Ad Hoc Nets - MAC layer

Part II – TDMA and Polling

- Bluetooth

Bluetooth• Bluetooth Piconet: a polling/TDMA scheme• Bluetooth working group history

– February 1998: The Bluetooth SIG is formed– promoter company group: Ericsson, IBM, Intel,

Nokia, Toshiba– + 3Com, Lucent, Microsoft, Motorola

• Where does the name come from?– To honor a 10th century king Bluetooth in Denmark

who united that country and established Christianity

Personal Ad-hoc Networks

Cable Replacement

- Synchronization - Cordless Headset

Landline

Data/Voice Access Points

What does Bluetooth do for you?

…and combinations!

Example...

Bluetooth Physical link

• Point to point link– master - slave relationship– radios can function as

masters or slavesm s

ss

m

s

• Piconet– Master can connect to 7 slaves– Each piconet has max capacity =1 Mbps ~ 10 - 100 Meter– 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

Piconet formation

Master

Active Slave

Parked Slave-Connected-Not in Pico

Standby

• Page - scan protocol– to establish links with

nodes in proximity

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

Piconet MAC protocol : Polling

m

s1

s2

625 µ sec

f1 f2 f3 f4

1600 hops/sec

f5 f6FH/TDD

Multi slot packets

m

s1

s2

625 µsec

f1 f4 f5 f6

FH/TDD

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

m

s1

s2

SCO SCO SCOSCO SCO SCOACL ACL ACLACL ACL ACLSCO SCO SCO

Packet Types

Controlpackets

Data/voicepackets

ID*NullPollFHSDM1

Voice data

HV1HV2HV3DV

DM1DM3DM5

DH1DH3DH5

FHS – Frequency Hop SynchronizationDM – Data Medium rateHV – High quality VoiceDV – Data VoiceDH – Data High rate

Packet Format

72 bits 54 bits 0 - 2744 bitsAccess code

Header Payload

DataVoice CRC

No CRCNo retries

625 µs

master

slave

header

ARQ

FEC (optional) FEC (optional)

Packet Header

• Addressing (3)• Packet type (4)• Flow control (1)• 1-bit ARQ (1)• Sequencing (1)• HEC (8)

Access code Header Payload

54 bits

Purpose

Encode with 1/3 FEC to get 54 bits

Broadcast packets are not ACKed

For filtering retransmitted packets

18 bitstotal

ss

m

s

16 packet types (some unused)

Max 7 active slaves

Verify header integrity

Inter piconet communication

Cell phone Cordlessheadset

Cordless

headset

Cell phone

Cordlessheadset

Cell phone

mouse

Scatternet- Gateway node participates in more than one piconet

on a time-division basis

Scatternet, scenario 2

How to schedule presence in two piconets?

Forwarding delay ?

Missed traffic?

Baseband: Summary

• 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)

Baseband Baseband

L2CAPL2CAPLMPLMP

Physical

Data link

Device 2Device 1

Link Manager Protocol

Setup and management of Baseband connections

• Piconet Management• Link Configuration• Security

LMP

RF

Baseband

AudioLink Manager

L2CAP

Data Con

trol

SDP RFCOMM

IP

Applications

Piconet Management• Attach and detach slaves• Master-slave switch• Establishing SCO links• Handling of low power modes ( Sniff, Hold, Park)

req

response

Paging

Master

Slaves

s

m

s

L2CAP

L2CAP - Logical Link Control and Adaptation Protocol

L2CAP provides• Protocol multiplexing• Segmentation and Re-assembly• Quality of service negotiationRF

Baseband

AudioLink Manager

L2CAP

Data

SDP RFCOMM

IP

Applications

RFCOMM (Radio Frequency Communication)-- Serial Port Emulation using RFCOMM

Serial Port emulation on top of a packet oriented link• Similar to HDLC (High level Data Link Control protocol)

• RS232• For supporting legacy apps

RF

Baseband

AudioLink Manager

L2CAP

Data

SDP RFCOMM

IP

Applications

Serial Port

GOALS

IP over Bluetooth V 1.0

• Internet access using cell phones

• Connect PDA devices & laptop computers to the Internet via LAN access pointsRF

Baseband

AudioLink Manager

L2CAP

Data

SDP RFCOMM

IP

Applications

Inefficiency of layering

• Emulation of RS-232 over the Bluetooth radio link could be eliminated

L2CAP

RFCOMM

rfc 1662

PPP

IP

L2CAP

RFCOMM

rfc 1662

PPP

IP

Palmtop LAN access point

packet oriented

packet oriented

byte oriented

master

slave 1

slave 2

slave 3

masterslave 4 slave 5

Bluetooth

IPIP

Ethernet-like Ethernet-like broadcast broadcast segmentsegment

Bluetooth Networking: A Layer 2 Support

Where is BNEP in the Bluetooth Stack?

Bluetooth Radio

Baseband

LMP

L2CAP

Bluetooth Network Encapsulation Protocol

Host Controller Interface

RFCOMM

PPP

IP

TCP / UDP

SDP

Applications

BNEP

IP

TCP / UDP

Applications

The Bluetooth Network Encapsulation Protocol (BNEP)

Purpose? Create a Ethernet-likeEthernet-like broadcast environment for

IP in a Bluetooth Scatternet, hiding Bluetooth specifics (e.g. notion of piconet/scatternet forming and maintenance) from IP and above

Features:• Clear division between Bluetooth spec and IP • IP and IP networking applications will work as

usual (DHCP, ARP)• Easy to apply zeroconf protocols• across scatternets

– Ad-hoc L2 routing, handle loop-free broadcast

BNEP Overhead

• Type: 7 bit Bluetooth value identifies the type of BNEP header contained in this packet

• 1 bit extension flag that indicates if one or more extension headers follow the BNEP Header before the data payload.

• 1M of Data transfer– Additional ~0.2% Overhead– Additional Bluetooth Transmission time: 11

mSec

0 4 8 12 16 20 24 28 31

Extension Headeror BNEP Payload ...

BNEP Type =0x02

Networking Protocol TypeE

Bluetooth Personal Area Networks - Ad Hoc and extend to Mesh

• PANs extend the Internet to the user personal domain• 3G (2.5G) networks will give Internet access to PANs• PANs will generate more traffic than a single device• Utilize an aggregate of access networks (WLAN, 3G, DSL)

IP Bluetooth Networking - Conclusions

Bluetooth IP networking opens up new possibilities ---- Mesh networks

• Enables spontaneous Ad Hoc networking – Between people,– Between machines,

• Mainly small, short range ad-hoc networks– Solves your “personal problems”...– Limited complexity and security risks

• The enabler for PANs! – Gives a natural extension of Internet into the PAN

via 3G– Enables stepwise upgrading of devices -- not tied to

one multimedia terminal!– Makes use of the 3G bandwidth immediately

• QoS ~ Bluetooth ?