1. QoS Provisioning in Wireless Mesh Networks
Ali Hamidian and Ulf Körner
In this talk I’ll present our latest work (still in progress) with EDCA/RR, which is our proposed extension to e
Fourth EuroNGI/FGI Workshop on Wireless and Mobility
January , Barcelona, Spain

2. Outline
Overview of IEEE e
EDCA with Resource Reservation (EDCA/RR)
Multi-hop resource reservation in EDCA/RR
Summary

3. IEEE e 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.)

4. EDCA HCCA Contention-based “Enhanced DCF” Distributed
Service differentiation
Contention-free
“Enhanced PCF”
Centralized
Resource reservation

5. 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

6. Outline
Overview of IEEE e
EDCA with Resource Reservation (EDCA/RR)
Multi-hop resource reservation in EDCA/RR
Summary

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

8. 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.
destination
source

9. EDCA/RR Operation If admission control OK: schedule the new stream
broadcast ADDTS request containing TSPEC
wait for ADDTS response
destination
source
ADDTS request

10. 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.
destination
source
ADDTS response

11. EDCA/RR Operation
Now the source has periodic and contention-free access to the medium.
destination
source
HP data frames

12. Simulation Setup
EDCA/RR implementation in ns-2.26 based on Mike Moreton’s enhanced /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

13. 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
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
(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)

14. Outline
Overview of IEEE e
EDCA with Resource Reservation (EDCA/RR)
Multi-hop resource reservation in EDCA/RR
Summary

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

16. Motivation: Why EDCA/RR for Wireless Mesh Networks (WMNs)?
Results from a 4-hop g WMN
CS = Counter Strike server to clients: ( ×n) B every 60 ms clients to server: 42 B every 50 ms

17. 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 s
reactive part: RM-AODV (Radio Metric AODV)
proactive part: tree-based routing

18. Multi-hop Resource Reservation in EDCA/RR
Copy TSPEC from HP-packet to RRQ
Do admission control
Temporarily mark resources as reserved and broadcast RRQ
RRQ (route and reservation request) is a RREQ extended with some TSPEC fields. A B C
The routing protocol copies the TSPEC from the packet into a route and reservation request
(RRQ) and sends it down to the MAC sublayer (EDCA/RR). EDCA/RR does admission
control. If OK, broadcast RRQ.
An HP-packet is sent down the protocol stack and reaches the routing protocol (AODV).

19. Multi-hop Resource Reservation in EDCA/RR
Copy TSPEC from RRQ
Do admission control
Temporarily mark resources as reserved and rebroadcast RRQ A B C

20. Multi-hop Resource Reservation in EDCA/RR
Copy TSPEC from RRQ
Do admission control
Schedule the traffic request and send a RRP A B C

21. Multi-hop Resource Reservation in EDCA/RR
Schedule traffic and forward RRP A B C

22. Multi-hop Resource Reservation in EDCA/RR
Schedule traffic; TXOP reservation done A B C

23. 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