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Theory & Applications

Internet Applications

- Ibrahim Otieno -

[email protected]

+254-0722-429297

SCI/ICT Building 2nd Floor Rm. 201

Communication Communication ProtocolsProtocols

Networking h/w without software is useless

Software for network systems are necessary as part of solution to communication problems

Normally large and very complicated

Most networking software structured into layers for modularity, each with a specific function

Layering is a structuring technique to organize networking software design and implementation

Why Network software?Why Network software?

Sending data through raw hardware is complex

Equivalent to accessing files by making calls to disk controller to position read/write head and accessing individual sectors

Network software provides interface to applications and hides the intricacies involved in sending information to a remote destination

Why network software?Why network software? Networks (devices) need some protocol in

order to communicate and understand each other

Protocols implemented by protocol software

Computer communication complicated problem

Network solution may require multiple protocols, each managing a part of the problem

Protocols may be simple or complex, but all work together.

Why network software?Why network software? Designers analyze communication problem,

divide into sub-problems then design a protocol for each sub-problem

Well-designed protocol suite:◦ efficient and effective – no redundancy, use of

resources◦ allows replacement of individual protocols

without changes to other protocols

Layering model is a solution to the problem of complexity in network protocols

Model suggests dividing network protocol into layers, each solving part of comm. problem

Layers have constraints that ease design

ISO OSI Reference Model ISO OSI Reference Model Group called ISO introduced OSI

Model

OSI model - layered network architecture, with goal of standardization of network protocols

OSI model an open system architecture because it connects systems open for communications with other systems

Systems don’t have to be from same vendor or have the same O/S

The Seven-Layer OSI The Seven-Layer OSI ModelModel

OSI model is composed of seven layers that define functions of communication protocols

Each layer represents function performed on transfer of data between two applications

A layer doesn’t have to define a single protocol;

Defines function performed by any number of protocols

ISO OSI Reference Model ISO OSI Reference Model

Layers were defined with the following in mind:

◦ Created where different level of abstraction is needed

◦ Each layer performs a well-defined function

◦ Function of each layer should be chosen with the goal of defining standardized protocols

◦ Boundaries defined to minimize info flow across interfaces

◦ Number of layers large enough for distinct functions but small enough that the architecture not unwieldy


Related modules at same level are called a protocol stack or a stack

Two constraints to be observed: ◦ Each layer depends on services by

lower layers◦

◦ Layer n of destination receives same message sent by layer n of sender


ISO OSI Reference Model ISO OSI Reference Model Application Layer

Provides end-user service like file transfer/e-mailUsers interacts with this layer

Presentation LayerControls how data is representedData compression and decompressionPerforms data manipulation functions

Session LayerManages the process-to-process communication sessions between hostsEstablishes and terminates connections

Transport LayerEnd-to-end error detection and correctionGuarantees application receive same data sent

ISO OSI Reference Model ISO OSI Reference Model Network Layer

Manages network connections, packet routing between source and destination as well as network congestion

Data Link LayerProvides reliable data delivery across networkDoesn’t assume underlying network is reliable

Physical LayerTransmits and receives raw bits over a physical communication channel e.g. ethernetHas knowledge of voltage levels and of the pin connections to the physical hardware media

TCP/IP and the OSI TCP/IP and the OSI Model Model

TCP/IP suite composed TCP, IP & other protocols

Others include UDP, ICMP, ARP, FTP, HTTP

Sometimes referred as "Internet protocol suite"

IP is unreliable n/w-layer protocol that moves data between host

TCP &UDP are transport protocols - provide end-to-end delivery between endpoints of a connection

Transport protocols use IP to provide data delivery for application protocols

TCP/IP and the OSI TCP/IP and the OSI ModelModel

User Datagram Protocol (UDP) Simple transport-layer protocol, faster,

less reliable

Delivers independent datagrams between applications by use of headers with 3 parts: port no, message length & checksum

Uses "best effort'' delivery - datagrams may be lost, delivered out of order, etc.

Checksum guarantees integrity of data delivered

Unlike TCP, UDP is not 'receipted’


TCP is the most widely reliable transport-layer protocol

TCP moves data between applications with no losses, duplication or errors

Compensates for loss, delay, duplication etc

TCP – connection-oriented: application requests connection to destination and uses it to transfer data


TCP/IP doesn’t directly follow OSI model OSI model driven by a International Standards TCP/IP driven by need of US govt Some say TCP/IP isn’t a very “pure”

architecture


Application Layer Consists of applications that make use of

network e.g. file-transfer utility Application and presentation layers of OSI

model fit into this layer - compression & decompression

Transport layer absorbed this layer, however, still consider its function as a logical layer

Transport Layer Provides end-to-end data delivery OSI’s session & transport layers fit into this

layer Uses sockets - end-point of communication

composed of address and port on computer TCP provides for reliable data delivery

TCP/IP and the OSI TCP/IP and the OSI ModelModelInternet Layer

Defines datagram & handles routing and delivery

Datagram contains the source & destination address, data, as well as other control fields

OSI’s network and data link layers fit into this layer

IP is analogous to the network layer Data link layer usually not represented but IP

could be used to support this function

Physical Layer TCP/IP makes no effort to define the underlying

network physical connectivity, instead, makes use of existing standards such as (IEEE)


Movement of data through TCP/IP layers

Internet ProtocolInternet Protocol

What is the difference between a repeater, bridge and a router ?

What is the role of a router in internetworking?

Internet is a virtual network created by software?

Addresses for the Virtual Addresses for the Virtual InternetInternet

Goal of internetworking to provide a seamless communication system

Achieved by IP software hiding physical details of n/w and provide large virtual network (VN)

VN operate like normal n/w, computers send & receive packets of data

Difference between internet and physical network is that internet is an abstraction created entirely by software


Designers free to choose addresses, packet formats and delivery techniques independent of the physical hardware

All host computers use a uniform addressing scheme and each address must be unique to have illusion of single system

Physical network addresses not used because an internet can have different technologies with different addressing formats


Protocol s/w defines uniform addressing scheme independent of underlying physical address

Sender places destination’s address in packet and passes packet to protocol software for delivery

Software uses destination protocol address to forward the packet to the destination computer

Uniform address create illusion of large seamless network hiding details of physical addresses

Applications communicate without knowing their hardware addresses

IP Addressing SchemeIP Addressing Scheme TCP/IP addressing is specified by

Internet Protocol

IP standard specifies that each computer assigned unique 32-bit number known as the IP address

Each packet sent across the internet has IP address of both sender and the destination host

To transmit data,computer must know IP address of remote computer to which data is being sent

The IP Address The IP Address HierarchyHierarchy

IP address divided into prefix and suffix Prefix identifies the physical network

computer is attached and suffix identifies a particular computer on the network

No two networks assigned the same number and no two computers on same network can have the same number

IP address hierarchy guarantees two properties

◦ Each computer is assigned a unique address

◦ Although network number assignments coordinated globally, suffixes can be assigned locally without global coordination.

Classes of IP AddressesClasses of IP Addresses Prefix of IP address need sufficient bits to

allow a unique no. to be assigned to each network

Suffix needs sufficient bits to permit each computer to be assigned a unique number

Large prefix accommodates many networks, but limits size of each network and vice versa

Internet can consist of few large or many small networks or contain mixture of large & small networks

Consequently, the designers chose a compromise addressing scheme that can accommodate large and small networks.

Classes of IP Addresses Classes of IP Addresses ……

Original scheme, divides IP address space into 3 primary classes, each with different size prefix/suffix

First 4 bits determine class to which the address belongs, and specifies how the remainder is divided into prefix and suffix:

◦ Class A – First bit 0 used for class identification, prefix consists of next 7 and rest 24 for suffix

◦ Class B – First 2 bits start with 10 (class identification) prefix consists of next 14 and rest 16 for suffix

◦ Class C – First 3 bits start with 110 (class identification) prefix consists of next 21 and rest 8 for suffix

◦ Class D – First 4 bits start with 1110 (class identification) and rest used as multicast address

◦ Class E – First 4 bits start with 1111 used for class identification, and rest reserved for future use


Figure 2.the mapping between the first four bits of an IP address and the class of the address. The mapping was used with the original classful scheme.


Dotted Decimal Notation Users seldom use 32-bit binary IP address no Instead, software uses a notation that is more

convenient to understand: dotted decimal notation

Expresses each 8-bit section of a 32-bit number as decimal value and uses . to separate sections

Figure 2.2 illustrates examples of binary numbers and their equivalent dotted decimal forms.

Division of address Division of address SpaceSpace Class scheme does not divide 32-bit address

space into equal size classes, and the classes don’t contain same no. of networks

For example, half of all the IP addresses (those in which the first bit is zero) lie in class A

Surprisingly, class A can contain only 128 networks because first bit of class A address must be 0 and prefix occupies 8 bits

Thus only 7 bits remain to use for numbering class A networks

Routers and IP Routers and IP Addressing Addressing

The IP protocol specifies that routers be given IP addresses as well

Each router assigned two or more IP addresses

To understand why, recall two facts:◦ Router has connections to multiple

networks◦ Each IP address contains a prefix

that specifies a physical n/w

Routers and IP Routers and IP Addressing Addressing A single IP address does not suffice for

a router because each router connects multiple networks

This is the fundamental principle of IP addresses:

◦ An IP address does not identify a specific computer

◦ Instead, each IP address identifies a connection between a computer and a network

◦ Computer with multiple network connections (e.g. router) must be assigned one IP address for each connection

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