10-01-K.Steenhaut & J.Tiberghien - VUB1
TelecommunicationsConcepts
Chapter 3.1
Packet Switched
Local Area Networks
10-01-K.Steenhaut & J.Tiberghien - VUB2
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.
10-01-K.Steenhaut & J.Tiberghien - VUB3
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.
10-01-K.Steenhaut & J.Tiberghien - VUB4
Shared Media Networks
Need for Medium Access Control Protocols
Commonly used in Local Area Networks
The network itself has practically no storage capacity
10-01-K.Steenhaut & J.Tiberghien - VUB5
The 7 OSI layers
Applications Layer
Transport Layer
Networks Layer
Co
nn
ecti
vity
Inte
rop
erab
ilit
y
Internet Sublayer
1 : Physical
2 : Data Link
3 : Network
4 : Transport
5 : Session
6 : Presentation7 : Application
10-01-K.Steenhaut & J.Tiberghien - VUB6
The 3 lower OSI layers
For Shared Medium Networks
Network
Internet
3
Physical
Medium Access Control2
1
Data Link Control
10-01-K.Steenhaut & J.Tiberghien - VUB7
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.
10-01-K.Steenhaut & J.Tiberghien - VUB8
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
10-01-K.Steenhaut & J.Tiberghien - VUB9
Aloha(N.Abramson, F.Kuo,
1970)
Communication between terminals and mainframevia geostationary satelliteh = 36 000 KmPropagation delay = 240 mS
REPEAT Transmit data block B; Receive same block Br; ok := B = Br; IF NOT ok THEN Wait Random Delay ENDUNTIL ok
10-01-K.Steenhaut & J.Tiberghien - VUB10
ALOHA Performance
t : Transmission time for one data block.
G : Total proposed traffic ( # of blocks in time t )
S : Throughput ( # of successful blocks in time t )
0 <= S <= 1
p : Probability that a block will avoid collision
S = G . p
10-01-K.Steenhaut & J.Tiberghien - VUB11
ALOHA Collision Window
Station A
Station B
2t
Blocks transmitted according to Poisson Distribution
p = e - 2G
S = G . e - 2G
10-01-K.Steenhaut & J.Tiberghien - VUB12
ALOHA Throughput
0
0.1
0.2
0 0.5 1 1.5
0.184
)S( G
G
10-01-K.Steenhaut & J.Tiberghien - VUB13
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
10-01-K.Steenhaut & J.Tiberghien - VUB14
Carrier Sense
A
A
A
B
B
B
Listen before talking(carrier sense)
Send data
Listen and wait
No carrier sensed,transmission starts
10-01-K.Steenhaut & J.Tiberghien - VUB15
Collision Enforcement
A
A
B
B
Collision
Collided signals propagateB detects collision and transmits jam
A B
Collided signals reach AStation A should detect the collision BEFORE it has send its last databit
10-01-K.Steenhaut & J.Tiberghien - VUB16
Minimum packet size
A B
A BNo carrier sensed,transmission starts
Min. packet time > max. round trip delay
Collided signals reach AStation A should detect the collision BEFORE it has send its last databit
10-01-K.Steenhaut & J.Tiberghien - VUB17
1 2 4 8 16 320 64 128 256
0,1
0,2
0,3
0,4
0,5
0,6
0,7
0,8
1,0
0,9
Size of frames (bytes)
1024
512
256
128
64
Ch
an
nele
ffic
ien
cy
Number of stations trying to send
Efficiency of channel
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Ethernet Data Frame
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)
Min
: 6
4 b
ytes
Max
: 1
518
byt
es
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Thick Ethernet
Thick cableTotal Length
<= 500 m
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Ethernets with repeaters
RepeatersDistance <= 3000 m
Half RepeatersOptical Link
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Thin Ethernets
Thin cableTotal Length
<= 185 m
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Thin Ethernets
Repeaters
Thin cableDistance <= 3000 m
Segment Length<= 185 m
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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)
Repeaters (= hubs)
Twisted pairsDistance <= 3000 m
Segment Length<= 100 m
Class 3 utp
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Cascade of Ethernet hubs
A
B
HUB = Set of repeaters > all frames broadcasted
B
B
B
B
B B B
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High-performance Ethernet(100 Mb/s)
Repeaters
Twisted pairsDistance <= 400mSegment Length
<= 100 m
4 twisted pairs (class 3)2 twisted pairs (class 5)
10-01-K.Steenhaut & J.Tiberghien - VUB28
Ethernet in office buildings
10-01-K.Steenhaut & J.Tiberghien - VUB29
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.
10-01-K.Steenhaut & J.Tiberghien - VUB30
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.
10-01-K.Steenhaut & J.Tiberghien - VUB31
IEEE 802 Standards
in the OSI model
802
.7B
roa
db
and
802
.3~
Eth
ern
et
802
.4~
To
ke
n B
us
802
.5~
To
ke
n R
ing
802
.6M
etr
op
olit
an
802
.??
??
IEEE 802.2Logical Link Control
IEEE 802.1Management, interconnection , Upper layers interface
2
1
MAC
LLC
Physical
3
10-01-K.Steenhaut & J.Tiberghien - VUB32
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.
10-01-K.Steenhaut & J.Tiberghien - VUB33
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.
10-01-K.Steenhaut & J.Tiberghien - VUB34
IEEE 802.2Logical 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 : 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.
Flag CRCAddress Control FlagPayload
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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.
0100110111110101101111111110111111000110000
0100110111110010110111110111101111101000110000
Message to be transmitted :
Message effectively transmitted :
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LLC Frame Types
Unnumberedused to set up connections
used to transfer data in connectionless mode
Supervisoryused for managing the sliding window
in connection oriented mode
Informationused to transfer data in connection oriented
mode
10-01-K.Steenhaut & J.Tiberghien - VUB38
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.
10-01-K.Steenhaut & J.Tiberghien - VUB39
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
10-01-K.Steenhaut & J.Tiberghien - VUB40
Repeaters
Layer 1
Layer 2a
Layer 2b
Layer 3b
Layer 3a
Layer 1Layer 1
Repeater
Layer 2a
Layer 2b
Layer 3b
Layer 3a
Layer 1
Internet
Data Link
Medium Access Control
Network
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Practical Ethernets
RepeatersDistance <= 3000 m
Half RepeatersOptical Link
10-01-K.Steenhaut & J.Tiberghien - VUB42
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
10-01-K.Steenhaut & J.Tiberghien - VUB43
Application Level GatewaysApplication gateway
Layer 2
Layer 3
Layer 1
Layer 5
Layer 4
Layer 7
Layer 6
Layer 2
Layer 3
Layer 1
Layer 5
Layer 4
Layer 7
Layer 6
Layer 2
Layer 3
Layer 1
Layer 5
Layer 4
Layer 7
Layer 6
Layer 2
Layer 3
Layer 1
Layer 5
Layer 4
Layer 7
Layer 6
10-01-K.Steenhaut & J.Tiberghien - VUB44
Gateway exampleX400 - SMTP mail gateway
X400 users SMTP usersmailgateway
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Firewalls
An application gateway between the Internet and an intranet is a fairly secure firewall.
IntranetInternetFirewall
10-01-K.Steenhaut & J.Tiberghien - VUB46
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
10-01-K.Steenhaut & J.Tiberghien - VUB47
Routers
Layer 1
Layer 2a
Layer 2b
Layer 3b
Layer 3a
Layer 1Layer 1
Layer 2a
Layer 2b
Layer 3b
Layer 3a
Layer 1
Layer 2aLayer 2a
Layer 3b
Layer 2b
Layer 3a
Layer 3b
Layer 2b
Layer 3a
Router
10-01-K.Steenhaut & J.Tiberghien - VUB48
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
10-01-K.Steenhaut & J.Tiberghien - VUB49
Bridges
Layer 1
Layer 2a
Layer 2b
Layer 3b
Layer 3a
Layer 1Layer 1
BRIDGE
Layer 2a
Layer 2b
Layer 3b
Layer 3a
Layer 1
Internet
Data Link
Layer 2aLayer 2a
Network
10-01-K.Steenhaut & J.Tiberghien - VUB50
Bridges
Bridge
10-01-K.Steenhaut & J.Tiberghien - VUB51
Bridges
Bridge
WiFi
10-01-K.Steenhaut & J.Tiberghien - VUB52
Bridges and multiple Network Protocols
BRIDGE
IP
IPX
10-01-K.Steenhaut & J.Tiberghien - VUB53
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.
10-01-K.Steenhaut & J.Tiberghien - VUB54
Filtering Bridges
Lan 1 Lan 2
RX
RX
Filter
FilterBuffer
Buffer
TX
TX
Addresses Database
123536234
831556246456
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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.
10-01-K.Steenhaut & J.Tiberghien - VUB56
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
10-01-K.Steenhaut & J.Tiberghien - VUB58
Backbones
Half Bridges
FDDIMANATMISDNF.R.X25
10-01-K.Steenhaut & J.Tiberghien - VUB59
Level 2a tunneling
via level 2a intermediate network
2a
2b
4
3
1
2a
1
2a
1
2a
2b
4
3
1
2a
1
2a
1
Specific labels can be added
to the frames to identify data flow
10-01-K.Steenhaut & J.Tiberghien - VUB60
Level 2a tunneling
via level 2b intermediate network
2a
2b
4
3
1
2a
1
2a
2b
1
2a
2b
4
3
1
2a
1
2a
2b
1
10-01-K.Steenhaut & J.Tiberghien - VUB61
Level 2a tunneling
via level 3 intermediate network
2a
2b
4
3
1
2a
1
2a
2b
3
1
2a
2b
4
3
1
2a
1
2a
2b
3
1
10-01-K.Steenhaut & J.Tiberghien - VUB62
Virtual LAN’s
10-01-K.Steenhaut & J.Tiberghien - VUB63
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.
10-01-K.Steenhaut & J.Tiberghien - VUB64
High performance Ethernet
less collisions
Data rate
10 MB/s
100 MB/s
1 GB/s
Single segment (broadcast)
One station per segment = no collisions (switching)
Throughput
10-01-K.Steenhaut & J.Tiberghien - VUB65
Switched LAN’s
10-01-K.Steenhaut & J.Tiberghien - VUB66
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.
10-01-K.Steenhaut & J.Tiberghien - VUB67
Cable TV Networks
Head-endTrunk cables
Distribution cables
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Cable TV Networks
frequency
VTM RTBF VRT RTLTF1
7-8 MHz
10-01-K.Steenhaut & J.Tiberghien - VUB69
Data over Cable TV
frequency
VTM RTBF BRTN RTLReturn
7-8 MHz
Data
Cablemodem
Cablemodem
10-01-K.Steenhaut & J.Tiberghien - VUB70
Gigabit Ethernet as MAN
Head-end Distribution cables(optical fibers)
Backbone (WDM optical fibers)
10-01-K.Steenhaut & J.Tiberghien - VUB71
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.
10-01-K.Steenhaut & J.Tiberghien - VUB72
IEEE 802.1Management, interconnection, upper layers interface
802
.3~
Eth
ern
et
802
.4~
To
ke
n B
us
802
.5~
To
ke
n R
ing
802
.11
Wir
ele
ss
IEEE 802.2Logical Link Control
2
1
MAC
LLC
Physical
3
IEEE 802 Standards
in the OSI model
10-01-K.Steenhaut & J.Tiberghien - VUB73
IEEE 802.11
Fre
qu
en
cy
ho
pp
ing
s
pre
ad
sp
ec
tru
m
??
?
Infr
ared
IEEE 802.11Medium Access Control
Dir
ec
t S
eq
uen
ce
sp
rea
d s
pe
ctr
um
1 or 2 Mb/s(provisions for migrationto higher speeds)
One common MAC layer
Provisions for a variety
of physical layers
10-01-K.Steenhaut & J.Tiberghien - VUB74
802.11 Hidden Station
A
B
C
RTS
CTSCTS