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Chapter 4 Circuit-Switching Networks. Multiplexing SONET. Circuit Switching Networks. End-to-end dedicated circuits between clients Client can be a person or equipment (router or switch) Circuit can take different forms Dedicated path for the transfer of electrical current

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circuit switching networks
Circuit Switching Networks
  • End-to-end dedicated circuits between clients
    • Client can be a person or equipment (router or switch)
  • Circuit can take different forms
    • Dedicated path for the transfer of electrical current
    • Dedicated time slots for transfer of voice samples
    • Dedicated frames for transfer of Nx51.84 Mbps signals
    • Dedicated wavelengths for transfer of optical signals
  • Circuit switching networks require:
    • Multiplexing & switching of circuits
    • Signaling & control for establishing circuits
  • These are the subjects covered in this chapter
how a network grows
How a network grows
  • A switch provides the network to a cluster of users, e.g. a telephone switch connects a local community

Network

Access network

(b) A multiplexer connects two access networks, e.g. a high speed line connects two switches

a network keeps growing

a

b

A

d

c

Network of Access Subnetworks

A Network Keeps Growing

1*

b

a

2

4

(a)

Metropolitan network A viewed as Network A of Access Subnetworks

3

A

c

d

Metropolitan

(b)

National network viewed as Network of Regional Subnetworks (including A)

A

  • Very high-speed lines

Network of Regional Subnetworks

National & International

multiplexing

(a)

(b)

A

A

A

A

B

B

MUX

MUX

B

B

C

C

C

C

Multiplexing
  • Multiplexing involves the sharing of a transmission channel (resource) by several connections or information flows
    • Channel = 1 wire, 1 optical fiber, or 1 frequency band
  • Significant economies of scale can be achieved by combining many signals into one
    • Fewer wires/pole; fiber replaces thousands of cables
  • Implicit or explicit information is required to demultiplex the information flows.

Shared Channel

frequency division multiplexing
Channel divided into frequency slots

Guard bands required

AM or FM radio stations

TV stations in air or cable

Analog telephone systems

B

f

A

f

0

Wu

C

C

0

Wu

f

0

Wu

B

A

f

W

0

Frequency-Division Multiplexing

(a) Individual signals occupy Wu Hz

(b) Combined signal fits into channel bandwidth

time division multiplexing

A1

A2

t

0T

6T

3T

B1

B2

t

6T

3T

0T

C1

C2

t

0T

6T

3T

C2

A2

B2

A1

C1

B1

t

0T 1T 2T 3T 4T 5T 6T

Time-Division Multiplexing

(a) Each signal transmits 1 unit every 3T seconds

  • High-speed digital channel divided into time slots
  • Framing required
  • Telephone digital transmission
  • Digital transmission in backbone network

(b) Combined signal transmits 1 unit every T seconds

north american digital multiplexing hierarchy

1

DS1 signal, 1.544Mbps

.

.

Mux

24

1

DS2 signal, 6.312Mbps

.

24 DS0

.

4 DS1

Mux

4

1

DS3 signal, 44.736Mpbs

.

.

7 DS2

Mux

7

1

.

.

6 DS3

Mux

6

DS4 signal

274.176Mbps

North American Digital Multiplexing Hierarchy
  • DS0, 64 Kbps channel
  • DS1, 1.544 Mbps channel
  • DS2, 6.312 Mbps channel
  • DS3, 44.736 Mbps channel
  • DS4, 274.176 Mbps channel
ccitt digital hierarchy

1

2.048 Mbps

.

.

Mux

30

1

8.448 Mbps

.

64 Kbps

.

Mux

4

1

34.368 Mpbs

.

.

Mux

139.264 Mbps

1

.

.

Mux

4

CCITT Digital Hierarchy
  • CCITT digital hierarchy based on 30 PCM channels
  • E1, 2.048 Mbps channel
  • E2, 8.448 Mbps channel
  • E3, 34.368 Mbps channel
  • E4, 139.264 Mbps channel
wavelength division multiplexing
Optical fiber link carries several wavelengths

From few (4-8) to many (64-160) wavelengths per fiber

Imagine prism combining different colors into single beam

Each wavelength carries a high-speed stream

Each wavelength can carry different format signal

e.g. 1 Gbps, 2.5 Gbps, or 10 Gbps

Optical

deMUX

Optical

MUX

1

1

2

1

2

2.

m

Optical

fiber

m

m

Wavelength-Division Multiplexing
sonet overview
SONET: Overview
  • SynchronousOptical NETwork
  • North American TDM physical layer standard for optical fiber communications
  • 8000 frames/sec. (Tframe = 125 sec)
    • compatible with North American digital hierarchy
  • Greatly simplifies multiplexing in network backbone
  • Protection & restoration
sonet simplifies multiplexing

MUX

MUX

DEMUX

DEMUX

Insert

tributary

Remove

tributary

MUX

DEMUX

ADM

Insert

tributary

Remove

tributary

SONET simplifies multiplexing

Pre-SONET multiplexing

SONET Add-Drop Multiplexing: Allows taking individual channels in and out without full demultiplexing

sonet specifications
SONET Specifications
  • Defines electrical & optical signal interfaces
  • Electrical
    • Multiplexing, Regeneration performed in electrical domain
    • STS – Synchronous Transport Signals defined
    • Very short range (e.g., within a switch)
  • Optical
    • Transmission carried out in optical domain
    • Optical transmitter & receiver
    • OC – Optical Carrier
sonet adm networks

MUX

DEMUX

ADM

Insert

tributary

Remove

tributary

SONET ADM Networks
  • SONET ADMs: the heart of existing transport networks
  • ADMs interconnected in linear and ring topologies
  • SONET signaling enables fast restoration (within 50 ms) of transport connections
sonet rings

(a)

(b)

a

a

OC-3n

OC-3n

b

c

b

c

OC-3n

Logical fully connected topology

Three ADMs connected in physical ring topology

SONET Rings
  • ADMs can be connected in ring topology
  • Clients see logical topology created by tributaries
sonet ring options
SONET Ring Options
  • 2 vs. 4 Fiber Ring Network
  • Unidirectional vs. bidirectional transmission
  • Path vs. Link protection
  • Spatial capacity re-use & bandwidth efficiency
  • Signaling requirements
two fiber unidirectional path switched ring
Two-Fiber Unidirectional Path Switched Ring

Two fibers transmit in opposite directions

  • Unidirectional
    • Working traffic flows clockwise
    • Protection traffic flows counter-clockwise
    • 1+1 like
  • Selector at receiver does path protection switching
slide22
UPSR

1

W

2

4

P

W = Working Paths

P = Protection Paths

Each path uses 2x bw

3

upsr path recovery
UPSR path recovery

1

W

2

4

P

W = Working line P = Protection line

3

upsr properties
UPSR Properties
  • Low complexity
  • Fast path protection
  • 2 TX, 2 RX
  • Suitable for lower-speed access networks
  • Different delay between W and P path
four fiber bidirectional line switched ring
Four-Fiber Bidirectional Line Switched Ring
  • 1 working fiber pair; 1 protection fiber pair
  • Bidirectional
    • Working traffic & protection traffic use same route in working pair
    • 1:N like
  • Line restoration provided by either:
    • Restoring a failed span
    • Switching the line around the ring
4 blsr
4-BLSR

1

Equal

delay

W

P

Standby

bandwidth

is shared

2

4

Spatial

Reuse

3

blsr span switching
BLSR Span Switching

1

W

Equal

delay

P

  • Span Switching restores failed line

2

4

Fault on working

links

3

blsr span switching1
BLSR Span Switching

1

W

Equal

delay

P

  • Line Switching restores failed lines

2

4

Fault on working and protection

links

3

4 blsr properties
4-BLSR Properties
  • High complexity: signalling required
  • Fast line protection for restricted distance (1200 km) and number of nodes (16)
  • 4 TX, 4 RX
  • Spatial re-use; higher bandwidth efficiency
  • Good for uniform traffic pattern
  • Suitable for high-speed backbone networks
  • Multiple simultaneous faults can be handled
backbone networks consist of interconnected rings

Regional

ring

Metro

ring

Interoffice

rings

Backbone Networks consist of Interconnected Rings

UPSR OC-12

BLSR OC-48, OC-192

UPSR or BLSR OC-12, OC-48

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