Download principles of switching

NETWORK ARCHITECTURE
PRINCIPLES
Professor
OF
SWITCHING
Saad Haj Bakry,
PhD, CEng, FIEE
Network Architecture
Switching
CONTENTS
MULTIPLEXING
STORE
&
CIRCUIT
SWITCHING
FORWARD
SUGGESTED WORK
Saad Haj Bakry
Network Architecture
Switching / Multiplexing
MULTIPLEXING
PRINCIPLES
FREQUENCY DIVISION: FDM
TIME DIVISION: TDM
PROBLEM
Saad Haj Bakry
Network Architecture
Switching / Multiplexing
PRINCIPLES
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)
Saad Haj Bakry
Network Architecture
Switching / Multiplexing
FREQUENCY DIVISION MULTIPLEXING
1
2
3
f1
f2
FDM
f3
N
Saad Haj Bakry
F = f1 + f2 + f3 + ...+fN = N.f
F: Bandwidth of Shared Channel
I
I
Shared Channel
fN
fi: Bandwidth for “i = 1......N”
f: Average / Fixed Bandwidth per Subchannel
Network Architecture
Switching / Multiplexing
TIME DIVISION MULTIPLEXING
1
2
Shared Channel
TDM
3
I
S: Sync
Time Frame
2 1 S N
NI Frame of “Slots”, where a
3 2 1
user is regularly
assigned the same sequenced slot in each frame.
Saad Haj Bakry
Network Architecture
Switching / Multiplexing
PROBLEM
MAIN PROBLEM:
USE:
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”.
Suitable for
Continuous Use,
Not for Burst /
Random Use
Saad Haj Bakry
SOLUTION:
Use of “Circuit
Switching”
Network Architecture
Switching / Circuit
CIRCUIT SWITCHING
PRINCIPLES
TELEPHONE
OPERATION
TELEPHONE
TRAFFIC
ERLANG-B FORMULA
Saad Haj Bakry
Network Architecture
Switching / Circuit
PRINCIPLES: 1/2
OBJECTIVE:
Enabling
Sub-channels to be
Assigned to Users
“Dynamically”
on
Demand
(Not on Fixed Basis)
CONCEPT:
Subchannels Assigned
on Demand for
Active Use and
Released when
Activity is
Completed
USE: Suitable for Burst / Random Use
Saad Haj Bakry
Network Architecture
U
S
E
R
S
Switching / Circuit
PRINCIPLES: 2/2
“N” Sub-Channels
CIRCUIT
SWITCHING
Dynamic
Assignment
Users
Generating / Release on
Demand
Demands
Saad Haj Bakry
TDM /
FDM
Channel
Sharing
Shared
Channel
Network Architecture
Switching / Circuit
TELEPHONE OPERATION
1. DIAL-UP
2. SIGNALLING / ROUTING / ASSIGNMENT
3. CALL PROGRESS
4. CALL TERMINATION
Saad Haj Bakry
5. RELEASE
Network Architecture
Switching / Circuit
TELEPHONE TRAFFIC: 1/3
TWO RANDOM PROCESSES
CALL ARRIVALS:
Random
Distribution
(Poisson Process)
Saad Haj Bakry
CALL DURATION:
Random
Distribution
(Negative Exponential
Distribution / Related
to Poisson Process)
Network Architecture
Switching / Circuit
TELEPHONE TRAFFIC: 2/3
R [Calls / Time Unit]:
Rate of Generated Calls
BUSY HOUR
PRINCIPLE
D [Time Unit]:
ERLANG:
Average Call Duration
“1” Erlang is Full
Channel
Occupancy For
“1” Time Unit
A [Erlang]: A = R.D
Saad Haj Bakry
Network Architecture
Switching / Circuit
TELEPHONE TRAFFIC: 3/3
R=
“1”
ERLANG
R=
1 [Calls / Hour]
R=
12 [Calls / Hour]
D=
4 [Calls / Hour]
D=
60 [Minutes]
D=
5 [Minutes]
A=
15 [Minutes]
A=
1
A=
[Erlang]
1
Saad Haj Bakry
[Erlang]
1
[Erlang]
Network Architecture
Switching / Circuit
ERLANG-B FORMULA: 1/4
TYPICAL / SIMPLE CASE STUDY
SYSTEM:
“N”
(Sub)
Channels
Fully
Available to
All Call
Saad Haj Bakry
DEMANDS /
TRAFFIC
OFFERED BY
ALL USERS:
“ A”
[Erlang]
PERFORMANCE
/ GRADE OF
SERVICE /
BLOCKING
PROBABILITY
“ B”
Network Architecture
Switching / Circuit
ERLANG-B FORMULA: 2/4
iN
B=
(AN
iN
i / i!)
(A
/ N!) / 
i 0
i (N - i)!))
(N!
/
(A
B=1 /
i 0
Saad Haj Bakry
Network Architecture
Switching / Circuit
ERLANG-B FORMULA: 3/4
OTHER IMPORTANT FACTORS
TRAFFIC CARRIED /
SERVICED:
K = A (1 - B)
Saad Haj Bakry
AVERAGE CHANNEL
UTILIZATION /
OCCUPANCY:
Q=K/N
Network Architecture
Switching / Circuit
ERLANG-B FORMULA: 4 /4
POSSIBLE USE
SYSTEM
EVALUATION:
SYSTEM
CAPACITY:
SYSTEM
DESIGN:
Given: N / A
Find:
B/K/Q
Given: N / B
Find:
A/K/Q
Given:
A/B/K
Find: N / Q
Saad Haj Bakry
Network Architecture
STORE
Switching / S&F
&
CONCENTRATION
PERFORMANCE
TRAFFIC
ANALYSIS
Saad Haj Bakry
FORWARD
MESSAGE /
PACKET /
FRAME /
CELL
(SWITCHING
/ RELAY)
Network Architecture
Switching / S&F
CONCENTRATION: 1/2
1
c
2
c
I
[bps]
c
I
N
I
+
Saad Haj Bakry
c
STORE
P
&
FORWARD
M M
SHARED C
CHANNEL [bps]
PROCESSOR BUFFER
Dynamic Channel Assignment
(Active Users Only) / Efficiency
USERS > N Where N = C/c
Network Architecture
Switching / S&F
CONCENTRATION: 2/2
BURST
USE
USE
LOSS
SENSITIVE
INFORMATION:
“DATA / TEXT”
Saad Haj Bakry
NO DELAY
SENSITIVE
INFORMATION:
“VOICE / PICTURE”;
EXCEPT IN HIGH
SPEED
Network Architecture
Switching / S&F
MESSAGE
MESSAGE:
•An Information
Signal Sent by a
Single User
•Physical Block
•(Basic Name:
for M / P / F / C)
Saad Haj Bakry
PROBLEM:
•Fluctuating Size
•Need for Size
Control “P / F / C”
(Logical Units)
•Providing Better
Sharing
Network Architecture
Switching / S&F
PACKET / FRAME / CELL: 1 / 3
INFORMATION: CONTROLLED SIZE
INFORMATION
HEADER
HEADER: SOURCE / DESTINATION / CONTROL
PACKET:
FRAME:
CELL / ATM:
X.25 / 64 kbps
T-1 / E-1
OC-3 / OC-12
Variable Size
H: 8 bytes
Variable Size
H: 2 bytes
Fixed: 48 Bytes
H: 5 bytes
Saad Haj Bakry
Network Architecture
Switching / S&F
PACKET / FRAME / CELL: 2 / 3
DATAGRAM:
Logical Units
(Packets) are
Routed
Independently
Through the
Network from
Source to
Destination
Saad Haj Bakry
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
Network Architecture
Switching / S&F
PACKET / FRAME / CELL: 3 / 3
ERROR
CONTROL
PACKET:
Point-toPoint
&
End-toEnd
Saad Haj Bakry
FRAME:
End-to-End
Only
CELL / ATM:
End-to-End
(Header Only)
LOW NOISE: Eases Error Control
Protocols.
HIGHER SPEED: Reduces Delay and
Helps Information Integration (Data /
Voice / Picture)
Network Architecture
Switching / S&F
PERFORMANCE: DELAY (1/3)
DELAY ELEMENTS
M [bits]
P
M M
p
q
C [bps]
v [km/s] / l [km]
s
g
NEXT
NOD
E
PROCESSING QUEUING TRANSMISSION PROPAGATION
DELAY “s”
DELAY “g”
DELAY “p” DELAY “q”
MESSAGE DELAY:
Saad Haj Bakry
d=p+q+s+g
Sec.
Network Architecture
Switching / S&F
PERFORMANCE: DELAY (2/3)
PROCESSING DELAY:
Processing Dependent
Traffic Independent
TRANSMISSION
DELAY: s = M / C
Message / Capacity
(System) Dependent
Independent of Traffic
Volume / Fluctuation
Saad Haj Bakry
QUEUING DELAY:
Traffic / Capacity
(System) Dependent
Analysis Required
PROPAGATION DELAY:
g=l/v
Channel / Distance
Dependent
Traffic / Capacity
Independent
Network Architecture
Switching / S&F
PERFORMANCE: DELAY (3/3)
TRANSMISSION DELAY:
QUEUING DELAY:
An Essential Element, as it
is Associated with the
Capacity / “System” , and
the Message Length /
“Demands”
An Essential Element,
as it is Associated with
the Capacity / “System”,
and Traffic Volume /
Fluctuation / “Demands”
PROCESSING DELAY:
PROPAGATION DELAY:
Significant in High
Speed Links
Significant in Satellites
g = 36 / 300 = 0.12 sec
Saad Haj Bakry
Network Architecture
Switching / S&F
TRAFFIC: 1/2
TWO RANDOM PROCESSES
MESSAGE
ARRIVALS:
Poisson
Process
Saad Haj Bakry
MESSAGE LENGTH:
Negative Exponential
Distribution /
Fixed Size Messages
(Deterministic)
Network Architecture
Switching / S&F
TRAFFIC: 2/2
R [Messages / Sec]:
Rate of Generated
Messages
M [Bits]:
Average / Fixed
Message Length
Saad Haj Bakry
BUSY HOUR
PRINCIPLE
TRAFFIC RATE:
A [bps] = R . M
Network Architecture
Switching / S&F
ANALYSIS: 1/4
QUEUING DELAY:
Variable Message Length
qv = (RM / C) / ( (C/M) - R)
Fixed Message Length
qf = (1/2) . qv
Saad Haj Bakry
Network Architecture
Switching / S&F
ANALYSIS: 2/4
ESSENTIAL DELAY ELEMENTS: d
= qv + s = 1 / ( (C/M) - R)
LIMITATION: RM < C
UTILIZATION / OCCUPANCY: U = (RM) / C
Saad Haj Bakry
Network Architecture
Switching / S&F
ANALYSIS: 3/4
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)
Saad Haj Bakry
Network Architecture
Switching / S&F
ANALYSIS: 4/4
POSSIBLE USE
SYSTEM EVALUATION:
SYSTEM CAPACITY:
Given: C / M / R
Find: d / U / D
Given: C / U (d/D) / M
Find: R
SYSTEM DESIGN:
Saad Haj Bakry
Given: R / M / U Find: C
Network Architecture
Switching: Work
SUGGESTED WORK
GENERAL:
Computations
Concerned with
“Circuit
Switching” and
“Store & Forward”
Saad Haj Bakry
SPECIAL:
Investigations of
Practical “CS” and
“S&F” Systems