OSI v TCP/IP

OSI:

you can see it, HERE

TCP/IP:

• Rout able: it can pass through routers.
• Connect dissimilar systems: Win, Mac, Unix, etc...
• Method of access to the inventor. 

App Layer: using an app, it gains access to the network.

Telnet, FTP, TFTP , NFS, SMTP, LPD, DNS, DHCP.

Transportation: provides communication sessions between the two computers.  TCP, UDP

Internet Layer: routers the data from it's source to it's source to its destination.   ARP, RARP, IP, ICMP, IGMP.

Network Layer: it sends & receive data on the wire.  Ethernet, Token Ring, Frame, Relay, ATM 

(Well-Know Port Numbers:

FTP: 20 & 21, SMTP: 25,  DNS: 53, Telnet:23, HTTP: 80, HTTPS: 443)

** IMPORTANT  FIELDS

TCP Segment:

• Source port: sending App port number
• Destination port: receiving App number
• Sequence number: maintains reliability & sequencing
•  Acknowledgement number: used to acknowledge received segments formation .
• Windows: the number of segments that are allowed to be sent before waiting for an acknowledgement from the destination.
• Checksum:  CRC of the header & data.
• Data: user App information.