5
Introduction
physical and data link layers are dependent on the technology. Thus,
for each new technology, these layers are defined.
• The network layer defines how a packet is transmitted over the network from an arbitrary sender to an arbitrary receiver directed by the
receiver’s network address. This layer is also technology dependent.
• The transport layer is technology independent. In this layer, message
size can be variable. This layer breaks the message into network
layer packets.
Interconnection networks have been studied for more than the past two
decades and a solid foundation of design techniques has been described in
several text books (Duato et al. 2003; Dally and Towles 2004). With increasing
communication demand, the introduction of interconnection network in SoC
design has paved the route to NoC research almost a decade ago. Mullins
(2009) has listed more than 400 related articles addressing all these aspects.
NoC is today becoming an emerging research topic including hardware communication infrastructure, software and operating system services, CAD
tools for NoC synthesis, and so on.
1.3 Research Issues in NoC Development
The major research problems in NoC design can be broadly classified into
four different dimensions—communication infrastructure, communication
paradigm, evaluation framework, and application mapping—as addressed
in the works of Ogras et al. (2005) and Marculescu et al. (2009). This section
first highlights these issues briefly followed by other associated issues.
The first dimension of research is focused on choice of communication infrastructure. The communication infrastructure design essentially points to
the design of underlying hardware acting as the backbone for the on-chip
communication network. Selection of network topology, design of router
architecture with proper buffer organization, determining inter-router link
width, clocking strategies, floorplanning, and layout design are the key
design aspects of this dimension. The routers are often connected in certain
topologies whose performance behaviors are well known to the distributed
system design community and suit well for on-chip realizations. Individual
routers are designed using some specific switching techniques, such as
wormhole and virtual cut-through. Flow control is performed via handshaking signals between adjacent routers. The router’s buffer space minimization
and simplified buffer control mechanisms are two important features of the
NoC design, as they directly affect the overall area–power overheads and
network latency. To solve the problem of clock skew, the individual cores