1. Ethernet LAN 1 1

2. LANs Local Area Networks Limited Geographical Area
Single office
Single building
University campus or industrial park
Generally, high speeds
Now, most operate at around 10 Mbps
100 Mbps is emerging as the new “base speed”
Most Data Traffic is Local 2 2

3. Standards Setting LANs are Subnets (single networks)
Subnet technology is Dominated by OSI Standards (true for LANs)
IEEE Creates most LAN Standards
Institute for Electrical and Electronic Engineers
Submits its standards to ISO and ITU-T for ratification
IEEE 802 Committee
LAN standards are set by the IEEE 802 Standards Committee.
802.3 for Ethernet Standards
802.5 for Token-Ring LAN Standards
for Radio and Infrared Wireless LANs 3 3

4. LANs and OSI Architecture
OSI is a 7-layer architecture
LAN transmission only uses Layers 1 and 2
Layer 1: Physical Layer
Connectors, Media, Electrical signaling
Layer 2: Data Link Layer
Packaging data into frames
Managing transmission over link (error handling, etc.)
Access control: when each station may transmit 4

5. OSI Physical and Data Link Layers
Physical Layer (OSI Layer 1)
Physical (plugs, media, etc.); Electrical (voltages, timing, etc.)
Electrical Signal
Station A
Station B
Transmission Medium
(telephone wire, etc.)
Connector
Plug
Connector
Plug
F4-1 5 5

6. OSI Physical and Data Link Layers
Data Link Layer (OSI Layer 2)
Frame 2
Frame 1
Station A
Station B 6 6

7. Data Link Layer For point-to-point transmission
A point-to-point connection is a data link
So is a transmission system shared by multiple devices, only one of which can transmit at a time because of collisions
Transmission 7

8. Data Link Layer First function: Packaging of Data (1s and 0s)
PDU at Data Link Layer is called a frame
Second Function: Access Control
Only one station can transmit at any time
If another transmitted, their signals would scramble one another
Must control access to (transmission into) the transmission medium 8

9. Logical Link Control Layer Media Access Control (MAC) Layer
Data Link Layer
Logical Link Control Layer
OSI
Data Link
Layer
(Layer 2)
Media Access Control (MAC) Layer
OSI
Physical
Layer
(Layer 1)
802.3
10Base-T
802.3
10Base-5
802.3
Other
Physical
Layer
802.5
Physical
Layer
4 Mbps
802.5
Physical
Layer
16 Mbps
Other
Physical
Layer
OSI Data Link Layer is subdivided into two layers
Media access control
Logical link control 9 9

10. Media Access Control (MAC) Layer
OSI
Physical
(Layer 1)
802.3
10Base-T
802.3
10Base-5
802.3
Other
Physical
Layer
802.5
Physical
Layer
4 Mbps
802.5
Physical
Layer
16 Mbps
Other
Physical
Layer
MAC layer implements media access control:
When a station may transmit
Controls the framing of data along the wire 10 10

11. Logical Link Control Layer
LLC
802.2 Logical Link Control Layer
802.3 Media Access Control
(MAC Layer)
802.5
MAC
4 Mbps
802.5
MAC
16 Mbps
Other
MAC
OSI
Physical
(Layer 1)
802.3
10Base-T
802.3
10Base-5
802.3
Other
Physical
Layer
802.5
Physical
Layer
4 Mbps
802.5
Physical
Layer
16 Mbps
Other
Physical
Layer
Provides Control Function
Begin/end connections between stations
Error correction (optional) 11 11

12. Simple LAN Using Ethernet 10Base-T
RJ-45 jacks
10Base-T Hub (Multiport Repeater)
10Base-T
UTP Wiring
Bundles:
4 Pairs
EIA
Category
3, 4, or 5
Unshielded Twisted Pair (UTP) Wiring
(4-Pair Bundle) PC
Network
Interface
Card
RJ-45
Jack
NIC 12 14 12

13. NICs Network Interface Cards Implement Physical Layer
Plug and Electrical Signaling
Implements the Data Link Layer (data packaging, access control, etc.)
LLC (802.2)
MAC (802.3 MAC) 13

14. Wiring Unshielded Twisted Pair (UTP) Categories of UTP Wiring
Twisted several times per foot to reduce interference, T in 10Base- and Unshielded
No protection except for plastic coating
Distance limitation: 100 meters (attenuation, distortion, noise and interference, crosstalk) -- propagation
Categories of UTP Wiring
Category 5, 6: The best. Good for 100 Mbps
Category 3 and 4: lower. May be OK for 100 Mbps
Wiring Plugs: RJ-45 Standard
Similar to home (RJ-11) jacks, but wider 14

15. Layering in 802 Networks Internet Layer TCP/IP Internet
Layer Standards
(IP, ARP, etc.)
Other Internet
Layer Standards
(IPX, etc.)
Data
Link
Layer
Logical
Link
Control
Layer
802.2
Media
Access
Control
Layer
Ethernet MAC Layer
Standard
Non-Ethernet
MAC Standards
(802.5,
802.11, etc.)
<Read the box near the top.>
Physical Layer
100BASE- TX
1000
BASE- SX …
Non-Ethernet
Physical
Layer
Standards
(802.11, etc.) 15 15

16. Ethernet Physical Layer Standards
UTP Physical
Layer
Standards
Speed
Maximum
Run
Length
Medium
Required
10BASE-T
10 Mbps
100 meters
4-pair Category 3 or higher
100BASE-TX
100 Mbps
100 meters
4-pair Category 5 or higher
1000BASE-T
(Gigabit
Ethernet)
1,000 Mbps
100 meters
4-pair Category 5 or higher
Let’s look first at Ethernet physical layer standards.
We will begin with standards that use 4-pair UTP copper wiring.
-T in the names indicates twisted-pair wire.
<Go through the rows.>
100BASE-TX dominates access links today,
Although 1000BASE-T is growing in access links today
[Note the TX in 100BASE-TX. The Working Group actually created two 100 Mbps UTP standards. Only 100BASE-TX was produced and used.]
100BASE-TX dominates access links today,
Although 1000BASE-T is growing in access links today 16 16

17. Ethernet Physical Layer Standards
Fiber Physical
Layer
Standards
Speed
Maximum
Run
Length
Medium
850 nm light (inexpensive)
Multimode fiber
1000BASE-SX
1 Gbps
220 m
62.5
microns
160
MHz-km
1000BASE-SX
1 Gbps
275 m
62.5
200
1000BASE-SX
1 Gbps
500 m 50
400
At 1 Gbps and higher speeds, Ethernet offers the option of using optical fiber.
1000BASE-SX dominates switch-to-switch trunk lines for gigabit Ethernet.
Ethernet normally uses 850 nm light. This is short wavelength, so the standard is called 1000BASE-SX.
Note that maximum distance depends on both core diameter (50 or 62.5 microns) and modal bandwidth.
1000BASE-SX
1 Gbps
550 m 50
500
The 1000BASE-SX optical fiber standard dominates trunk links today S means that the standard uses short wavelength light (850 nm) 17 . 17

18. Shared media LANs Limits to Shared Media LANs
FDDI, 100Base-X, 1000Base-SX are all shared media LANs
Only one station can transmit at a time, causing latency
Every station hears every message, so as the number of stations grow, the LAN saturates
100, 1000 Mbps speed only delays saturation 18 21

19. Switched LANs In a switched network
Incoming frame arrives on a single port
Frame sent out again only on a single port--the one leading to the receiver
No congestion on other ports
Switch 19 21

20. Switch
With a switch, multiple stations may transmit simultaneously: no congestion as traffic grows.
Switch
Station C
Station A
Connection 1
A-C
Connection 1
A-C
Station D
Station B
Connection 2
B-D
Connection 2
B-D 20 22

21. Switch connections
paths called connections must be pre-defined between stations
a fixed logical data link (logical connection) is established between stations before transmission even begins
during the transmission, all traffic between the stations must pass over that data link
unless a data link has been pre-established, two stations may not communicate at all
only OSI Layer 2 (Data Link Layer) protocols are needed 21

22. Hierarchical Ethernet LAN
In Ethernet, hosts connect to workgroup switches.
Core switches connect switches together.
The group of all core switches is called the network’s core.
Ethernet switches MUST be organized in a hierarchy.
If you create a loop, bad things happen.
<Trace the single path between Client PC1 and Server X.>
<Trace the single possible path between Client PC1 and Server Y.>
Ethernet switches must be arranged in a hierarchical topology
In a hierarchical LAN, there is only one possible path between any hosts 22 22

23. Routed LAN with Ethernet Subnets
<Read the text box.>
[Even the largest LANs can be completely switched.
However, if routers are used, this gives the network manager better control over transmission because routers are very sophisticated.]
When a routed LAN links multiple Ethernet switched networks, individual switched networks are called subnets 23 23