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NETWORKED EMBEDDED SYSTEMS

SRIKANTH SUBRAMANIAN

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Agenda Overview Networked Embedded

Systems (NES) NES built on ASIPs NES built on General Purpose

Processors Quantitative performance comparison of

various NES for TCP and UDP Online HW/SW partitioning of NES

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Overview

NES are employed in Devices that form the backbone of communication networks

Routers, Network Bridges (Switches), Telephone Switches etc

Perform the task of data processing, Network Connectivity and Service delivery

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NES were mostly implemented on Single Purpose Processors (SPPs)

SPPs - No Flexibility Pose problems when the requirements

change Alternatives : General purpose

processors or ASIPs (Network Processors)

Overview

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Network Processors ICs specifically built for networking

application Software Programmable Devices Optimized features for networking

applications : pattern Matching, Queue management, Data bit field manipulation etc.

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Stareast:

Consists of a Baseboard and two daughter boards

Baseboard contains Intel IXP425 (533MHz) Processor

NES based on ASIPs

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Scalable performance, Reduced power consumption, Low cost

Deliver a range of data, voice, security and I/O features

Distributed processing Architecture Combination of Intel XScale (an ARM

Processor) and 3 Network Processing Engines (NPEs)

Intel IXP425 Processor

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XScale - Control plane NPEs - computationally intensive data Parallel Operation of Xscale and NPEs

Intel IXP425 Processor

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Netgear WAG302: Most commonly

used wireless Access Point

Based on Intel IXP422B processor (266 MHz)

NES based on ASIPs

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Soekris net4826-50

Based on AMD Geode Processor (266 MHz)

NES based on GPPs

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Used to create fully customized routers and access points

Low cost, advanced communication features

AMD Geode processor comes under the X86 processor family

NES based on GPPs

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Quantitative Performance Comparison

Objectives:

a) Performance comparison Between NES based on GPP and NES based on ASIP

b) Performance comparison between Two NESs based on ASIP with one running on a commercial Operating system and another running Open source operating system

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Experimental Setup Three Stareast boards:a) One running Montavista 4.0 OSb) The other two running Snapgear

versions 3.1 and 3.3 Netgear WAG302 Running openWRT Soekris net 4826 running Voyage

Linux (Debian) distribution for X86 processors

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Experimental Setup

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Experimental Setup To Study the behavior of the NESs, D-

ITG traffic generator is used Can generate IPv4/IPv6 traffic

replicating the appropriate stochastic processes for both IDT( Inter Departure time) and PS (packet size)

Collect Statistics of Quality of Service (QOS) parameters: Throughput, Jitter, Packet loss and Delay (Latency)

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Experimental Analysis NES boards are connected back to

back with the Workstation Testing is performed using both TCP

and UDP in the transport layer Two types of tests are performed:a) Discover the number of packets per

second the devices are able to generate for fixed packet size

b) Measure bit rates, jitter, packet loss for different packet rates and sizes

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Packet Rate:

Results

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Bitrate for UDP:

Results

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Bitrate for TCP:

Results

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Jitter for UDP:

Results

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Results Jitter for TCP:

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Packet Loss for UDP:

Results

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Conclusions NES based on ASIP running a commercial

OS provides better performance as compared a NES based on GPP running a commercial OS

NES based on ASIP running open source OS are still less efficient as compared to commercial OS

Hence NES using network processors can play a major role in data intensive real time applications.

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Online HW/SW Partitioning

Need:a) Optimal partitioning of load into HW

and SW during compile time is difficultb) Arrival of new tasks during execution

time c) Failure of a node during run time

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Graph Theory:

Structure of Network ga = (N,C)

Network Architecture

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Network Architecture Laplacian Matrix: Given a graph G with n vertices (without

loops or multiple edges), its Laplacian matrix is defined as

3 -1 -1 -1

-1 3 -1 -1

-1 -1 3 -1

-1 -1 -1 3

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Assumptions w.r.t Networka) Architecture graph is undirectedb) each computational task may be assigned to

each node in the network without restrictionc) HW Reconfiguration Temporal partition: Temporal HW/SW

partition at time t is an assignment of each task p Є P(t) to a resource N ( t ) as well as the indication whether the task is implemented in HW or SW.

Network Architecture

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Workload characterization: Each task pj Є P(t) causes a unique load wh

j on resource ni Є N ( t ) if implemented in HW and a load of ws

j, if implemented in SW. Load: For HW - The fraction of total area occupied by

the load For SW - The fraction of execution time and

period.

Network Architecture

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load exchanges between two adjacent nodes are determined in each iteration as:

yk-1c = β(wk-1

i – wk-1j) for all c = {ni, nj} Є C

wki = wk-1

i - ∑ yk-1c

c = {ni, nj} Є C Changing β in each iteration k has shown that the

convergence speed can be drastically improved to exactly m - 1 iterations

Choosing β = 1/גk where 1 ≤ k ≤ m – 1

m – Number of distinct Eigen Values of the Laplacian matrix

Diffusion Algorithm

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Optimization Flow

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Objectives:• Find a bi-partition such that the load is

balanced between HW and SW i.e.; minimize ∑|N| wS

i - ∑|N| wHi

i = 1 i = 1 • Effective Load Balance i.e.; minimize |w’ – max{maxi:niЄN{wS

i }, max{maxi:niЄN{wHi }|

by using Evolutionary Algorithm applied to encode

implementation selection• Diffusion Algorithm only balances load

between nodes not HW/SW load

Optimization Flow

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Need: It is advisable not to split one process and

distribute it to multiple nodes. This increases the data traffic in the network.

Let ycontkc be the real-valued continuous and

ydisckc the discrete flow on one edge c in iteration

k such that ydisckc doesn’t exceed ycontk

c

ydisckc ≤ ycontk

c + ek-1c with e0

c = 0

ekc = ycontk

c + ek-1c - ydisck

c for all c={ni, nj} Є C

An additional adjustment step is introduced em

c = em-1c - yadj

c

Discrete Diffusion Algorithm

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Experimental Analysis Evaluation the discrete diffusion

algorithm for different types of a network like meshes with 3x3 or 4x4 nodes, a ring and a chordal ring with 8 nodes

In the beginning all tasks are mapped onto a single resource node

Focus is set on the load error |w’ – wi| and the congestion in the network

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Experimental Analysis

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Experimental Analysis

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Questions?

Thank You