PIERO MAESTRINI: PRINCIPALI INTERESSI DI
RICERCA
- Protezione e sicurezza dell`informazione
nelle reti wireless mobili (MANET) e nelle reti di sensori.
Si segue un
approccio basato sulla frammentazione e dispersione dellĠinformazione dati, realizzata mediante
unĠopportuna codifica dei dati.
Si vedano ad
esempio [CM-2003], [CM-2009]
- Protocolli
di routing per reti wireless mobili (MANET)
Si studiano
protocolli proattivi basati sul una rete virtuale statica sovrapposta alla rete
mobile reale (Virtual Routing Protocols)
MANET routing protocols are classified into the main families of proactive
and reactive protocols. The additional family of hybrid protocols attempts to
bridge the gap.
Proactive routing protocols periodically discover and update routes
connecting every pair of nodes in the network. The availability of such routes
allows nodes to start communication promptly. This advantage is counterbalanced
by increased congestion, due to the flow of control packets needed to discover
routes, even those that may actually be unneeded.
Reactive routing protocols set up routes on demand. This saves network
bandwidth at the expense of some latency, due to the time needed to discover
routes. Established protocols in this family are the Dynamic Source Routing
Protocol (DSR) and the Ad-hoc On
Demand Distance Vector Protocol (AODV).
In DSR every data packet carries the list of intermediate hops to be
traversed from the source to the destination. Routes are discovered by source
nodes on demand and, once discovered, are cached in the source for subsequent
use.
In AODV, routes are set up by means of Distance Vectors stored in the
nodes traversed by the routes themselves. For any route with given destination,
a distance vector identifies the destination node and the next hop on the
route. Packets travel from source to destination as directed by distance
vectors and, contrary to DSR, they do not carry the hop list. Route discovery
is initiated by the source on demand and ends up with distributing distance
vectors over the discovered
sequence of hops. Once setup, the distance vectors are cached for subsequent
use of the route.
Hybrid routing protocols combine proactive and reactive behaviours,
aiming at some trade-off between overhead and latency. For every node, routes
to a given set of destination nodes are discovered and updated proactively,
while routes to remaining nodes are discovered on demand. Among hybrid
protocols, the best known is the Zone Routing Protocol (ZRP). For every node i,
ZRP defines the local neighbours of i as the nodes that can be reached from i
in a number of hops less than or equal to a predefined radius, and the border
nodes as the local neighbours which are adjacent to some node not in the set of
local neighbours. Every node runs a proactive protocol, such as OLSR, to keep
routes to its local neighbours. Routes to nodes which are not local neighbours
are discovered using a reactive protocol augmented with the Bordercasting Routing
Protocol (BRP). With BRP, RREQ packets are sent to respective border nodes,
until a local neighbour of the destination node is reached. As compared to the
usual technique of flooding, this saves overhead.
Somehow related to hybrid protocols are the Virtual Routing
Protocols. Here every node i in
the network, in the role of a scout, discovers and updates routes to its peers,
i.e., to nodes in a predefined subset, denoted Peers(i). Contrary to what occurs in ZRP, where
the sets of local neighbours are defined based on physical distances and are
variable in time, sets Peer(i) are unrelated to the actual placement of nodes
and invariable in time. Denoting N the set of nodes in the network (from now on
referred to as the Physical Network), and Rsp the set of the
scout-peer routes kept proactively by nodes in N (i.e., the routes from every ië N to every node in Peers(i)), the directed graph V(N, Rsp),
is called a Virtual Network. The
Virtual Network. has the same node set as the Physical Network and it is
overlaid on the latter or, otherwise said, is an overlay of the Physical
Network. If V(N, Rsp) is strongly connected, it provides proactive
routes along which any source may communicate without latency with any
destination node. In comparison with the proactive protocols, the number of
routes to be maintained and the overhead paid for route discovery and
maintenance is reduced; although at the expense of increased route length and
communication delay.
Beside the requirement of strong connectivity, desirable features
of a Virtual Network are regularity of structure and small
diameter. Examples of Virtual Routing Protocols with different structures for
the Virtual Network, are VRP [ ],
VDV [ ] and Shen-Cai-Xu [ ]. In the latter protocol the virtual network
is an Augmented Ring, while VRP and VDV use a Ring Connected Ring. Both
structures satisfy the requirement of regularity and small diameter.
Si veda anche [RM-2007]
- Application
of Residue Erasure Codes to Secure Data Streaming