Now we're gonna move on to the transport layer. The transport layer controls communications between end host or between end devices between end hosts. The Transport Lear controls communication between end devices. This communication between UN devices can either be reliable or unreliable.
So transmission Control Protocol, or TCP, provides for this reliable communication or this reliable service.
This reliability is provided by
data and then expecting an acknowledgment for that sent data
any data that is not acknowledge it's simply recent.
So the protocol data unit at Layer four this data being sent is called a segment. What does the segment look like? Well, before we look at the segment again at Layer four, we need some kind of an address ing scheme.
So some kind of a source address and some kind of a destination address
the address ING scheme used at Layer four are simply called ports.
Ports one through 10 23 are well known ports. For example, tell net the service tell net away to remotely log into AH device Uses TCP Port 23
Port 10 24 to 49 151 are registered ports with Diana.
These are ports requested by companies for certain service is, and I am a registered them with that company for certain service.
The last type of pores are ephemeral pores, and these are your open ports. Any port a car, any service may use Port the port range between 49 152 and 65 5 35
when you add port to a packet, it is called the segment. So the segment is the protocol data unit used at layer four.
You have your destination, I p. Your source. I pee. And then I have inserted the destination port number and the sore sport number, followed by the data field and again, the frame check sequence field housing the cyclic redundancy check.
reliable communication can happen, or before the segments are are sent between devices, the devices go through or create a virtual connection with each other by going through what is called a three way handshake.
So here we have depicted Host one and host to performing this three way handshake.
Host One sends host to a segment with the sin synchronized bit turned on, or a synchronized segment or sin segment
host two replies with an acknowledgment to that sink with a sink AC or synchronized acknowledgement. And then host one sends back an acknowledgment acknowledging the think AC
After this three handshake is completed, a virtual connection is built between the two end devices, and now data transfer may begin.
So by default for every segment that is sent, I expect Anak Knowledge mint in return from the other end.
If I do not return or if I do not get an acknowledgement from the other end, I simply recent this segment.
Now the number of segments that can be sent
per data flow without expecting an acknowledgment back is called a window size by default
or in the very beginning, the window size is one. So one acknowledgment for each segment sent
this window size can increase because that that way, it's more efficient. I may be able to send 10 segments and just expect one acknowledgement back to quicken the data flow.
This ends the transport layer lecture