Transcript Internet services

Networks - Internet services
• Internet is a global public communication system. It
accommodates many various user services referred as
Internet services.
• The most frequently used Internet services:
– Internet Electronic Mail Service
– Remote access to file systems and file transfer service
– Remote session service - remote terminal
– Web system service
– Peer-to-peer interactive communication service (ICQ,
Skype ….)
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Internet Access
• The user shares with many other users Internet services which are
offered by local LAN servers or by remote servers.
• Two ways which perform users connections to the Internet
– Through LAN where each computer within has its own IP address
and one (or more) domain names. A LAN is usually connected to the
Internet by a leased high-speed line entering to the LAN border router.
– Through ISP Access Network. ISP (Internet Service Provider) is
usually an owner of high-speed lines (a telecommunication provider).
ISP (Internet service provider) is a company that provides
individuals and small companies broadband access to the Internet and
other related services such as Web hosting and Mail service.
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Characteristics of networks LAN and WAN
• The small (home/office ) „SOHO“ LAN network has typically
few computers. The small LAN is usually connected to Internet
through ISP network called „Autonomous System“ (AS).
• The larger LAN (Campus LAN or Enterprise LAN) covers the
campus area or several buildings. It can accommodate many
thousands of computers. The large LAN is usually connected to
Internet by the leased high-speed link.
• The ISP backbone (WAN network) is the telecommunications
network. It is the high speed, high capacity, long-distance
communications system
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ISP has the network that consists of access networks and the
backbone. ISP backbone is connected by the border router with
other ISP networks.
ISP access networks – “The last mile” networks connect the user-end
modem to the POP which is located in the backbone of ISP network.
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• ISP side - POP (point-of-presence) access point to the Internet. A POP
necessarily has a unique IP address
(Internet Protocol Address)
• Client side – a modem
(modulator/demodulator) is a
communication device that converts
digital signals from computer into
analogue signals for conventional
lines. There are various types of
modems designed for specific lines
(DSL, TV cable, modems for wireless
connection ….)
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• The access network provides the end users access
to Internet from a single home computer or from a
very small home network or office network.
• The connection to the Internet may be or
permanent connection (broadband access) or dialup connection.
• The broadband access technologies implement
usually an asymmetrical load system. An
asymmetrical system is that in which the data
speed or quantity differs in one direction with the
other direction, averaged over time.
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Data Transmission Methods
• Asymmetrical data flow can make more efficient use of
the available infrastructure than symmetrical data flow,
in which the speed of data is the same in both directions.
• In the term of asymmetric system we use the terms
“upstream speed” or “uplink speed” (in the direction
from the user-end) and “downstream speed” or
“downlink speed” (the direction towards the user-end).
• The downstream speed is usually twice or more higher
then upstream speed.
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Internet Access Technologies
• The types of broadband access technologies
– Wireless (FWA - Fixed Wireless Access or WiMAX –
Worldwide Interoperability for Microwave Access) – radio
waves are transmit from POP transmission device to userend receiving device (i.e. the antenna system)
– ADSL (Asymmetric Digital Subscriber Line) – transmission
media is an existing telephone line that is shared by voice
signal and data signal (from user-end computer)
– CATV (Cable TV) - the transmission media is an existing
TV cable that is shared by TV signal and data signal (from
user-end computer)
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The network requirements common to all
broadband technologies are:
– The ability to support modern voice, data and
multimedia communications over a diverse
topology.
– The ability to extend existing networks and
create new ones quickly, economically with
minimal infrastructure requirements.
– The ability to deliver carrier-class quality and
reliability with minimal maintenance
requirements.
– The ability to support mobile data and voice
devices.
– The ability to support low-cost customer
premises equipment (CPE).
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Principle of ADSL
DSL Access Multiplexor
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Principle of CATV
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Principle of FWA (Fixed Wireless Access)
• An alternative to copper- or cable-based highspeed access
• Systems utilize a small microwave antenna that is
attached to a radio system at the customer
premises
• The CPE (Customer Premises Equipment) is
pointed back to the ISPs AP (Access Point ) typically a tall building or radio tower
• Both point-to-point and point-to-multipoint
systems, operating in licensed as well as
unlicensed bands (Wi-Fi) are available
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Principle of WiMAX
• WiMAX (Worldwide Interoperability for Microwave Access) is a
telecommunications technology that provides wireless transmission of data
using a variety of transmission modes, from point-to-multipoint links to
portable and fully mobile internet access.
• The technology provides up to 1 Gbit/s broadband speed without the need for
cables.
• The technology is based on the IEEE 802.16 standard (also called Broadband
Wireless Access).
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Principles of Internet services
• The most of Internet services is based on the principle
Client/Server.
• Client/Server describes the relationship between two computer
programs in which one program, the client, makes a service
request from another program, the server performs the request.
– The „client side“ is usually implemented in a program running
on the user´s PC
– The „server side“ is implemented in a program running on a
common enterprise computer (often called „the server“)
• Typically, multiple client programs share the services of a
common server program.
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• The different way of communications is Peer-to-Peer
communications model
– Each party has the same capabilities
– Either party can initiate a communication session.
• Both sides of peer-to-peer communication model are
implemented in the similar programs running on remote
computers
• The typical Internet service which is based on the peerto-peer model is ICQ (I seek you)
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• The primary network architecture of Internet is a TCP/IP
protocol suite
• The key concepts of Internet services are:
– TCP (Transmission Control Protocol) for controlled transmission
of data packets
– IP (Internet Protocol) for addressing of Internet nodes and
provision of the routes across the Internet
– DNS (Domain Name System) for enabling us to use for
specification of Internet nodes rather the domain names instead of
numeric IP addresses
– URL (Uniform Resource Locator) for addressing of WWW
documents and other Internet resources (for example mail service,
file transfer service, etc….)
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• The URL contains the name of the protocol required to access the
resource, a domain name that identifies a specific computer on the
Internet, and a pathname (hierarchical description of a file location)
on the computer.
• On the WWW which uses the HTTP (Hypertext Transfer Protocol),
an example of a URL is http://www.ietf.org/rfc/rfc2396.txt
• A URL for a program such as a script written in program language
Perl is
http://whatis.com/cgi-bin/comments.pl
• A URL for a file meant to be downloaded would require that the "ftp"
protocol be specified like this one
ftp://www.somecompany.com/whitepapers/widgets.ps
• A URL for a mail service requested for to send message to the user
specific address is
mailto:[email protected]
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Electronic Mail System
• SMTP (Simple Mail Transfer Protocol) provides mail message
exchange between SMTP client and server
• POP (Post Office Protocol) and IMAP (Internet Message Access
Protocol) protocols provide the access to the mailboxes from
remote stations
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File Transfer Service
• FTP (File Transfer Protocol) is used to transfer files
between computers on a network
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Remote session (remote terminal)
• Protocol TELNET
• Protocol SSH (Secure Shell) – secure version of the
remote session
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Internet Web system
• HTTP (Hypertext Transfer Protocol) is the set of rules
for transferring files (text, graphic images, sound,
video, and other multimedia files) on the World Wide
Web.
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