OSI
| lAYER INDEX | LAYER | Protocol Data Unit(PDU) | Functions | Protocals |
|---|---|---|---|---|
| 7 | Application | Data | TFTP，HTTP，SNMP，FTP，SMTP，DNS，Telnet, DHCP | |
| 6 | Presentaton | Data | encoding, decoding, encrypt, decrypt | SSL, WPA, WEP, Kerberos |
| 5 | Session | Data | maintaining communication between two devices | PPTP, TSL/SSL, RTP, NetBios, SOCKS, RTP |
| 4 | Transport | Segments | TCP，UDP | |
| 3 | Network | Packets | Add logical address of sender and receiver | IP，ICMP，RIP，OSPF，BGP，IGMP |
| 2 | Data link | Frame | Error control | SLIP，CSLIP，PPP，ARP，RARP，MTU |
| 1 | Physical | Bits | SO2110，IEEE802，IEEE802.2 |
Five Layers
| lAYER | LAYER | Value |
|---|---|---|
| 5 | Application | Data |
| 4 | Transport | Segments |
| 3 | Network | Packets |
| 2 | datalink | Frame |
| 1 | Physical | Bits |
TCP
- Connection Oriented
- Reliable
- ACK, SYN (every message)
- Sender -> SYN
- Receiver -> ACK
- Congestion control
TCP 3-Way Handshake Process
- Step 1 (SYN) : In the first step, client wants to establish a connection with server, so it sends a segment with SYN(Synchronize Sequence Number) which informs server that client is likely to start communication and with what sequence number it starts segments with
- Step 2 (SYN + ACK): Server responds to the client request with SYN-ACK signal bits set. Acknowledgement(ACK) signifies the response of segment it received and SYN signifies with what sequence number it is likely to start the segments with
- Step 3 (ACK) : In the final part client acknowledges the response of server and they both establish a reliable connection with which they will start the actual data transfer