P RINCIPLES OF S WITCHING Professor Saad Haj Bakry, PhD, CEng, FIEE N ETWORK A RCHITECTURE

PRINCIPLES OF SWITCHING

Professor Saad Haj Bakry, PhD, CEng, FIEE

NETWORK ARCHITECTURE

CONTENTS

Saad Haj Bakry

Network Architecture Switching

CIRCUIT SWITCHING MULTIPLEXING

STORE & FORWARD

SUGGESTED WORK

MULTIPLEXING

Saad Haj Bakry

Network Architecture Switching / Multiplexing

TIME DIVISION: TDM

PRINCIPLES

FREQUENCY DIVISION: FDM

PROBLEM

PRINCIPLES

Saad Haj Bakry


OBJECTIVE: Enabling “N” Signals to Share a Channel

CONCEPT: Dividing the Channel

into “N” Sub-channels

FIXED DIVISION: SPACE DIVISION

(“N” Physical Links into One Conduit)

FREQUENCY DIVISION TIME DIVISION

DYNAMIC DIVISION: CONCENTRATION (S&F)

FREQUENCY DIVISION MULTIPLEXING

Saad Haj Bakry


FDM

1

N

I

I

2

3

f2

f1

f3

fN

F = f1 + f2 + f3 + ...+fN = N.f

F: Bandwidth of Shared Channel

fi: Bandwidth for “i = 1......N”

f: Average / Fixed Bandwidth per Subchannel

Shared Channel

TIME DIVISION MULTIPLEXING

Saad Haj Bakry


TDM

1

I

I

2

3

N

Shared Channel

3N2 1 S 12

Frame of “Slots”, where a user is regularly assigned the same sequenced slot in each frame.

Time Frame

S: Sync

PROBLEM

Saad Haj Bakry


USE: Suitable for

Continuous Use, Not for Burst / Random Use

MAIN PROBLEM: Sub-channels of the Shared Channels are Reserved to Users on “Fixed” Basis Not on “Dynamic / Demand”

Basis. Sub-channels are “Wasted” when their

Users are “Not Active”.

SOLUTION: Use of “Circuit

Switching”

CIRCUIT SWITCHING

Saad Haj Bakry

Network Architecture Switching / Circuit

PRINCIPLES

ERLANG-B FORMULA

TELEPHONE OPERATION

TELEPHONE TRAFFIC

PRINCIPLES: 1/2

Saad Haj Bakry


OBJECTIVE: Enabling

Sub-channels to be Assigned to Users

“Dynamically” on Demand

(Not on Fixed Basis)

USE: Suitable for Burst / Random Use

CONCEPT: Sub-channels Assigned on

Demand for Active Use and Released

when Activity is Completed

Saad Haj Bakry


PRINCIPLES: 2/2

TDM / FDM

CIRCUIT SWITCHING

USERS

Users Generating Demands

Dynamic Assignment / Release on

Demand

“N” Sub-Channels

Channel Sharing

Shared Channel

TELEPHONE OPERATION

Saad Haj Bakry


1. DIAL-UP

3. CALL PROGRESS

4. CALL TERMINATION

2. SIGNALLING / ROUTING / ASSIGNMENT

5. RELEASE

TELEPHONE TRAFFIC: 1/3

Saad Haj Bakry


TWO RANDOM PROCESSES

CALL ARRIVALS: Random

Distribution (Poisson Process)

CALL DURATION: Random

Distribution (Negative Exponential Distribution / Related to Poisson Process)


Saad Haj Bakry


R [Calls / Time Unit]: Rate of Generated

CallsD [Time Unit]:

Average Call Duration

A [Erlang]: A = R.D

BUSY HOUR PRINCIPLE

ERLANG: “1” Erlang is Full

Channel Occupancy For “1” Time Unit


Saad Haj Bakry


“1” ERLANGR = 1 [Calls / Hour]

D = 60 [Minutes]

A = 1 [Erlang]

R = 4 [Calls / Hour]

D = 15 [Minutes]

A = 1 [Erlang]

R = 12 [Calls / Hour]

D = 5 [Minutes]

A = 1 [Erlang]

ERLANG-B FORMULA: 1/4

Saad Haj Bakry


TYPICAL / SIMPLE CASE STUDY SYSTEM:

“N” (Sub)

Channels Fully

Available to All Call

DEMANDS / TRAFFIC

OFFERED BY

ALL USERS: “A”

[Erlang]

PERFORMANCE

/ GRADE OF

SERVICE /

BLOCKING

PROBABILITY “B”


Saad Haj Bakry


B = (AN / N!) / i 0

i N

(Ai / i!)

B = 1 /

i 0

i N

(N! / (Ai (N - i)!))


Saad Haj Bakry


OTHER IMPORTANT FACTORS

TRAFFIC CARRIED /

SERVICED:

K = A (1 - B)

AVERAGE CHANNEL

UTILIZATION /

OCCUPANCY:

Q = K / N

ERLANG-B FORMULA: 4 /4

Saad Haj Bakry


POSSIBLE USE

SYSTEM

EVALUATION:

Given: N / A Find:

B / K / Q

SYSTEM

CAPACITY:

Given: N / B Find:

A / K / Q

SYSTEM

DESIGN:

Given: A / B / K

Find: N / Q

STORE & FORWARD

Saad Haj Bakry

Network Architecture Switching / S&F

CONCENTRATION

PERFORMANCE

TRAFFIC

ANALYSIS

MESSAGE / PACKET / FRAME /

CELL (SWITCHING / RELAY)

CONCENTRATION: 1/2

Saad Haj Bakry


1

+I

2

N

I

I

P M MSHARED CHANNEL

BUFFERPROCESSOR

STORE & FORWARDc

c

c [bps]

c

C [bps]

Dynamic Channel Assignment (Active Users Only) / Efficiency

USERS > N Where N = C/c

Saad Haj Bakry


CONCENTRATION: 2/2

BURST USE USE

LOSS SENSITIVE

INFORMATION: “DATA / TEXT”

NO DELAY SENSITIVE

INFORMATION: “VOICE / PICTURE”; EXCEPT IN HIGH

SPEED

Saad Haj Bakry


MESSAGE

MESSAGE: •An Information Signal Sent by a Single User •Physical Block

•(Basic Name: for M / P / F / C)

PROBLEM: •Fluctuating Size•Need for Size Control “P / F / C” (Logical Units)•Providing Better Sharing

Saad Haj Bakry


PACKET / FRAME / CELL: 1 / 3

PACKET: X.25 / 64 kbps Variable Size H: 8 bytes

FRAME: T-1 / E-1

Variable Size H: 2 bytes

INFORMATION HEADER HEADER: SOURCE / DESTINATION / CONTROL

INFORMATION: CONTROLLED SIZE

CELL / ATM: OC-3 / OC-12 Fixed: 48 Bytes

H: 5 bytes

Saad Haj Bakry



DATAGRAM: Logical Units (Packets) are

Routed Independently Through the

Network from Source to

Destination

VIRTUAL CIRCUIT: Physical Units

(Messages) Sent from Source to Destination Look as if they Passed

Through a Circuit Example: DATAGRAM with the Packets of a

Message Reassembled at Destination

Saad Haj Bakry



PACKET: Point-to- Point

& End-to-

End

FRAME: End-to-End

Only

ERROR CONTROL

CELL / ATM: End-to-End

(Header Only)

LOW NOISE: Eases Error Control Protocols. HIGHER SPEED: Reduces Delay and Helps Information Integration (Data / Voice / Picture)

PERFORMANCE: DELAY (1/3)

Saad Haj Bakry


P M M

M [bits]

NEXT

NODE

DELAY ELEMENTS

PROCESSING DELAY “p”

QUEUING DELAY “q”

TRANSMISSION DELAY “s”

PROPAGATIONDELAY “g”

p q s g

MESSAGE DELAY: d = p + q + s + g

C [bps]l [km]v [km/s] /

Sec.


Saad Haj Bakry


PROCESSING DELAY: Processing Dependent

Traffic Independent

QUEUING DELAY: Traffic / Capacity

(System) Dependent Analysis Required

TRANSMISSION DELAY: s = M / C

Message / Capacity (System) Dependent

Independent of Traffic Volume / Fluctuation

PROPAGATION DELAY: g = l / v Channel / Distance

Dependent Traffic / Capacity

Independent

Saad Haj Bakry



PROCESSING DELAY: Significant in High

Speed Links

QUEUING DELAY: An Essential Element,

as it is Associated with the Capacity / “System”,

and Traffic Volume / Fluctuation / “Demands”

TRANSMISSION DELAY: An Essential Element, as it

is Associated with the Capacity / “System” , and

the Message Length / “Demands”

PROPAGATION DELAY: Significant in Satellites

g = 36 / 300 = 0.12 sec

Saad Haj Bakry


TRAFFIC: 1/2

TWO RANDOM PROCESSES

MESSAGE ARRIVALS:

Poisson Process

MESSAGE LENGTH: Negative Exponential

Distribution / Fixed Size Messages

(Deterministic)

TRAFFIC: 2/2

Saad Haj Bakry


R [Messages / Sec]: Rate of Generated

Messages

M [Bits]: Average / Fixed Message Length

BUSY HOUR PRINCIPLE

TRAFFIC RATE: A [bps] = R . M

ANALYSIS: 1/4

Saad Haj Bakry


QUEUING DELAY:

Variable Message Length qv = (RM / C) /

( (C/M) - R)Fixed Message Length

qf = (1/2) . qv

ANALYSIS: 2/4

Saad Haj Bakry


ESSENTIAL DELAY ELEMENTS: d = qv + s = 1 / ( (C/M) - R)

LIMITATION: RM < C

UTILIZATION / OCCUPANCY: U = (RM) / C

ANALYSIS: 3/4

Saad Haj Bakry


D: NORMALIZED DELAY: (MESSAGE TRANSMISSION TIME “s”) IN

TERMS OF UTILIZATION “U”:

D = d / s = 1 / (1 - U) D [Unit-less]: Number of Messages in

the System (queued & transmitted)

ANALYSIS: 4/4

Saad Haj Bakry


POSSIBLE USE

SYSTEM EVALUATION: Given: C / M / R

Find: d / U / D

SYSTEM CAPACITY: Given: C / U (d/D) / M

Find: R

SYSTEM DESIGN: Given: R / M / U Find: C

SUGGESTED WORK

Saad Haj Bakry

Network Architecture Switching: Work

GENERAL: Computations

Concerned with “Circuit

Switching” and “Store &

Forward”

SPECIAL: Investigations of

Practical “CS” and “S&F” Systems

Documents

P RINCIPLES OF S WITCHING Professor Saad Haj Bakry, PhD, CEng, FIEE N ETWORK A RCHITECTURE