Transcript A Small PC Network

A Small PC
Network
Small Peer-Peer PC Network
• No dedicated (fulltime) server
• User PCs supply
services to each
other
• So user PCs act
both as clients and
as servers
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Small Peer-Peer PC Network
• File Sharing
– Each PC can make
certain disk drives or
directories available to
to other user PCs
– Can allow others readonly or full access to
files there
• Printer Sharing
– Each PC can make
one or more
printers attached to
it available to
others
– Can require password
for access
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Small Peer-Peer PC Network
• Advantage
– No dedicated server
to purchase and
maintain
• Disadvantages
– If someone turns off
their PC or crashes
it, people using its
files or printer are cut
out
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Small Peer-Peer PC Network
• Disadvantages
• Overall
– Users often set up
security poorly giving
access to
unauthorized people
– Beyond about 2-5
users, problems
become too
pronounced
– Special problem if
home network is
connected to the
Internet
– Beyond about 10
users, very bad
idea
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Elements of a Simple PC
Network
with a DedicatedClient
Server
PC
Hub or Switch
Wiring
Server
Server
Client PC
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Elements of a Small PC
Network
• LAN Standards
– We will focus on LANs that follow the
Ethernet standard (80% do)
• Small Ethernet PC networks use only
inexpensive UTP wiring
• Speeds for NICs and Hubs or Switches
– 10Base-T (10 Mbps, baseband, UTP)
– 100Base-TX (100 Mbps, baseband, UTP)
– 1000Base-T (Gigabit Ethernet) (1 Gbps)
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Elements of a Small PC
Network
• Need a hub or switch to connect the PCs
– Connector box with multiple plug-in jacks
– Hubs and switches are described later
• Each PC needs a network interface card
(NIC)
– Implements physical and
data link layer connection
to the LAN
• Wire
– Business-grade UTP telephone wiring
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Elements of a Simple PC
Network
• Ethernet UTP Wiring
– 4-pair bundle (8 wires)
– Each pair is twisted
– Terminates in RJ-45
connector
• Quality Level
– Category 5
– Older categories (3 and 4) exist but are now fairly
rare
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Elements of a Simple PC
Network
• Ethernet UTP Wiring
– Come pre-cut in many useful lengths (1 m,
2 m, 25 m, etc.) with connectors already
added to both ends
– Can also cut to precise lengths needed
and then attach connectors
• Must test the wire after cutting it and attaching
connectors!
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Elements of a Simple PC
Network
• Plenum Wiring
– For wiring run through airways; covering
does not give off toxic fumes if it burns
• Required if wires are run through air
conditioning ducts
• Not needed in false ceilings
– More expensive but required by law and
concern for employee safety
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Elements of a Small PC
Network
• Ethernet Hub Operation
– One station transmits a single bit to a hub (physical layer operation)
– Hub broadcasts bit to all attached stations
– All but the destination PC should ignore the message
– Broadcasting is simple, so
– Hubs are inexpensive
Hub
Hub
Bit
Bit
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Elements of a Small PC
Network
• Ethernet Hubs Can Create Latency
– Only one station may transmit at a time or the signals
will collide and be unreadable
– Other stations must wait (latency)
– Becomes a problem with 100+ PCs and 10 Mbps hub
– 200 PCs is upper limit for tolerable service with a 10
Mbps hub
Must Wait
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Elements of a Small PC
Network
• Ethernet Switches
– One station transmits a frame to a switch (data link layer
operation)
– Switch only transmits frame out port of destination PC
– No broadcasting out all ports
Switch
– Multiple conversations can take place
simultaneously because there is no broadcasting,
which ties up all ports
Switch
– No wait to transmit; no Latency
Frame
Frame
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Elements of a Simple PC
Network
• Client PCs
– End user’s desktop or notebook PC
– Add network interface card (NIC)
– With Win95, Win98, Win NT, or Win 2000,
no extra software is needed
– Networks have many client PCs
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Elements of a Simple PC
Network
• Servers
– Provide services to client PCs
– Usually PCs themselves
– Most PC nets have multiple servers
– Require a NIC
– Require a server operating
system (SOS)
– Require application software
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Elements of a Simple PC
Network
• Server Operating System (SOS)
– Servers need operating systems more reliable
than client PC operating systems
– Windows NT/2000 Server, Novell NetWare, UNIX,
LINUX
• Application Software
– Provides the services offered by the servers
– E-mail, word processing, file sharing, etc.
– More expensive than the SOS
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Elements of a Simple PC
Network
• Novell NetWare SOS
– Once dominant, but market share has
shrunk
– Excellent file and print service
– Excellent directory service (later)
– Until recently, was not sufficiently robust
and scalable for servers other than file
servers
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Elements of a Small PC
Network
• Microsoft Windows Server Operating System
– More robust than desktop Windows (Win 95, Win
98, etc.)
– All 32-bit code
– Microsoft Windows NT Server before 2000
– Newer Microsoft Windows 2000 Server
• Versions in order of increasing functionality: Windows
2000 Server, Advanced Server, DataCenter Server
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Elements of a Small PC
Network
• Microsoft Windows Server Operating System
– Easy to install, learn, and use because resembles
desktop Windows
– Becoming dominant for small business and small
department servers
– NT Server has had serious reliability and
scalability problems
– Windows 2000 Server versions promise to
improve reliability and scalability
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Elements of a Small PC
Network
• UNIX
– Workstation servers run UNIX
– Extremely reliable
– Dominate for large enterprise servers
– Expensive to buy
– Must retrain staff or hire UNIX staff
– Many versions of UNIX exist
• Most run the same application software
• However, have different management utilities, etc., requiring
training for each version used
– Not for Small PC Networks
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Elements of a Small PC
Network
• LINUX
– Version of UNIX
– Runs on PCs for low cost
– Available free
• But usually pay around $50 for packaged version
– Reliable like other UNIX versions
– Open Source: Many people are developing tools to add to
the LINUX core
– Requires Extensive Labor to Set Up, Maintain
– Device driver software often is lacking for printers, disk
drives, and other devices
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Elements of a Small PC
Network
• LINUX
– Available in Distributions
• A distribution has the LINUX kernel plus other programs
• Available on CD-ROM or by downloading
• Distributions from different LINUX vendors differ in the
specific programs included
• Differences make selection, implementation difficult
– Requires more training because it is UNIX
– Better distributions and support coming?
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Servers
• Options
– Put all services on one server, or
– One server per service, or
– In-Between solutions
• Option: Put All Services on One Server
– Cheapest for small organizations
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Option: One Service
• Option: Hybrid with
Application per Server Some Servers Offering
– Can optimize hardware for
One Service, Others
application
Offering Several
– More reliable, because a
crashing service does not
crash others
– Security: users cannot log
into one service, switch to
another easily
– Distribute services in
ways that make sense
for the services,
organization size, etc.
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Servers
• Cost (Which is Cheapest?)
– Difficult to know
– For small organization, most or all services on one
usually is cheapest
– For larger organizations, optimization through multiple
servers often minimizes costs
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Server Application Software
• File Service Allows File Sharing
– File server stores program and data files
– Can be accessed by any user with access rights
– Built into most SOSs
Access Rights
File
Server
No Access Rights
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Server Application Software
• File Service
– For sharing application program files also
– No need to install applications on each PC
• Greatly reduces installation labor
File
Server
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Server Application Software
• File Server Program Access
– Program is STORED on the file server
– But program is EXECUTED on the client PC
– Limited by power of client PCs, which do not get very
large
File Server
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Server Application Software
• Typical Application Software
– Word processing, e-mail, etc.
– Must buy multiuser versions, not just a single
copy from a retail store
– License will limit the number of users
– Will cost more than the SOS
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Server Application Software
• Print Service
–
–
–
–
Also built into SOSs
Print jobs go to shared printers
But they first go to the file server
Not directly to the print server!
Print Server
File Server
Client PC
Shared
Printer
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Server Application Software
• Print Service
– File server stores print job in a print queue until print server is
ready to print it
– File server sends the print job to the print server
– Print server feeds the print job to the printer
– Print servers are simple and inexpensive because the file server
does most of the work
– Low print server cost allows shared printers can be scattered
throughout the office
Print Server
File Server
Shared
Printer
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Server Application Software
• Print Server Location
RJ-45 Port
– Connects to printer via parallel port on the print
server; no special printer needed
– Has NIC to connect to the hub or switch
– Requires an RJ-45 port on the hub or switch
– Parallel cable distance limitation requires print
server to be within 1-2 meters of the printer
– UTP allows print server to be up to 100 meters
from the hub or switch
UTP (up to 100 m)
Parallel Cable
(1-2 m only)
Print Server
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Server Application Software
• Remote Access Service (RAS)
–
–
–
–
User dials into a remote access server
Server authenticates the user (user must prove identity)
If authenticated, user may use internal services
Client PC needs RAS software
RAS
Internal
Server
LAN
RAS
Client
Software
Dial-Up
Telephone
Line
Dial-In
Client
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Server Application Software
• Internet Access for a Simple PC LAN
– Serial Router
– Simple, inexpensive router
– One RJ-45 port for LAN, one suitable port
for ISP Connection
Access
Line
Serial Router
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Server Application Software
• Serial Routers
– May provide security to stop outside hackers
• Network address translation (NAT) hides addresses of
internal machines
• Only serial router’s IP address appears in outgoing
packets
• May provide a firewall to prevent unauthorized access
from Internet hackers
Serial Router
Access
Line
IP Packet with Serial
Router’s IP Address
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Server Application Software
• Directory Servers
– Problem: Most networks have many
servers
– To use a resource, must know the server
• To send e-mail, address is user@server
• Files must be accessed on particular servers
Directory
Server
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Server Application Software
• Directory Servers
– Directory server knows all resources on all
servers
– Can send mail to user (without @server)
– Can search for a specific file across
servers
– Know user access rights on all servers
– Single login to directory server
– Get access to all other servers where user
has access rights
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File Server Systems
Administration
• Set Up Access Rights for Each
Directory, File
– The ability to even see a directory or file
(otherwise, it will be invisible)
– The ability to get a read-only copy of a file in a
directory (a copy that cannot be edited and then
saved under the same name)
– The ability to create, edit, and delete files and
subdirectories
– The ability to assign access rights in a directory to
other users
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File Server Systems
Administration
• Set Up Access Rights for Each Directory, File
– Must be done for each individual in each directory!
– Usually, however, assign individual to groups
– Give access rights to groups
– Members of groups then get those rights
– Using groups greatly simplifies the assignment of
access rights
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File Server Systems
Administration
• Automatic Inheritance of Access Rights
– Assign rights to individual or group in a directory
– Rights automatically inherited in lower directories
– Simplifies rights assignment
Inherits Browse
And Read Rights
Assigned Browse
And Read Rights
Application
Word Processing
Inherits Browse
And Read Rights
Database
Oracle
QuickDB
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File Server Systems
Administration
• Blocking of Inheritance
– If assign rights explicitly in subdirectory, inheritance is
blocked
– Only assigned rights are effective
Assigned Browse
And Read Rights
Word Processing
Assigned Browse
And Execute Rights
Inherit Browse
And Read Rights
Application
Database
QuickDB
Oracle
(Browse and Execute Only)
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File Server Systems
Administration
• The Assignment of Rights: Recap
– Rights can be assigned to individuals or group
• Group members receive all rights assigned to the group
– Rights are automatically inherited in lower-level
directories, unless
– Rights are explicitly assigned in a directory, in
which case automatic inheritance is blocked and
only explicitly assigned rights are in effect in that
directory
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File Server Systems
Administration
• Omnibus Rights
– Administrator normally has omnibus rights
– Can read, delete, etc. any file in any directory
– Serious security concern
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