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Topic No. 1
OSI and TCP/IP Model
Deepak Chopade
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Computer Network?
A computer network is a collection of computers and other devices(nodes) that use a common network protocol to share resources
with each other over a network medium.
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Why Computer Network?
To share information or receive a service via a network, groupmembers must be able to communicate with each other
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Communication Model
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Communication Model
Source Generates data to be transmitted
Transmitter Converts data into transmittable signals
Transmission System Carries data
Receiver Converts received signal into data
Destination Takes incoming data
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Classification of Computer Networks
Wired, Wireless and Fiber Optic Networks LANs, MANs and WANs Circuit Switched, Packet Switched and Virtual Circuit Switched
Networks
Access, Distribution and Core Networks
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Classification of Computer Networks
ArchitectureCommon LAN architectures: Ethernet IEEE 802.3, Token
Ring, and FDDI.
Access Possibilitiesshared-media networks
switching networks
Transmission TechnologyBroadcast links
Point-to-point links
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Types of Networks
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Local Area Networks (LANs)
Local Area Networks are privately-owned networks within a small
area, usually a single building or campus of up to a few kilometers.
Since it is restricted in size, that means their data transmission time
can be known in advance, and the network management would be
easier.
LAN characteristics are determined by
Topologies MAC (Medium Access Control)
Transmission media Size of coverage
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LAN
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Various Local Area Networks
A local area network is a small group of interconnected workstations
and associated devices that share the resources within a small
geographic area. Usually, a local area network may serve as few as
several users or many more.
The nowadays main local area network technologies are: Ethernet (Fast Ethernet, Gigabit Ethernet, 10G Ethernet) Hipper LAN Token ring ATM LAN FDDI (Fiber Distributed Data Interface) Wireless LANThere are also some other technologies such as 100VG, token bus
but those are almost obsolete.
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LAN Approaches
There are two methods of networking computers together,
1) Peer-to-Peer2) Client-Server.The proper method to use depends on the requirements.
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Peer-to-Peer Networking
It offers a quick way to tie all your resources and people together.Users can access information from and share it directly with others
in the network. Users can easily share files and directories in a
peer-to-peer network
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Peer-to-Peer Networking
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Client/Server Networking
Clients are connected to a centralized server. The server providescentralized security, backup, and recover capability and controls
access to sensitive files and expensive peripherals. A dedicated
server improves data integrity, because the most current version of
a document will be saved in one location. This type of networkrequires a network operating system.
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Client/Server Model with Dedicated Servers
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Client/Server Model with a General Server
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LAN Selections - Wired
Wired LAN
CSMA/CD
RF modem
Headend
CATVThick-wireThin-wire
Carrier band Coaxial
cable
Twisted pair
Fiber optic
Star
Ring
Bus
Hub/tree
Ap
plication
domains
Universities/hospitals
Office automation
Factory automation
Standards
bodies
Closed systems
ISO
IEEE
NBS
EIAECMA
EIA: Electrical Industries Association (USA)
ECMA: European Computer Manufacturers Association
NBS: National Bureau of Standards
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IEEE LAN Standards 802.1 Higher LAN Protocols 802.2 Logical link control (LLC) 802.3 CSMA/CD (Ethernet) 802.4 Token Bus
802.5 Token Ring 802.6 Metropolitan area network 802.7 Broadband technical advisory 802.8 Fiber optic technical advisory (Obsolete) 802.9 Integrated services LAN 802.10 Interoperable LAN Security
802.11 Wireless LAN 802.12 100 VG-AnyLAN 802.14 Cable-TV based broadband (Obsolete) 802.15 Wireless Personal Area Network 802.16 Broadband Wireless Access (WiMAX)
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LAN
LAYERS
OSI
LAYERS
Logical link control(LLC)Medium access control
(MAC)
Physical (PHY)
Higher layers
Application
Presentation
Session
Transport
Network
Data link
Physical
Layers of LAN and OSI Model
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MAN
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MAN
As we have seen, a local area network covers a room, a building or a
campus.
A metropolitan area network (MAN) covers a city or a region of a city.
A wide area network (WAN) covers multiple cities, states, countries, andeven the solar system.
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Metropolitan Area Network BasicsMANs borrow technologies from LANs and WANs.
MANs support
high-speed disaster recovery systems
real-time transaction backup systems
interconnections between corporate data centers and internet service
providers, and government, business, medicine, and education high-
speed interconnections.
Almost exclusively fiber optic systems
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Metropolitan Area Network BasicsMANs have very high transfer speeds
MANs can recover from network faults very quickly (failover time)
MANs are very often a ring topology (not a star-wired ring)
Some MANs can be provisioned dynamically
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Figure 1-4
WAN
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Wide Area Network Basics
WANs used to be characterized with slow, noisy lines. Today WANs are
very high speed with very low error rates.
WANs often follow a mesh topology.
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Wide Area Network Basics
Astation is a device that interfaces a user to a network.
A node is a device that allows one or more stations to access the physical
network and is a transfer point for passing information through a network.
A node is often a computer, a router, or a telephone switch.
Thesubnet(old terminology) or physical network is the underlying
connection of nodes and telecommunication links.
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WAN
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Why WANs?
Federal Express package routing system.
American Airlines reservation system.
Amazon.com.
Visa International payment process system.
Any application system that is based on the Internet.
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Internet
The Internet is a global system of interconnected computer networks thatuse the standard Internet Protocol Suite (TCP/IP) to serve billions of usersworldwide.
It is a network of networks that consists of millions of private and public,academic, business, and government networks of local to global scope that
are linked by a broad array of electronic and optical networkingtechnologies.
The Internet carries a vast array of information resources and services,most notably the inter-linked hypertext documents of the World Wide Web(WWW)
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Internetwork
(Internet)
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Intranet
An intranet is a private computer network that uses Internet Protocol technologiesto securely share any part of an organization's information or operational systemswithin that organization.
The term is used in contrast to internet, a network between organizations, andinstead refers to a network within an organization.
Sometimes the term refers only to the organization's internal website, but may be amore extensive part of the organization's information technology infrastructure.
It may host multiple private websites and constitute an important component andfocal point of internal communication and collaboration.
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The OSI Model
An ISO (International standard Organization) that covers all aspects ofnetwork communications is the Open System Interconnection (OSI)model.
An open system is a model that allows any two different systems tocommunicate regardless of their underlying architecture (hardware or
software). The OSI model is not a protocol; it is model for understanding and designing
a network architecture that is flexible, robust and interoperable.
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The OSI model is a layered framework for the design of networksystems that allows for communication across all types of computersystems.
The OSI model is built of seven ordered layers:1. (layer 1) physical layer2. (layer 2) data link3. (layer 3) network layer4. (layer 4) transport layer5. (layer 5) session layer6. (layer 6) presentation layer7. (layer 7) application layer
The OSI Model
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Peer-to-Peer Process
Within a single machine, each layer calls upon services of the layerjust below it.
Layer 3, for example, uses the services provided by layer 2 andprovides services for layer 4.
Between machines, layer x on one machine communicates with layer xon another machine, by using a protocol (this is Peer-to-PeerProcess).
Communication between machines is therefore a peer-to-peerprocess using protocols appropriate to a given layer.
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Internet Layers (TCP/IP)
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Interfaces between Layers
There is an interface between each pair of adjacent layers. This interface defines what information and services a layer must
provide for the layer above it.
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Physical Layer
The physical layer coordinates thefunctions required to transmit a bitstream over a physical medium. It
also defines the procedures andfunctions that physical devices
and interfaces have to perform for
transmission occur.
The physical layer is responsible for transmitting individual bits from one node
to the next.
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Physical layer
The physical layer is concerned with the following: Physical characteristics of interfaces and media: The physical layer
defines the characteristics of the interface between devices and thetransmission media, including its type.
Representation of the bits: the physical layer data consist of astream of bits without any interpretation. To be transmitted, bitsmust be encoded into signals electrical or optical-. The physical
layer defines the type ofencoding. Data rate: The physical layer defines the transmission rate, the
number of bits sent each second.
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Physical Layer Line configuration: the physical layer is concerned with the
connection of devices to the medium.
Physical topology Transmission Mode
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Data Link Layer
The data link layer transforms thephysical layer, a raw transmissionfacility, to a reliable link and is
responsible for node-to-nodedelivery. It makes the physical
layer appear error free to theupper layer (network layer).
The data link layer is responsible for transmitting frames from one node
to the next.
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Node-to-node delivery
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Functions of the data link layer
Framing. The data link layer divides the stream of bits received fromthe network layer into data units called frames.
Physical addressing. If frames are to be distributed to differentsystems on the network, the data link layer adds a header to the
frame to define the physical address of the sender (source address)
and/or receiver (destination address) of the frame.
If the frame is intended for a system outside the senders network,the receiver address is the address of the device that connects one
network to the next.
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Flow Control. If the rate at which the data are absorbed by the receiveris less than the rate produced in the sender, the data link layerimposes a flow control mechanism to prevent overwhelming thereceiver.
Error control. The data link layer adds reliability to the physical layerby adding mechanisms to detect and retransmit damaged or lostframes. Error control is normally achieved through a trailer to the end ofthe frame.
Access Control. When two or more devices are connected to the samelink, data link layer protocols are necessary to determine which devicehas control over the link at any time.
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Network Layer
The Network layer is responsible for the source-to-destination delivery of a packetpossible across multiple networks.
If two systems are connected to the same link, there is usually no need for a networklayer. However, if the two systems are attached to different networks, there is often a
need for the network layer to accomplish source-to-destination delivery.
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Network Layer
Functions:
Logical addressing.Routing
The network layer is responsible for the delivery of packets from the original
source to the final destination.
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Source-to-destination delivery
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Logical addressing. The physical addressing implemented by the datalink layer handles the addressing problem locally.
The network layer adds a header to the packet coming from the upperlayer, among other things, includes the logical address of the sender
and receiver.
Routing. When independent networks or links are connected togetherto create an internetwork (a network of networks) or a large network,
the connecting devices (called routers or gateways) route or switch thepackets to their final destination.
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Transport Layer
The transport layer is responsible for process-to-process delivery of theentire message.
The network layer oversees host-to-destination delivery of individualpackets, it does not recognize any relationship between those packets.
The transport layer ensures that the whole message arrives intact and inorder, overseeing both error control and flow control at the process-to-process level.
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Transport layer
The transport layer is responsible for delivery of a message from one process to
another.
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Reliable process-to-process delivery of a message
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Functions of the transport layer
Port addressing:computer often run several processes (running programs)at the same time. Process-to-process delivery means delivery from aspecific process on one computer to a specific process on the other.
The transport layer header include a type of address called port address. The network layer gets each packet to the correct computer; the transport
layer gets the entire message to the correct process on that computer.
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Functions of the transport layer
Segmentation and reassembly: a message is divided intotransmittable segments, each having a sequence number. Thesenumbers enable the transport layer to reassemble the messagecorrectly upon arrival at the destination.
Connection control: The transport layer can be either connectionlessor connection-oriented.
A connectionless transport layer treats each segment as anindependent packet and delivers it to the transport layer at thedestination machine.
A connection-oriented transport layer makes a connection with thetransport layer at the destination machine first before delivering thepackets. After all the data are transferred, the connection is terminated.
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Functions of the transport layer
Flow control: the transport layer performs a flow control end to end.The data link layer performs flow control across a single link.
Error control: the transport layer performs error control end to end.The data link layer performs control across a single link.
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The session layeris the network dialog controller. It was designed toestablish, maintain, and synchronize the interaction between
communicating devices.
The presentation layer was designed to handle the syntax andsemantics of the information exchanged between the two systems. Itwas designed for data translation, encryption, decryption, and
compression.
The application layerenables the user to access the network. Itprovides user interfaces and support for services such electronicemail, remote file access, WWW, and so on.
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Application layer
The application layer is responsible for providing services to the user.
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Summary of duties
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Internet Protocol (V4)
IP Packet Format IP Addressing (Classful) Different Classes of Addressing
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IP Header
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The next section
contains three flags.
The first flag isreserved for future
use and is set to 0.
0 DF MF
0 1 2
DF=0=may fragment
DF=1=dont fragment
MF=0=last fragment
MF=1=more fragments
Fragmentation Flags
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Fragmentation Sample
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1-ICMP,2 -IGMP,6-TCP,17-UDP
IP Header Contd.,
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Every hardware technology specification includes the definition ofthe maximum size of the frame data area called the maximum
transmission unit (MTU)
Any datagram encapsulated in a hardware frame must be smallerthan the MTU for that hardware
Maximum Transmission Unit
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An internet may have networks with different MTUs Suppose downstream network has smaller MTU
than local network?
MTU and Heterogeneous Networks
H1 Net 1 (MTU =1500)
Net 2 (MTU = 1000) H2
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IP Addressing IP addresses are 32 bits long. They are represented as four octets in dotted decimal format.
233.14.17.0
The IP address has two components: The network ID The host ID
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Layer 3 Addresses
Network ID assigned by ARIN
(www.iana.org)
identifies the network to whicha device is attached
may be identified by one, two,or three of the first threeoctets
Host ID assigned by a network
administrator
identifies the specific device onthat network
may be identified by one, two, orthree of the last three octets
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IP addresses are divided into 5 classes, each of which is designatedwith the alphabetic letters A to E.
Class D addresses are used for multicasting.
Class E addresses are reserved for testing & some mysterious futureuse.
IP Address Classes
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32 bit address represented as 8 bit dotted decimals different class addresses reserve different amounts of bits for the network and host
portions of the address
Network & Host RepresentationBy IP Address Class
Class Octet1 Octet2 Octet3 Octet4
Class A Network Host Host Host
Class B Network Network Host Host
Class C
Network
Network Network Host
IP Address Classes
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The 5 IP classes are split up based on the value in the1st octet:
IP Address Classes
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The maximum number of hosts vary for each class.Class A has 16,777,214 available hosts (224 2)Class B has 65,534 available hosts (216 2)
Class C has 254 available hosts (28
2) The first address in each network is reserved for the network address and the
last address is reserved for the broadcast address.
Number of Hosts
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Address Layout
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Class Address or Range StatusA 0.0.0.0
1.0.0.0 through 126.0.0.0127.0.0.0
Reserved
AvailableReserved
B 128.0.0.0
128.1.0.0 through 191.254.0.0
191.255.0.0
Reserved
Available
ReservedC 192.0.0.0
192.0.1.0 through 223.255.254223.255.255.0
Reserved
AvailableReserved
D 224.0.0.0 through 239.255.255.255 Multicast group
addresses
E 240.0.0.0 through 255.255.255.254
255.255.255.255
Reserved
Broadcast
Reserved and Available Address
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Address Class Network Host
10.2.1.1
128.63.2.100
201.222.5.64
192.6.141.2
130.113.64.16
256.241.201.10
A
B
C
C
B
Nonexistent
10.0.0.0
128.63.0.0
201.222.5.0
192.6.141.0
130.113.0.0
0.2.1.1
0.0.2.100
0.0.0.64
0.0.0.2
0.0.64.16
IP Address Class Exercise Answers
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How severe is the IPv4 address depletion
problem?
There is a shortage of available IPv4 addresses in many areas ofthe planet.
Unequal distribution of available IPv4 addresses during the lastdecade
Europe and South America, even if they have been allocated asufficient number of IPv4 addresses, are going to face the same
problem by the time new terminals will join the Internet.
Some examples are: 3rd generation mobile phones, electronicsdevises, sensors, home appliances, transportation vehicles,
airplanes, etc.
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Does IPv6 enhance the Internet security in the
data communications?
RFC2460 Internet Protocol Version 6 Specifications notes thatAuthentication and Encapsulation Security Payload SP
extensions headers should be supported by the IPv6 hosts
The use of the above headers is not compulsory. Similar functionality is supported from IPv4 Security
The avoidance of NAT/PAT in the IPv6 world improve the e2esecurity in data transfers.
Security in the IPv6 networks is questionable not because of theprotocol limitations but due to administrators inexperience.
IPv6 protocols, techniques and transition mechanisms may arisesecurity problems in the future.
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Does End User privacy is in danger in an
IPv6 world?
An IPv6 end systems may automatically create its IPv6 addressbased on its MAC address and the route advertisement.
MAC address is always the same and thus the suffix of the IPv6address remains the same.
RFC3041 Privacy Extensions tries to sort this out allowinghosts to change IPv6 address while connected
The use of IP-based authentication may become tricky. DoS attacks are more difficult to be traced.
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Does IPv6 traffic experience more delays
than IPv4 traffic?
New hardware/software is designed to switch IPv6 packets as fast as IPv4traffic
Obsolete hardware or software could impose performance penalties toIPv6 traffic compared to IPv4 traffic.
The use of tunnels is gradually minimized in the networks leading to moreefficient and stable routing topologies.
More and more dual stack applications are designed to use IPv6 before fallback to IPv4.
Problems may arise if the IPv6 connectivity is broken. QoS Support in IPv6 header
Two header fields; Traffic Class (8-bit) and Flow Label (20-bit) The QoS provisioning means much more than few bits at the IP4/6
packet headers, such as service provisioning, monitoring and SLA/SLSverification, admission control and policy enforcement, etc.
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Is IPv6 technology mature?
Latest operating systems support IPv6 protocols, most ofthem by default.
Network equipment vendors support all the IPv6functionality that is needed for a typical network.
Large scale IPv6 deployments have become a reality. IPv6 services are offered in the telecommunication
market.
Wh IP 6?
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Why IPv6?
(Theoretical Reasons)
Only compelling reason: more IP addresses!
for billions of new users (Japan, China, India,) for billions of new devices (mobile phones, cars, appliances,) for always-on access (cable, xDSL, ethernet-to-the-home,) for applications that are difficult, expensive, or impossible to operate
through NATs (IP telephony, peer-to-peer gaming, home servers,)
to phase out NATs to improve the robustness, security, performance,and manageability of the Internet
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IPv4 Header Details
VersionIndicates the format of the IP header. This field = 4 for IPv4 Header Length-The length of the internet header in 32 bit words, and thus points to the beginning of data. Type of Service-An indication of the abstract parameters of the quality of service desired for the packet. Length-The total length of the datagram, measured in octets, includinginternet header and data. Identification-A value assigned by the sender to aid in reassembling the fragments of a datagram. FlagsVarious control flags. FragOffset-Field indicating where in the datagram this fragment belongs. It is measured in units of 64 bits. Time to LiveField indicating the maximum time the datagram is allowed to remain in the internet system. Protocol-Field indicating the next level protocol used in the data portion of the internet datagram. HDR Checksum-A checksum on the header only. Since some header fields are modified (e.g., time to live), this is
recomputed and verified at each point that the internet header is processed.
Source Address32 bit IPv4 source address. Destination Address32 bit IPv4 destination address. OptionsA variable length grouping of zero or more option values. Padding-This variable length field ensures the internet header ends on a 32 bit boundary. The padding is zero.
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IPv6 Header Details
Version4-bit Internet Protocol version number = 6. Traffic Class-8-bit traffic class field. Flow Label-20-bit flow label. Payload Length-16-bit unsigned integer. Length of the
IPv6 payload, i.e., the rest of the packet following the
IPv6 header, in octets.
Next Header8-bit selector. Identifies the type ofheader immediately following the IPv6 header. Uses the
same values as the IPv4 Protocol field [RFC-1700 et
seq.].
Hop Limit-8-bit unsigned integer. Decremented by 1 byeach node that forwards the packet. The packet isdiscarded if Hop Limit is decremented to zero.
Source Address128-bit address of the originator ofthe packet.
Destination Address128-bit address of the intendedrecipient of the packet (possibly not the ultimate
recipient, if a Routing header is present)
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IPv6 Header compared to IPv4 Header
Ver."
Time to"Live"
Source Address"
Total Length"Type of"Service"Hdr"Len"Identification" Fragment"Offset"Flg"
Protocol" Header"Checksum"
Destination Address"Options..."
Ver." Traffic"Class"
Source Address"
Payload Length" Next"Header" Hop"Limit"
Destination Address"
Hdr"Len"
Identification" Fragment"Offset"Flg"Header"
Checksum"
Options..."
shaded fields have no equivalent in the"
other version"IPv6 header is twice as long (40 bytes) as"IPv4 header without options (20 bytes)"
Flow Label"Flow Label"
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IPv6 Address Representation
Preferred Form Compressed Form Mixed Form
Preferred Form x:x:x:x:x:x:x:x
'x'sare the hexadecimal values of the eight 16-bit pieces of the
address.
It is not necessary to place leading zeros in a field. Examples:
FEDC:BA98:7654:3210:FEDC:BA98:7654:3210
1080:0:0:0:8:800:200C:417A
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Compressed Form x:x::x:x
The use of "::" indicates one or more groups of 16 bits of zeros.
The "::" can only appear once in an address. Examples:
1080:0:0:0:8:800:200C:417A = 1080::8:800:200C:417A
0:0:0:0:0:0:0:1 = ::1
Mixed Form x:x:x:x:x:x:d.d.d.d
xsare the hexadecimal values of the six high-order 16-bit pieces of theaddress.
dsare the decimal values of the four low-order 8-bit pieces of the address
(standard IPv4 representation). Examples:
0:0:0:0:0:0:13.1.68.3
0:0:0:0:0:FFFF:129.144.52.38
IPv6 Address Representation
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Thank You
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