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Ch 5. MAC in WMNs. Myungchul Kim [email protected] Wireless routers called wireless mesh points (MPs) MAC protocols with omni directional antennas for sharing a single channel: Aloha, Slotted Aloha, CSMA, CSMA/CA IEEE 802.11 MAC and IEEE 802.11e MAC: single channel Directional antennas

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Ch 5. MAC in WMNs

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Ch 5 mac in wmns

Ch 5. MACin WMNs

Myungchul Kim

[email protected]


Ch 5 mac in wmns

Wireless routers called wireless mesh points (MPs)

MAC protocols with omni directional antennas for sharing a single channel: Aloha, Slotted Aloha, CSMA, CSMA/CA

IEEE 802.11 MAC and IEEE 802.11e MAC: single channel

Directional antennas

Multiple channels at mesh nodes

IEEE 802.11b: three orthogonal channels could be used simultaneously in a neighborhood without interfering.

Introduction


Ch 5 mac in wmns

Control and management of WMNs have to be distributed across all nodes.

Distributed MAC, distributed channel selection and/or channel assignment

Multihop transmission: hidden node problem and exposed node problem

Design objectives and challenges


Ch 5 mac in wmns

Design objectives and challenges


Ch 5 mac in wmns

Directional antennas or a multichannel MAC protocol may suffer from a deafness problem

Dyanmic nature: variations in link quality, changing congestion levels, and user mobility

Error-prone nature of wireless channels

Design objectives and challenges


Ch 5 mac in wmns

Contention-based protocols vs collision-free channel partition protocols

Aloha and slotted aloha

Conventional wireless MAC protocols


Ch 5 mac in wmns

CSMA and CSMA/CA

CSMA

CSMA/CA

Hidden node problem

RTS/CTS

Collision?

IEEE 802.11 DCF protocol

Distributed coordination function (DCF) on CSMA/CA

Point coordination funtion (PCF) on CSMA/CA

Distributed inter frame space (DIFS)

Short inter frame space (SIFS)

Network allocation vector (NAV)

Conventional wireless MAC protocols


Ch 5 mac in wmns

IEEE 802.11 DCF protocol

Conventional wireless MAC protocols


Ch 5 mac in wmns

IEEE 802.11e MAC protocol

Define the channel access functions and the traffic specification (TSPEC) management

Channel access function -> hybrid coordination function (HCF)

A contention-based protocol called enhanced distributed channel access (EDCA)

A polling mechanism called HCF controlled channel access (HCCA): central control

Conventional wireless MAC protocols


Ch 5 mac in wmns

IEEE 802.11e MAC protocol

EDCA: enhance the original DCF by providing prioritized medium access based on different traffic classes, access categories (ACs)

TXOP: a bounded time interval in which a node is allowed to transmit a series of frames.

Conventional wireless MAC protocols


Ch 5 mac in wmns

IEEE 802.11e MAC protocol

Conventional wireless MAC protocols


Ch 5 mac in wmns

IEEE 802.11e MAC protocol

Conventional wireless MAC protocols


Ch 5 mac in wmns

Protocols for mesh nodes equipped with directional antennas

Spatial reuse

New MAC

A different kind of hidden node problem, a deafness problem, and a higher directional interference

Advanced MAC protocols for WMNs


Ch 5 mac in wmns

Protocols for mesh nodes equipped with directional antennas

Directional MAC (D-MAC)

CTS is transmitted omnidirectionally to reduce the number of hidden nodes

Or RTS packets are sent omnidirectionally

Tone-based directional MAC (Tone MAC)

Use omnidirectional out-of-band tones to indicate deafness to blocked transmitter

After a DATA/ACK, send out tones to indicate that they were recently engaged in communication.

Directional virtual carrier sensing (DCVS)

Caching the angle of arrival, beam locking and unlocking, and use of directional NAV

Advanced MAC protocols for WMNs


Ch 5 mac in wmns

Protocols for mesh nodes equipped with directional antennas

Circular directional RTS

Inform the neighbors about the intended transmissions

Exploit the benefits of beam-forming

Advanced MAC protocols for WMNs


Ch 5 mac in wmns

Protocols for mesh nodes equipped with directional antennas

Advanced MAC protocols for WMNs


Ch 5 mac in wmns

Multichannel MAC protocols

Channel selection techniques

Handshake-based channel selection

Channel hopping

Cross-layer channel assignment

Common control channel or not

One transmitter and multiple receivers

One transceiver

Advanced MAC protocols for WMNs


Ch 5 mac in wmns

Multichannel MAC protocols

Handshake-based channel selection

Dynamic channel assignment (DCA)

One control channel and n euqivalent data channels

All nodes with a channel usage list (CUL) and a free channel list (FCL)

RTS with FCL, CTS with the channel to use and RES through control channel

Advanced MAC protocols for WMNs


Ch 5 mac in wmns

Multichannel MAC protocols

Handshake-based channel selection

Multichannel CSMA MAC

Similar to DCA

Multichannel MAC (MMAC)

Becon intervals

The first interval for channel negotiation and the second for data packets

Ad hoc traffic indication message (ATIM) window

Common control channel

Prefearable channel list (PCL)

All channel negotiation occur in ATIM windows over the common control channel.

RTS, CTS, ACK and data are all transmitted on the negotiated data channel.

Advanced MAC protocols for WMNs


Ch 5 mac in wmns

Multichannel MAC protocols

Handshake-based channel selection

Multichannel MAC (MMAC)

Stringent syncronized requirements

No broadcasting

the channel negotiation in on a per-packet basis -> high control overhead

Advanced MAC protocols for WMNs


Ch 5 mac in wmns

Multichannel MAC protocols

Channel hopping

Receiver-initiated channel-hop with dual polling (RICH-DP)

All nodes in a network follow a common channel-hopping sequence and each hop lasts just long enough for the nodes to receive a collision-avoidance control packet from a neighbor.

Slotted seeded channel hopping (SSCH)

No dedicated control channel and clock sysncronization among nodes

Advanced MAC protocols for WMNs


Ch 5 mac in wmns

Multichannel MAC protocols

Cross-layer channel assignment

Combing channel assignment with the routing protocol -> simple MAC

Seperation of channel assignments and MAC

One common control channel and multiple data channels

Nodes are assigned data channels by the routing protocol

All channel assignments are piggybacked onto routing protocol messages -> lower communication overhead

Advanced MAC protocols for WMNs


Ch 5 mac in wmns

Multichannel MAC protocols

Cross-layer channel assignment

RTS and CTS with data channel index

Advanced MAC protocols for WMNs


Ch 5 mac in wmns

Multichannel MAC protocols

Cross-layer channel assignment

Combining routing with intelligent channel assignment -> a factor of 6 to 7 throuput improvement compared to a conventional single-channel scheme

Advanced MAC protocols for WMNs


Ch 5 mac in wmns

Advanced MAC protocols for WMNs


Ch 5 mac in wmns

Contention-free MAC protocols for synchronized mesh networks

IEEE 802.16, WiMax

Point to multipoint and mesh network

TDMA

Connection oriented

Subscriber station (SS), connection ID (CID), base station (BS)

The MAC layer schedules the usage of the airlink resources and provide QoS differentiation

Advanced MAC protocols for WMNs


Ch 5 mac in wmns

Contention-free MAC protocols for synchronized mesh networks

Advanced MAC protocols for WMNs


Ch 5 mac in wmns

802.11e, 11i and 11k for one-hop wireless networks

Intramesh congestion control

End-to-end flow control at the transport layer?

Multimedia application over UDP

TCP congestion control does not work well across a multihop wireless network

Advanced MAC features proposed by the 802.11 TDs group


Ch 5 mac in wmns

Intramesh congestion control

Hop-by-hop congestion control mechanism that operates at the data link layer

Broadcast “neighborhood congestion announcement” and/or unicast “congestion control request”

Detecting congestion

Monitor effective MAC transmission and receiving rate for the packets to be forwarded

Monitor queue size

Advanced MAC features proposed by the 802.11 TDs group


Ch 5 mac in wmns

Common channel framework

Simultaneous transmissions on multiple channels

Request-to-switch (RTX) and clear-to-switch (CTX)

Advanced MAC features proposed by the 802.11 TDs group


Ch 5 mac in wmns

Mesh deterministic access

Better QoS

Contention-free time period: MDA opportunity (MDAOP)

Set up procedure for an MADOP set

Advanced MAC features proposed by the 802.11 TDs group


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