Multiplexing Methods Daubing the Information 2005/03/11 (C) - - PowerPoint PPT Presentation

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Multiplexing Methods Daubing the Information 2005/03/11 (C) - - PowerPoint PPT Presentation

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Multiplexing Methods Daubing the Information 2005/03/11 (C) Herbert Haas I think there is a world market for about five computers. Thomas Watson, chairman of IBM 1943 Multiplexing Types TDM Most important Statistical and

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SLIDE 1

2005/03/11 (C) Herbert Haas

Multiplexing Methods

Daubing the Information

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SLIDE 2

“I think there is a world market for about five computers.”

Thomas Watson, chairman of IBM 1943

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SLIDE 3

3 (C) Herbert Haas 2005/03/11

Multiplexing Types

  • TDM

 Most important  Statistical and Deterministic

  • SDM
  • FDM and (D)WDM
  • CDM

Will be covered in

  • ther chapters
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SLIDE 4

4 (C) Herbert Haas 2005/03/11

TDM (1)

00110011001101000111100010010000101001010010101001110100010011001 10011100010101001010101010011110001010001101011011100010101001011 11000111000111100000000000000000000000000000000000000001000000000 101010010111

User A User B User C User D

0011100001101 1011100100100 1000011101101

SDM

User A User B User C User D

1011100111 1011100111 1011100111 1011100111 1011100111 Framed Mode

Save wires

User a User b User c User d User a User b User c User d

TDM

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SLIDE 5

5 (C) Herbert Haas 2005/03/11

TDM (2)

  • Requires framed link layer
  • Saves wires
  • Is slower than SDM
  • Requires multiplexers and

demultiplexers

  • Two fundamentally different methods:

Two fundamentally different methods:

 Deterministic TDM Deterministic TDM  Statistical TDM Statistical TDM

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SLIDE 6

6 (C) Herbert Haas 2005/03/11

C A

Deterministic TDM (1)

User A2 User B2 User C2 User D2

A B C D

"Trunk"

User A1 User B1 User C1 User D1

A B C D A B C D D A B C D A B C D

Framing

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SLIDE 7

7 (C) Herbert Haas 2005/03/11

Deterministic TDM (2)

  • Trunk speed = Number of slots × User access rate
  • Each user gets a constant timeslot of the trunk

C A

User A2 User B2 User C2 User D2

A B C D

User A1 User B1 User C1 User D1

A B C D A B C D D A B C D A B C D

4 × 64 kbit/s + F ≅ 256 kbit/s

64 kbit/s 64 kbit/s 64 kbit/s 64 kbit/s

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SLIDE 8

8 (C) Herbert Haas 2005/03/11

Deterministic TDM – Facts

  • Order is maintained
  • Frames must have same size
  • No addressing information required
  • Inherently connection-oriented
  • No buffers necessary (QoS)
  • Protocol transparent
  • Bad utilization of trunk
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SLIDE 9

9 (C) Herbert Haas 2005/03/11

Statistical TDM (1)

256 kbit/s

  • Trunk speed dimensioned for average usage
  • Each user can send packets whenever she wants

User A2 User B2 User C2 User D2 User A1 User B1 User C1 User D1

A B C D A C D B C D A C C D

Average date rates ≅ 64 kbit/s

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SLIDE 10

10 (C) Herbert Haas 2005/03/11

D D

Statistical TDM (2)

  • If other users are silent, one (or a few) users can

fully utilize their access rate

256 kbit/s

User A2 User B2 User C2 User D2 User A1 User B1 User C1 User D1

D D D A

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SLIDE 11

11 (C) Herbert Haas 2005/03/11

Statistical TDM – Facts

  • Good utilization of trunk

 Statistically dimensioned

  • Frames can have different size
  • Multiplexers require buffers
  • Variable delays
  • Address information required
  • Not protocol transparent
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SLIDE 12

12 (C) Herbert Haas 2005/03/11

Networking: Fully Meshed

User A User B User C User D User F User E

  • Metcalfe's Law:

n(n-1)/2 links

  • Good fault

tolerance

  • Expensive
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SLIDE 13

13 (C) Herbert Haas 2005/03/11

Networking: Switching

User A User B User C User D User F User E

  • Only 6 links
  • Switch supports

either deterministic or statistical TDM

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SLIDE 14

14 (C) Herbert Haas 2005/03/11

Circuit Switching

T1 T2 T3 TA T2 T3 T1 T4 T4 T4 T4 T1 TB

User A2 User B5

TA(1) → T1(4) : A1-C9 TA(2) → T2(7) : A2-B5 TA(3) → T2(6) : A3-D1 . . . . . . . . . . . . T2(6) → T4(1) T2(7) → T3(18) . . . . . . . . . . . . T3(18) → T4(5) T3(19) → T1(1) . . . . . . . . . . . . T4(4) → TB(9) T4(5) → TB(5) . . . . . . TA(2) → T2(7) : A2-B5 T2(7) → T3(18) T3(18) → T4(5) T4(5) → TB(5)

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SLIDE 15

15 (C) Herbert Haas 2005/03/11

Circuit Switching – Facts

  • Based on deterministic TDM

 Minimal delay  Protocol transparent  Possibly bad utilization  Good for isochronous traffic (voice)

  • Switching table entries

 Static (manually configured)  Dynamic (signaling protocol)  Scales with number of connections!

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SLIDE 16

16 (C) Herbert Haas 2005/03/11

Typical User-Configuration

CSU/DSU

PBX

Example: V.35/RS-530/RS-422 Synchronous serial ports Channel Service Unit/ Data Service Unit (CSU/DSU

  • r "modem")
  • CSU performs protective

and diagnostic functions

  • DSU connects a terminal

to a digital line

Example: E1 or T1 circuit Switch Router

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SLIDE 17

17 (C) Herbert Haas 2005/03/11

Packet Switching

T1 T2 T3 TA T2 T3 T1 T4 T4 T4 T4 T1 TB

User A2 User B5

Address Information

  • Each switch must analyze

address information

  • "Store and Forward"
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SLIDE 18

18 (C) Herbert Haas 2005/03/11

Technology Differences

  • Datagram

Datagram Principle

 Global and routable addresses  Connectionless  Routing Table

  • Virtual Call

Virtual Call Principle

 Local addresses  Connectionoriented  Switching Table

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SLIDE 19

19 (C) Herbert Haas 2005/03/11

Datagram

User A.2 User B.5

R1 R2 R4 R3 R5

Destination Next Hop A local B R2 C R2 ..... ..... A2 B5 A2 B5 A2 B5 Destination Next Hop A R1 B R4 C R3 ..... ..... A2 B5 Destination Next Hop A R2 B R5 C R2 ..... ..... A2 B5 Destination Next Hop A R4 B local C R4 ..... .....

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SLIDE 20

20 (C) Herbert Haas 2005/03/11

Datagram – Facts (1)

  • Addresses contain topological information

 Must be globally unique

  • Routing table is configured

 Static (manually)  Dynamic (routing protocols)

  • Endless circling in case of routing loops

 Important issue among routing protocols

  • Requires "routable" or "routed" protocols
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SLIDE 21

21 (C) Herbert Haas 2005/03/11

Datagram – Facts (2)

  • No connection establishment

necessary

 Faster delivery of first data  No resource reservation (bad QoS)

  • Sequence not guaranteed

 Rerouting on topology change  Load sharing on redundant paths  End stations must care

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SLIDE 22

22 (C) Herbert Haas 2005/03/11

Datagram – Facts (3)

  • Best effort service

 Router may drop packets  Reliable data transport requires good transport layer ("Dumb network, smart hosts")

  • Simple protocols

 Easy to implement (Internet's success)

  • Proactive flow control difficult

 Since routes might change

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SLIDE 23

23 (C) Herbert Haas 2005/03/11

Examples

  • IP
  • IPX
  • Appletalk
  • OSI CLNP
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SLIDE 24

24 (C) Herbert Haas 2005/03/11

P1

Virtual Call – CR

P1 P2 P3 P0 P0 P1 P2 P0 P0 P2

User A.2 User B.5

PS1 PS2 PS3 PS4 PS5

44 CR B5 A2 Destination Next Hop A local B PS2 C PS2 ..... .....

In Out P0:44 P2:10

P2 P0 10 CR B5 A2 Destination Next Hop A PS1 B PS4 C PS3 ..... .....

In Out P0:10 P3:02

Destination Next Hop A PS2 B PS5 C PS2 ..... ..... 02 CR B5 A2

In Out P1:02 P2:69

Destination Next Hop A PS4 B local C PS4 ..... ..... 69 CR B5 A2

In Out P0:69 P2:19

19 IC B5 A2

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SLIDE 25

25 (C) Herbert Haas 2005/03/11

P1

Virtual Call – CA

P1 P2 P3 P0 P0 P1 P2 P0 P0 P2

User A.2 User B.5

PS1 PS2 PS3 PS4 PS5

P2 P0

In Out P0:10 P3:02

02 CA B5 A2 19 CA B5 A2

In Out P0:69 P2:19 In Out P1:02 P2:69

69 CA B5 A2

In Out P0:44 P2:10

10 CA B5 A2 44 CC B5 A2

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SLIDE 26

26 (C) Herbert Haas 2005/03/11

Virtual Call – Data

P1 P1 P2 P3 P0 P0 P1 P2 P0 P0 P2

User A.2 User B.5

PS1 PS2 PS3 PS4 PS5

P2 P0

In Out P0:10 P3:02 In Out P0:69 P2:19 In Out P1:02 P2:69 In Out P0:44 P2:10

44 10 02 69 19

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SLIDE 27

27 (C) Herbert Haas 2005/03/11

Virtual Call – Facts (1)

  • Connection establishment

 Through routing process (!)  Globally unique topology-related addresses necessary  Creates entries in switching tables  Can reservate switching resources (QoS)

  • Packet switching relies on local identifiers

 Not topology related  Only unique per port

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SLIDE 28

28 (C) Herbert Haas 2005/03/11

Virtual Call – Facts (2)

  • Packet switching is much faster than

packet forwarding of routers

 Routing process is complex, typically implemented in software  Switching is simple, typically implemented in hardware

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SLIDE 29

29 (C) Herbert Haas 2005/03/11

Virtual Call – Facts (3)

  • Connection can be regarded as

virtual pipe

 Sequence is guaranteed  Resources can be guaranteed

  • Network failures disrupt pipe

 Connection re-establishment necessary  Datagram networks are more robust

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SLIDE 30

30 (C) Herbert Haas 2005/03/11

Virtual Call – Facts (4)

  • Virtual call multiplex

 Multiple virtual pipes per switch and interface possible  Pipes are locally distinguished through connection identifier

  • Other names for connection

identifier

 LCN (X.25)  DLCI (Frame Relay)  VPI/VCI (ATM)

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SLIDE 31

31 (C) Herbert Haas 2005/03/11

Example

BANG

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SLIDE 32

32 (C) Herbert Haas 2005/03/11

Two Service Types

  • Switched Virtual Circuit (SVC)

 Dynamic establishment as shown  At the end a proper disconnection procedure necessary

  • Permanent Virtual Circuit (PVC)

 No establishment and disconnection procedures necessary  Switching tables preconfigured by administrator

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SLIDE 33

33 (C) Herbert Haas 2005/03/11

Taxonomy

Circuit Switching Packet Switching Dynamic Signaling Static Configuration Datagram Virtual Call

  • Deterministic Multiplexing
  • Low latency
  • Designed for isochronous

traffic

  • Statistical Multiplexing
  • Store and forward
  • Addressing necessary
  • Designed for data traffic

ISDN PDH SONET/SDH IP IPX Appletalk X.25 Frame Relay ATM

Connectionless Connectionoriented Q.931, SS7, ... Manual configuration

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SLIDE 34

34 (C) Herbert Haas 2005/03/11

Summary

  • Only two worlds: circuit switching or

packet switching

 The first is good for voice the latter is good for data  Everybody wants to have the best of both worlds

  • Datagram (CL) versus Virtual Call (CO)

 Different address types (!)

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SLIDE 35

35 (C) Herbert Haas 2005/03/11

Layer N

Synchronization Revisited

Layer N+1

(a)synchronous Multiplexing (a)synchronous Transport

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SLIDE 36

36 (C) Herbert Haas 2005/03/11

Quiz

  • Derive Metcalfe's law. Which well-

known formula looks very similar?

  • Let's improve the VC principle!

What's the advantage of using more than one label per packet?

  • How do hash tables work?
  • How can we get the best of both

worlds (circuit/packet) ?