Post on 29-Mar-2015
ComparisonComparison OfOf NetworkNetwork On Chip On Chip TopologiesTopologies
Ahmet Salih BÜYÜKKAYHAN2007706435 - 2009 Fall
OUTLINEOUTLINEIntroductionBasic DefinitionsProperties of a TopologyNOC TopologiesEvaluationConclusion
Introduction to NOCIntroduction to NOC
NOC◦ A micronetwork of components◦ Transfers information between nodes
Challenges◦ Performance requirements
Latency as small as possible As many concurent transfers as possible
◦ Tight energy boundaries◦ Reliability requirements◦ Low Cost
NOC MotivationNOC MotivationMoore’s Law, doubling the number of
gates every18 months by shrinking the technology dimensions
wire dimensions resistance (R=L/A) inter-wire spacing capacitance (C =
εoA/d) Require the periodic insertion of repeaters Consume more dynamic and leakage
power50% of the power dissipation is due to the
(long) wires.[1]
What Chracterizes NOCWhat Chracterizes NOCTopology (What)
◦ Physical interconnection structure of the network graph
Routing Algorithm (Which)◦ Restricts the set of paths that msgs may follow
Switching Strategy (How)◦ How data in a message traverse a route◦ Circuit / Packet / Wormhole
Flow Control Mechanism (When)◦ when a msg or portions of it traverse a route◦ what happens when traffic is encountered?
Properties of a TopologyProperties of a TopologyPerformance
◦ Diameter (Max routing Distance)◦ Average Distance
Cost◦ Avg. Nodal Degree (Avg number of links for
each node)◦ Number of links (Total number of links)
Reliability ◦ Min number of links to disconnect the
graph
NOC TopologiesShared-Medium Local Networks
◦Contention Bus, Token Bus and Token Ring
Direct Networks◦1D: Linear, Ring ◦2D: Mesh, Tree◦3D: Cube, Toroid
Indirect Networks◦Crossbar, Benes, Perfect shuffle and
OmegaHybrid Networks
Shared-Medium Local Shared-Medium Local NetworksNetworks
Local Area Networks◦Contention Bus(Ethernet)◦Token Bus (Arcnet)◦Token Ring (FDDI Ring, IBM Token Ring)
All communication devices share the transmission medium.
Only one device can drive network at a time
Contention Bus (Ethernet)Contention Bus (Ethernet)
All devices can monitor the state of the bus, such as idle, busy, and collision.
“collision” means that two or more devices are using the bus at the same time and their data collided.
When the collision is detected, the competing devices will quit transmission and try later.
Ethernet adopts carrier-sense multiple access with collision detection (CSMA/CD) protocol.
Token Bus & Token RingToken Bus & Token Ring
◦ Contention Bus has an undeterministic nature◦ Not suitable for Real-Time applications
Solution: ◦ Passing a token among network devices◦ The owner of the token has the right to acess to the bus◦ Maximum token holding time
Token Ring: ◦ Natural extension of token bus◦ Passing of the token forms a ring structure
Properties of Shared Medium Properties of Shared Medium LAN LAN Bus system is not scalable because bus becomes the
bottleneck. Fully connected to each other Bus systems:
◦ Diameter = 1
◦ Avg. Dist = 1
◦ Reliability = 1
◦ Number of links = N + Bus
◦ Nodal Degree = 1
Ring Systems:◦ Diameter: N/2
◦ Avg. Dist = N/2 = (N-1)*(N) / 2*(N-1)
◦ Number of links : N-1
◦ Nodal Degree = 2
◦ Reliability = 2
Direct Networks (Router Direct Networks (Router Based)Based)
◦ Strictly Orthogonal Topologies Mesh Torus Hypercube
◦ Other Topologies Trees Cube connected cycles
Node processors are connected directly with each other by the network
Each node performs dataflow routingEvery direct network can be represented as
indirect, by splitting each node into a terminal and a switch
Orthogonal
Every link and node can be arranged in such a way that it produces a displacement in a single dimension
Most of the implemented networks have an orthogonal topology.
Orthogonal Topologies
4 ary 2 dim Mesh 8 – Cube◦ Diameter = 6 Diameter = 3◦ Number of Links = 24 # of Links = 12◦ Node Degree = 3 Node Degree = 3◦ Avg Distance = 3 Avg. Distance = 1.71◦ Reliability = 2 Reliability = 3
HypercubesHypercubesDiameter = logN Node Degree = logN Reliability = logN
TreesTrees
Binary Tree ◦ diameter: 2 log(N)◦ Reliability: 1◦ Total Number of links : N-1◦ Nodal Degree : 1<Nodal Degree <2
Problems◦ Congestion◦ Fault tolerance is low
Fat TreesFat Trees
Fatter links (really more of them) as you go up, so bisection BW scales with N
There are many possible paths, so at each level the routing processor chooses a path at random, in order to balance the load.
Cube Connected CyclesCube Connected CyclesLike n-dimensional
hypercube of virtual nodes
each virtual node is a ring with n nodes, for a total of n2n nodes
Each node in the ring is connected to a single dimension of the hypercube
diameter is same with hypercube of similar size
Cube Connected CyclesCube Connected Cycles
Total number of links : ( n2n * n )/ 2
Node Degree = Reliability : nDiameter: 2*n
Embed Multiple Embed Multiple DimensionsDimensions
Embed multiple logical dimension in one physical dimension using long wires
Indirect Networks(Switch Indirect Networks(Switch Based)Based)
◦Crossbar◦Fully Connected◦Perfect Shuffle◦Multistage Interconnection Networks
Blocking Networks Omega Banyan
Non Blocking Networks Clos Network Benes Network
node processors (1 n ) node switches
Switches
Switches◦Perform the routing ◦Provide a programmable connection
between their ports◦Do not perform information
processing
CrossbarCrossbar
Free of interconnect contentionCrossbar networks are used in the design
of high-performance small-scale multiprocessors
However, the bit energy will increase linearly with the number of input and output ports N
Fully Connected SwitchFully Connected Switch
Using a single N × N crossbar is much cheaper than using a fully connected direct network topology
Requiring N routers, each one having an internal N × N crossbar
Perfect ShuPerfect Shuffffle Networkle Network
a) The perfect shuffleb) Inverse perfect shufflec) Bit reversal permutations for N=8
Omega NetworksOmega Networks
The omega network is another example of a banyan multistage interconnection network that can be used as a switch fabric
The omega uses the “perfect shuffle”
Omega NetworksOmega Networks
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Path ContetionPath ContetionThe omega network has the
problems as the delta network with output port contention and path contention
Again, the result in a bufferless switch fabric is cell loss (one cell wins, one loses)
Path contention and output port contention can seriously degrade the achievable throughput of the switch
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Batcher Sorter & Banyan NetworkOne solution to the contention
problem is to sort the cells into increasing order based on desired destination portBanyan networks are a
class of MINs with the property that there is a unique path between any pair of source and destination
Batcher-Banyan Example
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Clos NetworksClos NetworksClos networks have three stages:
the ingress stage, middle stage, and the egress stage. Each stage is made up of a number of crossbar switches
BenesNetworksBenesNetworks
Clos networks may also be generalised to any odd number of stages. By replacing each centre stage crossbar switch with a 3-stage Clos network, Clos networks of five stages may be constructed. By applying the same process repeatedly,
Hybrid NetworksHybrid Networks◦ Multiple-backplane ◦ Hierarchical buses
Cluster tightly coupled computational units with high communication bandwidth
Provide lower bandwidth intercluster communication link sctures◦ performance comparable with
homogeneous,◦ high-bandwidth architectures◦ energy efficiency is a strong driver toward
using hybrid architectures.
Cluster Based 2-D Mesh
At the lower level, each cluster consists of four processors connected by a bus.
At the higher level, a 2-D mesh connects the clusters. The broadcast capability of the bus is used at the cluster level
Evaluation I
# of links Nodaldegree Diameter Avg. Dist Reliability
7 BinTree 6 1.71 4 2.21 1
8 Ring 8 2 4 2.21 2
9 Mesh 12 2,66 4 2 2
8 Cube 12 3 3 1,71 3
Evaluation I
# of links Nodaldegree Reliability Diameter Avg. Dist
15 BinTree 14 1.87 1 6 3.5
16 Mesh 24 3 2 6 3
16 HyperCube 32 4 4 4 2.13
16 Chord.Ring 32 4 4 3 2
Power Consumption Under Different Number of Ports
ConclusionConclusionShared Medium topologies have a
bottleneck on shared medium. So not extensible
Direct topologies can be easily extensible but there are thresholds between cost, performance and reliability
Embed multiple logical dimension in one physical dimension using long wires is another disadvantage
ConclusionConclusionIndirect topologies blocking
topologies have contention problems. Non blocking networks have extra stages and costs.
Non-Blocking networks are cheaper than a crossbar with the same size
Hybrid networks have high bandwith and energy efficiency using clustering
ConclusionConclusionInterconnect contention (internal
blocking) induces significant power consumption on internal buffers, and the power consumption on buffers will increase sharply as throughput increases.
ReferencesReferences [1]N. Magen, A. Kolodny, U. Weiser, and N. Shamir.
Interconnect-power dissipation in a microprocessor. In SLIP’04, Feb. 2004.
[2]Cidon, I., Keidar, I.: Zooming in on Network on Chip Architectures. Technion Department of Electrical Engineering, 2005
[3]Jose Duato , Sudhakar Yalamanchili , Lionel Ni, Interconnection Networks: An Engineering Approach, IEEE Computer Society Press, Los Alamitos, CA, 1997
[4]T.T. Ye: On-Chip Multiprocessor Communication Network Design and Analysis. Standford University of Electrical Engineering, Dec. 2003
[5] L Benini and G.D. Micheli, Networks on chips: a new SoC paradigm. IEEE Computer 35 1 (2002), pp. 70–78
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