Reliable MAC Layer Multicast in Reliable MAC Layer Multicast in IEEE 802.11Wireless NetworksIEEE 802.11Wireless Networks

Min-Te Sun, Lifei Huang, Anish Arora, Ten-Hwang Lai

Department of Computer and Information Science

The Ohio State University

ICPP’02

Speaker: Chien-Wen Chang

2003/01/07

OutlineOutline

Introduction Existing Multicast MAC Protocols Problems with Existing Multicast MAC Protoc

ols Batch Mode Multicast MAC Protocol Location Aware Multicast MAC Protocol Simulation Conclusion

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IntroductionIntroduction

many random access MAC protocols do not deal directly with multicast

There is no MAC-level recovery on multicast frame

treat broadcast as a special case of multicast several higher layer protocols rely on reliable

MAC layer multicast/broadcast delivery acceptable quality of service in many

applications

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Existing Multicast MAC Protocols(1)

In IEEE 802.11, the RTS/CTS extension is not used for broadcast/multicast

In [19] attempts to extend the IEEE 802.11 broadcast/multicast protocol with RTS/CST

In [20] augments the MAC protocol in [19] with the NAK frame and additional rules

In [21] is introduced to provide a reliable broadcast MAC

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Existing Multicast MAC Protocols(2)

In [19] the basic DCF MAC adding the RTS/CTS handshaking

In [20], the Broadcast Support Multiple Access (BSMA)

adding NAK and the following rules After the sender transmits a data frame, it waits for

NAK If a receiver does not receive the data frame after it

transmitted the CTS frame, it transmits a NAK frame.

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Existing Multicast MAC Protocols(3)

In [21], the Broadcast Medium Window (BMW) basic idea is to treat each broadcast request as multiple

unicast requests. Each unicast is processed using the reliable IEEE 802.

11 DCF MAC protocol each node maintains three lists:

NEIGHBOR BUFFER SEND BUFFER RECEIVER BUFFER.

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Existing Multicast MAC Protocols(4)

NEIGHBOR BUFFER list contains the current neighbors.

SEND BUFFER list contains the ongoing broadcast messages.

RECEIVE BUFFER list contains the sequence numbers of the data frames received by the node.

based on RTS/CTS/DATA/ACKserves the nodes in NEIGHBOR BUFFER list

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Problems with Existing Multicast MAC Protocols

(1) In [19]

the MAC protocol does not coordinate the transmission of CTS

an assumption is made in [19] that the sender’s radio has the Direct Sequence (DS) capture ability.

In [23] is reported that this probability quickly drops to 0.2 at the presence of more than 5 nodes

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Problems with Existing Multicast MAC Protocols

(2) In [20], BSMA

The additional NAK frame does not help resolve the collision of the CTS frame

In [21], BMWBMW is inefficient for following reasons:

Contention phase at least n contention phases for each multicast data frame some other node wins the contention

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Problems with Existing Multicast MAC Protocols

(3) In [21], BMW (cont.)

Timeout the prolonged multicast process can easily lead to a

timeout in the higher layer

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Batch Mode Multicast MAC Protocol (1)

consolidate the n contention phases into one the required time to serve a multicast can be

greatly reduced To achieve this goal,

coordinate the transmissions of the control frames uses RTS frames to sequentially instruct CTS

transmissions uses RAK frames to coordinate the ACK

transmissions

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Batch Mode Multicast MAC Protocol (2)

several advantages:reduces the number of contention phasesdoes not modify any control frame formatco-exist with the other IEEE 802.11 protocols

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Location Aware Multicast MAC Protocol(1)

When the size of S is large, it may be desirable to reduce S’s size

Find a cover set, S’, of S, and send RTS only to the addresses of nodes in S’

expect only those nodes in S’ to return a CTS and ACK

the sender is able to conclude that all nodes in S have received the multicast data frame

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Location Aware Multicast MAC Protocol(2)

To achieve the above goaluse the location information obtained by GPSsome theorems

location information US Federal Communications Commissions

(FCC) mandated wireless service carriers to provide the location service

including the location information in beacons

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Location Aware Multicast MAC Protocol(3)

some theoremsTheorem 1

Let S be the set of all intended receivers of the multicast data frame. In the Batch Mode Procedure(), suppose that the sender receives an ACK from every node in a subset S’ of S. A node p in S \ S’ is guaranteed to have received the data frame without collision if and only if S’ is a cover set of S.

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T

d

f

c

b

ep

Neighbors ={a,b, c, d, e, f, p}

a

S’={b, e, c}

S\S’={p}

S={b, e, c, p}

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Location Aware Multicast MAC Protocol(4)

some theorems (cont.) Theorem 2 ([18]) The minimum cover set of a neighbo

r set S can be computed in O(n4/3) time Theorem 3 Let S be the set of all intended receivers of

the multicast data frame. In the Batch Mode Procedure(), suppose that the sender receives an ACK from every node in a subset SACK S’, where S’ is a cover set of S. Under the assumption that the primary transmission error is caused by collision, a node p in S\S’ is guaranteed to have received the data frame without collision if and only if A(p) A(SACK)

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Location Aware Multicast MAC Protocol(5)

some theorems (cont.)Theorem 4 Assume that all nodes have the sa

me transmission radius R. Given a node p and a set of nodes C, if the union of the cover angles is p’s cover angle for the transmission area of p, A(p), is completely covered by C

angle-based scheme

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Location Aware Multicast MAC Protocol(6)

Cover Angle of node p for node q ([α,β])

αβ

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T

d

f

c

b

ep

S={b, e, c, p}

a

S’={b, e, c}

S\S’={p}x

y z

t

v

doesn’t return ACK

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Location Aware Multicast MAC Protocol(7)

a refinement of the Batch Mode Multicast MAC protocol

MCS(S) the minimum cover set computation procedure

denote UPDATE(S, S’) the angle-based procedure Batch Mode Procedure (S, SACK) => (MCS(S), SACK)

S = UPDATE(S, SACK)S’

returns the set of nodes in S that are not completely covered by SACK

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Simulation(1)

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Simulation(2)

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Simulation(3)

A multicast message transmission is considered successful if the message reaches a certain percentage of the intended receivers

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Simulation(4)

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Simulation(5)

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Conclusion

co-exist with the current unreliable IEEE 802.11 multicast MAC protocol

reduce the number of contention phases decreases the average total time required to

complete a multicast request Future work

multicast MAC protocol that solves both the hidden and exposed terminal problems