The document discusses the transport layer of the OSI model, focusing on the two main protocols, TCP and UDP, as well as ICMP. TCP is a reliable delivery method that ensures packets are delivered in order, while UDP is an unreliable, 'best effort' method prioritized for speed over reliability. ICMP operates at the network layer, providing messaging services for IP and is used in utilities like ping and tracert for network diagnostics.

1. The transport
layer plus ICMP.

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– TCP and UDP.
– ICMP (Internet Control Message Protocol).
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The transport layer plus ICMP.

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– The transport layer.
» Most networking models follow the Open Systems
Interconnection (OSI) model.
• It is composed of seven different layers: application,
presentation, session, transport, network, data link, and
physical.
• The layers work together to create a system of
communication that allows different types of computing
systems or networks to communicate with each other.
» Layer 4, or the transport layer, receives data from the session
layer (Layer 5) and determines what method (or type) of
delivery is required for the data.
• The transport layer then hands the data (with the instructions
for method of delivery) to Layer 3 (the network layer), which is
responsible for determining where the data is going.
– The transport layer’s protocols.
» There are two main protocols used by the transport layer.
• TCP and UDP.
The transport layer plus ICMP.
OSI Model
Layer 7 Application
Layer 6 Presentation
Layer 5 Session
Layer 4 Transport
Layer 3 Network
Layer 2 Data link
Layer 1 Physical

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– Introduction to TCP (Transmission Control
Protocol).
» A protocol that determines the type of delivery method that will
be used in network communication.
» TCP uses a reliable method to deliver network packets.
» TCP helps to set up the connection session.
» It establishes error control.
» It helps to tear down the network session.
– Reliable delivery method.
» It uses a three-way handshake.
1. Requests the connection,
2. Receives the response from the other end, and
3. Sends an acknowledgement back that sets the sequence
number that will be used.
» Every packet that gets sent must be acknowledged by the
receiver. If the sender doesn’t receive the acknowledgement of
a packet, the sender will resend the packet.
» All packets are sent and received in order.
The transport layer plus ICMP.

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– Introduction to UDP (User Datagram
Protocol).
» A protocol that determines the type of delivery method that will
be used in network communication.
» UDP uses an unreliable method to deliver network packets.
» It doesn’t help to set up the connection session.
» It doesn’t establish error control.
» It doesn’t help to tear down the network session.
– Unreliable delivery method.
» Could be better described as a “best effort” delivery method.
» It sends the data stream to the destination, trusting that the
destination is:
• A) listening for the data stream.
• B) willing to accept the data stream.
» The data steam flows with no acknowledgement of it being
received.
The transport layer plus ICMP.

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Not all communication can
be treated the same; that is
why there are both reliable
and unreliable delivery
methods.
With TCP, the sender can be assured that the other end of the
line has received all of the packets that were sent and that the
packets were received in the proper order. This works well for
communication that is not sensitive to latency issues that are
associated with the overhead of reliable deliveries.
UDP strips off the overhead, but sacrifices reliability. It is well
suited for network communication in which speed is more
important than reliability. When using VoIP, it is more important
for the flow of packets to be continuous than for communication
The transport layer plus ICMP.
to be held up while waiting for packets to arrive in the right
order (VoIP communication can survive the occasional
dropped packet).

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The transport layer plus ICMP.

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ICMP works at Layer 3, or
the network layer, of the OSI
model and it is used by IP
(Internet Protocol) to
perform several services.
As a messaging service for IP, its packets are carried as
encapsulated IP datagrams. It provides information about
networking issues.
The ping utility uses ICMP to test for end-to-end connectivity
between two devices using ICMP echo request packets.
The tracert utility uses a combination of ICMP echo requests
and destination unreachable packets to map the actual route
between two endpoints.
The transport layer plus ICMP.
If a router’s memory buffers are full, it will send out an ICMP
Buffer Full message until the congestion has been reduced,
allowing other routers to slow down to avoid packet loss.

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The transport layer plus ICMP.
The transport layer is the fourth layer of the OSI reference model. This layer
is responsible for the delivery of network packets. The two main protocols
used by the transport layer are TCP and UDP. TCP is a reliable delivery
protocol that uses a variety of methods to ensure that the packets sent are
delivered. UDP is an unreliable delivery protocol that transports network
packets without regard to them being received.
Topic
TCP and UDP.
Summary
ICMP is a network layer protocol and functions as a messaging service and
management protocol for IP. ICMP messages are encapsulated as IP
datagrams. Both the ping and tracert utilities use ICMP to fulfill their
functions. A router that is suffering from a full memory buffer will also use
ICMP messages to inform other routers of the issue.
ICMP (Internet Control
Message Protocol).

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