Chapter 15:
LAN Systems
Business Data Communications,
4e
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
2
High-Speed LANs
3
Traditional Ethernet
Ethernet and CSMA/CD (IEEE 802.3)
Carrier sense multiple access with collision
detection
Carrier Sense
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
See P. 405
Collision Detection
Back-Off
(Binary Exponential Back-Off Algorithm)
4
IEEE 802.3 Frame Format
Preamble: 10101010…
SFD: Start of Frame Delimiter (10101011)
DA: Destination Address
MAC Address
SA: Source Address
(Physical Address)
FCS: Frame Check Sequence (32-bit CRC)
5
MAC Address Format
24 bits
24 bits
Vendor
Interface
Example:
00-E0-18-2C-B9-DE
00:E0:18:2C:B9:DE
Broadcast Address: FF-FF-FF-FF-FF-FF
Vendor Code:
http://www.cavebear.com/CaveBear/Ethernet/
6
802.3 Medium Notation
10Base-T
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
7
802.3 10BaseX Media Options
8
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
9
802.3 100Base-T Options
X : Two
10
802.3 100BaseX Media Options
11
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
12
Gigabit Ethernet Media Options
13
Example 100-Mbps Ethernet
Backbone Strategy
14
Example Gigabit Ethernet Backbone
Strategy
15
Token Ring LANs (802.5):
Medium Access Control
Based on the use of a small frame, called a
token, that circulated when all stations are idle.
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
16
17
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).
18
Fibre Channel
combine the best features of channel and
protocol-based 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
packet-switched network, in contrast to
the typical shared-medium LAN
19
Fibre Channel Network
20
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
21
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
22
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
23
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.
24
Single-Cell Wireless LAN Configuration
CM: Control Module (Access Point)
25
Multiple-Cell Wireless LAN Configuration
26
Infrastructure Wireless LAN
Ad Hoc LAN
27
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
28
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 (DSSS)
Frequency-hopping spread spectrum in the 2.4-GHz
ISM band, at data rates of 1 and 2 Mbps. (FHSS)
29
Wireless LAN Standards
http://www.networkmagazine.com/article/NMG20020206S0006/2
30
Discrete Sequence Spread Spectrum
31
Frequency-Hopping Spread Spectrum
32
ISM Band
ISM stands for Instrumentation, Scientific,
and Medical.
An unlicensed publicly owned part of the
radio spectrum in the 900MHz, 2.4GHz
and 5GHz ranges.
33
Hidden Terminal
A
B
C
※ C cannot hear from A.
 Collision at B cannot be detected by A and C.
34
IEEE 802.11 MAC - CSMA/CA
Carrier Sense Multiple Access / Collision
Avoidance
Listen before talk. If the medium is busy, the
transmitter backs off for a random period.
Send a short message: Ready to send (RTS),
including dest. address and duration of transmission.
Destination sends: Clear to send (CTS)
Send data.
Receive acknowledgement.
35
4-Way Handshake
36
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http://www.seattlewireless.net/