A Small PC Network

A Small PC Network

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Small Peer-Peer PC Network

• No dedicated (full-time) server

• User PCs supply services to each other

• So user PCs act both as clients and as servers

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• File Sharing

– Each PC can make certain disk drives or directories available to to other user PCs

– Can allow others read-only or full access to files there

– Can require password for access

• Printer Sharing

– Each PC can make one or more printers attached to it available to others

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• 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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• Disadvantages

– Users often set up security poorly giving access to unauthorized people

– Special problem if home network is connected to the Internet

• Overall

– Beyond about 2-5 users, problems become too pronounced

– Beyond about 10 users, very bad idea

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Elements of a Simple PC Network

with a Dedicated ServerHub or Switch

Server

Client PC

Client PC

Server

Wiring

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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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• 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 connectionto the LAN

• Wire– Business-grade UTP telephone wiring

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• 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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• 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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• 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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• 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

HubHub

Bit

Bit

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• 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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• 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

– Multiple conversations can take place simultaneously because there is no broadcasting, which ties up all ports

– No wait to transmit; no LatencySwitch

Switch

Frame Frame

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• 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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• 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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• 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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• 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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• 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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• 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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• 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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• 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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• 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 Application per Server– Can optimize hardware for

application– More reliable, because a

crashing service does not crash others

– Security: users cannot log into one service, switch to another easily

• Option: Hybrid with Some Servers Offering One Service, Others Offering Several– 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

FileServer

Access Rights

No Access Rights

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• File Service– For sharing application program files also– No need to install applications on each PC

• Greatly reduces installation labor

FileServer

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• 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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• 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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• 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!

File Server

Print Server

SharedPrinterClient PC

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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

File Server

Print Server

SharedPrinter

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Server Application Software• Print Server Location

– 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

Print Server

Parallel Cable(1-2 m only)

UTP (up to 100 m)

RJ-45 Port

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• 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

LAN

InternalServer

RAS

Dial-InClient

Dial-UpTelephone

Line

RASClient

Software

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• Internet Access for a Simple PC LAN– Serial Router– Simple, inexpensive router– One RJ-45 port for LAN, one suitable port

for ISP Connection

Serial Router

AccessLine

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• 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 AccessLine

IP Packet with SerialRouter’s IP Address

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• 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

DirectoryServer

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• 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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• 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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• Automatic Inheritance of Access Rights– Assign rights to individual or group in a directory

– Rights automatically inherited in lower directories

– Simplifies rights assignment

Application

Word Processing Database

Oracle QuickDB

Assigned BrowseAnd Read Rights

Inherits BrowseAnd Read Rights

Inherits BrowseAnd Read Rights

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• Blocking of Inheritance– If assign rights explicitly in subdirectory, inheritance is

blocked

– Only assigned rights are effective

Application

Word Processing Database

Oracle(Browse and Execute Only)

QuickDB

Assigned BrowseAnd Read Rights

Inherit BrowseAnd Read Rights

Assigned BrowseAnd Execute Rights

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• 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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• Omnibus Rights

– Administrator normally has omnibus rights

– Can read, delete, etc. any file in any directory

– Serious security concern

Date post:	06-Jan-2016
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A Small PC Network

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