modified cell delineation strategy for packet switched networks
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Modified Cell Delineation Strategy Modified Cell Delineation Strategy for Packet Switched Networksfor Packet Switched Networks
Department of Computer ScienceDepartment of Computer ScienceBar-Ilan UniversityBar-Ilan University
Department of Communication EngineeringDepartment of Communication EngineeringHolon Academic Institute of TechnologyHolon Academic Institute of Technology
Marina KopeetskyMarina Kopeetskyandand
Avi LinAvi Lin
22
OutlineOutline
The Packet Network Computational ModelThe Packet Network Computational Model
The Packets’ Errors Handling ProblemThe Packets’ Errors Handling Problem
The Modified Cell Delineation StrategyThe Modified Cell Delineation Strategy
Example: the Three-States Cell Delineation Example: the Three-States Cell Delineation
Strategy Realization.Strategy Realization.
33
Talk Key IssuesTalk Key Issues Presenting a new Cell Delineation (CD) Strategy for any Presenting a new Cell Delineation (CD) Strategy for any
Packet Switching technology of a fixed length Data Units Packet Switching technology of a fixed length Data Units (DUs)(DUs)
This special strategy offers algorithms for differentiating This special strategy offers algorithms for differentiating between synchronization failures and other channel and between synchronization failures and other channel and environment errors with a sufficiently high confidence levelenvironment errors with a sufficiently high confidence level
This algorithms’ family is analyzed and optimized.This algorithms’ family is analyzed and optimized. A possible implementation of this strategy is illustrated for A possible implementation of this strategy is illustrated for
the ATM network case:the ATM network case:– The Cell Delineation cycle implementation time is discussed and The Cell Delineation cycle implementation time is discussed and
analyzed. analyzed.
– Numerical results are presented for the case of the standard CD Numerical results are presented for the case of the standard CD protocol. protocol.
44
The Packets’ Errors HandlingThe Packets’ Errors Handling
A new strategy, algorithms and relevant techniques are:A new strategy, algorithms and relevant techniques are:
offered for properly recognize and maintain cell or packet's offered for properly recognize and maintain cell or packet's
boundaries boundaries
designed to tackle and handle general error packets, with the designed to tackle and handle general error packets, with the
major objectives to differentiate in Real Time between major objectives to differentiate in Real Time between
synchronization failures and other noisy environment channel synchronization failures and other noisy environment channel
errors errors
For handling corrections:For handling corrections:
– The algorithms are properly modified for cell The algorithms are properly modified for cell
synchronization recovery and other noisy channel errors synchronization recovery and other noisy channel errors
– corrections are proposed, analyzed and optimized corrections are proposed, analyzed and optimized
55
Introduction and Packet Network Introduction and Packet Network ModelModel
We propose a new Cell Delineation (CD) Strategy We propose a new Cell Delineation (CD) Strategy for any Packet Switching technology with the for any Packet Switching technology with the fixed length Data Units (DUs). A special strategy fixed length Data Units (DUs). A special strategy that differentiates between synchronization that differentiates between synchronization failures and other channel errors with the failures and other channel errors with the sufficiently high confidence level is proposed, sufficiently high confidence level is proposed, analyzed and optimized.analyzed and optimized.
The strategy implementation is illustrated on the The strategy implementation is illustrated on the Asynchronous Transfer Mode (ATM) network Asynchronous Transfer Mode (ATM) network example. The Cell Delineation cycle example. The Cell Delineation cycle implementation time is discussed and analyzed. implementation time is discussed and analyzed. The numerical results are presented for the case The numerical results are presented for the case of the standard Cell Delineation (CD) protocol. of the standard Cell Delineation (CD) protocol.
66
Main Research ConclusionsMain Research Conclusions
The expansion of the number of the CD protocol The expansion of the number of the CD protocol discrete states is necessary in order to construct discrete states is necessary in order to construct the Cell Delineation recovery procedure in the the Cell Delineation recovery procedure in the optimal/near optimal manner.optimal/near optimal manner.
The CD protocol parameters should be chosen The CD protocol parameters should be chosen dynamically based on the traffic transmission dynamically based on the traffic transmission conditions.conditions.
The presented strategy is appropriated to any The presented strategy is appropriated to any fixed cell/packet network technology.fixed cell/packet network technology.
Construction of the distribution function of the CD Construction of the distribution function of the CD protocol cycle time in the precise way.protocol cycle time in the precise way.
77
FixedFixed Cell Network Protocol StructureCell Network Protocol Structure
Payload Field
n bytes
n=48 for ATM
Header
m bytes
m=5 for ATM
H
E
C
H
E
C
L=m+n bytes
88
Classical Cell Delineation Process Classical Cell Delineation Process StructureStructure
SYNCH
HUNT
PRESYNCH
checkbitbyBit
cellscorrecteconsecutivδm
cellscorrect-noneconsecutivαn
CD process parameters should be allocated in a dynamic fashion!
HEC indicates on out of synchronism state
99
Synchronization failures and other channel errors are mixed together and treated in the same way leading to cell drop and information transfer lose.
Thus
• Different types of errors must be treated differently!
•Traffic based Dynamic allocation of the CD process parameters.
Critique of the Standard CD ProtocolCritique of the Standard CD Protocol
1010
Modified Cell Delineation Process Modified Cell Delineation Process StructureStructure
2. recovers and corrects random errors in the cell Header
ERROR state:
1. distinguishes between various errors generated by different sources
SYNCH
HUNT
ERROR
PRESYNCH
1111
The General Cell Delineation The General Cell Delineation Process StructureProcess Structure
SYNCH
HUNT
ERROR
PRESYNCH
FAILURE
FAILURE state is relevant for the channel degradation case
1212
Modified CD Protocol FeaturesModified CD Protocol Features
1.1. The nature of the CD The nature of the CD protocol is its rapid protocol is its rapid execution execution (comparing to the (comparing to the traffic rate) and its traffic rate) and its effectivenesseffectiveness
2.2. There exists a single There exists a single stable state stable state SYNCH.SYNCH.
3.3. The parameter The parameter should be should be determined determined dynamically subject dynamically subject to the following to the following arguments:arguments:
The noisy channel error The noisy channel error flow model in respect to flow model in respect to the current BER;the current BER;
The accumulated The accumulated channel errors history;channel errors history;
The traffic type (CBR, The traffic type (CBR, VBR, ABR or UBR). VBR, ABR or UBR).
stateSYNCHtheinecteddetbeenhave
HECscorrectnon
utivesecconnifstate
HUNTthetofollowsSystem
1313
Modified CD Protocol Features – Modified CD Protocol Features – Cont’d (1)Cont’d (1)
4.4. The incoming cells The incoming cells stream is composed stream is composed of two cells types:of two cells types:
BlackBlack (B) type (B) type erroneous cells erroneous cells
WhiteWhite (W) type cells (W) type cells that are correct onesthat are correct ones
5.5. The random length of The random length of the sequential B-type the sequential B-type cells is studied and cells is studied and analyzed within a analyzed within a certain time window certain time window TT
The near-optimal The near-optimal choice of T is critical choice of T is critical in order to create the in order to create the effective and robust effective and robust delineation strategydelineation strategy
1414
Modified CD Protocol Features – Modified CD Protocol Features – Cont’d (2)Cont’d (2)
6.6. Denote by Denote by B*B* and and W*W* the average lengths the average lengths of B and W-type cells of B and W-type cells streams received streams received within the T time within the T time window respectively, window respectively, thenthen
is very small. is very small.
*)W*B(*B
1515
The ObjectiveThe Objective
We seek a strategy or a mechanism We seek a strategy or a mechanism that will enable to distinguish that will enable to distinguish between non-synchronous and between non-synchronous and other erroneous packets or cells other erroneous packets or cells among sequential B-type cells in a among sequential B-type cells in a precise fashion, enjoying the above precise fashion, enjoying the above features.features.
1616
Main Solution PreliminariesMain Solution Preliminaries
1.1. Evaluate the Evaluate the optimal/minimal optimal/minimal B-Type sequential B-Type sequential cells stream cells stream length, , that length, , that identifies the identifies the synchronization synchronization failure occurrence failure occurrence subject to a subject to a certain certain confidence level .confidence level .
2.2. The near-optimal real time The near-optimal real time implementation of the implementation of the synchronization recovery synchronization recovery strategy depends on:strategy depends on:
The error flow modelThe error flow model of the of the noisy channel in respect to noisy channel in respect to the current BER (Feature 3)the current BER (Feature 3)
The synchronization failuresThe synchronization failures modelmodel that includes that includes dependencies on the dependencies on the current value of the cell current value of the cell non-synchronous state final non-synchronous state final probability as well as one probability as well as one the synchronization failures the synchronization failures history;history;
The different traffic typesThe different traffic types and the Quality of Service and the Quality of Service (QoS) parameters. (QoS) parameters.
minb
1717
Near-optimal Choice of the Time Near-optimal Choice of the Time Window TWindow T
T must be large enough so that the large scale T must be large enough so that the large scale statistics will be stable.statistics will be stable.
T is a function of B* parameter, which depends on T is a function of B* parameter, which depends on the probabilities of the different error types: the probabilities of the different error types:
T=f( traffic model, traffic intensity)T=f( traffic model, traffic intensity)
The value of T must be continuously considered The value of T must be continuously considered for update each time step t.for update each time step t.
The updated value of T is based on its current The updated value of T is based on its current value as well as on the historical values.value as well as on the historical values.
Ergodic Markov Chain in order to predict the new T Ergodic Markov Chain in order to predict the new T value. value.
1818
Modified Cell Delineation StrategyModified Cell Delineation Strategy
1.1. The value of with respect to :The value of with respect to : SYNCHSYNCHERROR ERROR
SYNCHSYNCHERRORERROR
SYNCHSYNCHHUNTHUNT
SYNCHSYNCHHUNT HUNT
Nk,kbmin
kbkb minmin
kbmin
ratetolerancecertainaisNk
iancevarbais min
1919
Modified Cell Delineation StrategyModified Cell Delineation Strategy
2.2. : any number of B-Type cells that have : any number of B-Type cells that have been received within next time windows T, pass to been received within next time windows T, pass to the HUNT state. the HUNT state.
Note: the traffic modeling is needed for error bursts Note: the traffic modeling is needed for error bursts analysis and prediction.analysis and prediction.
3.3. Error sensitiveError sensitive network: network: HUNT->FAILURE, ERROR->FAILUREHUNT->FAILURE, ERROR->FAILURE4.4. HUNT <-> ERROR : no definit limitations on CD HUNT <-> ERROR : no definit limitations on CD
process time executionprocess time execution ERROR-> HUNT: errors cannot be detected using ERROR-> HUNT: errors cannot be detected using
CRCCRC HUNT-> ERROR: HUNT state operations have been HUNT-> ERROR: HUNT state operations have been
failed. failed.
kbmin
2020
Dynamic Assignment of Dynamic Assignment of ParameterParameter
Correct value assignment of will influence:1. The probability of a non-correct decision about
synchronization failure or establishment respectively.2. The robust synchronization recovery after the
synchronization failure occurs.3. Minimization of the cell loss probability.
Then the min number of sequential B-Type cells within a specific time window T is equal to
k,bmin
n
ii
i
n
imin
average
min
CER
CERbb
i
1
1
Denote
minb
kbb minmin cellserroneous
ofnumberaveragei
)i(Piminb
)cellserroneousutivesecconi(probiP
1
CER- Cell Error Rate
2121
Main Research ConclusionsMain Research Conclusions
The expansion of the number of the CD protocol The expansion of the number of the CD protocol discrete states is necessary in order to construct discrete states is necessary in order to construct the Cell Delineation recovery procedure in the the Cell Delineation recovery procedure in the optimal/near optimal manner.optimal/near optimal manner.
The CD protocol parameters should be chosen The CD protocol parameters should be chosen dynamically based on the traffic transmission dynamically based on the traffic transmission conditions.conditions.
The presented strategy is appropriated to any The presented strategy is appropriated to any fixed cell/packet network technology.fixed cell/packet network technology.
Construction of the distribution function of the CD Construction of the distribution function of the CD protocol cycle time in the precise way.protocol cycle time in the precise way.
2222
Statement of the OptimizationStatement of the Optimization Problem Problem
The problem is to define number The problem is to define number required for deciding on the following required for deciding on the following synchronization failure issues: synchronization failure issues:
Synchronization failure final probability Synchronization failure final probability Probability of non correct decision Probability of non correct decision
about the synchronization failure;about the synchronization failure; Average CD cycle time ;Average CD cycle time ; CD cycle time variance CD cycle time variance VV..
2
ncp
cT
2323
The Objective Function DefinitionThe Objective Function Definition
0
,Nk
kb)k,b(F average
minmin
similarityselfnetworkofcasetheinCB
Aek
2
VV
TTc
22 Subject to:
K is a function of synchronization failures model and synchronization failure final probability
,b
C,B,Aaverage
min
0
should be determined based on the real statistical data of the communication channel
02022
)(glimanddecreases)(gk
2424
* Analysis of the CD Cycle Average * Analysis of the CD Cycle Average TimeTime
The computational strategy is based on the different branches of the CD probabilistic graph execution.
Six general possibilities to cover the CD graph:
1. SYNCH->HUNT->PRESYNCH->SYNCH
2. SYNCH->HUNT->PRESYNCH->HUNT->PRESYNCH->SYNCH
3. SYNCH->ERROR->HUNT->PRESYNCH->HUNT->
PRESYNCH->SYNCH4. SYNCH->ERROR->HUNT->PRESYNCH->SYNCH5. SYNCH->HUNT->ERROR->PRESYNCH->SYNCH6. SYNCH->ERROR->PRESYNCH->SYNCH
2525
* *Analysis of the CD Cycle Average Analysis of the CD Cycle Average Time-Cont’dTime-Cont’d
6
1
3411
26
324125
32411
24
32411
23
32112
32121
43
21
40140016
401400115
40140014
4014003
4014001
2
4014001
i
icc
ikb
ic
bc
ikb
ic
ikb
ic
HUNTabs
ccc
minc
TT
TTT)),(P),(P(T.
TTTT)),(P),(P(T.
TTTT)),(P),(P(T.
TTTT),(P),(PT.
),(P),(P(p̂
PRESYNCHHUNTprobHUNTPRESYNCHprobp̂
TTp̂THUNTPRESYNCHTTT.
TTTb),(P),(PT.
ERRORTT,PRESYNCHTT
,HUNTTT,SYNCHTT
min
min
min
min
Denote
Note: 40 bit=5 bytes for ATM cell Header
2626
* Example of the Three-States * Example of the Three-States CD Strategy RealizationCD Strategy Realization
The CD Process is best described by Semi-Markovian because:
1. 1) The real-time analysis 2. 2) It is possible to include the statistical correlation between the
sequential discrete states of the process. 3. 3) It has the needed ingredients to describe and to differentiate the
different sources of the CD failures. The following failures are considered:
distortion of the cell Header that is caused by channel errors synchronization failures channel failures.
2727
The General Analysis of the Three-States CD Protocol
Using the Following Aspects:
• Different error transmission models (Markov and Bernoulli) of the communication channel
• Basic and Advanced PRESYNCH protocol
• Different models of the synchronization failures: Self-recovery and non-self-recovery synchronization failures.
2828
The Formal Model
GERT (Graphical Evaluation and Review Technique) method: Definition G={V,A} is stochastic if the execution of a specific set of arcs actions is sufficient for a whole network project execution. Set of conditional Moments Generating Functions (MGF) of a
random variable xyg with argument s: xysg
xy eEsM
W-functions: .,, VyxsMpsW xyxyxy
.)()(
)(
0s
0j00s
j
0j
j sWsd
d
0W
1
sd
sMd
0W - general W-function that corresponds to the CD process
execution
2929
W-functions of the typical topological structures
31322312 WWWW ,,, are the W-functions that correspond to the
transitions SYNCHPRESYNCH,HUNTPRESYNCH
,PRESYNCHHUNT,HUNTSYNCH
Consecutive Connection of Arcs
SYNCHPRESYNCHHUNTSYNCH
iyxixyiyxixixy WWMpMpW .
.WWWn
xx,xxn
1
2111
SYNCH HUNT
PRESYNCH
*
3030
Parallel connection of arcs with the transition probabilities mh,...,h,h 21
A various number of recurrences from PRESYNCH to HUNT within a given CD cycle must be taken into consideration
.xzxyxzxy
xzxzxyxyxzxy WW
pp
MpMp)pp(W
PRESYNCH HUNT
22 w,h
nn wh ,
11 w,h
11 w,h
*
3131
Loops or cycles that prevent the next arc execution
.
L
1i
i2332 WWW
PRESYNCH
HUNT
PRESYNCH
SYNCH
HUNT
PRESYNCH
HUNT
PRESYNCH
HUNT
PRESYNCH
HUNT
PRESYNCH
*
3232
Calculation Procedure
13132
2
23123123120i
iWWWWWWWW
121212 MpW
.p 112
112
i
SYNCHabs
st iesM i
.itt i
t is the cell transmission time
iepW HUNTabs
ts i2323
itis the processing time of i bits, itti ,
tis a bit processing time.
13131
13232
2
1
i
PRESYNCHabs
st
i
PRESYNCHabs
st
iepW
iepW
i
i
.3231 p1p
3333
Basic PRESYNCH protocol:
.
ie
),(P),(P),(P),(PW
L
j iPRESYNCHabs
st
LL
i
1 132
2
4014004014001
Advanced CD protocol:
.iπeU)(1
P(1,40)P(0,40)1UP(1,40)P(0,40)1
1W
1i
PRESYNCH
abs
stLδ
1j
j
32
2
i
L
W32
*
3434
Numerical Results
Average cycle time 1M as a function of . Markov error flow model,
,62 10 basic PRESYNCH protocol,
Poisson model of synchronization failures, .1210 Case 1 corresponds to
,2 case 2 corresponds to .14
0.0001
0.001
2 8 14
case 1
case 2
1M
3535
Average cycle time 1M as a function of . Markov error flow model, .6
2 10 Case 1 corresponds to ,2 case 2 corresponds to .14
0.00064
0.00066
0.00068
0.0007
0.00072
0.00074
0.00076
0.00078
0.0008
0.00082
0.00084
0.00086
2 8 14
case 1
case 2
1M
3636
.
,,,elsmodflow
errorMarkovandBernoulli
foroffunctionasp
12
62
10
108
P*
3737
.,,
,,offunctionaasp3612
62
101010
10
3838
0.00E+00
1.00E-07
2.00E-07
3.00E-07
4.00E-07
5.00E-07
6.00E-07
7.00E-07
8.00E-07
2 8 14
Case 1
Case 2
2M as a function of . Markov errorflow model, ,6
2 10 basic PRESYNCH protocol, Poisson model of
synchronization failures, .1210 Case 1 corresponds to ,2 case 2
corresponds to .14
3939
Average CD cycle time cT normal distribution function. Basic PRESYNCH protocol. Case 1 (red) corresponds to ., 22 Case 2 (green) corresponds to ., 88 Case 3 (yellow) corresponds to ., 1414 Markov error flow model, .6
2 10 Self-
recovery synchronization failures, .1210
4040
Average CD cycle time normal distribution function. Advanced PRESYNCH protocol. Case 1 (red) corresponds to ., 142 Case 2 (green) corresponds to ., 82
4141
Time occurrence in the non-synchronous state HUNT nsT normal distribution function. Case 1 (red) corresponds to ., 22 Case 2 (green) corresponds to ., 88 Markov error flow model, .6
2 10 Self-
recovery synchronization failures, .1210
4242
Average CD cycle time cT distribution function. Basic PRESYNCH protocol. Case 1 (red) corresponds to ., 22 Case 2 (green) corresponds to ., 88 Case 3 (yellow) corresponds toMarkov error flow model, .6
2 10 Self-recovery
synchronization failures, .1210
4343
Average CD cycle time cT distribution function. Advanced PRESYNCH protocol. Case 1 (red) corresponds to ., 142 Case 2 (green) corresponds to ., 82 Markov error flow model, .6
2 10 Self-recovery synchronization failures,
.1210
4444
Time occurrence in the non-synchronous state distribution function.
Case 1 (red) corresponds to ., 22 Case 2 (green) corresponds to ., 88 Markov error flow model, .6
2 10 Self-
recovery synchronization failures, .1210
4545
Conclusions
1. Referring to both types of error flow model (Bernoulli and Markov) the average cycle time 1M is, essentially, the increasing function of the arguments and . 2. The final probability of the cell non-synchronous state p is the decreasing function of the and arguments. 3. The final probability of cell non-synchronous state p increases by the increment of or . 4. Considering Bernoulli and Markov error flow models, the average cycle time ,M 1 as well as any distribution moment of higher order 2j,j are higher in the second case.
4646
Main Research ConclusionsMain Research Conclusions
The expansion of the number of the CD protocol The expansion of the number of the CD protocol discrete states is necessary in order to construct discrete states is necessary in order to construct the Cell Delineation recovery procedure in the the Cell Delineation recovery procedure in the optimal/near optimal manner.optimal/near optimal manner.
The CD protocol parameters should be chosen The CD protocol parameters should be chosen dynamically based on the traffic transmission dynamically based on the traffic transmission conditions.conditions.
The presented strategy is appropriated to any The presented strategy is appropriated to any fixed cell/packet network technology.fixed cell/packet network technology.
Construction of the distribution function of the CD Construction of the distribution function of the CD protocol cycle time in the precise way.protocol cycle time in the precise way.
4747
βα, Statement of the Optimization Problem
p - probability of the non-synchronous system state ncp - probability of non-correct decision about synchronization failure in the SYNCH state The objective function:
00 b,a,bpapp,pH ncnc
a and b - the parameters that define the relative weight of the variables p and ncp in the combined optimization problem. The main goal is to find ncp,pHmin considering the constraint imposed on the average cycle time 1M :
.ncp,pHmin
*MM
1
The continuous function .),(H 0
4848
Example Basic CD protocol, Markov error flow model,
.62 10 Non-self-recovery synchronization
failures, ,1210 .b,a, 118
ncp as a function of
1E-841E-801E-761E-721E-681E-641E-601E-561E-521E-481E-441E-401E-361E-321E-281E-241E-201E-161E-121E-08
0.00011
2 4 6 8 10 12 14
4949
ncp,pH values in the range
52
1.40E-07
-1.10E+00
-8.80E-01
-6.60E-01
-4.40E-01
-2.20E-01
0.00E+00
2.20E-01
2 4 6 8 10
5050
ncp,pH values in the range 155
1.00E-07
1.00E-06
1.00E-05
1.00E-04
5 6 7 8 9 10 11 12 13 14 15
5151
Conclusions
In the range 5 ncp,pH is the drastically increasing function of the argument. In the range 65 ncp,pH increases
slowly. At the point 6 ncp,pH has its maximum value.
For 6 ncp,pH is a very slowly decreasing function.
Using small values of 6 is very dangerous. The reason is that the probability of non-correct decision about synchronization failure is very high in this case.
For ,7 the influence of ncp on
ncp,pH is extremely small. Besides, ncp decreases drastically in the mentioned range. The optimal (minimal) ncp,pH value is investigated on the right end. The higher is the smaller the ncp,pH value is.
For the other values of the CD process parameters the result can be different.
5252
Main Research ConclusionsMain Research Conclusions
The expansion of the number of the CD protocol The expansion of the number of the CD protocol discrete states is necessary in order to construct discrete states is necessary in order to construct the Cell Delineation recovery procedure in the the Cell Delineation recovery procedure in the optimal/near optimal manner.optimal/near optimal manner.
The CD protocol parameters should be chosen The CD protocol parameters should be chosen dynamically based on the traffic transmission dynamically based on the traffic transmission conditions.conditions.
The presented strategy is appropriated to any The presented strategy is appropriated to any fixed cell/packet network technology.fixed cell/packet network technology.
Construction of the distribution function of the CD Construction of the distribution function of the CD protocol cycle time in the precise way.protocol cycle time in the precise way.
5353
Future PerspectivesFuture PerspectivesNew research issues in High Speed New research issues in High Speed
Network EngineeringNetwork Engineering
Optimal/near-optimal choice of the Optimal/near-optimal choice of the HEC Generating PolynomialHEC Generating Polynomial
Forward Error Correction Technique Forward Error Correction Technique in improving the CD process in improving the CD process characteristicscharacteristics
Defining of the precise CD strategy Defining of the precise CD strategy model that is based on the real model that is based on the real numerous data of the noisy channelnumerous data of the noisy channel
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