unit 2 - osi model and network protocols

UNIT 2 THE OPEN SYSTEMS

INTERCONNECTION

(OSI) MODEL AND

NETWORK PROTOCOLS 1

Learning Outcomes

At the end of this topic, student should be able to:

1. Describe the purpose of the OSI Model and each of its layers.

2. Define specific functions belonging to each OSI Model layer.

3. Explain how two network nodes communicate through the

OSI Model.

4. Explain the structure and purpose of data packets and frames.

5. Explain two types of addressing covered by the OSI Model.

2.1 Network Communications

2.1 Describe Network Communications

What is networking? o Communication, sharing, delivering

An interconnection of computers and other devices including: o Client computers o Servers (computers)

o Network Devices Hubs and Switches Routers Firewall etc

2.1.1 Describe the purpose of the OSI

Model and each of its layers.

In the early 1980s, ISO began work on a universal set of

specifications that would enable computer platforms across the

world to communicate openly.

The result was a helpful model for understanding and

developing computer-to-computer communications over a

network.

This model, called the OSI (Open Systems Interconnection)

model, divides network communications into seven layers:

Physical, Data Link, Network, Transport, Session, Presentation,

and Application. Each layer has their own task and protocol

involved.

OSI or Open Systems Interconnection is a standard reference

model for communication between two end users in a network.

2.1.1 Describe the purpose of the OSI

Model and each of its layers. (cont.)

While performing those services, the protocols also interact with protocols in the layers directly above and below.

In addition, at the top of the OSI model, Application layer protocols interact with the software you use (such an e-mail or spreadsheet program).

At the bottom, Physical layer services act on the networking cables and connectors to issue and receive signals.

Please Do Not Touch Steve Pets Alligator

1.2 Define specific functions belonging

to each OSI Model layer.

Provides interface between

software applications and network for interpreting applications request and requirements.

Application (Layer 7)

Allow hosts and applications to use a common language; perform data formatting, encryption and compression

Presentation (Layer 6)

Establishes, maintains and terminates user connection

SESSION (Layer 5)

Ensure accurate delivery of data through flow control, segmentation and reassembly, error correction and acknowledgment

TRANSPORT (Layer 4)

Establishes network connections;

translate network addresses into their physical counterparts and determines routing

NETWORK (Layer 3)

Packages data in frames appropriate to network transmission method

DATA LINK (Layer 2)

Manages signaling to and form physical network connections

Physical (Layer 1)

Summary

2.1.3 Explain how two network nodes

communicate through the OSI Model.

The OSI model is a theoretical representation of

what happens between two nodes communicating

on a network.

Every process that occurs during network

communications can be associated with a layer of

the OSI model, so you should be familiar with the

names of the layers and understand the key

services and protocols that belong to each.

When Data Passes from Host A to Host B :

Application, Presentation and Session layer take user input and converts it into data

Transport layer adds a segment header converting the data into segments

Network layer adds a network header and converts the segments into packets

Data Link layer adds a frame header converting the packets into frames

MAC sublayer layer converts the frames into a bits which the Physical layer can put on the wire.

When the bits stream arrives at the

destination (Host B):

Physical layer takes it of the wire and converts it

into frames.

Each layer will remove their corresponding header

while the data flows up the OSI model until it is

converted back to data and presented to the user.

2.1.4 Explain the structure and

purpose of data packets and frames.

Data frames are small blocks of data with control,

addressing, and handling information attached to

them.

Frames are composed of several fields. The

characteristics of these fields depend on the type

of network on which the frames run and the

standards that they must follow.

Ethernet and token ring networks use different

frame types, and one type of network cannot

interpret the others frames.

Frame Specifications

You have learned that frames are composed of several smaller components, or fields.

The characteristics of these components depend on the type of network on which the frames run and on the standards that they must follow.

By far, the most popular type of networking technology in use today is Ethernet, which uses Ethernet frames.

Youll learn much more about Ethernet in Chapter 5, but the following serves as an introduction, as well as a comparison between this favored network type and its historical rival, token ring.

Ethernet is a networking technology originally

developed at Xerox in the early 1970s and

improved by Digital Equipment Corporation,

Intel, and Xerox.

There are four different types of Ethernet frames.

The most popular form of Ethernet is

characterized by the unique way in which devices

share a common transmission channel, described

in the IEEE 802.3 standard.

A much less common networking technology, token ring, was developed by IBM in the 1980s.

It relies upon direct links between nodes and a ring topology.

Nodes pass around tokens, special control frames that indicate to the network when a particular node is about to transmit data.

Although this networking technology is nearly obsolete, there is a remote chance that you might work on a token ring network.

The IEEE has defined token ring technology in its 802.5 standard.

Ethernet frames are different from token ring frames, and the two will not interact with each other on a network.

In fact, most LANs do not support more than one frame type, because devices cannot support more than one frame type per physical interface, or NIC. (NICs can, however, support multiple protocols.)

Although you can conceivably transmit both token ring and Ethernet frames on a network, Ethernet interfaces cannot interpret token ring frames, and vice versa.

Normally, LANs use either Ethernet or token ring, and almost all contemporary LANs use Ethernet.

NOTE :

The terms frame, packet, datagram, and protocol data unit (PDU) are often used interchangeably to refer to a small piece of data formatted for network transmission.

Technically, however, a packet is a piece of information that contains network addressing information, and a frame is a piece of data enclosed by a Data Link layer header and trailer.

Datagram is synonymous with packet.

PDU generically refers to a unit of data at any layer of the OSI model.

However, networking professionals often use the term packet to refer to frames, PDUs, and Transport layer segments alike.

2.1.5 Explain two types of addressing

covered by the OSI Model.

Addressing is a system for assigning unique

identification numbers to devices on a network.

Each node has two types of addresses.

2 Types of Address

Network Address

Physical Address

Network Address

Network addresses follow a hierarchical addressing scheme and can be assigned through operating system software.

They are hierarchical because they contain subsets of data that incrementally narrow down the location of a node, just as your home address is hierarchical because it provides a country, state, ZIP code, city, street, house number, and persons name.

Network layer address formats differ depending on which Network layer protocol the network uses. Example : IP, ICMP, IGMP, IPX/SPX

Network addresses are also called network layer addresses, logical addresses, or virtual addresses.

MAC (Media Access Control) Address

The MAC (Media Access Control) sublayer, the lower sublayer of the Data Link layer, manages access to the physical medium.

It appends the physical address of the destination computer onto the data frame.

The physical address is a fixed number associated with the hosts NIC; it is initially assigned at the factory and stored in the NICs on-board memory.

Because this address is appended by the MAC sublayer of the Data Link layer, it is also known as a MAC address or a Data Link layer address. Sometimes, its also called a hardware address.

PHYSICAL ADDRESS LOGICAL ADDRESS

The 48 bit MAC address that manufactures

encode in their network interface cards

A 32 bit IP address that is not embedded in

the network card

Address is unique, referred to as the

Ethernet or hardware address.

The purpose of routing between networks.

Associated with layer2 of the OSI Model. Operates at Layer 3 of the OSI Model.

2.2 Construct a Local Wired Network

Learning Outcomes

Student should be able to:

1. Determine the MAC address of a host using ipconfiq/all command.

2. Build a standard IEEE 802.3 Ethernet Frame based on a given

source and destination devices.

3. Indicate logical address of a computer.

4. Prepare IP address of a computer.

2.2.1 Determine the MAC address of a

Host using ipconfig /all command.

You will need to know how to find and interpret

MAC addresses when supporting networks. In

this project, you will discover two ways of finding

your computers MAC address, also known as its

physical address, or sometimes, its hardware

address.

If your workstation is running the Windows XP or Windows Vista operating system, perform the following steps:

1. Click the Start button, point to All Programs, select Accessories, and then select Command Prompt. The Command Prompt window opens with a cursor blinking at the C:\> prompt.

2. Type ipconfig /all then press Enter. A list of your Windows XP or Windows Vista configuration and Ethernet adapter parameters appears. This includes your workstations TCP/IP properties, as well as its MAC address.

3. Search the output for the 12-digit hexadecimal MAC address currently assigned to your NIC. (Hint: Look for the Physical Address line.) On a separate piece of paper, write down the MAC address.

4. Type exit and then press Enter to close the Command Prompt window.

Network+ Guide to Networks, 4e 31

IEEE Networking Specifications

Apply to connectivity, networking media, error

checking algorithms, encryption, emerging

technologies, and more

Specifications fall under IEEEs Project 802 Effort to standardize physical and logical elements of a network



(continued)

Table 2-2: IEEE 802 standards



(continued)

Table 2-2 (continued): IEEE 802 standards


Summary

Standards are documented agreements containing precise criteria that are used as guidelines to ensure that materials, products, processes, and services suit their purpose

ISOs OSI Model divides networking architecture into seven layers

Each OSI layer has its own set of functions and interacts with the layers directly above and below it

Application layer protocols enable software to negotiate their formatting, procedural, security, and synchronization with the network


Summary (continued)

Presentation layer protocols serve as translators between the application and the network

Session layer protocols coordinate and maintain links between two devices for the duration of their communication

Transport layer protocols oversee end-to-end data delivery

Network layer protocols manage logical addressing and determine routes based on addressing, patterns of usage, and availability


Summary (continued)

Data Link layer protocols organize data they receive from the Network layer into frames that contain error checking routines and can then be transmitted by the Physical layer

Physical layer protocols generate and detect voltage to transmit and receive signals carrying data over a network medium

Data frames are small blocks of data with control, addressing, and handling information attached to them

Determine the MAC address of a Host using

ipconfig /all command

Build a standard IEEE 802.3 Ethernet Frame

based on a given source and destination devices

2.2 Comprehend a Local Wired

Network

Explain logical address of a computer Appears to reside from the perspective of an executing

application.

Determine the IP address of a computer Using ipconfig

2.3 The Importance of Network

Protocols

Learning Outcomes


Identify the characteristics of TCP/IP, IPX/SPX, NetBIOS and

NetBEUI, AppleTalk.

Differentiate how network protocols correlate to layers of the OSI

Model

Explain the functions of the core protocols of the TCP/IP suite


Introduction to Protocols

Protocols vary according to purpose, speed,

transmission efficiency, utilization of resources,

ease of setup, compatibility, and ability to travel

between different LANs.

Multiprotocol networks: networks running more

than one protocol

Most popular protocol suite is TCP/IP Others: IPX/SPX, NetBIOS, and AppleTalk

Networking Protocol Suites:

a) Transmission Control Protocol/Internet

Protocol (TCP/IP)

b) Internetwork Packet Exchange/ Sequenced

Packet Exchange (IPX/SPX)

c) NetBIOS and NetBEUI

d) AppleTalk

7.Application

6.Presentation

5.Session

4.Transport

3.Network

2.Data Link

1.Physical

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HARDWARE

LAYER

APPLICATION

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INTERNETWORK

LAYER

Internetwork Layer

Internetwork layer connect the application

software in the application layer with the

hardware layer that actually move messages from

one computer to another.

TCP/IP

Transmission Control Protocol/Internet Protocol

Consist of dozens of difference protocols, but only a few are the core protocol.

Two core protocol the most important : IP protocol and TCP protocol.

Develop for the US Department of Defenses Advance Research Project Agency Network (ARPAnet) by Vinton Cerf and Bob Kahn in 1974.


TCP/IP

Suite of specialized subprotocols TCP, IP, UDP, ARP, and many others

De facto standard on Internet Protocol of choice for LANs and WANs

Protocols able to span more than one LAN are routable

Can run on virtually any combination of NOSs or network media

TCP/IP core protocols operate in Transport or Network layers

TCP

Transmission Control Protocol


The TCP Protocols

Provides reliable data delivery services Operates in Transport layer

Connection-oriented

Establishes a connection before transmitting data.

Three-way handshake

Require acknowledgements from receiver to ensure data was received correctly.

Ensures reliable data delivery through sequencing and checksums

Checksum for data integrity

Provides flow control

Port hosts address where an application makes itself available to incoming or outgoing data


The TCP Protocols (TCP Segment)

Figure 4-1: A TCP segment



Figure 4-2: TCP segment data


The TCP Protocols (connection)

Figure 4-3: Establishing a TCP connection

To establish a connection, TCP uses a three-way handshake. Before a client

attempts to connect with a server, the server must first bind to a port to open

it up for connections: this is called a passive open. Once the passive open is

established, a client may initiate an active open. To establish a connection, the

three-way (or 3-step) handshake occurs:

SYN: The active open is performed by the client sending a SYN to the server.

The client sets the segment's sequence number to a random value A.

SYN-ACK: In response, the server replies with a SYN-ACK. The

acknowledgment number is set to one more than the received sequence

number (A + 1), and the sequence number that the server chooses for the

packet is another random number, B.

ACK: Finally, the client sends an ACK back to the server. The sequence

number is set to the received acknowledgement value i.e. A, and the

acknowledgement number is set to one more than the received sequence

number i.e. B.

At this point, both the client and server have received an acknowledgment of

the connection.


UDP (User Datagram Protocol)

Figure 4-4: A UDP segment


The UDP Protocols

Provides reliable data delivery services Operates in Transport layer

Connection-less

Do not establishes a connection before transmitting data.

No handshake.

No effort to ensure data is delivered free of errors.

Faster than conneciton-oriented protocol.

Useful when data must be transferred quickly such as streaming

music or video.



Figure 4-1: A TCP segment

The TCP/IP Services

IP

Internet Protocol


IP (Internet Protocol) Protocol

Provides information about how and where data

should be delivered Datas source and destination addresses

Network layer protocol

Enables TCP/IP to internetwork

Unreliable, connectionless protocol

IP datagram: packet, in context of TCP/IP Envelope for data


IP (continued)

Figure 4-5: An IP datagram


IP (continued)

Figure 4-6: IP datagram data


ICMP (Internet Control Message

Protocol)

Network layer protocol that reports on success or

failure of data delivery Indicates when part of network congested

Indicates when data fails to reach destination

Indicates when data discarded because allotted time for delivery

(TTL) expired

Cannot correct errors it detects


IGMP (Internet Group Management

Protocol)

Network layer protocol that manages

multicasting Transmission method allowing one node to send data to defined

group of nodes

Point-to-multipoint method

Teleconferencing or videoconferencing over Internet

Routers use IGMP to determine which nodes

belong to multicast group and to transmit data to

all nodes in that group


ARP (Address Resolution Protocol)

Network layer protocol Obtains MAC (physical) address of host

Creates database that maps MAC address to hosts IP (logical) address

ARP table or cache: local database containing

recognized MAC-to-IP address mappings Dynamic ARP table entries created when client makes ARP

request that cannot be satisfied by data already in ARP table

Static ARP table entries entered manually using ARP utility


RARP (Reverse Address Resolution

Protocol)

Allows client to broadcast MAC address and receive

IP address in reply If device doesnt know own IP address, cannot use ARP

RARP server maintains table of MAC addresses and

associated IP addresses


BOOTP (Bootstrap Protocol)

Uses central list of IP addresses and associated

devices MAC addresses to assign IP addresses to

clients dynamically Dynamic IP addresses

Application layer protocol

Client broadcasts MAC address, BOOTP server replies with:

Clients IP address

IP address of server

Host name of server

IP address of a default router


DHCP (Dynamic Host Configuration

Protocol)

Automated means of assigning unique IP address to every device on a network Application layer protocol

Reduces time and planning spent on IP address management

Reduces potential for errors in assigning IP addresses

Enables users to move workstations and printers without having to change TCP/IP configuration

Makes IP addressing transparent for mobile users

Three method in DHCP: Dynamic allocation

Automatic allocation

Static allocation


DHCP (continued)

Figure 4-11: The DHCP leasing process


APIPA (Automatic Private IP Addressing)

Provides computer with IP address automatically For Windows 98, Me, 2000, XP client and

Windows 2003 server

For situations where DHCP server unreachable

Assigns computers network adapter IP address from predefined

pool of addresses

169.254.0.0 through 169.254.255.255

Computer can only communicate with other nodes using

addresses in APIPA range

http://pic.dhe.ibm.com/infocenter/zos

/v2r1/index.jsp?topic=%2Fcom.ibm.zo

s.v2r1.hala001%2Fitctcpipcon.htm TCP Transmission Control Protocol is a transport protocol providing a reliable, full-duplex byte

stream. Most TCP/IP applications use the TCP transport protocol. UDP User Datagram Protocol is

a connectionless protocol providing datagram services. UDP is less reliable because there is no

guarantee that a UDP datagram ever reaches its intended destination, or that it reaches its

destination only once and in the same condition as it was passed to the sending UDP layer by a UDP

application. ICMP Internet Control Message Protocol is used to handle error and control

information at the IP layer. The ICMP is most often used by network control applications that are

part of the TCP/IP software product itself, but ICMP can be used by authorized user processes as

well. PING and TRACEROUTE are examples of network control applications that use the ICMP

protocol. IP Internet Protocol provides the packet delivery services for TCP, UDP, and ICMP. The

IP layer protocol is unreliable (called a best-effort protocol). There is no guarantee that IP packets

arrive, or that they arrive only once and are error-free. Such reliability is built into the TCP

protocol, but not into the UDP protocol. If you need reliable transport between two UDP

applications, you must ensure that reliability is built into the UDP applications. ARP/ND The IPv4

networking layer uses the Address Resolution Protocol (ARP) to map an IP address into a hardware

address. In the IPv6 networking layer, this mapping is performed by the Neighbor Discovery (ND

function). On local area networks (LANs), such an address would be called a media access control

(MAC) address. RARP Reverse Address Resolution Protocol is used to reverse the operation of the

ARP protocol. It maps a hardware address into an IPv4 address. Note that both ARP packets and

RARP packets are not forwarded in IP packets, but are themselves media level packets. ARP and

RARP are not used on all network types, as some networks do not need these protocols

2.4 Addressing Schemes for TCP/IP

Suite

Learning Outcomes


Understand addressing schemes for TCP/IP suite.

Describe the purpose and implementation of DNS (Domain Name

System) and WINS (Windows Internet Naming Service)

Install protocols on Windows XP clients

2.4 Addressing Schemes for TCP/IP

Suite

Learning Outcomes


Compare the addressing scheme of TCP/IP: classes, binary, dotted

decimal notation and subnet mask.

Label Public and Private IP address.

Label Unicast, Broadcast and Multicast address.

Relate how IP address are obtained : static address or dynamic address.


Addressing in TCP/IP (IP address)

Figure 4-8: IP addresses and their classes

222.32.1.1 ____

179.21.9.0 ____

90.43.2.1 ____

220.11.6.6 ____

43.55.45.0 ____

126.32.1.0 ____

111.45.3.2 ____


Addressing in TCP/IP (continued)

Many Internet addresses go unused Cannot be reassigned because they are reserved

IP version 6 (IPv6) will incorporate new addressing scheme

Some IP addresses reserved for special functions 127 reserved for a device communicating with itself

Loopback test

ipconfig: Windows XP command to view IP

information ifconfig on Unix and Linux


Binary and Dotted Decimal Notation

Most common way of expressing IP addresses Decimal number between 0 and 255 represents each binary

octet

Separated by period

Each number in dotted decimal address has

binary equivalent


Subnet Mask

Every device on TCP/IP-based network identified by subnet mask

32-bit number that, when combined with devices IP address, informs rest of network about segment or network to which a device is attached

Subnetting: subdividing single class of networks into multiple, smaller logical networks or segments


Assigning IP Addresses

Nodes on a network must have unique IP

addresses

Static IP address: manually assigned Can easily result in duplication of addresses

Most network administrators rely on network

service to automatically assign IP addresses


Sockets and Ports

Every process on a machine assigned a port number 0 to 65535

Well Known Ports: in range 0 to 1023 Assigned to processes that only the OS or system administrator can access

Registered Ports: in range 1024 to 49151 Accessible to network users and processes that do not have special

administrative privileges

Dynamic and/or Private Ports: in range 49152 through 65535 Open for use without restriction

Processs port number plus host machines IP address equals processs socket Ensures data transmitted to correct application

http://en.wikipedia.org/wiki/Internet_port


TCP Segment


IP datagram


Addressing in IPv6

IPv6 slated to replace current IP protocol, IPv4 More efficient header, better security, better prioritization

Billions of additional IP addresses

Differences: Address size

Representation

Distinguishes among different types of network interfaces

Format Prefix

Comparison between IPv6 and IPv4:

-Larger address space

-Better multicasting

-Better on auto configurations

-Better on security (network layer)

-Better on supporting mobility


Host Names and DNS (Domain Name

System): Domain Names

Every host can take a host name

Every host is member of a domain Group of computers belonging to same organization and has part of

their IP addresses in common

Domain name usually associated with company or other type of

organization

Fully qualified host name: local host name plus

domain name

Domain names must be registered with an Internet

naming authority that works on behalf of ICANN


Host Files

ASCII text file called HOSTS.TXT

Associate host names with IP addresses

Growth of Internet made this arrangement impossible to maintain

Figure 4-13: Example host file


DNS (Domain Name System)

DNS translates Internet domain and host names to IP addresses. DNS automatically converts the names we type in our web browser address bar to the IP addresses of web servers hosting those sites.

Hierarchical method of associating domain names with IP addresses Refers to Application layer service that accomplishes association and organized

system of computers and databases making association possible Relies on many computers around world

Thirteen root servers Three components:

Resolvers - a piece of software that's understands how to formulate a DNS query and is built into practically every Internet-capable application.

Name servers - DNS is a globally connected network of "name servers Name space - establishes the syntactical rules for creating and structuring legal

DNS names.

http://compnetworking.about.com/od/dns_domainnamesystem/f/dns_servers.htm

http://blog.datakl.com/tag/dns-resolver/
http://compnetworking.about.com/od/dns_domainnamesystem/f/dns_servers.htmhttp://blog.datakl.com/tag/dns-resolver/http://blog.datakl.com/tag/dns-resolver/http://blog.datakl.com/tag/dns-resolver/

unit 2 - osi model and network protocols

Documents

osi model layer

network protocols

routing network layer

network nodes

network addresses

helpful model

divides network communications

application layer protocols