In the previous tutorial, reference architecture for IOT was compared with OSI and TCP-IP models and various data communication protocols for different layers of IOT architecture were mentioned. In this tutorial, the physical and data link layer protocols will be discussed in details.
The physical and data link layer comprises of the IOT objects and physical networks connecting them with other objects or network. The constituent bits of the original data or information are encoded and decoded at this layer and exchanged over a wired or wireless physical link. There are many protocols and standard technologies specified by different bodies and organizations for physical and network access protocols. These protocols and technologies suits variable applications and network sites. Some of the popular physical and data link layer protocols and standards are as follow –
• Bluetooth Low Energy
• Wi-Fi Direct
• Wireless HART
• IEEE 802.11.ah
• IEEE 802.15.4e
• ISA 100.11a
• EPC Global
• EC-GSM-IOT (Extended Coverage GSM-IOT)
• LTE-MTC (LTE-Machine Type Communication)
• Cellular (GPRS/2G/3G/4G/5G)
In this tutorial, popular standards and protocols nowadays used for interconnecting computers and mobile devices are discussed. These protocols are so widely used that they are ubiquitous in urban and metropolitan connectivity. These protocols are as follow –
2) Bluetooth 4.0
4) Wi-Fi Direct
1) Ethernet – Ethernet is most popular wired networking technology. It is widely used for connecting computers in a Personal Area Network (PAN), Home Area Network (HAN), Local Area Network (LAN), Wide Area Network (WAN) and Metropolitan Area Network (MAN). It is based on IEEE 802.3 standard. Within an IOT system, Ethernet can be used to connect stationary or fixed IOT devices. Like, it can be used to connect sensor networks in an industry, appliance control circuits in a home automation system or IOT devices in an office automation system.
The data transfer rate in Ethernet can be up to 10 Giga Bits per Second (Gbit/s) for cat-6 cables. The data speed over Ethernet depends on the cable type and can be limited by the network administrator. There may be fiber optic, co-axial or twisted pair cables used for Ethernet networking. The Ethernet has very low latency which makes it suitable for mission critical IOT applications where devices may be co-located or located in a long range.
2) Bluetooth Low Energy (BLE) – Bluetooth is a wireless technology standard for exchanging data over short distances among fixed and mobile devices, creating a personal area network (PAN) with high level of security. Bluetooth Low Energy, also known as Bluetooth Smart is developed and proposed by the Bluetooth Special Interest Group. BLE is low power version of Original 2.4 GHz Bluetooth. BLE was introduced as Bluetooth 4.0 in year 2011.
BLE has been designed to transfer low volumes of data at high speed (1Mbps) where one device might be connected to several devices in a star topology. BLE has a range limited to 100 Meter so, it usually suits for Personal Area Network (PAN). The devices connected through BLE go in sleep mode when not transmitting data. When connected, BLE devices may have connection time for only few milliseconds compared to average time of 100 Milli Seconds in Classic Bluetooth. Due to short connection time and high data rate, BLE is extremely power efficient compared to any other competing protocols.
Architecture of Bluetooth Low Energy (BLE) Protocol
BLE is designed for IOT devices that could be powered for few years on a small battery. Both physical and data link layers of OSI model are implemented on Bluetooth Low Energy. The BLE protocol stack has two parts – controller and host. In the architecture, the physical and link layer are implemented in the controller part. The controller is typically a SOC (System on Chip) with a radio on Bluetooth device. The rest of the things like GAP, GATT services, security manager are included in the host part. At a minimum, the GAP (Generic Access Profile) service in Bluetooth enables the BLE device to observe and connect to the other BLE devices (only when required). The GATT (Generic Attribute Profile) service in Bluetooth LE enables other devices to access the services and characteristics that are present in that Bluetooth device.
The BLE protocol stack is similar to the stack used for classic Bluetooth technology but BLE is not compatible with the classic Bluetooth. The major difference is that BLE does not support data streaming. Instead, it only supports quick transfer of small packets of data (packet size is small) with a data rate of 1 Mbps.
There are two types of devices in BLE – master and slave. The master acts as a central device that can connect to various slaves. Considering an IOT scenario, a phone or PC may serve as the master device and smart lock with BLE embedded acts as slave device. The master device controls the slave based on the commands given by it. In such cases, Slave must be very power efficient.
Whereas, in classic Bluetooth, the connection is on all the time even if no data transfer is going on. Also, Classic Bluetooth supports 79 data channels (with 1 MHz channel bandwidth) whereas BLE supports 40 channels with 2 MHz channel bandwidth (double of classic Bluetooth).
The BLE protocol stack also supports IP based communication.
3) Wi-Fi – Proposed by Wi-Fi Alliance, Wireless Fidelity (Wi-Fi) is a standard for Wireless Local Area Networks (WLAN). It is based on IEEE 802.11 standard with various version numbers indicated as a, b, c, g, n etc where a to n are latest versions. The Wi-Fi uses 2.4, 3.6, 5 and 60 GHz radio frequency bands and can have data rates from 2 Mbps (for Legacy 802.11) to 1.73 Gbps (for 802.11ac wave 2). The quite common 802.11 n has data speed up to 450 Mbps.
Through Wi-Fi, a device connects to a router configured as hotspot or network access point and other Wi-Fi enabled devices connect to the device through the access point. The major drawbacks with Wi-Fi networking are latency and poor security. It is easier to hack a Wi-Fi hotspot and gain access to physical link medium. However, a Wi-Fi network can be secured using WPA types and beacon packets management.
The Wi-Fi also allows ad-hoc communication where Wi-Fi enabled devices can directly communicate without access point or router. For this, the devices need to share internet connection using ad hoc and configure themselves as hotspot or virtual access points. Wi-Fi is widely used for networking computers, laptops and mobile devices. In IOT systems, it can be used for setting up Personal Area Networks (PAN), Local Area Network (LAN) and Wide Area Network (WAN).
The range of any Wi-Fi hotspot can be up to 100 Meter. The coverage area of a Wi-Fi network can be extended using Multi-hop Routing. In Multi-hop Routing, one node (hotspot) can use another node (hotspot) as relay thereby increasing the total coverage area of the network.
4) Wi-Fi Direct – Wi-Fi direct is a pear to pear version of Wi-Fi standard. It allows two devices to setup communication without any router or access point. Wi-Fi Direct is a single hop standard so, its range cannot be extended. Nowadays, Wi-Fi Direct is widely used in Laptops, Mobile devices, Camera, Televisions and Game Consoles. It is the Wi-Fi Direct in smart phones which allow them to configure as internet hotspot and share internet connection. The Wi-Fi Direct has a range limited to 100 Meter.
5) WPA/WPA2/WPA3 – Wireless Protected Access (WPA) is a security protocol for Wi-Fi standard. It was proposed considering vulnerability of Wi-Fi networks. It is based on IEEE 802.11i standard and uses 64-bit or 128 bit encryption key to secure data. WPA standard was followed by WPA2 and WPA2 will be replaced by WPA3 which will have 192-bit encryption to secure data over Wi-Fi network. While Wi-Fi Direct allowed using Wi-Fi standard for Personal Area Network (PAN) applications, WPA standards have made Wi-Fi networks secure enough to be used for WLAN based IOT applications.
These standards and protocols are most ubiquitous among all others and are widely used for connecting computers, consumer appliances and mobile devices together. In the next tutorial, the discussion on physical and data link layer protocols will be continued.
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