INTRODUCTION
 The protocols of the OSI model Network layer specify
addressing and processes that enable Transport layer
data to be packaged and transported. The Network
layer encapsulation allows its contents to be passed to
the destination within a network or on another
network with minimum overhead.

ROLE
 Examining how it divides networks into groups of
hosts to manage the flow of data packets within a
network. We also consider how communication
between networks is facilitated. This communication
between networks is called routing.

OBJECTIVE
 Identify the role of the Network layer as it describes
communication from one end device to another end
device.
 Examine the most common Network layer
protocol, Internet Protocol (IP), and its features for
providing connectionless and best-effort service.
 Understand the principles used to guide the division, or
grouping, of devices into networks.
 Understand the hierarchical addressing of devices and how
this allows communication between networks.
 Understand the fundamentals of routes, next-hop
addresses, and packet forwarding to a destination network.

FUNCTION OF NETWORK LAYER
 Connection model
 Host addressing
 Message forwarding

NETWORK LAYER PROTOCOL
• A communications protocol is a formal description of
digital message formats and the rules for exchanging those
messages in or between computing systems and in
telecommunications.

• Protocols may include signaling, authentication and error
detection and correction capabilities.

• Communicating systems use well-defined formats for
exchanging messages. Describes the syntax, semantics, and
synchronization of communication.

 A programming language describes the same for computations, so
there is a close analogy between protocols and programming
languages: protocols are to communications what programming
languages are to computations.
 Protocol exists in Network Layer:

 IPv4/IPv6, Internet Protocol
 DVMRP, Distance Vector Multicast Routing Protocol
 ICMP, Internet Control Message Protocol
 IGMP, Internet Group Multicast Protocol
 PIM-SM, Protocol Independent Multicast Sparse Mode
 PIM-DM, Protocol Independent Multicast Dense Mode
 IPsec, Internet Protocol Security
 IPX, Internetwork Packet Exchange
 RIP, Routing Information Protocol
 DDP, Datagram Delivery Protocol

 The level of a sub-document determines the class it belongs to. The
sub-documents belonging to a class all provide similar functionality
and, when form follows function, have similar form.

 The Network Layer is Layer 3 of the seven-layer OSI model of
computer networking.

 The Network Layer is responsible for routing packets delivery including
routing through intermediate routers, whereas the Data Link Layer is
responsible for Media Access Control, Flow Control and Error
Checking.

 The Network Layer provides the functional and procedural means of
transferring variable length data sequences from a source to a
destination host via one or more networks while maintaining the
quality of service functions.

Connection model(connectionless communication)
 For example, IP is connectionless, in that a frame can travel
from a sender to a recipient without the recipient having to
send an acknowledgement.

Host addressing
 Every host in the network needs to have a unique address
which determines where it is. This address will normally be
assigned from a hierarchical system.

BASIC REQUIREMENT OF PROTOCOL
 Data formats for data exchange. In digital message bit strings are exchanged.
The bit strings are divided in fields and each field carries information relevant
to the protocol. Conceptually the bit string is divided into two parts called the
header area and the data area.

 Address formats for data exchange. The addresses are used to identify both the
sender and the intended receiver(s).

 Address mapping. Sometimes protocols need to map addresses of one scheme
on addresses of another scheme. For instance to translate a logical IP address
specified by the application to a hardware address.

 Routing. When systems are not directly connected, intermediary systems along
the route to the intended receiver(s) need to forward messages (instead of
discarding them) on behalf of the sender.

 Detection of transmission errors is necessary, because no network is
error-free. Bits of the bit string become corrupted or lost.

 Acknowledgements of correct reception of packets by the receiver are
usually used to prevent the sender from retransmitting the packets.
Some protocols, notably datagram protocols like the Internet Protocol
(IP), do not acknowledge.

 Loss of information - timeouts and retries. Sometimes packets are lost
on the network or suffer from long delays. To cope with this, a sender
expects an acknowledgement of correct reception from the receiver
within a certain amount of time.

 Direction of information flow needs to be addressed if transmissions
can only occur in one direction at a time (half-duplex links). To gain
control of the link a sender must wait until the line becomes idle and
then send a message indicating its wish to do so.

 Sequence control. We have seen that long bitstrings are divided in
pieces, that are send on the network individually. The pieces may get
'lost' on the network or arrive out of sequence, because the pieces can
take different routes to their destination.

 Flow control is needed when the sender transmits faster than the
receiver can process the transmissions or when the network becomes
congested. Sometimes, arrangements can be made to slow down the
sender, but in many cases this is outside the control of the protocol.

 Getting the data across is only part of the problem. The data received
has to be evaluated in the context of the progress of the
conversation, so a protocol has to specify rules describing the context
and explaining whether the (form of the) data fits this context or not.

EX: ENTHERNET PROTOCOL
 Ethernet was invented at Xerox PARC in the early 1970s. It has gained
widespread use on LANs and became standardized as IEEE standard
802.3.To connect to a LAN, a computer has to be equipped with an
Ethernet network interface card.

 Conceptually, all stations share a single communication channel called
a shared bus. Transmissions on this channel are received by all stations
at (nearly) the same time. The hardware provides no indication to the
sender about whether the transmission was delivered and is therefore
called a best-effort delivery mechanism.

 Stations wanting to transmit, wait for the channel to become free and
then start transmitting one single frame and then stop for a small
amount of time before transmitting a next frame to allow others to
transmit.

INTERNET PROTOCOL
 The Internet Protocol (IP) is the principal communications protocol
used for relaying datagram (packets) across an internetwork using the
Internet Protocol Suite. Responsible for routing packets across network
boundaries, it is the primary protocol that establishes the Internet.

 As a consequence of this design, the Internet Protocol only provides best
effort delivery and its service can also be characterized as unreliable. In
network architectural language it is a connection-less protocol, in contrast
to so-called connection-oriented modes of transmission.

The lack of reliability allows any of the following fault events to occur:
 data corruption
 lost data packets
 duplicate arrival
 out-of-order packet delivery

 The Internet Protocol is responsible for addressing
hosts and routing datagram (packets) from a
source host to the destination host across one or
more IP networks.
 For this purpose the Internet Protocol defines an
addressing system that has two functions.
 Addresses identify hosts and provide a logical
location service.

IPv4
 Internet Protocol version 4 (IPv4) is the fourth revision in the development
of the Internet Protocol (IP) and it is the first version of the protocol to be
widely deployed.

 Together with IPv6, it is at the core of standards-based internetworking
methods of the Internet. IPv4 is still by far the most widely deployed Internet
Layer protocol. As of 2011, IPv6 deployment is still in its infancy.

 IPv4 uses 32-bit (four-byte) addresses, which limits the address space to
4,294,967,296 (232) possible unique addresses. However, some are
reserved for special purposes such as private networks (~18 million
addresses) or multicast addresses (~270 million addresses).

 IPv4 addresses may simply be written in any notation expressing a 32-bit
integer value, but for human convenience, they are most often written in dot-
decimal notation, which consists of the four octets of the address expressed
separately in decimal and separated by periods.

BEST DELIVERY
 Best effort delivery describes a network service in which the network does
not provide any guarantees that data is delivered or that a user is given a
guaranteed quality of service level or a certain priority.

 Conventional telephone networks are not based on best-effort communication,
but on circuit switching. During the connection phase of a new call, resources
are reserved in the telephone exchanges, or the user is informed that the call is
blocked due to lack of free capacity.

 The mailman will make his "best effort" to try to deliver a message, but the
delivery may be delayed if too many letters arrive to a postal office suddenly.
The sender is not informed if a letter has been delivered successfully.

 However, the best-effort paradigm is to some extent abandoned on the
Internet. Modern IP routers provide mechanisms for differentiated or
guaranteed quality of service to certain data flows, based on for example the
IntServ or DiffServ protocols.

ADDRESSING
 It is a common misunderstanding that addresses ending with an octet of 0 or
255 can never be assigned to hosts.

 In glassful addressing (now obsolete with the advent of CIDR), there are only
three possible subnet masks: Class A, 255.0.0.0 or /8; Class B, 255.255.0.0 or /16;
and Class C, 255.255.255.0 or /24.

 However, this does not mean that every addresses ending in 255 cannot be used
as a host address. For example, in the case of a Class B subnet
192.168.0.0/255.255.0.0 (or 192.168.0.0/16), equivalent to the address range
192.168.0.0–192.168.255.255, the broadcast address is 192.168.255.255.

 However, one can assign 192.168.1.255, 192.168.2.255, etc. (though this can cause
confusion). Also, 192.168.0.0 is the network identifier and so cannot be
assigned, but 192.168.1.0, 192.168.2.0, etc. can be assigned (though this can also
cause confusion).

PACKET STRUCTURE
Header
 The fields in the header are packed with the most significant byte first (big
endian), and for the diagram and discussion, the most significant bits are
considered to come first (MSB 0 bit numbering). The most significant bit is
numbered 0, so the version field is actually found in the four most significant
bits of the first byte, for example.

Version
 The first header field in an IP packet is the four-bit version field. For IPv4, this
has a value of 4 (hence the name IPv4).

GROUPING DEVICE IN NETWORK & HIERARHICAL
ADDRESSING

FUNDAMENTAL OF ROUTER,NEXT HOP,ADDRESS &
PACKET FOWARDING

 .

FUNDAMENTAL OF ROUTER,NEXT HOP,ADDRESS
& PACKET FOWARDING

 Route assignment, route choice, or traffic assignment concerns
the selection of routes (alternative called paths) between origins and
destinations in transportation networks. It is the fourth step in the
conventional transportation forecasting model, following Trip
Generation, Destination Choice, and Mode Choice.

 The zonal interchange analysis of trip distribution provides origin-
destination trip tables. Mode choice analysis tells which travelers will
use which mode.

PROBLEM WHEN USING MANY DEVICES IN A NETWORK

 The packets are passed to the router and waiting to
be deployed.
 Host doesn’t know how to deliver the data.
 Because the delivery of data is done by the
gateway.
 This will result in communication problems.

ROUTER

 Process of taking a URL endpoint and decomposing it into
parameters to determine which module, controller, and
action of that controller should receive the request.

 Routes may be used numerous times to create a chain or
user defined application.

 A module name may be specified as the first path element.

ROUTING PROTOCOL
 The purpose of routing protocols is to tell the
hardware between the transmitter and receiver where
to send all the pieces of a network transmission.
 Routing protocol shares this information first among
immediate neighbors, and then throughout the
network.
 This way, routers gain knowledge of the topology of
the network.

SUMMARY
 Understand the role of the network layer as it function
communication from one end device to another end
device.

 Explain the purpose of the Hierarchical Addressing of
device and how this allows the communication between
network.

 Understand the Fundamentals of Routes, Next Hop
Addresses and Packet Forwarding

Network fundamental