1

Wireless Networks

By. P. Victer Paul

Dear, We planned to share our eBooks and project/seminar contents for free to all needed friends like u.. To get to know about more free computerscience ebooks and technology advancements in computer science. Please visit....

http://free-computerscience-ebooks.blogspot.com/

http://recent-computer-technology.blogspot.com/

http://computertechnologiesebooks.blogspot.com/

Please to keep provide many eBooks and technology news for FREE. Encourage us by Clicking on the advertisement in these Blog.

3

Bluetooth Systems

• Piconet: Basic unit is a Piconet, consisting of a master and from one to seven active slave devices.

•Scatternet: A device in one piconet may also exist as part of another piconet and may function as either a slave or master in each piconet and this form of overlapping is called a scatternet.

4

Bluetooth Systems- Fundamentals

5

Bluetooth Systems• A slave may only communicate with the master and may only communicate when granted permission by the master.

•The advantage of the piconet/scatternet scheme is that it allows many devices to share the same physical area and make efficient use of the bandwidth.

6

Bluetooth Systems

• Bluetooth uses the Industrial, Scientific and Medical (ISM) band, which is free to use in most countries.

•Two main methods are used for spreading out the power:

Direct Sequence Spread Spectrum (DSSS): Transmission across a wide range of frequencies at low power.

Frequency-Hopping Spread Spectrum FHSS): Uses a small bandwidth but changes (or hops) frequency after each packet.

7

Bluetooth Systems

• Bluetooth uses FHSS.

•There are 79 channels of 1MHz each; after each transmit or receive, devices hop to a new channel.

•A Bluetooth system uses a frequency-hopping scheme with a carrier spacing of 1 MHz. Typically, up to 79 different frequencies are used, for a total bandwidth of 80 MHz.

•At any given time, the bandwidth available is 1 MHz, with a maximum of eight devices sharing the bandwidth. Different logical channels (different hopping sequences) can simultaneously share the same 80 MHz bandwidth.

8

Bluetooth Systems

• It is possible for a device to take part in two different Piconets by swapping between two different frequency-hopping sequences.

• So, Collisions will occur when devices in different piconets, on different logical channels, happen to use the same hop frequency at the same time.

•As the number of piconets in an area increases, the number of collisions increases, and performance degrades.  In summary, • The physical area and total bandwidth are shared by the Scatternet.

•The logical channel and data transfer are shared by a Piconet.

9

Bluetooth Systems

•It is not possible to be a master of two different piconets.

•This is because a piconet is a group of devices all synchronized on a hopping sequence set by the master.

•By definition, any devices that share a master must be on the same piconet.

•A device that is present on two different piconets must visit each piconet often enough to keep the link supervision timeout from elapsing.

•Obviously, Scatternets are not the most efficient way to use Bluetooth bandwidth. The problem arises because the piconets that make up scatternets aren't synchronized.

10

Bluetooth Architecture

11

Bluetooth Architecture

12

Bluetooth Architecture

13

Bluetooth Systems

1. RF Layer:•At the lowest level, the radio layer of the core specification defines the wireless interface.

•FHSS occurs in the 2.4 GHz ISM band using either 79 radio frequencies in countries with restrictions in the ISM band.

2. Baseband Layer:•The Baseband specifies how the radio layer should be employed to facilitate communication between Bluetooth devices.•This layer defines the concept of a piconet, which is BT_s fundamental logical topology for organising group-wise communication, under decentralisation.

14

Bluetooth Systems

•At this point, homogeneous devices are distinguished by their Bluetooth device address which is a unique 48-bit address, hard-coded into the Bluetooth chip.

•The first device to initiate the formation of a Piconet becomes the master. Every other device in range is assigned a locally unique active member address - Slaves within the master_s piconet.

•At most seven active slaves participate in each Piconet, but additional slaves can be registered with the master and sustain the parked mode. Devices outside of any piconet sustain the stand-by mode.

15

Bluetooth SystemsDevice Admission / Bluetooth Link Formation

The link formation process specified in the Bluetooth Baseband specification consists of Four processes:

• Inquiry: This process consists of broadcasting inquiry packets, which do not contain the senders identity or other any information.

• Inquiry scan: In this state, devices listen for inquiry packets, and upon detection of an inquiry packet, the device broadcasts an inquiry response packet.

This contains the devices identity and clock of the device in inquiry scan mode.

16

Bluetooth Systems

Device Admission / Bluetooth Link Formation

Page : Under this process, a device tries to establish a connection with a device whose identity and clock are known. Page packets are sent, which contain the sending devices address and clock for synchronisation.

The packets sent can only be received by those devices with particular identities.

• Page scan: In this state, a device listens for a page packet. Receipt is acknowledged and synchronisation between the page and page scan devices is established.

17

Bluetooth Systems

Device Admission / Bluetooth Link Formation

The goal of the Inquiry process is for a master node to discover the existence of neighboring devices and to collect enough information about the low-level state of those neighbors (primarily related to their native clocks) to allow it to establish a frequency hopping connection with a subset of those neighbors.

The goal of the Page process is to use the information gathered in during the Inquiry process to establish a bi-directional frequency hopping communication channel.

18

Bluetooth Systems

Device Admission / Bluetooth Link Formation

19

Bluetooth Systems

3. MAC Layer

•Bluetooth uses baseband packets that can span 1, 3, or 5 time-slots.

•The capacity of a frequency hopping channel is 1 Mbps.

•Each Bluetooth packet is sent at a different frequency.

•For packets that span multiple time-slots, however, the frequency is not changed until the packet is fully transmitted.

•Bluetooth uses TDD (Time Division Duplex) scheme is as the duplexing method to provide two-way communication.

20

Bluetooth Systems3. MAC Layer

•For packets that span multiple time-slots, however, the frequency is not changed until the packet is fully transmitted.

•Bluetooth uses baseband packets that can span 1, 3, or 5 time-slots.

Multi-Slot Packets

21

Bluetooth Systems3. MAC LayerIn a Piconet there are two possible links:• Synchronous Connection-Oriented (SCO) link

•The SCO link is like a circuit-switched connection.

•An SCO link is established using reserved time slots at regular time intervals.

•Designed for time-critical connections – voice packets.

•A node (either master or slave) can support at most three SCO links.

•It is Point-Point connection. There is no broadcast option with SCO links.

22

Bluetooth Systems3. MAC LayerIn a Piconet there are two possible links:• Asynchronous Connection-Less (ACL) link

•The ACO link is like a packet-switched connection.

•An ACO link is established using unreserved time slots at regular time intervals.

•Designed for Non time-critical connections – data packets.

•A node (either master or slave) can support at most ONE ACL link.

•It is a Point-Multi Point connection. There is broadcast option with ACL links.

23

Bluetooth Systems3. MAC LayerReservation of Slots

Polling by master is the declaration of the slave node that will use the next time slot for sending data.

Polled node is stated by its AM ADDR in the header of the polling message sent by the master node.

In the next slot that is assigned to a slave, the slave can send either a data packet or a NULL packet.

If no slave is addressed in a packet sent the master node, i.e. AM ADDR is set to zero, that packet is a broadcast packet to all slaves in the piconet.

24

Bluetooth Systems3. MAC LayerReservation of Slots

Polling in Piconet

25

Bluetooth Systems3. MAC LayerReservation of Slots

• Scheduling by master node for polling and sending data has impact on performance of intra-piconet data traffic.

•In even numbered time-slots, a master node sends data to its slaves and polls them.

•In odd numbered time-slots, polled slaves start sending their data packets.

•Multi-slot packet is in transmission, the frequency carrier that is used by the first slot is also used by the other slotsthat multi-slot packet occupies.

26

Bluetooth Systems3. MAC LayerPacket Format

•Three parts: Access Code, Header, and Payload.

•Each of these three parts also have sub-fields.

•Packets are send in Little-Endian format.

27

Bluetooth Systems3. MAC LayerPacket Format – ACCESS CODE

Three types:

• Channel Access Code (CAC): The access code used as part of data packets during data transmission. It is 72 bits long.

• Device Access Code (DAC): The access code used during piconet formation processes. It is 68 bits.

• Inquiry Access Code (IAC): The access code used during inquiry process, as an identification of a single node that wants to join the piconet. It is 68 bits long.

28

Bluetooth Systems3. MAC LayerPacket Format – ACCESS CODE

Three fields:• Preamble: Fixed zero-one pattern (0101 or 1010) to indicate the beginning of a packet and facilitate the reception of the packet.

• Sync word: The field that is used for identification purposed. The value of this field is derived from the hardware (Bluetooth) address of either the master or a slave. In CAC type of access codes, the value is derived from the hardware address of the master of the piconet. In DAC and IAC type of access codes, which is used during inquiry and page procedures, it is derived from the hardware address of the slave node that will join to the piconet.

• Trailer: Fixed zero-one pattern to indicate the end of the access code.

29

Bluetooth Systems3. MAC LayerPacket Format – HEADER

• Header defines • target node • ordering • acknowledging information

• Length is shown as 18 bits. With error coding 54 bits long.

30

Bluetooth Systems3. MAC LayerPacket Format – HEADER

Header is composed of Six fields:

• AM ADDR: Active member address of the target node.

• Type: Defines the type of the packet that is sent. Type value indicates the number of slots that the packet will occupy and also the type of the data (SCO or ACL data) that is carried inside the payload field.

• Flow: Defines the receive buffer availability of the receiver.

• ARQN: Used for acknowledgment of previously received packets.

• SEQN: Used for numbering of streamed packets

• HEC: Used to check header integrity.

31

Bluetooth Systems3. MAC LayerPacket Format – PAYLOAD

Payload is composed of Two fields:

• Payload Header: The payload header stores information about the length of the data that is stored in the payload part.

May have two different sizes depending on the size of the packet in terms of time-slots that it occupies.

For single-slot packets, payload header is one byte long.

For multi-slot packets, payload header length is two bytes long.

• Data: Actual Information

32

Bluetooth SystemsPower Management

Different Modes of operation for minimizing power consumption.

Idle mode: The device performs the scan operation for less than 1% of the time.

Park mode: Reduces device activity further, but can only be applied to slave devices after a piconet has been formed.

In park mode, devices remain synchronised with the master but do not return a packet with a payload.

Park mode permits more than seven slaves to participate in a piconet.

33

Bluetooth SystemsPower Management

Different Modes of operation for minimizing power consumption.

Sniff mode: The slave does not scan in every master–slave time slot, but has a low duty cycle.

Effectively the device only wakes up periodically to communicate with the master.

Hold mode: Used to put devices to sleep.

This is used to suspend intra-piconet communication while the master searches for new devices to admit to the piconet.

34

Infrared Systems

What is the difference between Infrared and Bluetooth? • Bluetooth operates using radio waves while infra-red communication works on fast pulses of light.

•Sensors of both the devices must be in each other's immediate line of sight. If something comes in the way of the two mobiles devices, the message or data will not pass through.

• Bluetooth technology however can pass through walls. You can send messages, data files, audio- files, video-files etc from your mobile to the other person in the next room, as long as the other mobile is within the radius of 10 meters.

•Infrared also only works between two devices at a time while Bluetooth can work with as many as mobile devices as you want.

35

Infrared Systems

36

Infrared SystemsComponents of IrDA Architecture:

IrDA has defined a group of short-range, high speed, bidirectional wireless infrared protocols, generically referred to as IrDA.

IrDA allows a variety of devices to communicate with each other. Cameras, printers, portable computers, desktop computers, and personal digital assistants (PDAs) can communicate with compatible devices using this technology.

37

Infrared SystemsComponents of IrDA Architecture: IrDA has Three layers:

IrPHY - Infrared Physical Layer

IrLAP - Infrared Link Access Protocol

IrLMP - Infrared Link Management Protocol

Serial Infrared (SIR) supporting speeds up to 115.2 Kbps

Medium Infrared (MIR) supporting 0.576 Mbps and 1.152 Mbps

Fast Infrared (FIR) supporting a 4.0 Mbps data rate

Very Fast Infrared (VFIR) supporting 16.0 Mbps.

In addition to the base standards, IrDA has specified several optional layers such as Tiny TP, IrCOMM, and IrOBEX.

38

Infrared Systems

39

Infrared SystemsComponents of IrDA are:

Winsock:    Winsock is an API that allows Windows-based applications to access the transport protocols. The IrDA protocol stack is made available to applications by using Winsock.

IrTran-P:    IrTran-P is a bidirectional image transfer protocol. Many cameras have digital ports and can beam infrared data to a receiving computer. That data is then placed in a user-specified (or default) directory.

IrDA Print Monitor:    IrDA Print Monitor is a software component that interfaces with an IrDA-connected printer.

IrXfer:    IrXfer is an IrDA file transfer application. IrXfer has bidirectional transfer capabilities.

40

Infrared SystemsComponents of IrDA are:

Tiny TP:    Tiny TP is a flow control mechanism for IrDA. Tiny TP acts as a regulator to control the rate of data input or output. This prevents an overflow of data from occurring and creating data errors.

IrDA.sys:    IrDA.sys is the transport protocol stack that supports IrDA. It provides support for applications through Winsock to the NDIS layer.

IrCOMM:    IrCOMM is a software component that supports IrTran-P. The IrTran-P server must be disabled if other applications need to use the IrCOMM port.

IrLPT:    IrLPT is the protocol support that is used by IrDA Print Monitor. IrLPT enables printing directly from IrDA devices to IrDA printers.

41

Infrared SystemsComponents of IrDA are:

IrLMP: Infrared Link Management Protocol is used to multiplex various connections over one IrDA link.

IrLAP: Infrared Link Access Protocol is a media access control software component that determines which component can access the media during each time slice.

FIR Driver: A Fast Infrared driver (FIR) is a miniport driver provided by a hardware vendor to link hardware devices on the lower side of the protocol stack to the transport protocol above, such as TCP/IP or IPX/SPX.

FIR devices can exchange data up to 4 megabytes (MB) per second. All FIR devices are also required to support serial transmission using Serial Infrared driver (SIR).

42

Infrared SystemsComponents of IrDA are:

IrSIR.sys:  Serial Infrared driver is a Microsoft-provided miniport driver. It is an alternate driver to the Fast Infrared driver and can be used only in combination with Serial.sys. The maximum data transfer rate is 115.2 kilobytes per second (Kbps).

Serial.sys:   Serial.sys is used to connect infrared devices to the IrSIR.sys driver above in the protocol stack and the hardware device below. It is a software driver that sends and receives data from a hardware device and presents it to the IrSIR.sys driver in a format that conforms to the requirements of IrSIR.sys.