2. Transport Layer
❖ The transport layer is an
essential component of the
network architecture,
responsible for providing
reliable and efficient
communication services.
❖ The network layer plays a
crucial role in providing
services to the transport
layer at the
network/transport layer
interface.
3. The network layer services are carefully designed with the following goals in mind:
1. The services should be independent of the router technology.
2. The transport layer should be shielded from the number, type, and topology of the routers present.
3. The network addresses made available to the transport layer should use a uniform numbering
plan, even across LANs and WANS
4. Network Layer Design Freedom and Service
Specifications
● Designers of the network layer enjoy considerable freedom in defining the detailed
specifications of services offered to the transport layer. This allows for
customization based on specific requirements and goals.
● A divisive debate arises between two factions regarding the nature of network layer
services. One camp, represented by the Internet community, argues that the
network layer's role is to move packets, favoring connectionless service.
● The proponents of connectionless service argue that the network itself is inherently
unreliable.
5. Connectionless Approach
◆ Advocates of connectionless services
argue for a minimalistic network layer,
providing basic primitives like SEND
PACKET and RECEIVE PACKET.
◆ Packet ordering and flow control are
left to the hosts, leveraging the end-to-
end argument design principle.
✔The end-to-end argument is a
significant design principle in shaping
the Internet, supports the
connectionless approach.
✔It suggests that the network itself is
inherently unreliable and should focus
on forwarding packets.
Connection-Oriented Perspective
Proponents of connection-oriented
services, often represented by
telephone companies, argue for reliable,
connection-oriented network services
The End-to-End Argument
6. controversy between connectionless and connection-oriented
network architectures.
● Even after several decades, this controversy is still very much alive. Early
widely used data networks, such as X.25 in the 1970s and its successor Frame
Relay in the 1980s, were connection-oriented.
● However, since the days of the ARPANET and the early Internet, connectionless
network layers have grown tremendously in popularity. The IP protocol is now
an ever-present symbol of success.
● The IP protocol is now an ever-present symbol of success. It was undeterred by
a connection-oriented technology called ATM that was developed to overthrow it
in the 1980s.
● Two examples of connection-oriented technologies are MPLS (Multi Protocol
Label Switching), which we will describe in this chapter and VLAN (Virtual Local
Area Network)
7. Services provided to the transport layer
The services provided to the transport layer are as follows −
●
●
Logical Addressing: Network layer adds header to incoming packet which includes
logical address to identify sender and receiver.
Routing: It is the mechanism provided by Network Layer for routing the packets to the
final destination in the fastest possible and efficient way.
● Flow control: is layer routes the packet to another way, If too many packets are present
at the same time preventing bottlenecks and congestion.
Breaks Large Packets: Breaks larger packets into small packets.
●
● Connection Oriented service: It is a network communication mode, where a
communication session is established before any useful data can be transferred and
where a stream of data is delivered in the same order as it was sent.
