Introduction to Multiprocessors - Fundamentals of Computer Organization and Architecture - page 252

a node to a node until they reach the destination node. The technique is also
known as the store-and-forward packet-switching technique.
Although store-and-forward packet-switching networks eliminate the need for a
complete path at the start of transmission, they tend to increase the overall network
latency. This is because packets are expected to be stored in node buffers waiting for
the availability of outgoing links. In order to reduce the size of the required buffers
and decrease the incurred network latency, wormhole routing (see above) has been
introduced.
Having touched on some of the machine categories based on the Flynn's classi-
fications, we now provide an introduction into the interconnection networks used in
these machines. We provide detailed coverage of multiprocessor interconnection
networks in Chapter 2 of our topic on Advanced Computer Architecture and Parallel
Processing (see reference list).
11.5. INTERCONNECTION NETWORKS
A number of classification criteria exist for interconnection networks (INs). Among
these criteria are the following.
11.5.1. Mode of Operation
According to the mode of operation, INs are classified as synchronous versus
asynchronous. In synchronous mode of operation, a single global clock is used by
all components in the system such that the whole system is operating in a lock-
step manner. Asynchronous mode of operation, on the other hand, does not require
a global clock. Handshaking signals are used instead in order to coordinate the
operation of asynchronous systems. While synchronous systems tend to be slower
compared to asynchronous systems, they are race and hazard-free.
11.5.2. Control Strategy
According to the control strategy, INs can be classified as centralized versus decen-
tralized. In centralized control systems, a single central control unit is used to over-
see and control the operation of the components of the system. In decentralized
control, the control function is distributed among different components in the
system. The function and reliability of the central control unit can become the bottle-
neck in a centralized control system. While the crossbar is a centralized system, the
multistage interconnection networks are decentralized.
11.5.3. Switching Techniques
Interconnection networks can be classified according to the switching mechanism as
circuit versus packet switching networks. In the circuit switching mechanism, a