Image Processing Reference
In-Depth Information
any path redundancy. Source routing is therefore only intended to be used for network diagnostics,
not any process-related messages.
.... Security
SecurityismandatoryinWirelessHART;thereisnooptiontoturnitofortoscaleitup/down.
WirelessHART provides end-to-end and hop-to-hop security measures through payload encryption
and message authentication on the network and data-link layers. However, the security measures are
transparent to the application layer.
WirelessHART uses CCM
∗
mode in conjunction with AES- block cipher, using symmetric
keys, for the message authentication and encryption.
A set of different security keys are used to ensure secure communication. A new device is pro-
visioned with a “Join key” before it attempts to join the wireless network. The Join key is used to
authenticate the device for a speciic WirelessHART network. Once the device has successfully joined
the network, the network manager will provide it with proper Session and network keys for further
communication.
The actual key generation and management are handled by a “plant wide” “Security manager,”
which is not specified by WirelessHART, but the keys are distributed to the Network devices by the
Network manager. A “Session key” is used on the Network layer to authenticate the end-to-end com-
munication between two devices (e.g., a Field device and the Gateway). Different Session keys are
used for each pair-wise communication (e.g., Field device to Gateway, Field device to Network man-
ager,etc.).hedata-linklayer(DLL)usesa
network key
to authenticate messages on a one-hop basis
(e.g., to and from neighbors). A well-known network key is used when a device attempts to join the
network,i.e.,beforeithasreceivedthepropernetworkkey.Keysarerotatedbasedonthesecurity
procedures of the process automation plant.
27.5.2.3 ISA100
hefollowingdescriptionofISA.aisasnapshotofwhatthestandardlookslikeatthetimeof
writing (March ). ).The standard will very likely undergo some (minor) changes before the final
version is released.
.... Architecture
ISA.a is designed to fit the needs of many industrial protocols, such as HART, Profibus,
FoundationFieldbus,etc.Itsscopealsoincludespartsoftheplantbackbonenetwork.
Figure . shows an ISA.a network that includes a part of the backbone. he leftmost part,
from the backbone routers and to the left, is called the “data-link” layer subnet, i.e., it consists of non-
routing devices, routing devices, and backbone routers. However, in the simplest network scenario,
the backbone routers are replaced by one gateway and manager device, which is directly connected
to the plant automation network.
Figure . shows the architecture of ISA.a described in terms of the OSI reference. The
“physical”layerisbasedonIEEE..-andsoistheMACpartofthe(DLL).heupperpart
of the DLL layer handles all communications aspect in the DLL subnet part of an ISA.a network.
A DLL subnet corresponds to a WirelessHART network, i.e., a time synchronized, frequency hopping
mesh network composed of field devices. he “network” layer is based on a subset of the loWPAN
(IETF RFC ) specification, i.e., sending IPv packets over .. networks. he transport layer
is also based on loWPAN, which specifies the use of UDP for end-to-end delivery of packets. Note
∗
Counter with CBC-MAC (corrected).
