Transport Layer
- use
- main responsibility, transfer the data completely
- receives the data from the upper layer and converts them into smaller units known as segments.
- termed as an end-to-end layer,provides a point-to-point connection between source and destination to deliver data reliably.
- ensures that messages are transmitted in the order in which they are sent and there is no duplication of data.
- end to end delivery of the data
- udp and tcp protocols are used
- flow control - don't send more data
- congestion control - too many packets in the network
- segmentation - dividing into packets
- error correction
- protocols
- pdu
Ports
- both udp and tcp have - (1-65535) number of ports, \(2^{16} - 1 = 65535\)
- because port no is a 18 bit number (2 byte)
- well known ports - 1 to 23
- registered ports - 1024 - 49151, assigned by IANA, internet assigned number authority
- dynamic ports, generated by pc, bound by the port you create on pc, rest of remaining ports
- use
netstat
on windows
Some common ports
tcp
- ftp - 21, file transfer protocol
- ssh - 22
- telnet - 23
- smtp - 25
- http - 80
- https - 443
- pop - 110
- dns - 53
udp
- tftp - 69, trivial ftp
- dhcp - 67/68
- smtp
- dns - 53