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I. Introduction to Networking

A computer network is a group of computer systems and other computing devices that are connected

by a physical communication medium such as:

wire,

radio wave, or

light beam.

Computer networks are commonly used to facilitate:

communication and

resource-sharing among a wide range of computing devices.

Computer networking is an active and rapidly changing field.

Companies continue to create commercial networking products and services, often by using technologies

in new unconventional ways.

Many technologies exist, and each one has features that distinguish it from the others.

There is no underlying theory that explains the relationship among all the parts of a network.

Corporate marketing groups often associate a product with a generic technical term or invent new terms

just to distinguish their products or services from those of competitors.

I.1 Key Aspects of Networking

The five key aspects of networking follow:

a. Network applications and network programming.

b. Data communications.

c. Packet switching and networking technologies.

d. Internetworking with TCP/IP.

e. Additional networking concepts and technologies.

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A. Network Applications and Network Programming

Network application services include the following:

Email,

File upload or download,

Web browsing,

Audio and voice telephone calls,

Distributed database access, and

Video teleconferencing.

These services are each provided by application software:

An application program running on one computer communicates across a network with an application

program running on another computer.

Programmers who design and write network applications need to learn about the network interface and a

basic set of functions which are used in all application programs that communicate over a network.

B. Data Communications

Data communications are about low-level mechanisms and technologies used to send information across

a physical communication medium such as a wire, radio wave, or light beam.

These low-level mechanisms and technologies use the physical properties of the communication media to

transfer information and primarily fall in the domain of Electrical Engineering.

However, data communications provide a foundation of concepts over which the rest of networking is

built.

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C. Packet Switching and Networking Technologies

The packet switching technology allows multiple senders (computers) to transmit data over a shared

network.

The data to be sent is subdivided into small blocks called packets that also include the identification

of the intended receiver of these packets.

The maximum size of a packet depends on the packet switching technology. But a common

maximum packet size is 1500 bytes.

Statistical Multiplexing

A packet switching network uses statistical multiplexing to send the packets from multiple sources

on the same communication medium at the same time. That means:

Packets from multiple sources are sent one after another on the same communication medium

and,

the system allows other senders to transmit some of their packets before the first sender can

transmit the next packet.

Characteristic of a Packet Switching Network

A packet switching network has the following characteristics:

Arbitrary, asynchronous communication:

It allows a sender to communicate with more than one recipient.

A given recipient can receive messages from more than one sender.

The sender can generate and send data at any time, and

A sender can delay arbitrary long time between two messages.

Connectionless communication service:

The sender does not need to pre-establish communication before sending data.

It does not need to inform the network when a communication terminates.

Performance varies due to statistical multiplexing among packets:

A packet switching network is designed in such a way that each sender sharing a network has

a fair share of the communication medium.

That means, if N senders have packets ready to send, a given sender should be able to transmit

1/N of all packets.

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Local, Metropolitan, and Wide Area Packet Switching Networks

Packet switching networks are commonly classified according to the distance that they span as

follows:

Local Area Network (LAN):

A local area network (LAN) is a computer network that interconnects computers within a

limited area such as a residence, school, laboratory, university campus or office building and has

its network equipment and interconnects locally managed.

A LAN is referred to as a multi-access network because computers on a LAN share a

communication medium in such a way that any computer can communicate with any other.

Professionals usually say that LANs connect computers, with the understanding that a device

such as a printer can also connect to a LAN.

The most widely used standards for LANs have been created by the Project 802 LAN/WAN

Standards Committee of the Institute for Electrical and Electronics Engineers (IEEE).

LAN standards are assigned the identifiers 802.1, 802.2, . . . etc.

Metropolitan Area Network (MAN):

Spans a major city (is moderately expensive).

Few MAN technologies have been created and MAN networks have not been commercially

successful.

Wide Area Network (WAN):

A wide area network (WAN) covers a larger geographic distance, and also generally involves

leased telecommunication circuits or Internet links.

Ethernet and Wi-Fi are the two most common transmission technologies in use for local area

networks.

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Ethernet

The Ethernet is a family of computer networking technologies commonly used in wired local area

networks (LAN).

It was commercially introduced in 1980 and first standardized by IEEE in 1983 as IEEE 802.3.

A computer is connected to a wired LAN by a network interface controller (NIC).

Wi-Fi

Wi-Fi or WiFi is a technology for wireless local area networking with devices based on the IEEE

802.11 standards.

Devices that can use Wi-Fi technology include

personal computers,

video-game consoles,

smartphones,

digital cameras,

tablet computers,

smart TVs,

digital audio/video players and

modern printers

To connect to a Wi-Fi LAN, a computer has to be equipped with a wireless network interface

controller.

The combination of computer and interface controller is called a station.

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Network Interface Controller (NIC) and Media Access Control (MAC) Address

A network interface controller (NIC), also known as a network interface card, network adapter,

LAN adapter or physical network interface, is a computer hardware component that connects a

computer to a computer network.

The NIC allows computers to communicate over a computer network, either by using cables.

It does the following:

Connect to a network.

Handle the details of data communication such as sending and receiving frames.

Handle address recognition.

Perform the Cycle Redundancy Check (CRC) computation for error correction of the data.

Handle frame recognition (check the destination address on a frame and ignore frames that are not

destined for the computer).

The media access control (MAC) address (also referred to as the Ethernet address) of a computer

is the 48-bit address that is assigned to the NIC of that computer.

The standard (IEEE 802) format for printing a MAC address in human-friendly form is a group of 6

bytes (in hexadecimal) separated by hyphens.

Examples: 01-23-45-67-89-AB and 48-2C-6A-1E-59-3D

Every NIC is assigned a unique 48-bit MAC address as follows:

The left-most group of 3 bytes (in hexadecimal) is assigned by IEEE and is used to identify the

manufacturer of the NIC.

It is referred to as the Organizationally Unique Identifier (OUI).

The right-most group of 3 byte (in hexadecimal) is assigned by the manufacturer to identify a

particular NIC.

Examples:

MAC Address OUI NIC identification

01-23-45-67-89-AB 01-23-45 67-89-AB

48-2E-6C-1A-59-3D 48-2E-6C 1E-59-3D

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An Ethernet network controller typically has an 8P8C (8 position 8 contact) socket where the network cable is connected.

Older NICs also supplied BNC, or AUI connections.

A few LEDs inform the user of whether the network is active, and whether or not data transmission occurs.

Ethernet network controllers typically support 10 Mbit/s Ethernet, 100 Mbit/s Ethernet, and 1000 Mbit/s Ethernet

varieties.

Such controllers are designated as "10/100/1000", meaning that they can support a notional maximum transfer rate of 10,

100 or 1000 Mbit/s.

10 Gigabit Ethernet NICs are also available, and, as of November 2014, are beginning to be available on computer

motherboards.

A Qlogic QLE3442-CU SFP+ dual port NIC

An 8P8C modular plug before being crimped onto a cable Connector and cable

Wireless Network Interface Controller (WNIC)

A wireless network interface controller (WNIC) is a network interface controller which connects

to a wireless radio-based computer network, rather than a wired network.

This card uses an antenna to communicate via microwave radiation.

Early wireless network interface controllers were commonly implemented on expansion cards that

plugged into a computer bus.

Newer mobile computers have a wireless network interface built into the motherboard.

You may also use a wireless network interface device with a USB interface and internal antenna on

communication devices that do not come with a WNIC.

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D. Internetworking with TCP/IP

Internetwork

An internetwork or internet consists of two or more networks (with possible different networking

technologies) connected to one another by using a computing device called a router.

A router contains a processor, a memory, and a separate NIC for each network connection:

The router in the figure that follows must have at least two NICs.

Internet with two networks

Network 1 Network 2

The network treats a connection to a router in the same way that it treats a connection to any other

computer.

The goal of internetworking is to provide a packet communication system that allows a program

running on one computer to send data to a program running on anther computer:

These programs are unaware of the underlying physical networks. That means that:

They can send and receive data without knowing the following:

the details of the local network to which the source computer is connected

the remote network to which the destination computer is connected, or

the interconnection between the two networks (that means the presence of the router).

The Internet software provide the appearance of a single, seamless communication system to which

each computer is attached:

Each computer is assigned an address (which is different from the MAC address), and any

computer can send a packet to any other computer using its address.

The Internet protocol software hides the details of physical network connections, physical

addresses, and routing information.

router

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Network Protocols

Basic communication hardware consists of mechanisms that transfer bits of information from one

computer to another.

However, computers attached to a network or an internet must use network software to provide an

interface between application programs and the hardware.

Application programs rely on network software to communicate; they do not interact with the

network hardware directly.

Computer 1 Computer 2

For a communication to be successful, all entities in a network must agree on how information will

be represented and communicated. For example:

At the hardware level, when two computers communicate over a wired network, they must agree

on:

o The voltages to be used,

o The exact way that electrical signals are used to represent data,

o The procedures used to initiate and conduct communication.

At the application level, there may be an agreement that text files must be transferred in ASCII or

that they should be encrypted using a given encryption formula.

For a communication to be successful there must also be a specification of the appropriate action to

take for each abnormal condition such as when an error or an unexpected condition occurs.

These sets of rules are known as computer communication protocol or network protocol.

Network protocols and the network hardware and software that implement the protocols are

organized in layers.

Application program Application program

Network Software Network Software

Communication Hardware

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Each protocol belongs to one of the layers and

Each layer provides its service by performing certain actions within the layer and by using the

services of the layer directly below it.

A protocol layer can be implemented in software, in hardware, or in a combination of the two.

The collection of protocols that corresponds to a layering model is referred to as protocol suite,

protocol stack, or protocol family.

Each protocol in a suite solves one part of the communication problem, and together, they solve the

entire communication problem.

In the early days of networking, each manufacturer used to develop its own networking protocols and

systems for identifying and locating computers on a network.

However, these protocols and systems were all incompatible: a computer on a network was not able

to communicate with a computer on a different network.

To address this incompatibility issue, two network protocol reference models were developed in

order to provide a common blueprint from which software and hardware developers can work:

The internet protocol suite that resulted from research and development conducted by the Defense

Advanced Research Projects Agency (DARPA) in the late 1960, and

The Open Systems Interconnection (OSI) reference model developed by the International

Organization for Standardization (ISO).

Although the OSI reference model was developed after the Internet Protocol suite, it has never been

implemented by software and hardware developers.

Communication Services on an Internet

Communication services on an internet can be connection-oriented, connectionless, or both.

In a connection-oriented communication service,

An application must first request a connection to a destination, and then use that connection to

transfer data.

It must also close the connection after the transfer of data is complete.

In a connectionless communication service,

A sender transmits individual packets of data (that contains the address of the intended recipient)

across the internet.

Each packet travels independently to get to the intended recipient.

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TCP/IP Protocol Suite and the Internet

TCP/IP (Transfer Control Protocol/ Internet protocol) is the most commonly used protocol suite

used for internets.

The fundamental delivery service of TCP/IP internets is connectionless.

However, a connection-oriented communication service that uses the underlying connectionless

service is also provided.

The Internet (with uppercase I) refers to the global Internet and the associated protocols.

It is built by the Internet Service Providers (ISP) such as telephone companies or a cable

companies.

An individual or a business must subscribe to an Internet Service Provider in order to have access to

the Internet.

An internet subscriber (typically a private residence or a business) is connected to the Internet by

using a data communication system known as Internet access technology.

Examples of Internet access technologies are:

Dialup telephone connections

Leased circuit using modems

Digital Subscriber Line (DSL) technologies

Cable modem technologies, and

Wireless access technologies

An intranet is an internet that is owned by a private organization such as a company, and is designed

for use only by the organization’s employees.

Some organizations now use the same equipment and protocol software to build their intranet as ISPs

use to build the global Internet.

Organizational intranets can be viewed as part of the global Internet because they connect directly to

the global Internet.

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IP Addressing

Each computing device on a TCP/IP internet is assigned a unique number known as its Internet

Protocol address, IP address, or Internet address.

Two addressing schemes are used:

The original scheme known as IPv4 uses 32-bit addresses, and

The scheme IPv6 uses 128-bit addresses.

When sending a packet across an internet, the sender must specify:

its own IP address (the source address), as well as

The address of the intended recipient (the destination address).

IPv4 Addresses

When interacting with users, software use a notation known as dotted decimal notation to specify

IPv4 addresses because it is more convenient for humans to understand.

An IPv4 address is specified in the dotted decimal notation by writing each of the four consecutive

8-bit section of the 32-bit address as a decimal value and use periods to separate the sections.

Examples

(a) 10000001 00110100 00000110 00000000 == > 129. 52 . 6 . 0

(b) 11000000 00000101 00110000 00000011 == > 192. 5 . 48 . 3

An IP address consists of two parts:

A prefix that is used to identify a network, and

A suffix that is used to identify a computing device connected to that network.

The original IPv4 scheme (known as classful IP addressing) divided the IPv4 address space into the

following five classes:

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bits

Class A

bits

Class B

bits

Class C

bits

Class D

bits

Class E

Class A Addresses

An address that belongs to class A has an 8-bit suffix that starts with 0 and

A network which is assigned one of these suffixes can have up to 224

= 16 mega computing devices.

Class B Addresses

An address that belongs to class B has a 16-bit suffix that starts with 10 and

A network which is assigned one of these suffixes can have up to 216

= 64 kilo computing devices.

Class C Addresses

An address that belongs to class C has a 24-bit suffix that starts with 110 and

A network which is assigned one of these suffixes can have up to 28 = 256 computing devices.

0 1 2 3 4 8 16 24 31

0 prefix suffix

0 1 2 3 4 8 16 24 31

1 0 Prefix Suffix

0 1 2 3 4 8 16 24 31

1 1 0 Prefix Suffix

0 1 2 3 4 8 16 24 31

1 1 1 0 Multicast address

0 1 2 3 4 8 16 24 31

1 1 1 1 Reserved (not assigned)

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Class D Addresses

A class D address is called a multicast address.

It starts with 1110, and does not have a suffix that identifies a particular network.

It is used to identify a group of computers, and

Once a multicast group has been established, a copy of any packet sent to the multicast address is

delivered to each of the host in the group.

In practice, multicasting is restricted to computers at individual network sites: it is not available

across the global Internet.

Class E Addresses

Addresses in this class start with 1111 and are special address.

They are not assigned.

Authority for Addresses

The Internet Corporation for Assigned Names and Numbers (ICANN) was established to handle

the assignment of IP address prefixes to individual networks as follows:

It divides the world into geographic regions (for examples, North America, Europe, Asia, and so

on).

Each of these regions has a register that makes large blocks of IP addresses available to major

ISPs.

These major ISPs make these addresses available to smaller ISPs, and

ISPs provide each subscriber with a set of prefixes that he/she uses for his/her networks.

An individual or a corporation must therefore contact an ISP to obtain a network prefix.

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IPv4 Subnet and Classless Addressing

One limitation of the original classful IP addressing is that many addresses were not used:

For example, a corporation that is assigned a network prefix from the class C address may have

less than 256 computing devices in his network: so, the remaining IP addresses with this address

prefix could not be used by another network.

Two new mechanisms were invented to overcome this limitation:

Subnet addressing, and

Classless addressing.

With these two mechanisms, there is no longer a distinction between address classes A, B, and C, and

The length of the prefix of an address can now vary.

These mechanisms allow an ISP to allocate to an organization the smallest number of addresses

possible that it needs to identify the computing devices on its network.

For example, if an organization has a network with more than 8, but less than or equal to16

computing devices, it could be assigned IP addresses with the same 28-bit prefix and a 4-bit suffix

(because with 4 bits we can have 24 = 16 different addresses).

In order to specify the boundary between the prefix and the suffix of a classless address, a 32-bit

value (known as address mask) is used.

An address mask has a 1 bit for each position in the address that corresponds to the prefix and a 0 bit

in each position that corresponds to the suffix.

Examples

If the prefix is an 8-bit value, then the address mask will be:

11111111 00000000 00000000 00000000

If the prefix is a 12-bit value, then the address mask will be:

11111111 11110000 00000000 00000000

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CIDR Notation used with IPv4

The classless addressing scheme is formally known as Classless Inter-Domain Routing (CIDR).

To make it easier for human beings to specify and interpret mask values, dotted decimal notation of

an IP address is extended by following the dotted decimal notation with a forward slash and the

number of bit in the address prefix as follows:

ddd.ddd.ddd.ddd/m

This new notation is referred to as the CIDR notation, and

The CIDR prefix of an address is that address (with the bits of its suffix set to bit 0) followed by a

forward slash and the number of bit in the address prefix.

Examples

CIDR Address CIDR Prefix Address Mask

192.5.48.69/8 192.0.0.0/8 255.0.0.0

192.5.48.69/16 192.5.0.0/16 255.255.0.0

192.5.48.69/26 192.5.48.64/26 255.255.255.192

Special Ipv4 Addresses

A set of CIDR addresses are reserved and cannot be assigned to a computing device.

These addresses are described as follows:

Ipv4 Network Address

The network address of a network is its CIDR prefix.

That means an IP address consisting of its prefix followed by a suffix consisting of 0 bits.

This address is used to identify a particular network and must not be assigned to a computing device.

Examples: 192.0.0.0/8 192.5.0.0/16 192.5.48.64/26 192.5.48.128/26 and 192.5.48.192/26

Ipv4 Directed Broadcast Address

The directed broadcast address of a network consists of its prefix followed by a suffix consisting of

1 bits.

This address is used to send a copy of a packet to all the hosts on a physical network.

This is done by specifying the directed broadcast address of the network as the destination address of

that packet.

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Examples:

Network Address Broadcast Address

192.0.0.0/8 192.255.255.255/8

192.5.0.0/16 192.5.255.255/16

192.5.48.0/26 192.5.48.127/26

192.5.48.128/26 192.5.48.191/26

192.5.48.192/26 192.5.48.255/26

Note:

An early implementation of TCP/IP by the Berkeley Software Distribution (BSD) UNIX defined

the directed broadcast address of a network as consisting of its prefix followed by a suffix

consisting of 0 bits.

Many computer manufacturers derived their early TCP/IP software from this implementation, and

a few sites still use this broadcast address.

Commercial TCP/IP software often include a confirmation parameter that can select between the

TCP/IP standard and the Berkeley broadcast address forms.

This selection must be specified by the network manager for each network.

Ipv4 Limited Broadcast Address

The limited broadcast address is the address consisting of 32 1 bits. That means: 255.255.255.255.

This address is used as the destination address by a computer that does not yet know its network

address during system startup to send a copy of a packet to all hosts directly connected to the

network.

Ipv4’s This Computer Address

This computer address is the address consisting of 32 0 bits when it is used as the source address of

a packet. That means: 0.0.0.0.

When a computer boots, it executes a startup protocol that sends a packet with this address as the

source address in order to obtain its IP address.

Ipv4 Loopback Address

The network with network address 127.0.0.0/8 is a special network that is reserved for testing

network application programs.

A loopback address in any host address on this network. For example127.0.0.1 or 127.0.0.2.

Network application programs that send packets to each other are tested on the same computer by

using a loopback address as the computer host address.

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Assigning a CIDR Prefix to a Customer

An internet service provider (ISP) assigns a network address (or CIDR prefix) to a customer in a way

that the number of digits n in the suffix of an address is such that 2n-2 is greater than the number of

host in the network.

For example, assume that an ISP has the address block 128.211.0.0/16 to assign.

Also assume that the ISP has two customers, with one needing twelve IP addresses and the other

needing nine.

Since 24 – 2 = 14 is greater than 12, the optimal way to assign CIDR prefixes to these customers is

to use a CIDR prefix with 32 – 4 = 28 bits.

It can then assign the CIDR prefixes as follows:

CIDR Prefix Minimum Host Address Maximum Host Address

Customer 1 28.211.0.16/28 128.211.0.17/28 128.211.0.30/28

Customer 2 128.211.0.32/28 128.211.0.33/28 128.211.0.46/28

Assigning IPv4 Host Addresses to a Router

A router belongs to each network to which it is connected.

Therefore each router’s connection to a network must be assigned an IPv4 host address like any other

computing device on that network.

Example

CIDR Prefix: 28.0.0.0/8 CIDR Prefix: 63.126.0.0/16

Connection Host Address: 28.0.0.9 Connection Host Address: 63.126.0.3

Network 1 Network 2 router

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IPv6 Addressing

An IPv6 address is a 128-bit address that consists of the following part:

A 64-bit prefix that consists of the global prefix followed by the subnet, and

A 64-bit suffix that is used to identify a computer (host) in the network.

The global prefix is a variable length value that is used to identify an organization, and

The subnet is used to identify a network in the organization.

IPv6 Address

K bits 64 – k bits 64 bits

Global Prefix (organization) Subnet Connection Interface (computer)

An IPv6 address is specified in the colon hexadecimal (colon hex) notation by converting each

consecutive 4 bits of each consecutive 16-bit section of the address in hexadecimal and use colons to

separate the sections.

Example: 69DC : 5AFE : 0 : FFFF : 1280 : 6C0B : FFFF : 0

An additional optimization known as zeroes compression reduces the size of an IPv6 address in

colon hex notation by replacing sequences of zeroes with two colons:

Example: FF0C : 0 : 0 : 0 : 0 : 0 : 0 : B1 can be written as: FF0C : : B1

IPv6 Types of Addresses

Each IPv6 address is one of the three basic types that follow:

Type Purpose

unicast

The address corresponds to a single computer (or connection interface).

A packet sent to this type of address is routed along a shortest path to the

computer.

multicast

The address corresponds to a set of computers, and membership in the set can

change at any time.

A copy of the packet sent to this address is delivered to each member of the set.

anycast

The address corresponds to a set of computers that share a common prefix

A packet sent to this address is delivered to exactly one of the computers (for

example, the computer closest to the sender).

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IPv6 does not reserve special broadcast addresses.

Instead, a set of multicast addresses must be used to handle special cases.

Multihomed Hosts

A host computer with multiple network connections is said to be a multihomed.

Multihoming is used for the following two reasons:

To increase reliability: if one network fails, the host can still reach the internet through the

second connection.

To increase performance: connection to multiple networks can make it possible to send traffic

directly and avoid routers.

Bothe IPv4 and IPv6 allow a host computer to be multihomed.

IPv6 also allow an organization to assign multiple IPv6 prefixes to a network.

E. Additional Networking Concepts and Technologies

In addition to the hardware and the protocols that are used to build networks and internets, additional

technologies are being developed to expand networks and internets capabilities. Some of these

technologies are described as follows:

Technologies that assess network performance.

Technologies that allow multimedia and IP telephony to be transferred over a packed switched

network infrastructure.

Technologies that keep networks secure.

A technology known as Software Defined Network (SDN) allows managers to configure and

manage networks.

The Internet of Things makes it possible for embedded devices to communicate over the internet

without a human involvement.

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I2. The Internet Protocol Suite

The internet protocol suite which is commonly known as TCP/IP because the original protocols in the

suite are the Transmission Control Protocol (TCP) and the Internet Protocol (IP) is the reference

model implemented by developers today.

It provides a standard procedure for transferring data from a source application to a destination

application over the Internet by specifying:

how data should be put into packets,

addressed,

transmitted,

routed, and

received.

This functionality is organized into the five layers that are used to classify all related protocols according

to the part of the networking involved as follows:

Layer 1: Physical layer

Layer 2: network interface layer

Layer 3: Internet layer

Layer 4: Transport layer

Layer 5: Application layer

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Layer 1: Physical Layer

Protocols in the physical layer specify details about the underlying transmission medium and the

associated hardware.

For example for a communication over a wired network a protocol may specify:

o the voltages to be used in the transmission,

o the exact way that electrical signals are used to represent data, and

o the procedures used to initiate and conduct communication.

Layer 2: Network Interface Layer

This layer is also referred to as Link layer or MAC (Media Access Control) layer.

Protocols in this layer specify the details about communication between two computers on the same

packet switch network (or link) and the interface between the network hardware and layer 3.

The processes of transmitting and receiving packets (known as frames) on a given link can be controlled

both in the software device driver for the network Interface card, as well as on firmware or specialized

chipsets.

These processes perform link layer (data link) functions such as adding a packet header to prepare it for

transmission, then actually transmit the frame over a physical medium.

This layer also includes specifications about the maximum frame size and about translating IP addresses

used in the Internet Protocol to Media Access Control (MAC) addresses.

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Layer 3: Network (Internet) Layer

The internet layer has the responsibility of sending packets known as datagrams from one host to

another across potentially multiple networks.

This layer includes the Internet (IP) protocol and numerous routing protocols.

There is only one IP protocol, and

All internet components that have an internet layer must run the IP protocol.

The Internet Protocol is responsible for hosts and routers addressing and identification by using IP

addresses.

It also defines the fields in a datagram, as well as how hosts and routers act on these fields.

Packet routing is the basic task of sending datagrams from source to destination by forwarding them to

the next network router closer to the final destination.

Routing protocols determine the routes that datagrams take between a source host and a destination

host.

There are many routing protocols and within a network, the network administrator can run any routing

protocol desired.

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Layer 4: Transport layer

Protocols in this layer take care of the communication from an application program on one computer to

an application program on another computer.

Transport-layer packets are referred to as segments.

There are two major transport protocols:

The Transmission Control (TCP) Protocol, and

The User Data Protocol (UDP) protocol.

Either TCP or UDP can transport application-layer messages.

TCP provides a connection-oriented service to its applications.

These service includes:

Guaranteed delivery of application-layer messages to the destination, and

Flow control (that is, sender/receiver speed matching)

It also breaks long messages into shorter segments and

Provides a congestion-control mechanism so that a source throttles its transmission rate when the

network is congested.

UDP provides a connectionless service to its applications.

It provides none of the following:

Reliability,

Flow control, or

Congestion control.

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Layer 5: Application layer

Protocols in this layer specify how a pair of applications (potentially from two different networks)

interacts when they communicate.

Layer 5 protocols specify the details about:

The format and meaning of packets that applications can exchange as well as,

The procedures to be followed during communication.

An application layer protocol is distributed over multiple hosts, with the application in one host

using the protocol to exchange packets of information (referred to as messages) with the application

in another host.

The application layer includes many protocols, such as:

HTTP (Hypertext Transfer Protocol) which provides for web document request and transfer

SMTP (Simple Mail Transfer Protocol) which provides for the transfer of e-mail messages)

FTP (file Transfer Protocol) which provides for the transfer of files between two hosts

How Data Passes through the Layers

stack on the sending computer stack on the receiving computer

Each computer (sending or receiving computer) contains software for an entire suite of protocols.

Software in a given layer on the sending computer adds information to the ongoing data, and software in

the same layer on the receiving computer uses the additional information to process the incoming data.

Application Application

Transport

Internet

Net. Interface

Physical (network Hardware)

Transport

Internet

Net. Interface

Ht message

Hi Ht message

Hn Hi Ht message

Message

Hi Ht message

Ht message

Hn Hi Ht message

Message

©2017 Gilbert Ndjatou Page 26

I3. ISO and the OSI Seven Layer Reference Model

Early in the history of networking, the International Organization for Standardization (ISO) defined

the 7-layer Reference Model that follows:

LAYER 7 Application

LAYER 6 Presentation

LAYER 5 Session

LAY

ER 4 Transport

LAYER 3 Network

LAYER 2 Data Link

LAYER 1 Physical

Nowadays, protocol designs have changed and many modern protocols do not fit the old model.

However, much of the ISO terminology still persists and when a networking professional refers to Layer

i, he usually means ISO’s ith

layer.

Layer 1: Physical protocols in this layer give a detailed specification of the basic network hardware.

Layer 2: Data Link protocols in this layer specify how to organize data into frames and how to

transmit frames over a network.

Layer 3: Network layer 3 protocols specify how addresses are assigned and how packets are

forwarded from one end of the network to another.

Layer 4: Transport layer 4 protocols specify how to handle the details of reliable transfers.

Layer 5: Session layer 5 protocols specify how to establish a communication session with a remote

system such as to login to a remote timesharing computer. Specifications for

security details such as authentication using passwords belong to this layer.

Layer 6: Presentation layer 6 protocols specify how to represent data. Such protocols are needed

because different brands of computers use different internal representations for

integers and characters. Layer 4 protocols are needed to translate from the

representation on one computer to the representation on another one.

Layer 7: Application each protocol in layer 7 specifies how a particular application uses a network.

For example, for an application that transfers files from one computer to another,

the protocol specifies how an application on one machine makes a request and how

the application on another machine responds to that request.

©2017 Gilbert Ndjatou Page 27

Exercises:

1. What is a computer network

2. What is the purpose of a computer network

3. Give three examples of an Internet application.

4. How are messages from different sending hosts transmitted over a packet switching network?

5. What are the three major categories of networks and what are their characteristics?

6. What is the family of networking technologies commonly used in wired LAN?

7. What is the technology used for wireless LAN?

8. How do you connect a computer to a wired LAN?

9. How do you connect a computer to a wireless LAN?

10. What is the MAC address of a computer?

11. What are the two parts of a MAC address?

12. What is an internetwork or internet?

13. What is the network protocol stack used on most internets?

14. How are computers identified on an internet that uses the TCP/IP protocol stack?

15. What are the two types of IP addresses?

Chapter 1, page 15: Nos 1.8, 1.11, 1.12, 1.13

Chapter 20, page 343: No 20.6

Chapter 21, Page 365 - 366: Nos 21.3, 21.8, 21.11, 21.12, 21.13, 21.14, 21.19, 21.20, 21.21, 21.23.

Solutions

1. What is a computer network?

A computer network is a group of computer systems and other computing devices that are connected by a

physical communication medium such as wire, radio wave, or light beam.

2. What is the purpose of a computer network?

The purpose of a computer network is to facilitate communication and resource sharing

3. Give three examples of an Internet application.

Email, web browsing, file upload and download, audio and voice telephone calls, distributed database,

and video teleconferencing.

4. How are messages from different sending hosts transmitted over a packet switching network?

Messages are subdivided into small blocks called packets that include the identity of the receiving host.

These packets are sent one after another on the same communication medium and

the system allows other senders to send their own packets before the first sender can transmit the next packet.

5. What are the three major categories of networks and what are their characteristics?

©2017 Gilbert Ndjatou Page 28

local area network (LAN)

is a computer network that interconnects computers within a limited area such as a residence,

school, laboratory, university campus or office building.

Metropolitan Area Network (MAN): spans a major city

Wide Area Network (WAN):

covers a larger geographic distance, and also generally involves leased telecommunication

circuits or Internet links.

6. What is the family of networking technologies commonly used in wired LAN?

Ethernet

7. What is the technology used for wireless LAN?

Wi-Fi

8. How do you connect a computer to a wired LAN?

By using a Network Interface Card (NIC)

9. How do you connect a computer to a wireless LAN?

By using a Wireless Network Interface Card (WNIC)

10. What is the MAC address of a computer?

It is the 48-bit address that is assigned to the NIC of that computer.

11. What are the two parts of a MAC address?

The left-most three bytes are called Organization Unique Identifier (OUI) and is used to identify the

manufacturer of the NIC.

The right-most three bytes are used to identify the NIC.

12. What is an internetwork or internet?

An internetwork or internet consists of two or more networks connected to one another by using a

computing device called a router.

13. What is the network protocol stack used on most internets?

TCP/IP

14. How are computer identified on an internet that uses the TCP/IP protocol stack?

By using their IP address

15. What are the two type of IP addresses?

IPv4 and IPv6

©2017 Gilbert Ndjatou Page 29

Chapter 1, page 15:

Nos 1.8,

A communication protocol specifies how information will be represented and communicated.

It specifies how data is represented and how it is transmitted.

1.11

Layer 1: Physical Layer

Protocols in the physical layer specify details about the underlying transmission medium and the associated

hardware.

Layer 2: Network Interface Layer

This layer is also referred to as Link layer or MAC (Media Access Control) layer.

Protocols in this layer specify the details about communication between two computers on the same packet switch

network (or link) and the interface between the network hardware and layer 3.

Layer 3: Network (Internet) Layer

The internet layer has the responsibility of sending packets known as datagrams from one host to another across

potentially multiple networks.

Layer 4: Transport layer

Protocols in this layer take care of the communication from an application program on one computer to an

application program on another computer.

Layer 5: Application layer

Protocols in this layer specify how a pair of applications (potentially from two different networks) interacts

when they communicate.

1.12

stack on the sending computer stack on the receiving computer

1.13

The Institute for Electrical and Electronics Engineers (IEEE).

The International Organization for Standardization (ISO).

Application Application

Transport

Internet

Net. Interface

Physical (network Hardware)

Transport

Internet

Net. Interface

Ht message

Hi Ht message

Hn Hi Ht message

Message

Hi Ht message

Ht message

Hn Hi Ht message

Message

©2017 Gilbert Ndjatou Page 30

Chapter 20, page 343: No 20.6 refer to 1.11

Chapter 21, Page 365 - 366: Nos

21.3 Yes. By looking at the first few bits of the address:

Class A: 0; class B: 10; class C: 110; class D: 1110; class E: 1111

21.8 24 – 2 = 16 – 2 = 14

21.11 The CIDR prefix 1.2.3.4/29 is invalid because its suffix is 100 which is not all 0’s.

21.12 28 – 2 = 256 – 2 = 254. The answer is No!

21.13 In order to accommodate four customers, the prefix must be extended by at least 2 bits for a total of at least 24

bits. So, the suffix should be at most 8 bits.

60 < 64 – 2 ==> 60 < 26 – 2 ==> each customer has a /26 IP address block

21.14 Yes. Create two subnets A & B: A is identified with prefix 0 and B with prefix 1.

21.19

21.20 No.

21.21 N. Because IP addresses are assigned to network connections.

21.23. Yes. If it is connected to more than one network.