Topic 7: LANs & Backbone
Networks
- Chapter 15: LAN Systems
Business Data Communications,
4e
Ethernet Standards
Ethernet
Cable
Features
10Base-2
10Base-5
10Base-T
100Base-T4
100Base-TX
100Base-FX
RG-58 coax (thin)
RG-8 coax (thick)
Cat 3 UTP
Cat 3 UTP x 4
Cat 5 UTP/STP
Fiber optic
185m, 10Mbps
500m, 10Mbps
100m, 10Mbps
100m, 100Mbps
100m, 100Mbps
100m, 100Mbps
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Types of Ethernet
 10BASE-T (10 Mbps)

Uses a twisted-pair cable with maximum distance of 100 meters
 100BASE-T (100Mbps)

Based on 10Base-T standard, 10 times faster, uses cat-5 UIP/STP
cable. NIC is downward compatible to 10Base-T
 Gigabit Ethernet
 Three new types of Ethernet. They can use Ethernet traditional
half-duplex approach, but most are configured to use fullduplex. Also they can run over fiber-optic cables.



1000Base-T Ethernet, sometimes is called 1 GbE.
10 GbE
40 GbE
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802.3 10BaseX Media Options
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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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100Base-T Ethernet (IEEE
802.13)
 It gives a 100 Mbps data rate using the standard
Ethernet bus topology, data link packets and
CSMA/CD media access protocol.
 Three versions of 100Base-X differing only at the
physical layer:



100BaseTX uses cat 5 UTP
100BaseFX uses fiber optic cable
100BaseT4 uses 4 sets of cat 3 UTP (inverse
multiplexed)
 100Base-T Ethernet can co-exist with 10Base-T
Ethernet.
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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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100Base-T Ethernet
(IEEE 802.13)
Virtually identical to 10Base-T (IEEE 802.3). It gives
a 100 Mbps data rate using the standard Ethernet
bus topology, data link packets and CSMA/CD
media access protocol.
Three versions of 100Base-X differing only at the
physical layer:



100BaseTX uses cat 5 UTP
100BaseFX uses fiber optic cable
100BaseT4 uses 4 sets of cat 3 UTP (inverse
multiplexed)
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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
 May not be good for LAN (explain why) and
has been used in backbone networks for
point-to-point connections.
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Gigabit Ethernet
 1000BASE-LX: Long-wavelength, supports up
to 550m (m-mode fiber) or 5km (single-mode
fiber)
 1000BASE-SX: Short-wavelength, supports up
to 275 - 550 m(m-mode fiber)
 1000BASE-CX: uses copper jumpers in a
single room or equipment rack
 1000BASE-T: uses 4 pairs of Cat-5 UTP
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Gigabit Ethernet Media
Options
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Example 100-Mbps Ethernet
Backbone Strategy
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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
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Fiber Channel Network
N_port
F_port
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Fibre Channel Elements
 Nodes


The end systems
Includes one or more N_ ports for interconnection
 Fabric



Collection of switching elements 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 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
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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Fibre Channel - Maximum
Distance
800Mbps
400Mbps
200Mbps
100Mbps
10,000m
10,000m
10,000m
10,000m
M-mode
500m
1,000m
2,000m
Coaxial
Cable
50m
71m
100m
100m
STP
28m
46m
57m
80m
Single
Mode
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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 LANs (IEEE802.11)
 Wireless LANs are growing very rapidly. Wireless
LANs transmit data through the air (space) rather
than through wire or cable.
 New terms:


WLAN (Wireless LAN)
LAW (Local Area Wireless Network)
 IEEE 802.11 standard is likely to be the dominant
standard for wireless LAN
 It is easy to connect wireless LANs to Ethernet. So, it
is usually called wireless Ethernet
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Wireless LANs (IEEE802.11)
 Topology. The same as traditional Ethernet. It is both
a physical star and a logical bus.

A central wireless access point (AP) is a radio transceiver
that plays the role of hub. The maximum range is 100-500
feet depending on interference
 Wireless LANs use CSMA/CA (Carrier Sense Media
Access with Collision Avoidance) similar to CSMA/CD
by Ethernet. Two methods are simultaneously used:


Physical carrier sense method. Packets are sent using stopand-wait ARQ. Receiver waits less time to send ACK than
other computers waiting for available time slots.
Virtual carrier sense method. Using AP hidden node problem
must be solved. It is optional.
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Hidden Node Problem
 When one computer transmits packets, a computer in another
side of AP may not detect the signal and send packets as well.
This causes collision at AP.
 So, AP is the only device that is able to communicate with both
computers. To solve the problem, AP uses controlled access
method instead of the contention based method. A computer
wanting to send packets must send a request (RTS) to AP. If no
other computer is using the circuit, AP will respond with a clear
to transmit (CTS) specifying the amount of time for the circuit
reserved for the computer.
 All other computers hear the CTS and remain silent for the
specified time period.
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Types of Wireless Ethernet
 IEEE 802.11b. Two basic forms:


Direct-sequence spread-spectrum (DSSS)
Frequency-hopping spread-spectrum (FHSS)
 IEEE 802.11a. Expected to run at 5 GHz. Not completely defined
yet.
 Other type of wireless LANs:

Infrared wireless LAN. Less flexible because most require direct line
of sight between transmitters and receivers.
 The primary advantage: the reduction of wiring.
 The primary disadvantage: the low speed (1-4 Mbps).

Bluetooth. Provide seamless networking of devices in a very small
area (up to 30 feet)
 Small, cheap
 Called Piconet with no more than 8 devices
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IEEE 802.11b
 Two basic forms:


Direct-sequence spread-spectrum (DSSS), in 2.4 GHz band.
Transmits signals through a wide spectrum of radio
frequencies simultaneously. The signal is divided into many
different parts and sent on different frequencies. 1, 2, 5.5,
11 Mbps speeds. 20 Mbps version is in the way out.
Frequency-hopping spread-spectrum (FHSS). Uses the same
band, but once each frequency in turn. Sender and received
synchronize in a frequency. So, minimizes jamming an
eavesdropping. 1 Mbps and 2 Mbps.
 They are shared media implementation. As the
number of devices increases the speed will be
reduced.
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Infrared Wireless LANs
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Fiber Distributed Data
Interface (FDDI)
Fiber Distributed Data Interface (FDDI) is a set
of standards originally designed in the late
1980s, but has since made its way into
backbone networks.
FDDI is a token-passing ring network that
operates at 100 Mbps over two-counterrotating fiber optic cable rings.
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Topology
The FDDI standard assumes a maximum of 1000
stations and a 200-kilometers (120 miles) path that
requires a repeater every 2-kilometers. The second
ring is for backup.
Single attachment stations (SAS) and dual-attachment
stations (DAS) are both computer that can connect to
one or both of the rings, respectively.
If the cable in the FDDI ring is broken, the ring can still
operate in a limited fashion.
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Topology
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Topology
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Media Access Control
The FDDI-MAC scheme uses a variation of the IEEE
802.5 token-passing standard.
 Messages and the token are sent in different frames separately in a
FDDI LAN. A computer can send data only when it captures the token.
 When a computer on an FDDI network waiting for transmission
receives the token, it holds the token and then transmits all messages
that were attached to it. The computer then transmits whatever
messages its wants before transmitting the token.
 When receiver receives the data frame it simply copy the data frame
leaving it to be absorbed by the sender.
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Backbone Network
Architecture
LAN
LAN
LAN
LAN
LAN
LAN
Core Layer
Distribution
Layer
Access Layer
Figure 7-5 Backbone network design layers (FD)
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*Backbone Network
Architectures
 Routed backbone – using routers


Advantage – clearly segment each part of the network
Disadvantage – Delay, and more management
 Bridged backbone – using bridges, not popular any more


Advantages – cheaper, simpler
Disadvantages – difficulties in management
 Collapsed backbone –using switches, is most commonly used.



Advantages - Better performance, Fewer network devices are used
Disadvantages – switch problem may fail whole network, more
cabling work
Two types
 Rack-based collapsed backbone
 Chassis-based collapsed backbone
 Virtual LAN (VLAN)
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Client
Computer
Client
Computer
10/100 Ethernet
Client
Computer
Layer-2
Switch
Client
Computer
Client
Computer
Router
to WAN
1GbE
on fiber
1000Base-T
Client
Computer
10/100 Ethernet
Router
to Internet
Layer-3
Switch
Client
Computer
1GbE
on fiber
1GbE
on fiber
Client
Computer
10/100 Ethernet
Client
Computer
Layer-2
Switch
Client
Computer
Client
Computer
Server
Server
1000Base-T
Client
Computer
Server
Server
Figure 7-11 Central Parking’s collapsed backbone (FD)
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*Virtual LAN (VLAN)
 A new type of LAN backbone network
architecture by intelligent high-speed
switches. VLAN is configured using software
not hardware.


Single-switch VLAN – VLAN inside a switch
Multiswitch VLAN – VLAN using several switches.
 VLAN is normally faster than traditional LANs,
and provide better opportunity to manage
data flows
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Client
Computer
VLAN switch
VLAN switch
Client
Computer
VLAN switch
10/100 Ethernet
Client
Computer
VLAN switch
Client
Computer
VLAN switch
Client
Computer
1GbE
on fiber
1000Base-T
Client
Computer
VLAN switch
1GbE
on fiber
VLAN switch
VLAN switch
VLAN switch
1GbE
on fiber
VLAN switch
VLAN switch
VLAN switch
1GbE
on fiber
VLAN switch
VLAN switch
VLAN switch
VLAN switch
VLAN switch
Figure 7-14 IONA VLAN network (FD)
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How is a packet transmitted
through the Internet?
 An IP address tells the destination
 Transmission is done one hop after another actually
at data link layer
 This is just like you bought a flight ticket from
Lubbock to New York. The ticket package indicates
New York is your destination (IP address). However,
you may have three coupons for three flights that
connect your route via two more cities between:
Dallas and Chicago. Each coupon indicates your
arriving airport (destination data link layer address),
e.g. DFW, CHI and JFK.
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A TCP/IP Example
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How TCP/IP Works
 How a client access a web server in the
same subnet with a known address?
 How a client access a web server in a
different subnet with a known address?
 How a client access a web server in the
same subnet with an unknown address?
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*NetBIOS vs. NetBEUI
 NetBIOS has 18 commands for PC
connections.
 NetBEUI adds 8 more and is used as a
transport protocol. It is faster and more
efficient than NetBIOS
 When NetBEUI is in use, NETBIOS becomes
API that invokes NetBeui.
 They can support a LAN with less than 200
PCs.
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*Windows Network Model
Windows Network Model
Internet Model
Application layer:
I/O
Named Pipes Mail Server
Environment Subsystem
FTP, TELNET,
HTTP, etc.
Transport layer:
TCP, UDP
Network layer: IP
Data link layer
Physical layer
Layer 7
Layer 6
Provider Interface
NetBIOS (Redirector)
TDI
NetBEUI
WINSOCK
Layer 5
Layer 4
TCP/IP
Layer 3
NDIS 3.0
NDIS Environment
and Drivers
Layer 2
Layer 1
802.2 802.3 802.4 802.5
NDIS:
Driver Interface Specification
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*NDIS
 NDIS (Network Driver Interface
Specification) is a Windows specification
for how communication protocol
programs (such as TCP/IP) and network
device drivers should communicate with
each other.
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*NetBIOS
NetBIOS (Network Basic Input/Output
System)
 Created by IBM for its early PC Network, was adopted
by Microsoft, and has since become a de facto industry
standard.
 A program that allows applications on different
computers to communicate within a local area network
(LAN).
 Used in Ethernet, token ring, and Windows NT
networks.
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*NetBEUI
NetBEUI (NetBIOS Extended User
Interface)
 Developed by IBM for its LAN Manager product and
has been adopted by Microsoft for its Windows NT,
LAN Manager, and Windows for Workgroups
products.
 A new, extended version of NetBIOS, the program
that lets computers communicate within a local area
network.
 Formalizes the frame format (or arrangement of
information in a data transmission) that was not
specified as part of NetBIOS.
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*NetBIOS over TCP/IP
 NetBIOS over TCP/IP runs over the TCP/IP, so that you
can share drives and printers over the Internet.
 In the "Network" configuration window in Windows 95,
there is no option for NetBIOS over TCP/IP, but a
"NetBEUI" entry, with which Microsoft actually means
NetBIOS over NetBEUI.
 With the installation of TCP/IP protocol, Windows
automatically installs the "NetBIOS over TCP/IP”.
 If you do want the TCP/IP protocol, but not "NetBIOS
over TCP/IP" (because of security problem), you should
uncheck "Files and Printer Sharing" in the Bindings tab
of the TCP/IP entry in Network Configuration.
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Data transmission using
TCP/IP and Ethernet
Ethernet
packet header
IP
packet
TCP
packet
HTTP
packet
User Data
Ethernet
packet trailer
IP address
Data link layer address
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