J.Tiberghien - VUB09-06-K.Steenhaut & J.Tiberghien - VUB 1 Telecommunications Concepts Chapter 1.6 Multiplexing & Routing

J.Tiberghien - VUB09-06-K.Steenhaut & J.Tiberghien - VUB1

TelecommunicationsConcepts

Chapter 1.6

Multiplexing & Routing


Contents

• Multiplexing

• Circuit switching

– Frequency domain multiplexing

– Synchronous time domain multiplexing

• Packet switching

– Connectionless = datagrams

– Connection oriented = Virtual circuit

• Side-tracks

– routing

– Network coding


Contents

• Multiplexing• Circuit switching

– Frequency domain multiplexing– Synchronous time domain multiplexing

• Packet switching– Connectionless = datagrams– Connection oriented = Virtual circuit

• Side-tracks– routing– Network coding


Circuit vs. Packet SwitchingA resource multiplexing issue !!!

Main shared resource in networks = transmission capacity between nodes

How to share such resource optimally?

Shared resource examples

Fixed transmission capacity


Contents






Circuit Switching


The preferred multiplexing technique in the traditional telephony world.

• A predefined share is allocated to each user.• The allocation remains valid until revocation, whether it is used or not.• Charges are duration based.


Contents






Frequency Domain Multiplexing

sin(t)

sin(t)X

cos((t2

cos((t2

cos((t2+

~ /~

Modulation allows shifting the frequency spectrum:

frequency0

power

Ω

Example: amplitude modulation of carrier at frequency Ω by signal at frequency ω

Other modulation techniques have a similar effect


FDM in broadcasting

Mod

Ω1

Mod

Ω2

Basebandsignal

Carrier

Mod

Ω3

Mod

Ω1

Basebandsignal

LocalOscillator

Mod

Ω3

Mod

Ω1


FDM in broadcasting

frequency

VTM RTBF VRT RTLTF1

7-8 MHz

frequency

Premiere Nostalgie CampusStuBru

50 KHzFM radio:

105.5087.60

Cable TV:


Contents






Time Domain MultiplexingSynchronous

Unique bit pattern to delimit frames

1 0 0 1

0 1 0 1

1 0 0 10 1 0 1 XX


Contents






Packet Switching(Invented by Paul Baran, 1960)The preferred multiplexing technique in

the data world.

• Data streams are separated in data packets.• Packets belonging to different streams are intermixed for transmission over the shared link.• Packets are eventually queued while waiting for access to the shared resource.• Charges can be volume based.



Circuit vs. Packet Switching

• Peak data rate / Average data rate

– Voice : ~2 (both speakers talk 50% of time)

– Data : >> 2 (think and processing times > transmission times)

t

Typical voice traffic

Typical data traffic


Circuit vs. Packet Switching

• Circuit Switching peak data rates <= transmission capacity

» Acceptable for voice and image transmission» wasteful of resources for data transmission

– Fixed total delay • Packet Switching

average data rates <= transmission capacity» Optimal use of transmission capacity» Congestion control to handle traffic peaks

– Variable total delay» caused by queuing in front of shared resource» problematic for transmission of voice or images


Contents


– Frequency domain multiplexing– Synchronous Time domain multiplexing




Connection oriented vs. Connectionless

• Circuit Switching– Intrinsically connection oriented

• Packet Switching– Connectionless

» Each packet carries the destination address» Routing decisions to be made for each packet» Typical example : Internet Protocol

– Connection oriented : Virtual Circuits» Each packet carries a local identifier (VCN) of

the data flow it belongs to» Routing decisions at virtual circuit set-up. » Typical examples : X25, Frame Relay, ATM


Internal vs. External Policies

Network services (NUI)

Connection oriented

Connectionless

Network operation (NNI)

Connection oriented

Connectionless


Contents






Datagram RoutingBased upon routing tables

a

b

c

d

1

2

3 3

2

1

4 4

3

2

1

2

1

3a:1b:2c:3d:3

a:3b:3c:2d:2

a:3b:3c:1d:1

a:3b:3c:1d:2


Contents






Routing• Routing table gives next hop on best route to all

destination nodes

• Best route is application dependant

– Shortest latency

– Highest throughput

– Lowest cost

• Best route can change

– Nodes can go down or can become congested

– Links can be interrupted

• Routing tables maintained by exploring periodically the network


Finding the best route

Example : Distance Vector Routing

E

B

C

A

D

? VUB, 7

VUB, 20

VUB, 5VUB, 10 1

3

41

What is E’s shortestpath to VUB ?


Finding the best route

Example : Distance Vector Routing

E

B

C

A

D

VUB, 7

VUB, 20

VUB, 5VUB, 10 1

3

41

VUB, 8

Known as Old ARPANET routing Based on Bellman-Ford algorithmBase of Routing Information Protocol


Best route consequence

a

b

c

d

1 1

1

1

1

Risk ofcongestion

Idle


Routing in large networks

• Complete routing tables impossible in large networks

• Hierarchical routing is the solution

– Routing table restricted to one level of hierarchy


Contents






Virtual Circuit Number

a

b

c

d

a>ba>ca>d

101112

b>cb>da>b

111221

d>ca>db>d

112021

b>ca>cd>c

202122

a>ca>db>cb>d

10111213

Each virtual circuit is identified by a specificnumber on each physical link


Forwarding Tables

a

b

c

d

11 21

101

2

3 1

2

3

1.11>3.10 1.10>3.21


Permanent Virtual CircuitForwarding tables set-up and cleared

by network manager through “separate” network

a

b

c

d

a>c 11a>c 21

1

2

3 1

2

3

1.11>3.10 1.10>3.21

“Separate” signaling network

Signaling and data packets travel through different (virtual) circuits


Contents






Network CodingClassical packet routing

a

b

c

d

3 3

All links : t b/s

m1: a > d m2: c > b

Bottleneck:2t b/s

needed


Network CodingMessage merging

a

b

c

d

3 3

All links : t b/s

m1: a > d m2: c > b

m1 m2 t b/s needed

+

m1 m2 m1+ + m2 m1 m2+ +


Introduced concepts• Circuit switching for uniform traffic

– Fixed bandwidth multiplexing

» FDM vs. TDM

– Connection oriented

• Packet switching for bursty traffic

– Statistical multiplexing

– Connectionless : datagrams

– Connection oriented : Virtual circuits

» Switched vs. permanent virtual circuits

• Routing

– Centralized vs. decentralized

– Best route, but risk for unbalanced loads

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J.Tiberghien - VUB09-06-K.Steenhaut & J.Tiberghien - VUB 1 Telecommunications Concepts Chapter 1.6 Multiplexing & Routing