Bluetooth Simulation

Introduction:

Bluetooth was originally conceived to replace the rat’s nest of cables typical in any PC setup today and this remains a compelling home application.

However, as the Bluetooth evolved it became clear that it would also enable a totally new networking paradigm, Personal Area Networks (PANs)! With PAN technology a user will be able to organize a collection of personal electronic products (their PDA, cell phone, laptop, desktop, MP3 player, etc. ) to automatically work together. For instance the contact manager and calendar in the PDA, laptop, and desktop could all automatically synchronize whenever they are within range of each other). Over time PANs will revolutionize the user experience of consumer electronics.

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Finally, Bluetooth’s dynamic nature will also revolutionize connectivity to the rest of the world. Bluetooth will automatically discover devices and services nearby so available servers, internet access, printers etc. will automatically become visible to a Bluetooth device wherever it is.

History:

Bluetooth is an open specification for short range wireless voice and data communications that was originally developed for cable replacement in personal area networking to operate all over the world.

By enabling standardized wireless communication between any electrical devices, Bluetooth has created the notion of a personal Area Network (PAN), a kind of close range wireless network that looks set to revolutionize the way people interact with the information technology landscape around them. In 1994 the initial study for development of this technology started at Ericsson, Sweden. In 1998, Ericsson, Nokia, IBM, Toshiba, and Intel formed a Special Interest Group (SIG) to expand the concept and develop a standard under IEEE 802. 15 WPAN (Wireless Personal Area Network ).

In 1999, the first specification was released and accepted as the IEEE 802. 15 WPAN standard for 1Mbps networks. The Bluetooth SIG considers three basic scenarios: The first basic scenario is the Cable Replacement ie. the wire replacement to connect a PC or laptop to its keyboard, mouse, microphone, and notepad. It avoids the multiple short range wiring surroundings of today’s personal computing devices. The second scenario is ad hoc networking of several different users at very short range in an area such as a conference room. The third scenario is to use Bluetooth as an AP to the wide area voice and data services provided by the cellular networks, wired connections or satellite links. Why the name Bluetooth? The story of origin of name Bluetooth is interesting. ”Bnluetooth” was the nickname of Harald Blaatand, 10th century Viking who united Denmark and Norway. When Bluetooth specification was introduced to public, a stone carving, erected from Harald Blaatand’s capital city Jelling was also presented. This strange carving was interpreted as Bluetooth connecting a cellular phone and a wireless notepad in his hands.

The picture was used to symbolize the vision in using Bluetooth to connect personal computing and communication devices.

What is BLUETOOTH?

All commands from the host to the Bluetooth module and events from the module to the host go through the HCI interface. The protocol stack is above the radio and baseband hardware, partly residing in the Bluetooth unit and partly in the host device. A Bluetooth solution can also be implemented as a one-processor architecture (embedded solution) where the application resides together with the Bluetooth protocols in the same hardware. In that case, the HCI is not needed. This is a feasible implementation for simple devices such as accessories or micro servers.

Requirements of Bluetooth technology: If Bluetooth technology is to replace cables, it can not be much more expensive than a cable or nobody will buy it. Because Bluetooth technology is designed for mobile devices it must be able to run on batteries. So it must be very low power and should run on low voltages. It must also be lightweight and small enough not to intrude on the design of compact mobile devices such as cellular phones, handsets etc. It must be as reliable as the cable it replaces and also it must be resilient. d by interference on one channel, the retransmission will always be on a different channel. Each Bluetooth time slot lasts 625 microseconds giving rise to frequency hopping rate of 1600 hops per seconds. Generally devices hop once per packet. .For long data transmission, particular users may occupy multiple time slots using the same transmission frequency thus slowing instantaneous hopping rate to below 1600 hops/ sec.

Bluetooth Networks: Picconets and Scatternet:

The Bluetooth network is called a piconet. In the simplest case it means that two devices are connected (see Figure 2a). The device that initiates the connection is called a master and the other devices are called slaves. The majority of Bluetooth applications will be point-to-point applications. Bluetooth connections are typically ad hoc connections, which means that the network will be established just for the current task and then dismantled after the data transfer has been completed. A master can have simultaneous connections (point-to-multipoint) to up to seven slaves (see Figure2b).

Then, however, the data rate is limited. One device can also be connected in two or more piconets. The set-up is called scatternet (see Figure 2c). A device can, however, only be a master to one piconet at a time. Support for hold, park, or sniff mode is needed for a device to be part of the scatternet. In these modes a device does not actively participate in a piconet, leaving time for other activities such as participating in another piconet, for example. The master/slave roles are not necessarily fixed and can also be changed during the connection if, for example, the master does not have enough esources to manage the piconet. Master/slave switch is also needed in the scatternet. Master/slave switch support is not mandatory. Most of current Bluetooth implementations support piconets only. Point-to-multipoint support depends on the implementation Figure 2. Bluetooth piconet and scatternet scenarios: a) Point-to-point connection between two devices b) Point-to-multipoint connection between a master and three slaves c) Scatternet that consists of three piconets Modes of operation: In connection state, the Bluetooth unit can be in several modes of operation.

Sniff, hold, and park modes are used to save power or to free the capacity of a piconet: Active mode: In the active mode, the Bluetooth unit actively participates on the channel. Sniff mode: In the sniff mode, the duty cycle of the slave’s listen activity can be reduced. This means that the master can only start transmission in specified time slots. Hold mode: While in connection state, the ACL link to a slave can be put in a hold (possible SCO links are still supported). In hold mode, the slave can do other things, such as scanning, paging, inquiring, or attending another piconet.

Park mode: If a slave does not need to participate in the piconet but still wants to remain synchronized to the channel (to participate in the piconet again later), it can enter the park mode. It gives up its active member address. Park mode is useful if there are more than seven devices that occasionally need to participate in the same piconet. The parked slave wakes up regularly to listen to the channel in order to re-synchronize and to check for broadcast messages sent by the master..

Frequency Hopping :

Bluetooth technology uses a frequency hopping technique, which means that every packet is transmitted on a different frequency. In most countries, 79 channels can be used. With a fast hop rate (1600 hops per second), good interference protection is achieved. Another benefit is a short packet length. If some other device is jamming the transmission of a packet, the packet is resent in another frequency determined by the frequency scheme of the master. This scenario is depicted in Figure 3 where packets of device 1 (colored packets) and device 2 (banded packets) are trying to use the same frequency.

Note that this case only refers to situations where there are two or more simultaneous active piconets or a non-Bluetooth device using the same frequency in range. The error correction algorithms are used to correct the fault caused by jammed transmissions Figure 4. Three-slot and five-slot long packets reduce overhead compared to one-slot packets. 220 µs switching time after the packet is needed for changing the frequency. Subsequent time slots are used for transmitting and receiving. The nominal slot length is 625 (s.

A packet nominally covers a single slot, but can be extended to cover three or five slots, as depicted in Figure 4. In multi-slot packets the frequency remains the same until the entire packet is sent. When using a multi-slot packet, the data rate is higher because the header and a 220 (s long switching time after the packet are needed only once in each packet. On the other hand, the robustness is reduced: in a crowded environment the long packets will more probably be lost

How Does Bluetooth Works?

Bluetooth devices have 4 basic States.

They can be a Master (in control of a Piconet -- represented by a large blue circle above), an Active Slave (connected and actively monitoring/participating on a Piconet -- medium orange circles), a Passive Slave (still logically part of a Piconet but in a low power, occasionally monitoring but still synchronized, inactive, state -- medium gray circles), and Standby (not connected to a Piconet, occasionally monitoring for inquiries from other devices, but not synchronized with any other devices -- small white circles). IN IDEAL STATE Bluetooth devices initially know only about themselves and in this state they will be in Standby mode.

Standby is a passive mode where a Bluetooth device listens on an occasional basis performing what are called Inquiry and/or Page Scans for 10 milliseconds out of every 1. 28 seconds to see if any other Bluetooth devices are looking to communicate. Passive behavior is inherent to half of Bluetooth’s states and is a key mechanism to achieving very low power. In Standby mode the Bluetooth device’s occasional attention reduces power consumption by over 98%. While all of the Bluetooth devices in the same mode it is important to note that they are NOT synchronized or coordinated in any way.

Thus they are all listening at different times and on different frequencies. [pic] Enquiry and page procedures lead to connections ENQUIRY: Inquiry is how a Bluetooth device learns about other devices that are within its range. In the illustration above Node A executes a Page Function on the BT Inquiry ID and receives replies from other devices. Through these replies device A learns the explicit identity of these other devices (i. e. their unique Bluetooth device ID). During the Inquiry process device A continuously broadcasts the Page command using the reserved Inquiry ID which identifies it as as a Page Inquiry.

These broadcasts are spread across a standard pattern of 32 Standby radio frequencies which all devices in Standby mode monitor on an occasional basis. Over a duration of some seconds it is certain that every Standby device within range will have received the Inquiry Page even though they are not synchronized in any way. By convention these nodes will respond with a standard FHS packet that provides their unique BT ID and their clock offset. With these parameters the Inquiring node can effect low latency synchronized connections.

Node H (the dotted circle above) illustrates how a Bluetooth device can be programmed to remain anonymous (Undiscoverable in BT jargon). This is a user controlled feature that suspends Inquiry Scanning, and thus device A’s Inquiry Procedure cannot discover Device B It is important to note that device H will continue to support Page Scanning however, and thus a user’s other personal devices (i. e. PAN) can penetrate this barrier by Paging directly to its unique Bluetooth ID. This is information that PAN devices can be configured to know and remember thus enabling private collaboration even when devices are undiscoverable.

PAGING: In its general form the Page command establishes a formal device to device link between a Master (the originator) and a Slave. Master/Slave connections in Bluetooth are referred to as a Piconet. To create the piconet device A broadcasts the Page command with the explicit device ID of the target Slave (B in the illustration above) which was learned earlier through an Inquiry Procedure. Further, this connection can be very low latency if the Inquiry data is recent (and thus synchronization can be accurate), but the process will simply take longer if this is not the case.

All Bluetooth devices except B will ignore this command as it is not addressed to them. When the device B replies, device A will send it an FHS packet back and assign it an Active Member Address in the Piconet. As an Active Slave device B will begin continuously monitoring for further commands from device A in synchronization with device A’s hopping pattern and clock offset. Further, standard Piconet activity continuously updates the clock offset data keeping the synchronization extremely accurate. Thus the Master and Slave states are not low power but exhibit very low transaction latencies.

Expanding a Picconet:

Through successive Page commands a Bluetooth Master can attach up to 7 Active Slaves. 7 is a hard limit as only 3 bits are allocated in Bluetooth for the Active Member Address (AMA) with 000 reserved for the Master and the remaining addresses allocated to Slaves. Practically, 7 is more than sufficient given Bluetooth’s modest performance and dynamic configurability. Again, all Active Slaves to A continuously monitor for further commands addressed to them in synchronization with device A’s hopping pattern. PARKING: Parking is a mechanism that allows a Bluetooth Master to connect to an additional 256 devices. 56 is a hard limit as 8 bits are allocated in Bluetooth for the Parked Member Address (PMA). To Park a device the Bluetooth Master issues a Park command to an Active Slave and assigns it a PMA. This Slave then enters the Parked mode and surrenders its AMA. As a Parked Slave the device will revert to a passive mode and only monitor for commands on an occasional basis. The difference between Standby and Parked however is that the Slave will remain synchronized to the Master’s hopping pattern and regularly update its clock offset. Thus this device can be reconnected at any time with a minimum latency.

Bluetooth Protocols:

Protocols are needed to implement different profiles and usage models. Every profile uses at least part of the protocol stack. In order to achieve interoperability between two Bluetooth devices, they both must have the same vertical profile of the protocol stack. Bluetooth Core Protocols Baseband and Link Control together enable a physical RF link between Bluetooth units forming a piconet. This layer is responsible for synchronizing the transmission-hopping frequency and clocks ofdifferent Bluetooth devices [Whitepaper1, p. ]. Audio is routed directly to and from Baseband. Any two Bluetooth devices supporting audio can send and receive audio data between each other just by opening an audio link . Link Manager Protocol (LMP) is responsible for link set-up (authentication and encryption, control, and negotiation of baseband packets) between Bluetooth devices and for power modes and connection states of a Bluetooth unit. Logical Link Control and Adaptation Protocol (L2CAP) takes care of multiplexing, reassembly, and segmentation of packets.

Service Discovery Protocol (SDP) is needed when requesting device information, services, and the characteristics of other devices. Devices have to support the same service in order to establish a connection with each other. Cable Replacement Protocol RFCOMM emulates RS-232 signals and can thus be used in applications that were formerly implemented with a serial cable (e. g. , a connection between a laptop computer and a mobile phone). Telephony Protocol Binary (TCS-BIN) defines the call control signaling for the establishment of speech and data call between Bluetooth devices.

AT commands provide means for controlling a mobile phone or a modem. Adopted Protocols OBEX (Object Exchange) is adopted from IrDA. It is a session protocol that provides means for simple and spontaneous object and data transfer. It is independent of the transport mechanism and transport Application Programming Interface (API). TCP/UDP/IP is defined to operate in Bluetooth units allowing them to communicate with other units connected, for instance, to the Internet. The TCP/IP/PPP protocol configuration is used for all Internet Bridge usage scenarios in Bluetooth 1. and for OBEX in future versions. The UDP/IP/PPP configuration is available as transport for WAP. PPP in the Bluetooth technology is designed to run over RFCOMM to accomplish point-to-point connections. PPP is a packet-oriented protocol and must therefore use its serial mechanisms to convert the packet data stream into a serial data stream. The Wireless Application Protocol (WAP) stack can reside on top of RFCOMM (based on LAN Access Profile) or on top of L2CAP (based on PAN Profile). The latter reduces overhead and is likely to become the preferred solution for WAP over Bluetooth.

Wireless Application Environment (WAE) hosts the WAP browser environment. Dial up networking (DUN) profile protocol stack: DUN profile is inside the Serial Port Profile and therefore partly reuses the capabilities of the Serial Port Profile. For the DUN Profile, there are two device configurations (roles): Gateway (GW) is the device that provides access to the public network (typically mobile phones and modems) Data terminal (DT) is the device that uses the dial-up services of the gateway (typically PCs) The DUN Profile needs a two-piece protocol stack and an SDP branch.

PPP over RFCOMM is needed for transferring payload data. AT commands are delivered over RFCOMM to control the modem (mobile phone). The application on top of the stack is either a driver application on a PC (data terminal) or the modem emulation on a phone (gateway). Bluetooth security: secret key All Bluetooth devices (master and slave) share a secret key in a particular system. This key is used during the authentication and encryption process. This key is not transmitted over the channel but is rather in-built by the manufacturer.

Authentication

Authentication ensures the identity of Bluetooth devices. Authorization is a process of deciding if a device is allowed to have access to a specific service. User interaction may be required unless the remote device has been marked as "trusted. " Usually the user an set authorization on/off to every remote device separately. Authorization always requires authentication. Authentication in Bluetooth is performed by an encryption engine which uses the SAFER+ algo. This algorithm requires the following:  Number to be encrypted or decrypted master address. Master clock secret key shared by master and slave. A random number is generated by the encryption engine using various keys. This random number is encrypted by the master using the secret key. This number is also sent to the slave. The encrypted reply of the slave is compared with the master encrypted data. If it is a match then the slave is authentic. BONDING AND PAIRING Pairing is a procedure that authenticates two devices based on a common passkey, thereby creating a trusted relationship between those devices. An arbitrary but identical passkey must be entered on both devices.

As long as both devices are paired, the pairing procedure is not required when connecting those devices again (the existing link key is used for authentication). Devices without any input method, like headsets, have fixed passkeys. When two devices are linked with a common link the connection is called as bonding. There are two types of bonding: Dedicated bonding: Used to create and exchange a link key between two devices. General bonding: Data over the link is available for higher layers. Encryption protects communication against eavesdropping.

For example, it ensures that nobody can listen to what a laptop transmits to a phone. Encryption demands the following: Negotiating encryption mode Negotiating key sizes-The key size could vary from 8 to 128 bits  Starting encryption. Stopping encryption

Security Levels

A trusted device has been previously authenticated, a link key is stored, and the device is marked as "trusted" in the security database of a device. The device can access Bluetooth services without user acceptance. An untrusted device has been previously authenticated, a link key is stored, but the device is not marked as "trusted. Access to services requires acceptance of the user. An unknown device means that there is no security information on this device. This is also an untrusted device. Security Level of Services Authorization required: Access is only granted automatically to trusted devices or untrusted devices after an authorization procedure (‘Do you accept connection from remote device? ’). Authentication is always required. Authentication required: The remote device must be authenticated before connecting to the application. Encryption required: The link must be changed to encrypted before accessing the service.

It is also possible that a service does not require any of these mechanisms. On the other hand, the application (service) might have its own user authentication mechanisms (a PIN code, for example).

Applications:

Bluetooth in the home will ultimately eliminate most every cable related to consumer electronics (except power). Your PC, scanner, and printer will simply need to be within 10 meters of each other in order to work. Your PDA, digital camera, and MP3 player will no longer need a docking station to transfer files or get the latest tunes (the exception will be to recharge, that power thing again).

And, your home stereo and other equipment will join the party too. On the telephone front your cell phone will synchronize its address book with your PC and function as a handset to your cordless phone in the house (answering incoming calls to your home number and calling out on the cheaper land line too). Finally, even though its only 720Kbps, Bluetooth is still pretty fine for broadband internet access since DSL and cable modems are typically throttled to about 384K anyway. Bluetooth access points could well be as ubiquitous as 56K modems in 2 or 3 years. . On the road much of your Bluetooth PAN goes with you. Even when your laptop is in your briefcase and your cell phone is in your pocket they will be able to collaborate to access e-mail. And, next generation cell phones featuring Bluetooth and General Packet Radio (GPR) technology will function as a wireless modems with internet access at 100Kbps+. With such performance it is likely web based e-business will flourish and these devices will become the most prevalent Bluetooth access points.

This may well be the Killer App that ensures Bluetooth’s widespread adoption and success. When you are literally on the road your car will join your PAN too. Here your cell phone may operate in a hands free mode using the car audio system and an in-dash microphone even while comfortably in your pocket. Or you may use a wireless Bluetooth headset instead. And, your MP3 player will likely play music in 8 speaker surround sound, rip music right off of an FM broadcast, or record your phone calls for later review. And all without wires!!!

Fixed land line access points (supporting up to 720Kbps) such as a pay phone in the airport terminal or lounge, or the desk phone in your hotel, will provide true broadband access in these strategic locations. Also look for the pay phone to evolve to compete for your cell phone calls too with its low cost land lines. In the world of deregulation and open competition future smart phones may even put your calls out for bid and channel the traffic over the carrier offering the lowest cost!

Telephone applications

• Hands free use
• File synchronization
• Calendars
• Contact management Land line I/F for voice and data
• Consumer applications
• File transfer
• MP3
• Digital pictures
• Peripheral connectivity
• Keyboard/mouse/remote
• Printer

Advantages:

1. Point to point and point to multiple links
2. Voice and data links 3. Compact form factor
3. Low power
4. Low cost
5. Robust frequency hopping and error correction
6. Profiles ensure application level
7. High level of security through frequency hopping, encryption and authentication
8. Non directional
9. Unlicensed ISM band LIMITATIONS:

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