Basic Infrastructure for Electronic Business on the Internet

1
Basic Infrastructure for Electronic Business on
the Internet

• Authors
• Miroslava Mitrovic (mirka_at_galeb.etf.bg.ac.yu)
• Veljko Milutinovic (vm_at_galeb.etf.bg.ac.yu)

2
Network

• 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)

3
(No Transcript)
4
Network Hardware

• Physically connects
• computers in the network together
• Main hardware components
• Nodes
• Communication equipment
• Additional components
• Topology

5
Nodes

• 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)

6
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

7
Additional Components

• Peripherals
• (printers, fax machines, modems, cd readers)
• Safety devices
• UPS (Uninterruptible Power Supply),
• SPS (Standby Power Supply)
• Network tools

8
Topology

• 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

9
Topology
10
Topology
11
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

12
Internetting

• 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

13
Internetting
14
Internet

• 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 (users point of
  view)
• No one owns the Internet!

15
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

16
Internet architecture
17
Internet architecture
18
Internet architecture

• Gateways provide all interconnections
• among physical networks
• Usually minicomputers
• Gateways route packets based on destination
  network, not on destination host!

19
Internet architecture
20
Internet architecture
21
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

22
The ISO OSI-RMInternational Organization for
StandardizationOpen System Interconnection
Reference Model

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

23
Grouping of OSI Layers
24
Upper Layers Application/Presentation/Session

• Applications oriented
• Presents the interface to the user
• Dont care how data gets to the application!

25
Middle LayerTransport

• Separate application oriented upper layers from
  network oriented lower layers

26
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 !

27
Communication in OSI-RM
28
Application Layer

• Highest layer in the OSI reference model
• Concerned with the users 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

29
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

30
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

31
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

32
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

33
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)

34
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

35
Data Transfer over the Internet
36
OSI vs. TCP/IP
37
The TCP/IP protocol family

• TCP
• UDP
• IP
• ICMP
• RIP
• OSPF
• ARP
• DNS
• RARP
• BOOTP

• FTP
• Telnet
• EGP
• GGP
• IGP
• BGP
• NFS
• NIS
• RPC
• SMTP
• SNMP

38
Transport

• Transmission Control Protocol (TCP)
• connection-based services
• User Datagram Protocol (UDP)
• connectionless services

39
Routing

• 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

40
Network Addresses

• Address Resolution Protocol (ARP)
• determines addresses
• Domain Name System (DNS)
• determines addresses from machine names
• Reverse Address Resolution Protocol (RARP) -
  determines addresses

41
User Services

• Boot Protocol (BOOTP)
• starts up a network machine
• File Transfer Protocol (FTP)
• transfers files
• Telnet
• allows remote logins

42
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

43
Others

• 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

44
Datagram

• 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

45
Datagram
46
Datagram
47
Datagram
48
Datagram
49
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

50
Internet Addresses
51
Internet Addresses
52
Internet Addresses

• The IP address is expressed
• in dotted decimal notation (DDN)
• by taking the 32 binary bits and
• forming 4 groups of 8 bits, each separated by a
  dot
• 10.4.8.2 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
• 172.16.9.190 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

53
Internet Addresses

• Host any attached device on a subnet,
• including PCs, 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

54
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

55
ARP - Address Resolution Protocol

• Allows host to find
• the physical address of a target host
• on the same physical network,
• given only the targets 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'

56
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.

57
ARP - Address Resolution Protocol
58
ARP - Address Resolution Protocol
59
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

60
RARP - Reverse Address Resolution Protocol
61
RARP - Reverse Address Resolution Protocol
62
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

63
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

64
ICMP-The Internet Control Message Protocol
65
ICMP-The Internet Control Message Protocol
66
Type field
67
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

68
UDP - User Datagram Protocol
69
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
  

70
UDP - User Datagram Protocol
Conceptual Layering
71
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

72
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

73
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

74
TCP - Transmission Control Protocol
Server Site
Receiver Site
Network Messages
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
75
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
76
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

77
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
78
TCP - Transmission Control Protocol
Conceptual Layering
79
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 users 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 users terminal

80
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

81
Telnet remote login protocol
server sends to pseudo terminal
client reads from terminal
client sends to server
server receives from terminal
82
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

83
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

84
FTP File Transfer Protocol
FTP channel connections
85
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

86
FTP File Transfer Protocol

• Start Data Transfer
• Enables user commands
• Stop Data Transfer
• Closes connection

87
TFTP Trivial File Transfer Protocol

• Does not log on to remote machine
• Uses UDP connectionless transport
• TFTP transfer identifiers (TIDs)
• 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

88
Electronic Mail

• The most widely used application service
• Differs fundamentally from other uses of network
• Usually timeout and retransmission
• if no acknowledgement
• Sender dont 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

89
Conceptual components of an electronic mail system
90
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

91
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

92
Example of SMTP Transfer

• S 220 Beta.gov Simple Mail Transfer Service
  Ready
• C HELO Alpha.edu
• S 250 Beta.gov
• C MAIL FROM ltSmith_at_Alpha.edugt
• S 250 OK
• C RCPT TO ltGreen_at_Beta.govgt
• S 550 No such user here

93
Example of SMTP Transfer

• C RCPT TO ltBrown_at_Beta.govgt
• S 250 OK
• C DATA
• S 354 Start mail input end with
  ltCRgtltLFgt.ltCRgtltLFgt
• C sends body of mail message
• C continues for as many lines as message
  contains
• C ltCRgtltLFgt. ltCRgtltLFgt
• S 250 OK
• C QUIT
• S 221 Beta.gov Service closing transmission
  channel

94
References

• The Internet Unleashed, SAMS Publishing
• Internetworking With TCP/IP, Douglas Comer
• Teach yourself TCP/IP in 14 days, Tim Parker
• Novells Complete Encyclopedia of Networking,
  Werner Feibel
• http//www.ieee-occs.org

95
Conclusion