Chapter 15:
LAN Systems
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High-Speed LANs
Why?
Extraordinary growth in speed, power, and storage
capacity of PCs
Increasing use of LANs as computing platforms
Examples
Server farms
Workgroups with “power” requirements
High-speed backbones
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Traditional Ethernet
Ethernet and CSMA/CD (IEEE 802.3)
Carrier sense multiple access with collision detection
Four step procedure
If medium is idle, transmit
If medium is busy, listen until idle and then transmit
If collision is detected, cease transmitting
After a collision, wait a random amount of time before
retransmitting
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802.3 Medium Notation
Notation format:
<data rate in Mbps><signaling method><maximum
segment length in hundreds of meters>
e.g 10Base5 provides 10Mbps baseband, up to 500
meters
T and F are used in place of segment length for
twisted pair and fiber
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802.3 10BaseX Media Options
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Fast Ethernet (100Mbps)
Easy to integrate with existing systems
Can use UTP (-TX) or fiber (-FX)
Uses star-wired topology, using a central multiport
repeater (broadcast method)
If NICs support full-duplex mode, switched hub
must be used
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802.3 100Base-T Options
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802.3 100BaseX Media Options
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Gigabit Ethernet
Still under development
Retains CSMA/CD protocol and Ethernet format,
ensuring smooth upgrade path
Uses optical fiber over short distances
1-gbps switching hub provides backbone
connectivity
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Gigabit Ethernet Media Options
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Example 100-Mbps Ethernet
Backbone Strategy
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Token Ring LANs (802.5):
Medium Access Control
Token “seized” by changing a bit on the circulating
frame to indicate start of frame rather than token
Default configuration requires sender to complete
transmission and begin receiving transmitted frame
before releasing the token
“Early token release” allows release of token after
transmission but before receipt of frame
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802.5 Transmission Media
Original specified shielded twisted pair with data
rates of 4 and 16mbps
New addition to standard allows use of UTP for
4mbps
Utilizes differential Manchester encoding
1997 update to IEEE 802.5 introduced dedicated
token ring (DTR).
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Fibre Channel
combine the best features of channel and protocolbased technologies
the simplicity and speed of channel communications
the flexibility and inter-connectivity that characterize
protocol-based network communications.
more like a traditional circuit-switched or packetswitched network, in contrast to the typical sharedmedium LAN
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Fibre Channel Goals
 Full-duplex links with two fibers
per link
 Performance from 100 Mbps to
800 Mbps on a single link (200
Mbps to1600 Mbps per link)
 Support for distances up to 10
km
 Small connectors
 High-capacity utilization with
distance insensitivity
 Greater connectivity than
existing multidrop channels
 Broad availability (i.e., standard
components)
 Support for multiple
cost/performance levels, from
small systems to supercomputers
 Ability to carry multiple existing
interface command sets for
existing channel and network
protocols
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Fibre Channel Elements
Nodes
The end systems
Includes one or more N_ ports for interconnection
Fabric
Collection of switching elements s between systems
Each element includes multiple F_ ports
Responsible for buffering and for routing frames between
source and destination nodes
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Fibre Channel
Protocol Architecture
 FC-0 Physical Media: Includes optical fiber, coaxial cable,
and shielded twisted pair, based on distance requirements
 FC-1 Transmission Protocol: Defines the signal encoding
scheme
 FC-2 Framing Protocol: Defines topologies, frame format,
flow/error control, and grouping of frames
 FC-3 Common Services: Includes multicasting
 FC-4 Mapping: Defines the mapping of various channel and
network protocols to Fibre Channel
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Wireless LANS
 LAN extension
 Wireless network connected to a main wire-based network
 Cross-building interconnect
 Point-to-point link between networks in separate buildings
 Nomadic access
 Wireless link between a LAN hub and a mobile data terminal
 Ad hoc networks
 a peer-to-peer network (no centralized server) set up temporarily to
meet some immediate need.
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Wireless LAN Requirements
 Throughput
 Number of nodes:
 Connection to backbone
LAN
 Service area
 Battery power consumption
 Transmission robustness
and security
 Co-located network
operation
 License-free operation
 Handoff/roaming
 Dynamic configuration
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IEEE 802.11 Standards
Association/Re-Association/Disassociation
Authentication
Privacy
Physical Media
 Infrared at 1 or 2 Mbps at a wavelength of 850-950 nm
 Direct-sequence spread spectrum in the 2.4-GHz ISM band
 Frequency-hopping spread spectrum in the 2.4-GHz ISM band, at
data rates of 1 and 2 Mbps.
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