Image Processing Reference
In-Depth Information
utilities such as power, gas, water supply, etc.; internal transportation systems to mention lifts,
escalators, etc.
In terms of the QoS requirements imposed on the ield area networks, building automation systems
differ considerably from their counterparts in industrial automation, for instance. There is seldom
a need for hard real-time communication; the timing requirements are much more relaxed. Traf-
fic volume in normal operation is low. Typical traffic is event driven, and mostly uses peer-to-peer
communication paradigm. Fault-tolerance and network management are important aspects. As with
industrial fieldbus systems, there are a number of bodies involved in the standardization of tech-
nologies for building automation, including the field area networks. he communication architecture
supporting automation systems embedded in the buildings has typically three levels: field, control,
and management levels. he ield level involves operation of elements such as switches, motors, light-
ing cells, dry cells, etc. he peer-to-peer communication is perhaps most evident at that level; toggling
a switch should activate a lighting cell(s), for instance. The automation level is typically used to
evaluate new control strategies for the lower level in response to the changes in the environment;
reduction in the day light intensity, external temperature change, etc. LonWorks [], BACnet [],
and EIB/KNX [-] are open system networks, which can be used at more than one level of the
communication architecture. A round up of LonWorks will be provided in the following, as the most
widely used in building automation specialized field area network.
LonWorks (EIA-), a trademark of Echelon Corp. [], employs LonTalk protocol which imple-
ments all seven layers of the ISO/OSI reference model. The LonTalk protocol was published as a
formal standard [], and revised in [].
In EIA-, layer supports various communication media-like twisted pair cables ( kbps
(EIA-.) or . Mbps), power line communication ( kbps, EIA-.), radio frequency chan-
nel, infrared connections, fiber-optic channels (. Mbps), as well as IP connections based on the
EIA- protocol standard [] to tunnel EIA- data packets through IP (Intranet, Internet) net-
works. A p-persistent CSMA bus arbitration scheme is used on twisted pair cables. For other
communication media, the EIA- protocol stack uses the arbitration scheme defined for the very
media.
The EIA- layer supports a variety of different addressing schemes and advanced routing capa-
bilities. he entire routable address space of a LonTalk network is referred to as the domain. A domain
is restricted to subnets; a subnet allows for up to nodes. he total number of addressable nodes
in a domain can reach ; up to
domains can be addressed. Domain gateways can be built
between logical domains to allow communication across domain boundaries. Groups can be formed
to send a single data packet to a group of nodes using a multicast-addressed message. Routing is
performed between different subnets only. An EIA- node can send a unicast-addressed message
to exactly one node using either a unique -bit node identification
(Node ID)
address or the logical
subnet/node address. A multicast addressed message can be sent to either a group of nodes (group
address), or to all nodes in the subnet, or all nodes in the entire domain (broadcast address).
The EIA- layer supports four types of services. The unacknowledged service transmits the
data packet from the sender to the receiver. The unacknowledged repeated service transmits the
same data packet a number of times. he number of retries is programmable. he acknowledged ser-
vice transmits the data packet and waits for an acknowledgement from the receiver. If not received
by the transmitter, the same data packet is sent again. The number of retries is programmable. The
requested response service sends a request message to the receiver; the receiver must respond with a
response message, for instance, with statistics information. here is a provision for authentication of
acknowledged transmissions, although not very efficient.
Network nodes (which, typically, include Neuron chip, RAM/Flash, power source clock, network
transceiver, and input/output interface connecting to sensor and actuator) can be based on the Eche-
lon's Neuron chip series manufactured by Motorola, Toshiba, an Cypress; recently also based on other
platform-independent implementations such a LoyTec LC controller. he Neuron chips-based
