Handover mechanisms in next generation heterogeneous wireless ...

SECURITY FOR HANDOVER ACROSS HETEROGENEOUS WIRELESS NETWORKS
table is consulted by Diameter agents to find the message destination or the next AAA
hop that may reside in other realms.
A Diameter node can process a request message locally, or forward the message
according to the final destination of that message. The Local Action value of the realm
routing entry in a Diameter node determines how a message with a specific Destination-
Realm AVP is processed. The Diameter base protocol [62] defines four types of actions
that can be imposed on a message: Local, Relay, Proxy and Redirect. It is noted in [62]
that Diameter agents must support at least one of the Local, Relay, Proxy and Redirect
modes of operation, but do not support all modes of operation.
Diameter defines relay, proxy, and redirect agents, and requires that agents maintain
transaction state, which is used for failover purposes.
� Relay Agents: accept requests and route messages to other Diameter nodes based
on the Destination-Realm of messages. Relay agents can manipulate Diameter
messages through inserting and removing routing information without modifying
any non-routing AVPs;
� Proxy Agents: route messages using the realm routing table as relay agents do.
However, they can modify messages to apply local policies, and add new AVPs to
Diameter messages prior to routing;
� Redirect Agents: do not route messages, but simply return an answer with the
information necessary for Diameter agents to communicate directly, without
modifying messages.
As discussed in Sec. 3.2, the EAP three-party authentication model is considered as a
standard method to accomplish access control through an AAA protocol in modern
wireless networks. The Diameter NAS application specification (NASREQ), describing
the interaction between NAS and Diameter server is standardised in IETF RFC 4005
[63]. Along with the Diameter EAP application (RFC 4072) [65], it supports the EAP
authentication through a NAS with a Diameter server. The Diameter NAS application
defines a number of commands and AVPs for authentication and authorisation. The
NAS and Diameter server utilises these commands to conduct operations such as re-
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