4.packets_frames

packets

small pieces of data sent in pieces across a network that contain headers with information such as IP addresses.

frames

data units operating in the data link layer of the OSI model for communication between devices on the same network.

An image is divided into individual pieces and then rearranged when received by the other device.

example how data is sent in packets from one device to another

internet protocol

A protocol that structures packets with headers that contain routing and addressing information to send data across a network

header

the additional piece of data added to packets

time to live

header that adds a timer of expiration to a packet to prevent them from clogging up and slowing down a network

checksum

A header is added to a packet that ensures integrity by working like a hash. If the data has been modified, the value in the header will be different than what’s expected

source address

header added to a packet that includes the IP address of the sender so the packet knows where to return to

destination address

header added to a packet that contains the IP addresses of the destined device so the packet knows where to send the data too

application, transport, internet, and network interface

the 4 layers of the TCP protocol

a connection between a client and server is required for data transfer

what is the significance of TCP being connection-based?

three-way handshake

process within TCP guarantying that data sent will be received

source port

header that’s the port opened by sender to send the TCP packet from. The value of this TCP port is randomly chosen

0-65535

what is the range of the random values selected by the source port header?

destination port

header representing the port number of the application or service running on a remote host receiving the packets

sequence number

header representing number assigned to a first piece data sent

acknowledgement number

header representing the number given to the next piece of sent data after the sequence number

data

TCP header where information is stored

flag

header determining how the packet should be handled by a device during the handshake process

syn, syn/ack, and ack

the three messages of the three-way handshake in messages

syn

three-way handshake message where the client requests synchronization with a server

syn/ack

three-way handshake message where the receiving device or server acknowledges the synchronization message sent by the client

ack

three-way handshake message sent by either the client or sever acknowledging that packets have been received

data

three-way handshake message appearing when data has been sent

fin

three-way handshake message indicating that a connection has been closed and completed

rst

three-way handshake message used to abruptly ends a connection due to an error

Alice sends a synchronization request to Bob who acknowledges the request. Alice acknowledges Bob’s acknowledgement.

example of three-way handshake where Alice is the client and Bob is the server

it’s incremented by 1

what happens to the initial sequence number sent by the client during the three-way handshake

client provides initial sequence number, server provides its own initial sequence number and acks. Client acknowledges and increments the sequence number by 1

three-way handshake incrementation process

Unlike TCP which acknowledges and requires a constant connect, UDP doesn’t

differences between TCP and UDP

Bob sends a request to Alice who replies with multiple responses

example of the UDP process with Alice and Bob

source and destination ports, source and destination IPs, sequence number, acknowledgment number, checksum, data, flag

headers used during TCP

time to live, source and destination addresses, source and destination ports, and data

headers used during UDP