Network On Chip
Encyclopedia
Network-on-Chip or Network-on-a-Chip (NoC or NOC) is an approach to designing the communication subsystem between IP cores
in a System-on-a-Chip
(SoC). NoCs can span synchronous and asynchronous clock domains or use unclocked asynchronous
logic. NoC applies networking
theory and methods to on-chip communication
and brings notable improvements over conventional bus
and crossbar
interconnections. NoC improves the scalability of SoCs, and the power efficiency of complex SoCs compared to other designs. Research has been done on integrated optical waveguides and devices comprising an Optical Network-on-Chip (ONoC).
for communication
s within large VLSI
systems implemented on a single silicon chip
. Sgroi et al. call "the layered-stack approach to the design of the on-chip intercore communications the Network-on-Chip (NOC) methodology."
In a NoC system, modules such as processor cores
, memories
and specialized IP block
s exchange data
using a network as a "public transport
ation" sub-system for the information traffic.
A NoC is constructed from multiple point-to-point data link
s interconnected by switches (a.k.a. routers), such that messages can be relayed from any source module to any destination module over several links, by making routing decisions at the switches.
A NoC is similar to a modern telecommunications network
, using digital bit-packet switching
over multiplexed links
.
Although packet-switching
is sometimes claimed as necessity for a NoC, there are several NoC proposals utilizing circuit-switching
techniques. This definition based on routers is usually interpreted so that a single shared bus, a single crossbar switch
or a point-to-point network are not NoCs but practically all other topologies
are. This is somewhat confusing since all above mentioned are networks (they enable communication between two or more devices) but they are not considered as network-on-chips.
Note that some articles erroneously use NoC as a synonym for mesh
topology although NoC paradigm does not dictate the topology. Likewise, the regularity of topology is sometimes considered as a requirement which is, obviously,
not the case in research concentrating on "application-specific NoC topology synthesis".
is achieved, because all links
in the NoC can operate simultaneously on different data packets
. Therefore, as the complexity of integrated systems
keeps growing, a NoC provides enhanced performance (such as throughput
) and scalability
in comparison with previous communication architectures (e.g., dedicated point-to-point signal wire
s, shared buses
, or segmented buses
with bridges). Of course, the algorithms must be designed in such a way that they offer large parallelism and can hence utilize the potential of NoC.
viewpoint. The wires occupy much of the area of the chip, and in nanometer CMOS
technology, interconnects dominate both performance and dynamic power dissipation
, as signal propagation in wires across the chip requires multiple clock cycles
. (See Rent's rule
for a discussion of wiring requirements for point-to-point connections).
NoC links can reduce the complexity of designing wires for predictable speed, power, noise, reliability, etc., thanks to their regular, well controlled structure. From a system design viewpoint, with the advent of multi-core processor
systems, a network is a natural architectural choice. A NoC can provide separation between computation
and communication
, support modularity and IP
reuse via standard interfaces
, handle synchronization
issues, serve as a platform
for system test, and, hence, increase engineering productivity.
. In particular, NoC switches should be small, energy-efficient, and fast. Neglecting these aspects along with proper, quantitative comparison was typical for early NoC research but nowadays they are considered in more detail. The routing algorithms
should be implemented by simple logic
, and the number of data buffers
should be minimal. Network topology
and properties may be application-specific.
Some researchers think that NoCs need to support quality of service
(QoS), namely achieve the various requirements in terms of throughput
, end-to-end delays and deadlines. Real-time computation, including audio and video playback, is one reason for providing QOS support. However, current system implementations like VxWorks
, RTLinux
or QNX
are able to achieve sub-millisecond real-time computing without special hardware. This may indicate that for many real-time applications the service quality of existing on-chip interconnect infrastructure is sufficient, and dedicated hardware logic would be necessary to achieve microsecond precision, a degree that is rarely needed in practice for end users (sound or video jitter need only tenth of milliseconds latency guarantee). Another motivation for NOC-level quality-of-service is to support multiple concurrent users sharing resources of a single chip multiprocessor
in a public cloud computing
infrastructure. In such instances, hardware QOS logic enables the service provider to make contractual guarantees
on the level of service that a user receives, a feature that may be deemed desirable by some corporate or government clients.
To date, several prototype
NoCs have been designed and analyzed in both industry and academia but only few have been implemented on silicon. However, many challenging research problems remain to be solved at all levels, from the physical link level through the network level, and all the way up to the system architecture and application software. The first dedicated research symposium on Networks on Chip was held at Princeton University
, in May 2007. The second IEEE
International Symposium on Networks-on-Chip was held in April 2008 at Newcastle University.
Semiconductor intellectual property core
In electronic design a semiconductor intellectual property core, IP core, or IP block is a reusable unit of logic, cell, or chip layout design that is the intellectual property of one party. IP cores may be licensed to another party or can be owned and used by a single party alone...
in a System-on-a-Chip
System-on-a-chip
A system on a chip or system on chip is an integrated circuit that integrates all components of a computer or other electronic system into a single chip. It may contain digital, analog, mixed-signal, and often radio-frequency functions—all on a single chip substrate...
(SoC). NoCs can span synchronous and asynchronous clock domains or use unclocked asynchronous
Asynchronous circuit
An asynchronous circuit is a circuit in which the parts are largely autonomous. They are not governed by a clock circuit or global clock signal, but instead need only wait for the signals that indicate completion of instructions and operations. These signals are specified by simple data transfer...
logic. NoC applies networking
Computer network
A computer network, often simply referred to as a network, is a collection of hardware components and computers interconnected by communication channels that allow sharing of resources and information....
theory and methods to on-chip communication
Communication
Communication is the activity of conveying meaningful information. Communication requires a sender, a message, and an intended recipient, although the receiver need not be present or aware of the sender's intent to communicate at the time of communication; thus communication can occur across vast...
and brings notable improvements over conventional bus
Computer bus
In computer architecture, a bus is a subsystem that transfers data between components inside a computer, or between computers.Early computer buses were literally parallel electrical wires with multiple connections, but the term is now used for any physical arrangement that provides the same...
and crossbar
Crossbar switch
In electronics, a crossbar switch is a switch connecting multiple inputs to multiple outputs in a matrix manner....
interconnections. NoC improves the scalability of SoCs, and the power efficiency of complex SoCs compared to other designs. Research has been done on integrated optical waveguides and devices comprising an Optical Network-on-Chip (ONoC).
Emerging paradigm
Network-on-Chip (NoC) is an emerging paradigmParadigm
The word paradigm has been used in science to describe distinct concepts. It comes from Greek "παράδειγμα" , "pattern, example, sample" from the verb "παραδείκνυμι" , "exhibit, represent, expose" and that from "παρά" , "beside, beyond" + "δείκνυμι" , "to show, to point out".The original Greek...
for communication
Telecommunication
Telecommunication is the transmission of information over significant distances to communicate. In earlier times, telecommunications involved the use of visual signals, such as beacons, smoke signals, semaphore telegraphs, signal flags, and optical heliographs, or audio messages via coded...
s within large VLSI
Very-large-scale integration
Very-large-scale integration is the process of creating integrated circuits by combining thousands of transistors into a single chip. VLSI began in the 1970s when complex semiconductor and communication technologies were being developed. The microprocessor is a VLSI device.The first semiconductor...
systems implemented on a single silicon chip
Integrated circuit
An integrated circuit or monolithic integrated circuit is an electronic circuit manufactured by the patterned diffusion of trace elements into the surface of a thin substrate of semiconductor material...
. Sgroi et al. call "the layered-stack approach to the design of the on-chip intercore communications the Network-on-Chip (NOC) methodology."
In a NoC system, modules such as processor cores
Multi-core (computing)
A multi-core processor is a single computing component with two or more independent actual processors , which are the units that read and execute program instructions...
, memories
Computer storage
Computer data storage, often called storage or memory, refers to computer components and recording media that retain digital data. Data storage is one of the core functions and fundamental components of computers....
and specialized IP block
Semiconductor intellectual property core
In electronic design a semiconductor intellectual property core, IP core, or IP block is a reusable unit of logic, cell, or chip layout design that is the intellectual property of one party. IP cores may be licensed to another party or can be owned and used by a single party alone...
s exchange data
Data
The term data refers to qualitative or quantitative attributes of a variable or set of variables. Data are typically the results of measurements and can be the basis of graphs, images, or observations of a set of variables. Data are often viewed as the lowest level of abstraction from which...
using a network as a "public transport
Public transport
Public transport is a shared passenger transportation service which is available for use by the general public, as distinct from modes such as taxicab, car pooling or hired buses which are not shared by strangers without private arrangement.Public transport modes include buses, trolleybuses, trams...
ation" sub-system for the information traffic.
A NoC is constructed from multiple point-to-point data link
Data link
In telecommunication a data link is the means of connecting one location to another for the purpose of transmitting and receiving information. It can also refer to a set of electronics assemblies, consisting of a transmitter and a receiver and the interconnecting data telecommunication circuit...
s interconnected by switches (a.k.a. routers), such that messages can be relayed from any source module to any destination module over several links, by making routing decisions at the switches.
A NoC is similar to a modern telecommunications network
Telecommunications network
A telecommunications network is a collection of terminals, links and nodes which connect together to enable telecommunication between users of the terminals. Networks may use circuit switching or message switching. Each terminal in the network must have a unique address so messages or connections...
, using digital bit-packet switching
Packet switching
Packet switching is a digital networking communications method that groups all transmitted data – regardless of content, type, or structure – into suitably sized blocks, called packets. Packet switching features delivery of variable-bit-rate data streams over a shared network...
over multiplexed links
Multiplexing
The multiplexed signal is transmitted over a communication channel, which may be a physical transmission medium. The multiplexing divides the capacity of the low-level communication channel into several higher-level logical channels, one for each message signal or data stream to be transferred...
.
Although packet-switching
Packet switching
Packet switching is a digital networking communications method that groups all transmitted data – regardless of content, type, or structure – into suitably sized blocks, called packets. Packet switching features delivery of variable-bit-rate data streams over a shared network...
is sometimes claimed as necessity for a NoC, there are several NoC proposals utilizing circuit-switching
Circuit switching
Circuit switching is a methodology of implementing a telecommunications network in which two network nodes establish a dedicated communications channel through the network before the nodes may communicate. The circuit guarantees the full bandwidth of the channel and remains connected for the...
techniques. This definition based on routers is usually interpreted so that a single shared bus, a single crossbar switch
Crossbar switch
In electronics, a crossbar switch is a switch connecting multiple inputs to multiple outputs in a matrix manner....
or a point-to-point network are not NoCs but practically all other topologies
Network topology
Network topology is the layout pattern of interconnections of the various elements of a computer or biological network....
are. This is somewhat confusing since all above mentioned are networks (they enable communication between two or more devices) but they are not considered as network-on-chips.
Note that some articles erroneously use NoC as a synonym for mesh
Mesh
Mesh consists of semi-permeable barrier made of connected strands of metal, fiber, or other flexible/ductile material. Mesh is similar to web or net in that it has many attached or woven strands.-Types of mesh:...
topology although NoC paradigm does not dictate the topology. Likewise, the regularity of topology is sometimes considered as a requirement which is, obviously,
not the case in research concentrating on "application-specific NoC topology synthesis".
Parallelism and scalability
The wires in the links of the NoC are shared by many signals. A high level of parallelismParallel computing
Parallel computing is a form of computation in which many calculations are carried out simultaneously, operating on the principle that large problems can often be divided into smaller ones, which are then solved concurrently . There are several different forms of parallel computing: bit-level,...
is achieved, because all links
Data link
In telecommunication a data link is the means of connecting one location to another for the purpose of transmitting and receiving information. It can also refer to a set of electronics assemblies, consisting of a transmitter and a receiver and the interconnecting data telecommunication circuit...
in the NoC can operate simultaneously on different data packets
Packet switching
Packet switching is a digital networking communications method that groups all transmitted data – regardless of content, type, or structure – into suitably sized blocks, called packets. Packet switching features delivery of variable-bit-rate data streams over a shared network...
. Therefore, as the complexity of integrated systems
Very-large-scale integration
Very-large-scale integration is the process of creating integrated circuits by combining thousands of transistors into a single chip. VLSI began in the 1970s when complex semiconductor and communication technologies were being developed. The microprocessor is a VLSI device.The first semiconductor...
keeps growing, a NoC provides enhanced performance (such as throughput
Throughput
In communication networks, such as Ethernet or packet radio, throughput or network throughput is the average rate of successful message delivery over a communication channel. This data may be delivered over a physical or logical link, or pass through a certain network node...
) and scalability
Scalability
In electronics scalability is the ability of a system, network, or process, to handle growing amount of work in a graceful manner or its ability to be enlarged to accommodate that growth...
in comparison with previous communication architectures (e.g., dedicated point-to-point signal wire
Wire
A wire is a single, usually cylindrical, flexible strand or rod of metal. Wires are used to bear mechanical loads and to carry electricity and telecommunications signals. Wire is commonly formed by drawing the metal through a hole in a die or draw plate. Standard sizes are determined by various...
s, shared buses
Computer bus
In computer architecture, a bus is a subsystem that transfers data between components inside a computer, or between computers.Early computer buses were literally parallel electrical wires with multiple connections, but the term is now used for any physical arrangement that provides the same...
, or segmented buses
Computer bus
In computer architecture, a bus is a subsystem that transfers data between components inside a computer, or between computers.Early computer buses were literally parallel electrical wires with multiple connections, but the term is now used for any physical arrangement that provides the same...
with bridges). Of course, the algorithms must be designed in such a way that they offer large parallelism and can hence utilize the potential of NoC.
Benefits of adopting NoCs
Traditionally, ICs have been designed with dedicated point-to-point connections, with one wire dedicated to each signal. For large designs, in particular, this has several limitations from a physical designIntegrated circuit design
Integrated circuit design, or IC design, is a subset of electrical engineering and computer engineering, encompassing the particular logic and circuit design techniques required to design integrated circuits, or ICs...
viewpoint. The wires occupy much of the area of the chip, and in nanometer CMOS
CMOS
Complementary metal–oxide–semiconductor is a technology for constructing integrated circuits. CMOS technology is used in microprocessors, microcontrollers, static RAM, and other digital logic circuits...
technology, interconnects dominate both performance and dynamic power dissipation
CMOS
Complementary metal–oxide–semiconductor is a technology for constructing integrated circuits. CMOS technology is used in microprocessors, microcontrollers, static RAM, and other digital logic circuits...
, as signal propagation in wires across the chip requires multiple clock cycles
Clock signal
In electronics and especially synchronous digital circuits, a clock signal is a particular type of signal that oscillates between a high and a low state and is utilized like a metronome to coordinate actions of circuits...
. (See Rent's rule
Rent's Rule
Rent's rule pertains to the organization of computing logic, specifically the relationship between the number of external signal connections to a logic block with the number of logic gates in the logic block, and has been applied to circuits ranging from small digital circuits to mainframe...
for a discussion of wiring requirements for point-to-point connections).
NoC links can reduce the complexity of designing wires for predictable speed, power, noise, reliability, etc., thanks to their regular, well controlled structure. From a system design viewpoint, with the advent of multi-core processor
Multi-core (computing)
A multi-core processor is a single computing component with two or more independent actual processors , which are the units that read and execute program instructions...
systems, a network is a natural architectural choice. A NoC can provide separation between computation
Computation
Computation is defined as any type of calculation. Also defined as use of computer technology in Information processing.Computation is a process following a well-defined model understood and expressed in an algorithm, protocol, network topology, etc...
and communication
Communication
Communication is the activity of conveying meaningful information. Communication requires a sender, a message, and an intended recipient, although the receiver need not be present or aware of the sender's intent to communicate at the time of communication; thus communication can occur across vast...
, support modularity and IP
IP address
An Internet Protocol address is a numerical label assigned to each device participating in a computer network that uses the Internet Protocol for communication. An IP address serves two principal functions: host or network interface identification and location addressing...
reuse via standard interfaces
Interface (computer science)
In the field of computer science, an interface is a tool and concept that refers to a point of interaction between components, and is applicable at the level of both hardware and software...
, handle synchronization
Synchronization
Synchronization is timekeeping which requires the coordination of events to operate a system in unison. The familiar conductor of an orchestra serves to keep the orchestra in time....
issues, serve as a platform
Platform (computing)
A computing platform includes some sort of hardware architecture and a software framework , where the combination allows software, particularly application software, to run...
for system test, and, hence, increase engineering productivity.
Research on on-chip networks
Although NoCs can borrow concepts and techniques from the well-established domain of computer networking, it is impractical to blindly reuse features of "classical" computer networks and symmetric multiprocessorsSymmetric multiprocessing
In computing, symmetric multiprocessing involves a multiprocessor computer hardware architecture where two or more identical processors are connected to a single shared main memory and are controlled by a single OS instance. Most common multiprocessor systems today use an SMP architecture...
. In particular, NoC switches should be small, energy-efficient, and fast. Neglecting these aspects along with proper, quantitative comparison was typical for early NoC research but nowadays they are considered in more detail. The routing algorithms
Routing
Routing is the process of selecting paths in a network along which to send network traffic. Routing is performed for many kinds of networks, including the telephone network , electronic data networks , and transportation networks...
should be implemented by simple logic
Logic gate
A logic gate is an idealized or physical device implementing a Boolean function, that is, it performs a logical operation on one or more logic inputs and produces a single logic output. Depending on the context, the term may refer to an ideal logic gate, one that has for instance zero rise time and...
, and the number of data buffers
Buffer (computer science)
In computer science, a buffer is a region of a physical memory storage used to temporarily hold data while it is being moved from one place to another. Typically, the data is stored in a buffer as it is retrieved from an input device or just before it is sent to an output device...
should be minimal. Network topology
Network topology
Network topology is the layout pattern of interconnections of the various elements of a computer or biological network....
and properties may be application-specific.
Some researchers think that NoCs need to support quality of service
Quality of service
The quality of service refers to several related aspects of telephony and computer networks that allow the transport of traffic with special requirements...
(QoS), namely achieve the various requirements in terms of throughput
Throughput
In communication networks, such as Ethernet or packet radio, throughput or network throughput is the average rate of successful message delivery over a communication channel. This data may be delivered over a physical or logical link, or pass through a certain network node...
, end-to-end delays and deadlines. Real-time computation, including audio and video playback, is one reason for providing QOS support. However, current system implementations like VxWorks
VxWorks
VxWorks is a real-time operating system developed as proprietary software by Wind River Systems of Alameda, California, USA. First released in 1987, VxWorks is designed for use in embedded systems.- History :...
, RTLinux
RTLinux
RTLinux or RTCore is a hard realtime RTOS microkernel that runs the entire Linux operating system as a fully preemptive process.It was developed by Victor Yodaiken , Michael Barabanov , Cort Dougan and others at the New Mexico Institute of Mining and Technology and then as a commercial product at...
or QNX
QNX
QNX is a commercial Unix-like real-time operating system, aimed primarily at the embedded systems market. The product was originally developed by Canadian company, QNX Software Systems, which was later acquired by Canadian BlackBerry-producer Research In Motion.-Description:As a microkernel-based...
are able to achieve sub-millisecond real-time computing without special hardware. This may indicate that for many real-time applications the service quality of existing on-chip interconnect infrastructure is sufficient, and dedicated hardware logic would be necessary to achieve microsecond precision, a degree that is rarely needed in practice for end users (sound or video jitter need only tenth of milliseconds latency guarantee). Another motivation for NOC-level quality-of-service is to support multiple concurrent users sharing resources of a single chip multiprocessor
Multi-core (computing)
A multi-core processor is a single computing component with two or more independent actual processors , which are the units that read and execute program instructions...
in a public cloud computing
Cloud computing
Cloud computing is the delivery of computing as a service rather than a product, whereby shared resources, software, and information are provided to computers and other devices as a utility over a network ....
infrastructure. In such instances, hardware QOS logic enables the service provider to make contractual guarantees
Service Level Agreement
A service-level agreement is a part of a service contract where the level of service is formally defined. In practice, the term SLA is sometimes used to refer to the contracted delivery time or performance...
on the level of service that a user receives, a feature that may be deemed desirable by some corporate or government clients.
To date, several prototype
Prototype
A prototype is an early sample or model built to test a concept or process or to act as a thing to be replicated or learned from.The word prototype derives from the Greek πρωτότυπον , "primitive form", neutral of πρωτότυπος , "original, primitive", from πρῶτος , "first" and τύπος ,...
NoCs have been designed and analyzed in both industry and academia but only few have been implemented on silicon. However, many challenging research problems remain to be solved at all levels, from the physical link level through the network level, and all the way up to the system architecture and application software. The first dedicated research symposium on Networks on Chip was held at Princeton University
Princeton University
Princeton University is a private research university located in Princeton, New Jersey, United States. The school is one of the eight universities of the Ivy League, and is one of the nine Colonial Colleges founded before the American Revolution....
, in May 2007. The second IEEE
Institute of Electrical and Electronics Engineers
The Institute of Electrical and Electronics Engineers is a non-profit professional association headquartered in New York City that is dedicated to advancing technological innovation and excellence...
International Symposium on Networks-on-Chip was held in April 2008 at Newcastle University.
NoC Benchmark
NoC development and studies require comparing different proposals and options. And NoC benchmarks are developed to help such evaluations. Existing NoC benchmarks include NoCBench and MCSL NoC Benchmark Suite.External links
- DATE 2006 workshop on NoC
- NoCS 2007 - The 1st ACM/IEEE International Symposium on Networks-on-Chip
- NoCS 2008 - The 2nd IEEE International Symposium on Networks-on-Chip
- Cristian Grecu, Andrè Ivanov, Partha Pande, Axel Jantsch, Erno Salminen, Umit Ogras, Radu Marculescu, An Initiative towards Open Network-on-Chip Benchmarks, OCP-Ip white paper, 2007, [Online] http://www.ocpip.org/uploads/documents/NoC-Benchmarks-WhitePaper-15.pdf