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Networking Basics

2012-11-24T22:09:00.004-08:00

Networking Basics

Networking: An Overview:

A network is a group of interconnected systems which share services and interact with each other by means of a shared communication link.

These systems can be located anywhere.

Network is often classified according to its geographical size.

Benefits of networking:

Goal of having networking environment is to provide services and to reduce the equipment

costs. The primary reasons for networking PC's are as follows:

Sharing printers and other devices
Providing Distributed Computing.
Sharing Files
Centralized administration of resources
Security of Resources.
Personal communications (like e-mail, chat, audio/video conferencing)
World Wide Web ... and many other uses

Networking Basics:

Network consist many components:
– Hardware
» Transmission Facilities
»Access Devices
»Devices that repeat transmitted signals

– Software
»Protocol that define and regulate the way two or more device communicate.
»Drivers, that guide the functionality of Network Interface Card (NIC)
»Communication Software.

Networking Basics: Hardware:

Transmission Facilities
– Are the media used to transport network’s signals to their destination.
» Coaxial Cable, Twisted Pair, Fiber- Optic

Access Devices
– Is known as Network Interface Card (NIC), and is responsible for
» Properly formatting data so that it can be accepted in the network
» Placing data on the network
» Accepting transmitted data that’s addressed to it.

Repeaters/Hubs
– Accepts transmitted signals, amplify it and puts them back on the network

Network Basics : Software:

Protocol
– Are standards that allow computer to communicate.
– Define how computer identify one another on a network
– How information be processed once it reach its final destination.
– Define procedure for handling lost or damaged packets.

Device Drivers
– Is a hardware level program that control NIC
– NIC, provide an interface for its host’ operating system

Communication Software
– That enable the users to communicate and share resources
» Windows Explorer, WWW, Telnet, FTP

Multiaccess vs. Point-to-point:

Multiaccess means shared medium.
– many end-systems share the same physical communication resources (wire, frequency, ...)
– There must be some arbitration mechanism.
Point-to-point
– only 2 systems involved
– no doubt about where data came from !

LAN - Local Area Network:

Connects computers that are physically close together ( < 1 mile).
– high speed
– multi-access
Technologies:
– Ethernet 10 Mbps, 100Mbps
– Token Ring 16 Mbps
– FDDI 100 Mbps

WAN -Wide Area Network:

Connects computers that are physically far apart. “long-haul network”.
– Typically slower than a LAN.
– Typically less reliable than a LAN.
– Point-to-point
Technologies:– Telephone lines
– Satellite communications

MAN - Metropolitan Area Network:

Larger than a LAN and smaller than a WAN
- Example: campus-wide network
- Multi-access network

Technologies:
– Coaxial cable
– Microwave (Wireless Technology)

Internetwork:

Connection of 2 or more distinct (possibly dissimilar) networks.
Requires some kind of network device to facilitate the connection.

Network Models:

Using a formal model allows us to deal with various aspects of Networks abstractly.

We will look at a popular model (OSI reference model).

The OSI reference model is a layered model.

What is LOCAL Area Network ?

2011-11-19T02:24:00.000-08:00

Any device whose resources can be share and controlled

Which device can be connected :

1. Any device,which has a interface
2. Has a software to control its operation

What is interface ?
Serial, Parallel, Ethernet,ATM, Packet Switch , etc

Telnet, http,SNMP, SMPT etc are application to access / control the resources.

Network

LAN Topologies :

1. Bus : 10base2,10base5
2.Star : 10base-T,100bassTx,
3. Ring : FDDI, Token Ring,

Ethernet

1. Ethernet Overview
2. Definition : Ethernet is defined as protocol using Carrier Sense Multiple Access with Collision Detection (CSMA/CD). It supports data transmission rate of 10 Mb/s using Coaxial, Twisted pair or Fiber optic. Other versions of Ethernet is Fast Ethernet and Gigabit Ethernet , supporting 100 Mb/s and 1000Mb/s respectively. It comes in the 1st and 2nd Layer of OSI model.
3. History : It was first developed by Xerox in 1970 to connect Computers with Printers. Later in 1979 , DEC, Intel and Xerox joined hand for its standardization and formally released on 1982.

The 1st IEEE standard was released on 1983 as IEEE 802.3 . Later other improved version were
developed for different media .

.IEEE 802.3a is for Thin Ethernet or 10Base2 for cheaper coaxial cable.
.IEEE 802.3I or 10Base-T for twisted pair cable.
.IEEE 802.3d or 10Base –FL Fiber Optic cable.
.IEEE 802.3x or 1000Base-X for full duplex connection
.IEEE 802.3ab or 1000Base_T is the latest standard for 1Gb/s speed on UTP Cat5 cables.

Ethernet Standards:
. 10Base2/IEEE 802.3a: This supports data rate up to 10 Mb/s through thin coaxial cable for maximum distance of 185 m.
. 10Base5 : This is for Thick cable and supports up to 500 m .
. 10Base-T/IEEE802.3I :This supports data rate up to 10 Mb/s through UTP cable for maximum distance of 100 m.
•IEEE802.3u :This version is called Fast Ethernet and supports data rate up to 100 Mb/s through :
a) 100Base-TX on two pair UTP Cat 5 cable for maximum distance of 100 m,. b) 100Base-T4 on four pair UTP Cat 3 cable for maximum distance of 100 m,. c) 100Base-FX on one pair Multi-mode Fiber Optic Cable up to 2000m .
. 1000Base-X or IEEE 802.3z : This version is called Gigabit Ethernet and support three types of media as Single mode, Multi mode Fiber Optic cable and STP cable
. 1000Base-T or IEEE 802.3ad is for 1Gb/s over 4 pairs of UTP cables up to 100 m.

Ethernet Media Access Control

There are two type of topology in Ethernet one Bus and Star structure. The 10Base2 and 10Base5 are traditional Bus structure which operates only in half duplex transmission. 10Base –T and 100Base-tx are Star topology supports full as well as half duplex transmission.
1. Half Duplex
2. Full Duplex
3. VLAN
4. Multilink Trunking
5. Layer 3 Switch

Half Duplex Ethernet : TX or RX at a time with 10 MBPS data speed

Full Duplex Ethernet : TX and RX simultaneously with 10 MBPS effective speed 20MBPS

Full Duplex Fast Ethernet : TX and RX simultaneously with 100 MBPS effective speed 200MBPS

Multilink Trunking : Both the links works simultaneously with 200 MBPS effective speed 400MBPS

VLANs are technology which groups ports into VLANs into broadcast domains .This is a way to logically divide the switch. The packets, IP multicast, unicast frames can be forwarded to the ports of same VLAN.

1.5 Multilink Trunking
This technology allows to group many ports into one link together to increase the bandwidth and throughput between the devices.

Servers

Layer 3 Switch

LAN segment 2

LAN segment 4

Layer 3 Switch

LAN segment 2

LAN segment 4

1.5 Multilink Trunking
This technology allows to group many ports into one link together to increase the bandwidth and throughput between the devices.

Servers

Ethernet Physical Layer Specifications.
Brief summary of various physical layer specification defined in Ethernet is as follows.
2.1 10 Base-5
2.2 10 Base-2
2.3 10 Base-T
2.4 10 Base-FL
2.5 100 Base TX
2.6 100 Base FX
2.7 1000 Base X

2.1 10 Base-5
Transmission Rate:
10 Mb/s (full-duplex not supported)

Cable Type:
A single "thick" (10mm) coaxial cable with 50 ± 2 ohms impedance,
Supports bend radius of 2.54 cm (10 inches),
Eg. Belden part numbers 9880 (PVC) & 89880 (plenum rated)

Maximum Segment Length: 500 meters (1640 feet)
Maximum Transceiver Cable(AUI) Length: 50 meters (164 feet)
Maximum Number of Transceivers per Segment: 100
Connector Technology: N-type coaxial connectors, barrel connectors, & terminators
Signal Encoding: Manchester encoding

2.2 10Base2
10Base2 supports a 10 Mb/s transmission rate over "thin" (5mm) coaxial cable. Transmission Rate
10 Mb/s (full-duplex not supported)

Cable Type:
A single "thin" (5mm) coaxial cable with 50 ± 2 ohms impedance, G58A/U or RG58C/U, Supports bend radius of 5 cm (2 inches), Belden part numbers 9907 (PVC) & 89907 (plenum rated)
Maximum Segment Length: 185 meters (606.9 feet)
Minimum Spacing Between Stations: 0.5 meters
Maximum Number of Transceivers per Segment: 30
Connector Technology: BNC Tee coaxial connectors, barrel connectors, & terminators
Signal Encoding: Manchester encoding

2.3 10 Base-T
Transmission Rate:
10 Mb/s (20 Mb/s in optional full-duplex mode) Cable Type two pairs of Category 3 or better unshielded twisted pair (UTP) cabling,also known as voice grade or telephone twisted pair cabling,100-ohm impedance rating AMP, Lucent etc.
Maximum Segment Length:100 meters (328 feet)
Maximum Number of Transceivers per Segment: 2
Connector Technology: RJ-45 style modular jack ( 8-pins)
Signal Encoding: Manchester encoding

2.4 10Base-FL
10Base-FL ("fiber link") supports a 10 Mb/s transmission rate over two fiber optic cables. The 10Base-FL standard updates and expands the prior Fiber Optic Inter-Repeater Link (FOIRL) standard. 10Base-FL supports a maximum segment length of 2000 meters compared with 1000 meters supported by FOIRL.

10Base-FL may be used to connect two switch, two repeaters, or a computer and a repeater port. All 10Base¬FL segments are point-to-point with one transceiver on each end of the segment. The transceiver attaches to the two fiber optic cables through connectors that are commonly known as "ST". One fiber optic cable is used to transmit data, and the other is used to receive data.

The fiber optic cable typically used with 10Base-FL is multi-mode fiber (MMF) known as "62.5/125". The wavelength of light used with 10Base-FL is 850 nanometers. In addition to supporting longer segment lengths, fiber optic cables are immune to electrical hazards such as lightning strikes and ground currents that can occur when connecting separate buildings. Fiber is also immune to electrical noise that can be generated by motors or other electrical equipment.

Transmission Rate:
10 Mb/s (20 Mb/s in optional full-duplex modeCable Type two multi-mode fiber optic cables (MMF),
typically 62.5/125 fiber, (62.5 micron fiber core with 125 micron outer cladding) 850 nanometer light wavelength
Maximum Segment Length: 2000 meters (6561 feet)
Maximum Number of Transceivers per Segment: 2
Connector Technology: ST connector
Signal Encoding: Manchester encoding

2.5 100Base-TX
100Base-TX supports a 100 Mb/s transmission rate over two pairs twisted pair cabling. It uses one pair of wires for transmitting data, and the other pair for receiving data. The two pairs of wires are bundled into a single cable that may often include two additional pairs of wires. If present, the two additional pairs of wires must remain unused since 100Base-TX is not designed to tolerate the "cross talk" that can occur when the cable is shared with other signals. Each end of the cable is terminated with an 8 position RJ-45 connector, or "jack". It supports transmission over up to 100 meters of 100 ohm Category 5 unshielded twisted pair (UTP) cabling. 100Base-TX transmits data using the "4B/5B" signal encoding scheme .

The 100Base-TX standard supports the option of using 150 ohm shielded twisted pair (STP) cabling.

Transmission Rate:
100Mb/s (200 Mb/s in optional full-duplex mode) Cable Type two multi-mode optical fibers (MMF), typically 62.5/125 multi-mode fiber,1300 nanometer light wavelength
Maximum Segment Length: Half-Duplex: 412 meters (1351 feet)
Full-Duplex: 2000 meters (6561 feet)
Maximum Number of Transceivers per Segment: 2
Connector Technology:
duplex SC connector preferred, ST connector and FDDI MIC
connector also permitted
Signal Encoding: 4B/5B

2.6 100Base-FX
100Base-FX supports a 100 Mb/s transmission rate over two fiber optic cables. It allows maximum segment lengths of 412 meters for half-duplex links, and 2000 meters or more for full-duplex links. Even longer distances can be supported with the more expensive single mode fiber (SMF). 100Base-FX is essentially a "fiber" version of the 100Base-TX standard. The twisted pair cabling and connectors used in 100Base-TX components are replaced with fiber optic cabling and connectors in 100Base-FX components. Both standards use the same 4B/5B signal encoding scheme.
The fiber optic cable typically used with 100Base-FX is multi-mode fiber (MMF) known as "62.5/125". The wavelength of light used with 100Base-FX is 1300 nanometers.
The 100Base-FX standard allows several types of fiber optic connectors to be used. Duplex "SC" connectors are recommended, but "ST" and FDDI "MIC" connectors are also permitted.
Transmission Rate 100Mb/s (200 Mb/s in optional full-duplex mode) Cable Type two multi-mode optical fibers (MMF), typically 62.5/125 multi-mode fiber,1300 nanometer light wavelength
Maximum Segment Length Half-Duplex: 412 meters (1351 feet)
Full-Duplex: 2000 meters (6561 feet)
Maximum Number of Transceivers

2.7 1000Base-X
The identifier "1000Base-X" refers collectively to the 1000Base-LX, 1000Base-SX, and 1000Base-CX "Gigabit Ethernet" standards described in the following sections. Each of these standards are based on physical layer specifications adopted for Fibre Channel. In particular, 1000Base-X uses the same "8B/10B" coding scheme as Fibre Channel, and similar optical and electrical specifications.
With 8B/10B signaling, every 8-bits of user data are converted into a 10-bit symbol prior to transmission over the media. The overhead associated with the extra bits requires that a signal transmission rate of 1.25 gigabaud be used to transfer a net 1 Gb/s of user data.
The 1000Base-X standard defines a Gigabit Media Independent Interface (GMII) that attaches the Media Access Control (MAC) and Physical Layer (PHY) functions of a Gigabit Ethernet device. GMII is analogous to the Attachment Unit Interface (AUI) in 10 Mb/s Ethernet, and the Media Independent Interface (MII) in 100 Mb/s Ethernet.

2.7.1 1000Base-LX
The "L" in 1000Base-LX stands for "long" as it uses long wavelength lasers to transmit data over fiber optic cable. The long wavelength lasers specified by the standard operate in the wavelength range of 1270 to 1355 nanometers. Both single mode and multi-mode optical fibers are supported. Long wavelength lasers are more expensive than short wavelength, but have the advantage of being able to drive longer distances.

Transmission Rate:
1000 Mb/s (2000 Mb/s in optional full-duplex mode) Cable Type two 62.5/125 or 50/125 multi-mode optical fibers (MMF), or two 10 micron single mode optical fibers (SMF), 1270 to 1355 nanometer light wavelength
Maximum Segment Length: Half-Duplex MMF & SMF: 316 meters (1036 ft)
Full-Duplex MMF: 550 meters (1804 ft)
Full-Duplex SMF: 5000 meters (16,404 ft)
Maximum Number of Transceivers per Segment: 2
Connector Technology: duplex SC connector
Signal Encoding: 8B/10B

3 Ethernet Switch
Ethernet Hub receives a packet in one port and repeats it to all the ports, this allows all the machines to share the medium and
communicate one at a time. In case of Switch the packets are forwarded to only the port in which machine is connected. Thus the
medium is shared by multiple systems at a time.

The functions of Ethernet switch has been improved drastically from 10 Mb/s half duplex to 1 Gb/s full duplex.

Many new features are added as VLAN, tunneling , filtering etc. The architecture of Switches have been changed store and forward to cut through , or a combination of both.

The functionality and the performance of the switch are compared by the following parameters.

1. Architecture : whether cut-through or store and forward.
2. Physical functionality : on the basis of number and type of ports, up gradability, type of uplink etc.
3. Logical functionality : on the basis of type and level of filtering, broadcast / multicast / runt packets.
4. VLASN support : No. of VLANs, Type of VLASN support Port wise, MAC, service etc.
5. Manageability : Levels of RMON and SNMP supported
6. Latency : Backplane speed and forwarded speed.
7. MAC address Table size : The application of the switch mostly depends upon the size of MAC table.

The Switches can be grouped into the following types according to the application :

1. Desktop switch : these are used for connecting Client directly. The size of MAC table is small.

2. Work group switch : these are used to connect hubs/ desktop switches to the backbone network. Usually their one or more uplink ports with MAC table size more than 500 entries. Other features as VLAN , filtering.

3. Backbone switch : these are used for connecting different LANs. The backbone switch should have high latency table, medial independent port, large MAC table size, hot swappability , redundant power supply.

Configuring the Baystack 350 10/100/1000 Switch.
Configuration task :
1.connect a console to a Terminal ( 9600 baud , no parity, 8 bits, 1 stopbits ) using the DB-9 pin RS232 straight cable.

2. From the Main menu ,Select IP Configuration/Setup..Enter the IN-Band IP address, Subnet Mask and default gateway.

3.From the Main menu , Select the SNMP Configuration .. There are 4 Traps , provide IP address of the SNMP Station one by one.

This is the minimum configuration required to access the switch from the SNMP station. To check try to telnet from the SNMP Station to the switch . If you get the login prompt then the basic configuration is OK.
For special configuration as VLAN, Trunking, etc,select Switch Configuration from the Main menu.

Configuring the Baystack 350 10/100/1000 Switch.
Configuration task :
1.connect a console to a Terminal ( 9600 baud , no parity, 8 bits, 1 stopbits ) using the DB-9 pin RS232 straight cable.
2. From the Main menu ,Select IP Configuration/Setup..Enter the IN-Band IP address, Subnet Mask and default gateway.
3.From the Main menu , Select the SNMP Configuration .. There are 4 Traps , provide IP address of the SNMP Station one by one.

This is the minimum configuration required to access the switch from the SNMP station. To check try to telnet from the SNMP Station to the switch . If you get the login prompt then the basic configuration is OK.
For special configuration as VLAN, Trunking, etc, select Switch Configuration from the Main menu. , Select Switch configuration

VLAN Configuration Examples
The Network diagram There are two User groups in VLAN 1 and VLAN2 , who access the application
Servers Server 1 and Server 2 respectively.

The Mail servers and the Router for WAN connection is accessed by all , and is member of VLAN3.
The two Back bone 350 switches are connected through multi link trunks.
The configuration includes .

1. Configuring Backbone switches SWB1 and SWB2.
\SWB1 :
ports 1,5,7,11are untagged member of VLAN1 with PVID of port 1 & 11 is= 1
ports 2,5,7,12 are untagged member of VLAN 2 with PVID of port 2 & 12 is =2
ports 1,2,5,7,11 & 12 are untagged member of VLAN 3 with PVID of port 5 & 7 is =3

SWB2:
ports 1,2,3,5,7,9,11 & 12 are untagged member of VLAN1 with PVID of port 3,5,7, & 9 is =1
ports 1,2,4,6,8,10,11&12 are untagged member of VLAN 2 with PVID of port 4,6,8 & 10 is=2
ports 1,2,3,4,5,6,7,8,9,10,11 & 12 are untagged member of VLAN 3 with PVID of port 1,2,11& 12 is =3

To configure SWB1
1. VLAN 1: select Switch configuration from Main menu, then VLANconfiguration.
2. From the VLAN configuration , select VLAN configuration.
Create a VLAN : [ 1 ]
Delete a VLAN :[ ]
VLAN Name : [ VLAN1]
port numbers :
1 2 3 4 5 6 7 8 9 10 11 12
U ---U -U ---U ¬

Create a VLAN : [ 2 ]
Delete a VLAN :[ ]
VLAN Name : [ VLAN2]
port numbers :
1 2 3 4 5 6 7 8 9 10 11 12
-U --U -U ----U

Create a VLAN : [ 3 ]
Delete a VLAN :[ ]
VLAN Name : [ VLAN3]
port numbers :
1 2 3 4 5 6 7 8 9 10 11 12
U U --U -U ---U U

To configure the PVID
From the VLAN configuration Menu , select VLAN port configuration
port : [ 5]
Filter Tagged Frames [ no]
Filter Untagged Frames [no]
Filter unregistered Frames [no]
port name : [trunk1]
PVID : [ 3]

Similarly configure all the ports as per the PVID for both the switch.

2. Configuration of Desktop switches ( 303) SW1 and SW2.
In 303/304 switch don’t support the multiple VLAN on one port.To connect both the VLANs to the backbone switch one extra ports are configured.Select switch SW1
1. From the main menu , select -2 ( System configuration)
2. Select 8 ( port VLA configuration )
3. Select VLAN1 , mark port 1 to 6
4. Select VLAN 2 , mark port 7 to 12

Similarly for SW2 configure port 1 to 6 for VLAN1 and port 7 to 12 for VLAN 2.

Disable Spanning Tree protocol for all the Switches

3. To configure Multi Link Trunk :
1 From the switch configuration menu, select Multi link Trunk configuration Menu.

Trunk Trunk Members STP learning Trunk Mode Trunk Status
1 [5][7] disabled basic enabled

WORLD WIDE WEB

2011-10-10T06:36:00.000-07:00

What is the World Wide Web?
The World Wide Web (WWW) is a global interactive, dynamic, cross platform, graphical hypertext information system that runs on the Internet.

What is WWW ?

WWW is a system for creating and browsing distributed HyperTexts. WWW hypertexts link machines around the globe. They contain links to

files, newsgroups, ftp, telnet, gopher, archie, and WAIS .

HYPERTEXT

What is “The Web”

Hypermedia means that you can retrieve text, sounds (music or spoken language), movies, or pictures.
You are only limited by your computer’s hardware and software.

Enter the World Wide Web

With a Web client, users can access the internet
Seek scientific information
Surf for the heck of it
Buy and sell products and information

What is a Web Page?

A Web Page is a single document written in HTML (Hyper Text Mark-up Language) that includes the text of the document, its structure, any links to other documents and graphic images and other media.

Jargon for the Internaut ....

HTTP ,
HyperText Transfer Protocol is the stateless protocol used for data transfer within WWW.
HTML ,
WWW documents are authored using the HyperText Markup Language ,a subset of SGML.

Jargon for the Internaut ...

World Wide Web Client

A client /browser is a program that enables you to access the World Wide Web .

Formatted text with fonts
Inline / External images
Sound
Video
Java
VRML and more ...

What is a Web Browser?

A Web Browser is special software such as Netscape, Mosaic or Internet Explorer. These browsers allow a user to view Web pages delivered from a client server (Web Site) situated at a particular URL on the World Wide Web.

Clients galore ...

Character Based Lynx
Graphical User Interface Netscape Navigator, Cello, PowerBrowser, Cyberjack, Microsoft Internet Explorer, Mozilla Firefox, NCSA Mosaic , Spyglass Mosaic , HotJava,WebSurfer, and many more ...

Internet Explorer

Mozilla Firefox

Search Engines on the WWW

Tools on the WWW used to search and find web sites related to a particular topic
provide for searching using keywords and boolean operators
Popular ones are Google, Alta Vista, Infoseek, HotBot,Web Crawler, Lycos and Yahoo
Over 600 + at present

World Wide Web Server

A Web Server is the software on an Internet site that enables Web Browsers to access HyperMedia Documents sitting

on the Web site .

Homepage is a HyperText document a server will serve as default .

How a server works !?!

The Client request received at the port where server daemon is waiting
The request is interpreted following the Rule Set defined at the server
The server sends a response containing a status code and the text of the document, if available

Servers Galore !

NCSA , CERN , Netsite , Basis Web Server, WebForce, Netscape Commerce, Netscape Enterprise and scores of others

...

Serve what ? How ?

Web Authoring
Documents are created in HTML
Multimedia Elements in respective tools
Common Gateway Interface (CGI)
HTML
HTML versions 1.0, 2.0, 3.2, 4.0
Tags
Presentation Style
Perceived audiences
Bandwidth

Hang In There !

It can frustrating at times.
Have patience and remember that you are on a great frontier.

Assemble PC

2011-09-28T06:21:00.000-07:00

How to assemble your own PC (Personal Computer)

If you are thinking of building your own PC (Personal Computer), or need practical information about PC hardware or software, you have come to the right place. With easy to follow step by step guide combined with many images even a beginner can build, configure and setup their own PC.

To Know more about Click Hear.

Replication Concept

2011-09-13T22:46:00.000-07:00

Replication Concept

Ø Replication

ü Allows you to make duplicate copies of your data

ü Move the copies to different locations, and synchronize the data automatically so that all the copies have the same data values.

ü Replication can be implemented between databases on the same server or different servers connected by LANs, WANs, or the Internet.

Ø Components of Replication

ü Publisher , distributor and subscriber

ü Publication

ü Push and Pull subscriptions

ü Replication agents

Ø Publisher

ü Is a server that makes data available for replication to other servers.

ü Identifies which data is to be replicated

ü Detects any changed data and maintains information about all publications at that site.

Ø Subscriber

ü Are servers that store replicated data and receive updates.

ü Subscribers can make updates to data.

ü A Subscriber can, in turn, become a Publisher to other Subscribers

Ø Distributor

ü The Distributor server

o Contains the distribution database

o Stores metadata, history data, and (for transactional publications) transactions.

Ø Publication

ü Is a collection of articles, and an article is a grouping of data to be replicated.

ü An article can be an entire table, only certain columns (using a vertical filter), only certain rows (using a horizontal filter), or even a stored procedure (in some types of replication).

ü A publication can have multiple articles.

Ø Push Subscription

ü Publisher propagates the changes to a Subscriber without a request from the Subscriber to do so.

ü Typically, used in applications that are required to send changes to Subscribers whenever and as soon as they occur.

ü Best for publications that require near real-time movement of data .

ü Used in cases when the higher processor overhead at the Publisher does not affect performance.

ü Changes can also be pushed to Subscribers on a scheduled basis.

Ø Pull Subscription

ü With a pull subscription, the Subscriber asks for periodic updates of all changes at the Publisher.

ü Pull subscriptions are best for publications having a large number of Subscribers eg.Subscribers using the Internet.

ü Pull subscriptions allow the user to determine when the data changes are synchronized.

ü A single publication can support a mixture of push and pull subscriptions.

Ø Agents

ü Snapshot agent

ü Log reader agent

ü Distribution agent

ü Merge agent

Ø Snap shot Agent

ü Prepares schema and initial data files of published tables and stored procedures.

ü Stores the snapshot on the Distributor and records information about the synchronization status in the distribution database.

ü Each publication has its own Snapshot Agent that runs on the Distributor and connects to the Publisher.

ü The Snapshot Agent is run typically under SQL Server Agent and can be administered directly using SQL Server Enterprise Manager.

Ø Log reader Agent

ü The Log Reader Agent moves transactions marked for replication from the transaction log on the Publisher to the distribution database.

ü Each database published using transactional replication has its own Log Reader Agent that runs on the Distributor and connects to the Publisher.

Ø Distribution Agent

ü The Distributor receives all changes to published data, stores the changes in its distribution database, and transmits them to Subscribers.

ü The Distributor may or may not be the same computer as the Publisher.

ü Push subscriptions to either snapshot or transactional publications have Distribution Agents that run on the Distributor.

ü Pull subscriptions to either snapshot or transactional publications have Distribution Agents that run on the Subscriber instead of the Distributor.

ü Merge publications do not have a Distribution Agent.

Ø Merge Agent

ü It is the agent in merge replication, that applies initial snapshot jobs held in publication database tables to Subscribers.

ü It also merges incremental data changes that have occurred since the initial snapshot was created.

ü Push subscriptions to merge publications have Merge Agents that run on the Publisher.

ü Pull subscriptions to merge publications have Merge Agents that run on the Subscriber.

Ø Types of replication

ü Snapshot

ü Transactional

ü Merge

Ø Snapshot replication

ü Simplest type of replication

ü A picture, or snapshot, of the published data in the database at a moment in time.

ü All this data is sent to the Subscriber instead of sending just the changes in data.

ü Hence subscribers are updated by a total refresh of the data set.

ü Guarantees transactional consistency between the Publisher and Subscriber.

ü Snapshot replication is carried out by the Snapshot Agent and the Distribution Agent.

ü The Snapshot Agent prepares snapshot files containing schema and data of published tables and stores the files in the snapshot folder on the Distributor, and records synchronization jobs in the distribution database on the Distributor.

ü The Distribution Agent moves the snapshot jobs held in the distribution database tables to the destination tables at the Subscribers.

ü The distribution database is used only by replication and does not contain any user tables.

Ø Transactional replication

ü Used to replicate two distinct types of objects: tables and stored procedures.

ü Uses the transaction log to capture changes that were made to data in an article.

ü The modifications made to the data like Insert, Delete etc are monitored and stores these changes in the distribution database.

ü Changes are then sent to Subscribers and applied in the same order.

Ø The Snapshot Agent

ü Prepares snapshot files containing schema and data of published tables,

ü stores the files in the snapshot folder on the Distributor

ü records synchronization jobs in the distribution database on the Distributor.

Ø The Log Reader Agent

ü monitors the transaction log of each database set up for replication

ü copies the transactions marked for replication from the transaction log into the distribution database.

Ø The Distribution Agent

ü moves the transactions and initial snapshot jobs held in the distribution database tables to Subscribers.

Ø Merge replication

ü Merge replication tracks changes in a source database and synchronizes the values between the Publisher and Subscribers, all of whom may update data.

ü Data changes at the destination database are propagated to the source database.

Replication is carried out by the Snapshot Agent and

Merge Agent.

Ø The Snapshot Agent

ü prepares snapshot files containing schema and data of published tables,

ü stores the files in the snapshot folder on the Distributor,

ü records synchronization jobs in the publication database.

Ø The Merge Agent

ü applies the initial snapshot jobs held in the publication database tables to the Subscriber.

ü merges incremental data changes that occurred at the Publisher after the initial snapshot was created

ü reconciles conflicts according to rules you configure or using a custom resolver you create.

Steps in replication:

1. Configuring replication

(a) Done by replication wizards, available from the SQL Server Enterprise Manager Tools menu. You can use these wizards to enable, modify, and disable servers as Distributors, Publishers, and Subscribers.

Tools >>Replication >> Configure Publishing, Subscribers and distribution

(b) Using the GUI of Enterprise manager

Click on the server name

Select replicate data >>configure replication

2. Create Publication Wizard to create a publication

(a) Using the Enterprise Manager Tools menu

Tools >>Replication >>Create or manage publication

(b) Use the GUI of Enterprise manager Select the create or manage publication icon

3. Use the push or pull subscription

Ø Push Subscription Wizard

Push Subscription Wizard to create one or more push subscriptions to each publication on a Publisher.

ü Using the wizard, you can specify:

o One or more servers or server groups to receive the publication as Subscribers.

o The destination database, which must exist on all Subscribers.

o Subscription properties

ü Tasks to be performed before the subscription can be created:

o Create the publication

o Create a destination database at each subscribing server

o If selecting more than one server or server group, use the same destination database name at each Subscriber.

Ø How to start the Push Subscription Wizard (Enterprise Manager)

To start the Push Subscription Wizard

ü Expand a server group; then expand the Publisher.

ü On the Tools menu, point to Replication, and then click Push Subscription to Others.

ü Expand the database containing the publication in which to create a subscription.

ü Click the publication; then click Push New Subscription.

ü Complete the steps in the wizard.

Ø Pull subscription wizard

Using the Pull Subscription Wizard, you can specify:

ü The publication to which you want to subscribe.

ü The name of the destination database to be used for the subscription.

ü Subscriber properties, such as the synchronization schedule with the Publisher, the visibility of the subscription to other Subscribers, whether the subscription can update data, and what priority each Subscriber has when there is a conflict of changes.

Ø How to start the Pull Subscription Wizard (Enterprise Manager)

To start the Pull Subscription Wizard

ü Expand a server group; then expand the Subscriber.

ü On the Tools menu, point to Replication, and then click Pull Subscription To....

ü Click Pull New Subscription.

ü Complete the steps in the wizard.

Electronic mail

2011-08-31T05:23:00.000-07:00

Electronic mail

Objectives:

1. Understanding concept of e-mail ?

2. How does it work ?

3. Becoming an e-mail user.

Understanding e-mail:

ü Electronic mail Is a popular Network
application that allows you to exchange written messages electronically over computer Networks.

ü You can send the electronic messages to: - people anywhere in the world
- someone right next to you

Advantages:

ü Message can be communicated to people around the world in a quick & Fast manner any time of day or night.

ü It allows asynchronous communication in which, it is not necessary that the recipient should be on line, when a message addressed to him / her is being sent / received.

ü One need not be very formal in composing the email messages, However, one should follow netiquette rules.

ü This is a very inexpensive mode of communication, in which large no of people spread all over the world can be covered, without additional costs.

Disadvantages:

ü Low Security, low privacy or less confidential as messages may be intercepted by individuals other than sender or recipient:
- Due to wrong address
- Due to transmission error
- Due to hacking
- Legal issues associated with authentication of email messages

Note: Technology is already trying to provide solutions like encryption/ decryption and digital signatures, which are not being covered in the basic lecture on email.

How does it work s?

E-mail is a “Store and Forward Service”

ü The process of communication through e-mail is based on the Client-Server technology.

ü The computer which provides e-mail facility is called Server or Email Service provider.

ü The computer which avails of this facility is called Client.

How to become an E-mail user:

ü Apply to an E-mail Service Provider for an e-mail address (sometimes referred as email account also)

ü Load necessary Software in your computer.

ü Your computer should get connected to email server, either through: – dialup connectivity ( via a modem) – lease line – Satellite based connectivity

Structure of an E-mail address:

E-mail address has two parts

user_name@Host_name

Person’s user name Tells the e-mail server on which
computer the recipient’s e-mail account is

E.g.: ashok@akbdevhelper.blogspot.com

E-mail Software: (Few examples)

ü Server software

Ø SMTP

Ø POP

Ø Microsoft Exchange

Ø Lotus Notes

ü Client Software

Ø Eudora

Ø PINE

Ø MS-Outlook

Ø Outlook Express

What you can do with any of the e-mail Software?

ü Send e-mails to an individual or a group of people

ü Receive e-mails

ü Send mails with attachments

ü Reply to / Forward to

ü Delete messages

ü Printing / Saving to file on your computer

ü Organizing mails (making folders and address books)

But for that …….

“You have to CONFIGURE your system”

WHAT EXACTLY IS CONFIGURATION?

Ø Your E-mail does not come automatically to your system.

Ø On invoking the email S/W, it first goes to the E-mail server in which you have registered.

Ø The mail waits for you to go an pick it up with a E-mail software like MS Outlook, Outlook Express etc.

Ø For this you have to give correct information about yourself and only then you are able to collect your mail.

How to configure?

Every email S/W has a procedure of configuring the system. Usually, the steps of configurations are guided through wizard.

Email Marketing By the Numbers: How to Use the World's Greatest Marketing Tool to Take Any Organization to the Next Level

The Complete Guide to E-mail Marketing: How to Create Successful, Spam-free Campaigns to Reach Your Target Audience and Increase Sales

Working in Windows

2011-08-06T02:59:00.000-07:00

1. What is an Operating System?
An operating system is system software that Provides:

Ø An interface for a user to communicate with the computer (Text based / Windows based)

Ø Manages hardware devices

Ø Manages and maintains disk file systems

Ø Supports application programs

Ø Does memory management

Ø Does peripherals management

WORKING WITH WINDOWS

Ø Don’t let the jargon scare you More often a buzzword that sounds serious and difficult to grasp turns out to be no big deal when you find out what it really means (e.g. of Stiff neck Vs. torticollis)

Also note that there is lot of similarity in user Interface of various Windows based S/W.

Desktop Screen For Windows

Let us start working in Windows

Basic Concepts of Computers

2011-07-30T05:11:00.000-07:00

A Computer is a device which allows you to

Input raw data
Perform Computations/Processing
Store the data for retrieval
Obtain desired information

Characteristics of a Computer

Speed
Accuracy
Storage and Retrieval
Repeated Processing Capabilities
Reliability
Flexibility
Low Cost

COMPUTER TECHNOLOGY IS COMPLEX BUT BASED ON SIMPLE PRINCIPLE

Instructions
Input as Raw Data
Output as Information
Storage

LET US HAVE A LOOK INSIDE

What are the main components ?

i. Hardware

ii. Software

iii. Computing Environments

iv. Computer Limitations

v. Know more about Keyboard & Mouse

Computing Environments

Single user
Multi user
Networke

Software:
A set of instruction (programs) that makes the hardware perform a particular set of tasks

Ø System Software (Operating Systems & Utilities)

o DOS, UNIX,LINUX, WINDOWS 98 / 2000 / NT , etc.

o Memory Management, File Management, Anti Virus etc.

Ø Application Software

o General Purpose:
Ms-Office, Lotus SmartSuite, Ventura, PageMaker, etc.

o Language Compilers:
C, C++, Visual Basic, JAVA, Smalltalk, ASP, etc.

Ø User Designed Application Software Scientific, Business, Design, Marketing, Entertainment, etc.

Networking

What is networking?
Classification of Network
Goals of a Networking

Personal Computer

Single User System

Ø One user can work on it

Ø No efficient use of System

Ø Operating System like MSDOS, Windows 95/

Ø Windows 98 / Windows 2000 –Professional etc.

Resource sharing cannot be done

Multi User System

Ø More than one user can work on the system in time sharing mode

Ø Operating System like Unix, Linux , Windows NT, Windows 2000–Server etc.

Ø Resource sharing can be done

Ø Optimal utilization of resources

Networking

Ø What is a Network?

o A network is a group of interconnected systems which share services and interact with each other by means of a shared communication link

o These systems can be located anywhere

o Network is often classified according to its geographical size.

Classification of Network

The most common classification of networks are:

Ø Local Area Network (LAN)

Ø Wide Area Network (WAN)

Ø Metropolitan Area Network (MAN) (eg. A city cable network)

Mouse Pointer Forms

Ø      Standard Pointer form. ↕ Form when changing a window’s height ↔ Form when changing a window’s width
   Form when changing height and width simultaneously
   Form when changing a width of a field in a table I Form when inserting the text
   Form when moving a field to a new position in the table
   Form when application being executed or a wait state

Computer Configuration: An Illustration

Ø Characteristic & Example

o Present day PC Family

§ Pentium i7/ i5/ i3/ IV

o Memory

§ 4 GB/ 2GB/ 1GB

o Microprocessor chip

§ Intel i7/ i5/ i3

o Clock Speed

§ 2.2/ 1.7/ 1.6 GHz

o Cache Memory

§ 3/ 2/ 1 Mega Bytes

o Hard Disk Drive

§ 500/ 320/ 160 Giga Bytes

o Floppy Disk Drives

§ 1.44 MB

o CD Drive

§ 72/ 56/ 52 X

o Monitor

§ LCD, LED (1280 X 1024)

Computer Limitations

Ø Thinking limitations

o Computer virus

o Fast technological advancements resulting in obsolescence

o Risk of equipment failure

o Equipment downtime and recovery

Problems associated with Computerization

Ø Human Ego problems

Ø Standards enforcement problems

Ø Imbalance between Transparency and Security

Ø Mismatch between technological advancements and their implementation

Ø Misuse of computer resources

Ø Computer crimes

INTRODUCTION TO DATABASE MANAGEMENT SYSTEM

2011-07-28T22:40:00.000-07:00

INTRODUCTION TO DATABASE MANAGEMENT SYSTEM

A database management system (DBMS) consists of collection of interrelated data and a set of programs to access that data. The collection of data, usually referred to as the database contains information about one particular enterprise The primary goal of a DBMS is to provide an environment that is both convenient and efficient to use in retrieving and storing database information.

Database systems are designed to manage large bodies of information The management of data involves both the definition of structures for the storage of information and the provision of mechanisms for the manipulation of information. In addition, the database system must provide for the safety of the information stored, despite system crashes or attempts at unauthorized access. If data are to be shared among several users, the system must avoid possible anomalous results.

The following topics have been discussed here :

· Why Database

· Characteristics of Data in Database

· Drawbacks in File System

· Data redundancy and inconsistency

· DBMS Components

· DBMS Advantages

Why Database

A database can be defined as a collection of non-redundant data which can be shared by user.

Changes (or updation) can be made to data without affecting other components of the system. These changes include, for example, change of data format or file structure or relocation from one device to another.

Advantages of a Database

· Reduction in data redundancy

· Maintenance of data integrity and quality

· Avoidance of inconsistency

· Reduced cost of software development

· Security restrictions

View of the Database

The database can present different views of itself to users, programmers and the database administrator.

· The internal data representation (internal view) is normally not seen by the user or application programmer.

· The conceptual view or conceptual schema is the primary means by which the DBA builds and manages the database.

· The DBMS can present multiple views of the conceptual schema (external views) to programmers and users, depending on the application.

Characteristics of Data in Database

In general, the data in the database-at least in a large system –will be both integrated and shared.

· By integrated, we mean that the database can be thought of as a unification of several otherwise distinct data files, with any redundancy among those files wholly or partly eliminated.

· By shared, we mean that individual pieces of data in the database can be shared among several different users, in the sense that each of those users can have access to the same piece of data (and different users can use it for different purposes). As indicated earlier, different users can even be accessing the same piece of data at the same time (“concurrent access”). Such sharing (concurrent or otherwise) is partly a consequence of the fact that the database is integrated.

Drawbacks in File System

Data redundancy and inconsistency

Since different programmers create application programs over a long period, various files are likely to have different formats and the programs may be written in several programming languages. Moreover, the same information may be duplicated in several places (files). For example, the address and telephone number of particular customer may appear in a file that consists of savings account records and in file that consists of checking-account records. This redundancy leads to higher storage and access cost. In addition, it may lead to data inconsistency, that is, the various copies of the same data may no longer agree. For example, changed customer address may be reflected in savings-account records but not elsewhere in the system.

Difficulty in accessing data

Suppose that one of the bank officers needs to find out the names of all customers who live within the city's 78733 zip code. The officer asks the data -processing department to generate such a list. Because this request was not anticipated when the original system was designed, there is no application program on hand to meet it. There is, however, an application program to generate the list of all customers. The bank officer has now two choices: either obtain the list of all customers and have the needed information extracted manually, or ask the data-processing department to have system programmer write the necessary application program. Both alternatives are obviously unsatisfactory. Suppose that such a program is written, and that, several days later, the same officer needs to trim that list to include only those customers who have an account balance of Rs10,000 or more. As expected, a program to generate such a list does not exist. Again, the officer has the preceding two options, neither of which is satisfactory. The point here is that conventional file-processing environments do not allow needed data to be retrieved in a convenient and efficient manner. More responsive data-retrieval systems must be developed for general use.

Data isolation

Because data are scattered in various files, and files may be in different formats, it is difficult to write new application programs to retrieve the appropriate data.

Integrity problems

The data values stored in the database must satisfy certain types of consistency constraints. For example, the balance of a bank account may never fall below a prescribed amount (say, Rs25). Developers enforce these constraints in the system by adding appropriate code in the various application programs. However, when new constraints are added, it is difficult to change the programs to enforce them. The problem is compounded when constraints involve several data items from different files.

Atomicity problems

A computer system, like any other mechanical or electrical device, is subject to failures. In many applications, it is crucial to ensure that, once a failure has occurred and has been detected, the data are restored to the consistent state that existed prior to the failure. Consider a program to transfer Rs50 from account A to B. If a system failure occurs during the execution of the program, it is possible that the Rs50 was removed from account A but was not credited to account B, resulting in an inconsistent database state. Clearly, it is essential for database consistency that either both the credit or debit occur, or that neither occur. That is, the funds transfer must be atomic-it must happen in the entirety or not at all. It is difficult to ensure this property in a conventional file-processing system.

Concurrent-access anomalies

So that the overall performance of the system is improved and a faster response time is possible, many systems allow multiple users to update the data simultaneously. In such an environment, interaction of concurrent updates may result in inconsistent data. Consider bank account A, containing Rs 500. If two customers withdraw funds (say Rs 50 and Rs 100 respectively) from account A at about the same time, the result of the concurrent executions may leave the account in an incorrect (or inconsistent) state. Suppose that the programs executing on behalf of each withdrawal read the old balance, reduce that value by the amount being withdrawn, and write the result back. If the two programs run concurrently, they may both read the value Rs 500, and write back Rs 450 and Rs 400, respectively. Depending on which one writes the value last, the account may contain either Rs450 or Rs400, rather that the correct value of Rs350. To guard against this possibility, the system must maintain some form of supervision. Because many different application programs that have not been coordinated previously may access data, therefore, supervision is difficult to provide.

Security problems

Not every user of the database system should be able to access all the data, for example, in a banking system, payroll personnel need to see only that part of the database that has information about the various bank employees. They do not need access to information about customer accounts. Since application programs are added to the system in an adhoc manner, it is difficult to enforce such security constraints.

DBMS Components

Data: Data stored in a database include numerical data which may be integers (whole numbers only) or floating point numbers (decimal), and non-numerical data such as characters (alphabetic and numeric characters), date or logical (true or false). More advanced systems may include more complicated data entities such as pictures and images as data types.

Standard operations: Standard operations are provided by most DBMSs. These operations provide the user with basic capabilities for data manipulation. Examples of these standard operations are sorting, deleting and selecting records.

Data definition language (DDL): DDL is the language used to describe the contents of the database. It is used to describe, for example, attribute names (field names), data types, location in the database, etc.

Data manipulation and query language: Normally a query language is supported by a DBMS to form commands for input, edit, analysis, output, reformatting, etc. Some degree of standardization has been achieved with SQL (Structured Query Language).

Programming tools: Besides commands and queries, the database should be accessible directly from application programs through function calls (subroutine calls) in conventional programming languages.

File structures: Every DBMS has its own internal structures used to organize the data although some common data models are used by most DBMSs.

DBMS Advantages

There are three main features of a database management system that make it attractive to use a DBMS in preference to other systems. These features are:

· Centralized data management,

· Data independence

· Systems integration.

In a database system, the data is managed by the DBMS and all access to the data is through the DBMS providing a key to effective data processing. This contrasts with conventional data processing systems where each application program has direct access to the data it reads or manipulates.

In the conventional data processing application programs, the programs usually are based on a considerable knowledge of data structure and format. In such environment any change of data structure or format would require appropriate changes to the application programs. If major changes were to be made to the data, the application programs may need to be rewritten.

In a database system, the database management system provides the interface between the application programs and the data. When changes are made to the data representation, the metadata maintained by the DBMS is changed but the DBMS continues to provide data to application programs in the previously used way. The DBMS handles the task of transformation of data wherever necessary.

This independence between the programs and the data is called data independence. Data independence is important because every time some change needs to be made to the data structure, the programs that were being used before the change would continue to work. To provide a high degree of data independence, a DBMS must include a sophisticated metadata management system.

In DBMS, all files are integrated into one system thus reducing redundancies and making data management more efficient. In addition, DBMS provides centralized control of the operational data. Some of the advantages of data independence, integration and centralized control are:

Redundancies and inconsistencies can be reduced
Better service to the Users
Flexibility of the system is improved
Cost of developing and maintaining systems is lower
Standards can be enforced
Security can be improved
Integrity can be improved
Enterprise requirements can be identified
Data model must be developed

Developer helper

2011-07-27T22:10:00.000-07:00

This blog contains the articles related to general computer awareness, O.S., Networking, SQL Server, M.S. Access and OOP Concepts. Primarily for an audience of software developers.