1. OSI and TCP Model

8/6/2019 1. OSI and TCP Model

1/92

Topic No. 1

OSI and TCP/IP Model

Deepak Chopade


2/92

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.


3/92

Why Computer Network?

To share information or receive a service via a network, groupmembers must be able to communicate with each other


4/92

Communication Model


5/92

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


6/92

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


7/92

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


8/92

Types of Networks


9/92

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


10/92

LAN


11/92


12/92

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.


13/92

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.


14/92

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


15/92

Peer-to-Peer Networking


16/92

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.


17/92

Client/Server Model with Dedicated Servers


18/92

Client/Server Model with a General Server


19/92

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


20/92

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)


21/92

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


22/92

MAN


23/92

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.


24/92

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


25/92

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


26/92

Figure 1-4

WAN


27/92

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.


28/92

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.


29/92

WAN


30/92


31/92

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.


32/92

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)


33/92

Internetwork

(Internet)


34/92

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.


35/92

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.


36/92

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


37/92


38/92

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.


39/92

Internet Layers (TCP/IP)


40/92

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.


41/92

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.


42/92

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.


43/92

Physical Layer Line configuration: the physical layer is concerned with the

connection of devices to the medium.

Physical topology Transmission Mode


44/92

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.


45/92

Node-to-node delivery


46/92

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.


47/92


48/92

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.


49/92

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.


50/92

Network Layer

Functions:

Logical addressing.Routing

The network layer is responsible for the delivery of packets from the original

source to the final destination.


51/92

Source-to-destination delivery


52/92

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.


53/92


54/92

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.


55/92

Transport layer

The transport layer is responsible for delivery of a message from one process to

another.


56/92

Reliable process-to-process delivery of a message


57/92

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.


58/92


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.


59/92


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.


60/92


61/92

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.


62/92

Application layer

The application layer is responsible for providing services to the user.


63/92

Summary of duties


64/92

Internet Protocol (V4)

IP Packet Format IP Addressing (Classful) Different Classes of Addressing


65/92

IP Header


66/92

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


67/92

Fragmentation Sample


68/92

1-ICMP,2 -IGMP,6-TCP,17-UDP

IP Header Contd.,


69/92

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


70/92

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


71/92

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


72/92

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


73/92

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


74/92

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


75/92

The 5 IP classes are split up based on the value in the1st octet:

IP Address Classes


76/92

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


77/92

Address Layout


78/92

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


79/92

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


80/92


81/92

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.


82/92

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.


83/92

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.


84/92

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.


85/92

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?


86/92

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


87/92

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.


88/92

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)


89/92

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"


90/92

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


91/92

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


92/92

Thank You

Documents

1. OSI and TCP Model