Transcript Local Area Networks

Local Area Networks
LAN Overview roadmap
• Why a LAN?
• How does a computer attach to a LAN?
• What’s the difference between switch and
a hub?
• How is a host configured?
• What’s an OS and a NOS?
• Network Computing Models: Mainframe,
File Server, Client/Server, Peer to Peer.
Why a Local Area Network?
• Aggregate users of common resources
• Share access to:
– Internet
– file, database, application or compute servers
– printers
• Share Resources - Share Costs - Save
Money
• Share information - Save Time and
Increase Productivity
Why a Local Area Network?
Workstation
Shared 10Mbps
Dedicated 100 Mbps
Multimedia
Workstation
Ethernet
Hub
Ethernet
Switch
Server
Dedicated 100 Mbps
Router
Internet or
Corporate Intranet
Printer
Local Area Networks
“Just as computer networks have grown
across continents and oceans to
interconnect major computing facilities
around the world, they are now growing
down corridors and between buildings to
interconnect minicomputers in offices and
labs.”
Robert M. Metcalfe, Xerox, 1976
How does a computer attach to a
LAN? Server
Large disk stores
files and databases,
Fast processor computes
on demand
Wire
Cat 5 UTP
Personal
Computer
Accesses LAN
resources
Wiring Hub
Serves as center of network,
contains multiple independent
but connected modules where
network equipment can be connected
Network Interface Card (NIC)
Amplifies electronic signals,
packages data for transmission, and
controls access to the network cable
Networking Operating
Software/System (NOS)
Coordinates access to LAN,
provides software interface
for PC applications
How does a computer attach to a
LAN?
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Computer with appropriate interface bus.
NIC (Network Interface Card)
NOS (Network Operating System)
Cable (normally Cat 5 UTP for 10BaseT)
Ethernet Hub or Switch
Server or peer
Your LAN connected computer
• Computer needs appropriate bus for NIC
• for example, if it’s a PC:
– ISA (Industry Standard Architecture) is passe
– PCI (Intel’s Peripheral Component Interconnect) is
modern
– PC-Card (used to be called PCMCIA) for laptops.
– Parallel printer port ( for old laptops).
– Serial port (generally for external modem)
– USB (Universal Serial Bus) is newest approach
The Network Interface Card (NIC)
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NIC are the I/O device for NOS
Also known as LAN adapters
NICs Amplifies electronic signals
Packages data for transmission
Physically connects computer to
transmission media (cable)
• Associated with the NIC is a
unique address called the MAC
(Media Access Control) address
• OSI Layers 1 and 2
Network Connector Port
PC or Workstation
loaded with
OS and NOS
Network Interface
Card (NIC)
The Network Interface Card
• Today, NIC generally means Ethernet NIC
– Could be 10BaseT, 100BaseT if more modern, 10 or
100BaseF if fiber, or 1000BaseT - GigE
• may do speed/duplex autonegotiation
– 10/100 Mbps, Full/Half Duplex
• may offload some upper layer protocol
processing from CPU
– checksumming and CRC (Cyclic Redundancy Check)
calculation
– automatic decision to accept (in promiscous or sniffing
mode) or reject (normally) packets not addressed for this
workstation
– multicast address recognition
The Wire
• Today, generally Category 5 UTP (Unshielded Twisted Pair)
– 4 pairs of copper wire, twisted and bundled to tight
specification
– properly installed, provides 100-350 Mhz signalling
bandwidth.
– Ethernet and Fast (100 Mbps) Ethernet use two of four
pairs.
• Cat 5 Ethernet uses “RJ-45” connectors
• In older installations, could also be Cat 3, 10Base2 (“thinnet”) or even 10Base5 (“thicknet”)
• In newer installations: Cat 5e, Cat 6, or even Category 7.
Ethernet hub or switch
• Switch is a multi-port bridge
– provides dedicated bandwidth to each port
– may provide VLANS, multicast services
• Hub
– fine for small LANs (under about 6 people)
– shared bandwidth
• Hubs normally require no configuration
• Sophisticated switches need administration
Hub
Hub: Device that serves as the center
of a star-topology network, sometimes
referred to as a multiport electrical
repeater, or in Ethernet, a wire
concentrator; not intelligent
Hubs: A Single Bus
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Hub
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1 single Segment
1 single Segment
Hub Summary
• OSI physical Layer
• Amplifies signals
• Propagates signals through the network
– Must observe 4 repeater diameter limit
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No filtering
No path determination or switching
Used as network concentration point
Single physical Collision Domain
Bridge: The Switch’s Predecessor
• Bridge:
– Very simple device that connects and passes
packets between two or three network
segments
– Bridge is intelligent -- analyzes incoming
packets and forwards or drops based on MAC
Layer 2 addressing information.
– Two kinds of bridging methods primarily-• Transparent Bridging (Ethernet)
• Source-route Bridging (used in token-ring
environments)
Bridge Example
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BRIDGE
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Segment 1
Segment 2
Learning
0260.8c01.1111
E0:
E0:
E1:
E1:
Port Eth. 0
0260.8c01.2222
0260.8c01.1111
0260.8c01.2222
0260.8c01.3333
0260.8c01.4444
0260.8c01.4444
Port Eth.1
0260.8c01.3333
• Source MAC addresses are
associated with Ethernet ports
Bridge Learning
• The source MAC address of all frames received is
compared against the information in the forwarding
database.
• If the source MAC address is not found in the forwarding
database, it is added along with the port identifier it
received on.
• The age value of this database entry is reset to indicate
that this is a "fresh" entry
• If the MAC address was last seen on a different bridge
port, then the port identifier for the entry is changed to
the new port identifier, and the age value of this entry is
reset.
• If the frame is received on the same port as the port in
the database entry, then only the age value of this entry
is reset.
Forwarding
0260.8c01.1111
E0:
E0:
E1:
E1:
Port Eth. 0
0260.8c01.1111
0260.8c01.2222
0260.8c01.3333
0260.8c01.4444
0260.8c01.4444
Port Eth.1
0260.8c01.3333
0260.8c01.2222
• Traffic propagated to
specific destinations
Filtering, Dropping
0260.8c01.1111
E0:
E0:
E1:
E1:
Port Eth. 0
0260.8c01.1111
0260.8c01.2222
0260.8c01.3333
0260.8c01.4444
0260.8c01.4444
Port Eth.1
X
0260.8c01.3333
0260.8c01.2222
• Congestion control through
network knowledge
Spanning Tree Removes Loops
• Problem: a frame gets flooded
Segment 1
B
or forwarded in both
directions around a loop
Root
Segment 2
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B
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B
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B
10 Cost
10
10
Segment 3
B
10
Segment 4
- Denotes blocked port
• Solution: makes one of the
ports inactive until needed
for redundancy
• 1) elect root
• 2) cheapest “port to root”
for every bridge
• 3) cheapest bridge (designated)
for every segment
• 4) block more
expensive,unused port
Switch? Hub?
What’s the difference?
Hub Gives
Shared Bandwidth
Switch Gives
Dedicated Bandwidth
Switches
• Use bridging technology to forward traffic
between ports;
• Provides full dedicated data transmission
rate between two stations that are directly
connected to the switch ports
• Builds and maintains address tables called
content addressable memory (CAMs)
• CAMs match MAC addresses to make rapid
forwarding decisions
Switches are better than Bridges
10 Mbps
Coaxial Cable
“shared”
Workstation
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BRIDGE
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Segment 1
Segment 2
Switches are better than Bridges
Workstation
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10 Mbps
UTP Cable
“dedicated”
SWITCH
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N Segments
N Segments
Switch Advantages
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Packets switched over dedicated links
Users experience better performance
LAN switches permits users to transmit simultaneously.
Assigning users bandwidth based on need.
– Some users use 10 megabit ports and NICs
– Some users and servers get 100 megabit ports
• Full Duplex transmission possible
The Big Picture
Shared 10Mbps
Workstation
Dedicated 100 Mbps
Multimedia
Workstation
Ethernet
Hub
Ethernet
Switch
Server
Dedicated 100 Mbps
Router
Internet or
Corporate Intranet
Printer
Operating Systems and Network
Operating Systems
The Operating System ties
together all the computer’s
hardware
HW
HW
HW
HW
HW HW
OS
HW
HW
HW
HW
HW
HW
OS Definition
• The central control program on a computer that
manages all aspects of the computer's hardware
and controls the execution of software operations
• Collection of programs which provide the
computer with capabilities and functionality not
specifically supported in the computer's
hardware.
• Usually linked closely to a vendor-specific
computer architecture, called a platform.
Examples include DOS, OS/2, Apple Mac OS,
UNIX and Microsoft Windows 95/98 and Windows
NT.
The OS coordinates all this
Fax/
Modem
Mouse,
Keyboard
Driver Driver
OS
Driver
Monitor
Driver
NIC
Driver
Scanner
OS Features
• An OS:
– Makes devices available to applications via
software
– Allows users to interact with applications by
using these devices
• Examples of devices:
– Input: mouse, keyboard, tablets, scanners
– Output: printer, plotter, fax modem, phone line,
monitor, HD, Backup Tapes, video camera.
Network Operating System (NOS)
• If OS is the software
that manages the
resources
of the computer, then
• NOS is the software
that manages the
resources
of the network
• NOS models:
– Peer-to-peer model
– Server Based model
PCs, hub/Switch, printer
servers, routers
Server Based NOS
Peer
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Peer
Peer
MS Windows NT (TCP/IP mainly)
Novell’s Netware (IPX and TCP/IP)
Banyan Vines
IBM’s LAN Server
NOS Services
• File Service
• Messaging Service
• Data Base
Service
• Directory Service
• Print Service
• Communication
Service
• Usually, NOS services are provided by one or
more centralized servers
• Services often administered by the IS
department
O/S and NOS
• Modern Operating Systems have built in network
drivers (OSI compliant stacks)
• Network Operating Systems (NOS) support some
form of network-oriented client/server application:
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Novell Netware for PC’s (Client/Server)
Appletalk for Apple Macintoshes
NFS for UNIX systems
TCP/IP, NetBEUI, DLC, etc.. Systems under MS-OS
OS and NOS Examples - UNIX
• First OS with integrated networking, based on IP
• Unix services were inspiration for most other NOS
vendors
– NFS (Network File System) for file serving
– LPR (line printer) for printer sharing
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TCP/IP and UDP, etc. standard on all UNIX platforms
Examples of UNIX OS:
– LINUX, HP-UX, IBM AIX, DEC Ultrix, SunOS, Solaris,
SCO UNIX, BSD4.3, System5.4
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Supported NICs: Ethernet, Token-Ring, Fast
Ethernet, Gigabit-Ethernet, ATM
O/S and NOS Examples :
MS-DOS/Windows 95/98
• Most popular O/S for 32-bit Intel compatible PC’s
• Market share over 90%
• Initially without network capabilities
– Networking only possible with additional software:
Novell Netware, Microsoft LAN Manager
• Enhanced version Windows95/98, integrate
networking capabilities
– NetBEUI, TCP/IP, Novell IPX ODI Protocol, IBM DLC,
Microsoft DLC, Banyan VINES protocol, ATM Call Manager,
etc..
O/S and NOS Examples :
Windows NT (Now improved into Windows 2000)
• A 32-bit preemptive multitasking, multithreaded, multiprocessing
operating system
• Developed by Microsoft with the same w95/98 GUI
• Initially deployed on Intel PC architecture, then ported to Motorola
PowerPC, Digital Alpha AXP, and MIPS R4000 platforms
• Brings Windows closer to UNIX performance
• Two level approach: Windows NT Server 4.0 and Windows NT
Workstation
• Extended HTML/Java Services
• NOS: mainly TCP/IP based
• All Kind of NIC cards and protocols supported
LAN software and client
configuration
• Windows Networking, pre 2000, minimizes
configuration, but can’t be routed globally.
– Workstations learn about neighbors by
broadcasting identity
• TCP/IP networking must be explicitly
configured
– Allows global connectivity from PC Host
– Dynamic Host Configuration Protocol (DHCP)
solves configuration problem
• Windows 2000 seeks best of both worlds
Windows Networking
(before Windows 2000)
• Workstation can be locally administered
– Don’t need (or get) globally recognized name or number
(like an IP address).
– NetBIOS (used by Windows) is not a routable protocol
• Windows broadcasts your computer’s name so
others can locate it.
• If necessary, locates a Domain Controller to
authenticate username and password
• Uses WINS server (Windows Internet Name
Service) to resolve other workstation names
TCP/IP host configuration
• Need to configure computer with:
– IP address: 207.140.138.120
– Subnet size or “mask”: 255.255.255.0
– Default router IP address: 207.140.138.1
• use this gateway to access hosts outside this
subnet
– DNS (Domain Name Server) IP address
• can be located outside local subnet
– Domain name: lucent.com or sales.lucent.com
• for locating local machines, domain name is
added
• for example, vail.lucent.com could be called
“vail”
TCP/IP host configuration - DHCP
• Configuration is complicated, so DHCP
(Dynamic Host Configuration Protocol)
was invented
– Client broadcasts DHCP requests
– DHCP server responds with:
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Unique IP address for client to use
correct subnet mask
default router, DNS server, Domain name
Other services: WINS very common
– DHCP provides client with everything needed.
Windows 2000 Networking
• Uses TCP/IP, but with a twist
– Tries to maintain Windows “ease of use”
– DHCP to configure workstations
– Dynamic DNS to name workstations
• Active Directory powerful way to replicate
data between servers.
The path to Client/Server
Mainframe Architecture
File Sharing Architecture
Client Server Architecture
Mainframe architecture
• Not a client/server architecture.
• All intelligence is within the central host
computer
• Users interact with the host through a
terminal
• Terminals send keystrokes directly to the
host
• User interaction can be done using PCs and
UNIX workstations
• Older mainframe software architectures do
not easily support graphical user interfaces
(GUI)
File sharing architecture
• Not a client/server architecture
• The original PC networks were based on file sharing
architectures
• The server downloads files from the shared location
to the desktop environment
• The requested user job is then run (including logic
and data) in the desktop environment
• Limitations: works if shared usage is low, update
contention is low, and the volume of data to be
transferred is low.
• In the 1990s, PC LAN computing changed because the
capacity of the file sharing was strained as the
number of online users grew and graphical user
interfaces (GUIs) became popular
• PCs are now being used in client/server architectures
Client/Server architecture
• As a result of the limitations of file sharing
architectures, the client/server architecture
emerged
• Database server replaces the file server
• Using a relational database management system
(DBMS), user queries could be answered directly
• Reduces network traffic by providing a query
response rather than total file transfer
• Improves multi-user updating through a GUI front
end to a shared database
• Remote Procedure Calls (RPCs) or Structured
Query Language (SQL) statements are typically
used to communicate between the client and
server
Client/Server The future
• Two tier architectures
– good solution 10 to 100 people interacting on a LAN
simultaneously by maintaining a connection via "keepalive" messages with each client, even when no work is
being done
• Three tier architectures (multi-tier architecture)
– middle tier was added between the client and the database
management server environment. Good for large number of
users (in the thousands)
• Distributed/Collaborative Enterprise Architectures
– emerged in 1993 Based in Object Request Broker (ORB)
and Common Object Request Broker Architecture (CORBA)
– Based on Object Oriented data bases (C++, SmallTalk,
JAVA)
The Client/Server Basics
The Client
• Application sitting in a PC or workstation,
along with its associated software,
actually operated by an end user.
• Some important attributes of the client
include:
– the applications software installed on the
computer;
– the client's user interface, which provides a
method for interacting with the server (back
office).
– the computer's processor, memory, and
networking options.
The Server
• Back end Application (called daemon in Unix)
installed in a central PC, workstation,
minicomputer or large computing system
• Provides a central service to user stations on a
Local Area Network or across the WAN
• Typical examples of these centralized services
are:
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Data bases
File storage (file servers),
Printer sharing (print servers),
Centralized application software storage/processing
(application servers),
– and Wide Area Network access (communication
servers).
Compact Definition
• Client server is referring to a model which
divides applications in two parts:
– Client or front-end: the software process used
by the end-user
– Server or back-end: the software process
created by the actual application running in the
server
• On a machine you can find multiple clients
and multiple servers at the same time
An Example: Checking Bank
account
• Authentication process for security
• The client program in your computer forwards
your request to an intermediate server program at
the bank
• That program may in turn forward the request to
its own client program that sends a request to a
database server at another bank computer to
retrieve your account balance.
• The balance is returned back to the bank data
client, which in turn serves it back to the client in
your personal computer, which displays the
information for you.
Client/Server and Internet
• Web browser is a client program that
requests services (the sending of Web
pages or files) from a Web server (which
technically is called a Hypertext Transport
Protocol or HTTP server) in another
computer somewhere on the Internet.
• Your PC with TCP/IP installed allows you
to make client requests for files from File
Transfer Protocol (FTP) servers in other
computers on the Internet.
Drivers To adopt Client/Server
• TCO Model - Total Cost of Ownership is lower
• Central high performance is cheaper than
distributed performance.
– One fast printer is cheaper than 10 slow
– One large fast file server is cheaper than 100 medium
sized disks in PC’s
– One fast computer server is cheaper than 100
medium-fast PC’s or workstations (TCO)
SAP
Oracle
PeopleSoft Financial
Server Based Model
• All communications centers around the server
– Client-to-server
– Server-to-server
• Client is a user of services, Server is a provider
• Clients do not directly communicate with other
clients
• 85% of the marketplace
• Servers are a high-powered micro, mini or
mainframe computer
Server Based Pros and Cons
• Pros:
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Scalable
Ease of management and security
Single point of administration and maintenance
Easy to to provide fault-tolerant services
• Redundant power supply, mirrored servers, back-up
– Advanced services
• Cons:
– Difficult to install
– Requires staff expertise
Peer-to-Peer Model
• Allows communication between any two devices
in the LAN
• Good for small networks environment
• Pros:
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Flexible
Each workstation can provide services to other devices
Easy to install and run
Basic services: file sharing, printer sharing, e-mail
services
• Cons:
– Difficult to administer when network begins to grow
– Do not offer a central point of administration
Peer-to-Peer
Peer
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Peer
Peer
Apple Talk
Windows 95/98 using NetBEUI
Novell Personal Netware
Napster!
Napster is a big Peer-to-Peer
network
• Other Internet-wide file sharing services
are coming too
– Freenet, Gnutella, FileFury
• All of Internet becomes as easy to access
as the LAN.
• Directory Servers automate administration
• Capitalizes and insists on high speed
Internet and WAN connections.
• Servers on WAN seem as “local” as the
LAN.
The Future of Local Area Networks
• Today, LAN is gateway to Internet and WAN
• Wireless, IP telephony latest in a series of
important LAN drivers
• Ethernet (and soon wireless) only way to go
• Fast Ethernet and Gigabit Ethernet are easy
upgrade paths for older networks.
• Client/Server will continue to evolve
– Agents, Java, B2B, B2C.
• Web-based computing paradigm keeps older
networks, computers viable while driving new
application and software innovation.
Food for Thought
• What are the advantages or disadvantages
of a Web server/client architecture?
• What’s the difference between the
mainframe/terminal relationship, the
client/server relationship, and the web
server/web browser relationship?