14
Network-on-Chip
paths exist from source to destination, a good routing mechanism selects a
path through which the number of hops will be minimized. Another important aspect in routing is the load balancing. If a particular path is overutilized
while another sits idle, known as load imbalance, the total bandwidth of messages being delivered by the network is reduced. Flow control, however, manages the allocation of resources to packets as they progress along their route.
A good flow control mechanism forwards packets with minimum delay and
is also capable of handling faults in communication. Each of these aspects has
been described in detail in the subsequent sections as follows.
Section 2.2 focuses on the basics of network topology, the parameters to consider while selecting a topology, and also the merits and demerits of selecting
a topology in network-on-chip (NoC) paradigm. Section 2.3 depicts different
switching techniques applicable to NoC. Section 2.4 describes the routing
strategies of NoC. It shows how a deadlock can occur in a network and also
the deadlock avoidance techniques. Section 2.5 and Section 2.6 discusses the
flow control technique and the quality of service, respectively. Section 2.7
describes the design of network interface module, whereas Section 2.8 summarizes the chapter.
2.2 Network Topologies
Selecting a network topology is the most important step of NoC design as it
deals with the wire length, the node degree, the routing strategies, and so on.
The interconnection architectures having smaller diameter, lower average
distance, smaller node degree, more number of links, and larger bisection
width are preferable (Dally and Towles 2004). A network diameter is defined
as the maximum shortest distance (in terms of the number of hops) between
any pair of nodes in a network graph, whereas an average distance is the
average of the distances (hop count) between all pairs of nodes in a network
graph. A large diameter signifies that packets have to cross more number of
hops to reach their farthest destinations, whereas a large average distance
denotes the higher average overall latency. A bisection width is defined as
the minimum number of wires to be removed to bisect the network. A larger
bisection width enables faster information exchange. A node degree can be
defined as the number of channels connecting the node to its neighbors.
Lower the number of node degree is easier to build the network. The number
of links is another important parameter for choosing any topology. A topology with large number of links can support high bandwidth.
In the NoC paradigm, researchers have come up with a number of interconnection architectures with their pros and cons. The mesh architecture having
a single core connected with each router is the most common interconnection topology. A mesh-based interconnection architecture called Chip-Level
Network-on-Chip
paths exist from source to destination, a good routing mechanism selects a
path through which the number of hops will be minimized. Another important aspect in routing is the load balancing. If a particular path is overutilized
while another sits idle, known as load imbalance, the total bandwidth of messages being delivered by the network is reduced. Flow control, however, manages the allocation of resources to packets as they progress along their route.
A good flow control mechanism forwards packets with minimum delay and
is also capable of handling faults in communication. Each of these aspects has
been described in detail in the subsequent sections as follows.
Section 2.2 focuses on the basics of network topology, the parameters to consider while selecting a topology, and also the merits and demerits of selecting
a topology in network-on-chip (NoC) paradigm. Section 2.3 depicts different
switching techniques applicable to NoC. Section 2.4 describes the routing
strategies of NoC. It shows how a deadlock can occur in a network and also
the deadlock avoidance techniques. Section 2.5 and Section 2.6 discusses the
flow control technique and the quality of service, respectively. Section 2.7
describes the design of network interface module, whereas Section 2.8 summarizes the chapter.
2.2 Network Topologies
Selecting a network topology is the most important step of NoC design as it
deals with the wire length, the node degree, the routing strategies, and so on.
The interconnection architectures having smaller diameter, lower average
distance, smaller node degree, more number of links, and larger bisection
width are preferable (Dally and Towles 2004). A network diameter is defined
as the maximum shortest distance (in terms of the number of hops) between
any pair of nodes in a network graph, whereas an average distance is the
average of the distances (hop count) between all pairs of nodes in a network
graph. A large diameter signifies that packets have to cross more number of
hops to reach their farthest destinations, whereas a large average distance
denotes the higher average overall latency. A bisection width is defined as
the minimum number of wires to be removed to bisect the network. A larger
bisection width enables faster information exchange. A node degree can be
defined as the number of channels connecting the node to its neighbors.
Lower the number of node degree is easier to build the network. The number
of links is another important parameter for choosing any topology. A topology with large number of links can support high bandwidth.
In the NoC paradigm, researchers have come up with a number of interconnection architectures with their pros and cons. The mesh architecture having
a single core connected with each router is the most common interconnection topology. A mesh-based interconnection architecture called Chip-Level