Download Ethernet

E-Business: Ethernet and OSI
Specific Outcomes
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Explain the overall hierarchy of the OSI stack
Describe general specifications of cable and
connector types and explain where they may be
used within a Local Area Network (LAN)
Compare and contrast the functionality of hubs vs.
switches
Explain how the Spanning Tree Protocol works
Describe the Ethernet Frame and explain how a
frame is routed through a LAN
Apply all of the above theory to a given scenario
Open Systems Interconnection
Comparison of OSI vs. TCP stacks
Ethernet Dominance
The “hoover” of networks
Ethernet is the dominant LAN technology
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Over 95% of LAN ports are Ethernet
You need to know it well
Basic Ethernet switching is very simple
However, large Ethernet networks require
more advanced knowledge
Ethernet History
Developed at Xerox Palo Alto Research Center
in the 1970s

After a trip to the University of Hawaii’s Alohanet
project.
Taken over by the IEEE
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802 LAN/MAN Standards Committee is in charge of
LAN Standards.
802.3 Working Group develops specific Ethernet
standards.
802.16 Busy refining WiMax standards.
Other working groups create other standards.
Ethernet Standards
Ethernet standards are LAN standards
LANs (and WANs) are single networks
Single networks are based on Layer 1 (physical)
and Layer 2 (data link) standards
OSI dominates standards at these layers
Ethernet standards are OSI standards

Must be ratified by ISO, but this is a mere formality
Layer 3 and above
Layer 2
Layer 1
Baseband and Broadband
Baseband Transmission
Signal
Source
Transmitted Signal (Same)
Transmission Medium
Signal is injected directly into the transmission medium
(wire, optical fiber)
Inexpensive, so dominates wired LAN transmission technology
Baseband and Broadband
Broadband Transmission
Modulated Signal
Source
Radio
Tuner
Radio Channel
Signal is first modulated to a higher frequency,
then sent in a radio channel
Expensive but needed for radio-based networks
Ethernet Physical Standards
Physical
Layer
Standard
UTP
10Base-T
*100Base-TX
1000Base-T
Speed
Maximum Medium
Run
Length
10 Mbps* 100 meters 4-pair Category 3
or better
100 Mbps 100 meters 4-pair Category 5
or better
1,000 Mbps 100 meters 4-pair Category 5
or better
*With autosensing, 100Base-TX NICs and switches will slow to
10 Mbps for 10Base-T devices. Often called 10/100 Ethernet
Ethernet Physical Layer
Standards
Physical
Layer
Standard
Speed Maximum Medium
Run
Length
1000Base-SX 1 Gbps
(short wavelength)
1000Base-SX 1 Gbps
(short wavelength)
1000Base-SX 1 Gbps
(short wavelength)
1000Base-SX 1 Gbps
(short wavelength)
220 m 62.5/125 micron multimode,
850 nm, 160 MHz-km
modal bandwidth
275 m 62.5/125 micron multimode,
850 nm, 200 MHz-km
500 m 50/125 micron multimode,
850 nm, 400 MHz-km
550 m 50/125 micron multimode,
850 nm; 500 MHz-km
Gigabit Ethernet, 850 nm, various core sizes and modal bandwidths
Gigabit Ethernet usage is dominated by 1000Base-SX
Ethernet Physical Layer
Standards
Physical
Layer
Standard
Speed
1000Base-LX
1 Gbps
550 m 62.5/125 micron multimode,
1300 nm
1 Gbps
5 km 9/125 micron single-mode,
1300 nm
(long wavelength)
1000Base-LX
(long wavelength)
Maximum Medium
Run
Length
Gigabit Ethernet, 1300 nm, multimode versus single-mode
Ethernet Physical Layer
Standards
Physical
Layer
Standard
Speed
10GBase-SR/SW
10 Gbps
10GBase-LX4
10 Gbps
Maximum Medium
Run
Length
10 Gbps Ethernet, multimode
S = 850 nm, L = 1300 nm
R=LAN, W=WAN
65 m 62.5/125 micron
multimode, 850 nm
300 m
62.5/125 micron
multimode, 1300
Ethernet Physical Layer
Standards
Physical
Layer
Standard
10GBase-LR/LW
Speed
Maximum Medium
Run
Length
10 Gbps
10 km 9/125 micron single
mode, 1300 nm.
10GBase-ER/EW 10 Gbps
40 km 9/125 micron single
mode, 1550 nm.
10 Gbps Ethernet, for wide area networks
L = 1300 nm, E = 1550 nm (E for extremely long wavelength)
R = LAN, W = WAN
Ethernet Physical Layer
Standards
Fiber Standards
Ethernet Physical Layer
Standards
FTTH – (F)iber (T)o (T)he (H)ome
Ethernet Perspective
Access links to client stations today are
dominated by at least 100Base-TX or 1000
Base T
Trunk links today are dominated by 1000BaseSX
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Short trunk links, however, use UTP
Longer and faster trunk links use other fiber
standards
Ethernet: Multiple Switches
Original
Signal
Received Regenerated
Signal
Signal
Switches regenerate signals before sending them out;
This removes errors
We need to carefully consider switch placement
Centralised versus Decentralised wiring etc
Ethernet: Mutiple Switches
(Datalink)
Received
Original Received Regenerated Signal
Received
Signal
Regenerated Signal
Signal
Signal
Signal
Thanks to regeneration, signals can travel far across
a series of switches
Ethernet: Mutiple Switches
(Datalink)
Received
Original Received Regenerated Signal
Received
Signal
Regenerated Signal
Signal
Signal
Signal
UTP
100Base-TX
(100 m maximum)
Physical Link
62.5/125
Multimode Fiber
UTP
1000Base-SX
(220 m maximum)
Physical Link
100Base-TX
(100 m maximum)
Physical Link
Each transmission line along the way has a distance limit.
Ethernet: Mutiple Switches
(Datalink)
Received
Original Received Regenerated Signal
Received
Signal
Regenerated Signal
Signal
Signal
Signal
UTP
100Base-TX
(100 m maximum)
Physical Link
62.5/125
Multimode Fiber
UTP
1000Base-SX
(220 m maximum)
Physical Link
100Base-TX
(100 m maximum)
Physical Link
Data Link Does Not Have a Maximum Distance
(420 m distance spanned in this example)
802 Layering
Internet Layer
Data
Link
Layer
Logical
Link
Control
Layer
Governs aspects of the communication
Needed by all LANs, e.g., error correction.
These functions not used in practice.
Media
Access
Control
Layer
Governs aspects of the communication
Specific to a particular LAN technology,
e.g., Ethernet, 802.11 wireless LANs, etc.
Physical Layer
802 Layering
Internet Layer
Data
Link
Layer
TCP/IP Internet
Layer Standards
(IP, ARP, etc.)
Logical
Link
Control
Layer
Media
Access
Control
Layer
Physical Layer
Other Internet
Layer Standards
(IPX, etc.)
802.2
Ethernet 802.3 MAC Layer
Standard
Other MAC
Standards
(802.5,
802.11, etc.)
1000
BaseSX
Other Physical
Layer
Standards
(802.11, etc.)
10Base-T
…
Ethernet Frame
Field
Preamble (7 Octets)
10101010 …
Start-of-Frame Delimiter (1 Octet)
10101011
Destination MAC Address (48 bits)
Note, last bit is a 1
symbolising end of
synchronisation
Source MAC Address (48 bits)
No minimum length for
802.3 MAC layer
however if data field
<46 Octets, PAD field
added by sender so that
total length of data field
=46 octets
Used for error detection
4 Octet field. If error is
detected, frame is
simply discarded
Length (2 Octets)
Data Field
(Variable
Length)
LLC Subheader
(8
Octets)
Packet
(Variable
Length)
PAD Field
Frame Check Sequence (4 Octets)
Logical link control
layer subheader
8 Octets (64bits)
Purpose: Describe
the type of packet
contained within the
Data Field ie (IP
Packet or TCP
packet etc)
Ethernet Frame 1/2
Field
Preamble (7 Octets)
10101010 …
Start-of-Frame Delimiter (1 Octet)
10101011
Destination MAC Address (48 bits)
Source MAC Address (48 bits)
Computers use raw
48-bit MAC addresses;
Humans use
Hexadecimal notation
(A1-23-9C-AB-33-53),
Which is discussed
Later.
Ethernet Frame 2/2
May contain IP or IPX packet
Field
Length (2 Octets)
Data Field
(Variable
Length)
LLC Subheader
(Usually 7
Octets)
Packet
(Variable
Length)
PAD Field
Frame Check Sequence (4 Octets)
Added if data field
is less than 46 octets;
Length set to make
data field plus PAD
field 46 octets; Not
added if data field
is greater than 46
octets long.
If an error is found,
the frame is
discarded.
Multi Switch: Ethernet LAN
The Situation:
A1… Sends to E5…
Switch 2
Port 5 on Switch 1
to Port 3 on Switch 2
Port 7 on Switch 2
to Port 4 on Switch 3
Switch 1
Switch 3
C3-2D-55-3B-A9-4F
Switch 2, Port 5
B2-CD-13-5B-E4-65
Switch 1, Port 7
A1-44-D5-1F-AA-4C
Switch 1, Port 2
D4-47-C4-B6-9F
Switch 3, Port 2
E5-BB-47-21-D3-56
Switch 3, Port 6
Multi Switch:
Ethernet LAN
Switch 2
Switching Table Switch 2
Port Station
3
A1-44-D5-1F-AA-4C
3
B2-CD-13-5B-E4-65
5
C3-2D-55-3B-A9-4F
7
D4-47-55-C4-B6-9F
7
E5-BB-47-21-D3-56
Switching Table Switch 1
Port Station
2
A1-44-D5-1F-AA-4C
7
B2-CD-13-5B-E4-65
5
C3-2D-55-3B-A9-4F
5
D4-47-55-C4-B6-9F
5
E5-BB-47-21-D3-56
Switching Table Switch 3
PortStation
4 A1-44-D5-1F-AA-4C
4
B2-CD-13-5B-E4-65
4
C3-2D-55-3B-A9-4F
2
D4-47-55-C4-B6-9F
Switch 3
6
E5-BB-47-21-D3-56
Switch 1
C3-2D-55-3B-A9-4F
Switch 2, Port 5
B2-CD-13-5B-E4-65
Switch 1, Port 7
A1-44-D5-1F-AA-4C
Switch 1, Port 2
D4-47-C4-B6-9F
Switch 3, Port 2
E5-BB-47-21-D3-56
Switch 3, Port 6
Ethernet Switch Operation
Ethernet
Switch
Switch Sends Frame Out One Port;
If A Is Transmitting to C,
Frame Only Goes Out
C’s Port.
A
B
C
D
Hierarchical Ethernet LAN
Single
Possible Path
Between
Client PC 1
and Server Y
Ethernet
Switch A
Ethernet
Switch C
Ethernet
Switch B
Ethernet
Switch D
Ethernet
Switch F
Ethernet
Switch E
Server X
Client PC1
Server Y
Ethernet Switch Operation
Only one possible path between stations
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Therefore only one entry per MAC address in
switching table
The switch can find the one address quickly, with
little effort
This makes Ethernet switches inexpensive per
frame handled
Port Station
Low cost has led
2 A1-44-D5-1F-AA-4C
to Ethernet’s
7 B2-CD-13-5B-E4-65
5 E5-BB-47-21-D3-56
LAN dominance
Hierarchical Ethernet LAN
Core and
Workgroup
Switches
Core Ethernet
Switch A
Core Ethernet
Switch B
Workgroup
Ethernet
Switch D
Core
Core Ethernet
Switch C
Workgroup Ethernet
Switch F
Workgroup
Ethernet
Switch E
Hierarchical Ethernet LAN
Workgroup switches connect to stations via access
lines
Core switches higher in the hierarchy connect
switches to other switches via trunk lines
The core is the collection of all core switches
Core switches need more capacity than workgroup
switches because they have to handle the traffic of
many conversations instead of just a few
Single Point of Failure in
Switch Hierarchy
Switch Fails
No Communication
Switch 1
C3-2D-55-3B-A9-4F
B2-CD-13-5B-E4-65
A1-44-D5-1F-AA-4C
Switch 2
No Communication
Switch 3
D4-47-55-C4-B6-9F
E5-BB-47-21-D3-56
802.1D Spanning Tree Protocol
Normal Operation
Loop, but
Spanning Tree Protocol
Deactivates One Link
Switch 2
Activated
Switch 1
Activated
Deactivated
C3-2D-55-3B-A9-4F
B2-CD-13-5B-E4-65
A1-44-D5-1F-AA-4C
Switch 3
D4-47-55-C4-B6-9F
E5-BB-47-21-D3-56
802.1D Spanning Tree Protocol
Switch 2 Fails
Deactivated
Switch 2
Deactivated
Reactivated
Switch 1
C3-2D-55-3B-A9-4F
B2-CD-13-5B-E4-65
A1-44-D5-1F-AA-4C
Switch 3
D4-47-55-C4-B6-9F
E5-BB-47-21-D3-56
Virtual LAN (VLAN) in Ethernet
Switch
Servers Sometimes
Broadcast; Goes
To All Stations;
Latency Results
Server
Broadcast
Client C
Client B
Client A
Server D
Server E
Virtual LAN (VLAN) in Ethernet
Switch
With VLANs,
Broadcasts Only Go
To a Server’s VLAN
Clients; Less
Latency
Server
Broadcast
No
No
Client C
on VLAN1
Client A
on VLAN1
Client B
on VLAN2
Server D
on VLAN2
Server E
on VLAN1
Tagged Ethernet Frame (802.1Q)
Basic 802.3 MAC Frame
Tagged 802.3 MAC Frame
Data Field (variable)
Tag Control Information
(2 Octets) Priority Level (0-7)
(3 bits); VLAN ID (12 bits)
1 other bit
PAD (If Needed)
Length (2 Octets)
Frame Check Sequence
(4 Octets)
Data Field (variable)
With VLAN’s switches do not use their
normal switching tables but they use
special VLAN Tables which associate
VLAN ID numbers with one or more
ports. Switches from different vendors
can build their VLAN tables using
standard VLAN ID numbers
PAD (If Needed)
Frame Check Sequence
(4 Octets)
Over-Provisioning
Congestion and Latency
Traffic
Network Capacity
Momentary Traffic Peak:
Congestion and Latency
Time
Over-Provisioning and Priority
for Traffic Handling
Traffic
Overprovisioned Network Capacity
Momentary Peak:
No Congestion
Time
Priority in Ethernet
Priority in Ethernet
Traffic
Network Capacity
Momentary
Peak
High-Priority Traffic Goes
Low-Priority Waits
Time
Switch Purchasing
Considerations
Number and Speeds of Ports
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Decide on the number of ports needed and the speed of
each
Often can by a pre-built switch with the right
configuration
Modular switches can be configured with appropriate
port modules before or after purchase
Switch Purchasing
Considerations
Switching Matrix Throughput
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Aggregate throughput: total speed of switching matrix
Nonblocking capacity: switching matrix sufficient even if
there is maximum input on all ports
Less than nonblocking capacity is workable
For core switches, at least 80%
For workgroup switches, at least 20%
Switch Purchasing
Considerations
100 Mbps
100 Mbps
100 Mbps
100 Mbps
1
2
3
4
100Base-TX
Input
Input Ports Queue(s)
400 Mbps
Aggregate
Capacity
to Be
Nonblocking
1
2
3
Port 1
to
Port 3
4
Any-to-Any
Switching
Matrix
100Base-TX
Output Ports
Switch Purchasing
Considerations
Store-and-Forward Versus Cut-Through Switching
(Figure 4-18)
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Store-and-forward Ethernet switches read whole frame
before passing it on
Cut-through Ethernet switches read only some fields
before passing it on
Perspective: Cut-through switches have less latency, but
this is rarely important
Store and Forward Cut-through
Preamble
Start-of-Frame Delimiter
Cut-Through Based
On MAC Destination
Address (14 Octets)
Destination Address
Source Address
Store-andForward
Processing
Ends Here
(Often
Hundreds
Of Bytes)
Tag Fields if Present
Length
Data (and Perhaps PAD)
Cyclical Redundancy Check
Cut-Through for
Priority or VLANs
(24 Octets)
Jitter
Jitter
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Variability in latency from cell to cell. Makes
voice sound jittery (Figure 4-19)
High Jitter (High Variability in Latency)
Low Jitter (Low Variability in Latency)
Switch Purchasing Decisions
Manageability
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Manager controls many managed switches (Figure
4-20: Managed Switches)
Polling to collect data and problem diagnosis
Fixing switches remotely by changing their
configurations
Providing network administrator with summary
performance data
Managed Switches
Get Data
Data Requested
Managed Switch
Manager
Command
to Change
Configuration
Managed Switch
Managed Switches
Manageability
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Managed switches are substantially more
expensive than unmanageable switches
To purchase and even more to operate
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However, in large networks, the savings in labor
costs and rapid response are worth it
Physical and Electrical Features
Form Factor
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Switches fit into standard 19 inch (48
cm) wide equipment racks
Sometimes, racks are built into
enclosed equipment cabinets
Switch heights usually are multiples
of 1U (1.75 inches or 4.4 cm)
19 inches
(48 cm)
Physical and Electrical Features
Port Flexibility
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Fixed-port switches
No flexibility: number of ports is fixed
1U or 2U tall
Most workgroup switches are fixed-port switches
Physical and Electrical Features
Port Flexibility
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Stackable Switches
Fixed number of ports
1U or 2U tall
High-speed interconnect bus connects stacked switches
Ports can be added in as few as 12
Physical and Electrical Features
Port Flexibility

Modular Switches
1U or 2U tall
Contain one or a few modules
Each module contains 1 to 4 ports
Physical and Electrical Features
Port Flexibility

Chassis switches
Several U tall
Contain several expansion
slots
Each expansion board
contains 6 to 12 slots
Most core switches are
chassis switches
Switch Interconnection
UTP Uplink Ports
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Normal Ethernet RJ-45 switch ports transmit on
Pins 3 and 6 and listen on Pins 1 and 2 (NICs do
the reverse)
If you connect two normal ports on different
switches, they will not be able to communicate
Most switches have an uplink port, which
transmits on Pins 1 and 2. You can connect a UTP
uplink port on one switch to any normal port on
a parent switch
References:
Napier, A., Judd, P.,
Rivers, O., and Adams, A.,
(2003)
E-Business Technologies
Thomson Course Technologies
ISBN: 0-619-06319-x
Panko, R (2005)
Business Data Networks and Communications, 5th
edition, Prentice Hall
ISBN: 0-13-127315-9
Schneider
E-Business, Eighth Edition
ISBN-13: 978-0-324-78807-5
Hogan, F., (2005)
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