Chapter 1 Circuit Switching

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Oct 30, 2013 (4 years and 11 days ago)

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Chapter 1 Circuit Switching


Switching Networks


Circuit Switching Networks


Switching Concepts


Routing in Circuit
-
Switched Networks


Control Signaling

1.1
Switching Networks


Switching from node to node


Data from station are routed to the
destination by switching


ref) Data : voice, image, video, and etc(text,.)


ref) Network: the collection of nodes


ref) station: PC, WS, terminals, telephones, communication
devices,…..

1.1.1
Switching Networks1

1.1.1.1
Node
-
node links


Node
-
node links: are multiplexed,
using FDM or TDM


FDM: Frequency Division Multiplexing


TDM: Time Division Multiplexing

1.1.1.2
WAN: Wide Area Networks


Circuit Switching

Packet Switching

Frame Relay


ATM

(
evolving)

(
evolving)

1.2
Circuit Switching Networks


Implies that is a dedicated
communication path between two
stations


Three phases of communication


Circuit Establishment


Data Transfer


Circuit Disconnect

1.2.1
Circuit Switching Networks


WAN using four generic architecture
component



Subscribers : the device attached to the network.


Local Loop:the link between the subscriber and the
network.


Exchanges: The switching centers in the network


Trunks: the branched between exchange


(Trunk carrier: FDM or TDM )

(
continue…CSN)


Node
-
node links are usually multiplexed, using
FDM or TDM


switching
node

switching
node

mux

mux

FDM,TDM

1.2.1.1
Public Circuit
-
Switching Network

long
-
distance
office

long
-
distance
office

End
office

End
office

subscriber
loop

connecting
trunk

Intercity trunk

1.2.1.2
components of CSN


Subscribers: The devices that attach to the network


Local loop: The link between the subscriber
and the network


Exchanges: The switching centers in the
network.


Trunks: The branches between exchanges.


carry multiple voice frequency circuits using either
FDM or synchronous TDM

1.2.2
Switching Concepts1

Digital
Switch

Control Unit

Full
-
duplex
lines to
attached
devices

Network

Interface


a


b

TS1 TS2

a

b

TS1 TS2

b

a

A/D

.

.

A/D

TS1

TS2

a

b

TS1 TS2


b a

Time Switch

1.2.2.1
Switching Concepts2


Digital Switch:
provide a signal path between a
calling device and called device.


Network
-
interface:
represent the functions needed
to connect devices


Control Unit:
performs three tasks


establishes connection


.
handle and acknowledge the request


. determine if the intended destination is free


. construct a path through the switch


maintain the connection


tear down the connection


perform maintenance and administration

1.2.2.2
Control Unit of Switching System

1.2.2.3
Establishment of Control Unit

channel table

1111 :
off hook

0000 :
on hook

1111 :
off hook

0000 :
on hook

ch0

ch1

ch2

ch3

ch3

TS1: busy

TS2: idle

TS3: idle

TS4: busy

source time
table

1.
assign TS2 for Register of


receiving dialing digits

2. assign TS2 for sending voice


data

Periodically
scanning

a(scan)

b (assign)

8
8
ms

0 0 0 1 1 1 1 …...

Real time clock
by counter

1.2.2.4
Characteristic of a Circuit
Switching Device


Blocking:

Unable to connect all stations at once.


Non
-
blocking
: permits at all stations to be connected
at once.


1.2.3
Space
-
division Switching


separate physically from one another (device in
space)


dedicated solely to the transfer of signals between
the end points

ch0

ch1

ch23

ch0

ch1

ch23

Ch0 1 2 3……………………….22 23

1.2.3.1
Crossbar Matrix

Input
device

Output device

ex)

-
. 10 full duplex I/O lines

-
. 100 crosspoints

-
. non blocking


.
Disadvantage

-
. crosspoints
증가

----
>
cost
증가

-
.
crosspoints


loss
--
>prevent


connections

-
. crosspoints
---
>
비효율적


(
linear
증가
)


1.2.3.2
Multistage network
등장

2
x2 switch

1

2

3

4

5

1

2

3

4

5

5
4
3
2
1

5
4
3
2
1

2
x2
switch

first stage

5x2 switch

third stage

2x5 switch

.

Advantages:


-

reduce the number of


crosspoints.


(ex: 100
--
> 48 ea)



-

increasing reliability


(switch stage
--
분산
)


.
Disadvantage


-

Non
-
blocking

fig. 8. 6 three
-
stage space
-
division switch

1.2.4
Routing in Circuit
-
Switched
Networks


route through the network from calling
subscriber to called subscriber


Routing strategy


efficiency


resilience
(recovery power)

-

need trade off


Routing approach


static hierarchical approach


dynamic routing approach

1.2.4.1
Dynamic routing algorithms


Alternate routing


사전에

대체

route


결정하여

놓고



route


Busy
이면

미리

지정된

대체

route


연결하는

방식


routing sequences reflect an analysis based on
the historical traffic patterns





Adaptive routing


t1 t2 t3 t4 …………….tn

R1(route 1)

R2 (route2)

1.2.4.2
Routing topology


X


I


J


K


Y

route d

route b

route a

route c

ex) X
----
> Y routes : 4 ea stages

ref) AT&T : DNHR
적용


DNHR : Dynamic Non
-
historical


Routing



:
End office

: Intermediate Switching Node


Route a : X
--
> Y


Route b : X
--
>J
---
> Y


Route c : X
--
>K
--
> Y


Route d : X
--
> I
--
> J
--
> Y

Time period first route second route third route fourth route

morning a b c d

afternoon a d b c

evening a d c b

weekend a c b d

routing table

1.2.4.3
ex) Routing


a


d


c


b


오전

정오

오후

자정


d


c




b



a

1.2.4.4
Adaptive Routing

:
Routing adaptively according to the change of traffic pattern on the


network.


-

routing by Dynamic Traffic Management


-

DTM find
the best alternate route choices

depending on congestion.


-

collects
status data

from each switch in the network


Traffic pattern
변화에

적응적으로

routing


best alternate route choices depending on
congestion


collects status data from each switch in the network
every 10 seconds

(
continue..adaptive routing)

1.2.5
Control signaling


Control signals


managing Network


establishing calls


maintaining call


terminating call

(
continue..)


Call management and network
management

require
exchanging
information


between subscriber and switch, and


between switch and network management
center.

(continue..
Signaling Functions)


Signaling functions


Tone:

audible communication with the subscriber(dial tone, ringing tone,busy tone..)


Dialing :
transmission of the number dialed


Not completing call signal :
indicating that a call cannot be completed.


Path disconnecting signal
:
indicating that the path can be disconnected
.


Ringing signal :
telephone ring(20hz, ringing)


Billing signal :
use for billing purposes


Status signal :

giving the status of equipment or trunks in the network. use for
routing and maintenance purposes


Diagnosing signal :

diagnosing and isolating system failures


Control of a special equipment signal :

control of special equipment
such as satellite channel equipment.

(
continue..ex.for control signaling)


Ex. for control signaling of telephone connection
sequence


Off hook


dial tone :
responds to caller


dialing :

the caller dial the number


ringing to called party
: If the called party is not busy,


ring back tone :


busy tone to caller :

If the called party is busy.


message to caller :

If the call cannot to be completed.


connecting path :

by off
-
hook of called party, signal to the switch.


disconnect ringing tone :

establishes a connection between two subscribers.


disconnection :
release when either subscriber hangs up.

(
continue..ex. for trunk signaling )

originating
switch

terminating
switch

1.
Originating Switch


. seizes
an idle trunk


. ends
off
-
hook indication

on the trunk


. request
a digit register at the far end


2. Terminating Switch


. sends
an off
-
hook

followed by an on hook signal


(send
register
-
ready status
)

3. Originating Switch


. sends
the address digits

to the terminating switch.


(
continue..
Basic function of signaling
)


Signaling functions


Supervisory

:
control functions such as request for
service, answer, alerting, etc.


Address

:

identify a subscriber


Call
-
information

:
provide information to the
subscriber about the status of call


Network management

:
used for the
maintenance, troubleshooting, and overall operation
management


Name of signal calling originating intermediate terminating called


station end office exchange(s) end of office station

(
continue..control signaling through CSN)


Name of signal calling originating intermediate terminating called


station end office exchange(s) end of office station

connect

disconnect

answer(off
-
hook)

hand
-
up(on
-
hook)

delay
-
dial(delay pulsing)

wing
-
start(ready register)

start dial(start pulsing)

dial tone

stop

go

called station identity


DTMF pulsing


dial pulsing


multi
-
frequency pulsing

Calling station identity


verbal


MF pulsed digits

line busy

reorder

No circuit

ringing

audible ringing

ringing start

reorder warning tone

announcements

(
continue..Location of signaling)


Control signaling consist of


signaling between a subscriber and the network.


signaling within the network
(
internal signaling
)



:
Internal signaling



-

be connected with the management of subscriber



-

be connected with the management of network itself

(
continue..
common channel signaling
)


Common Channel Signaling


: Physically separate from the path for voice or other subscriber
signals.


-

support signaling protocol


:
Two mode of operation



-

associated mode




: common network with signaling network and speech
network



: tracks along its entire length the inter
-
switch trunk.



-

non
-
associated mode



: two separate network with signaling network and speech



network.




:ref)
ccs


simple telephone network
에는

사용치

않으나

ISDN





포함한

sophisticated digital network


사용
.

(
continue.. ccs)

(
continue..
CCS mode of operation
)

(
a) Associated mode

:
Switching paths

:
speech

: signaling links

:
Switching points


(speech)

: Switching points


(signal transfer points)

: signaling network

: speech network

(
b) Non
-
associated mode

(
continue..Signaling techniques)



Description

Comment

In
-
channel



In
-
band :
Transmit
control signals
in the


same frequency band

used by the


voice signals
.




Out
-
of
-
band : Transmit
control signals
in the


different frequency band

used


by voice signals .

Common channel



:
Transmit
control signals

over


signaling channels

that are


dedicated to control signals

and


common to a number of voice


channels

It is necessary for
call
information signals

and can be
used over
any type of
subscriber line interface
.

It provides
continuous
supervision

for the duration of
a connection.


It
reduces
call setup time

compared with in
-
channel
.


It is also more adaptable to

evolving functional needs




1.2.4
Time
-
division Switching


Time
-
division switching


partitioning of a lower
-
speed bit stream into pieces( or slot).


A set of inputs is samples in turn.



ex) PCM (Pulse Code Modulation)


125 us/24 =5.208 us = 1ch


125 us/32 = 3.90 us= 1ch


if 8bits /ch
----
> 1 bit = 1.59 us


8 bits(=1ch)/ 125 us = 0.064 x 10 e
-
6 sec=64 kbps