Internet of Things (IoT) and its protocols.

Networking Protocols  and  Standards  for Internet  of  Things 

Internet  of  Things  (IoT)  and its  protocols  are  among the  most  highly funded topics  in both industry  and  academia. The  rapid evolution of  the  mobile  internet, mini-  hardware manufacturing, microcomputing, and  machine  to  machine  (M2M)  communication  has  enabled the  IoT  technologies. According  to Gartner, IoT  is  currently on the  top of  their  hype-cycle,  which implies  that  a  large  amount  of  money is  being  invested on  it  by the  industry. Billions  of  dollars are  being spent  on IoT  enabling  technologies  and  research  while much  more is expected  to  come in the  upcoming years.

IoT  technologies  allow  things, or  devices  that  are  not  computers,  to act  smartly and make collaborative decisions that  are beneficial  to  certain  applications. They allow  things  to hear, see, think or  act  by allowing  them  to communicate  and coordinate  with others  in order  to  make decisions  that  can be  as  critical  as  saving lives  or  buildings. They transform "things"  from  being passively computing and  making individual  decisions  to actively and ubiquitously communicating and collaborating to  make  a  single  critical  decision. The  underlying technologies of  ubiquitous  computing, embedded  sensors,  light  communication and  internet  protocols  allow IoT  to provide  its  significant, however, they  impose  lots  of  challenges  and introduce  the  need for specialized standards  and  communication protocols.

IoT  Ecosystem

Figure  1  shows a 7-layer  model  of  IoT  ecosystem. At  the  bottom  layer  is  the  market  or application  domain, which may be  smart  grid, connected home, or  smart  health,  etc.  The  second layer  consists of  sensors  that  enable  the application.  Examples of  such  sensors are temperature sensors,  humidity  sensors,  electric utility  meters,  or  cameras.  The  third layer consists  of interconnection layer  that  allows  the  data  generated by sensors  to be  communicated,  usually  to a computing facility, data  center, or  a  cloud. There  the  data  is  aggregated with other  known data sets such  as  geographical  data, population data, or  economic  data. The  combined data  is  then analyzed using  machine  learning and  data  mining techniques.  To enable  such large  distributed applications,  we  also need the  latest  application  level  collaboration and  communication software, such as, software  defined networking (SDN), services  oriented architecture  (SOA), etc. Finally, the top  layer  consists of  services that  enable  the  market  and  may  include energy  management, health management, education,  transportation etc. In addition  to these  7  layers  that are  built on the top  of  each  other,  there are security  and  management  applications that  are required  for  each of  the  layers  and are,  therefore, shown on the  side.

In  this paper,  we concentrate on  the interconnection  layer.  This layer  itself  can  be shown  in  a multi-layer  stack as  shown in  Figure  2.  We  have  shown only the  datalink,  network, and transport/session  layers.  The datalink  layer  connects two  IoT  elements which  generally  could  be two sensors  or  the  sensor  and the  gateway device  that  connects  a set  of  sensors to  the Internet.

Often  there is a need  for  multiple  sensors to  communicate and  aggregate information  before getting to the  Internet. Specialized protocols  have  been designed for  routing among sensors  and are  part  of  the  routing layer. The  session  layer  protocols  enable messaging  among  various elements  of  the  IoT  communication  subsystem. A  number  of  security and  management  protocols have  also been developed for  IoT  as  shown in the  figure.

 IoT Data Link  Protocol

1. IEEE  802.15.4

 IEEE  802.15.4 is  the  most  commonly used IoT  standard for  MAC. It  defines a frame format, headers  including source  and destination addresses, and how  nodes  can communicate  with each other.  The  frame  formats  used  in  traditional networks  are  not  suitable  for low  power  multi-hop networking  in IoT  due  to  their  overhead. In 2008,  IEEE802.15.4e  was  created to extend IEEE802.15.4 and support  low  power  communication. It  uses  time  synchronization and channel hopping to enable  high  reliability,  low  cost  and  meet  IoT  communications  requirements. Its specific MAC  features can  be summarized  as follows

•  Slotframe  Structure:  IEEE  802.15.4e  frame  structure  is  designed for  scheduling and telling each  node  what  to do. A  node  can sleep,  send, or  receive  information. In the  sleep mode, the  node  turns  off  its radio  to  save power  and  stores all  messages that  it  needs  to send at  the  next  transmission opportunity. When transmitting,  it  sends  its  data  and waits for  an acknowledgment.  When receiving, the  node  turns  on  its  radio before  the  scheduled receiving time, receives  the  data, sends  an acknowledgement, turn off  its  radio, delivers the  data  to the  upper  layers  and goes  back to sleep. 

•  Scheduling:  The  standard does  not  define  how  the  scheduling  is  done  but  it  needs  to be built  carefully  such  that  it handles  mobility  scenarios.  It  can  be centralized  by  a manager node  which is  responsible  for  building the  schedule, informing others  about  the  schedule and other  nodes  will  just  follow  the  schedule.

 •  Synchronization:  Synchronization  is  necessary to  maintain nodes’  connectivity  to  their neighbors  and to the  gateways. Two approaches  can be  used:  acknowledgment-based or frame-based  synchronization. In  acknowledgement-based mode, the  nodes  are  already  in communication and they  send acknowledgment  for  reliability  guarantees,  thus can  be used to maintain connectivity  as  well. In frame-based mode,  nodes  are  not communicating and hence, they send  an empty frame  at  pre-specified  intervals (about  30 second typically).

  •  Channel Hopping:  IEEE802.15.4e  introduces  channel  hopping  for  time slotted  access  to the  wireless  medium.  Channel  hopping requires  changing the  frequency  channel  using a pre-determined random  sequence. This  introduces  frequency  diversity and reduces  the effect  of  interference and  multi-path fading. Sixteen channels  are available  which  adds  to network  capacity  as two  frames over  the same link  can  be transmitted  on  different frequency  channels at  the same time. 

•  Network formation:  Network formation  includes  advertisement  and joining components. A  new  device  should  listen for  advertisement  commands  and upon receiving at  least  one  such command, it  can  send a  join  request  to  the  advertising device.  In a centralized  system,  the join  request  is routed  to  the manger  node and  processed  there while  in distributed systems, they  are processed  locally.  Once  a device  joins the network and  it  is  fully  functional,  the  formation  is  disabled  and  will be  activated  again  if  it receives another  join  request. 

2. WirelessHART

WirelessHART  is  a  datalink protocol  that  operates  on the  top of  IEEE  802.15.4 PHY  and adopts Time  Division  Multiple  Access  (TDMA) in  its  MAC.  It  is a  secure  and  reliable MAC  protocol that  uses  advanced encryption to  encrypt  the  messages  and calculate  the  integrity in order  to offer reliability.  The  architecture,  as  shown  in  Figure  3  consists of  a network  manager,  a security manager,  a gateway  to  connect  the wireless network  to  the wired networks,  wireless devices  as field  devices,  access points,  routers and adapters.

Easy “no-programming” tag-name data access:

• Digital process values and engineering units
• Range values and other instrument properties
• Continuous device status and diagnostics

   Easy connection to HART Devices:

• Directly connect to HART devices, or
• Connect through HART-capable I/o Systems
• Communicate with one or thousands of HART devices

   Powerful Client-Server Architecture:

• Ethernet-TCP/IP network access to HART devices
• Client Application on same PC or anywhere on the Ethernet
• Multiple clients can simultaneously access same HART device
• OPC Interfaces for process values and operation parameters
• HART Pass-through interface for device specific parameters

   Easy to use:

• Develop OPC client applications without being a HART expert
• Modular architecture allows easy integration of your own I/O
• "Browse" and "Learn" features automatically connect HART networks and devices.

 3. Z-Wave

Z-Wave is a  low-power  MAC  protocol  designed  for  home  automation and  has  been used  for  IoT communication, especially for  smart  home  and small  commercial  domains. It  covers  about  30meter  point-to-point  communication  and  is suitable for  small  messages in  IoT  applications,  like light  control, energy control, wearable  healthcare  control  and  others.  It uses  CSMA/CA  for collision  detection  and  ACK  messages for  reliable  transmission.  It  follows  a master/slave architecture  in which the  master  control  the  slaves, send them  commands, and handling scheduling of  the  whole  network.

4. Bluetooth  Low  Energy Bluetooth  low  energy or  Bluetooth smart  is  a  short  range  communication  protocol  with PHY  and MAC layer  widely used  for  in-vehicle networking.  Its low  energy  can  reach  ten  times less than the classic Bluetooth  while its latency  can  reach  15  times.  Its access control  uses a contentionless MAC  with  low  latency  and  fast  transmission.  It  follows  master/slave  architecture  and  offers two  types of  frames:  adverting  and  data frames.  The Advertising  frame is used  for  discovery and is sent  by  slaves on  one  or  more of  dedicated  advertisement  channels.  Master  nodes sense advertisement  channels to  find  slaves  and  connect  them.  After  connection,  the master  tells the slave  it’s waking  cycle and  scheduling  sequence.  Nodes are usually  awake  only when they are communicating and they  go to sleep  otherwise  to  save  their  power.

5. Zigbee  Smart  Energy   ZigBee smart  energy  is  designed  for  a large range of  IoT  applications  including smart  homes, remote  controls  and healthcare  systems. It  supports  a  wide  range  of  network topologies  including star,  peer-to-peer,  or  cluster-tree. A  coordinator  controls  the  network and is  the  central  node  in a star  topology,  the  root  in  a  tree  or  cluster  topology and may be  located anywhere  in peer-to-peer. ZigBee standard  defines  two  stack  profiles:  ZigBee and  ZigBee Pro.  These stack  profiles support full  mesh networking and work with different  applications  allowing implementations  with  low memory and processing  power. ZigBee  Pro offers  more  features  including  security using symmetric-key  exchange,  scalability  using  stochastic  address  assignment,  and  better performance using  efficient  many-to-one  routing  mechanism.

6. DASH7   DASH7 is  a  wireless  communication  protocol for active  RFID  that operates  in  globally  available Industrial Scientific  Medical  (ISM) band  and  is  suitable  for IoT  requirements.  It is  mainly designed  for  scalable,  long range  outdoor  coverage  with higher  data  rate  compared to traditional ZigBee.  It  is  a  low-cost  solution that  supports  encryption and IPv6  addressing.  It  supports  a master/slave  architecture  and is  designed for  burst, lightweight, asynchronous  and transitive traffic.  Its MAC  layer  features can  be  summarized  as follows

•  Filtering:  Incoming  frames are filtered  using  three processes;  cyclic redundancy  check (CRC) validation,  a  4-bit  subnet  mask, and link quality  assessment.  Only  the frames that pass all  three checks are  processed  further. 

•  Addressing:  DASH7 uses  two types  of  addresses:  the  unique  identifier  which is  the  EUI64 ID  and dynamic  network identifier  which  is  16-bit  address  specified  by the  network administrator.

 •  Frame format:  The  MAC  frame  has  a  variable  length of  maximum  255  bytes  including addressing,  subnets, estimated power  of  the  transmission and some  other  optional  fields.


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