Modified Cell Delineation Strategy For Packet Switched Networks

Modified Cell Delineation Strategy for Packet Switched Networks Department of Computer Science Bar-Ilan University Department of Communication Engineering Holon Academic Institute of Technology Marina Kopeetsky and Avi Lin

Outline

The Packet Network Computational Model

The Packets’ Errors Handling Problem

The Modified Cell Delineation Strategy

Example: the Three-States Cell Delineation Strategy Realization.

Talk Key Issues

Presenting a new Cell Delineation (CD) Strategy for any Packet Switching technology of a fixed length Data Units (DUs)

This special strategy offers algorithms for differentiating between synchronization failures and other channel and environment errors with a sufficiently high confidence level

This algorithms’ family is analyzed and optimized.

A possible implementation of this strategy is illustrated for the ATM network case:

The Cell Delineation cycle implementation time is discussed and analyzed.

Numerical results are presented for the case of the standard CD protocol.

The Packets’ Errors Handling

A new strategy, algorithms and relevant techniques are:

offered for properly recognize and maintain cell or packet's boundaries

designed to tackle and handle general error packets, with the major objectives to differentiate in Real Time between synchronization failures and other noisy environment channel errors

For handling corrections:

The algorithms are properly modified for cell synchronization recovery and other noisy channel errors

corrections are proposed, analyzed and optimized

Introduction and Packet Network Model

We propose a new Cell Delineation (CD) Strategy for any Packet Switching technology with the fixed length Data Units (DUs). A special strategy that differentiates between synchronization failures and other channel errors with the sufficiently high confidence level is proposed, analyzed and optimized.

The strategy implementation is illustrated on the Asynchronous Transfer Mode (ATM) network example. The Cell Delineation cycle implementation time is discussed and analyzed. The numerical results are presented for the case of the standard Cell Delineation (CD) protocol.

Main Research Conclusions

The expansion of the number of the CD protocol discrete states is necessary in order to construct the Cell Delineation recovery procedure in the optimal/near optimal manner.

The CD protocol parameters should be chosen dynamically based on the traffic transmission conditions.

The presented strategy is appropriated to any fixed cell/packet network technology.

Construction of the distribution function of the CD protocol cycle time in the precise way.

Fixed Cell 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

Classical Cell Delineation Process Structure CD process parameters should be allocated in a dynamic fashion! HEC indicates on out of synchronism state SYNCH HUNT PRESYNCH

Critique of the Standard CD Protocol

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.

Modified Cell Delineation Process Structure

recovers and corrects random errors in the cell Header

ERROR state:

distinguishes between various errors generated by different sources

SYNCH HUNT ERROR PRESYNCH

The General Cell Delineation Process Structure SYNCH HUNT ERROR PRESYNCH FAILURE FAILURE state is relevant for the channel degradation case

Modified CD Protocol Features

The nature of the CD protocol is its rapid execution (comparing to the traffic rate) and its effectiveness

There exists a single stable state SYNCH.

The parameter should be determined dynamically subject to the following arguments:

The noisy channel error flow model in respect to the current BER;

The accumulated channel errors history;

The traffic type (CBR, VBR, ABR or UBR).

Modified CD Protocol Features – Cont’d (1)

The incoming cells stream is composed of two cells types:

Black (B) type erroneous cells

White (W) type cells that are correct ones

The random length of the sequential B-type cells is studied and analyzed within a certain time window T

The near-optimal choice of T is critical in order to create the effective and robust delineation strategy

Modified CD Protocol Features – Cont’d (2)

Denote by B* and W* the average lengths of B and W-type cells streams received within the T time window respectively, then

is very small.

The Objective

We seek a strategy or a mechanism that will enable to distinguish between non-synchronous and other erroneous packets or cells among sequential B-type cells in a precise fashion, enjoying the above features.

Main Solution Preliminaries

Evaluate the optimal/minimal B-Type sequential cells stream length, , that identifies the synchronization failure occurrence subject to a certain confidence level .

The near-optimal real time implementation of the synchronization recovery strategy depends on:

The error flow model of the noisy channel in respect to the current BER (Feature 3)

The synchronization failures model that includes dependencies on the current value of the cell non-synchronous state final probability as well as one the synchronization failures history;

The different traffic types and the Quality of Service (QoS) parameters.

Near-optimal Choice of the Time Window T

T must be large enough so that the large scale statistics will be stable.

T is a function of B* parameter, which depends on the probabilities of the different error types:

T=f( traffic model, traffic intensity)

The value of T must be continuously considered for update each time step t.

The updated value of T is based on its current value as well as on the historical values.

Ergodic Markov Chain in order to predict the new T value.

Modified Cell Delineation Strategy

The value of with respect to :

SYNCH  ERROR

SYNCH  ERROR

SYNCH  HUNT

SYNCH  HUNT

Modified Cell Delineation Strategy

: any number of B-Type cells that have been received within next time windows T, pass to the HUNT state.

Note: the traffic modeling is needed for error bursts analysis and prediction.

Error sensitive network:

HUNT->FAILURE, ERROR->FAILURE

HUNT <-> ERROR : no definit limitations on CD process time execution

ERROR-> HUNT: errors cannot be detected using CRC

HUNT-> ERROR: HUNT state operations have been failed.

Dynamic Assignment of Parameter

Correct value assignment of will influence:

The probability of a non-correct decision about synchronization failure or

establishment respectively.

The robust synchronization recovery after the synchronization failure occurs.

Minimization of the cell loss probability.

Then the min number of sequential B-Type cells within a specific time window T is equal to CER- Cell Error Rate Denote

Statement of the Optimization Problem

The problem is to define number required for deciding on the following synchronization failure issues:

Synchronization failure final probability

Probability of non correct decision about the synchronization failure;

Average CD cycle time ;

CD cycle time variance V .

The Objective Function Definition K is a function of synchronization failures model and synchronization failure final probability Subject to: should be determined based on the real statistical data of the communication channel

* Analysis of the CD Cycle Average Time The computational strategy is based on the different branches of the CD probabilistic graph execution. Six general possibilities to cover the CD graph: