LAN (IEEE 802.x) Ethernet - UTK-EECS

ECE453 – Introduction to
Computer Networks
Lecture 8 – Multiple Access Control (II)
1
LAN (IEEE 802.x)
Network Layer
IEEE 802.2 (logical link control sublayer)
IEEE 802.3 (Ethernet) 802.11 (wireless LAN)
IEEE 802.15 (Bluetooth) 802.16 (wireless MAN)
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Ethernet
“dominant” LAN technology
cheap $20 for 100Mbs!
first wildly used LAN technology
Simpler, cheaper than token LANs and ATM
Kept up with speed race: 10, 100, 1000 Mbps
Metcalfe’s Ethernet
sketch
Read Sec 4.3.10
Retrospective on Ethernet
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1
Ethernet
Ethernet Cabling
Ethernet framing and Manchester
Encoding
The Ethernet MAC Sublayer Protocol
„
„
CSMA/CD
Binary Exponential Backoff
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Ethernet Cabling
5
Ethernet Cabling
Transmission
Speed is 10Mbps
Baseband
transmission
Fiber
Twisted pair
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2
Ethernet Cabling – Wiring a Building
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Ethernet Frame Structure
Preamble:
„
„
7 bytes with pattern 10101010 followed by one
byte with pattern 10101011
used to synchronize receiver, sender clock rates
Type: upper layer protocol
Data
„
„
maximum length 1500 bytes
Minimum length 64 bytes (from dest. to CRC)
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Ethernet MAC Sublayer Protocol
Collision detection can take as long as 2τ .
9
3
Manchester Encoding
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Ethernet’s CSMA/CD – Binary
Exponential Backoff
Goal: adapt retransmission attempts
„
heavy load: random wait will be longer
first collision: choose K from {0,1}; delay is K
x 512 bit transmission times
after second collision: choose K from
{0,1,2,3}…
after ten or more collisions, choose K from
{0,1,2,3,4,…,1023}
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10Base2 Ethernet
Bus topology
How to connect a dozen PCs
in your office using 10Base2
Ethernet?
Without a repeater,
the maximum length
of a 10Base2 bus is
185 meters, the
maximum number of
nodes is 30.
Repeater can be used
to connect 10Base2
segments in a linear
fashion. Up to 4
repeaters can be
included in a 10Base2
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Ethernet
4
10/100BaseT Ethernet
The maximum length of
the connection between
an adapter and the hub
is 100 meters.
Star topology
Two pairs of
twisted-pair
copper wire
Hub has network
management features
Both 10/100BaseT
Ethernet technologies
can employ fiber links.
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The 802.11 Protocol Stack
Direct sequence spread spectrum
Transmits at 2.4GHz
Orthogonal frequency-division multiplexing
Transmits at 5GHz-6GHz
Data rate 54Mbps
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The 802.11 MAC Sublayer
Protocol
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5
The Exposed Station Problem
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The 802.11 MAC Sublayer
Protocol – CSMA/CA
DCF mode (distributed coordination function
„
„
RTS, CTS, NAV
MACAW
PCF mode (point coordination function)
„
Polling frame (beacon frame)
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Data Link Layer Switching
Hub
Repeater
Bridge
Switch
Router
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6
Hub
Repeaters with some network management
functionality
All of the LAN segment belong to the same collision
domain
The use of backbone hub
„
„
„
„
„
„
Provides interdepartmental communication
Extends the maximum distance between any pair of nodes
A degree of graceful degradation
One large common collision domain
Cannot interconnect various departments using different
Ethernet technologies
Restrictions on the maximum allowable number of hosts
connected
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Bridges
Examines the layer-2 destination address of the frame and
attempts to forward the frame on the interface that leads to the
destination
Each LAN segment is an isolated collision domain
Can interconnect different LAN technologies
No limit to how large a LAN can be
Bridge forwarding and filtering Address
Interface
Time
„
„
Bridge table
Runs CSMA/CD
DD-DD-DD-DD-DD-DD
EE-DE-DE-DD-DD-DD
1
2
9:32
9:45
Self-learning
„
„
Plug and play device
Example
Spanning tree
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Bridges vs. Routers
Typically, small networks consisting of a few
hundred hosts having a few LAN segments
use bridges.
Large networks consisting of thousands of
hosts typically include routers
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7
Interconnecting without a Backbone
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Switches vs. Bridges
More interfaces (dozens of
vs. 2/4)
No need for mediumaccess protocol
„
Two pairs of twisted-pair
cooper wire
Cut-through switching vs.
store-and-forward
switching
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A Comparison
Traffic isolation
Plug and play
Optimal routing
Cut-through
hubs
no
yes
no
yes
bridges
yes
yes
no
no
routers
yes
no
yes
no
switches
yes
yes
no
yes
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