Download Telecommunications Concepts

Telecommunications
Concepts
Chapter 3.1
Packet Switched
Local Area Networks
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10-01-K.Steenhaut & J.Tiberghien - VUB
Contents
• Original Local Area Networks
– Ethernet
– Token Ring, Token bus, Cambridge ring, Liu ring, …
• The IEEE 802 standards
– IEEE 802.3, IEEE 802.4, IEEE 802.5, ...
– IEEE 802.2 : Logical Link Control
– IEEE 802.1 : Learning bridges
• High Performance LAN’s and MAN's
– High performance Ethernet
– Metropolitan Networks
– Wireless LAN's
• Side Tracks
– Interconnection of data communication systems.
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10-01-K.Steenhaut & J.Tiberghien - VUB
Contents
• Original Local Area Networks
– Ethernet
– Token Ring, Token bus, Cambridge ring, Liu ring, …
• The IEEE 802 standards
– IEEE 802.3, IEEE 802.4, IEEE 802.5, ...
– IEEE 802.2 : Logical Link Control
– IEEE 802.1 : Learning bridges
• High Performance LAN’s and MAN's
– High performance Ethernet
– Metropolitan Networks
– Wireless LAN's
• Side Tracks
– Interconnection of data communication systems.
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Shared Media Networks
Need for Medium Access Control Protocols
Commonly used in Local Area Networks
The network itself has practically no storage capacity
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The 7 OSI layers
Connectivity
Interoperability
Applications Layer
5
Transport Layer
7 : Application
6 : Presentation
5 : Session
4 : Transport
Internet Sublayer
3 : Network
Networks Layer
2 : Data Link
1 : Physical
10-01-K.Steenhaut & J.Tiberghien - VUB
The 3 lower OSI layers
For Shared Medium Networks
Internet
3
Network
Data Link Control
2
Medium Access Control
1
6
Physical
10-01-K.Steenhaut & J.Tiberghien - VUB
Contents
• Original Local Area Networks
– Ethernet
– Token Ring, Token bus, Cambridge ring, Liu ring, …
• The IEEE 802 standards
– IEEE 802.3, IEEE 802.4, IEEE 802.5, ...
– IEEE 802.2 : Logical Link Control
– IEEE 802.1 : Learning bridges
• High Performance LAN’s and MAN's
– High performance Ethernet
– Metropolitan Networks
– Wireless LAN's
• Side Track
– Interconnection of data communication systems.
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Ethernet
• Developed in the seventies at Xerox Parc
– Invented by Lamport
– Commercially supported by Digital and Intel
– Still has a dominant market position
• Originally based on coaxial bus
– Passive broadcast medium
– Length limited by electrical properties of cable
» Thick coaxial : 500 m
» Thin coaxial : 185 m
– Repeaters ( = electronic amplifiers ) allow to
» extend cable length
» replace coaxial bus by twisted pairs star
• Medium access control inspired by Aloha
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Aloha
(N.Abramson, F.Kuo, 1970)
Communication between
terminals and mainframe
via geostationary satellite
h = 36 000 Km
Propagation delay = 240 mS
REPEAT
Transmit data block B;
Receive same block Br;
ok := B = Br;
IF NOT ok THEN
Wait Random Delay
END
UNTIL ok
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ALOHA Performance
t:
G:
S:
p:
Transmission time for one data block.
Total proposed traffic ( # of blocks in time t )
Throughput ( # of successful blocks in time t )
0 <= S <= 1
Probability that a block will avoid collision
S=G.p
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ALOHA Collision Window
Station A
Station B
2t
Blocks transmitted according to Poisson Distribution
p = e - 2G
S = G . e - 2G
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ALOHA Throughput
S( G)
0.2
0.184
0.1
G
0
12
0
0.5
1
1.5
10-01-K.Steenhaut & J.Tiberghien - VUB
CSMA/CD operation
• Carrier Sense
– Listen before sending
• Multiple Access
– Everybody noticing silence can start sending
• Collision Detect
– Stop sending when noticing that others sending
– Collision fragments characterized by insufficient
length and therefore discarded by MAC entity.
Graceful degradation due to average repetition delay
proportional to number of retransmissions
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Carrier Sense
A
Listen before talking
(carrier sense)
B
Send data
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A
Listen and wait
B
A
No carrier sensed,
transmission starts
B
10-01-K.Steenhaut & J.Tiberghien - VUB
Collision Enforcement
Collision
A
B
Collided signals propagate
B detects collision and
A transmits jam
B
Collided signals reach A
Station A should detect
A the collision BEFORE it
has send its last databit
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B
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Minimum packet size
A
No carrier sensed,
transmission starts
Collided signals reach A
Station A should detect
A the collision BEFORE it
has send its last databit
B
B
Min. packet time > max. round trip delay
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Channelefficiency
Efficiency of channel
0
17
Size of frames (bytes)
1024
1,0
0,9
0,8
0,7
0,6
0,5
0,4
0,3
0,2
0,1
512
256
128
64
1
2
4
8
16 32 64 128 256
Number of stations trying to send
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Min : 64 bytes
Max : 1518 bytes
Ethernet Data Frame
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Preamble (7 bytes)
Start Frame (1 byte)
Destination Address (6 bytes)
Source Address (6 bytes)
Length payload (2 bytes)
Payload (evt. + Padding)
Frame Check Sequence (4 bytes)
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Thick Ethernet
Thick cable
Total Length
<= 500 m
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Ethernets with repeaters
Repeaters
Distance <= 3000 m
Half Repeaters
Optical Link
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Thin Ethernets
Thin cable
Total Length
<= 185 m
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Thin Ethernets
Thin cable
Distance <= 3000 m
Segment Length
<= 185 m
Repeaters
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Repeaters for thin Ethernet
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Ethernet over twisted pairs
One or two pairs per direction
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Twisted pair Ethernet
(10 Mb/s)
Twisted pairs
Distance <= 3000 m
Segment Length
<= 100 m
Repeaters
(= hubs)
Class 3 utp
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Cascade of Ethernet hubs
B B
B B B
B
A
B
B
HUB = Set of repeaters > all frames broadcasted
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High-performance Ethernet
(100 Mb/s)
Twisted pairs
Distance <= 400m
Segment Length
<= 100 m
Repeaters
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2 twisted pairs (class 5)
4 twisted pairs (class 3)
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Ethernet in office buildings
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Contents
• Original Local Area Networks
– Ethernet
– Token Ring, Token bus, Cambridge ring, Liu ring, …
• The IEEE 802 standards
– IEEE 802.3, IEEE 802.4, IEEE 802.5, ...
– IEEE 802.2 : Logical Link Control
– IEEE 802.1 : Learning bridges
• High Performance LAN’s and MAN's
– High performance Ethernet
– Metropolitan Networks
– Wireless LAN's
• Side Track
– Interconnection of data communication systems.
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10-01-K.Steenhaut & J.Tiberghien - VUB
Contents
• Original Local Area Networks
– Ethernet
– Token Ring
• The IEEE 802 standards
– IEEE 802.3, IEEE 802.4, IEEE 802.5, ...
– IEEE 802.2 : Logical Link Control
– IEEE 802.1 : Learning bridges
• High Performance LAN’s and MAN's
– High performance Ethernet
– Metropolitan Networks
– Wireless LAN's
• Side Track
– Interconnection of data communication systems.
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10-01-K.Steenhaut & J.Tiberghien - VUB
IEEE 802 Standards
in the OSI model
3
31
802.?
???
802.7
Broadband
Physical
802.6
Metropolitan
1
802.5
~ Token Ring
MAC
802.4
~ Token Bus
LLC
IEEE 802.2
Logical Link Control
802.3
~ Ethernet
2
IEEE 802.1
Management, interconnection ,
Upper layers interface
10-01-K.Steenhaut & J.Tiberghien - VUB
Contents
• Original Local Area Networks
– Ethernet
– Token Ring
• The IEEE 802 standards
– IEEE 802.3, IEEE 802.4, IEEE 802.5, ...
– IEEE 802.2 : Logical Link Control
– IEEE 802.1 : Learning bridges
• High Performance LAN’s and MAN's
– High performance Ethernet
– Metropolitan Networks
– Wireless LAN's
• Side Track
– Interconnection of data communication systems.
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10-01-K.Steenhaut & J.Tiberghien - VUB
Contents
• Original Local Area Networks
– Ethernet
– Token Ring
• The IEEE 802 standards
– IEEE 802.3, IEEE 802.4, IEEE 802.5, ...
– IEEE 802.2 : Logical Link Control
– IEEE 802.1 : Learning bridges
• High Performance LAN’s and MAN's
– High performance Ethernet
– Metropolitan Networks
– Wireless LAN's
• Side Track
– Interconnection of data communication systems.
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10-01-K.Steenhaut & J.Tiberghien - VUB
IEEE 802.2
Logical Link Control
• Purpose :
– To fit LAN’s into the general OSI framework
– Correct transmission errors
• Services offered :
– Data link multiplexing by means of LLC addresses
– Data link error correction and flow control
» Class 1 : Connectionless, unacknowledged service
» Class 2 :
• Connection oriented reliable link control
• Sliding window protocol
• Window size = 128 frames.
» Class 3 : Connectionless, acknowledged.
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LLC Frame Format
Flag Address
Control
Payload
CRC Flag
• Flag : Unique bit pattern (01111110)
• Address (2*16 bit) : allows to multiplex a single
MAC address for different data links.
• Control (16 bit) : Controls the sliding windows
• Payload (variable length) : Data from layer 3
• CRC (16 bit) : Redundant bits obtained by dividing
the address, control and payload fields by a
predefined polynomial.
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LLC bit stuffing
• The bit pattern 01111110 should never occur in the
address, control, payload and CRC fields.
• After 5 consecutive 1’s a 0 is inserted by the TX
• A 0 preceded by 5 1’s is removed by the RX.
Message to be transmitted :
0100110111110101101111111110111111000110000
Message effectively transmitted :
0100110111110010110111110111101111101000110000
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LLC Frame Types
Unnumbered
used to set up connections
used to transfer data in connectionless mode
Supervisory
used for managing the sliding window
in connection oriented mode
Information
used to transfer data in connection oriented mode
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10-01-K.Steenhaut & J.Tiberghien - VUB
Contents
• Original Local Area Networks
– Ethernet
– Token Ring
• The IEEE 802 standards
– IEEE 802.3, IEEE 802.4, IEEE 802.5, ...
– IEEE 802.2 : Logical Link Control
– IEEE 802.1 : Learning bridges
• High Performance LAN’s and MAN's
– High performance Ethernet
– Metropolitan Networks
– Wireless LAN's
• Side Track
– Interconnection of data communication systems.
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10-01-K.Steenhaut & J.Tiberghien - VUB
Interconnection of LAN’s
• Layer 7 : Application level Gateways
• Layer 3 : ROUTERS
– Independent networks (lan or wan) interconnected by means
of an internet protocol.
• Layer 2 : BRIDGES
–
–
–
–
Independent MAC protocols on interconnected lan’s.
Distance restrictions apply to each lan individually
Half bridges can be interconnected by any lan or wan.
Traffic between lan’s can be filtered according to MAC level
addresses.
• Layer 1 : REPEATERS
– No influence on MAC protocol
– Same traffic in all interconnected lan’s
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Repeaters
Layer 3b
Internet
Layer 3b
Network
Layer 3a
Layer 3a
Data Link
Layer 2b
Layer 2b
Medium Access Control
Layer 2a
Layer 2a
Layer 1
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Repeater
Layer 1
Layer 1
Layer 1
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Practical Ethernets
Repeaters
Distance <= 3000 m
Half Repeaters
Optical Link
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Interconnection of LAN’s
• Layer 7 : Application level Gateways
• Layer 3 : ROUTERS
– Independent networks (lan or wan) interconnected by means
of an internet protocol.
• Layer 2 : BRIDGES
–
–
–
–
Independent MAC protocols on interconnected lan’s.
Distance restrictions apply to each lan individually
Half bridges can be interconnected by any lan or wan.
Traffic between lan’s can be filtered according to MAC level
addresses.
• Layer 1 : REPEATERS
– No influence on MAC protocol
– Same traffic in all interconnected lan’s
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Application Level Gateways
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Layer 7
Application gateway
Layer 7
Layer 7
Layer 7
Layer 6
Layer 6
Layer 6
Layer 6
Layer 5
Layer 5
Layer 5
Layer 5
Layer 4
Layer 4
Layer 4
Layer 4
Layer 3
Layer 3
Layer 3
Layer 3
Layer 2
Layer 2
Layer 2
Layer 2
Layer 1
Layer 1
Layer 1
Layer 1
10-01-K.Steenhaut & J.Tiberghien - VUB
Gateway example
X400 - SMTP mail gateway
X400 users
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mail
gateway
SMTP users
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Firewalls
Internet
Firewall
Intranet
An application gateway between the Internet and an
intranet is a fairly secure firewall.
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Interconnection of LAN’s
• Layer 7 : Application level Gateways
• Layer 3 : ROUTERS
– Independent networks (lan or wan) interconnected by means
of an internet protocol.
• Layer 2 : BRIDGES
–
–
–
–
Independent MAC protocols on interconnected lan’s.
Distance restrictions apply to each lan individually
Half bridges can be interconnected by any lan or wan.
Traffic between lan’s can be filtered according to MAC level
addresses.
• Layer 1 : REPEATERS
– No influence on MAC protocol
– Same traffic in all interconnected lan’s
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Routers
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Layer 3b
Router
Layer 3b
Layer 3b
Layer 3b
Layer 3a
Layer 3a
Layer 3a
Layer 3a
Layer 2b
Layer 2b
Layer 2b
Layer 2b
Layer 2a
Layer 2a
Layer 2a
Layer 2a
Layer 1
Layer 1
Layer 1
Layer 1
10-01-K.Steenhaut & J.Tiberghien - VUB
Interconnection of LAN’s
• Layer 7 : Application level Gateways
• Layer 3 : ROUTERS
– Independent networks (lan or wan) interconnected by means
of an internet protocol.
• Layer 2 : BRIDGES
–
–
–
–
Independent MAC protocols on interconnected lan’s.
Distance restrictions apply to each lan individually
Half bridges can be interconnected by any lan or wan.
Traffic between lan’s can be filtered according to MAC level
addresses.
• Layer 1 : REPEATERS
– No influence on MAC protocol
– Same traffic in all interconnected lan’s
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Bridges
Internet
Layer 3b
Layer 3b
Network
Layer 3a
Layer 3a
Data Link
Layer 2b
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Layer 2b
Layer 2a
BRIDGE
Layer 2a
Layer 2a
Layer 2a
Layer 1
Layer 1
Layer 1
Layer 1
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Bridges
Bridge
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Bridges
WiFi
Bridge
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Bridges
and multiple Network Protocols
IP
BRIDGE
IPX
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Contents
• Original Local Area Networks
– Ethernet
– Token Ring
• The IEEE 802 standards
– IEEE 802.3, IEEE 802.4, IEEE 802.5, ...
– IEEE 802.2 : Logical Link Control
– IEEE 802.1 : Learning bridges
• High Performance LAN’s and MAN's
– High performance Ethernet
– Metropolitan Networks
– Wireless LAN's
• Side Track
– Interconnection of data communication systems.
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Filtering Bridges
Lan 2
Lan 1
RX
Filter
123
536
234
TX
54
Buffer
Addresses
Database
Filter
Buffer
TX
831
556
246
456
RX
10-01-K.Steenhaut & J.Tiberghien - VUB
Learning Bridges
• Frames with unknown destination are always
forwarded (promiscuous mode)
• Source addresses of all frames are monitored and
added to the database, with a time stamp.
• Frames with a destination address known to be on
the same side as their source are not forwarded.
• Addresses which have not been confirmed since
some time are removed from the database.
• The learning algorithm requires that there are no
loops through the interconnected lan’s.
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Spanning Tree Algorithm
Root
(Lowest serial Nr)
Disabled
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Half Bridges
Half Bridges
Any Data Link
Ethernet frames are tunneled through the network
interconnecting the half bridges
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Backbones
FDDI
MAN
ATM
ISDN
F.R.
X25
Half Bridges
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Level 2a tunneling
via level 2a intermediate network
4
4
Specific labels
can be added
to the frames to
identify data flow
3
2b
59
3
2b
2a
2a
2a
2a
2a
2a
1
1
1
1
1
1
10-01-K.Steenhaut & J.Tiberghien - VUB
Level 2a tunneling
via level 2b intermediate network
4
4
3
3
2b
60
2b
2b
2b
2a
2a
2a
2a
2a
2a
1
1
1
1
1
1
10-01-K.Steenhaut & J.Tiberghien - VUB
Level 2a tunneling
via level 3 intermediate network
4
61
4
3
3
3
3
2b
2b
2b
2b
2a
2a
2a
2a
2a
2a
1
1
1
1
1
1
10-01-K.Steenhaut & J.Tiberghien - VUB
Virtual LAN’s
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Contents
• Original Local Area Networks
– Ethernet
– Token Ring
• The IEEE 802 standards
– IEEE 802.3, IEEE 802.4, IEEE 802.5, ...
– IEEE 802.2 : Logical Link Control
– IEEE 802.1 : Learning bridges
• High Performance LAN’s and MAN's
– High performance Ethernet
– Metropolitan Networks
– Wireless LAN's
• Side Track
– Interconnection of data communication systems.
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High performance Ethernet
Data rate
1 GB/s
100 MB/s
10 MB/s
less collisions
Single segment (broadcast)
One station per segment = no collisions (switching)
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Switched LAN’s
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Contents
• Original Local Area Networks
– Ethernet
– Token Ring
• The IEEE 802 standards
– IEEE 802.3, IEEE 802.4, IEEE 802.5, ...
– IEEE 802.2 : Logical Link Control
– IEEE 802.1 : Learning bridges
• High Performance LAN’s and MAN's
– High performance Ethernet
– Metropolitan Networks
– Wireless LAN's
• Side Track
– Interconnection of data communication systems.
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Cable TV Networks
Head-end
Trunk cables
Distribution cables
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Cable TV Networks
7-8 MHz
TF1
VTM
RTBF
VRT
RTL
frequency
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Data over Cable TV
7-8 MHz
Return
VTM
RTBF
BRTN
RTL
Data
frequency
Cable
modem
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Cable
modem
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Gigabit Ethernet as MAN
Head-end
Distribution cables
(optical fibers)
Backbone (WDM optical fibers)
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Contents
• Original Local Area Networks
– Ethernet
– Token Ring
• The IEEE 802 standards
– IEEE 802.3, IEEE 802.4, IEEE 802.5, ...
– IEEE 802.2 : Logical Link Control
– IEEE 802.1 : Learning bridges
• High Performance LAN’s and MAN's
– High performance Ethernet
– Metropolitan Networks
– Wireless LAN's
• Side Track
– Interconnection of data communication systems.
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IEEE 802 Standards
in the OSI model
3
MAC
1
72
Physical
802.11
Wireless
LLC
IEEE 802.2
Logical Link Control
802.3
~ Ethernet
802.4
~ Token Bus
802.5
~ Token Ring
2
IEEE 802.1
Management, interconnection,
upper layers interface
10-01-K.Steenhaut & J.Tiberghien - VUB
IEEE 802.11
???
Infrared
Provisions for a variety
of physical layers
Frequency
hopping
spread spectrum
Direct Sequence
spread spectrum
One common MAC layer
IEEE 802.11
Medium Access Control
1 or 2 Mb/s
(provisions for migration
to higher speeds)
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802.11 Hidden Station
B
A
74
C
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