Multiplexing

1
Chapter 5

• Multiplexing

2
Contents

• Link multiplexing
• Circuit switching
• Synchronous Time-domain Multiplexing
• Packet Switching
• Statistical Time-domain Multiplexing
• Connection oriented vs. Connectionless
• Datagrams Routing
• Virtual Circuits Forwarding
• Internal vs. External policies

3
Contents

• Link multiplexing
• Circuit switching
• Synchronous Time-domain Multiplexing
• Packet Switching
• Statistical Time-domain Multiplexing
• Connection oriented vs. Connectionless
• Datagrams Routing
• Virtual Circuits Forwarding
• Internal vs. External policies

4
Circuit vs. Packet SwitchingA resource
multiplexing issue !!!
Main shared resource in networks transmission
capacity between nodes How to share such resource
optimally among several users ?
Fixed transmission capacity
Shared resource examples
5
Contents

• Link multiplexing
• Circuit switching
• Synchronous Time-domain Multiplexing
• Packet Switching
• Statistical Time-domain Multiplexing
• Connection oriented vs. Connectionless
• Datagrams Routing
• Virtual Circuits Forwarding
• Internal vs. External policies

6
Circuit Switching
The preferred multiplexing technique in the
traditional telephony world.
Fixed transmission capacity

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

7
Circuit Switching
Also used for data communications
Fixed transmission capacity

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

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Circuit Switched Routing
Each switching node has a routing table Giving,
when the circuit is established, the outgoing
link to be used for each destination .
a
c
1
3
3
1
a1 b2 c3 d3
a1 b1 c3 d2
2
2
d
b

• Routing tables are set up by network management.
• They are, in general static, sometimes even
  implicit.
• For mobile user dynamic tables are required

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Time Domain Multiplexing
Synchronous time domain multiplexing is The main
technique used for circuit switching
1
0
0
1
0
1
0
1
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Contents

• Link multiplexing
• Circuit switching
• Synchronous Time-domain Multiplexing
• Packet Switching
• Statistical Time-domain Multiplexing
• Connection oriented vs. Connectionless
• Datagrams Routing
• Virtual Circuits Forwarding
• Internal vs. External policies

11
Packet Switching(Invented by Paul Baran, 1960)
The preferred multiplexing technique in the data
world.
Fixed transmission capacity

• 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.

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Circuit vs. Packet Switching

• Peak data rate / Average data rate
• Voice 2 (both speakers talk 50 of time)
• Data gtgt 2 (think and processing times gt
  transmission times)

Typical voice traffic
Typical data traffic
t
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Circuit vs. Packet Switching

• Circuit Switching
• ? peak data rates lt transmission capacity
• Acceptable for voice and image transmission
• wasteful of resources for data transmission
• Fixed total delay
• Packet Switching
• ? average data rates lt 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

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Contents

• Link multiplexing
• Circuit switching
• Synchronous Time-domain Multiplexing
• Packet Switching
• Statistical Time-domain Multiplexing
• Connection oriented vs. Connectionless
• Datagrams Routing
• Virtual Circuits Forwarding
• Internal vs. External policies

15
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

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Contents

• Link multiplexing
• Circuit switching
• Synchronous Time-domain Multiplexing
• Packet Switching
• Statistical Time-domain Multiplexing
• Connection oriented vs. Connectionless
• Datagrams Routing
• Virtual Circuits Forwarding
• Internal vs. External policies

17
Datagram RoutingBased upon routing tables
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Routing Tablesin Connectionless networks

• For ALL POSSIBLE destination addresses, they give
  the best outgoing link, but
• the best can be different for different
  applications
• the best can get congested
• For EACH packet routing table needs to be
  consulted
• Routing tables need to be updated regularly
• Set of possible destinations can change
• Set of available links can change
• Destinations can be mobile

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Best route consequences
1
1
1
Idle
1
1
Risk of congestion
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Contents

• Link multiplexing
• Circuit switching
• Synchronous Time-domain Multiplexing
• Packet Switching
• Statistical Time-domain Multiplexing
• Connection oriented vs. Connectionless
• Datagrams Routing
• Virtual Circuits Forwarding
• Internal vs. External policies

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Virtual Circuit Number
c
a
d
b
Each virtual circuit is identified by a
specific number on each physical link
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Forwarding Tables
11
21
c
a
10
1
3
1
3
2
2
1.11gt3.10
1.10gt3.21
d
b
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Permanent Virtual CircuitForwarding tables
set-up and cleared by network manager through
separate network
c
1
3
1
3
2
2
1.11gt3.10
1.10gt3.21
Separate signaling network
d
b
Signaling and data packets travel through
different (virtual) circuits
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Forwarding Tablesin Connection Oriented networks

• For Each V. C. in use, they give the outgoing
  link
• Different v.c. can connect the same end-points.
• Resources can be reserved for a v.c.
• They can be changed dynamically to follow mobiles
• Routing tables are only needed to establish a new
  V.C.

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Contents

• Link multiplexing
• Circuit switching
• Synchronous Time-domain Multiplexing
• Packet Switching
• Statistical Time-domain Multiplexing
• Connection oriented vs. Connectionless
• Datagrams Routing
• Virtual Circuits Forwarding
• Internal vs. External policies

26
Internal vs. External Policies

Network services (NUI) Connection
oriented Connectionless
Network operation (NNI) Connection
oriented Connectionless
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Introduced concepts

• Multiplexing
• Circuit Switching
• Synchronous time multiplexing
• Packet Switching
• Statistical time multiplexing
• Datagrams and routing
• Virtual Circuits packet forwarding
• Resource reservation for a Virtual Circuit
• Internal vs. External policies