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IEEE Oregon Section Bluetooth Seminar – April 27, 2001 1
Introduction to Bluetooth™ Introduction to Bluetooth™ Wireless TechnologyWireless Technology
Jon InouyeJon InouyeStaff Software EngineerStaff Software Engineer
Mobile Platforms GroupMobile Platforms Group
Intel CorporationIntel Corporation
Bluetooth is a trademark owned by Bluetooth SIG Inc. USABluetooth is a trademark owned by Bluetooth SIG Inc. USA
IEEE Oregon Section Bluetooth Seminar – April 27, 2001 2
Radio TechnologyRadio Technology
ll CellularCellular–– Licensed spectrumLicensed spectrum–– Voice drivenVoice driven–– Data services emergingData services emerging–– E.g., 3G, GPRS, WAP*E.g., 3G, GPRS, WAP*
ll Wireless LANWireless LAN–– Proliferation occurringProliferation occurring–– E.g., IEEE 802.11bE.g., IEEE 802.11b
ll Wireless PANWireless PAN–– Relative newcomerRelative newcomer–– E.g., Bluetooth*, 802.15E.g., Bluetooth*, 802.15
text
text
WPAN10 m
WLAN100 m
WWANKm
*Third-party marks and brands are the property of their respective owners.
IEEE Oregon Section Bluetooth Seminar – April 27, 2001 3
WHAT IS BLUETOOTH?WHAT IS BLUETOOTH?
ll a hardware descriptiona hardware description
ll an application frameworkan application framework
RFBaseband
AudioLink ManagerL2CAP
TCP/IP HID RFCOMM
Applications
Data
Cont
rol
IEEE Oregon Section Bluetooth Seminar – April 27, 2001 4
l Radiol Basebandl Connection Managementl Channel Operationl Piconet Management
l Software Stackl Profiles
OUTLINE
IEEE Oregon Section Bluetooth Seminar – April 27, 2001 5
RADIO
IEEE Oregon Section Bluetooth Seminar – April 27, 2001 6
l Frequency hoppingl ISM band at 2.45 GHz l 2402 + k MHz, k = 0, …, 78
l device-specific hopping sequence
l nominal rate 1600 hops/s
l Modulationl binary FSK
l Gaussian shapingl BT = 0.5; 0.28 < h < 0.35
l -20dB bandwidth of 1 MHz
RADIO PARAMETERS (1)
IEEE Oregon Section Bluetooth Seminar – April 27, 2001 7
l Transmit powerl nominal 0 dBm
l up to 20 dBm provided power control
l Receiver sensitivityl -70 dBm @ 0.1% BER
RADIO PARAMETERS (2)
IEEE Oregon Section Bluetooth Seminar – April 27, 2001 8
BASEBAND OPERATIONS
DISCOVERYAND
CONNECTION ESTABLISHMENT
IEEE Oregon Section Bluetooth Seminar – April 27, 2001 9
INQUIRY
l Radio wanting to discover other radiosl Repetitively probe first set of 16 frequenciesl Probes two frequencies every 625 microsecondsl Repeat at least 256 timesl Repetitively probe second set of 16 frequenciesl Repeat entire cycle at least two times
l Radio wanting to be discoveredl Listen to one of 32 frequencies for at least 11.25 msl Sleep no longer than 2.56 secondslWake up and listen to another frequencyl Repeat cycle
IEEE Oregon Section Bluetooth Seminar – April 27, 2001 10
A
INQUIRY OPERATION
IEEE Oregon Section Bluetooth Seminar – April 27, 2001 11
CREATING A PICONET
A
B
page
IEEE Oregon Section Bluetooth Seminar – April 27, 2001 12
CREATING A PICONET
slave B
master A
connected
IEEE Oregon Section Bluetooth Seminar – April 27, 2001 13
slave B
master A
slave Cslave D
CREATING A PICONET
IEEE Oregon Section Bluetooth Seminar – April 27, 2001 14
active slave
master
parked slave
standby
OPERATIONAL STATES
IEEE Oregon Section Bluetooth Seminar – April 27, 2001 15
l Bluetooth Device Address (BD_ADDR)l 48-bit IEEE 802 addressl 24-bit lower address part (LAP)l 8-bit upper address part (UAP)
l Active Member Address (AM_ADDR) l 3-bit active slave addressl all-zero broadcast address
l Parked Member Address (PM_ADDR)l 8-bit parked slave address
ADDRESSING
IEEE Oregon Section Bluetooth Seminar – April 27, 2001 16
BASEBAND OPERATIONS
PICONET CHANNEL
IEEE Oregon Section Bluetooth Seminar – April 27, 2001 17
625 µs
t
t
master
slave
f(2k) f(2k+1) f(2k+2)
FH/TDD CHANNEL
IEEE Oregon Section Bluetooth Seminar – April 27, 2001 18
2.402 2.480freq
timeslave
master
FREQUENCY HOPPING
IEEE Oregon Section Bluetooth Seminar – April 27, 2001 19
lmaster BD_ADDR → hop sequence
lmaster CLOCK → phase
master
slave 2
slave 1
slave 4slave 3
PHYSICAL CHANNEL
IEEE Oregon Section Bluetooth Seminar – April 27, 2001 20
NATIVE CLK HOP
MASTER BD_ADDR
sequence
phase
offset
HOP SELECTION
IEEE Oregon Section Bluetooth Seminar – April 27, 2001 21
access code packet header payload
72b 54b 0-2745b
PACKET FORMAT
IEEE Oregon Section Bluetooth Seminar – April 27, 2001 22
PREAMBLE SYNC WORD TRAILER
4 64 4
34 24 6
LSB MSB
PRT LAP BRK
ACCESS CODE
IEEE Oregon Section Bluetooth Seminar – April 27, 2001 23
ACCESS CODE TYPESACCESS CODE TYPES
ll Device access code (DAC)Device access code (DAC)ll unit identifierunit identifierll derived from unit LAPderived from unit LAP
ll Channel access code (CAC)Channel access code (CAC)ll channel identifierchannel identifierll derived from master LAPderived from master LAP
ll Inquiry access code (IAC)Inquiry access code (IAC)ll reserved identifierreserved identifierll derived from reserved addressderived from reserved address
IEEE Oregon Section Bluetooth Seminar – April 27, 2001 24
AM_ADDR HEC
3 1 8
AM_ADDR
TYPE
FLOW
ARQN
slave active member address
payload type
LC flow control
ACK/NAK
parameter information
FLOW
1
ARQN
1
SEQNTYPE
4
SEQN retransmit ordering
HEC header error check
PACKET HEADER
IEEE Oregon Section Bluetooth Seminar – April 27, 2001 25
Purpose: MULTI-MEDIA SUPPORT
Mixing:
PHYSICAL LINK DEFINITION
l circuit switchingl packet switching
IEEE Oregon Section Bluetooth Seminar – April 27, 2001 26
l Synchronous Connection-Oriented (SCO) Linkl circuit switchingl symmetric, synchronous servicesl slot reservation at fixed intervals
l Asynchronous Connection-Less (ACL) Link
l packet switchingl (a)symmetric, asynchronous servicesl polling access scheme
PHYSICAL LINK TYPES
IEEE Oregon Section Bluetooth Seminar – April 27, 2001 27
MASTER
SLAVE 1
SLAVE 2
SLAVE 3
ACLSCO SCO SCO SCOACLACL ACL
MIXED LINK EXAMPLE
IEEE Oregon Section Bluetooth Seminar – April 27, 2001 28
0000000100100011
NULLPOLLFHSDM1
NULLPOLLFHSDM1
1
0100010101100111
HV1HV2HV3
DH1
2
DV10001001101010111100
DM3DH33
110111101111
DM5DH54
typesegment ACL linkSCO link
AUX1
PACKET TYPES
IEEE Oregon Section Bluetooth Seminar – April 27, 2001 29
f(k)
625 µs
f(k+1) f(k+2) f(k+3) f(k+4)
f(k+3) f(k+4)f(k)
f(k)
f(k+5)
f(k+5)
f(k+5)
MULTI-SLOT PACKETS
IEEE Oregon Section Bluetooth Seminar – April 27, 2001 30
DM1
DH1
DM3
DH3
DM5
DH5
108.8
172.8
258.1
390.4
286.7
433.9
108.8
172.8
387.2
585.6
477.8
723.2
108.8
172.8
54.4
86.4
36.3
57.6
type symmetric asymmetric
DATA RATES (kb/s)
IEEE Oregon Section Bluetooth Seminar – April 27, 2001 31
l ID packet
l NULL packet
l POLL packet
l FHS packet
LINK CONTROL PACKETS
IEEE Oregon Section Bluetooth Seminar – April 27, 2001 32
l BD_ADDR
l DAC
l AM_ADDR
l class of device
l paging class
l real-time clock
FHS PACKET
IEEE Oregon Section Bluetooth Seminar – April 27, 2001 33
l Forward-Error Correction (FEC)l 1/3 rate: bit-repeat codel 2/3 rate: (15,10) shortened Hamming code
l Automatic Retransmission Query (ARQ)l 1-bit fast ACK/NAKl 1-bit sequence numberl header piggy-backing
ERROR CORRECTION
IEEE Oregon Section Bluetooth Seminar – April 27, 2001 34
MASTER
SLAVE 1
SLAVE 2
A B B CX
Z Z
G F H
NAK ACK
ARQ OPERATION
IEEE Oregon Section Bluetooth Seminar – April 27, 2001 35
1 1 0 0 0 0 0 0 1 0 1 1 1 1 1 0 1 0 0 0 0 1 1 1 0 0 0 1 0 1 0 1 0 . . . . . . .
CVSD WAVEFORM CODING
IEEE Oregon Section Bluetooth Seminar – April 27, 2001 36
BASEBAND OPERATIONS
PICONET MANAGEMENT
IEEE Oregon Section Bluetooth Seminar – April 27, 2001 37
OPERATIONAL STATES
l stand-by, scan
l page, inquiry
l connectionl activel holdl sniffl park
IEEE Oregon Section Bluetooth Seminar – April 27, 2001 38
SIMPLIFIED STATE MACHINE
ll StandbyStandby–– Waiting to join a piconetWaiting to join a piconet
ll InquireInquire–– Discover radiosDiscover radios
ll PagePage–– Connect to a specific radioConnect to a specific radio
ll ConnectedConnected–– Active on a Active on a piconetpiconet
ll Park/Hold/SniffPark/Hold/Sniff–– Low Power connected statesLow Power connected states
Inquiry Page
ConnectedAMA
TransmitdataAMA
Ttypical=0.6s
Ttypical=10.25s
HOLDAMA
PARKPMA
Ttypical=2 ms Ttypical=2 ms
ReleasesAMA
AddressLow Power
States
ActiveStates
Standby
ConnectingStates
UnconnectedStandby
Deta
ch
SNIFF
IEEE Oregon Section Bluetooth Seminar – April 27, 2001 39
MASTER
SLAVE 1
SLAVE 2
ACL
LOST
HOLD MODE
ACL
HOLD INTERVAL
ACL ACL ACL ACL ACL
IEEE Oregon Section Bluetooth Seminar – April 27, 2001 40
MASTER
SLAVE 1
SLAVE 2
ACL ACL ACL
LOST
SNIFF MODE
SNIFF INTERVAL
IEEE Oregon Section Bluetooth Seminar – April 27, 2001 41
active slave
parked slaves
l BEACON
l PM_ADDR
PARK MODE
master
IEEE Oregon Section Bluetooth Seminar – April 27, 2001 42
MASTER
SLAVE X
SLAVE 2
ACL
PARK INTERVAL
SLAVE Y
BC BCACL
PARK MODE
IEEE Oregon Section Bluetooth Seminar – April 27, 2001 43
slave 1
slave 2
slave 3
slave 4 / master B
slave 6
slave 5
SCATTERNET
master A
IEEE Oregon Section Bluetooth Seminar – April 27, 2001 44
BASEBAND OPERATIONS
SECURITY
IEEE Oregon Section Bluetooth Seminar – April 27, 2001 45
SECURITY COMPONENTS
l Authentication
l Payload encryption
l Key handling
IEEE Oregon Section Bluetooth Seminar – April 27, 2001 46
AUTHENTICATIONAUTHENTICATION
ll To verify claimed identityTo verify claimed identity
ll ChallengeChallenge--response systemresponse system
ll Algorithm Algorithm EE11::ll Input: RAND (128 bit), Claimant Input: RAND (128 bit), Claimant addraddr. (48 bit), . (48 bit),
link key (128)link key (128)ll Output:Output: SRESSRES (32 bit), (32 bit), ACOACO (96 bit)(96 bit)
ll OneOne--sided or mutual authenticationsided or mutual authentication
ACO = Authenticated Ciphering Offset
IEEE Oregon Section Bluetooth Seminar – April 27, 2001 47
ENCRYPTIONENCRYPTION
ll To prevent (un)intentional eavesdroppingTo prevent (un)intentional eavesdropping
ll Stream cipheringStream ciphering
ll Algorithm Algorithm EE00::ll Input: RAND (128 bit), master Input: RAND (128 bit), master addraddr./clock,./clock,
KKcc (128 bit)(128 bit)ll Output: cipher streamOutput: cipher stream
ll LFSR restart for every slotLFSR restart for every slot
ll Encryption of payload onlyEncryption of payload only
ll PointPoint--toto--point or pointpoint or point--toto--multipointmultipoint
IEEE Oregon Section Bluetooth Seminar – April 27, 2001 48
KEY TYPESKEY TYPES
Link keysLink keys
InitializationKey
InitializationKey
TemporaryTemporary
MasterKey
MasterKey
Semi-permanentSemi-permanent
UnitKey
UnitKey
CombinationKey
CombinationKey
Encryption keyEncryption key
IEEE Oregon Section Bluetooth Seminar – April 27, 2001 49
RADIO/BB SUMMARYRADIO/BB SUMMARY
l Frequency hopping radio at 2.4 GHz
l Intrinsic support for voice and data
l Maximum 723 Kbps MAC throughput
l Low power modes
l Point-to-multipoint configuration
l Support of basic security mechanisms
IEEE Oregon Section Bluetooth Seminar – April 27, 2001 50
SOFTWARE STACK
IEEE Oregon Section Bluetooth Seminar – April 27, 2001 51
OutlineOutlinell Software scope and goalsSoftware scope and goalsll Protocol ReviewProtocol Reviewll Profile ReviewProfile Reviewll SummarySummary
IEEE Oregon Section Bluetooth Seminar – April 27, 2001 52
Software ArchitectureSoftware Architecture
RF
Baseband
AudioLink Manager
LMPLMPL2CAP
TCS SDP RFCOMM
Applications
Data
Cont
rol Cover This
IEEE Oregon Section Bluetooth Seminar – April 27, 2001 53
Software Architecture GoalsSoftware Architecture Goalsll Support the target usage modelsSupport the target usage modelsll Support a variety of hardware platformsSupport a variety of hardware platformsll Protocol reuseProtocol reuse
–– Avoid duplicating existing technologyAvoid duplicating existing technology–– Promote better harmonization across technologiesPromote better harmonization across technologies
ll Good “out of box” user experienceGood “out of box” user experience–– InteroperabilityInteroperability
IEEE Oregon Section Bluetooth Seminar – April 27, 2001 54
OutlineOutlinell Software goalsSoftware goalsll Protocol ReviewProtocol Reviewll Profile ReviewProfile Reviewll SummarySummary
IEEE Oregon Section Bluetooth Seminar – April 27, 2001 55
Bluetooth Protocol StackBluetooth Protocol Stack
*Third-party marks and brands are the property of their respective owners.
L2CAP
OBEX*WAP* Printing
Host Controller Interface
Still Image
TCP/UDP RFCOMM
TCS
HID
IPService Discovery
AudiovCard/vCal*WAE
IEEE Oregon Section Bluetooth Seminar – April 27, 2001 56
HCI
Bluetooth Host
Bluetooth Module
HCI Transport Firmware
Host Drives and Applications
Bluetooth HCI Transport driver (USB*, PC Card*, PCI*)
Transport Bus
Bluetooth HCI driver
Bluetooth Host Controller
Link Manager
Bluetooth Radio
Bluetooth Baseband
HCIHCIll Host Controller Host Controller
Interface (HCI) Interface (HCI) provides a common provides a common interface between interface between the Bluetooth Host the Bluetooth Host and the Bluetooth and the Bluetooth ModuleModule
*Third-party marks and brands are the property of their respective owners.
IEEE Oregon Section Bluetooth Seminar – April 27, 2001 57
Link Layer Control and Link Layer Control and Adaptation ProtocolAdaptation Protocolll Also known as L2CAPAlso known as L2CAPll Basic data link layer protocol over BasebandBasic data link layer protocol over Basebandll Support for:Support for:
–– Protocol MultiplexingProtocol Multiplexing–– Segmentation and Reassembly (SAR)Segmentation and Reassembly (SAR)–– Quality of ServiceQuality of Service–– GroupsGroups
IEEE Oregon Section Bluetooth Seminar – April 27, 2001 58
L2CAP ArchitectureL2CAP Architecturell ConnectionConnection--orientedoriented
–– Channel identifier (CID) used to label each connection Channel identifier (CID) used to label each connection endpointendpoint
–– Channels may be uniChannels may be uni--directional or bidirectional or bi--directionaldirectional–– QoS flow specification assigned to each channel directionQoS flow specification assigned to each channel direction
ll ConnectionlessConnectionless–– Supports group abstractionSupports group abstraction
IEEE Oregon Section Bluetooth Seminar – April 27, 2001 59
L2CAP ChannelsL2CAP Channels
Device #2
L2CAPCID
L2CAP
CID
CID
CID
CID
Device #4
L2CAPCID
Device #3
L2CAPCID
Device #1
L2CAP CID
CID
Connection-Oriented Data Channel
Connectionless Data Channel
L2CAP Signalling Channel
IEEE Oregon Section Bluetooth Seminar – April 27, 2001 60
Service Discovery ProtocolService Discovery Protocolll Bluetooth SDP enables Bluetooth devices to Bluetooth SDP enables Bluetooth devices to
discover the characteristics and capabilities of discover the characteristics and capabilities of other Bluetooth devices within RF proximityother Bluetooth devices within RF proximity
ll Within Bluetooth SDP, a service is:Within Bluetooth SDP, a service is:–– any information, resource, or facility that is provided by (or any information, resource, or facility that is provided by (or
through) one Bluetooth device that is advertised as through) one Bluetooth device that is advertised as available to nearby Bluetooth devicesavailable to nearby Bluetooth devices
ll Bluetooth SDP does not provide a general Bluetooth SDP does not provide a general purpose service access/usage mechanism; SDP purpose service access/usage mechanism; SDP only enables discovery of servicesonly enables discovery of services
IEEE Oregon Section Bluetooth Seminar – April 27, 2001 61
Service DiscoveryService Discoveryll Two partsTwo parts
–– Service record formatService record format– Information about service provided by attributes– Attributes composed of an ID and a value– Ids may be universally unique identifiers (UUID)
–– Session protocol for enabling discoverySession protocol for enabling discovery– Searching for and browsing services
IEEE Oregon Section Bluetooth Seminar – April 27, 2001 62
Typical SDP Client/Server Typical SDP Client/Server InteractionsInteractions
Client Server
ServiceSearchRequest(SearchPattern)
ServiceSearchResponse(ServiceRecordHandleList)
ServiceAttributeResponse(AttributeList)
ServiceAttributeRequest(ServiceRecordHandle, AttributeIDList)
IEEE Oregon Section Bluetooth Seminar – April 27, 2001 63
SDP ScopeSDP Scopell Many Service Discovery ProtocolsMany Service Discovery Protocols
–– Service Location Protocol (SLP), Jini*, Universal Plug and Service Location Protocol (SLP), Jini*, Universal Plug and Play (UPnP*), etc.Play (UPnP*), etc.
ll Bluetooth SDP focuses on service discovery Bluetooth SDP focuses on service discovery within Bluetooth environmentwithin Bluetooth environment
ll SDP does not compete with other technologies.SDP does not compete with other technologies.
ll SDP compliments them by enabling their use in SDP compliments them by enabling their use in Bluetooth environmentsBluetooth environments
*Third-party marks and brands are the property of their respective owners.
IEEE Oregon Section Bluetooth Seminar – April 27, 2001 64
RFCOMMRFCOMMll Supports a large base of legacy applications Supports a large base of legacy applications
using the serial port as the primary using the serial port as the primary communications mechanism.communications mechanism.
ll Reuse GSM TS 07.10 as an existing standard for Reuse GSM TS 07.10 as an existing standard for multiplexing a single physical channel and V.24 multiplexing a single physical channel and V.24 emulation.emulation.
ll Designed to allow multiple “ports” over a single Designed to allow multiple “ports” over a single physical channel between a PC and a GSM physical channel between a PC and a GSM handsethandset
IEEE Oregon Section Bluetooth Seminar – April 27, 2001 65
TCS ProtocolTCS Protocol
ll Telephony Control Protocol SpecificationTelephony Control Protocol Specification
Group managementGateway may serve more cordless devicesDistributes group information
Call ControlCall setup and releaseSymmetrical derivative of Q.931
IEEE Oregon Section Bluetooth Seminar – April 27, 2001 66
TCS ImpactTCS Impactll Cordless Telephony ExampleCordless Telephony Example
–– Phone moves into range of voice access point and Phone moves into range of voice access point and establishes linkestablishes link
–– Phone link placed into a low power statePhone link placed into a low power state–– Incoming call is broadcast to all phonesIncoming call is broadcast to all phones–– On answer, a voice (SCO) link is setupOn answer, a voice (SCO) link is setup
ll IntercomIntercom–– Supports direct phoneSupports direct phone--toto--phone communicationphone communication
IEEE Oregon Section Bluetooth Seminar – April 27, 2001 67
Reuse and RecycleReuse and Recyclell Desire to reuse Desire to reuse IrDAIrDA* applications on mobile * applications on mobile
phones and PCsphones and PCs–– Decision to merge with IrDA’s OBEX (Object Exchange) Decision to merge with IrDA’s OBEX (Object Exchange)
protocol on top of RFCOMM or TCP.protocol on top of RFCOMM or TCP.–– Enables harmonized API across PAN technologiesEnables harmonized API across PAN technologies
ll Interaction with applications on phonesInteraction with applications on phones–– Handset manufacturers have agreed on an application Handset manufacturers have agreed on an application
framework called WAP*.framework called WAP*.–– Bluetooth is treated as a WAP “bearer” in a manner similar Bluetooth is treated as a WAP “bearer” in a manner similar
to GSM.to GSM.–– Reuse “browser” interface on mobile phone.Reuse “browser” interface on mobile phone.
*Third-party marks and brands are the property of their respective owners.
IEEE Oregon Section Bluetooth Seminar – April 27, 2001 68
OutlineOutlinell Software goalsSoftware goalsll Protocol ReviewProtocol Reviewll Profile ReviewProfile Reviewll SummarySummary
IEEE Oregon Section Bluetooth Seminar – April 27, 2001 69
Interoperability and ProfilesInteroperability and Profilesll Protocols define the communication language Protocols define the communication language
spoken between devicesspoken between devices
ll How do you avoid the “Tower of Babel” problem?How do you avoid the “Tower of Babel” problem?
ll Solution: Mandate the language spoken for a Solution: Mandate the language spoken for a given usage modelgiven usage model
IEEE Oregon Section Bluetooth Seminar – April 27, 2001 70
ProfilesProfilesll Represents the default solution for a specific Represents the default solution for a specific
usage modelusage modelll “Vertical slice” through the protocol stack“Vertical slice” through the protocol stackll Basis for interoperability and logo requirementsBasis for interoperability and logo requirementsll Each Bluetooth device supports one or more Each Bluetooth device supports one or more
profilesprofiles
IEEE Oregon Section Bluetooth Seminar – April 27, 2001 71
Profiles
Pro
toco
ls
Applications
Protocols and ProfilesProtocols and Profiles
RelationshipbetweenProtocolsand Profiles
IEEE Oregon Section Bluetooth Seminar – April 27, 2001 72
Profiles in the Bluetooth Profiles in the Bluetooth Specification 1.1Specification 1.1
Generic Access Profile
Service DiscoveryApplication Profile
TCS-BIN-based Profiles
Cordless PhoneProfile
Intercom Profile
Serial Port Profile
Dial-up NetworkingProfile
Fax Profile
Generic Object ExchangeProfile
Headset Profile
LAN Access Profile
File TransferProfile
Object Push Profile
SynchronizationProfile
IEEE Oregon Section Bluetooth Seminar – April 27, 2001 73
RFCOMM
Example: Dialup Networking Example: Dialup Networking ProfileProfile
ACL SCOBluetooth Baseband
LMP
L2CAP
AT Commands
PPP
IEEE Oregon Section Bluetooth Seminar – April 27, 2001 74
Software SummarySoftware Summary
ll Protocols defined for communicationProtocols defined for communication
ll Profiles defined to promote interoperabilityProfiles defined to promote interoperability
ll Existing protocols used where possibleExisting protocols used where possible