EE 489 Telecommunication Systems Engineering University of Alberta Dept. of Electrical and Computer...

EE 489EE 489Telecommunication Systems EngineeringTelecommunication Systems Engineering

University of AlbertaUniversity of AlbertaDept. of Electrical and Computer EngineeringDept. of Electrical and Computer Engineering

Switching Systems

Wayne GroverWayne Groverslides based on material developed by W. Grover for EE589, (1998-2002)

set in powerpoint with a few additions by J. Doucette 2002

Material prepared by W. Grover (1998-2002)

2

EE489 – Telecommunication Systems Engineering –University of Alberta, Dept. of Electrical and Computer Engineering

SwitchingSwitching• Circuit SwitchingCircuit Switching

– A path is established between the caller and destination.– Real-time connection formed.– Example: PSTN

• Message SwitchingMessage Switching– Also called store and forwardstore and forward.– A message is first stored in a buffer and then sent on in its

entirety step by step as resources become available.– No real-time connection (i.e. connectionlessconnectionless).– Example: E-mail

• Packet SwitchingPacket Switching– A message is broken down into parts and each part is sent

separately (possibly via different routes).– Example: Internet UDP protocol


3


Separating CircuitsSeparating Circuits• Four technologies for separating circuits:

– Space, RF frequency, time, optical wavelength• We want to logically connect circuits coming into a

switch with circuits at the output.• Example “space division” equivalent interconnection

pattern :

Input 1

Input 2

Input 3

Output 1

Output 2

Output 3


4


Space Division SwitchingSpace Division Switching• Connecting two channels that are separated in space.• Can be mechanical and/or electronic.• Several problems:

– Slow– Bulky with lots of interconnect wiring– Subject to cross-talk

Input 1

Input 2

Input 3

Output 1Output 2Output 3

Input 1

Input 2

Input 3

Output 1

Output 2

Output 3

Equals :


5


Strowger SwitchingStrowger Switching• Patented 12/March/1889 and in some places still in use

today.• First widely-used automatic exchange system.• A wiper assembly (contact armcontact arm) moves across a fixed set of

switch contacts (contact bankcontact bank).– Each contact is connected to an outgoing channel.

Uni-selector:

Source:M. P. Clark, Networks and Telecommunications Design and Operation – 2nd Edition, John Wiley & Sons Ltd, pp. 90, 1997.

Strowgeruni-selector


6


Strowger Switching (2)Strowger Switching (2)• Several uni-selectors can be “graded” together so multiple

incoming circuits can connect to multiple outgoing circuits.

Graded uni-Graded uni-selectors:selectors:

Unless there is heavy traffic, it is inefficient and uneconomical to provide each incoming circuit with a uni-selector.

• Or two uni-selectors can be wired back-to-back (line-line-findersfinders).– 1st uni-selector chooses the incoming circuit, the 2nd

chooses the outgoing circuit.Line-finder Line-finder (hunter):(hunter):

Incoming

Circuits

Outgoing Circuitsor other

uni-selectors

Line-finders can be graded together as well to form large switches.


7


Strowger Switching (3)Strowger Switching (3)• In general, multiple uni-selectors, line-finders, and two-

motion selectors (movable in two planes) can be connected in series.

• These switches respond to dialled digits, automatically switching an incoming circuit to the correct outgoing trunk.– Step-by-step switching will respond to each digit

individually.


Strowger two-motion selector


8


Crossbar SwitchingCrossbar Switching• Crossbar switching became popular in the 1940’s and is

still used in some places today.• Uses a simple rectangular matrix.

– Actuators are operated at incoming circuits and outgoing circuits to make metallic contact and form the desired connection.

1 2 3 4

A

B

C

D

Incoming

Circuits

Outgoing

Circuits


Crossbar switch


9


Time Division SwitchingTime Division Switching• In digital TDM systems (e.g. DS1), channels are divided by

time slot, but switching is still possible.• Switching is by a time-slot interchangertime-slot interchanger (TSITSI) and is

accomplished by rearranging the order in which data is read out of the buffer.

• Incoming data enters a speech storespeech store while the outgoing channels indicate to the speech address memoryspeech address memory (SAMSAM) which incoming timeslot it is assigned to.

• During each time-slot, the outgoing circuit reads the speech store slot corresponding to the SAM.

1A

2B

3C

4D

1A

2B

3C

4D

1A

2B

3C

4D TSI

1B

2D

3A

4C

1B

2D

3A

4C

1B

2D

3A

4C


10


Optical SwitchingOptical Switching• One wavelength (or colour) can be turned into another.

– Called wavelength conversionwavelength conversion or translationtranslation.– Important in reducing blocking due to wavelength

contention in routing and wavelength assignment (RWARWA) problem.

– Optoelectronic conversion consists of optical receiver, conversion to electronic signal (O/EO/E), and then transmitter generates optical signal at the desired new wavelength (E/OE/O).


11


Optical Switching (2)Optical Switching (2)• One (or several wavelengths) are switched from one

fibre into another.– Can use splitters and tunable filters, or– More recently - Micro-Electro-Mechanical SwitchesMicro-Electro-Mechanical Switches

(MEMSMEMS)• On the scale of a human hair (100 microns)

MEMS Mirror (Lucent Technolgies) WaveStarTM MEMS Mirror

(Lucent Technolgies)

WaveStarTM LambdaRouter OpticalCross-Connect (Lucent Technolgies)Source:

Lucent Technologies - Bell Labs Web-site:http://www.bell-labs.com/news/1999/november/10/1.htmlhttp://www.bell-labs.com/org/physicalsciences/timeline/1999_mems_expansion.html


12


Switching Network DesignSwitching Network Design• Several Points to Consider

– Blocking versus non-blocking switches– Number of cross-points (i.e. size of the switch)– Reliability– Overload– Growth– Cost and technology

• ““Trunk Switch” Trunk Switch” (aka traffic switchtraffic switch)– One-to-one connection.– One specific inlet must connect to one specific outlet.

• ““Access Switch”Access Switch”– One-to-any connection.– One specific inlet must connect to any free outlet.


13


Multi-Stage Switch FabricsMulti-Stage Switch Fabrics• Consider a switch with a 100 x 100 interconnect function.

(a) - Full Matrix Switch

1

100

1

100

Need 10 000 cross-points.

E.g.

Example: 4x4 = 16 cross-points

1 2 3 4

1

2

3

4

If bi-directional transmission, then connection from A to B is equivalent to a connection from B to A (and connection from A to A is meaningless).

1

100

1 100

(b) - Folded Matrix Switch

Need 4950 cross-points.

E.g. ( 1) 100 99 49502 2

n n


14


Multi-Stage Switch Fabrics (2)Multi-Stage Switch Fabrics (2)• Full matrix and even folded matrix switches may be inefficient since

they scale as O(n2).• A third method of achieving a 100 x 100 interconnect function is by

splitting the switch into two stages using smaller square matrices as building blocks.– Then to form a connection, two xptsxpts are operated, one in each stage, but:

• (i) fewer xpts needed in total• (ii) we may have introduced some blocking probability

• Example: 100 x 100 in 2 stages:

10 x 10

1

10

1

10

10 x 10

1

10

1

10

(10)

10 x 10

1

10

1

10

10 x 10

1

10

1

10

(10)

How many xpts?Each block is 10 x 10 = 100 xpts.Each stage is 10 blocks = 1000 xpts.Whole switch has 2 stages = 2000 2000 xptsxpts.


15


Multi-Stage Switch Fabrics (3)Multi-Stage Switch Fabrics (3)

• How does it work?– Divide the 100 inlets into groups of 10.– 1st outlet of each Stage 1 block is connected to an inlet of

the 1st Stage 2 block.– 2nd outlet of each Stage 1 block is connected to an inlet of

the 2nd Stage 2 block.– 3rd outlet of each Stage 1 block is connected to an inlet of

the 3rd Stage 2 block…– ith outlet of each Stage 1 block is connected to an inlet of

the ith Stage 2 block.

10 x 10

1

10

1

10

10 x 10

1

10

1

10

(10)

10 x 10

1

10

1

10

10 x 10

1

10

1

10

(10)100 Inlets

100 Outlets


16


Multi-Stage Switch Fabrics (4)Multi-Stage Switch Fabrics (4)Example: 16x16 2-stage switch using 4x4 non-blocking full matrices:

4 x 4

4 x 4

4 x 4

4 x 4

4 x 4

4 x 4

4 x 4

4 x 4

Using this example, we can see every path through the switch to connect any inlet in the 1st stage to any outlet in the 2nd stage.

Again, notice the connection pattern:The jjthth outlet of the kkthth Stage 1 block is connected to the kkthth inlet of the jjthth Stage 2 block.Using any size of n x n blocks, you can make an n2 x n2 2-stage switch.

We can also add a 3rd stage to the switch to get an n3 x n3 3-stage switch…How?


17


Multi-Stage Switch Fabrics (5)Multi-Stage Switch Fabrics (5)Adding a 3rd stage to a 2-stage switch:

Treat the original n2 x n2 2-stage switch as it’s own block, attach it to n2 new blocks of n x n and use the same connection pattern:The jjthth outlet of the kkthth Stage 1 block is connected to the kkthth inlet of the jjthth Stage 2 block.Then copy the original n2 x n2 2-stage switch n times and repeat.

3 x 3

3 x 3

3 x 3

3 x 3

3 x 3

3 x 3

3 x 3

3 x 3

3 x 3

3 x 3

3 x 3

3 x 3

3 x 3

3 x 3

3 x 3

3 x 3

3 x 3

3 x 3

3 x 3

3 x 3

3 x 3

3 x 3

3 x 3

3 x 3

3 x 3

3 x 3

3 x 3

How many xpts?27 x 27 3-stage switch: 24327 x 27 1-stage full matrix: 729


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Multi-Stage Switch Fabrics (6)Multi-Stage Switch Fabrics (6)

10 x 10

10 x 10

(10)

10 x 10

10 x 10

(10)

10 x 10

10 x 10

(10)

10 x 10

10 x 10

(10)

(10)

10 x 10

10 x 10

(10)

10 x 10

10 x 10

(10)

How many xpts?1000 x 1000 3-stage switch: 30 0001000 x 1000 1-stage full matrix: 1 million

Connection pattern used is called distributiondistribution, and in general:Stage nn - Module kk - Outlet jj connects to…Stage n+1n+1 - Module jj - Inlet kk

k

j

j

kExample:Stage 22 - Module 11 - Outlet 9191 connects to…Stage 33 - Module 9191 - Inlet 11


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Link BlockingLink Blocking• Because of the single link between each module and the

modules in the next stage, there’s a possibility of blocking.– Consider an inlet in the 1st block of stage 1 connected to an

outlet in the 3rd block of stage 2. – Now what happens if we want to connect another inlet the

1st block of stage 1 to another outlet of the 3rd block of stage 2?4 x 4

4 x 4

4 x 4

4 x 4

4 x 4

4 x 4

4 x 4

4 x 4

A problem arises because there is only a single only a single route availableroute available through a switch with only distribution-type of stages. Even though the entire switch is made up of non-blocking square matrices, we can still encounter we can still encounter blockingblocking.


20


Estimating BlockingEstimating Blocking• “Distribution” stages increase the overall inlet/outlet size of

the switch but introduce increasing probability of blocking.– there is only a single path between any specific 1st stage inlet and

any specific final stage outlet.– Mechanism of blockage is when an inter-stage link on required

path is in use.– The greater the number of links in the path, the greater the

probability that one of them is in use.– Therefore, the more distribution stages we have, the greater the

probability of blocking (but the larger the total switch size is).

Stage 1 Stage 2

Link 1

Stage 3

Link 2

Stage 4

Link 3

Stage 5

Link 4

Stage 6

Link 5


21


Estimating Blocking (2)Estimating Blocking (2)For a Pure “Distribution” switch:• Say we have aa Erlangs of traffic on an inlet, then the

proportion of time it is used is also aa, and…• assume that all connections are random, and so the

probability of any one link being occupied is also aa in any stage (if we use square blocks), so…

• Probability of any specific link being free is 1- a1- a.• But we need all links in the path to be free so probability

that the path is available is (1- a)(1- a)k-1k-1.1( ) 1 (1 )kP B a


22


Mixing StagesMixing Stages• We’ve seen that we can add distribution stages to

increase the switch size nk x nk (where n is the size of each square matrix block, and k is the number of distribution stages), but…– We need a way of reducing blocking.

• The solution is to add a mixing stagemixing stage (also called collection stagecollection stage) that keeps the overall switch size the same (in terms of nk inlets and outlets), but can reduce blocking by adding multiple paths through the adding multiple paths through the switchswitch.

n x n

n x n

(n)

n x n

n x n

(n)

Distribution Distribution

n x n

n x n

(n)

Mixing


23


Mixing Stages (2)Mixing Stages (2)Adding a 3rd distribution stagedistribution stage to a 2-stage switch:

3 x 3

3 x 3

3 x 3

3 x 3

3 x 3

3 x 3

3 x 3

3 x 3

3 x 3

3 x 3

3 x 3

3 x 3

3 x 3

3 x 3

3 x 3

3 x 3

3 x 3

3 x 3

3 x 3

3 x 3

3 x 3

3 x 3

3 x 3

3 x 3

3 x 3

3 x 3

3 x 3

Adding a mixing stagemixing stage to a 2-stage switch:

3 x 3

3 x 3

3 x 3

3 x 3

3 x 3

3 x 3

3 x 3

3 x 3

3 x 3

Connection pattern is the same as for distribution:Stage nn - Module kk - Outlet jj connects to…Stage n+1n+1 - Module jj - Inlet kkThe difference is that we don’t replicate the 2-stage switch n times.


24


Mixing Stages (3)Mixing Stages (3)• By how much does a mixing stage reduce blocking?

– Adding a mixing stage will provide n alternate paths through the switch.

Example (n = 3):

3 x 3

3 x 3

3 x 3

3 x 3

3 x 3

3 x 3

3 x 3

3 x 3

3 x 3

Recall that probability of blocking of each each pathpath is:

1( ) 1 (1 )kpathP B a

But for blocking to occur, we must have all n paths blocked:

1( ) 1 (1 )nk

switchP B a


25


Call PackingCall Packing• Analyze how blocking in a network occurs:

– There are generally free links in each stage.– Problem is that they are mismatched from stage to stage.

• For instance:

Even though there are free links throughout the switch, there is a conflict for specific links required for the brown brown connectionconnection.

5 x 5

5 x 5

5 x 5

5 x 5

5 x 5

5 x 5

5 x 5

5 x 5

5 x 5

5 x 5

5 x 5

5 x 5

5 x 5

5 x 5

5 x 5


26


Call Packing (2)Call Packing (2)• Call packing is a strategy of organizing new calls so that

they use free links corresponding to other busy links in the next stage if possible.

5 x 5

5 x 5

5 x 5

5 x 5

5 x 5

5 x 5

5 x 5

5 x 5

5 x 5

5 x 5

5 x 5

5 x 5

5 x 5

5 x 5

5 x 5

5 x 5

5 x 5

5 x 5

5 x 5

5 x 5

5 x 5

5 x 5

5 x 5

5 x 5

5 x 5

5 x 5

5 x 5

5 x 5

5 x 5

5 x 5

By appropriately packing the other connections, the brown brown connectionconnection can now find an available path.


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• Consider the call blocking mechanism:

Clos Non-Blocking SwitchesClos Non-Blocking Switches

The brown brown connectionconnection can’t find a path through the switch.

• Is there a way of designing the switch with appropriately sized modules and stages so that it’s impossible for there to be blocking, even if without call packing?

5 x 5

5 x 5

5 x 5

5 x 5

5 x 5

5 x 5

5 x 5

5 x 5

5 x 5

5 x 5

5 x 5

5 x 5

5 x 5

5 x 5

5 x 5


28


Clos Non-Blocking Switches (2)Clos Non-Blocking Switches (2)• Consider the worst possible case:

– Connect from an inlet in a first stage module (with n inlets) where n-1 of its outlets are already in usen-1 of its outlets are already in use to an outlet in a final stage module where (with n outlets) where n-1 inlets n-1 inlets are already in useare already in use, and none of the busy links are matched.

n

n

1

1

N/nNn

1N

n-1n-1

n-1

n-1

Need one extra module to connect through.


29


Clos Non-Blocking Switches (3)Clos Non-Blocking Switches (3)

n

n

1

1

N/nNn

1N

n-1n-1

n-1

n-1

For a guarantee of a free path through the switch, we need (n-1)+(n-1)+1 = 2n-12n-1 modules in the 2nd stage, and…

each 1st stage module needs 2n-12n-1 outlets, andeach 2nd stage module needs N/nN/n outlets and inlets, andeach 3rd stage module needs 2n-12n-1 inlets.


30


Clos Non-Blocking Switches (4)Clos Non-Blocking Switches (4)• A (non-blocking) Clos switchClos switch will have the following structure:

N

?

?

?

?

?

?

?

?

?

N

n x 2n-1

N/n

n x 2n-1

N/n x N/n

2n-1

N/n x N/n

2n-1 x n

N/n

2n-1 x n

# 2 1 2 1 2 1N N N Nxpts n n n n nn n n n

2 1 2N Nn nn n

2 2N NN nn n

Can also show that to minimize number of xpts: 2

Nn


31


To Minimize Number of Cross-To Minimize Number of Cross-PointsPoints

2

2# 4 2 2 1Nxpts x n N nn

2 2

24 2 2 N Nn N Nn n

To minimize the number of xpts:

0dxdn

2 2

2 34 0 2 2 0N NNn n

2 2

2 32 N NNn n

2 3

2 1 1N n n

2

2 1N n

3

1 0letn

2Nn


32


5-, 7-, 9-Stage Clos Switches 5-, 7-, 9-Stage Clos Switches • Clos switches can be nested together.

– Middle stage modules themselves are appropriately-sized 3-stage Clos switches.

N N

n x 2n-1

N/n

n x 2n-1

3-stage ClosN/n x N/n

2n-1

3-stage ClosN/n x N/n

2n-1 x n

N/n

2n-1 x n

• Why would we want to do this?– Each module is non-blocking (whether full matrix or Clos

network).– If we use Clos networks, we have fewer xpts.


33


Digital SwitchingDigital Switching• Time Slot Interchanger (TSITSI).

– A TSI is a time switch.– Switches one time slot channel in a single physical input to

another time slot channel on a single physical output.– Functionally equivalent to an n x n space-divided switch

where n is the number of time slots per frame.

1A

2B

3C

4D

1A

2B

3C

4D

1A

2B

3C

4D TSI

1B

2D

3A

4C

1B

2D

3A

4C

1B

2D

3A

4C

• Time multiplexed space switch (TMSSTMSS)– A space switch (multiple physical inputs and outputs) that

is potentially reconfigured entirely in every time slot of each frame.

– Data is switched such that for each time slot, specific inlets are connected (switched) to specific outlets.

– Data does not switch timeslots.


34


Time Slot InterchangerTime Slot Interchanger• In a TSITSI, one time slot is switched to another.• Performed through use of two memory stores:

– Speech storeSpeech store is RAM with capacity to store one full frame of data.

• For DS1 (1.544 Mbps) with 24 channels of 8 bits, the speech store is 24 bytes long.

• For E1 (2.048 Mbps) with 32 channels of 8 bits, the speech store is 32 bytes long.

– Speech address memorySpeech address memory (SAMSAM) or Time Switch Connection Store is RAM with capacity to store a “word” for each time slot, each word being a number identifying a specific time slot.

• For DS1, the SAM has capacity to store 24 words of 5 bits per word (need 5 bits to store a number between 1 and 24) for a total of 24x5 bits.

• For E1, the SAM has capacity to store 32 words of 5 bits per word (need 5 bits to store a number between 1 and 32) for a total of 32x5 bits.


35


Time Slot Interchanger (2)Time Slot Interchanger (2)• How does a TSI system work?

– Data is written to the speech store cyclically as it comes in (i.e. sequentially, one time slot at a time).

– Path set-up control signalling tells the SAM to store the name of the input time slot in the appropriate location corresponding to the output time slot it must be switched to.

• For example, if input time slot 7 is to be switched to output time slot 15, then location 15 of the SAM will store the number “7”.

– Data is read a-cyclically from the speech store in the order of the output time slots as stored in the SAM.

• Note that this means there could be a delay of up to nearly a full frame.


36


1234

Speech Speech StoreStore

RAM = 24 x 8 bits2324

Data Out(contents of timeslots

rearranged)

1234

SAMSAMRAM = 24 x 5

bits

2324

Data In (cyclic frame timeslot order)

Time Slot Interchanger (3)Time Slot Interchanger (3)

Timing

Write Address Counter

Speech StoreSpeech Store:Stores the data of time slot xtime slot x in location xlocation x.

Control Signallin

g

SAM Data In SAMSAM:Stores the name of the input time slot being switched to output time time slot yslot y.i.e. “In output time slot time slot yy, which speech store location do I read?”

TimingRead Address Counter

1

24

1

24

Space switch equivalent:

24 x 24full

matrix


37


Time Multiplexed Space SwitchTime Multiplexed Space Switch• A TMSSTMSS is a space switch (with multiple physical inputs

and outputs) that is potentially reconfigured entirely in every time slot of each frame.

• For instance, say we have 3 time slots on each of 4 physical inlets and 4 physical outlets (also called I/P highways and O/P highways):

TMSS

TS1TS2TS3TS1

TS2

TS3

Space switch equivalent:

Three 4 x 4 full matrices

(one for each time slot)


38


Time Multiplexed Space Switch Time Multiplexed Space Switch (2)(2)• How does a TMSS system work?

– A memory structure called cross-point address memorycross-point address memory (XAMXAM) is used to control switching.

• XAM is a RAM with capacity to store a “word” for each time slot, each word being a number identifying a specific physical input to connect to during each time slot.

– Control signalling tells the XAM to store the name of the physical input in the appropriate time slot location.

• For example, if input 6 must be connected to output 9 during time slot 7, the the XAM for output 9 will store the number “6” in location 7.

– The space switch is rapidly reconfigured at each time slot to affect the proper connections.

• Note that data is switched across physical inputs/outputs, but not across time slots.


39


Time Multiplexed Space Switch Time Multiplexed Space Switch (3)(3)• Column Oriented Control – “Who do I get it from?”I/P 1

I/P 2

I/P 3

I/P 4

O/P 1 O/P 2 O/P 3 O/P 4

XAM#1

XAM#2

XAM#3

XAM#4

1234

XAMXAMRAM = 24 x 5

bits

2324

Each XAM stores the name of the I/P to which its O/P is connected to in each time slot.

Example:To switch I/P 2 to O/P 4 in time slot 18, then XAM #4 stores the value “2” in location 18.


40


Time Multiplexed Space Switch Time Multiplexed Space Switch (4)(4)• Row Oriented Control – “Who do I give it to?”

I/P 1

I/P 2

I/P 3

I/P 4

O/P 1 O/P 2 O/P 3 O/P 4

XAM #1

XAM #2

XAM #3

XAM #4

1234

XAMXAMRAM = 24 x 5

bits

2324

Each XAM stores the name of the O/P to which its I/P is connected to in each time slot.

Example:To switch I/P 2 to O/P 4 in time slot 18, then XAM #2 stores the value “4” in location 18.


41


Time-Space-Time Switching Time-Space-Time Switching beam me up Scotty :-)beam me up Scotty :-)

Space Switch: Physical inputs are connected to physical outputs but data does not cross time slots.

Time Switch:

TSIABCDABCD BDACBDACData is switched between time slots but remains on the same physical connection.

Time-Space-Time Switch:

TST

A

A

A

B

B

B

C

C

C

D

D

D

A

A

A

B

B

B

C

C

C

D

D

D

B

D

C

D

C

B

A

A

D

A

B

C

B

D

C

D

C

B

A

A

D

A

B

C

Data is switched between time slots and physical connections.


42


Time-Space-Time Switching (2)Time-Space-Time Switching (2)• Time-Space-Time switching is when data is switched

across time slots and physical connections.• Affected by a combination of TSI and TMSS.

DS1 I/P

TSI #1

DS1 I/P

TSI #2

DS1 I/P

TSI #3

DS1 I/P

TSI #4

DS1 I/P

TSI #5

DS1 O/P

TSI #1

DS1 O/P

TSI #2

DS1 O/P

TSI #3

DS1 O/P

TSI #4

DS1 O/P

TSI #5

TMSS


43


Time-Space-Time Switching (3)Time-Space-Time Switching (3)• What is the space division equivalent of a TST switch?

Each input highway is

a DS1 line.

Each output

highway is a DS1 line.

24 x 24

One inlet for each time

slot. 5

24 x 24One

module for each I/P.

5 x 5

24

5 x 5

One module for each time slot in TMSS.

5

24 x 24

24 x 24One module

for each O/P.

One outlet for each time

slot.


44


Time-Space-Time Switching (4)Time-Space-Time Switching (4)• How does a time-space-time switch work?

– First, we find a time slot that is free from the input TSI to the TMSS and from the TMSS to the output TSI we wish to connect to.

– Next, switch the input channel’s time slot in question to the free time slot.

– Then at the TMSS, connect the proper input line to the proper output line during free time slot.

– Finally, at the output line’s TSI, switch the free time slot to the time slot we wish to switch to.

Input TSI

Switch to free TS

TMSS

Switch to desired O/P

TSI

Switch to desired TS

Output


45


Multiplexing TSI StagesMultiplexing TSI Stages• MultiplexingMultiplexing will increase the number of time slots into a TSI.• Example:

I/P #124 TS

I/P #824 TS

Data

8:1Channel #

8:1Data

Channel #

Data Speech StoreSpeech Store192 Bytes

Write Addres

s

Control Signallin

g

SAMSAM192 Slots- each slot

big enough to store number as big as 192

Control Signallin

g

Read Address

Output to TMSS(8 x 1.544

Mbps)192 TS


46


Multiplexing TSI Stages (2)Multiplexing TSI Stages (2)• What benefits do we get by multiplexing?

16 x 16

TMSS

TSI

TSI32 TS

32 TSTSI

TSI32 TS

32 TS

16 16 32

Inputs multiplexed together in groups of four.

4 x 4 TMSS

TSI

TSI128 TS

128 TSTSI

TSI128 TS

128 TS

4 4 128

Smaller P(B)

Date post:	25-Feb-2016
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EE 489 Telecommunication Systems Engineering University of Alberta Dept. of Electrical and Computer...

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