Unit 1- Intro to Wireless Standards.pdf

Lecture Notes on Introduction to
Wireless Standards
for
Pre-PhD Coursework Departmental Paper
on
Mobile Ad-Hoc and Sensor Networks(EC704)
by
Dr. Piyush Charan
Assistant Professor
Department of Electronics and Communication Engg.
Integral University, Lucknow

Contents
• Broadcasting and Multicasting
– Broadcast Storm,
– network flooding avoidance,
– multicast routing.
• TCP over mobile ad hoc networks
– IP address acquisition,
– effects of partitions on TCP,
– provisions for mobility and fairness.
20 March 2022 2
Dr. Piyush Charan, Dept. of ECE, Integral University, Lucknow

Contents contd…
• Wireless LAN (WiFi)
– IEEE 802.11 specifications,
• Medium Access Control Protocol issues;
– power control,
– spatial reusability, and
– Quality of Service (QoS)
• Bluetooth
– specifications,
– Piconet synchronization and master-slave switch,
– scatternet formations,
– interference issues,
– interoperability with WiFi.
20 March 2022 Dr. Piyush Charan, Dept. of ECE, Integral University, Lucknow 3

Casting
• Transmitting data (stream of packets) over the network is termed as casting.
• Unicast, multicast, and broadcast happen at layer-2 and layer-3.
• Remember layer-2 is the data-link layer where the switch device works using the
MAC addresses for communication, and layer-3 is the network layer where the
router device works using the IP addresses for communication.
• Here, “cast” refers to how many people or devices we send the data to. It can be
unicast, multicast, or broadcast. These 3 methods are the types of communication,
used to transmit packets over a network.
• Unicast means one-to-one, data send to only one device means sender sends data to
only one device. Multicast means one-to-many (or many-to-many), data sent to
multiple devices means sender sends data to many devices (not all devices like the
broadcast). Broadcast means one-to-all, data sent to all devices means sender sends
data to all devices.

Types of Casting
Types of
Casting
Unicast Broadcast
Limited
Broadcast
Direct
Broadcast
Multicast
Figure 1.1: Types of Casting

Unicast
• Uni: means- ‘one’
• Cast: means- ‘to send’ or ‘to throw’
• So, unicast means a communication
technique in which there is
– one-to-one Communication
– has only one source and one destination
node.
Figure 1.2: Unicast

Unicast Contd…
• Unicast is a one to one data transmission. In computer networking, Unicast is a term, that is used
when data is transmitted from one point to another point.
• It is a one-to-one communication; that is one sender and one receiver when one device transmits the
data to another device then it is called unicast transmission. Generally, we use one-to-one
communication on our daily basis like- sending a message, browsing a website, downloading a file
etc.
• Some Examples:
– Ex-1: A device having an IP address 20.1.3.0 in a network wants to transmit the data to the device with IP
address 30.10.5.0 in another network, then this transmission is called Unicast transmission.
– Ex-2: There are 4 computers connected to the switch device, so if pc1 wants to communicate with pc2, then
they can directly communicate with each other so this is unicast communication because it is one-to-one
communication.
– Ex-3: Browsing a website is also unicast communication, where the web server acts as a sender and our
computer acts as a receiver.
– Ex-4: Downloading a file from an FTP server is another example of unicast transmission, where the FTP
server acts as a sender and our computer acts as a receiver.

Multicast
• Transmitting data from one
source host to a particular group
of hosts having interest in
receiving the data is called as
multicast.
• It is a one-to-many transmission.
Figure 1.3: Multicast

Multicast contd…
• Multicast is a term, that is used when data is transmitted to multiple
devices. This type of multicast transmission is used, when data is sent to a
group. This type of transmission recline between the boundaries of unicast
(one-to-one) and broadcast (one-to-all).
• It can be one-to-many or many-to-many transmission means data send
efficiently from one source (or many sources) to many destinations
simultaneously, generally within a local network. So if we use the
multicast transmission in the local network, then a frame contains the
unique multicast MAC addresses of an application, protocol, or datastream.
• In multicast transmission, when a device sends one copy of data then it is
delivered to many devices (not delivered to all devices like in broadcast).

Broadcast
• A method of sending information over a
network. (specifically to all the nodes/motes
in a network)
– Data comes from one source and goes to all
other connected sources.
– This has the side effect of congesting a
medium or large network segment very
quickly.
Figure 1.4: Broadcast

Broadcast contd…
• Broadcast is a term, that is used when data is transmitted to all the devices.
• It is a one-to-all transmission means there is one sender, but the information
is delivered to all the connected receivers.
• In broadcast transmission, when a device sends one copy of data, then that
data will be delivered to all the devices.
• This term “broadcast", mostly used in cable TV transmission.TV signals
are sent from one source (one point) to all the possible destinations (all
points).

Types of Broadcast
• We can classify broadcasting
techniques into two types:
– Limited Broadcasting:
• Information is sent to all the
nodes on the same network.
• When a sensor node transfers
data to all nodes on the same
network, it is referred to as
limited broadcasting.
– Direct Broadcasting:
• Information is directly sent to all
the nodes on another network.
• When a sensor node in one
network transfers data packet
stream to all the nodes on the
other network, it is referred to as
direct broadcasting.
Figure 1.5: Types of Broadcast

Difference between Unicast, Multicast and
Broadcast
UNICAST MULTICAST BROADCAST
It has only one sender and one receiver
It has one or multiple senders and multiple
receivers.
It has one sender and multiple receivers.
Sends data from one device to single device
Data can be sent from one device to multiple
devices
Data sent from one device to all the other
devices in a network.
Works on Single Node Topology. Works on star, mesh, tree and hybrid topology. Works on star and bus topology
Two devices are connected to each other with a
single cable.
The switch is an example of a multicast device. Hub is an example of a broadcast device.

Broadcast Storm in WSNs
• A Broadcast Storm is basically a situation when an abruptly
large number of data packets arrive in a very small amount of
time.
• Due to the broadcast storm, the network quality degrades
significantly.
– It leads to broadcast and multicast traffic accumulation in a Wireless Sensor
network.
– The broadcast storm problems in WSNs such as high probability of collisions
and redundancy of broadcasting.

Flooding
• Flooding: Each node which receives a packet (queries/data) broadcasts it
until the packet reaches the destination node.
• Disadvantages:
– Implosion:
• Happens when duplicate messages sent to the same node.
• Occurs when a node receives copies of the same messages from many of its neighbors.
– Overlap:
• the same event may be sensed by more than one node due to overlapping regions of
coverage.
• This results in their neighbors receiving duplicate reports of the same event.
– Resource blindness: the flooding protocol does not consider the available
energy at the nodes and results in many redundant transmissions. Hence, it
reduces the network lifetime.

Gossiping
• It is a modified version of flooding
• The nodes do not broadcast a packet, but send it to a randomly
selected neighbor.
• Avoid the problem of implosion
• It takes a long time for message to propagate throughout the
network.
• It does not guarantee that all nodes of network will receive the
message.

Rumour Routing
• It is an agent based path creation algorithm.
• Agents are basically packets which are circulated in the network to
establish shortest path to events.
• They can also perform path optimizations at nodes they visit.
• When agent finds a node whose path to an event is longer than its
own, it updates the node’s routing table.
• When query is generated at a sink, it is sent on a random walk with
the hope that it will find a path leading to the required event.
• If query does not find an event path , the sink times out and uses
flooding as last resort to propagate the query.

TCP over MANETs
• With the proliferation of mobile computing devices, the demand for
continuous network connectivity regardless of physical location has
spurred interest in the use of mobile ad hoc networks.
• Since Transmission Control Protocol (TCP) is the standard network
protocol for communication in the internet, any wireless network
with Internet service need to be compatible with TCP.
• TCP is tuned to perform well in traditional wired networks, where
packet losses occur mostly because of congestion.

Issues of TCP in Ad-hoc N/w
• However, TCP connections in Ad-hoc mobile networks are
plagued by problems such as
– high bit error rates,
– frequent route changes,
– multi-path routing, and
– temporary network partitions.
• The throughput of TCP over such connection is not
satisfactory, because TCP misinterprets the packet loss or
delay as congestion and invokes congestion control and
avoidance algorithm.

• TCP is reliable, end-to-end, connection-
oriented TL protocol that provides a byte
stream based service.
– Congestion control.
– Flow control.
– In-order delivery of packets.
– Reliable transportation of packets.

Design Goals of A Transport Layer Protocol for
Ad Hoc Wireless Networks
❖ The protocol should maximize the throughput per connection.
❖ It should provide throughput fairness across contending flows.
❖ It should incur minimum connection set up and connection maintenance overheads.
❖ It should have mechanisms for congestion control and flow control in the network.
❖ It should be able to provide both reliable and unreliable connections as per the requirements of the
application layer.
❖ It should be able to adapt to the dynamics of the network such as rapid changes in topology.
❖ Bandwidth must be used efficiently.
❖ It should be aware of resource constraints such as battery power and buffer sizes and make efficient
use of them.
❖ It should make use of information from the lower layers for improving network throughput.
❖ It should have a well-defined cross-layer interaction framework.
❖ It should maintain End-to-End Semantics.

Why Does TCP Not Perform Well in
Ad Hoc Wireless Networks?
• Transmission Control Protocol (TCP) is designed to operate in wired Networks. But when TCP
is deployed with wireless or ad hoc networks. Then it fails to establish continuous
transmissions due to various reasons:
• The major reasons behind throughput degradation that TCP faces when used in ad hoc wireless
net works are the following.:
1. Misinterpretation of packet loss: Traditional TCP was designed for wired networks where the packet
loss is mainly attributed to network congestion. Network congestion is detected by the sender's
packet RTO period. Once a packet loss is detected, the sender node assumes congestion in the network
and invokes a congestion control algorithm. Ad hoc wireless networks experience a much higher
packet loss due to factors such as high bit error rate (BER) in the wireless channel, increased collisions
due to the presence of hidden terminals, presence of interference, location-dependent contention, uni-
directional links, frequent path breaks due to mobility of nodes, and the inherent fading properties of
the wireless channel.

Example WSN in Building
Figure 1.6: Cracks and Tilt Sensors as used in
Building Area Sensor Networks

2. Frequent path breaks: Ad hoc wireless networks experience dynamic changes in network
topology because of the unrestricted mobility of the nodes in the network. The topology
changes lead to frequent changes in the connectivity of wireless links and hence the route to
a particular destination may need to be recomputed very often. The responsibility of finding
a route and reestablishing it once it gets broken is attached to the network layer. Once a path
is broken, the routing protocol initiates a route reestablishment process. This route
reestablishment process takes a significant amount of time to obtain a new route to the
destination. The route reestablishment time is a function of the number of nodes in the
network, transmission ranges of nodes, current topology of the network, bandwidth of the
channel, traffic load in the network, and the nature of the routing protocol. If the route
reestablishment time is greater than the retransmission timeout (RTO) period of
the TCP sender, then the TCP sender assumes congestion in the network, retransmits the
lost packets, and initiates the congestion control algorithm. These retransmissions can lead
to wastage of bandwidth and battery power. Eventually, when a new route is found,
the TCP throughput continues to be low for some time, as it has to build up the congestion
window since the traditional TCP undergoes a slow start.

3. Effect of path length: It is found that the TCP
throughput degrades rapidly with an increase in
path length in string (linear chain) topology ad
hoc wireless networks. This is shown in Figure
(a) alongside. The possibility of a path break
increases with path length. Given that the
probability of a link break is Pl, the probability
of a path break (Pb) for a path of length k can be
obtained as 𝑃𝑏 = 1 − 1 − 𝑃𝑙
𝑘
.
– Figure (b) alongside shows the variation
of Pb with path length for Pl = 0.1.
Hence as the path length increases, the
probability of a path break increases,
resulting in the degradation of the
throughput in the network.
Figure 1.7:
Effect of Path
Length on
(a).Throughput
and (b). the
probability of
path breaks

4. Misinterpretation of congestion window: TCP considers the congestion
window as a measure of the rate of transmission that is acceptable to the network
and the receiver.
– In ad hoc wireless networks, the congestion control mechanism is invoked
when the network gets partitioned or when a path break occurs.
• Hence, when there are frequent path breaks, the congestion window may not reflect
the maximum transmission rate acceptable to the network and the receiver.

5. Asymmetric link behavior: The radio channel used in ad hoc wireless networks
has different properties such as location-dependent contention, environmental
effects on propagation, and directional properties leading to asymmetric links.
– The directional links can result in delivery of a packet to a node, but failure in the delivery of the
acknowledgment back to the sender.
– It is possible for a bidirectional link to become uni-directional for a while.
– This can also lead to TCP invoking the congestion control algorithm and several retransmissions.

6. Uni-directional path: Traditional TCP relies on end-to-end ACK for ensuring
reliability. Since the ACK packet is very short compared to a data segment, ACKs
consume much less bandwidth in wired networks. In ad hoc wireless networks,
every TCP ACK packet requires RTS-CTS-Data-ACK exchange in case IEEE
802.11 is used as the underlying MAC protocol. This can lead to an additional
overhead of more than 70 bytes if there are no retransmissions. This can lead to
significant bandwidth consumption on the reverse path, which may or may not
contend with the forward path. If the reverse path contends with the forward path,
it can lead to the reduction in the throughput of the forward path. Some routing
protocols select the forward path to be also used as the reverse path, whereas
certain other routing protocols may use an entirely different or partially different
path for the ACKs.
– Path break on an entirely different reverse path can affect the performance of
the network as much as a path breaks in the forward path.

7. Multipath routing: There exists a set of QoS routing and best-
effort routing protocols that use multiple paths between a source-
destination pair. There are several advantages in using multipath
routing. Some of these advantages include the reduction in route
computing time, the high resilience to path breaks, high call
acceptance ratio, and better security. For TCP, these advantages
may add to throughput degradation. Multipath Routing can lead to
a significant amount of out-of-order packets, which in turn
generates a set of duplicate acknowledgments (DUPACKs) which
cause additional power consumption and invocation of congestion
control.

8. Network Partitioning and Remerging: The randomly moving nodes in an ad hoc wireless
network can lead to network partitions. As long as the TCP sender, the TCP receiver, and all the
intermediate nodes in the path between the TCP sender and the TCP receiver remain in the same
partition, the TCP connection will remain intact. It is likely that the sender and receiver of the TCP
session will remain in different partitions and, in certain cases, that only the intermediate nodes are
affected by the network partitioning.
– A network with two TCP sessions A and B is shown in Figure 1.8 (a) at time instant t1.
– Due to dynamic topological changes, the network gets partitioned into two as in Figure
1.8 (b) at time t2.
– Now the TCP session A’s sender and receiver belong to two different partitions and the
TCP session B experiences a path break.
– These partitions could merge back into a single network at time t3 (refer to Figure 1.8
(c)).

Figure 1.8: Effect of Partitioning and Merging of Networks

9. The use of sliding-window-based transmission: TCP uses a sliding window for
flow control. The transmission of packets is decided by the size of the window,
and when the ACKs arrive from a destination, further packets are transmitted.
This avoids the use of individual fine-grained timers for transmission of each TCP
flow. Such a design is preferred in order to improve scalability of the protocol in
high-bandwidth networks such as the Internet where millions of TCP connections
may be established with some heavily loaded servers. The use of a sliding
window can also contribute to degraded performance in bandwidth-constrained ad
hoc wireless networks where the MAC layer protocol may not exhibit short-term
and long-term fairness. For example, the popular MAC protocols such as
CSMA/CA protocol show short term unfairness, where a node that has captured
the channel has a higher probability of capturing the channel again. This
unfairness can lead to a number of TCP ACK packets being delivered to the TCP
sender in succession, leading to a burstiness in traffic due to the subsequent
transmission of TCP segments.

A comparison of TCP solutions for ad hoc wireless
networks

IEEE802.11 Wireless LAN, WiFi
• IEEE 802.11 standard, popularly known as WiFi (Wireless Fidelity), lays
down the architecture and specifications of wireless LANs (WLANs).
• WiFi or WLAN uses high-frequency radio waves instead of cables for
connecting the devices in LAN.
• Users connected by WLANs can move around within the area of network
coverage.

IEEE 802.11 Architecture
• The components of an IEEE 802.11 architecture are as follows −
• Stations (STA) − Stations comprises of all devices and equipment that are
connected to the wireless LAN. A station can be of two types−
• Wireless Access Point (WAP) − WAPs or simply access points (AP) are
generally wireless routers that form the base stations or access.
• Client. Clients are workstations, computers, laptops, printers, smartphones, etc.
• Each station has a wireless network interface controller.
• Basic Service Set (BSS) − A basic service set is a group of stations
communicating at the physical layer level. BSS can be of two categories
depending upon the mode of operation−

IEEE 802.11 Architecture contd…
• Infrastructure BSS − Here, the devices
communicate with other devices through
access points.
• Independent BSS − Here, the devices
communicate in a peer-to-peer basis in
an ad hoc manner.
• Extended Service Set (ESS) − It is a set
of all connected BSS.
• Distribution System (DS) − It connects
access points in ESS.
Figure 1.9: IEEE802.11 Architecture

Frame Format of IEEE 802.11
• The main fields of a frame of wireless LANs as laid down by IEEE 802.11
are −
• Frame Control − It is a 2 bytes starting field composed of 11 subfields. It
contains control information of the frame.
• Duration − It is a 2-byte field that specifies the time period for which the
frame and its acknowledgment occupy the channel.
• Address fields − There are three 6-byte address fields containing addresses of
source, immediate destination, and final endpoint respectively.
• Sequence − It a 2 bytes field that stores the frame numbers.
• Data − This is a variable-sized field that carries the data from the upper layers.
The maximum size of the data field is 2312 bytes.
• Check Sequence − It is a 4-byte field containing error detection information.

Frame Format for IEEE802.11
Figure 1.10: IEEE802.11 Frame Format

Advantage/ Disadvantage of WLANs
• Advantages of WLANs
▪ They provide clutter free homes, offices and other networked places.
▪ The LANs are scalable in nature, i.e. devices may be added or removed from the network at a
greater ease than wired LANs.
▪ The system is portable within the network coverage and access to the network is not bounded
by the length of the cables.
▪ Installation and setup is much easier than wired counterparts.
▪ The equipment and setup costs are reduced.
• Disadvantages of WLANs
▪ Since radio waves are used for communications, the signals are noisier with more interference
from nearby systems.
▪ Greater care is needed for encrypting information. Also, they are more prone to errors. So, they
require greater bandwidth than the wired LANs.
▪ WLANs are slower than wired LANs.

MAC ISSUES IN ADHOC
NETWORKS
Unit 1:

MAC Layer
• MAC stands for the Medium Access Control Layer.
• The MAC layer is the “Brain” of WiFi.
• The first version of 802.11 (the 802.11 legacy published in 1997).
• the MAC layer is responsible for incorporating a number of crucial features, such as
sharing of speech among users, the terms of network connection, error control or
security.
• The MAC layer also defines the network addresses: all devices have an identifier of
48 bits (6 bytes) known as the “MAC address”.
• The first three bytes identify the manufacturer of the network equipment. For
example, in hexadecimal notation, 00-00-0c corresponds to Cisco constructor, 00-
04-23 corresponds to Intel Corporation, etc.
• The following three bytes define an identifier one chosen by the manufacturer, for
example 8B-B5-0B. An address will look like for example: 00-04-23-8B-B5-0B.

Responsibilities of MAC
Protocol in WSNs
➢Network overhead should be low.
➢Efficiently allocate the bandwidth.
➢Distributed MAC operation.
➢Power control mechanism should be present.
➢Maximum utilization of channel.
➢Hidden and Exposed problem should be removed.
➢Nodes should be sync with time.

Functions of MAC Layer
• It provides an abstraction of the physical layer to the LLC and upper layers
of the OSI network.
• It is responsible for encapsulating frames so that they are suitable for
transmission via the physical medium.
• It resolves the addressing of source node as well as the destination node, or
groups of destination nodes.
• It performs multiple access resolutions when more than one data frame is to
be transmitted. It determines the channel access methods for transmission.
• It also performs collision resolution and initiating retransmission in case of
collisions.
• It generates the frame check sequences and thus contributes to protection
against transmission errors.

Design issues of MAC Protocol
1. Bandwidth Efficiency –
– The shortage of data transfer capacity assets in these networks requires its proficient use.
– To evaluate this, we could state that bandwidth capacity is the proportion of the bandwidth used for data transmission to the
complete accessible bandwidth capacity.
2. Quality of Service Support –
– Quality of service support is difficult due to the mobility of the nodes. Once a node moves out of reach, the reservation in it is lost.
In these networks, QoS is extremely important because if it is being used in military environments, the service support needed time
to time.
3. Synchronization –
– Some instruments must be found so as to give synchronization among the nodes. Synchronization is significant for directing the
bandwidth reservation.
4. Hidden Terminal Problem –
– When there are two nodes, both are outside of each other’s range and try to communicate with same node within their range at the
same time, then there must be packet collision.
5. Exposed Terminal Problem –
– Uncovered nodes might be denied channel access pointlessly, which implies under usage of the bandwidth resources.

Bluetooth
• Bluetooth is a Wireless Personal Area Network (WPAN) technology and is
used for exchanging data over smaller distances.
• This technology was invented by Ericson in 1994.
• It operates in the unlicensed, industrial, scientific and medical (ISM) band at
2.4 GHz to 2.485 GHz.
• Maximum devices that can be connected at the same time are 7.
• Bluetooth ranges upto 10 meters.
• It provides data rates upto 1 Mbps or 3 Mbps depending upon the version.
• The spreading technique which it uses is FHSS (Frequency hopping spread
spectrum) and supports 1600hops/sec.
• A Bluetooth network is called a piconet and a collection of interconnected
piconets is called scatternet.

Bluetooth Architecture
• Bluetooth architecture defines two types of
networks:
1. Piconet
2. Scatternet

Piconet
• Piconet is a Bluetooth network that consists of one primary
(master) node and seven active secondary (slave) nodes.
• Thus, piconet can have up to eight active nodes (1 master
and 7 slaves) or stations within the distance of 10 meters.
• There can be only one primary or master station in each
piconet.
• The communication between the primary and the secondary
can be one-to-one or one-to-many.
• All communication is between master and a slave. Salve-
slave communication is not possible.
• In addition to seven active slave station, a piconet can have
up to 255 parked nodes. These parked nodes are secondary
or slave stations and cannot take part in communication
until it is moved from parked state to active state.

Scatternet
• Scatternet is formed by combining various
piconets.
• A slave in one piconet can act as a master or
primary in other piconet.
• Such a station or node can receive messages
from the master in the first piconet and deliver
the message to its slaves in other piconet
where it is acting as master. This node is also
called bridge slave.
• Thus a station can be a member of two
piconets.
• A station cannot be a master in two piconets.

Bluetooth layers and Protocol
Stack
• Bluetooth standard has many protocols that are organized into
different layers.
• The layer structure of Bluetooth does not follow OS1 model,
TCP/IP model or any other known model.
• The different layers and Bluetooth protocol architecture.

Bluetooth Protocol Stack
Radio
Baseband
Link Manager
Control
Host
Controller
Interface
Logical Link Control and Adaptation Protocol (L2CAP)
Audio
TCS BIN SDP
OBEX
vCal/vCard
IP
NW apps.
TCP/UDP
BNEP
RFCOMM (serial line interface)
AT modem
commands
telephony apps.
audio apps. mgmnt. apps.
AT: attention sequence
OBEX: object exchange
TCS BIN: telephony control
protocol specification – binary
BNEP: Bluetooth network
encapsulation protocol
SDP: service discovery
protocol
RFCOMM: radio frequency
comm.
PPP

Radio Layer
➢ The Bluetooth radio layer corresponds to the physical layer of OSI model.
➢ It deals with ratio transmission and modulation.
➢ The radio layer moves data from master to slave or vice versa.
➢ It is a low power system that uses 2.4 GHz ISM band in a range of 10
meters.
➢ This band is divided into 79 channels of 1MHz each. Bluetooth uses the
Frequency Hopping Spread Spectrum (FHSS) method in the physical layer
to avoid interference from other devices or networks.
➢ Bluetooth hops 1600 times per second, i.e. each device changes its
modulation frequency 1600 times per second.
➢ In order to change bits into a signal, it uses a version of FSK called GFSK
i.e. FSK with Gaussian bandwidth filtering.

Baseband Layer
➢ Baseband layer is equivalent to the MAC sublayer in LANs.
➢ Bluetooth uses a form of TDMA called TDD-TDMA (time division duplex TDMA).
➢ Master and slave stations communicate with each other using time slots.
➢ The master in each piconet defines the time slot of 625 µsec.
➢ In TDD- TDMA, communication is half duplex in which receiver can send and receive
data but not at the same time.
➢ If the piconet has only no slave; the master uses even numbered slots (0, 2, 4, …) and the
slave uses odd-numbered slots (1, 3, 5, …. ). Both master and slave communicate in half
duplex mode. In slot 0, master sends & secondary receives; in slot 1, secondary sends
and primary receives.
➢ If piconet has more than one slave, the master uses even numbered slots. The slave sends
in the next odd-numbered slot if the packet in the previous slot was addressed to it.

Baseband Layer-Types of Connections
• In Base-band layer, two types of links can be
created between a master and slave.
• These are:
1. Asynchronous Connection Less (ACL)
2. Synchronous Connection Oriented (SCO)

Asynchronous Connection Less
(ACL)
• It is used for packet switched data that is available at irregular intervals.
• ACL delivers traffic on a best effort basis. Frames can be lost & may have
to be re-transmitted.
• A slave can have only one ACL link to its master.
• Thus ACL link is used where correct delivery is preferred over fast
delivery.
• The ACL can achieve a maximum data rate of 721 kbps by using one, three
or more slots.

Synchronous Connection Oriented
(SCO)
• SCO is used for real time data such as sound. It is used where fast delivery
is preferred over accurate delivery.
• In an SCO link, a physical link is created between the master and slave by
reserving specific slots at regular intervals.
• Damaged packet; are not re-transmitted over SCO links.
• A slave can have three SCO links with the master and can send data at 64
Kbps.

Logical Link, Control Adaptation
Protocol Layer (L2CAP)
• The logical unit link control adaptation protocol is
equivalent to logical link control sub-layer of LAN.
• The ACL link uses L2CAP for data exchange but SCO
channel does not use it.
• The various function of L2CAP is:
1. Segmentation and reassembly
2. Multiplexing
3. Quality of Service (QoS)

Segmentation and Reassembly
• L2CAP receives the packets of up to 64 KB from upper layers
and divides them into frames for transmission.
• It adds extra information to define the location of frame in the
original packet.
• The L2CAP reassembles the frame into packets again at the
destination.

Multiplexing
• L2CAP performs multiplexing at sender side and de-
multiplexing at receiver side.
• At the sender site, it accepts data from one of the upper layer
protocols frames them and deliver them to the Base-band
layer.
• At the receiver site, it accepts a frame from the base-band
layer, extracts the data, and delivers them to the appropriate
protocol1ayer.

Quality of Service (QoS)
• L2CAP handles quality of service requirements, both when
links are established and during normal operation.
• It also enables the devices to negotiate the maximum payload
size during connection establishment.

Bluetooth Frame Format
1. Access Code: It is 72 bit field that contains
synchronization bits. It identifies the master.
2. Header: This is 54-bit field. It contain 18 bit pattern
that is repeated for 3 time.
The header field contains following sub-fields:
i. Address: This 3 bit field can define up to seven slaves (1 to
7). If the address is zero, it is used for broadcast
communication from primary to all secondaries.
ii. Type: This 4 bit field identifies the type of data coming from
upper layers.
iii. F: This flow bit is used for flow control. When set to 1, it
means the device is unable to receive more frames.
iv. A: This bit is used for acknowledgement.
v. S: This bit contains a sequence number of the frame to detect
re-transmission. As stop and wait protocol is used, one bit is
sufficient.
vi. Checksum: This 8 bit field contains checksum to detect
errors in header.
3. Data: This field can be 0 to 2744 bits long. It contains
data or control information coming from upper layers

Suggested Readings
• https://www.nielit.gov.in/sites/default/files/6.pdf - Wireless
Data Acquisition system for estimating the water quality of
Dal Lake in Srinagar
• https://www.informit.com/articles/article.aspx?p=361984&seq
Num=5 – Chapter 9 of Book Ad-hoc Wireless Networks:
Architectures and Principles.

Dr. Piyush Charan
Assistant Professor,
Department of ECE,
Integral University, Lucknow
Email: er.piyush.charan@gmail.com, piyush@iul.ac.in
20 March 2022
Dr. Piyush Charan, Dept. of ECE, Integral
University, Lucknow
62

Unit 1- Intro to Wireless Standards.pdf

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