Ad Hoc Nets - MAC layer Part II – TDMA and Polling
More MAC Layer protocols • Bluetooth Piconet: a polling/TDMA scheme • Cluster TDMA: based on TDMA (with random access and reserved slots) – research protocol developed at UCLA for the DARPA-WAMIS project (1994)
Bluetooth: Where does the name come from?
Bluetooth working group history • February 1998: The Bluetooth SIG is formed – promoter company group: Ericsson, IBM, Intel, Nokia, Toshiba • May 1998: Public announcement of the Bluetooth SIG • July 1999: 1.0A spec (>1,500 pages) is published • December 1999: ver. 1.0B is released • December 1999: The promoter group increases to 9 – 3Com, Lucent, Microsoft, Motorola • March 2001: ver. 1.1 is released • Aug 2001: There are 2,491+ adopter companies
What does Bluetooth do for you? Synchronization • Automatic synchronization of calendars, address books, business cards • Push button synchronization • Proximity operation
Cordless Headset Cordless headset User benefits • Multiple device access • Cordless phone benefits • Hands free operation
Putting it all together.. Landline Cable Replacement Data/Voice Access Points …and combinations! Personal Ad-hoc Networks
Example...
Bluetooth Physical link • Point to point link – master - slave relationship m s – radios can function as masters or slaves m • Piconet – Master can connect to 7 slaves s s – Each piconet has max capacity =1 Mbps s – hopping pattern is determined by the master
Connection Setup • Inquiry - scan protocol – to learn about the clock offset and device address of other nodes in proximity
Inquiry on time axis f1 f2 Slave1 Inquiry hopping sequence Master Slave2
Piconet formation • Page - scan protocol Master – to establish links with nodes in proximity Active Slave Parked Slave Standby
Addressing • Bluetooth device address (BD_ADDR) – 48 bit IEEE MAC address • Active Member address (AM_ADDR) – 3 bits active slave address – all zero broadcast address • Parked Member address (PM_ADDR) – 8 bit parked slave address
Bluetooth Piconet • Page - scan protocol Master – to establish links with nodes in proximity Active Slave Parked Slave Standby
Piconet MAC protocol : Polling FH/TDD f1 f2 f3 f4 f5 f6 m s 1 s 2 625 λ sec 1600 hops/sec
Multi slot packets FH/TDD f1 f4 f5 f6 m s 1 s 2 625 µsec Data rate depends on type of packet
Physical Link Types � Synchronous Connection Oriented (SCO) Link � slot reservation at fixed intervals • Asynchronous Connection-less (ACL) Link – Polling access method ACL SCO SCO ACL ACL ACL SCO SCO ACL SCO SCO ACL m s 1 s 2
Packet Types Data/voice Control packets packets Voice data ID* HV1 DH1 Null DM1 HV2 DH3 Poll DM3 HV3 FHS DH5 DM5 DV DM1
Packet Format 54 bits 72 bits 0 - 2744 bits Access Header Payload code header Data Voice CRC No CRC ARQ No retries FEC (optional) FEC (optional) 625 µs master slave
Access Code 72 bits Access Payload Header code Types Purpose � Channel Access Code (CAC) • Synchronization � Device Access Code (DAC) • DC offset � Inquiry Access Code (IAC) compensation • Identification • Signaling X
Packet Header 54 bits m Access Payload Header code s s s Purpose Max 7 active slaves • Addressing (3) 16 packet types (some unused) • Packet type (4) • Flow control (1) Broadcast packets are not ACKed • 1-bit ARQ (1) For filtering retransmitted packets • Sequencing (1) Verify header integrity • HEC (8) total 18 bits Encode with 1/3 FEC to get 54 bits
Voice Packets (HV1, HV2, HV3) 72 bits 54 bits 240 bits = 366 bits Access Header 30 bytes code Payload HV1 10 bytes + 1/3 FEC 20 bytes HV2 + 2/3 FEC HV3 30 bytes 3.75ms (HV3) 2.5ms (HV2) 1.25ms ( HV1 )
Data rate calculation: DM1 and DH1 625 µs 72 bits 54 bits 240 bits = 366 bits Access 30 bytes Header code Di Size Freq Rate Payload r ↑ 17 1600/2 108.8 2/3 ↓ DM1 17 108.8 1 17 2 FEC ↑ 27 172.8 DH1 2 1 27 ↓ 27 172.8 625 µs 1 2
Data rate calculation: DM3 and DH3 1875 µs 72 54 = 1626 bits 1500 bits bits bits Access 187 bytes Header code Di Size Freq Rate Payload r ↑ 121 1600/4 387.2 2/3 ↓ DM3 2 121 17 54.4 2 FEC ↑ 183 585.6 DH3 2 183 2 ↓ 27 86.4 1875 µs 1 2 3 4
Data rate calculation: DM5 and DH5 3125 µs 72 54 = 2870 bits 2744 bits bits bits Access 343 bytes Code Header Di Size Freq Rate Payload r ↑ 224 1600/6 477.8 2/3 ↓ DM5 2 224 17 36.3 2 FEC ↑ 339 723.2 DH5 2 339 2 ↓ 27 57.6 625 µs 3125 µs 1 2 3 4 5 6
Data Packet Types Asymmetric Symmetric DM1 108.8 108.8 108.8 258.1 387.2 54.4 DM3 2/3 FEC 286.7 477.8 36.3 DM5 Asymmetric Symmetric 172.8 172.8 172.8 No FEC DH1 390.4 585.6 86.4 DH3 433.9 723.2 57.6 DH5
Inter piconet communication Cordless headset mouse Cordless headset Cell phone Cell phone Cell phone Cordless headset
Scatternet
Scatternet, scenario 2 How to schedule presence in two piconets? Forwarding delay ? Missed traffic?
Baseband: Summary Device 1 Device 2 L2CAP L2CAP Data link LMP LMP Baseband Baseband Physical • TDD, frequency hopping physical layer • Device inquiry and paging • Two types of links: SCO and ACL links • Multiple packet types (multiple data rates with and without FEC)
Link Manager Protocol Applications IP SDP RFCOMM Control Data Setup and management of Baseband connections L2CAP Audio Link Manager LMP • Piconet Management Baseband • Link Configuration RF • Security
Piconet Management • Attach and detach slaves • Master-slave switch • Establishing SCO links • Handling of low power modes ( Sniff, Hold, Park) Paging m s s Master s req Slave response
Low power mode (hold) Hold offset Slave Hold duration Master
Low power mode (Sniff) Sniff offset Sniff duration Slave Sniff period Master • Traffic reduced to periodic sniff slots
Low power mode (Park) Slave Beacon instant Master Beacon interval • Power saving + keep more than 7 slaves in a piconet • Give up active member address, yet maintain synchronization • Communication via broadcast LMP messages
Cluster Network Architecture (UCLA-WAMIS) • Concept create a cluster based TDM infrastructure which: (a) enables guaranteed bandwidth for voice/video (b) can support mobility • Approach – distributed clustering algorithm – time division slotting within each cluster – slot reservation for real time traffic – virtual circuits for real traffic; datagrams for data – code separation across clusters – slot synchronization • Combines cellular radio and traditional packet radio features.
Lowest-ID cluster-head election 5 2 10 8 1 6 9 3 4 7
Distributed Cluster algorithm (lowest-ID) B A G H C • Each node is assigned a distinct ID. • Periodically, the node broadcast the list of nodes that it can hear. – “ClusterHead” hears only nodes with ID higher that itself (unless lower ID specifically gives up its role as CH) → A,B,C “Gateway” hears two or more CHs → G,H – “Ordinary” node otherwise → – • Properties – No cluster heads are directly linked. – In a cluster, any two nodes are at most two-hops away, since the CH is directly linked to any other node in the cluster. RE: Emphremides, et al “A Design Concept for Reliable Mobile Radio Networks with Frequency Hopping Signaling” Proceedings of IEEE, Vol. 75, No.1, 1987
Cluster network architecture • Dynamic, distributed clustering alg. partitions the system into clusters. • Code separation among clusters. • Local coordination provided within a cluster. • Clusterhead acts as local coordinator to – resolve channel scheduling – provide power measurement/control – support virtual circuit setup for real time (voice and video) traffic – maintain synchronization • Dynamic adaptation (via periodic updates) – mobility – failures – Interference – bandwidth requirements (B/W alloc.--TDMA slot assgn.)
Channel Access Within each cluster: time-slotted frame frame ….. data phase control phase fixed TDMA on common code at full power • Control Phase: • Data Phase: – clustering algorithm – voice/video (PRMA) – routing – data (Random Access) – power measurement and control – code and slot assignment – VC setup – acknowledgments
Virtual Circuit support in WAMIS Multimedia Traffic (eg, voice, video): • connection oriented; • QoS based admission control • VC based bandwidth allocation We need: • robust, QoS enabled routing • “elastic”, reconfigurable VCs
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