wilamowski-b-m-irwin-j-d-industrial-communication-systems-2011

7-4 Industrial Communication Systems
quality-of-service (QoS) parameters. It supports dynamic frequency selection, transmit power control,
and spectrum and energy management. Besides enhanced security measures, radio resource management
is also incorporated.
Bluetooth [B04] is a low-power short-range communication technology designed to connect portable
electronic devices like phones, PDAs, and keyboards. Whenever two Bluetooth-enabled devices
come within range of one another, they seamlessly establish a small network. Although the maximum
possible data rate is only 1.Mbps, low-cost and low-power capabilities of Bluetooth have stimulated its
penetration in the market.
Infrared is a point-to-point, ultra low-power, ad hoc data transmission standard designed to operate
over a distance of 1.m and is extendable to 2.m with high power. It can achieve data rates up to 16.Mbps.
Infrared is cheaper than Bluetooth technology, and both have their own advantages and disadvantages.
HomeRF is a short-range communication technology intended for small area such as homes or small
buildings. HomeRF uses frequency hopping spread spectrum (FHSS) while operating at 2.4.GHz and
offers data rates up to 10.Mbps.
ZigBee standard is a short-range wireless communication standard for PANs. It offers data rate up
to 250.kbps at 2.4.GHz, 40.kbps at 915.MHz, and 20.kbps at 868.MHz with a range of 10–100.m. ZigBee
uses IEEE 802.15.4 as physical and medium access control (MAC) layers. Upper layers as well as ZigBee
security architecture are defined by the ZigBee standard.
7.2 Protocol Stack
7.2.1 transport Layer
Transport layer protocols are responsible for end-to-end delivery of data. Transmission control protocol
(TCP) is a dominant transport layer protocol for wired networks. TCP is responsible for congestion and flow
control, and reliable and in-order delivery of packets. The unique characteristics of wireless ad hoc networks
such as lack of infrastructure, mobility, shared bandwidth [SAHS03], contention, and high bit error rate
(BER) as well as the design principles of TCP motivate to design customized transport layer protocols.
7.2.1.1 Why TCP Does Not Suit Ad Hoc Networks?
The failure of TCP to work well in ad hoc networks is because of the following known problems:
• In layered architectures, TCP implicitly assumes that packet loss is caused due to collisions.
Whereas, collisions in ad hoc wireless networks are one of the possible causes of packet loss,
although there are also other potential causes such as fading, varying link quality [CZWF04],
interference, and noise.
• Two communicating nodes as well as other nodes sharing the same medium contend for the medium.
• The packet loss in wireless networks is comparatively higher, and loss of retransmitted packet
further degrades the performance.
7.2.1.2 transport Layer Protocols for Ad Hoc Networks
Transport layer protocols for ad hoc networks can broadly be classified into two major approaches
[MK04]; TCP variants and non-TCP variants.
The basic idea of TCP variants is to retain TCP as a transport layer protocol, because of its global
existence, and to suggest modifications in order to overcome the problems associated with wireless links
and mobility. TCP feedback (TCP-f) [F94] is customized in such a way that the sender is able to differentiate
between congestion and a lost link. In this way, the invocation of congestion control algorithm
is restricted, which in turn stops performance degradation. In case of link failure, the sender node is
explicitly notified by the network layer of the neighbor node. The sender stops sending further packets,
while all other nodes listening to these notifications invalidate these routes to avoid packet loss. Explicit
© 2011 by Taylor and Francis Group, LLC