4.0 Network System Communication

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4.0 Network System Communication
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4.1 Data Frame (Ethernet Frame)
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• Preamble purposed for synchronization the
  frame reception portions of all stations on LAN.
• Destination address address of receiver
  (consist of 2 addresses MAC address and IP
  address)
• Source address address of sender
• ( unicast address)
• Type specifies the upper layer protocol to
  receive the data after Ethernet processing is
  completed.
• Data
• FCS contains 4-byte CRC (cyclical redundant
  check) value that is created by the sending
  device and is recalculated by the receiving
  device to check for damaged frame.

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Ethernet frame.

• Frames are the format of data packets on the
  wire.
• Types of Ethernet frame
• - Original Ethernet Version I (no longer
  used)
• - The Ethernet Version 2 or Ethernet
  II frame, known as
• DIX frame (named after DEC, Intel,
  and Xerox), often used
• directly by the Internet Protocol.
• - Novell's homegrown Variation of IEEE
  802.3 ("raw 802.3
• frame") without LLC
• - IEEE 802.2 LLC frame
• - IEEE 802.2 LLC/SNAP frame
• In addition, Ethernet frames may optionally
  contain a IEEE 802.1Q tag to identify what VLAN
  it belongs to and its IEEE 802.1p priority
  (quality of service). This doubles the potential
  number of frame types.
• The different frame types have different formats
  and MTU values, but it can coexist on the same
  physical medium.
•  

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The specifications of sections in the Ethernet
Frames.

• Basic Ethernet frame forms.

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• Frame Header SectionIn a data packet sent
  through the internet, the data (payload) are
  preceded by header information such as the
  sender's and the recipient's IP addresses, the
  protocol governing the format of the payload and
  several other formats. The header's format is
  specified in the Internet Protocol. Frame check
  sequence (FCS)
• A frame check sequence (FCS) refers to the extra
  checksum characters added to a Frame in a
  communication protocol for error detection and
  correction.

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• The sending host computes a checksum on the
  entire frame and sends this along. The receiving
  host computes the checksum on the frame using the
  same algorithm, and compares it to the received
  FCS. This way it can detect whether any data was
  lost on altered in transit. It may then discard
  the data, and request retransmission of the
  faulty frame. A cyclic redundancy check is often
  used to compute the FCS.

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Address Resolution Protocol (ARP)

• Three types of address information are used on
  TCP/IP internetworks
• Physical addresses. Used by the Data Link and
  Physical layers.
• IP addresses. Provide logical network and host
  IDs. IP addresses consist of four numbers
  typically expressed in dotted-decimal form. An
  example of an IP address is 134.135.100.13.
• Logical node names. Identify specific hosts with
  alphanumeric identifiers, which are easier for
  users to recall than the numeric IP addresses. An
  example of a logical node name is MYHOST.COM.

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• Given a logical node name, the Address Resolution
  
• Protocol (ARP) can determine the IP address
• associated with that name. ARP maintains tables
  of
• address resolution data and can broadcast
• packets to discover addresses on the
  internetwork.
• The IP addresses discovered by ARP can be
• provided to Data Link layer protocols. 

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4.2 Open Systems Interconnection reference Model
(OSI)

• The OSI model divides the functions of a protocol
  into a series of layers.
• Each layer has the property that it only uses
  the functions of the layer below, and only
  exports functionality to the layer above.
• A system that implements protocol behavior
  consisting of a series of these layers is known
  as a 'protocol stack' or 'stack'.
• Protocol stacks can be implemented either in
  hardware or software, or a mixture of both.
• Typically, only the lower layers are implemented
  in hardware, with the higher layers being
  implemented in software.

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• Osi Model Figure.

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• Physical layer Layer 1 The physical layer
  defines all electrical and physical
  specifications for devices.
• This includes the layout of pins, voltages, and
  cable specifications. Hubs and repeaters are
  physical-layer devices.
• The major functions and services performed by the
  physical layer are
• establishment and termination of a connection to
  a communications medium.
• participation in the process whereby the
  communication resources are effectively shared
  among multiple users. For example, contention
  resolution and flow control.
• modulation, or conversion between the
  representation of digital data in user equipment
  and the corresponding signals transmitted over a
  communications channel. These are signals
  operating over the physical cabling -- copper and
  fibre optic, for example. SCSI operates at this
  level.

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• Data link layer Layer 2 The Data link layer
  provides the functional and procedural,
• - means to transfer data between network
  entities and to detect and possibly correct
  errors that may occur in the Physical layer.
• The addressing scheme is physical which means
  that the addresses are hard-coded into the
  network cards at the time of manufacture.
• The addressing scheme is flat. Note The best
  known example of this is Ethernet.
• Other examples of data link protocols are HDLC
  and ADCCP for point-to-point or packet-switched
  networks and LLC and Aloha for local area
  networks.
• This is the layer at which bridges and switches
  operate.
• Connectivity is provided only among locally
  attached network nodes.

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• Network layer Layer 3 The Network layer provides
  the functional and procedural
• - means of transferring variable length data
  sequences from a source to a destination via one
  or more networks while maintaining the quality of
  service requested by the Transport layer.
• The Network layer performs network routing, flow
  control, segmentation/desegmentation, and error
  control functions.
• The router operates at this layer -- sending data
  throughout the extended network and making the
  Internet possible, although there are layer 3 (or
  IP) switches.
• This is a logical addressing scheme - values are
  chosen by the network engineer.
• The addressing scheme is hierarchical.

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• Transport layer Layer 4 The purpose of the
  Transport layer is to provide transparent
  transfer of data between end users
• - thus relieving the upper layers from any
  concern with providing reliable and
  cost-effective data transfer.
• The transport layer controls the reliability of a
  given link.
• Some protocols are stateful and connection
  oriented.
• This means that the transport layer can keep
  track of the packets and retransmit those that
  fail.
• The best known example of a layer 4 protocol is
  TCP.

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• Session layer Layer 5 The Session layer provides
  the mechanism for managing the dialogue between
  end-user application processes.
• It provides for either duplex or half-duplex
  operation and establishes checkpointing,
  adjournment, termination, and restart procedures.
  
• This layer is responsible for setting up and
  tearing down TCP/IP sessions.

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• Presentation layer Layer 6 The Presentation
  layer relieves the Application layer of concern
  regarding syntactical differences in data
  representation within the end-user systems.
• MIME encoding, encryption and similar
  manipulation of the presentation of data is done
  at this layer.
• An example of a presentation service would be the
  conversion of an EBCDIC-coded text file to an
  ASCII-coded file.

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• Application layer Layer 7, the highest layer
  This layer interfaces directly to and performs
  common application services for the application
  processes.
• The common application services provide semantic
  conversion between associated application
  processes.
• Examples of common application services include
  the virtual file, virtual terminal (for example,
  Telnet), and "Job transfer and Manipulation
  protocol" (JTM, standard ISO/IEC 8832).

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The connection between OSI model the protocol

• Above illustrates the origin of the term protocol
  stack.
• Each layer represents a category of related
  tasks.
• A protocol stack is an implementation of this
  layered protocol architecture.
• The protocols and services associated with the
  protocol stack interact to prepare, transmit, and
  receive network data.

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• Two computers must run compatible protocol stacks
  before they can communicate because each layer in
  one computers protocol stack must interact with
  a corresponding layer in the other computers
  protocol stack.

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• The FIGURE, for example, shows the path of a
  message that starts in the Transport layer.
• The message travels down the protocol stack,
  through the network medium, and up the protocol
  stack of the receiving computer.
• If the Transport layer in the receiving computer
  understands the protocols used in the Transport
  layer that originated the message, the message
  can be delivered.

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The concept of layered protocol.

• To communicate with its peer layer in another
  computer, each protocol layer adds its own
  information to the message being sent.

• Headers are added as the message is prepared for
  transmission, and headers are removed (stripped)
  by the receiving computer after the information
  in the header has been utilized.
• NOTE
• The Physical layer does not append a header
  because this layer deals with sending and
  receiving information on the individual bit
  level. The bits are assembled into longer message
  units in the Data Link layer.
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• Each protocol layer, except the Physical layer,
  adds a header to the frame.

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TCP / IP

• Also called internet protocol suite which it is
  the set of communications protocols that
  implement the protocol stack on which the
  Internet runs
• TCP/IP working each other together and provide
  the basis for much of the Internet.

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• A combination of two individual protocols
• TCP and IP.
• IP is a layer 3 protocol a connectionless
  service that provides best-effort (nonreliable)
  delivery across a network.
• TCP is a layer 4 protocol a connection-oriented
  service that provides flow control as well as
  reliability.
• Combination of two protocols (TCP IP) enables
  them to provide a wider range of services.

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Application File transfer, e-mail, remote login, network management, name management
Transport TCP, UDP
Network IPv4, IPv6, ICMP, ARP, IGMP,
Data Link Ethernet, Wi-Fi, Token ring, FDDI, PPP, ISDN,GPRS,HDLC,WiMAX
Physical Modem, STP, Twisted pair, FOC, SONET
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TCP/IP vs OSI

• The OSI model - lower layers - needs to be an
  extra layer (the Internetworking layer) between
  the Transport and Network layers.
• The top three layers of the OSI model
  (Application, Presentation and Session) -
  considered as a single Application Layer in the
  TCP/IP suite.
• TCP/IP integrates a few steps of the OSI model
  into its Application layer.
• The TCP/IP suite protocols as developed earlier
  than OSI reference model by DARPA (Defense
  Advanced Research Projects Agency) for
  internetwork communications and serves as the
  transport protocols for the internet

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TCP/IP OSI
Application (layer 7) HTTP, FTP, DNS Telnet, HTTP
4 Transport TCP, UDP, RTP, SCTP TCP, UDP,SPX
3 Network For TCP/IP this is the Internet Protocol (IP) IP, IPX
2 Data Link Ethernet, Token ring Ethernet, HDLC
1 Physical physical media, and encoding techniques, T1, E1 Physical media
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Internet Architecture
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Internet Address

• An IP address (Internet Protocol address) is a
  unique number, similar in concept to a telephone
  number, used by machines (usually computers) to
  refer to each other when sending information
  through the Internet

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IP address

• Represented by a 32-bit binary number written as
  four octets

Octet (8 bits) ? Octet (8 bits) ? Octet (8
bits) ? Octet (8 bits) 27262524232120 ?
27262524232120 ? 27262524232120 ?
27262524232120 11000000 ? 00000101 ?
00100010 ? 00001011 EQUALS 192 ? 5 ? 34 ?
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• The maximum decimal value of each octet is 255.
• The largest 8-bit binary number is 11111111.
• Those bits, from left to right, have decimal
  values of 128, 64, 32, 16, 8, 4, 2, 1. Added,
  they total 255.

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IP addressing format

• An IP address has a network number and a host
  number, and uses dotted-decimal notation.

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IP address classes

• The network number of IP address identifies the
  
• network to which a device is attached .
• The host portion of IP address identifies a
  specific
• device on a network.

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Class A

• Support extremely large networks
• First octet of Class A IP address recognize with
  range 1 to 126. (127 does start with a 0 bit, but
  it has been reserved for special purposes.
• The first bit of class A address always 0 in
  binary format.
• Class A IP addresses use only the first 8 bits (1
  octet) to identify the network part of the
  address.

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• The remaining three octets (24 bit) can be used
  for the host portion of the address.
• Every network that uses a Class A IP address can
  be assigned up to 224 2 possible IP addresses
  to devices attached to the network.
• Example of Class A IP address 124.95.44.15

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Class B

• Support the needs of moderate to large sized
  networks.
• The first 2 bits of Class B IP address are always
  10 (1 and 0)
• The first two octets identify the network number
  assigned by ISP.
• Class B IP network addresses always have values
  ranging from 128.0.0.0 to 191.255.0.0.

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• Class B IP addresses use the first 16 bits (2
  octets) to identify the network part of the
  address.
• The two remaining octets of the IP address can be
  used for the host portion of the address.
• Every network that uses a Class B IP address can
  have assigned up to 216 2 possible IP addresses
  to devices attached to the network.
• Example of Class B IP address 151.10.13.28

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Class C

• Most commonly used of the original IPv4 address
  classes.
• This address space was intended to support a
  small network.
• The first 3 bits of a Class C address are always
  110 (1,1,and 0).
• The first three octets identify the network
  number assigned by ISP.
• Class C IP network addresses always have values
  ranging from 192.0.0.0 to 223.255.255.0

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• Class C IP addresses use the first 24 bits (3
  octets) to identify the network part of the
  address.
• Only the last octet of a Class C IP address can
  be used for the host portion of the address.
• Every network that uses a Class C IP address can
  have assigned up to 28 2 possible IP addresses
  to devices attached to the network
• Example of a Class C IP address 201.110.213.28

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Subnet

• Network administrators sometimes need to divide
  networks, especially large ones, into smaller
  networks.
• These smaller divisions are called subnetworks
  and provide addressing flexibility.
• The concept of subnetting is based on the need
  for the third level in the Internets addressing
  hierarchy.
• A primary reason for using subnets is to reduce
  the size of a broadcast domain.
• Subnet addresses includes the network number,
  subnet number and host number.

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Subnetworks

• subnet addresses include the class A , class B,
  or class C network portion, plus a subnet field
  and a host field.
• The subnet field and the host field are created
  from the original host portion for the entire
  network.
• To create a subnet address, a network
  administrator borrows bits from the original host
  portion and designates them as the subnet field.
• The minimum number can be borrowed is 2.

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