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Chapter Nine: Transport layer (Transport layer function (TCP…
Chapter Nine: Transport layer
Transport layer function
is responsible for establishing a temporary communication session between two applications and for transmitting data between them.
Responsibilities of the transport layer
Track individual conversations
Segmentation of data and reassembly of segments
Identification of applications
Conversation multiplexing
segmentation makes multiplexing possible, since several applications can use the network at the same time
TCP and UDP manage these different simultaneous conversations through header fields that can uniquely identify these applications.
TCP
it is similar to sending packages that are tracked from source to destination.
There are three basic reliability operations:
Recognition of the data received
Retransmission of data without recognition after a certain time
Numbering and tracking of data segments transmitted to a specific host from a specific application
Characteristics
Establishing a session
Reliable delivery
Delivery in the same order
Flow control
Processes
Each application process running on the server is configured to use a port number, either default or manually
Establishing connections
Step 1: The originating client requests a client-to-server communication session with the server.
Step 2: The server recognizes the client-to-server communication session and requests a server-to-client communication session.
Step 3: The originating client recognizes the server-to-client communication session.
UDP
It is a better transport protocol.
provides the basic functions to deliver data segments between the appropriate applications, with very little overload and data review.
Characteristics
it is a lightweight transport protocol that offers the same data segmentation and reassembly as TCP, but without the reliability and control of TCP flow.
In a single device, users can use several applications and various services, such as email, the web and instant messaging to send messages or obtain information.
provides services
The division into segments of the data that is received from an application
The addition of a header to identify and manage each segment
The use of header information to reassemble the segments back into application data
The passage of the assembled data to the correct application
Port numbers
Port of origin
This process allows you to establish several conversations simultaneously. It is common for a device to send several HTTP service requests to a web server at the same time.
port of destination
The client places a destination port number in the segment to inform the destination server of the requested service, the server that receives the message knows that web services are requested. A server can offer more than one service simultaneously
Pair of sockets
The socket is the combination of the source IP address and the source port number, or the destination IP address and the destination port number.
The source and destination ports are placed within the segment. The segments are encapsulated within an IP packet.
The IP packet contains the source and destination IP addresses.
Groups of port numbers
Known ports (numbers from 0 to 1023)
Registered ports (numbers from 1024 to 49151)
Dynamic or private ports (numbers 49152 to 65535)