Title: comp app
1Computer Assignment
- Nameharsh kedia
- Std9
- DivA
- Roll no.18
2Twisted pair cables
3(No Transcript)
4(No Transcript)
5- Twisted pair cabling is a type of wiring in which
two conductors (the forward and return conductors
of a single circuit) are twisted together for the
purposes of canceling out electromagnetic
interference (EMI) from external sources for
instance, electromagnetic radiation from
Unshielded Twisted Pair (UTP) cables, and
crosstalk between neighboring pairs. Explanation - In balanced pair operation, the two wires carry
equal and opposite signals and the destination
detects the difference between the two. This is
known as differential mode transmission. Noise
sources introduce signals into the wires by
coupling of electric or magnetic fields and tend
to couple to both wires equally. The noise thus
produces a common-mode signal which is cancelled
at the receiver when the difference signal is
taken. This method starts to fail when the noise
source is close to the signal wires the closer
wire will couple with the noise more strongly and
the common-mode rejection of the receiver will
fail to eliminate it. This problem is especially
apparent in telecommunication cables where pairs
in the same cable lie next to each other for many
miles. One pair can induce crosstalk in another
and it is additive along the length of the cable.
Twisting the pairs counters this effect as on
each half twist the wire nearest to the
noise-source is exchanged. Providing the
interfering source remains uniform, or nearly so,
over the distance of a single twist, the induced
noise will remain common-mode. Differential
signaling also reduces electromagnetic radiation
from the cable, along with the attenuation that
it causes. - The twist rate (also called pitch of the twist,
usually defined in twists per meter) makes up
part of the specification for a given type of
cable. Where nearby pairs have equal twist rates,
the same conductors of the different pairs may
repeatedly lie next to each other, partially
undoing the benefits of differential mode. For
this reason it is commonly specified that, at
least for cables containing small numbers of
pairs, the twist rates must differ. - In contrast to FTP (foiled twisted pair) and STP
(shielded twisted pair) cabling, UTP (unshielded
twisted pair) cable is not surrounded by any
shielding. It is the primary wire type for
telephone usage and is very common for computer
networking, especially as patch cables or
temporary network connections due to the high
flexibility of the cables.
6Tcp/Ip
7- IP encapsulation
- Data from an upper layer protocol is encapsulated
as packets/datagrams (the terms are basically
synonymous in IP). Circuit setup is not needed
before a host may send packets to another host
that it has previously not communicated with (a
characteristic of packet-switched networks), thus
IP is a connectionless protocol. This is in
contrast to public switched telephone networks
that require the setup of a circuit for each
phone call (connection-oriented protocol). - edit Services provided by IP
- Because of the abstraction provided by
encapsulation, IP can be used over a
heterogeneous network, i.e., a network connecting
computers may consist of a combination of
Ethernet, ATM, FDDI, Wi-Fi, token ring, or
others. Each link layer implementation may have
its own method of addressing (or possibly the
complete lack of it), with a corresponding need
to resolve IP addresses to data link addresses.
This address resolution is handled by the Address
Resolution Protocol (ARP) for IPv4 and Neighbor
Discovery Protocol (NDP) for IPv6. - edit Reliability
- The design principles of the Internet protocols
assume that the network infrastructure is
inherently unreliable at any single network
element or transmission medium and that it is
dynamic in terms of availability of links and
nodes. No central monitoring or performance
measurement facility exists that tracks or
maintains the state of the network. For the
benefit of reducing network complexity, the
intelligence in the network is purposely mostly
located in the end nodes of each data
transmission, cf. end-to-end principle. Routers
in the transmission path simply forward packets
to next known local gateway matching the routing
prefix for the destination address. - As a consequence of this design, the Internet
Protocol only provides best effort delivery and
its service can also be characterized as
unreliable. In network architectural language it
is a connection-less protocol, in contrast to
so-called connection-oriented modes of
transmission. The lack of reliability allows any
of the following fault events to occur - data corruption
- lost data packets
- duplicate arrival
- out-of-order packet delivery meaning, if packet
'A' is sent before packet 'B', packet 'B' may
arrive before packet 'A'. Since routing is
dynamic and there is no memory in the network
about the path of prior packets, it is possible
that the first packet sent takes a longer path to
its destination. - The only assistance that the Internet Protocol
provides in Version 4 (IPv4) is to ensure that
the IP packet header is error-free through
computation of a checksum at the routing nodes.
This has the side-effect of discarding packets
with bad headers on the spot. In this case no
notification is required to be sent to either end
node, although a facility exists in the Internet
Control Message Protocol (ICMP) to do so. - IPv6, on the other hand, has abandoned the use of
IP header checksums for the benefit of rapid
forwarding through routing elements in the
network. - The resolution or correction of any of these
reliability issues is the responsibility of an
upper layer protocol. For example, to ensure
in-order delivery the upper layer may have to
cache data until it can be passed to the
application. - In addition to issues of reliability, this
dynamic nature and the diversity of the Internet
and its components provide no guarantee that any
particular path is actually capable of, or
suitable for performing the data transmission
requested, even if the path is available and
reliable. One of the technical constraints is the
size of data packets allowed on a given link. An
application must assure that it uses proper
transmission characteristics. Some of this
responsibility lies also in the upper layer
protocols between application and IP. Facilities
exist to examine the maximum transmission unit
(MTU) size of the local link, as well as for the
entire projected path to the destination when
using IPv6. The IPv4 internetworking layer has
the capability to automatically fragment the
original datagram into smaller units for
transmission. In this case, IP does provide
re-ordering of fragments delivered
out-of-order.1 - Transmission Control Protocol (TCP) is an example
of a protocol that will adjust its segment size
to be smaller than the MTU. User Datagram
Protocol (UDP) and Internet Control Message
Protocol (ICMP) disregard MTU size thereby
forcing IP to fragment oversized datagrams.2
8- Perhaps the most complex aspects of IP are IP
addressing and routing. Addressing refers to how
end hosts become assigned IP addresses and how
subnetworks of IP host addresses are divided and
grouped together. IP routing is performed by all
hosts, but most importantly by internetwork
routers, which typically use either interior
gateway protocols (IGPs) or external gateway
protocols (EGPs) to help make IP datagram
forwarding decisions across IP connected networks - Version history
- In May 1974, the Institute of Electrical and
Electronic Engineers (IEEE) published a paper
entitled "A Protocol for Packet Network
Interconnection."3 The paper's authors, Vint
Cerf and Bob Kahn, described an internetworking
protocol for sharing resources using
packet-switching among the nodes. A central
control component of this model was the
"Transmission Control Program" (TCP) that
incorporated both connection-oriented links and
datagram services between hosts. The monolithic
Transmission Control Program was later divided
into a modular architecture consisting of the
Transmission Control Protocol at the
connection-oriented layer and the Internet
Protocol at the internetworking (datagram) layer.
The model became known informally as TCP/IP,
although formally it was henceforth referenced as
the Internet Protocol Suite. - The Internet Protocol is one of the determining
elements that define the Internet. The dominant
internetworking protocol (Internet Layer) in use
today is IPv4 with number 4 assigned as the
formal protocol version number carried in every
IP datagram. IPv4 is described in RFC 791 (1981). - The successor to IPv4 is IPv6. Its most prominent
modification from Version 4 is the addressing
system. IPv4 uses 32-bit addresses (c. 4 billion,
or 4.3109, addresses) while IPv6 uses 128-bit
addresses (c. 340 undecillion, or 3.41038
addresses). Although adoption of IPv6 has been
slow, as of June 2008, all United States
government systems have demonstrated basic
infrastructure support for IPv6 (if only at the
backbone level).4 - Version numbers 0 through 3 were development
versions of IPv4 used between 1977 and
1979.citation needed Version number 5 was used
by the Internet Stream Protocol (IST), an
experimental stream protocol. Version numbers 6
through 9 were proposed for various protocol
models designed to replace IPv4 SIPP (Simple
Internet Protocol Plus, known now as IPv6), TP/IX
(RFC 1475), PIP (RFC 1621) and TUBA (TCP and UDP
with Bigger Addresses, RFC 1347). Version number
6 was eventually chosen as the official
assignment for the successor Internet protocol,
subsequently standardized as IPv6. - A humorous Request for Comments that made an IPv9
protocol center of its storyline was published on
April 1, 1994 by the IETF.5 It was intended as
an April Fool's Day joke. Other protocol
proposals named "IPv9" and "IPv8" have also
briefly surfaced, though these came with little
or no support from the wider industry and
academia.6
9DiFfErEnT TyPeS oF MoDeM
- Different types of computer modemkeeps everyone
connected, through the Internet technology,
wherever they are. Lets see what a computer
modem is.Modem, as a shortened form of
MOdulatorDEModulator, allows the computer to
convert data in useful information. -
- When it receives an analog data through a
connection, it has to convert it in digital data
to be usable by the computer. Likewise it
reverses the action when it has to send data. -
- It is not so important, here, to know how modems
do work but it is essential to make the
difference between the different types of
computer modem. -
- Internal computer modems. Some computers have an
internal modem which can be a built-in modem or a
PC card modem. -
- For the PC card modem, a PCI slot or even
sometimes an ISA slot is required, depending on
the available interface your motherboard uses to
receive the modem. - Internal comuter modems are used with Dial-Up
Internet connection through a couple of RJ-11
connection. Also called copper telephone lines,
the RJ-11 allows computer to receive and send
data as explained above. - Internal comuter modems are usually 56K modems
which mean that the modem is able to receive 56
Kbits/s (56 kilobits or 56000 bits per second) of
data. This kind of data transmission is called
downstream transmission, came from a provider and
transmitted over telephone lines. Commonly it is
the standard bandwidth with telephones lines. - However because Internet is a two-way system,
data must also flow from the client to the
(server) provider. For this purpose the computer
can use 56K modems V90 to flow back 33.6 Kbits/s
of upstream transmission rate. On the other hand
the 56K modems V 92 is able to provide 48 Kbits/s
of upstream transmission rate. -
- External modems. It is the second term we have to
consider from different types of computer modem.
An External modem can be used to the same purpose
and in the same conditions as internal computer
modem. However external modem is a small box that
uses other kind of interfaces to be connected to
the computer. - It could be a serial modem, named thus because
it uses the serial port to connect to the
computer. Usually installed on the back of the
computer, the serial port is an easy-to-install
option for the external modem. The same small
box, on the other hand, can be an USB modem which
normally uses USB port usually placed on the back
or in front of the computer. -
10- As well as another type of external modem you may
consider two important types of modem cable
modem and DSL modem if you need high-speed
internet services. All ISPs usually supply a
specialized modem named digital modem in the
broadband package. -
- Its important to notice that cablemodem has to
connect to an Ethernet card, placed on the
computer PCI slot to provide a broadband internet
connection to the user. This is true if you opt
to use Ethernet connection. However you won't
need it if your option goes to use an USB
connection. -
- Cable modem. The cable modem uses a coaxial cable
television lines to provide a greater bandwidth
than the dial-up comuter modem. An extremely fast
access to the Web is providing by the cable modem
with downstream transmission up to 38 Mbits/s and
an upstream transmission up to 1 Mbits/s. -
- Unfortunately this transmission rate fluctuates
with the number of users because of the shared
bandwidth on which the cable technology is based. -
- DSL modem. DSL (Digital Subscriber Line) modem is
exclusively used for connections from a telephone
switching office to the user. This technology,
available and frequently usable, split up into
two main categories - ADSLor Asymetric Digital Subcriber Line is used
in North America and supports from 1.5 Mbits/s up
to 9 Mbits/s of downstream transmission rate and
up to 3 Mbits/s of upstream transmission rate. - SDSL. SDSL or Symetric Digital Subcriber Line is
used in Europe and has the same data rates for
downstream and upstream transmission which is 128
Kbits/s. - One more thing
- Some modern modem include very interesting
features which allow your computer to do
important tasks such as auto-answer your incoming
calls, do voice mail, sending and receiving fax
and so forth. - Don't waste your time! Go enjoy these various
possibilities offered by the different types of
computer modem. - First of all external modem can be a
Dial-Up modem but more expensive than the
internal. -
11WIFI MAX
12(No Transcript)
13- Greater total valueWavion solutions are
comprised of best-of-breed components including
Wavion WBS base stations, CPEs, backhaul and
billing provisioning systems. We, at Wavion,
have spent significant time and effort, selecting
the best component and optimizing the solution
for each specific application.Short time to
marketWavion solutions have been tested and
certified by our engineering team to ensure - Interoperability between the solution components
- Optimization for various applications in both
urban and rural settings - Resolution of any issues that arise prior to
customer deployment - The process ensures that you will be able to
deploy your network quickly and effectively.
Furthermore, you will get the ideal solution for
your specific needs.Single point of
contactWith Wavion end-to-end solution you have
a single point of contact. We will take complete
responsibility for the rapid deployment of your
state-of-the-art wireless broadband solution. - Base Stations Wavion WBS is a family of a
carrier class, broadband wireless beamforming
base stations that provide superior coverage and
greater capacity. - WBS-2400 Omni-directional base station with 6
antenna array operating in 2.4 GHz - WBS-2400 Sector Directional base station with 3
antenna array in 120 sector operating in 2.4 GHz
- WBS-5800 Omni-directional base station with 6
antennas array operating in 5.8 GHz - WBS-5800 Sector Directional base station with 3
antenna array in 120 sector operating in 5.8 GHz
14E-mail protocols
15- E-mail protocols
- The Internet Message Access Protocol (commonly
known as IMAP, and previously called Internet
Mail Access Protocol, Interactive Mail Access
Protocol (RFC 1064), and Interim Mail Access
Protocol2) is an Application Layer Internet
protocol that allows an e-mail client to access
e-mail on a remote mail server. The current
version, IMAP version 4 revision 1 (IMAP4rev1),
is defined by RFC 3501. - IMAP supports both on-line and off-line modes of
operation. E-mail clients using IMAP generally
leave messages on the server until the user
explicitly deletes them. This and other
characteristics of IMAP operation allow multiple
clients to manage the same mailbox. Most e-mail
clients support IMAP in addition to POP to
retrieve messages however, fewer Internet
service providers (ISPs) support IMAP.3 IMAP
offers access to the mail store. Clients may
store local copies of the messages, but these are
considered to be a temporary cache. - E-mail messages are sent to an e-mail server that
stores messages in the recipient's email box. The
user retrieves messages with an e-mail client
that uses one of a number of e-mail retrieval
protocols. Some clients and servers
preferentially use vendor-specific, proprietary
protocols, but most support the Internet standard
protocols, SMTP for sending e-mail and POP and
IMAP for retrieving e-mail, allowing
interoperability with other servers and clients.
For example, Microsoft's Outlook client uses a
proprietary protocol to communicate with an
Microsoft Exchange Server server as does IBM's
Notes client when communicating with a Domino
server, but all of these products also support
POP, IMAP, and outgoing SMTP. Support for the
Internet standard protocols allows many e-mail
clients such as Pegasus Mail or Mozilla
Thunderbird (see comparison of e-mail clients) to
access these servers, and allows the clients to
be used with other servers (see list of mail
servers). - History
- IMAP was designed by Mark Crispin in 1986 as a
remote mailbox protocol, in contrast to the
widely used POP, a protocol for retrieving the
contents of a mailbox.4 - Original IMAP
- The original Interim Mail Access Protocol was
implemented as a Xerox Lisp machine client and a
TOPS-20 server. - No copies of the original interim protocol
specification or its software exist. Although
some of its commands and responses were similar
to IMAP2, the interim protocol lacked
command/response tagging and thus its syntax was
incompatible with all other versions of IMAP. - IMAP2
- The interim protocol was quickly replaced by the
Interactive Mail Access Protocol (IMAP2), defined
in RFC 1064 and later updated by RFC 1176. IMAP2
introduced command/response tagging and was the
first publicly distributed version. - IMAP2bis
- With the advent of MIME, IMAP2 was extended to
support MIME body structures and add mailbox
management functionality (create, delete, rename,
message upload) that was absent in IMAP2. This
experimental revision was called IMAP2bis its
specification was never published in non-draft
form. Early versions of Pine were widely
distributed with IMAP2bis support (Pine 4.00 and
later supports IMAP4rev1). - IMAP4
- An IMAP Working Group formed in the IETF in the
early 1990s and took over responsibility for the
IMAP2bis design. The IMAP WG decided to rename
IMAP2bis to IMAP4 to avoid confusion with a
competing IMAP3 proposal from another group that
never got off the ground.citation needed The
expansion of the IMAP acronym also changed to the
Internet Message Access Protocol. - Some design flaws in the original IMAP4 (defined
by RFC 1730) that came out in implementation
experience led to its revision and replacement by
IMAP4rev1 two years later. There were very few
IMAP4 client or server implementations based on
RFC 1730 due to its short lifetime.
16- IMAP4rev1
- The current version of IMAP since 1996, IMAP
version 4 revision 1 (IMAP4rev1), is defined by
RFC 3501 which revised the earlier RFC 2060. - IMAP4rev1 is backwards compatible with IMAP2 and
IMAP2bis and is largely backwards compatible
with IMAP4. However, the older versions are
either extinct or nearly so. - Unlike many older Internet protocols, IMAP
natively supports encrypted login mechanisms.
While IMAP servers can be configured to permit
plain-text transmission of passwords, RFC 3501
mandates support for authentication methods which
avoid this vulnerability. It is possible to
encrypt IMAP traffic using Transport Layer
Security (SSL), either by tunneling IMAP
communications over SSL on port 993, or by
issuing the STARTTLS command within an
established IMAP session (see RFC 2595). - Advantages over POP
- Connected and disconnected modes of operation
- When using POP, clients typically connect to the
e-mail server briefly, only as long as it takes
to download new messages. When using IMAP4,
clients often stay connected as long as the user
interface is active and download message content
on demand. For users with many or large messages,
this IMAP4 usage pattern can result in faster
response times. - Multiple clients simultaneously connected to the
same mailbox - The POP protocol requires the currently connected
client to be the only client connected to the
mailbox. In contrast, the IMAP protocol
specifically allows simultaneous access by
multiple clients and provides mechanisms for
clients to detect changes made to the mailbox by
other, concurrently connected, clients. - Access to MIME message parts and partial fetch
- Nearly all Internet e-mail is transmitted in MIME
format, allowing messages to have a tree
structure where the leaf nodes are any of a
variety of single part content types and the
non-leaf nodes are any of a variety of multipart
types. The IMAP4 protocol allows clients to
separately retrieve any of the individual MIME
parts and also to retrieve portions of either
individual parts or the entire message. These
mechanisms allow clients to retrieve the text
portion of a message without retrieving attached
files or to stream content as it is being fetched.
17- Message state information
- Through the use of flags defined in the IMAP4
protocol, clients can keep track of message
state for example, whether or not the message
has been read, replied to, or deleted. These
flags are stored on the server, so different
clients accessing the same mailbox at different
times can detect state changes made by other
clients. POP provides no mechanism for clients to
store such state information on the server so if
a single user accesses a mailbox with two
different POP clients, state informationsuch as
whether a message has been accessedcannot be
synchronized between the clients. The IMAP4
protocol supports both pre-defined system flags
and client defined keywords. System flags
indicate state information such as whether a
message has been read. Keywords, which are not
supported by all IMAP servers, allow messages to
be given one or more tags whose meaning is up to
the client. Adding user created tags to messages
is an operation supported by some web-based email
services, such as Gmail. - Multiple mailboxes on the server
- IMAP4 clients can create, rename, and/or delete
mailboxes (usually presented to the user as
folders) on the server, and move messages between
mailboxes. Multiple mailbox support also allows
servers to provide access to shared and public
folders. - Server-side searches
- IMAP4 provides a mechanism for a client to ask
the server to search for messages meeting a
variety of criteria. This mechanism avoids
requiring clients to download every message in
the mailbox in order to perform these searches. - Built-in extension mechanism
- Reflecting the experience of earlier Internet
protocols, IMAP4 defines an explicit mechanism by
which it may be extended. Many extensions to the
base protocol have been proposed and are in
common use. IMAP2bis did not have an extension
mechanism, and POP now has one defined by RFC
2449. - Disadvantages of IMAP
- While IMAP remedies many of the shortcomings of
POP, this inherently introduces additional
complexity. Much of this complexity (e.g.,
multiple clients accessing the same mailbox at
the same time) is compensated for by server-side
workarounds such as maildir or database backends. - Unless the mail store and searching algorithms on
the server are carefully implemented, a client
can potentially consume large amounts of server
resources when searching massive mailboxes. - IMAP4 clients need to maintain a TCP/IP
connection to the IMAP server in order to be
notified of the arrival of new mail. Notification
of mail arrival is done through in-band
signaling, which contributes to the complexity of
client-side IMAP protocol handling somewhat5. A
private proposal, push IMAP, would extend IMAP to
implement push e-mail by sending the entire
message instead of just a notification. However,
push IMAP has not been generally accepted and
current IETF work has addressed the problem in
other ways (see the Lemonade Profile for more
information). - Unlike some proprietary protocols which combine
sending and retrieval operations, sending a
message and saving a copy in a server-side folder
with a base-level IMAP client requires
transmitting the message content twice, once to
SMTP for delivery and a second time to IMAP to
store in a sent mail folder. This is remedied by
a set of extensions defined by the IETF LEMONADE
Working Group for mobile devices URLAUTH (RFC
4467) and CATENATE (RFC 4469) in IMAP and BURL
(RFC 4468) in SMTP-SUBMISSION. POP servers don't
support server-side folders so clients have no
choice but to store sent items on the client.
Many IMAP clients can be configured to store sent
mail in a client-side folder, or to BCC oneself
and then filter the incoming mail instead of
saving a copy in a folder directly. In addition
to the LEMONADE "trio", Courier Mail Server
offers a non-standard method of sending using
IMAP by copying an outgoing message to a
dedicated outbox folder.
18How does a search enginework???????
- Search Engines per definition are information
retrieval system designed to help find
information stored on a computer system. - There are many types of search engines but we
would limit our discussion to web search engines
which search for information on world wide web. - Search engines were begin with an idea to ease
the information finding on the internet. No body
had an idea at that time the way it will turn
internet business. - A search engine consist of three parts
- First part is the spider which is also called the
crawler or bot. This spider part visits a web
page, reads it, and then follows links to other
pages within the site. This process is often
referred to as crawling or spidering. - Crawling of a website is done on a very regular
basis, frequency of which is determined by the
frequency with which website adds the content. It
can vary from once in a month to several times in
a day. - The spiders visit a website following links from
other website or website submission it received. - The content that spider find is sent to its
database or index as it is popularly known. This
index is like a huge book that contains a copy of
web page or cache, that the spider finds out.
This constitutes second part of a search engine. - It also stores the structure and the way pages
are linked to each other. This information would
be updated every time there is a change in
content or linking. - There could be interval between spidering and
indexing which varies from site to site and
engine to engine. But until indexed, the web page
would not be available for the search terms. - Third part of a search engine is search engine
software that works behind the interface when we
use a search engine. This software will sift
through the trillions of indexed pages to match
the search query that user has asked. The pages
are ranked by search engines and the search
results are based on this ranking and relevance
to search term. This is how a search engine
determines what order shall be listed for a
particular search. - Next time you search,just imagine behind the
scene activity.
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