This document discusses wireless sensor network protocols. It covers multi-hop routing, where sensor nodes act as relays to propagate data to the base station. Common routing protocols are discussed, including reactive protocols like AODV that establish routes on demand and proactive protocols like DSDV that maintain routing tables with periodic updates. MAC protocols help manage access to the shared wireless medium and examples covered include S-MAC and B-MAC. The OSI model layers and responsibilities are also summarized.

1. 18ECE304: Wireless Sensor Network
UNIT 3- Wireless Protocols
Prepared by
Dr. Mohit Kumar Singh,
Assistant Professor

2. WIRELESS PROTOCOLS (9)
Routing protocols, MAC protocols: Classification of MAC Protocols, S-MAC
Protocol, B-MAC protocol, IEEE 802.15.4 standard and ZigBee.

3.  Multi Hop:
 In the single-hop routing model all sensor nodes are able to communicate
directly with the sink device. This direct communication model is the
simplest approach, where all data travels a single hop to reach the
destination.
Fig.: Single-hop routing model (left) versus multi-hop routing model
(right).

4. However, in practical settings, this single-hop approach is unrealistic and a multi-hop
communication model must be used. The critical task of the network layer of all sensor
nodes is to identify a path from the sensor to the sink across multiple other sensor nodes
acting as relays.
Sensor networks often cover large geographic areas and radio transmission power should be
kept at a minimum in order to conserve energy; consequently, multi-hop communication is
the more common case for sensor networks.
In mesh topology, sensor nodes must not only capture and disseminate their own data, but
also serve as relays for other sensor nodes, that is, they must collaborate to propagate
sensor data towards the base station.
The task of finding a multi-hop path from a sensor node to the base station is called routing.
The process of establishing paths from a source to a sink is called routing and is a key
responsibility of the network layer.

5. OSI MODEL 1. Physical Layer : It is responsible for the actual physical
connection between the devices.
2. Data Link Layer : The data link layer establishes and
terminates a connection between two physically-connected
nodes on a network.
• Logical Link Control (LLC), which identifies network
protocols, performs error checking and synchronizes
frames.
• Media Access Control (MAC), which uses MAC
addresses to connect devices and define permissions to
transmit and receive data.
3. Network Layer: The main functions of Network Layer is
routing packets by discovering the best path across a
physical network i.e., selection of the shortest path to
transmit the packet, from the number of routes available. The
network layer uses network addresses (IP addresses) to
route packets to a destination node.

6. 4. Transport Layer : It is responsible for the End to End Delivery of the
complete message. The transport layer also provides the acknowledgement
of the successful data transmission and re-transmits the data if an error is
found.
5. Session Layer : The session layer creates communication channels, called
sessions, between devices. It is responsible for opening sessions, ensuring
they remain open and functional while data is being transferred, and closing
them when communication ends.
6. Presentation Layer : The presentation layer prepares data for the
application layer. It defines how two devices should encode, encrypt, and
compress data so it is received correctly on the other end.
7. Application Layer : The application layer is used by end-user software
such as web browsers and email clients. It provides protocols that allow
software to send and receive information and present meaningful data to
users.

7. WSN ROUTING
PROTOCOLs
Node
Centric
Routing
protocol
Data
Centric
Routing
protocol
Source
Initiated
Routing
protocol
Destination
Initiated
Routing
protocol
Classification of routing protocols
 The routing protocols define how nodes will communicate with each other
and how the information will be disseminated through the network.
 There are many ways to classify the routing protocols of WSN.
 The basic classification of routing protocols is shown below:

8. (a) Node Centric:
In node centric protocols the destination node is specified with some numeric
identifiers and this is not expected type of communication in wireless sensor
networks.
(b) Data centric:
In most of the wireless sensor networks, the sensed data or information is
far more valuable than the actual node itself.
Therefore, in data centric routing techniques the prime focus is on the
transmission of information specified by certain attributes rather than
collecting data from certain nodes.
In data centric routing the sink node queries to specific regions to collect
data of some specific characteristics.

9. (c) Destination initiated (Dst-initiated):
Protocols are called destination initiated protocols when the path setup
generation originates from the destination node.
(d) Source initiated (Src-initiated):
In these types of protocols the source node advertises when it has data to
share and then the route is generated from the source side to the
destination.

10. Data Transmission Techniques
In order to transmit data in sensor networks, there are two
techniques being used:-
 Flooding:
The data packet is broadcast to all other neighbours.
The process of broadcasting is continued till any one of two
following conditions is satisfied:
• The packet has reached successfully to its
destination.
• Maximum number of hops of a packet has reached.
The main advantages of flooding are ease of implementation
and simplicity.
The drawbacks are blindness of resources and overlapping
and implosion.

11.  Gossiping
Here, the sensor node, which is getting a data packet, transmits it to the
arbitrarily selected neighbour.
At the next turn, the sensing nodes again randomly pick another nodes and
sends data to it.
This process is continued again and again.
The broadcasting is not used in gossiping protocol as it was used in
flooding.
In this way, implosion issue can be avoided easily.
But delay is enhanced in this way.

12. The routing protocol is mainly categorized as:
1. Route discovery based routing protocols
2. Network organization based routing protocols
3. Operation based routing protocols
Categories of routing protocols

13. Route discovery based routing protocols
• They are classified on the basis of the process they used to discover the
routes.
i. Reactive Protocols
ii. Proactive Protocols
iii. Hybrid Protocols
Reactive Protocols:
• Activated just on demand.
• The routes are created on demand when queries are initiated.
• Do not maintain the whole network topology.
• It employs the on-demand routing methodology for formations of route
among network nodes. Path is established solitary when source node
want to direct packs of data and pre-set route is maintained as long as
the source node needs.

14. The most commonly used reactive routing protocols are as follows:
Ad hoc on demand distance vector routing AODV)
Dynamic source routing (DSR)
Proactive Protocols (Table Driven Routing Protocols):
• Maintains the routing tables for the complete network by passing the network
information from node to node .
• The routes are pre-defined prior to their use and even when there is no traffic
flow.
• They are also known as table driven routing protocols.
• Table-driven routing protocols each node maintains one or more tables
containing routing information to every other node in the network.

15. • All nodes update these tables so as to maintain a consistent and up-to-date view of the
network.
• When the network topology changes the nodes propagate update messages
throughout the network in order to maintain a consistent and up-to-date routing
information about the whole network.
• These routing protocols differ in the method by which the topology change information
is distributed across the network and the number of necessary routing-related tables.
• The most commonly used algorithm is as follows:
Destination-Sequenced Distance Vector (DSDV)
Wireless Routing Protocol (WRP)
Optimized link state routing (OLSR)
Hybrid routing protocols:
Hybrid Routing Protocols have the merits of proactive and reactive routing
protocols by neglecting their demerits.

16. Network organization based routing protocols
i. Flat topology
ii. Hierarchical based routing
iii. Location-based routing (geo-centric)
Flat topology:
Flat topology treats all nodes equally.
Flat topology is mainly for homogeneous networks where all nodes
are of same characteristics and have same functionality.
Examples are:
• Gradient based routing (GBR)
• Cougar
• Constrained anisotropic diffusion routing (CADR)
• Rumour routing (RR)

17. Hierarchical based routing
Mostly heterogeneous networks apply hierarchical routing protocols where
some nodes are more advance and powerful than the other nodes.
In hierarchical (clustering) routing protocols, sometimes the nodes are grouped
together to form a cluster.
The cluster head is assigned to every cluster, which after data aggregation from
all the nodes, communicates with the base node.
The clustering scheme is more energy efficient and more easily manageable.
Examples are:
• Threshold sensitive energy efficient sensor network (TEEN)
• Adaptive threshold sensitive energy efficient sensor network (APTEEN)
• Low energy adaptive clustering hierarchy (LEACH)
• The power-efficient gathering in sensor information systems (PEGASIS)
• Virtual grid architecture routing (VGA)
• Self-organizing protocol (SOP)
• Geographic adaptive fidelity (GAF)

18. Location-based routing (geo-centric)
In location based routing the nodes have capability to locate their present
location using various localization protocols.
Location information helps in improving the routing procedure and also
enables sensor networks to provide some extra services.
Location information is required in order to calculate the distance between
two particular nodes so that energy consumption can be estimated and
reduced.
Examples are:
 SPEED(Protocol for Real-Time Communication in Sensor Networks)
 Geographical and energy aware routing (GEAR)
 SPAN

19. Operation based routing protocols
According to the operational basis the routing protocols are classified
as:
Multipath routing protocols
Query based routing
Negotiation based routing
QoS based routing
Coherent routing

20. Multipath routing protocols:
Multi-path routing protocols provide multiple paths for data to reach the
destination providing load balancing, low delay and improved network
performance as a result.
The multiple routing protocol also provide alternate path in case of failure
of any path.
To keep the paths alive some sort of periodic messages have to be sent
after some specific intervals hence multiple path routing is not more energy
efficient.
Dense networks are more interested in multiple path networks.

21. Query based routing:
These type of routing protocols are mostly receiver-initiated.
The sensor nodes will only send data in response to queries generated by
the destination node.
The destination node sends query of interest for receiving some information
through the network and the target node sense the information and send
back to the node that has initiated the request.
The examples are:
Sensor protocols for information via negotiation (SPIN)
Directed diffusion (DD)
COUGAR

22. Negotiation based routing:
In these types of protocols to keep the redundant data transmission level
at minimum.
The sensor nodes negotiate with the other nodes and share their
information with the neighbouring nodes about the resources available.
Data transmission decisions are made after the negotiation process.
Examples are :
Sensor protocols for information via negotiation (SPAN)
Sequential assignment routing (SAR)
Directed diffusion (DD)

23. QoS based routing:
To get good Quality of Service these protocols are used.
QoS aware protocols try to discover path from source to sink that satisfies
the level of metrics related to good QoS like throughput, data delivery,
energy and delay but also making the optimum use of the network
resources.
Examples are:
Sequential assignment routing (SAR)
SPEED
Multi path and Multi SPEED (MMSPEED)

24. Coherent routing:
In coherent data processing routing protocol, the nodes perform minimum
processing(time stamping, data compression etc.) on the data before
transmitting it towards the other sensor nodes or aggregators.
Aggregator performs aggregation of data from different nodes and then
passes to the sink node.

25. On-demand protocol
Ad Hoc On-Demand Distance Vector (AODV) Protocol
 AODV relies on a broadcast route discovery mechanism.
 The path discovery process of AODV is initiated whenever a source node
needs to transmit data to another node.
 To find a path to the destination, the source node broadcasts a route request
(RREQ) packet to its neighbours.
 The route request (RREQ) packet contains the addresses of the source and
the destination, a hop count value, a broadcast ID, and two sequence
numbers.

26. The neighbours in turn broadcast the packet to their neighbours till it
reaches an intermediate node that has a recent route information about the
destination or till it reaches the destination.
When a node forwards a route request packet to its neighbours, it also
records in its tables the node from which the first copy of the request came.
This information is used to construct the reverse path for the route reply
packet.
Upon receiving an RREQ packet, a node that possesses a current route to
the specified destination responds by sending a unicast route reply (RREP)
message directly back to the neighbour from which the RREQ was
received.
Otherwise the RREQ is rebroadcast to the intermediate node’s neighbours.
A node discards a route request packet that it has already seen.

27. As the route reply packet traverses back to the source , the nodes along
the path enter the forward route into their tables.
If the source moves then it can reinitiate route discovery to the destination.
If one of the intermediate nodes move then the moved nodes neighbour
realizes the link failure and sends a link failure notification to its upstream
neighbours and so on till it reaches the source upon which the source can
reinitiate route discovery if needed.

28. Fig. : Route discovery in AODV

29. Dynamic Source Routing
• The Dynamic Source Routing (DSR) protocol employs route discovery
and route maintenance procedures similar to AODV.
• In DSR, each node maintains a route cache with entries that are
continuously updated as a node learns new routes.
• A node wishing to send a packet will first inspect its route cache to see
whether it already has a route to the destination.
• If there is no valid route in the cache, the sender initiates a route
discovery procedure by broadcasting a route request packet, which
contains the address of the destination, the address of the source, and a
unique request ID.

30. • As this request propagates through the network, each node inserts its
own address into the request packet before rebroadcasting it. As a
consequence, a request packet records a route consisting of all nodes it
has visited.
• When a node receives a request packet and finds its own address
recorded in the packet, it discards this packet and does not rebroadcast it
further.
• Once a request packet arrives at the destination, it will have recorded the
entire path from the source to the destination.
• Unlike AODV, each packet in DSR carries route information, which allows
intermediate nodes to add new routes proactively to their own caches.

31. Proactive Protocols
Destination-Sequenced Distance Vector (DSDV)
 In distance-vector algorithms, every node i maintains a list of distances
{𝑑𝑖𝑗
𝑥
} for each destination x via each neighbour j.
 Then, node i selects node k as the next hop for packet forwarding if
{𝑑𝑖𝑘
𝑥
} = min{𝑑𝑖𝑗
𝑥
}.
 This information is stored in a routing table, along with a sequence
number for each entry, where this number is assigned by the
destination node.
 The purpose of the sequence numbers is to allow nodes to distinguish
existing routes from new ones in order to prevent routing loops.

32.  Each node broadcasts updates to the routing table periodically, but also
immediately whenever significant new information becomes available.
 DSDV uses two types of packets to share its routing table content. A full
dump contains all available routing information, whereas an incremental
packet contains only information that has changed since the last full dump.
 Incremental packets are typically much smaller than full dumps, therefore
reducing the control overhead of DSDV.
 When a node receives an incremental packet, the received information is
compared with the node’s current knowledge and a route indicated in the
packet replaces the corresponding route in the node’s table if the packet’s
route has a more recent sequence number.

33.  A packet’s route also replaces the node’s route in its table if the
sequence numbers are identical, but the packet’s route has a shorter
distance.
Fig.: Example of a network with a moving node.

34. The Wireless Routing Protocol (WRP)
 The Wireless Routing Protocol (WRP)is a table-based distance-vector routing protocol.
 Each node in the network maintains a Distance table, a Routing table, a Link-Cost table and a
Message Retransmission list.
 The Distance table of a node x contains the distance of each destination node y via each
neighbour z of x.
 It also contains the downstream neighbour of z through which this path is realized.
 The Routing table of node x contains the distance of each destination node y from node x, the
predecessor and the successor of node x on this path.
 It also contains a tag to identify if the entry is a simple path, a loop or invalid.
 Storing predecessor and successor in the table is beneficial in detecting loops and avoiding
counting-to-infinity problems.
 The Link-Cost table contains cost of link to each neighbour of the node and the number of
timeouts since an error-free message was received from that neighbour.
 The Message Retransmission list (MRL) contains information to let a node know which of its
neighbour has not acknowledged its update message and to retransmit update message to
that neighbour.
 Node exchange routing tables with their neighbours using update messages periodically as
well as on link changes.

35.  The nodes present on the response list of update message (formed using MRL) are
required to acknowledge the receipt of update message.
 If there is no change in routing table since last update, the node is required to send an
idle Hello message to ensure connectivity.
 On receiving an update message, the node modifies its distance table and looks for
better paths using new information.
 Any new path so found is relayed back to the original nodes so that they can update
their tables.
 The node also updates its routing table if the new path is better than the existing path.
 On receiving an ACK, the mode updates its MRL.
 A unique feature of this algorithm is that it checks the consistency of all its neighbors
every time it detects a change in link of any of its neighbors.
 Consistency check in this manner helps eliminate looping situations in a better way and
also has fast convergence.

36. Table: Comparison of routing protocols.

37. Medium Access Control
 In most networks, multiple nodes share a communication medium for transmitting their
data packets.
 The wireless medium must be shared by multiple network devices, therefore a
mechanism is required to control access to the medium. This responsibility is carried out
by the second layer of the OSI reference model called the data link layer.
 The medium access control (MAC) protocol is primarily responsible for regulating access
to the common medium.
Fig.: The MAC layer in the IEEE 802
reference model.
 The MAC layer operates directly on top of the
physical layer, thereby assuming full control over
the medium.
 The main function of the MAC layer is to decide
when a node accesses a shared medium and to
resolve any potential conflicts between competing
nodes.
 It is also responsible for correcting communication
errors occurring at the physical layer and
performing other activities such as framing,
addressing, and flow control.

38.  Most sensor networks and sensing applications rely on radio transmissions in
the unlicensed ISM band, which may result in communications significantly
affected by noise and interferences.
 The choice of MAC protocol has a direct bearing on the reliability and
efficiency of network transmissions due to these errors and interferences in
wireless communications.
 Other concerns include signal fading, simultaneous medium access by multiple
nodes, and asymmetric (unidirectional) links.
 Since energy efficiency is a primary concern in a wireless sensor network, it
also affects the design of the MAC protocol.

39. MAC protocols can be classified in two groups according to the approach
used to manage medium access: contention based and schedule based.
Contention-based protocols
It allow nodes to access the medium simultaneously, but provide
mechanisms to reduce the number of collisions and to recover from
such collisions.
Medium access is distributed; there is no need for central
coordination for the nodes to use the medium.
 Sensor MAC (S-MAC)
 Berkeley Media Access Control for Low-Power Sensor Networks (B-MAC)
 Predictive Wake-UP MAC (PW-MAC).

40. Schedule Based
Protocols arbitrate medium access by defining an order (called
schedule) for nodes to transmit, receive, or be inactive.
Generally speaking, each node communicates during specific time
slot(s) and can be inactive the rest of the time.
Schedule-based protocols use a variety of approaches like
 Low-Energy Adaptive Clustering Hierarchy (LEACH)
 Power-Efficient and Delay-Aware Medium Access Protocol
(PEDAMACS).
 Priority-Based MAC Protocol for Wireless Sensor Networks
(PRIMA)

41. Characteristics of MAC protocols in WSN
Most MAC protocols are built for fairness, that is, everybody should get
an equal amount of resources.
Instead, wireless nodes are mostly concerned with energy consumption
and sensing applications may value low latency or high reliability over
fairness.
Energy Efficiency:
Sensor nodes must operate using finite energy sources (batteries),
therefore MAC protocols must be energy-efficient.
Since MAC protocols have full control over the wireless radio, their
design can contribute significantly to the overall energy requirements of
a sensor node.
A common technique to preserve energy is dynamic power
management (DPM), where a resource can be moved between
different operational modes such as active, idle, and asleep.

42. Scalability
Adaptability
Reliability
Sensor MAC (S-MAC)
The major sources of energy waste are:
Collision: When a transmitted packet is corrupted it has to be
discarded, and the follow-on retransmissions increase energy
consumption. Collision increases latency as well.
Overhearing: It means that a node picks up packets that are
destined to other nodes.
Control packet overhead: Sending and receiving control packets
consumes energy too.
Idle listening: It means listening to receive possible traffic that is
not sent.

43. • The goal of the sensor MAC (S-MAC) protocol is to reduce
unnecessary energy consumption, while providing good scalability
and collision avoidance.
• S-MAC adopts a duty-cycle approach, that is, nodes periodically
transition between a listen state and a sleep state.
• Each node chooses its own schedule, though it is preferred when nodes
synchronize their schedules such that they listen or sleep at the same
time.
• The nodes using the same schedule are considered to belong to the
same virtual cluster, but no real clustering takes place.
• All nodes are free to communicate with nodes outside their clusters.

44. S-MAC uses novel techniques to reduce energy consumption and
support self configuration.
To reduce energy consumption in listening to an idle channel, nodes
periodically sleep.
Neighbouring nodes form virtual clusters to auto synchronize on
sleep schedules.
S-MAC also sets the radio to sleep during transmissions of other
nodes.
S-MAC applies message passing to reduce contention latency for
sensor network applications that require store and forward processing
as data move through the network.
This protocol tries to reduce energy consumption due to overhearing,
idle listening and collision.
A source node with an 802.11 like MAC consumes 2 to 6 times more
energy than S-MAC for traffic load with messages sent every 1 to 10s.

45. S-MAC tries to reduce wastage of energy from all four sources of
energy inefficiency.
Collision: by using Request to Send(RTS) and Clear to
Send(CTS).
Overhearing: by switching the radio off when there is no
transmission
Control Overhead: by message passing
Idle listening: by periodic listen and sleep
Components of S MAC
Periodic listen and sleep
Collision and Overhearing avoidance
Message passing

46. Fig.: Timing relationship between a receiver and
different senders.

47.  The listen/sleep scheme requires synchronization among neighbouring nodes.
 Neighbouring nodes need to periodically update each other their schedules.
 Updating schedules is accomplished by sending a SYNC packet.
 The SYNC packet includes the address of the sender and the time of its next
sleep.
 Receivers will adjust their timers immediately after they receive the SYNC packet.
 In order for a node to receive both SYNC packets and data packets, we divide its
listen interval into two parts.
 The first part is for receiving SYNC packets, and the second one is for receiving
RTS packets.
 If a sender wants to send a SYNC packet, it starts carrier sense when the receiver
begins listening.
 If it has not detected any transmission by the end of the time slot, it wins the
medium and starts sending its SYNC packet at that time. The same procedure is
followed when sending data packets.

48. Berkeley MAC (B-MAC)
B-MAC is a widely used WSN MAC protocol.
B-MAC features ultra low power operation.
It provides a flexible interface to obtain ultra-low power operation, effective
collision avoidance, and high channel utilization.
B-MAC employs an adaptive preamble to reduce idle listening.
It employs low-power listening (LPL) to minimize power consumption due to idle
listening.
Nodes have a sleep period, after which they wake up and sense the medium for
preambles (clear channel assessment – CCA).
If none is detected, the nodes go back to sleep. If there is a preamble, the nodes
stay awake and receive the data packet after the preamble.

49. When a node has a packet to send, it waits during a backoff time before checking
the channel.
 If the channel is clear, the node transmits; otherwise it begins a second
(congestion) backoff.
Each node must check the channel periodically using LPL (low-power listening); if
the channel is idle and the node has no data to transmit, the node returns to sleep.
The B-MAC preamble sampling scheme adjusts the interval in which the channel is
checked to equal the frame preamble size.
If a node wants to send a message, it first sends a preamble for at least the sleep
period in order for all nodes to detect it.
After the preamble, it sends the data packet. After the data packet (or data packet +
ACK) exchange, the nodes go back to sleep.

50. An advantage of using B-MAC in WSNs is that it does not use RTS,
CTS, ACK, or any other control frame.
No synchronization is required, and the protocol performance can be
tuned by higher layers to meet the needs of various applications.
The main disadvantage is that the preamble creates large overhead.
Fig.: B-MAC communication
example.

51. B-MAC Goals:
Low Power Operation
Effective Collision Avoidance
Simple Implementation
Small Code and RAM Size
Efficient Channel Utilization
Regardless of Data Rate
Reconfigurable by Network Protocols
Tolerant to Changing Network Conditions
Highly Scalable

52. The IEEE 802.15.4 standard was created for low-power devices
that operate in the 868 MHz, 915 MHz, and 2.45 GHz frequency
bands.
 The data rates supported by this standard are 20, 40, and 250
kbps; rather modest compared to other protocols such as IEEE
802.11 (e.g., IEEE 802.11a offers data rates of up to 54 Mbps).
Before this standard was developed, the ZigBee Alliance worked on
a low-cost communication technology for low data rates and low
power consumption.
The IEEE and the ZigBee Alliance ultimately joined forces and
ZigBee has become the commercial name for the IEEE 802.15.4
technology.
IEEE 802.15.4 and ZigBee

53. ZigBee standard was designed to meet the unique needs of
sensors and control devices.
Sensors don’t need high bandwidth but they do need low latency
and very low energy consumption for long battery lives and for
large device arrays.
Power needed for ZigBee nodes is very small i.e., 1mW (or less
power).
ZigBee protocol is supported solely by the ZigBee alliance that uses
the transport services of the IEEE 802.15.4 network specification.
ZigBee alliance includes hundreds of member companies like Ember,
Freescale, Chipcon, Invensys, Mitsubishi, CompXs, AMI
Semiconductors, ENQ Semi conductors etc. from semiconductor
and software developers to original equipment manufacturers.

54. ZigBee alliance defines the network, security and application layers
whereas IEEE 802.15.4 defines the physical and media access control
layers.
 ZigBee network can have up to 653356 devices.
The distance between these devices can be up to 50 meters, and each
node can relay data to other nodes in the network.
This results in very big network which are capable of covering
significant distances.
Fig.: Comparison between OSI
model and ZigBee
 In the Waspmote and SquidBee devices
this protocol is set using the Xbee ZB
Digi module.

55. There are three kinds of nodes in a ZigBee network:
Coordinator: is the “master” device, it governs all the network.
Routers: they route the information which are sent by the end devices.
End device: (the motes): they are the sensor nodes, the ones which gather
information from the environment.
Key 802.15.4 features include:
Real-time suitability by reservation of Guaranteed Time Slots (GTS).
Collision avoidance through CSMA/CA.
Integrated support for secure communications.
Power management functions such as link speed/quality and energy detection.
Support for time and data rate sensitive applications because of its ability to
operate either as CSMA/CA or TDMA access modes. The TDMA mode of
operation is supported via the GTS feature of the standard.
IEEE 802.15.4-conformant devices may use one of three possible frequency
bands for operation (868/915/2450MHz).

56. The ZigBee standard supports the use of the following optional
security services:
Encryption for data confidentiality
Device and data authentication
Replay (duplicate frame) protection

57. Fig.: Outline of the ZigBee Stack Architecture

58. The ZigBee protocol stack consists of four layers –
Physical (PHY) layer
 Medium access control (MAC) layer
 Network (NWK) layer
Application (APL) layer
The physical and MAC layers are governed by IEEE 802.15.4
standard.
The network and application layers are governed by the ZigBee
standard.

59. The Application layer (APL):
It consists of ZigBee device objects (ZDOs), Application support sub-layer (APS), and the
Application Framework.
ZigBee Device Objects (ZDO) are applications which employ network and application
support layer primitives to implement ZigBee End Devices, ZigBee Routers, and ZigBee
Coordinators. It provides an interface between the application objects, the device profile,
and the APS. The ZDO is responsible for initializing the APS, NWK, and the Security service
provider.
The APS provides an interface between the NWK and APL. It provides services for the
establishment and maintenance of security relationships. Services are provided via APS
data entity (APSDE: provides data transmission services between application entities) and
APS management entity (APMSE: provides security services, binding of devices and group
management).
Application Framework is the environment in which application objects are hosted (up to
254 can be defined). These are usually manufacturer defined application objects.

60. Network Layer (NWK)
The network layer ensures correct operation of the IEEE 802.15.4 MAC
sub-layer and provides a suitable service interface to the application
layer.
It interfaces with application layer via data entity (NLDE: generates
network level PDU, provides topology-specific routing and security) and
the management entity (NLME: configures a new device, starts a
network, performs joining, re joining and leaving a network functionality,
provides addressing capabilities, neighbour discovery, route discovery,
reception control and routing).
The NWK layer is responsible for the processing steps needed to
securely transmit outgoing frames and securely receive incoming
frames.

61. MAC Layer
The MAC layer’s responsibilities include controlling access to radio
channel via CSMA-CA mechanism, synchronization, and providing a
reliable transmission mechanism.
Physical Layer
It operates in two separate frequency ranges: 868/915 MHz and 2.4 GHz.
The physical layer is responsible for packet generation, packet reception,
data transparency, and power management.

62. Fig. Zigbee General APS Format
Applications of IEEE 802.15.4 :
Wireless sensor networks in the industry
Building and home automation
Remote controllers and interacting toys
Automotive networks

63. • Advantages of IEEE 802.15.4 :IEEE 802.15.4 has the following
advantages –
cheap cost
Long battery life
Quick installation
Simple
Extensible protocol stack
• Disadvantages of IEEE 802.15.4 :IEEE 802.15.4’s drawbacks include –
IEEE 802.15.4 causes interference and multipath fading.
Doesn’t employ a frequency-hopping approach.
Unbounded latency
Interference susceptibility

64. Table : WSNs MAC Protocol Comparison