Transport layer protocols
The transport layer protocols determine how to transfer the messages between hosts and be responsible for the reliability of conversation. The transport layer protocols include TCP and UDP.
TCP
The process of TCP
- Establishes a Session
- Ensures reliable delivery
- Provides same-order delivery
- Support flow control
TCP initiation – 3-way handshake
- Client -> (SYN [sequence number]) Server
- Server -> (SYN-ACK [Acknowledge number= Last sequence number+1] [sequence number]) Client
- Client -> (ACK [sequence number] [Acknowledge number= Last sequence number+1])
TCP termination – 4-way handshake
- Sender -> (FIN) Receiver
- Receiver -> (ACK) Sender
- Receiver ->(FIN) Sender
- Sender -> (ACK) Receiver
The header of TCP
| 16 bits | 16 bits | 32 bits | 32 bits |
|---|---|---|---|
| Source Port | Destination Port | Sequence Number | Acknowledgement Number |
| 4 bits | 6 bits | 6 bits | 16 bits | 16 bits | 16 bits |
|---|---|---|---|---|---|
| Header Length | Reserved | Control Bits | Window | Checksum | Urgent |
UDP
The characteristics of UDP
- Data is reconstructed in the order that it is received.
- Any segments that are lost are not resent.
- There is no session establishment.
- The sending is not informed about resource availability.
The header of UDP
| 16 bits | 16 bits | 16 bits | 16 bits |
|---|---|---|---|
| Source Port | Destination Port | Length | Checksum |
Ports Group
- Well-Known Ports 0 – 1023
- Registered Ports 1024 – 49151
- Private Dynamic Ports 49,152 – 65535
| Port Number | Protocol | Application |
|---|---|---|
| 20 | TCP | FTP data |
| 21 | TCP | FTP control |
| 22 | TCP | SSH |
| 23 | TCP | Telnet |
| 25 | TCP | SMTP |
| 53 | UDP,TCP | DNS |
| 67 | UDP | DHCP Server |
| 68 | UDP | DHCP Client |
| 69 | UDP | TFTP |
| 80 | TCP | HTTP |
| 110 | TCP | POP3 |
| 143 | TCP | IMAP |
| 161 | UDP | SNMP |
| 443 | TCP | HTTPS |