I T Y

Simulation Setup

• EDCA/RR implementation in ns-2.26 based on Mike Moreton’s enhanced 802.11/802.11e implementation

• EDCA vs. EDCA/RR• The impact of (hidden) LP-streams on an

HP-stream• HP stream (AC_VO): G.711, 180 B, UDP

datagrams every 20 ms• LP stream (AC_BE): FTP, 1000 B, TCP

segments

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L U N D U N I V E R S I T Y

Average End-to-End Delay - 0 % packet error

no. of LP-streams

average end-to-end delay (ms)

99 % confidence interval (ms)

EDCA EDCA/RR EDCA EDCA/RR

0 0.69 12.33 (0.69,0.69) (12.13,12.53)

1 6.21 12.22 (6.20,6.22) (12.02,12.42)

2 11.17 12.27 (11.14,11.19) (12.08,12.47)

3 13.93 12.22 (13.90,13.96) (12.01,12.42)

4 17.12 12.38 (17.08,17.16) (12.19,12.57)

5 20.51 12.25 (20.46,20.56) (12.06,12.45)

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L U N D U N I V E R S I T Y

Outline

• Overview of IEEE 802.11e• EDCA with Resource Reservation

(EDCA/RR)• Multi-hop resource reservation in EDCA/RR• Summary

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L U N D U N I V E R S I T Y

Motivation: Why EDCA/RR for Wireless Mesh Networks (WMNs)?

• EDCA/RR (with multi-hop capability) is especially well-suited for static wireless networks, like WMNs

• IEEE 802.11s for mesh networks is based on EDCA, so it is not too difficult/unrealistic extending 802.11s to support EDCA/RR

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L U N D U N I V E R S I T Y

Motivation: Why EDCA/RR for Wireless Mesh Networks (WMNs)?

• Results from a 4-hop 802.11g WMN

CS = Counter Strikeserver to clients: (50.4+6.15×n) B

every 60 msclients to server: 42 B every 50 ms

0 2 4 6 8 10 12 14

0,00

0,01

0,02

0,03

0,04

0,05

0,06

0,07

0,08

0,09

0,10

Average Jitter vs. Number of CS Streams

Without FTP

With FTP

Number of CS Streams

Ave

rag

e J

itte

r (s

)

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L U N D U N I V E R S I T Y

Multi-hop Resource Reservation in EDCA/RR

• Combined route discovery (AODV) and resource reservation (EDCA/RR)– search for route fulfilling the QoS

requirements– faster route discovery/resource reservation

• Why AODV? Because it will be part of HWMP (Hybrid Wireless Mesh Protocol), which is the default routing protocol suggested in 802.11s– reactive part: RM-AODV (Radio Metric AODV) – proactive part: tree-based routing

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L U N D U N I V E R S I T Y

Multi-hop Resource Reservation in EDCA/RR

An HP-packet is sent down the protocol stack and reaches the routing protocol (AODV).

A B C

RRQ (route and reservation request) is a RREQ extended with some TSPEC fields.

1. Copy TSPEC from HP-packet to RRQ

2. Do admission control

3. Temporarily mark resources as reserved and broadcast RRQ

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L U N D U N I V E R S I T Y

Multi-hop Resource Reservation in EDCA/RR

A B C

1. Copy TSPEC from RRQ

2. Do admission control

3. Temporarily mark resources as reserved and rebroadcast RRQ

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L U N D U N I V E R S I T Y

Multi-hop Resource Reservation in EDCA/RR

A B C

1. Copy TSPEC from RRQ

2. Do admission control

3. Schedule the traffic request and send a RRP

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L U N D U N I V E R S I T Y

Multi-hop Resource Reservation in EDCA/RR

A B C

Schedule traffic and forward RRP

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Multi-hop Resource Reservation in EDCA/RR

A B C

Schedule traffic; TXOP reservation done

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Summary

• EDCA/RR – is a MAC scheme with distributed

admission control and scheduling– allows stations to reserve TXOPs for

periodic and contention-free medium access

– suites well for WMNs