Osi layer and network protocol

OSI Layer and Network ProtocolOSI Layer and Network Protocol
B.Tech 3rd
Semester
ADTU

ISO/OSI Model in Communication Networks
• There are n numbers of users who use computer
network and are located over the world. So to
ensure, national and worldwide data
communication, systems must be developed which
are compatible to communicate with each other.
ISO has developed this. ISO stands for International
organization of Standardization. This is called a
model for Open System Interconnection (OSI) and is
commonly known as OSI model.
• The ISO-OSI model is a seven layer architecture. It
defines seven layers or levels in a complete
communication system.

Feature of OSI Model :
• Big picture of communication over network is
understandable through this OSI model.
• We see how hardware and software work
together.
• We can understand new technologies as they are
developed.
• Troubleshooting is easier by separate networks.
• Can be used to compare basic functional
relationships on different networks.

ISO/OSI 7 layer communication System:ISO/OSI 7 layer communication System:

Functions of each Layer :Functions of each Layer :
– Layer 1: The Physical Layer :
• It is the lowest layer of the OSI Model.
• It activates, maintains and deactivates the physical
connection.
• It is responsible for transmission and reception of
the unstructured raw data over network.
• Voltages and data rates needed for transmission is
defined in the physical layer.
• It converts the digital/analog bits into electrical
signal or optical signals.
• Data encoding is also done in this layer.

– Layer 2: Data Link Layer :
• Data link layer synchronizes the information which is to be
transmitted over the physical layer.
• The main function of this layer is to make sure data
transfer is error free from one node to another, over the
physical layer.
• Transmitting and receiving data frames sequentially is
managed by this layer.
• This layer sends and expects acknowledgements for
frames received and sent respectively. Resending of non-
acknowledgement received frames is also handled by this
layer.
• This layer establishes a logical layer between two nodes
and also manages the Frame traffic control over the
network. It signals the transmitting node to stop, when the
frame buffers are full.

– Layer 3: The Network Layer :
• It routes the signal through different channels
from one node to other.
• It acts as a network controller. It manages the
Subnet traffic.
• It decides by which route data should take.
• It divides the outgoing messages into packets
and assembles the incoming packets into
messages for higher levels.

– Layer 4: Transport Layer :
• It decides if data transmission should be on
parallel path or single path.
• Functions such as Multiplexing, Segmenting or
Splitting on the data are done by this layer
• It receives messages from the Session layer
above it, convert the message into smaller units
and passes it on to the Network layer.
• Transport layer can be very complex, depending
upon the network requirements.
• Transport layer breaks the message (data) into
small units so that they are handled more
efficiently by the network layer.

– Layer 5: The Session Layer :
• Session layer manages and synchronize the
conversation between two different applications.
• Transfer of data from source to destination
session layer streams of data are marked and are
resynchronized properly, so that the ends of the
messages are not cut prematurely and data loss
is avoided.

– Layer 6: The Presentation Layer :
• Presentation layer takes care that the data is
sent in such a way that the receiver will
understand the information (data) and will be
able to use the data.
• While receiving the data, presentation layer
transforms the data to be ready for the
application layer.
• Languages(syntax) can be different of the two
communicating systems. Under this condition
presentation layer plays a role of translator.
• It perfroms Data compression, Data encryption,
Data conversion etc.

– Layer 7: Application Layer :
• It is the topmost layer.
• Transferring of files disturbing the results to the
user is also done in this layer. Mail services,
directory services, network resource etc are
services provided by application layer.
• This layer mainly holds application programs to
act upon the received and to be sent data.

– Merits of OSI reference model:
• OSI model distinguishes well between the
services, interfaces and protocols.
• Protocols of OSI model are very well hidden.
• Protocols can be replaced by new protocols as
technology changes.
• Supports connection oriented services as well as
connectionless service.

Elaborate discussion of each layerElaborate discussion of each layer

FUNCTIONS OF PHYSICAL LAYER:
• Representation of Bits: Data in this layer consists of stream of bits. The
bits must be encoded into signals for transmission. It defines the type of
encoding i.e. how 0’s and 1’s are changed to signal.
• Data Rate: This layer defines the rate of transmission which is the
number of bits per second.
• Synchronization: It deals with the synchronization of the transmitter
and receiver. The sender and receiver are synchronized at bit level.
• Interface: The physical layer defines the transmission interface
between devices and transmission medium.
• Line Configuration: This layer connects devices with the medium: Point
to Point configuration and Multipoint configuration.
• Topologies: Devices must be connected using the following topologies:
Mesh, Star, Ring and Bus.
• Transmission Modes: Physical Layer defines the direction of
transmission between two devices: Simplex, Half Duplex, Full Duplex.
• Deals with baseband and broadband transmission.

FUNCTIONS OF DATA LINK LAYER:
• Framing: Frames are the streams of bits received from the network
layer into manageable data units. This division of stream of bits is done
by Data Link Layer.
• Physical Addressing: The Data Link layer adds a header to the frame in
order to define physical address of the sender or receiver of the frame,
if the frames are to be distributed to different systems on the network.
• Flow Control: A flow control mechanism to avoid a fast transmitter
from running a slow receiver by buffering the extra bit is provided by
flow control. This prevents traffic jam at the receiver side.
• Error Control: Error control is achieved by adding a trailer at the end of
the frame. Duplication of frames are also prevented by using this
mechanism. Data Link Layers adds mechanism to prevent duplication of
frames.
• Access Control: Protocols of this layer determine which of the devices
has control over the link at any given time, when two or more devices
are connected to the same link.

FUNCTIONS OF NETWORK LAYER:
• It translates logical network address into
physical address. Concerned with circuit,
message or packet switching.
• Routers and gateways operate in the network
layer. Mechanism is provided by Network Layer
for routing the packets to final destination.
• Connection services are provided including
network layer flow control, network layer error
control and packet sequence control.
• Breaks larger packets into small packets.

FUNCTIONS OF TRANSPORT LAYER:
• Service Point Addressing : Transport Layer header includes service
point address which is port address. This layer gets the message to the
correct process on the computer unlike Network Layer, which gets each
packet to the correct computer.
• Segmentation and Reassembling : A message is divided into segments;
each segment contains sequence number, which enables this layer in
reassembling the message. Message is reassembled correctly upon
arrival at the destination and replaces packets which were lost in
transmission.
• Connection Control : It includes 2 types :
– Connectionless Transport Layer : Each segment is considered as an
independent packet and delivered to the transport layer at the destination
machine.
– Connection Oriented Transport Layer : Before delivering packets,
connection is made with transport layer at the destination machine.
• Flow Control : In this layer, flow control is performed end to end.
• Error Control : Error Control is performed end to end in this layer to
ensure that the complete message arrives at the receiving transport
layer without any error. Error Correction is done through
retransmission.

FUNCTIONS OF SESSION LAYER:
• Dialog Control : This layer allows two systems to
start communication with each other in half-
duplex or full-duplex.
• Synchronization : This layer allows a process to
add checkpoints which are considered as
synchronization points into stream of data.
Example: If a system is sending a file of 800
pages, adding checkpoints after every 50 pages is
recommended. This ensures that 50 page unit is
successfully received and acknowledged. This is
beneficial at the time of crash as if a crash
happens at page number 110; there is no need to
retransmit 1 to100 pages.

FUNCTIONS OF PRESENTATION LAYER:
• Translation : Before being transmitted, information in
the form of characters and numbers should be changed
to bit streams. The presentation layer is responsible for
interoperability between encoding methods as different
computers use different encoding methods. It translates
data between the formats the network requires and the
format the computer.
• Encryption : It carries out encryption at the transmitter
and decryption at the receiver.
• Compression : It carries out data compression to reduce
the bandwidth of the data to be transmitted. The
primary role of Data compression is to reduce the
number of bits to be 0transmitted. It is important in
transmitting multimedia such as audio, video, text etc.

FUNCTIONS OF APPLICATION LAYER:
• Mail Services : This layer provides the basis for E-mail
forwarding and storage.
• Network Virtual Terminal : It allows a user to log on to a
remote host. The application creates software emulation
of a terminal at the remote host. User’s computer talks
to the software terminal which in turn talks to the host
and vice versa. Then the remote host believes it is
communicating with one of its own terminals and allows
user to log on.
• Directory Services : This layer provides access for global
information about various services.
• File Transfer, Access and Management (FTAM) : It is a
standard mechanism to access files and manages it.
Users can access files in a remote computer and manage
it. They can also retrieve files from a remote computer.

The TCP/IP Reference Model :The TCP/IP Reference Model :
TCP/IP means Transmission Control Protocol and
Internet Protocol. It is the network model used in
the current Internet architecture as well.
Protocols are set of rules which govern every
possible communication over a network. These
protocols describe the movement of data
between the source and destination or the
internet. These protocols offer simple naming
and addressing schemes.

TCP/IP 4 layer communication system :TCP/IP 4 layer communication system :
Overview of TCP/IP reference model
TCP/IP that is Transmission Control Protocol and Internet
Protocol was developed by Department of Defence's
Project Research Agency (ARPA, later DARPA) as a part of
a research project of network interconnection to connect
remote machines.
The features that stood out during the research, which led
to making the TCP/IP reference model were:
Support for a flexible architecture. Adding more machines
to a network was easy.
The network was robust, and connections remained intact
untill the source and destination machines were
functioning.
The overall idea was to allow one application on one
computer to talk to(send data packets) another
application running on different computer.

Description of different TCP/IP protocols :Description of different TCP/IP protocols :
Layer 1: Host-to-network Layer :
• Lowest layer of the all.
• Protocol is used to connect to the host, so
that the packets can be sent over it.
• Varies from host to host and network to
network.

Layer 2: Internet layer :
• Selection of a packet switching network which
is based on a connectionless internetwork
layer is called a internet layer.
• It is the layer which holds the whole
architecture together.
• It helps the packet to travel independently to
the destination.
• Order in which packets are received is
different from the way they are sent.
• IP (Internet Protocol) is used in this layer.

Layer 3: Transport Layer :
• It decides if data transmission should be on parallel
path or single path.
• Functions such as multiplexing, segmenting or
splitting on the data is done by transport layer.
• The applications can read and write to the
transport layer.
• Transport layer adds header information to the
data.
• Transport layer breaks the message (data) into
small units so that they are handled more
efficiently by the network layer.
• Transport layer also arrange the packets to be sent,
in sequence.

Layer 4: Application Layer :
• The TCP/IP specifications described a lot of applications
that were at the top of the protocol stack. Some of them
were TELNET, FTP, SMTP, DNS etc.
• TELNET is a two-way communication protocol which
allows connecting to a remote machine and run
applications on it.
• FTP(File Transfer Protocol) is a protocol, that allows File
transfer amongst computer users connected over a
network. It is reliable, simple and efficient.
• SMTP(Simple Mail Transport Protocol) is a protocol, which
is used to transport electronic mail between a source and
destination, directed via a route.
• DNS(Domain Name Server) resolves an IP address into a
textual address for Hosts connected over a network.

Merits of TCP/IP model :
• It operated independently.
• It is scalable.
• Client/server architecture.
• Supports a number of routing protocols.
• Can be used to establish a connection between two
computers.
Demerits of TCP/IP :
• In this, the transport layer does not guarantee
delivery of packets.
• The model cannot be used in any other application.
• Replacing protocol is not easy.
• It has not clearly separated its services, interfaces
and protocols.

Diagrammatic Comparison between OSI Reference
Model and TCP/IP Reference Model

Osi layer and network protocol

What is Protocol :
Sometimes referred to as an access method, a
protocol is a standard used to define a method of
exchanging data over a computer network such
as local area network, Internet, Intranet, etc.
Each protocol has its own method of how data is
formatted when sent and what to do with it once
received, how that data is compressed or how to
check for errors in data.

Example of popular Protocol:
• HTTP (Hyper Text Transfer Protocol)
• FTP (File Transfer Protocol)
• SMTP (Simple Mail Transfer Protocol)
• PPP (Point-to-Point Protocol)
• ARP (Address Resolution Protocol)
• TCP/IP (Transmission Control
Protocol/Internet Protocol)
• UDP (User Datagram Protocol)

Application Layer Protocol :Application Layer Protocol :
• FTP
• SOCKS (Socket Secure)
• SSH (Secure Shell)
• Telnet
• TLS/SSL (Transport Layer Security/Secure
Sockets Layer)
• XMPP (Extensible Messaging & Presence
Protocol)
• WAP & IRC

FTP (File Transfer Protocol):FTP (File Transfer Protocol):
The File Transfer Protocol (FTP) is a standard network protocol used to transfer
computer files between a client and server on a computer network.
FTP may run in active or passive mode, which determines how the data
connection is established. In both cases, the client creates a TCP control
connection from a random, usually an unprivileged, port N to the FTP server
command port 21.
• In active mode, the client starts listening for incoming data connections from
the server on port M. It sends the FTP command PORT M to inform the server
on which port it is listening. The server then initiates a data channel to the
client from its port 20, the FTP server data port.
• In situations where the client is behind a firewall and unable to accept
incoming TCP connections, passive mode may be used. In this mode, the client
uses the control connection to send a PASV command to the server and then
receives a server IP address and server port number from the server, which the
client then uses to open a data connection from an arbitrary client port to the
server IP address and server port number received.
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Data transfer can be done in any of three modes:
Stream mode: Data is sent as a continuous stream,
relieving FTP from doing any processing. Rather,
all processing is left up to TCP. No End-of-file
indicator is needed, unless the data is divided
into records.
Block mode: FTP breaks the data into several
blocks (block header, byte count, and data field)
and then passes it on to TCP.
Compressed mode: Data is compressed using a
simple algorithm (usually run-length encoding).

Secure Shell (SSH):Secure Shell (SSH):
Secure Shell (SSH) is a cryptographic network protocol for
operating network services securely over an unsecured
network. The best known example application is for remote
login to computer systems by users.
SSH provides a secure channel over an unsecured network in
a client-server architecture, connecting an SSH client
application with an SSH server. Common applications include
remote command-line login and remote command execution,
but any network service can be secured with SSH. The
protocol specification distinguishes between two major
versions, referred to as SSH-1 and SSH-2.
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SSH uses public-key cryptography to authenticate the
remote computer and allow it to authenticate the user,
if necessary. There are several ways to use SSH; one is
to use automatically generated public-private key pairs
to simply encrypt a network connection, and then use
password authentication to log on.
SSH is typically used to log in to a remote machine and
execute commands, but it also supports tunnelling,
forwarding TCP ports and X11 connections; it can
transfer files using the associated SSH file transfer
(SFTP) or secure copy (SCP) protocols. SSH uses the
client-server model.
The standard TCP port 22 has been assigned for
contacting SSH servers.

The SSH-2 protocol has an internal architecture (defined in RFC 4251)
with well-separated layers, namely:
• The transport layer (RFC 4253)
• The user authentication layer (RFC 4252)- widely used user
authentication methods are-
i. password
ii. Public key
iii. Keyboard interactive – (like OTP etc.)
iv. GSS API use Kerberos 5 or NTLM
• The connection layer (RFC 4254) - Standard channel types include:
• shell for terminal shells, SFTP and exec requests (including SCP transfers)
• direct-tcpip for client-to-server forwarded connections
• forwarded-tcpip for server-to-client forwarded connections
The SSHFP DNS record (RFC 4255) provides the public host key fingerprints in order to
aid in verifying the authenticity of the host.

Remote Terminal Control Protocol (Telnet):Remote Terminal Control Protocol (Telnet):
Telnet is an application layer protocol used on the Internet or local
area Networks to provide a bidirectional interactive text-oriented
communication facility using a virtual terminal connection. User
data is interspersed in-band with Telnet control information in an
8-bit byte oriented data connection over the Transmission Control
Protocol (TCP).
Telnet is a client-server protocol, based on a reliable connection-
oriented transport. Typically, this protocol is used to establish a
connection to Transmission Control Protocol(TCP) port number
23, where a Telnet server application (telnetd) is listening. Telnet,
however, predates TCP/IP and was originally run over Network
Control Program (NCP) protocols.
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Problems with Telnet :
Telnet, by default, does not encrypt any data sent over the
connection (including passwords), and so it is often feasible to
eavesdrop on the communications and use the password later for
malicious purposes; anybody who has access to a router, switch,
hub or gateway located on the network between the two hosts
where Telnet is being used can intercept the packets passing by
and obtain login, password and whatever else is typed with a
packet analyser.
• Most implementations of Telnet have no authentication that
would ensure communication is carried out between the two
desired hosts and not intercepted in middle ware.
• Several vulnerabilities have been discovered over the years in
commonly used Telnet daemons.

Transport Layer Security/Secure SocketsTransport Layer Security/Secure Sockets
Layer (TLS/SSL):Layer (TLS/SSL):
Transport Layer Security (TLS) and its predecessor, Secure Sockets
Layer (SSL), both frequently referred to as "SSL", are
cryptographic protocols that provide communications security
over a computer network. Several versions of the protocols find
widespread use in applications such as web browsing, email,
Internet faxing, instant messaging, and voice-over-IP (VoIP).
Major websites use TLS to secure all communications between
their servers and web browsers.
The Transport Layer Security protocol aims primarily to provide
privacy and data integrity between two communicating computer
applications. When secured by TLS, connections between a client
(e.g., a web browser) and a server (e.g., wikipedia.org) have one
or more of the following properties:
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• The connection is private (or secure) because symmetric
cryptography is used to encrypt the data transmitted.
• The identity of the communicating parties can be authenticated
using public-key cryptography. This authentication can be made
optional, but is generally required for at least one of the parties
(typically the server).
• The connection ensures integrity because each message
transmitted includes a message integrity check using a message
authentication code to prevent undetected loss or alteration of
the data during transmission.
The TLS protocol comprises two layers:
a. the TLS record protocol and
b. the TLS handshake protocol.
Client-server applications use the TLS protocol to communicate
across a network in a way designed to prevent eavesdropping
and tampering. Continue..

Once the client and server have agreed to use TLS, they negotiate a
stateful connection by using a handshaking procedure. During
this handshake, the client and server agree on various
parameters used to establish the connection's security:
• The handshake begins when a client connects to a TLS-enabled
server requesting a secure connection and presents a list of
supported cipher suites (ciphers and hash functions).
• From this list, the server picks a cipher and hash function that it
also supports and notifies the client of the decision.
• The server usually then sends back its identification in the form of
a digital certificate. The certificate contains the server name, the
trusted certificate authority (CA) and the server's public
encryption key.
• The client confirms the validity of the certificate before
proceeding.
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• To generate the session keys used for the secure connection, the
client either:
a. encrypts a random number with the server's public key and
sends the result to the server (which only the server should be
able to decrypt with its private key); both parties then use the
random number to generate a unique session key for subsequent
encryption and decryption of data during the session
b. uses Diffie-Hellman key exchange to securely generate a
random and unique session key for encryption and decryption
that has the additional property of forward secrecy: if the server's
private key is disclosed in future, it cannot be used to decrypt the
current session, even if the session is intercepted and recorded
by a third party.
This concludes the handshake and begins the secured connection,
which is encrypted and decrypted with the session key until the
connection closes. If any one of the above steps fail, the TLS
handshake fails, and the connection is not created.

Extensible Messaging & Presence ProtocolExtensible Messaging & Presence Protocol
(XMPP):(XMPP):
Extensible Messaging and Presence Protocol (XMPP) is a
communications protocol for message-oriented middleware
based on XML (Extensible Markup Language). It enables the near-
real-time exchange of structured yet extensible data between
any two or more network entities.
Unlike most instant messaging protocols, XMPP is defined in an
open standard and uses an open systems approach of
development and application, by which anyone may implement
an XMPP service and interoperate with other organizations'
implementations. Because XMPP is an open protocol,
implementations can be developed using any software license;

Wireless Application Protocol (WAP) :Wireless Application Protocol (WAP) :
Wireless Application Protocol (WAP) is a technical standard for
accessing information over a mobile wireless network. A WAPWAP
browserbrowser is a web browserweb browser for mobile devices such as mobile
phones that uses the protocol. Before the introduction of WAP,
mobile service providers had limited opportunities to offer
interactive data services, but needed interactivity to support
Internet and Web applications such as:
• Email by mobile phone
• Tracking of stock-market prices
• Sports results
• News headlines
• Music downloads
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The WAP standard described a protocol suite allowing the
interoperability of WAP equipment, and software with different
network technologies, such as GSM and IS-95 (also known as
CDMA).
WAP Protocol suite includes following protocols –
• Wireless Application Environment (WAE) WAP protocol suite
• Wireless Session Protocol (WSP)
• Wireless Transaction Protocol (WTP)
• Wireless Transport Layer Security (WTLS)
• Wireless Datagram Protocol (WDP)
• *** Any Wireless Data Network ***

Transmission Control Protocol/ Internet Protocol:Transmission Control Protocol/ Internet Protocol:
The Transmission Control Protocol (TCP)Transmission Control Protocol (TCP) is one of the main protocols of the
Internet protocol suite. It originated in the initial network
implementation in which it complemented the Internet Protocol (IP).
Therefore, the entire suite is commonly referred to as TCP/IP. TCP
provides reliable, ordered, and error-checkedreliable, ordered, and error-checked delivery of a stream of
octets between applications running on hosts communicating by an IP
network. Major Internet applications such as the World Wide Web,
email, remote administration and file transfer rely on TCP. Applications
that do not require reliable data stream service may use the User
Datagram Protocol (UDP), which provides a connectionless datagram
service that emphasizes reduced latency over reliability.
Transmission Control Protocol accepts data from a data stream, divides it
into chunks, and adds a TCP header creating a TCP segment. The TCP
segment is then encapsulated into an Internet Protocol (IP) datagram,
and exchanged with peers.
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To establish a connection, TCP uses a three-way handshakethree-way handshake. Before a client
attempts to connect with a server, the server must first bind to and listen at 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:
1. 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.
2. SYN-ACK: In response, the server replies with a SYN-ACK. The acknowledgment
number is set to one more than the received sequence number i.e. A+1, and the
sequence number that the server chooses for the packet is another random
number, B.
3. ACK: Finally, the client sends an ACK back to the server. The sequence number is
set to the received acknowledgement value i.e. A+1, and the acknowledgement
number is set to one more than the received sequence number i.e. B+1.
At this point, both the client and server have received an acknowledgment of the
connection. The steps 1, 2 establish the connection parameter (sequence
number) for one direction and it is acknowledged. The steps 2, 3 establish the
connection parameter (sequence number) for the other direction and it is
acknowledged. With these, a full-duplex communication is established.

User Datagram Protocol (UDP):User Datagram Protocol (UDP):
UDP uses a simple connectionless transmissionconnectionless transmission model with a minimum of
protocol mechanism. UDP provides checksums for data integrity, and
port numbers for addressing different functions at the source and
destination of the datagram. It has no handshaking dialogues, and thus
exposes the user's program to any unreliabilityunreliability of the underlying
network and so there is no guarantee of delivery, ordering, or duplicate
protection. If error correction facilities are needed at the network
interface level, an application may use the Transmission Control
Protocol (TCP) or Stream Control Transmission Protocol (SCTP) which
are designed for this purpose.
UDP is a minimal message-oriented transport layer protocol that is
documented in RFC 768. UDP provides no guarantees to the upper layer
protocol for message delivery and the UDP layer retains no state of UDP
messages once sent. For this reason, UDP sometimes is referred to as
Unreliable Datagram Protocol.
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A number of UDP's attributes make it especially suited for certain
applications.
• It is transaction-oriented, suitable for simple query-response protocols
such as the Domain Name System or the Network Time Protocol.
• It provides datagrams, suitable for modeling other protocols such as in
IP tunnelingIP tunneling or Remote Procedure CallRemote Procedure Call and the Network File SystemNetwork File System.
• It is simple, suitable for bootstrapping or other purposes without a full
protocol stack, such as the DHCPDHCP and Trivial File Transfer ProtocolTrivial File Transfer Protocol.
• It is stateless, suitable for very large numbers of clients, such as in
streaming media applications for example IPTVIPTV
• The lack of retransmission delays makes it suitable for real-time
applications such as Voice over IPVoice over IP, online games, and many protocols
built on top of the Real Time Streaming ProtocolReal Time Streaming Protocol.
• Works well in unidirectional communication, suitable for broadcast
information such as in many kinds of service discovery and shared
information such as broadcast time or Routing Information Protocol
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User Datagram Protocol is a simpler message-based connectionless protocol.
Connectionless protocols do not set up a dedicated end-to-end connection.
Communication is achieved by transmitting information in one direction from
source to destination without verifying the readiness or state of the receiver.
• UnreliableUnreliable – When a UDP message is sent, it cannot be known if it will reach its
destination; it could get lost along the way. There is no concept of
acknowledgment, retransmission, or timeout.
• Not orderedNot ordered – If two messages are sent to the same recipient, the order in
which they arrive cannot be predicted.
• LightweightLightweight – There is no ordering of messages, no tracking connections, etc. It
is a small transport layer designed on top of IP.
• DatagramsDatagrams – Packets are sent individually and are checked for integrity only if
they arrive. Packets have definite boundaries which are honored upon receipt,
meaning a read operation at the receiver socket will yield an entire message as
it was originally sent.
• No congestion controlNo congestion control – UDP itself does not avoid congestion. Congestion
control measures must be implemented at the application level.
• BroadcastsBroadcasts - being connectionless, UDP can broadcast - sent packets can be
addressed to be receivable by all devices on the subnet.

Datagram Congestion Control Protocol (DCCP):Datagram Congestion Control Protocol (DCCP):
The Datagram Congestion Control Protocol (DCCP) is a message-orientedmessage-oriented
transport layer protocol. DCCP implements reliable connection setup,
teardown, Explicit Congestion Notification (ECN), congestion control, and
feature negotiation. DCCP was published as RFC 4340, a proposed
standard, by the IETF in March, 2006. RFC 4336 provides an introduction.
FreeBSD had an implementation for version 5.1.[1] Linux also had an
implementation of DCCP first released in Linux kernel version 2.6.14
(released October 28, 2005).
DCCP provides a way to gain access to congestion control mechanisms
without having to implement them at the application layer. It allows for
flow-based semantics like in Transmission Control Protocol (TCP), but
does not provide reliable in-order delivery. Sequenced delivery within
multiple streams as in the Stream Control Transmission Protocol (SCTP) is
not available in DCCP.
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DCCP is useful for applications with timing constraints on the delivery
of data. Such applications include streaming media, multiplayerstreaming media, multiplayer
online games and Internet telephonyonline games and Internet telephony. The primary feature of these
applications is that old messages quickly become stale so that
getting new messages is preferred to resending lost messages.
Currently such applications have often either settled for TCP or
used User Datagram Protocol (UDP) and implemented their own
congestion control mechanisms, or have no congestion control at
all.
While being useful for these applications, DCCP can also be
positioned as a general congestion control mechanism for UDP-
based applications, by adding, as needed, a mechanism for reliable
and/or in-order delivery on the top of UDP/DCCP. In this context,
DCCP allows the use of different, but generally TCP-friendly
congestion control mechanisms.
Continue..

A DCCP connection contains acknowledgement traffic as well as data
traffic. Acknowledgments inform a sender whether its packets
have arrived, and whether they were marked by ExplicitExplicit
Congestion Notification (ECN)Congestion Notification (ECN). Acknowledgements are transmitted
as reliably as the congestion control mechanism in use requires,
possibly completely reliably.
DCCP has the option for very long (48-bit) sequence numbers
corresponding to a packet ID, rather than a byte ID as in TCP. The
long length of the sequence numbers is intended to guard against
"some blind attacks, such as the injection of DCCP-Resets into the
connection."

Stream Control Transmission Protocol (SCTP):Stream Control Transmission Protocol (SCTP):
Stream Control Transmission Protocol (SCTP) is a transport-layer protocol, serving
in a similar role to the popular protocols TCP and UDP. It is standardized by IETF
in RFC 4960RFC 4960.
SCTP provides some of the same service features of both: it is message-oriented
like UDP and ensures reliable, in-sequence transport of messages with
congestion control like TCP; it differs from these in providing multi-homing and
redundant paths to increase resilience and reliability.
In the absence of native SCTP support in operating systems it is possible to tunnel
SCTP over UDP, as well as mapping TCP API calls to SCTP ones.
SCTP applications submit their data to be transmitted in messages (groups of bytes)
to the SCTP transport layer. SCTP places messages and control information into
separate chunks (data chunks and control chunks), each identified by a chunk
header. The protocol can fragment a message into a number of data chunks,
but each data chunk contains data from only one user message. SCTP bundles
the chunks into SCTP packets. The SCTP packet, which is submitted to the
Internet Protocol, consists of a packet header, SCTP control chunks (when
necessary), followed by SCTP data chunks (when available).
Continue.

One can characterize SCTP as message-orientedmessage-oriented, meaning it transports a sequence
of messages (each being a group of bytes), rather than transporting an
unbroken stream of bytes as does TCP. As in UDP, in SCTP a sender sends a
message in one operation, and that exact message is passed to the receiving
application process in one operation. In contrast, TCP is a stream-oriented
protocol, transporting streams of bytes reliably and in order. However TCP
does not allow the receiver to know how many times the sender application
called on the TCP transport passing it groups of bytes to be sent out. At the
sender, TCP simply appends more bytes to a queue of bytes waiting to go out
over the network, rather than having to keep a queue of individual separate
outbound messages which must be preserved as such.
The term multi-streaming refers to the capability of SCTP to transmit several
independent streams of chunks in parallel, for example transmitting web page
images together with the web page text. In essence, it involves bundling
several connections into a single SCTP association, operating on messages (or
chunks) rather than bytes.
TCP preserves byte order in the stream by including a sequence number with each
segment. SCTP, on the other hand, assigns a sequence number to each
message sent in a stream. This allows independent ordering of messages in
different streams. However, message ordering is optional in SCTP; a receiving
application may choose to process messages in the order of receipt instead of

Resource reservation Protocol (RSVP):Resource reservation Protocol (RSVP):
The Resource Reservation Protocol (RSVP) is a Transport Layer protocolTransport Layer protocol
designed to reserve resources across a network for an integrated
services Internet. RSVP operates over an IPv4 or IPv6 Internet Layer and
provides receiver-initiated setup of resource reservations for multicast or
uni-cast data flows with scaling and robustness. It does not transport
application data but is similar to a control protocol, like Internet Control
Message Protocol (ICMP) or Internet Group Management Protocol
(IGMP). RSVP is described in RFC 2205RFC 2205.
RSVP can be used by either hosts or routers to request or deliver specific
levels of quality of service (QoS)quality of service (QoS) for application data streams or flows.
RSVP defines how applications place reservations and how they can
relinquish the reserved resources once the need for them has ended.
RSVP operation will generally result in resources being reserved in each
node along a path.
RSVP is not a routing protocol and was designed to interoperate with
current and future routing protocols.
Continue..

RSVP by itself is rarely deployed in telecommunications networks today but the
traffic engineering extension of RSVP, or RSVP-TE, is becoming more widely
accepted now a days in many QoS-oriented networksQoS-oriented networks. Next Steps in Signaling
(NSIS) is a replacement for RSVP.
1. RSVP requests resources for simplex flows: a traffic stream in only one direction
from sender to one or more receivers.
2. RSVP is not a routing protocol but works with current and future routing
protocols.
3. RSVP is receiver oriented: in that the receiver of a data flow initiates and
maintains the resource reservation for that flow.
4. RSVP maintains "soft state" (the reservation at each node needs a periodic
refresh) of the host and routers' resource reservations, hence supporting
dynamic automatic adaptation to network changes.
5. RSVP provides several reservation styles (a set of reservation options) and
allows for future styles to be added to protocol revisions to fit varied
applications.
6. RSVP transports and maintains traffic and policy control parameters that are
opaque to RSVP.

Explicit Congestion Notification (ECN):Explicit Congestion Notification (ECN):
Explicit Congestion Notification (ECN) is an extension to the Internet Protocolextension to the Internet Protocol and
to the Transmission Control Protocol and is defined in RFC 3168 (2001). ECN
allows end-to-end notification of network congestion without dropping packets.
ECN is an optional feature that may be used between two ECN-enabled
endpoints when the underlying network infrastructure also supports it.
Conventionally, TCP/IP networks signal congestion by dropping packets. When ECN
is successfully negotiated, an ECN-aware router may set a mark in the IP header
instead of dropping a packet in order to signal impending congestion. The
receiver of the packet echoes the congestion indication to the sender, which
reduces its transmission rate as if it detected a dropped packet.
ECN requires specific support at both the Internet layer and the transport layer for
the following reasons:
• In TCP/IP, routers operate within the Internet layer, while the transmission rate
is handled by the endpoints at the transport layer.
• Congestion may be handled only by the transmitter, but since it is known to
have happened only after a packet was sent, there must be an echo of the
congestion indication by the receiver to the transmitter.

Internet Protocol Version 4 (IP4):Internet Protocol Version 4 (IP4):
Internet Protocol version 4 (IPv4) is the fourth version of the Internet
Protocol (IP). It is one of the core protocols of standards-based
internetworking methods in the Internet, and was the first version
deployed for production in the ARPANET in 1983. It still routes
most Internet traffic today,[1] despite the ongoing deployment of
a successor protocol, IPv6. IPv4 is described in IETF publication RFC
791 (September 1981), replacing an earlier definition (RFC 760RFC 760,
January 1980).
IPv4 is a connectionless protocol for use on packet-switchedpacket-switched
networks. It operates on a best effort delivery model, in that it
does not guarantee delivery, nor does it assure proper sequencing
or avoidance of duplicate delivery. These aspects, including data
integrity, are addressed by an upper layer transport protocol, such
as the Transmission Control Protocol (TCP).
Continue..

IPv4 uses 32-bit (four-byte) addresses, which limits the address space
to 4294967296 (232) addresses. This limitation stimulated the
development of IPv6 in the 1990s, which has been in commercial
deployment since 2006.
Because of the demand of the growing Internet, the small address
space finally suffered exhaustion on February 3, 2011, after having
been significantly delayed by classfulclassful network design, Classless
Inter-Domain Routing, and network address translation (NAT).
IPv4 addresses may be represented in any notation expressing a 32-
bit integer value. They are most often written in the dot-decimal
notation, which consists of four octets of the address expressed
individually in decimal numbers and separated by periods.

Internet Protocol Version 6 (IP6):Internet Protocol Version 6 (IP6):
Internet Protocol version 6 (IPv6) is the most recent version of the Internet Protocol
(IP), the communications protocol that provides an identification and location
system for computers on networks and routes traffic across the Internet. IPv6 was
developed by the Internet Engineering Task Force (IETF) to deal with the long-
anticipated problem of IPv4 address exhaustion. IPv6 is intended to replace IPv4.
Every device on the Internet is assigned a unique IP address for identification and
location definition. With the rapid growth of the Internet after commercialization
in the 1990s, it became evident that far more addresses would be needed to
connect devices than the IPv4 address space had available. By 1998, the Internet
Engineering Task Force (IETF) had formalized the successor protocol. IPv6 uses a
128-bit address, theoretically allowing 2128, or approximately 3.4×1038 addresses.
The actual number is slightly smaller, as multiple ranges are reserved for special
use or completely excluded from use. The total number of possible IPv6 addresses
is more than 7.9×1028 times as many as IPv4, which uses 32-bit addresses and
provides approximately 4.3 billion addresses. The two protocols are not designed
to be interoperable, complicating the transition to IPv6. However, several IPv6
transition mechanisms have been devised to permit communication between IPv4
and IPv6 hosts.
Continue..

Advantages:Advantages:
IPv6 provides other technical benefits in addition to a larger addressing
space. In particular, it permits hierarchical address allocation methods
that facilitate route aggregation across the Internet, and thus limit the
expansion of routing tables. The use of multicast addressing is expanded
and simplified, and provides additional optimization for the delivery of
services. Device mobility, security, and configuration aspects have been
considered in the design of the protocol.
IPv6 is an Internet Layer protocol for packet-switched internetworking and
provides end-to-end datagram transmission across multiple IP networks,
closely adhering to the design principles developed in the previous
version of the protocol, Internet Protocol Version 4 (IPv4). IPv6 was first
formally described in Internet standard document RFC 2460, published in
December 1998.
The main advantage of IPv6 over IPv4 is its larger address space. The length
of an IPv6 address is 128 bits, compared with 32 bits in IPv4. The address
space therefore has 2128 or approximately 3.4×1038 addresses.

Internet Protocol Security (IPSEC):Internet Protocol Security (IPSEC):
Internet Protocol Security (IPsec) is a protocol suite for secure Internet Protocol (IP)
communications that works by authenticating andencrypting each IP packet of a
communication session. IPsec includes protocols for establishing mutual
authentication between agents at the beginning of the session and negotiation
of cryptographic keys to be used during the session. IPsec can be used in
protecting data flows between a pair of hosts (host-to-host), between a pair of
security gateways (network-to-network), or between a security gateway and a
host (network-to-host). Internet Protocol security (IPsec) uses cryptographic
security services to protect communications over Internet Protocol (IP)
networks. IPsec supports network-level peer authentication, data origin
authentication, data integrity, data confidentiality (encryption), and replay
protection.
IPsec is an end-to-end security scheme operating in the Internet Layer of the
Internet Protocol Suite, while some other Internet security systems in
widespread use, such as Transport Layer Security (TLS) and Secure Shell (SSH),
operate in the upper layers at the Transport Layer (TLS) and the Application
layer (SSH). Hence, only IPsec protects all application traffic over an IP network.
Applications can be automatically secured by IPsec at the IP layer.
Continue..

The IPsec suite is an open standard. IPsec uses the following protocols to perform
various functions:
• Authentication Headers (AH)Authentication Headers (AH) provide connectionless data integrity and data
origin authentication for IP datagrams and provides protection against replay
attacks.
• Encapsulating Security Payloads (ESP)Encapsulating Security Payloads (ESP) provide confidentiality, data-origin
authentication, connectionless integrity, an anti-replay service (a form of partial
sequence integrity), and limited traffic-flow confidentiality.
• Security Associations (SA)Security Associations (SA) provide the bundle of algorithms and data that
provide the parameters necessary for AH and/or ESP operations. The Internet
Security Association and Key Management Protocol (ISAKMP) provides a
framework for authentication and key exchange, with actual authenticated
keying material provided either by manual configuration with pre-shared keys,
Internet Key Exchange (IKE and IKEv2), Kerberized Internet Negotiation of Keys
(KINK), or IPSECKEY DNS records.
The IP security architecture uses the concept of a security association as the basis
for building security functions into IP. A security association is simply the bundle
of algorithms and parameters (such as keys) that is being used to encrypt and
authenticate a particular flow in one direction. Therefore, in normal bi-
directional traffic, the flows are secured by a pair of security associations.
Continue..Continue..

Security associations are established using the Internet Security Association and Key
Management Protocol (ISAKMP). ISAKMP is implemented by manual
configuration with pre-shared secrets, Internet Key Exchange (IKE and IKEv2),
Kerberized Internet Negotiation of Keys (KINK), and the use of IPSECKEY DNS
records.[14][20][21] RFC 5386 defines Better-Than-Nothing Security (BTNS) as an
unauthenticated mode of IPsec using an extended IKE protocol.
IPsec can be implemented in a host-to-host transport modetransport mode, or in a networknetwork
tunneling modetunneling mode.
In transport mode, only the payload of the IP packet is usually encrypted or
authenticated. The routing is intact, since the IP header is neither modified nor
encrypted; however, when the authentication header is used, the IP addresses
cannot be modified by network address translation, as this always invalidates the
hash value. The transport and application layers are always secured by a hash, so
they cannot be modified in any way, for example by translating the port
numbers.
A means to encapsulate IPsec messages for NAT traversal has been defined by RFC
documents describing the NAT-T mechanism.
In tunnel mode, the entire IP packet is encrypted and authenticated. It is then
encapsulated into a new IP packet with a new IP header. Tunnel mode is used to
create virtual private networks for network-to-network communications (e.g.

Internet Control Message Protocol (ICMP):Internet Control Message Protocol (ICMP):
The Internet Control Message Protocol (ICMP) is one of the main
protocols of the internet protocol suite. It is used by network
devices, like routers, to send error messages indicating, for
example, that a requested service is not available or that a host or
router could not be reached. ICMP can also be used to relay query
messages. It is assigned protocol number 1. ICMP differs from
transport protocols such as TCP and UDP in that it is not typically
used to exchange data between systems, nor is it regularly
employed by end-user network applications (with the exception of
some diagnostic tools like pingping and traceroutetraceroute).
The Internet Control Message Protocol is part of the Internet Protocol
Suite, as defined in RFC 792. ICMP messages are typically used for
diagnostic or control purposes or generated in response to errors
in IP operations (as specified in RFC 1122). ICMP errors are
directed to the source IP address of the originating packet.

Internet Group Management Protocol (IGMP) :Internet Group Management Protocol (IGMP) :
The Internet Group Management Protocol (IGMP) is a communications
protocol used by hosts and adjacent routers on IPv4 networks to
establish multicast group memberships. IGMP is an integral part of IP
multicast.
IGMP can be used for one-to-many networking applications such as onlineonline
streaming videostreaming video and gaminggaming, and allows more efficient use of resources
when supporting these types of applications.
IGMP is used on IPv4 networks. Multicast management on IPv6 networks is
handled by Multicast Listener Discovery (MLD) which uses ICMPv6
messaging in contrast to IGMP's bare IP encapsulation.
IGMP operates between the client computer and a local multicast router.
Switches featuring IGMP snooping derive useful information by
observing these IGMP transactions. Protocol Independent Multicast
(PIM) is then used between the local and remote multicast routers, to
direct multicast traffic from the multicast server to many multicast
clients.

A network designed to deliver a multicast service using IGMP might
use this basic architecture:

Address Resolution Protocol (ARP):Address Resolution Protocol (ARP):
The Address Resolution Protocol (ARP) is a telecommunication
protocol used for resolution of Internet layer addresses into link
layer addresses, a critical function in computer networks. ARP was
defined by RFC 826 in 1982, is Internet Standard STD 37, and is
also the name of the program for manipulating these addresses in
most operating systems.
ARP is used for mapping a network address (e.g. an IPv4 address) to a
physical address like an Ethernet address (also named a MAC
address). ARP has been implemented with many combinations of
network and data link layer technologies, like IPv4, Chaosnet,
DECnet and Xerox PARC Universal Packet (PUP) using IEEE 802
standards, FDDI, X.25, Frame Relay and Asynchronous Transfer
Mode (ATM). IPv4 over IEEE 802.3 and IEEE 802.11 is the most
common usage.
Continue..

In Internet Protocol Version 6 (IPv6) networks, the functionality of
ARP is provided by the Neighbor Discovery Protocol (NDP).
The Address Resolution Protocol is a request and reply protocol that
runs encapsulated by the line protocol. It is communicated within
the boundaries of a single network, never routed across
internetwork nodes. This property places ARP into the Link Layer
of the Internet Protocol Suite, while in the Open Systems
Interconnection (OSI) model, it is often described as residing in
Layer 3, being encapsulated by Layer 2 protocols. However, ARP
was not developed in the OSI framework.

Open Shortest Path First (OSPF):Open Shortest Path First (OSPF):
Open Shortest Path First (OSPF) is a routing protocola routing protocol for Internet
Protocol (IP) networks. It uses a link state routinglink state routing (LSR) algorithm
and falls into the group of interior routing protocols, operating
within a single autonomous system (AS). It is defined as OSPF
Version 2 in RFC 2328 (1998) for IPv4. The updates for IPv6 are
specified as OSPF Version 3 in RFC 5340 (2008).
OSPF is perhaps the most widely used interior gateway protocol (IGP)
in large enterprise networks. Intermediate System to Intermediate
System (IS-IS), another link-state dynamic routing protocol, is more
common in large service provider networks.
OSPF is an interior gateway protocol (IGP) for routing Internet
Protocol (IP) packets solely within a single routing domain, such as
an autonomous system. It gathers link state information from
available routers and constructs a topology map of the network.
Continue..

The topology is presented as a routing table to the Internet layer
which routes packets based solely on their destination IP address.
OSPF supports Internet Protocol Version 4 (IPv4) and Internet
Protocol Version 6 (IPv6) networks and supports the Classless
Inter-Domain Routing (CIDR) addressing model.
OSPF detects changes in the topology, such as link failures, and
converges on a new loop-free routing structure within seconds. It
computes the shortest-path tree for each route using a method
based on Dijkstra's algorithmDijkstra's algorithm. The OSPF routing policies for
constructing a route table are governed by link metrics associated
with each routing interface. Cost factors may be the distance of a
router (round-trip time), data throughput of a link, or link
availability and reliability, expressed as simple unitless numbers.
This provides a dynamic process of traffic load balancing between
routes of equal cost.
Continue..

OSPF does not use a transport protocol, such as UDP or TCP, but
encapsulates its data directly in IP packets with protocol number
8989. This is in contrast to other routing protocols, such as the
Routing Information Protocol (RIP)Routing Information Protocol (RIP) and the Border GatewayBorder Gateway
Protocol (BGP)Protocol (BGP). OSPF implements its own transport layer error
detection and correction functions. OSPF uses multicast addressing
for distributing route information within a broadcast domain. For
non-broadcast networks, special provisions for configuration
facilitate neighbor discovery. OSPF multicast IP packets never
traverse IP routers (never traverse Broadcast Domains), they never
travel more than one hop. OSPF is therefore a link layer protocol.
The OSPF protocol, when running on IPv4, can operate securely
between routers, optionally using a variety of authentication
methods to allow only trusted routers to participate in routing.
OSPFv3, running on IPv6, does not support protocol-internal
authentication. Instead, it relies on IPv6 protocol security (IPsec).

Neighbor Discovery Protocol (NDP):Neighbor Discovery Protocol (NDP):
The Neighbor Discovery Protocol (NDP, ND) is a protocol in the Internet
protocol suite used with Internet Protocol Version 6 (IPv6). It operates in
the Link Layer of the Internet model (RFC 1122), and is responsible for
address auto configuration of nodes, discovery of other nodes on the
link, determining the addresses of other nodes, duplicate address
detection, finding available routers and Domain Name System (DNS)
servers, address prefix discovery, and maintaining reachability
information of other active neighbor nodes.
The protocol defines five different ICMPv6 packet types to perform
functions for IPv6 similar to the Address Resolution Protocol (ARP) and
Internet Control Message Protocol (ICMP) Router Discovery and Router
Redirect protocols for IPv4. However, it provides many improvements
over its IPv4 counterparts (RFC 4861, section 3.1). For example, it
includes Neighbor Unreachability Detection (NUD), thus improving
robustness of packet delivery in the presence of failing routers or links,
or mobile nodes.
Continue..

Functions :Functions :
NDP defines five ICMPv6 packet types for the purpose of router solicitation, router
advertisement, neighbor solicitation, neighbor advertisement, and network
redirects.
Router Solicitation (Type 133) -Router Solicitation (Type 133) - Hosts inquire with Router Solicitation messages to
locate routers on an attached link. Routers which forward packets not
addressed to them generate Router Advertisements immediately upon receipt
of this message rather than at their next scheduled time.
Router Advertisement (Type 134) -Router Advertisement (Type 134) - Routers advertise their presence together with
various link and Internet parameters either periodically, or in response to a
Router Solicitation message.
Neighbor Solicitation (Type 135) -Neighbor Solicitation (Type 135) - Neighbor solicitations are used by nodes to
determine the link layer address of a neighbor, or to verify that a neighbor is
still reachable via a cached link layer address.
Neighbor Advertisement (Type 136) -Neighbor Advertisement (Type 136) - Neighbor advertisements are used by nodes
to respond to a Neighbor Solicitation message.
Redirect (Type 137) -Redirect (Type 137) - Routers may inform hosts of a better first hop router for a
destination.

Tunneling Protocol (Tunnels):Tunneling Protocol (Tunnels):
In computer networks, a tunneling protocol allows a network user to access
or provide a network service that the underlying network does not
support or provide directly. One important use of a tunneling protocol is
to allow a foreign protocol to run over a network that does not support
that particular protocol; for example, running IPv6 over IPv4. Another
important use is to provide services that are impractical or unsafe to be
offered using only the underlying network services; for example,
providing a corporate network address to a remote user whose physical
network address is not part of the corporate network. Because tunneling
involves repackaging the traffic data into a different form, perhaps with
encryption as standard, a third use is to hide the nature of the traffic that
is run through the tunnels.
The tunneling protocol works by using the data portion of a packet (the
payload) to carry the packets that actually provide the service. Tunneling
uses a layered protocol model such as those of the OSI or TCP/IP
protocol suite, but usually violates the layering when using the payload
to carry a service not normally provided by the network.
Continue..

Typically, the delivery protocol operates at an equal or higher level in the
layered model than the payload protocol.
As an example of network layer over network layer, Generic RoutingGeneric Routing
Encapsulation (GRE)Encapsulation (GRE), a protocol running over IP (IP protocol number 4747),
often serves to carry IP packets, with RFC 1918RFC 1918 private addresses, over
the Internet using delivery packets with public IP addresses. In this case,
the delivery and payload protocols are the same, but the payload
addresses are incompatible with those of the delivery network.
It is also possible to establish a connection using the data link layer. The
Layer 2 Tunneling Protocol (L2TP) allows the transmission of frames
between two nodes. A tunnel is not encrypted by default, it relies on the
TCP/IP protocol chosen to determine the level of security.
SSH uses port 22 to enable data encryption of payloads being transmitted
over a public network (such as the Internet) connection, thereby
providing VPN functionality. IPsec has an end-to-end Transport Mode,
but can also operate in a tunneling mode through a trusted security
gateway.

Point to Point Protocol (PPP):Point to Point Protocol (PPP):
In computer networking, Point-to-Point Protocol (PPP) is a data link
(layer 2) protocol used to establish a direct connection between
two nodes. It can provide connection authentication, transmission
encryption (using ECP, RFC 1968RFC 1968), and compression.
PPP is used over many types of physical networks including serial
cable, phone line, trunk line, cellular telephone, specialized radio
links, and fiber optic links such as SONET. PPP is also used over
Internet access connections. Internet service providers (ISPs) have
used PPP for customer dial-up access to the Internet, since IP
packets cannot be transmitted over a modem line on their own,
without some data link protocol.
Two derivatives of PPP, Point-to-Point Protocol over Ethernet (PPPoE)
and Point-to-Point Protocol over ATM (PPPoA), are used most
commonly by Internet Service Providers (ISPs) to establish a Digital
Subscriber Line (DSL) Internet service connection with customers.
Continue..

PPP is commonly used as a data link layer protocol for connection over
synchronous and asynchronous circuits, where it has largely superseded the
older Serial Line Internet Protocol (SLIP) and telephone company mandated
standards (such as Link Access Protocol, Balanced (LAPB) in the X.25 protocol
suite). The only requirement for PPP is that the circuit provided be duplex. PPP
was designed to work with numerous network layer protocols, including
Internet Protocol (IP), TRILL, Novell's Internetwork Packet Exchange (IPX), NBF,
DECnet and AppleTalk. Like SLIP, this is a full Internet connection over
telephone lines via modem. It is more reliable than SLIP because it double
checks to make sure that Internet packets arrive intact. It resends any damaged
packets.
PPP is a layered protocol that has three components:
• An encapsulation component that is used to transmit datagrams over the
specified physical layer.
• A Link Control Protocol (LCP) to establish, configure, and test the link as well as
negotiate capabilities.
• One or more Network Control Protocols (NCP) used to negotiate optional
configuration parameters and facilities for the network layer. There is one NCP
for each higher-layer protocol supported by PPP.
PPP is specified in RFC 1661RFC 1661.

Osi layer and network protocol

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