Handover mechanisms in next generation heterogeneous wireless ...

SECURITY FOR HANDOVER ACROSS HETEROGENEOUS WIRELESS NETWORKS
protocol, where requests are always initiated by the client, while responses (e.g.
challenge or accept/reject) are sent by the server.
In Diameter, all data are delivered in the form of Attribute Value Pairs (AVPs). These
AVP values can be used by the Diameter protocol itself, and applications that employ
Diameter. The Diameter base protocol supports the introduction of new AVPs so as to
make Diameter extensible. Instead of using message type (seen as Code field in a
RADIUS packet), Diameter defines the concept of “Command”, which is assigned for
each command request/answer pair and determines the action to be taken for a particular
message. The commands are distinguished by Command Code field in the Diameter
message as shown in Figure 3.10. Application ID is four octets and is used to identify to
which application the message is applicable for. Hop-by-Hop Identifier is used to match
requests and responses on a hop, which is denoted as a Connection to be discussed later
in Diameter. The sender must ensure that the hop-by-hop identifier is unique on a given
connection at any given time [62]. Another field, End-to-End Identifier, is used to detect
duplicate messages. The originator of an answer message must ensure that the end-toend
identifier value of the message is the same as the value found in the corresponding
request. Diameter AVPs carry specific authentication, authorisation, accounting, routing,
and security information for the Diameter transactions. The Diameter base protocol
defines a large number of AVPs, e.g. Origin-Host AVP, Origin-Realm AVP,
Destination-Host AVP and Destination-Realm AVP.
Figure 3.10 Diameter message format
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