networking- osi layer protocol functions
TRANSCRIPT
24/12/13
24/12/13
24/12/13
24/12/13
24/12/13
OSI Layers Protocol Functions
Presented by K.GAYATHRI
OSI Model
Introduction
The Open Systems Interconnection (OSI) model is a reference tool for understanding data communications between any two networked systems.
Some Benefits of OSI Model
1.Less complex,More quality
2.Easier to learn and Develop
3.Multivendor interoperability
4.Standard interface
5.Troubleshooting.
OSI Model 7 Layers With Protocols
Physical Layer
Purpose
Deals with the transmission of 0s and 1s over the physical mediaTranslation of bits into signals(Electrical,Mechanical)The Physical layer provides specifications for a variety of hardware: Cabling Connectors Network interface cards (NICs) Wireless radios Hubs
Ethernet
Ethernet is a family of technologies that provides data-link and physical specifications for controlling access to a shared network medium.
Ethernet has several benefits over other LAN technologies:
Simple to install and manage
Inexpensive
Flexible and scalable
Easy to interoperate between vendors
Cabling the LAN
Media Characteristics: Cable length
Cost
Ease of installation
Susceptibility to interference
Ethernet Cabling TypesCoaxial
Fiber Optic
Space
Category 5 unshielded twisted-pair cable (Cat 5 UTP)
Cabling is an integral part of building any network.
Cabling standards are a set of specifications for the installation and testing of cables.
Standards specify types of cables to use in specific environments, conductor materials, pin outs, wire sizes, shielding, cable lengths, connector types and performance limits.
Twisted Pair Cable
Twisted pair cable is most commonly used in network installations
The TIA/EIA organization defines two different patterns, or wiring schemes, called T568A and T568B.
Each wiring scheme defines the pin out, or order of wire connections, on the end of the cable.
There are two types of twisted pair cable STP,UTP
(Cat 5 UTP) is mainly used in network installations.
Unshielded Twisted Pair (UTP)
Unshielded twisted-pair cable (UTP) is a four-pair wire medium used in a variety of networks.
TIA/EIA-568-A contains specifications governing cable performance.
RJ-45 connectorUTP Cable Types
Straight-Through
Crossover
Rollover
RJ-45 Connector
Straight-through Cable
A Straight-through cable is the most common cable type.
It maps a wire to the same pins on both ends of the cable.
Straight-through cables used for following connections, Switch to router
Switch to PC or server
Hub to PC or server
Crossover Cable
A crossover cable uses both wiring schemes.
The wires on the cable are crossed over so that the receive signal pins on the RJ-45 connector on one end are connected to the transmit signal pins on the RJ-45 connector on the other end.
Crossover cables used for following connections,Switch to switch
Switch to hub
Hub to hub
Router to router
PC to PC
Router to PC
Rollover Cable
Rollover cable (also known as Cisco console cable) is a type of null-modem cable that is most commonly used to connect a computer terminal to a router's console port.
Cisco routers and switches are normally configured over their console ports.
The pin outs on one end are reversed from the other, as if the wire had been rolled over and you were viewing it from the other side.
Rollover cables used for following connectionsConnect a terminal to a console port.
Wireless Network
802.11 standard specifies the operating parameters of wireless local area networks (WLAN)
The 802.11 wireless networks operate in two basic modes: 1.Infrastructure mode 2.Ad-hoc mode
Infrastructure Mode
Wireless Network Security
Wired Equivalent Privacy (WEP): The original encryption protocol developed for wireless networks.WEP encryption is based on the RC4 stream cipheroperationWi-Fi Protected Access (WPA):Most current WPA implementations use a preshared key (PSK), commonly referred to as WPA Personal, and the Temporal Key Integrity Protocol (TKIP, pronounced tee-kip) for encryption.
WPA Enterprise uses an authentication server to generate keys or certificatesWi-Fi Protected Access version 2 (WPA2): Based on the 802.11i wireless security standard.
The most significant enhancement to WPA2 over WPA is the use of the Advanced Encryption Standard (AES) for encryption
WEP vs WPA vs WPA2
WEP
WPA
WPA2
ENCRYPTION
RC4
RC4
AES
KEY ROTATION
NONE
Dynamic Session Keys
Dynamic Session Keys
KEY DISTRIBUTION
Manually typed into each device
Automatic distribution available
Automatic distribution available
AUTHENTICATION
Uses WEP key as Authentication
Can use 802.1x & EAP
Can use 802.1x & EAP
Data Link Layer
Switching-Providing MAC address
Framing-Send blocks of data (frames) between physical devices
Dealing with transmission errors(Node-Node Error Control)
Regulating data flow(Flow control)
It mainly uses the hardware device Switches.
Switches
Switches do following functions,
Hardware address learning
Intelligent forwarding of frames
Loop avoidance
Switches support three methods of forwarding frames.
Store-and-Forward method
Cut-Through (Real Time) method
Fragment-Free (Modified Cut-Through) method
Spanning Tree Protocol(STP)
Switches (and bridges) needed a mechanism to prevent loops from forming.
Switches utilize the Spanning Tree Protocol (STP) to maintain a loop-free environment.
STP Process
To maintain a loop-free environment, STP performs the following functions:
A Root Bridge is elected
Root Ports are identified
Designated Ports are identified
If a loop exists, a port is placed in Blocking state. If the loop is
removed the blocked port is activated again.
STP Process
Point to Point protocol
PPP is a data-link layer protocol, PPP uses a stack of other protocols to establish the link, to authenticate the parties involved, and to carry the network layer data.Three sets of protocols are used by PPP: Link control protocol
Authentication protocol
Network control protocol
Link Control Protocol (LCP)
It is responsible for establishing, maintaining, configuring, and terminating links.
It also provides negotiation mechanisms to set options between endpoints.
Both endpoints of the link must reach an agreement about the options before the link can be established.
When PPP is carrying an LCP packet, it is either in the establishing state or in the terminating state.
All LCP packets are carried in the data field of the PPP frame.
Authentication Protocols
Authentication plays a very important role in PPP because PPP is designed for use over dial-up links where verification of user identity is necessary.
Authentication means validating the identity of a user who needs to access a set of resources.
PPP uses two protocols for authentication: Password Authentication Protocol (PAP)
Challenge Handshake Authentication Protocol (CHAP)
Password Authentication Protocol (PAP)
The user who wants to access a system sends an ID (identification) and a password.The system checks the validity of the identification and password and either accepts or denies a connection.
Challenge Handshake Authentication Protocol (CHAP)
The CHAP protocol is a three-way handshaking authentication protocol that provides greater security than PAP.In this method, the password is kept secret; it is never sent on-line.
Network Control Protocol (NCP)
After the link is established and authentication (if any) is successful, the connection goes on the networking state.
NCP is a set of control protocols to allow the encapsulation of data coming from network layer protocols into the PPP frame.
The set of packets that establish and terminate a network layer connection is called Internetwork Protocol Control Protocol (IPCP).
NCP Example
Network Layer
Routing and Forwarding
Logical addressing
Transport packet from sending to receiving hostsA logical address contains two components: Network ID identifies which network a host belongs to. Host ID uniquely identifies the host on that network.Logical addressing protocols include
Internetwork Packet Exchange (IPX)
Internet Protocol (IP).
IPv4 address Classes
Class First Octet Range Default Subnet Mask
Class A 1 126 255.0.0.0
Class B 128 191 255.255.0.0
Class C 192 223 255.255.255.0
Class D 224 239 -
Class E 240 255 -
Ranges 127.x.x.x are reserved for the loopback or localhost.
127.0.0.1 is a comman Loopback address.
Routing And Forwarding
1
2
3
0111
value in arrivingpackets header
routing algorithm
local forwarding table
header value
output link
0100010101111001
3221
Routing algorithm determines
end-end-path through network
Forwarding table determineslocal forwarding at this router
Routing-Determine route taken by packets from source to destination
Forwarding-Move packets from routers input to appropriate router output
Transport Layer
This layer is responsible for the reliable transfer of data, by ensuring that data arrives at its destination error-free and in order.
It provides Port number to specifies the Application.
It is Host-to-Host layer.
Transport layer communication falls under two categories:
Connection-oriented requires that a connection with specific agreed-upon parameters be established before data is sent.(TCP)
Connectionless requires no connection before data is sent.(UDP)
Some common Port numbers
Port Number Transport Protocol Application
20, 21 TCP FTP
22 TCP SSH
23 TCP Telnet
25 TCP SMTP
53 TCP/UDP DNS
80 TCP HTTP
110 TCP POP3
443 TCP SSL
666 TCP Doom
Transmission Control Protocol(TCP)
Connection establishment connections are established, maintained, and ultimately terminated between devices.
Segmentation and sequencing data is segmented into smaller pieces for transport. Each segment is assigned a sequence number, so that the receiving device can reassemble the data on arrival.
Acknowledgments receipt of data is confirmed through the use of acknowledgments. If a segment is lost, data can be retransmitted to guarantee delivery.
Flow control (or windowing) data transfer rate is negotiated to prevent congestion.
Connection Termination.
TCP Process
User Datagram Protocol(UDP)
The User Datagram Protocol (UDP) is a connectionless,unreliable transport protocol.
UDP experiences less latency(High speed transmission)
It provides no three-way handshake, no flow-control, no sequencing, and no acknowledgment of data receipt.
UDP essentially forwards the segment
UDP ideal for applications that require speed over reliability. For example, DNS primarily uses UDP as its transport protocol
Session Layer
The session layer is responsible for dialog
control and synchronization.
The session layer defines how to start, control and end conversations (called sessions) between applications.
This includes starting, stopping, and re-synchronizing communications between applications on two computers.
The session layer offers provisions for efficient data transfer.Session layer Protocols,
Structured Query Language (SQL)
Remote Procedure Call (RPC)
Network File system(NFS)
Basic Functions for the Session Layer
Managing multiple sessionsA computer can establish multiple sessions with several other computers
e.g., session 1: exchanging information over the World Wide Web with www.yahoo.comsession 2: exchanging information over the World Wide Web with www.google.comsession 3: exchanging information over the World Wide Web with www.espn.comTwo computers can also establish multiple sessions,
e.g., function 1: exchanging information over the World Wide Web; function 2: exchanging information over the FTP; function 3: exchanging information over the email
Session layer Examples
Software
music
news
Presentation Layer
The presentation layer is responsible for translation, compression, and encryption.
This layer controls the formatting and syntax of user data for the application layer.
This ensures that data from the sending application can be understood by the receiving application.
Examples of Presentation layer formats include: Text - RTF, ASCII, EBCDIC Images - GIF, JPG, TIF Audio - MIDI, MP3, WAV Movies - MPEG, AVI, MOV
Presentation Layer Protocols
This layer has two protocols for secure purpose of transmission
1.Transport layer Security Protocols(TLS)
The primary goal of the TLS protocol is to provide privacy and data integrity between two communicating applications
In practice, used to protect information transmitted between browsers and Web servers
2.Secured Socket Layer protocols(SSL)SSL is an Internet security protocol used by Internet browsers and Web servers to transmit sensitive information.
Both protocols works on three features like Confidentiality, integrity, and Availability.
SSL/TLS
Cryptography
Cryptography is the practice and study of hiding information. It is the Art or Science of converting a plain intelligible data into an unintelligible data and again retransforming that message into its original form.It provides Confidentiality, Integrity, Accuracy.Encryption The process of converting plain text into an unintelligible format (cipher text) is called Encryption.Decryption The process of converting cipher text into a plain text is called Decryption
Symmetric And Asymmetric Key Methods
Symmetric Key Cryptography (Secret Key Cryptography)Same Key is used by both partiesAdvantagesSimpler and FasterDisadvantagesLess Secured
Asymmetric Key Cryptography (Public Key Cryptography)2 different keys are usedUsers get the Key from an Certificate AuthorityAdvantagesMore SecuredAuthenticationDisadvantagesRelatively Complex
Application Layer
It mainly provides user interface
Everything at this layer is application-specific.
This layer provides application services for file transfers, e-mail, and other network software services
This layer handles issues like network transparency, resource allocation and problem partitioning.
Application Layer Protocols
DNS- Domain Name systemHTTP - Hyper Text Transfer ProtocolFTP - File Transfer ProtocolPOP 3-Post Office ProtocolIMAP- Internet Message Access protocolSMTP - Simple Mail Transfer ProtocolTelnet - Remote Access
Domain Name system(DNS)
DNS is a host name to IP address translation service.
DNS is a distributed database implemented in a hierarchy of name servers.
An application level protocol for message exchange between clients and servers.
Root DNS Servers
com DNS servers
org DNS servers
edu DNS servers
poly.eduDNS servers
umass.eduDNS servers
yahoo.comDNS servers
amazon.comDNS servers
pbs.orgDNS servers
DNS Process
Hyper Text Transfer Protocol(HTTP)
HTTP is the protocol that supports communication between web browsers and web servers
It provides web services.
HTTP can support multiple request-reply exchanges over a single TCP connection.
The well known TCP port for HTTP servers is port 80.
File Transfer Protocol(FTP)
File Transfer Protocol (FTP) is the standard mechanism provided by TCP/IP for copying a file from one host to another.FTP uses the services of TCP. It needs two TCP connections.The well-known port 21 is used for the control connection and the well-known port 20 for the data connection.
Electronics Mail(SMTP,POP3,IMAP)
SMTP-Uses TCP to reliably transfer email message from client to server, port 25.
It is a push protocol; it pushes the message from the client to the server.
POP- Protocol used to retrieve email from a mail server.
It stores and forwards messages
IMAP- Keep all messages in one place(The server).
Allows user to organize messages in folders.
Electronics Mailing
Internet
POPStore
IMAPstore
Mail Server
MailClient
Internet Message Access Protocol
IMAP
SMTP
SMTP
MailClient
POP
SMTP
Telnet
It is the standard TCP/IP protocol
Telnet allows a user to log into a computer across an internet.
Telnet establishes a TCP connection and then passes keystrokes from the users keyboard directly to the remote computer .
Telnet offers three basic services .1. It defines a network virtual terminal that provides a standard interface to remote systems.2. Telnet includes a mechanism that allows the client and server to negotiate options .3. Telnet treats both ends of the connection symmetrically.
TELNET Operation
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