LANs No. 1 Seattle Pacific University Small Local Area Networks: Single Collision-Domain Networks...
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Transcript of LANs No. 1 Seattle Pacific University Small Local Area Networks: Single Collision-Domain Networks...
LANs No. 1Seattle Pacific University
Small Local Area Networks:Single Collision-Domain Networks
Kevin BoldingElectrical Engineering
Seattle Pacific University
LANs No. 2Seattle Pacific University
Local Area Networks• General Definition(s) of a LAN
• Small (<100 stations, single building)
• Trusted users
• Single ownership
• Fast
• Single Collision Domain networks
• All devices connected to the network share the network at the same time
• Only one device may send data on the network at a time
• Data is sent to all receivers; no routing occurs
LANs No. 3Seattle Pacific University
Network Topologies
• Network topology
• Describes the physical layout of a network
• How are the computers and devices connected?
• Basic shape of design
• Bus (line)
• Ring
• Star
LANs No. 4Seattle Pacific University
Bus Topology
• One cable connects all components
• Cable may be straight or “snake” through the building
• Individual devices are connected on branches of the backbone
12 37 13 09
To: 37 Data:xxxx
• Each message is sent to all computers
• Only the addressed computer responds to the message
XX
LANs No. 5Seattle Pacific University
10Base-2 Bus LANs• Most Bus LANs are connected
using 10Base-2 Coaxial Cable
• 10Mbps, baseband transmission, 200m max
• 50, RG-58 A/U
• BNC-type connections
• Use a ‘T’ to make a spur to connect a workstation
• Terminators
• All cable ends must be terminated (50) to prevent reflections
LANs No. 6Seattle Pacific University
Bus Issues
• There’s only one cable system
• Any breaks will isolate part of the network• It’s even worse!
• Unplugging a single workstation creates an un-terminated end in the network• Communication in the whole network is stopped
• Like trying to talk in an echo chamber
• The Bus is a passive system
• Signals are simply sent through the wires
• No active components refresh the signals
• Repeaters can be used if necessary
LANs No. 7Seattle Pacific University
Bus Pros and Cons
• Simple
• “Plug and play”
• Many single-point failure modes
• Broken backbone
• Any unplugged computer that isn’t terminated
Advantages Disadvantages
• Cheap
• Mostly all cables
• Cables are relatively inexpensive
• Linear arrangement
• Just run your backbone in a path that goes near the workstations
• Difficult to trace errors
• All one big “wire”
• Problem could be anywhere
• Limits on cable length seriously constrain size
• Repeaters needed
LANs No. 8Seattle Pacific University
Star (Hub) topologies
• A Hub is a multi-port repeater
• Reads input from any one of its ports
• Repeats it to all other ports
• Systems built around a hub usually have a star topology
• Usually use 10Base-T or 100Base-T
• 10/100Mbps, Baseband, UTP
• RJ-45 Connectors
HP ProCurve Compact 10Base-T Hub 8
Standard Ports
Crossover Port
• Logically, the same as a bus
• Medium is still shared by all stations at all times
LANs No. 9Seattle Pacific University
Star (Hub) Pros and Cons
• Termination is no longer an issue
• An un-terminated line only effects communication to one device
• Can’t bring the network down by unplugging your network connection
• Single-point failure
• If the hub goes down, all is lost
Advantages Disadvantages
• Expansion is easier
• Active hubs reduce loading limitations
• Easier troubleshooting
• Isolated connections
• More cable needed
• All cables must reach from workstations to the hub
LANs No. 10Seattle Pacific University
Star-Star Multi-Hub LANs
• Connect multiple stars (hubs) together in a bus or star
• Isolates individual groups from each other
• Hierarchical• Logically, still one single shared medium
Star-Star
A Star-Star hub network is logically the same as a bus network
LANs No. 11Seattle Pacific University
Connecting Hubs
HP ProCurve Compact 10Base-T Hub 8
Crossover Port
RxTx
TxRxHub NIC
RxTx
TxRxHub Hub
TxRx
• Connection from hub-to-hub requires a crossover port or crossover cable
LANs No. 12Seattle Pacific University
Ethernet Physical Media and Signals• Most widely-accepted Ethernet standards use the same medium
and connectors
• 4-pair UTP – Cat 5e is the most common today
• RJ-45 connectors
• Cable length of up to 100m
LANs No. 13Seattle Pacific University
Ethernet – 10BaseT
• 10BaseT
0 1 0 1 1 1 0 1 0 0 0 1
• Uses Manchester coding at 10Msps to send 10Mbps
• Uses only 2 of the 4 pairs – one for each direction
LANs No. 14Seattle Pacific University
Ethernet – 100BaseTX
• 100BaseTX
0 1 0 1 1 1 0 1 0 0 0 1 0 1
• For error correction, uses a 4B/5B code – sends 5 bits to represent 4 actual bits (80% efficient)
• Uses MLT-3 3-level coding (similar to AMI) at 125M symbols/s
• 125M symbols/s x 4/5 bits/symbol = 100Mbps
• Uses only 2 of the 4 pairs – one for each direction
LANs No. 15Seattle Pacific University
Ethernet – 1000BaseT• 1000BaseT
00 01 11 10 11 10 00 01 00 11 00 10 00 11
000111
1011
• Each UTP pair uses a 5-level coding (2-bits per symbol) at 125M symbols/s to send 250Mbps• Warning – this reduces the tolerable SNR by 6dB, which increases the error rate
• Uses all four pairs at the same time – 4 x 250Mbps = 1Gbps in one direction
• Uses simultaneous bi-directional signaling (echo cancellation) to send signals at the same time in both directions on the wire – 1Gbps in both directions
• Uses a complex coding scheme (Trellis coding) to decrease the error rate. This is equivalent to adding back 6dB to the SNR
LANs No. 16Seattle Pacific University
Ethernet – 10GBaseT• 10GBaseT
• 10Gbps over twisted pair
• 55m over Cat-6 UTP
• 100m over Cat-6a UTP
• 16-level encoding (4 bits/symbol) * 800M symbols/s = 3.2 Gb/s per pair
• Encoding loses a few bits 2.5 Gb/s per pair
• 4 pairs, simultaneous bi-directional 10Gb/s in both directions
• Fiber – Several standards using single- or multi-mode fiber
• Up to 80 km!