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Basic Infrastructure for Electronic Business on the Internet. Authors: Miroslava Mitrovic ( Veljko Milutinovic ( Network. A network is a group of computers and peripherals connected together by some medium The connection can be

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Basic infrastructure for electronic business on the internet

Basic Infrastructure for Electronic Business on the Internet


Miroslava Mitrovic (

Veljko Milutinovic (


  • A network is

    a group of computers and peripherals

    connected together by some medium

  • The connection can be

    direct (through a cable) or

    indirect (through a modem)

  • The different devices on the network

    communicate with each other

    through a predefined set of rules (protocol)

Network hardware
Network Hardware

  • Physically connects

    computers in the network together

  • Main hardware components:


    Communication equipment

    Additional components



  • Network node (computer, printers, routers)

  • Computers in network

    can be used as

    work stations or servers or both

  • PC computers need

    NIC (Network Interface Card)

    to be able to be part of

    LAN (Local Area Network)

  • Different standards, different network cards! (Ethernet, Token Ring, ARC net)

Communication equipment
Communication equipment

  • Cables :

    (coaxial cables, fiber-optic cables, twisted pairs)

  • Wiring centers :

    (HUB , concentrator,

    MAU (Multi station Access Units))

  • Intranetwork links :

    (connectors, transceivers, repeaters)

  • Internetwork links :

    (bridges, gateways, routers, switches)

  • Wireless components

Additional components
Additional Components

  • Peripherals :

    (printers, fax machines, modems, cd readers)

  • Safety devices :

    UPS (Uninterruptible Power Supply),

    SPS (Standby Power Supply)

  • Network tools


  • Defines rules for connecting network nodes

  • Logical topology differs from physical topology!

  • Logical topology defines rules for

    transmitting information's (bus, ring, star)

  • Physical topology defines rules for

    electrical connection components in network

Network software
Network Software

  • Enables using hardware

    for communication and exchanging information

  • Protocols (set of rules) give formulas

    for passing messages,

    specifying the details of message formats,

    and for describing how to handle error conditions


  • Connecting many disparate physical networks

    and make them function

    as a coordinate unit

  • Internet technology hides

    the details of network hardware and

    permits computers to communicate

    independent of their physical network connection


  • Internet is network of all networks

  • Interconnected computer networks

    that communicate,

    usually via TCP/IP

  • Internet and internet

  • Set of application programs

    that use the network to carry out

    useful communication tasks (user’s point of view)

  • No one owns the Internet!

Internet architecture
Internet architecture

  • How are networks interconnected

    to form a internet work?

  • Computers that interconnect two networks

    and pass packets from one to the other

    are called internet gateways or internet routers

Internet architecture3
Internet architecture

  • Gateways provide all interconnections

    among physical networks

  • Usually minicomputers

  • Gateways route packets based on destination network, not on destination host!

Open systems
Open Systems

  • Architecture is not secret

  • The definition applies equally well

    to software and hardware

  • UNIX-classic example for

    an open software platform

  • Open system networking:

    network based on well-known and

    understood protocol

  • Three most popular services:

    File Transfer

    Electronic mail

    Remote login

Basic infrastructure for electronic business on the internet
The ISO OSI-RMInternational Organization for StandardizationOpen System Interconnection Reference Model

  • ISO has developed an architecture that defines seven layers of network protocol

Upper layers application presentation session
Upper Layers Application/Presentation/Session

  • Applications oriented

  • Presents the interface to the user

  • Don’t care how data gets to the application!

Middle layer transport
Middle LayerTransport

  • Separate application oriented upper layers from network oriented lower layers

Lower layers network data link physical
Lower LayersNetwork/Data Link/Physical

  • Oriented toward data transmission

  • Packages, routes, verifies and transmits datagrams

  • Type of data for application doesn't matter

  • Has no application dependencies !

Application layer
Application Layer

  • Highest layer in the OSI reference model

  • Concerned with the user’s view of the network

  • Handles network transparency, resource allocation and problem partitioning

  • Sends data and program tasks

    to the presentation layer,

    which is responsible

    for coding data from application layer

    in the appropriate form

Presentation layer
Presentation Layer

  • The second highest layer in the OSI reference model

  • Converts network data to application format

  • Performs function as

    text compression , code or format conversion

    to try to smooth out differences between hosts

  • Serves application layer, uses session layer

Session layer
Session Layer

  • The third highest layer in the OSI reference model

  • Synchronized data exchange

    between upper and lower layers

  • Manages the current connection, or session, between two computers

  • Handles security and creation of the session

  • Establishing connection

  • Closes connection

  • Uses the transport layer to establish a connection between processes on different hosts

  • Used by the presentation layer

Transport layer
Transport Layer

  • The middle layer in the OSI reference model

  • Uses the network layer to provide a

    virtual, error-free, point-to-point connection

    so that host A can send messages to host B

    and they will arrive uncorrupted and in the correct order

  • Hides details necessary to actually

    make a connection between two computers

  • Establishes and dissolves connections between hosts

  • Used by the session layer

Network layer
Network Layer

  • The third lowest layer in the OSI reference model

  • Determines addresses

  • Responsible for routing packets across the network

  • Establishing logical link between two nodes

  • Used by the transport layer, uses the data link layer

Data link layer
Data Link Layer

  • The second lowest layer in the OSI reference model

  • Splits data into frames for sending

    on the physical layer

  • Receives acknowledgment frames

  • Performs error checking and retransmission

  • Provides an error free virtual channel

    to the network layer

  • Split into

    an upper sublayer Logical Link Control (LLC)

    and lower sublayer Media Access Control (MAC)

Physical layer
Physical Layer

  • The lowest layer in OSI model

  • Transmits data

  • How bits are passed over the network medium,

    what control signals are used,

    and the mechanical properties of the network itself (cable size, connector, and so on)

  • Only layer in which actual communication occur

  • Used by the data link layer

The tcp ip protocol family






















The TCP/IP protocol family


  • Transmission Control Protocol (TCP):

    connection-based services

  • User Datagram Protocol (UDP):

    connectionless services


  • Internet Protocol (IP):

    handles transmission of information

  • Internet Control Message Protocol (ICMP):

    handles status messages for IP

  • Routing Information Protocol (RIP):

    determines routing

  • Open Shortest Path First (OSPF):

    alternate protocol for determining routing

Network addresses
Network Addresses

  • Address Resolution Protocol (ARP):

    determines addresses

  • Domain Name System (DNS):

    determines addresses from machine names

  • Reverse Address Resolution Protocol (RARP): - determines addresses

User services
User Services

  • Boot Protocol (BOOTP):

    starts up a network machine

  • File Transfer Protocol (FTP):

    transfers files

  • Telnet:

    allows remote logins

Gateway protocols
Gateway Protocols

  • Exterior Gateway Protocol (EGP):

    transfers routing information for external networks

  • Gateway-to-Gateway Protocol (GGP):

    transfers routing information between gateways

  • Interior Gateway Protocol (IGP):

    transfers routing information for internal networks

  • Border Gateway Protocol (BGP)

    newer than EGP, used within an autonomous network


  • Network File System (NFS):

    enables directories on one machine to be mounted on another

  • Network Information Service (NIS):

    maintains user accounts across networks

  • Remote Procedure Call (RPC):

    enables remote applications to communicate

  • Simple Mail Transfer Protocol (SMTP):

    transfers electronic mail

  • Simple Network Management Protocol (SNMP): sends status messages about the network


  • Basic unit of data send thought an internet

  • Moving packets between routers and/or hosts

  • Consists of a header followed by the data

  • Header:

    information necessary to move the packet

    across the Internet

  • Connectionless transport mechanism





The version of the IP protocol that created the datagram.


The length of the IP header in 32-bit words (the minimum value is 5).

Type of service

The quality of service (precedence, delay, throughput, and reliability) desired for the datagram.

Total length

The length of the datagram (both header and user data), in octets.


A 16-bit value assigned by the originator of the datagram, used during reassembly.




Control bits indicating whether the datagram may be fragmented, and if so, whether other later fragments exist.

Fragment offset

The offset in the original datagram of the data being carried in this datagram, for fragmented datagrams.

Time to live

The time in seconds the datagram is allowed to remain in the internet system.


The high level protocol used to create the message (analogous to the type field in an Ethernet packet).

Header checksum

A checksum of the header.



Source IP address

32-bit IP address of the sender.

Destination IP address

32-bit IP address of the recipient.


An optional field primarily used for network testing or debugging.


All bits set to zero - used to pad the datagram header to a length that is a multiple of 32 bits.

User data

The actual data being sent.


Internet addresses
Internet Addresses

  • Globally accepted method of identifying computers

  • Each host on a TCP/IP internet is assigned

    a unique 32-bit address that is used

    in all communication with that host

  • Must not be confused with physical addresses!

  • Each address is a pair (netid, hostid),

    where netid identifies a network,

    and hostid identifies a host on that network

  • In practice, each IP address must have

    one of the first three forms shown

    in the picture that follows

Internet addresses1


Maximum number ofpossible networks

Maximum number ofhosts per network











Reserved Class


Reserved Class

Internet Addresses

Internet addresses3
Internet Addresses

  • The IP address is expressed

    in dotteddecimalnotation (DDN)

    by taking the 32 binary bits and

    forming 4 groups of 8 bits, each separated by a dot

    • is a class A address

    • 10 is the DDN assigned network number

    • .4.8 are (possibly) user assigned subnet numbers

    • .2 is the user assigned host number

    • is a class B address

    • 172.16 is the DDN assigned network number

    • .9 is the user assigned subnet number

    • .190 is the user assigned host number

Internet addresses4
Internet Addresses

  • Host: any attached device on a subnet,

    including PC’s, mainframes and routers

  • Most hosts are connected to only one network,

    and they have a single IP address

  • Routers are connected to more than one network and they can have multiple IP addresses

  • Problem: IP type of addressing defines connection,

    not host!

  • Problem: what when an organization

    which has a class C address

    finds that they (.org) need to upgrade to class B

Dns the domain name system
DNS – The Domain Name System

  • Converts symbolic node name to IP address

  • Uses distributed database

  • Network Information Center (NIC) maintains names

    and network gateway addresses

  • Name Resolver on each network

    tries to complete address from own database

  • Examines Name Server for full NIC database

    if unsuccessful resolution

Arp address resolution protocol
ARP - Address Resolution Protocol

  • Allows host to find

    the physical address of a target host

    on the same physical network,

    given only the target’s IP address

  • It does this by sending out an ARP broadcast packet containing both the source

    and destination IP address

  • The broadcast is media-dependant

  • For Ethernet LANs the broadcast address

    is a packet whose destination address bits are all `1'

Arp address resolution protocol1
ARP - Address Resolution Protocol

  • All stations on the LAN receive this address,

    but only one host is able to recognize

    its own IP address

  • It replies, thereby giving the original host

    its physical address.

Rarp reverse address resolution protocol
RARP - Reverse Address Resolution Protocol

  • How does the diskless machine,

    one without access to secondary storage,

    determines its IP address at system startup?

  • A diskless machine uses RARP to obtain

    its IP address from a server

Ip internet protocol
IP - Internet Protocol

  • Defines unreliable, connectionless delivery mechanism

  • IP provides three important definitions:

    - Defines the basic unit of data transfer

    used throughout a TCP/IP internet

    - Performs routing function,

    choosing a path over which data will be sent

    - Includes a set of rules that embody

    the idea of unreliable packet delivery

Icmp internet control message protocol
ICMP - Internet Control Message Protocol

  • Integral part of IP

  • Allows gateways to send error or control messages

    to other gateways or hosts

  • Provides communication between

    the Internet Protocol software on one machine

    and the Internet Protocol Software on another

  • Only reports error conditions to the original source!

  • ICMP message is encapsuled in an IP datagram

Basic infrastructure for electronic business on the internet




Echo Reply


Destination Not Reachable


Source Quench


Redirection Required


Echo Request


Time to Live Exceeded


Parameter Problem


Timestamp Request


Timestamp Reply


Information Request (now obsolete)


Information Reply (now obsolete)


Address Mask Request


Address Mask Reply

Type field

Udp user datagram protocol
UDP - User Datagram Protocol

  • Connectionless protocol

  • Provides the primary mechanism that application programs use to send datagrams

    to other application programs

  • Provides protocol ports used to

    distinguish among multiple programs

    executing on a single machine

  • Uses IP to transport a message

    from one machine to another

  • Does not use acknowledgements to make sure messages arrive

  • UDP message is called a user datagram

Udp user datagram protocol2
UDP - User Datagram Protocol

  • Source port:

    An optional field with the port number

    If a port number is not specified, the field is set to 0

  • Destination port:

    The port on the destination machine

  • Length:

    The length of the datagram,

    including header and data

  • Checksum:

    A 16-bit one's complement

    of the one's complement sum of the datagram,

    including a pseudo header similar to that of TCP

Udp user datagram protocol3
UDP - User Datagram Protocol

Conceptual Layering

Tcp transmission control protocol
TCP - Transmission Control Protocol

  • TCP is a communication protocol,

    not a piece of software!

  • Provides reliable stream service

  • Positive acknowledgement with retransmission

  • Specifies the format of the data and acknowledgements that two computers exchange

    to achieve a reliable transfer

  • Specifies the procedures the computers use

    to ensure that the data arrives correctly

  • Specifies how TCP software distinguishes

    among multiple destinations on given machine

  • Specifies how communicating machines recover

    from errors like lost or duplicated packets

Tcp transmission control protocol1
TCP - Transmission Control Protocol

  • Specifies how two computers initiate

    a TCP stream transfer and

    how they agree when it is complete

  • Does not dictate the details of the interface

    between an application program and TCP

  • Does not specify the exact application programs

    to access these operations

  • Reason: flexibility

  • TCP uses the connection, not the protocol port,

    as its fundamental abstraction

  • Connections are identified by a pair of endpoints

Tcp transmission control protocol2
TCP - Transmission Control Protocol

  • TCP port number can be shared

    by a multiple connection on the same machine

  • The basic unit of transfer used by TCP is a segment

  • Segments are used

    to pass control information or data

Tcp transmission control protocol3
TCP - Transmission Control Protocol

Server Site

Network Messages

Receiver Site

Send Packet 1

Receive Packet 1

Send ACK 1

Receive ACK1

Send Packet 2

Receive Packet 2

Send ACK2

Receive ACK2

Sender awaits an acknowledgement for each packet sent

Tcp transmission control protocol4
TCP - Transmission Control Protocol

Network Messages

Receiver Site

Server Site

Packet lost

Send Packet1

Start Timer

Packet should arrive

ACK should be sent

ACK would normally

Arrive at this time

Timer Expires

Retransmit Packet1

Start Timer

Receive Packet1

Send ACK1

Receive ACK1

Cancel Timer

Timeout and retransmission that occurs when a packet is lost

Tcp transmission control protocol5
TCP - Transmission Control Protocol

  • A simple positive acknowledgement protocol

    wastes a substantial amount of network bandwidth

  • Delays sending a new packet until it receives

    an acknowledgement for the previous packet

  • Sliding window protocol

  • Keeps the network completely saturated with packets

  • Higher throughput than

    a simple positive acknowledgment protocol

Tcp transmission control protocol6
TCP - Transmission Control Protocol

Sender Site

Network Messages

Receiver Site

Send Packet1

Send Packet2

Receive Packet1

Send ACK1

Send Packet3

Receive Packet2

Send ACK2

Receive ACK1

Receive ACK2

Receive Packet3

Send ACK3

Receive ACK3

Three packet transmitted using a sliding window protocol

Telnet remote login protocol
Telnet – remote login protocol

  • Allows user at one site

    to establish a TCP connection

    to a login server at another site,

    and then it passes keystrokes

    from the user’s terminal

    directly to the remote machine

    as if they had been typed at

    a terminal on the remote machine

  • Carries output from the remote machine

    back to the user’s terminal

Telnet remote login protocol1
Telnet – remote login protocol

  • The service is called transparent

  • Telnet client software

  • User specifies a remote machine

    either by giving its domain name or IP address

  • Telnet offers three basic services

  • Defines a network virtual terminal (NVT)

  • Includes a mechanism that allows

    the client and server to negotiate options

  • Treats both ends of the connection symmetrically

Telnet remote login protocol2
Telnet – remote login protocol

server sends to

pseudo terminal

client reads

from terminal

client sends

to server

server receives

from terminal

Ftp file transfer protocol
FTP – File Transfer Protocol

  • Manages files across machines

    without remote Telnet session

  • Transfers files, manages directories, accesses e-mail

  • Does not enable access

    to remote machine for program execution

  • Uses two channels

    for simultaneous transfer

    of commands and data

  • Conducts all transfers in foreground

  • Does not use queues or spoolers

    so you are watching the transfer process in real time

Ftp file transfer protocol1
FTP – File Transfer Protocol

  • Relies on TCP to provide connection management

  • Protocol Interpreter PI transfers instructions

    using TCP port 21

  • Data Transfer Process DTP transfers files

    using TCP port 20

Ftp file transfer protocol2
FTP – File Transfer Protocol

FTP channel connections

Ftp file transfer protocol3
FTP – File Transfer Protocol

  • Login

    Verifies user ID and password

    Anonymous FTP allows access without login account

    Access and file transfer requires

    proper permissions on the remote side

  • Define directory

    Identifies starting directory

    Local and remote file system

  • Define File Transfer Mode

    Text uses ASCII characters separated by CR and NL

    Binary transfers without conversion or formatting

Ftp file transfer protocol4
FTP – File Transfer Protocol

  • Start Data Transfer

    Enables user commands

  • Stop Data Transfer

    Closes connection

Tftp trivial file transfer protocol
TFTP – Trivial File Transfer Protocol

  • Does not log on to remote machine

  • Uses UDP connectionless transport

    TFTP transfer identifiers (TID’s)

    set ends of connection

    Support basic error messages

    Any kind of error can result in transfer failure

  • Uses to boot diskless terminals and load applications

    Small executable size and memory requirements

    Cannot execute FTP until loaded with OS

  • Lax access regulations pose security risks

Electronic mail
Electronic Mail

  • The most widely used application service

  • Differs fundamentally from other uses of network

  • Usually timeout and retransmission

    if no acknowledgement

  • Sender don’t want to wait for

    the remote machine to become available

    before continuing work!

  • User don't want to have transfer abort merely because communication with the remote machine becomes temporary unavailable!

  • Spooling

Smtp simple mail transfer protocol
SMTP - Simple Mail Transfer Protocol

  • Standard for the exchange of mail

    between machines

  • Focuses specifically on

    how the underlying mail delivery system

    passes messages across a link

    from one machine to another

  • Messages transferred as 7-bit ASCII

  • Uses spools or queues

  • Does not specify

    how the mail system accepts mail from a user

    or how the user interface presents the user

    with incoming mail

Smtp simple mail transfer protocol1
SMTP - Simple Mail Transfer Protocol

  • Does not specify

    how mail is stored or

    how frequently the mail system

    attempts to send messages

  • Mail command identifies sender and provides message information

  • Response is acknowledgment with identification of recipient

Example of smtp transfer
Example of SMTP Transfer

S: 220 Simple Mail Transfer Service Ready


S: 250


S: 250 OK

C: RCPT TO: <>

S: 550 No such user here

Example of smtp transfer1
Example of SMTP Transfer

C: RCPT TO: <>

S: 250 OK


S: 354 Start mail input; end with <CR><LF>.<CR><LF>

C: …sends body of mail message…

C: …continues for as many lines as message contains

C: <CR><LF>. <CR><LF>

S: 250 OK


S: 221 Service closing transmission channel


  • The Internet Unleashed, SAMS Publishing

  • Internetworking With TCP/IP, Douglas Comer

  • Teach yourself TCP/IP in 14 days, Tim Parker

  • Novell’s Complete Encyclopedia of Networking, Werner Feibel