TCP/IP summary

Generals

TCP/IP is a combination of two protocols, TCP (Transfert Control Protocol) and IP (Internet Protocol).

The Internet Protocol is the most used protocol on the Internet, it allows the creation and the broadcast of data embedded within packets format.

Those packets are called datagrams and are made of several fields which some of them are source address, destination address, data, length, checksum …

The Transfer Control Protocol is used to manage the incoming and outgoing data packets.

It is a connection oriented protocol and very safe to connect two or more computer on a large network.

Why using TCP/IP

Connection oriented protocol:

When you want to connect a computer to a network, you need to be sure that the data are sent to the right address.

TCP/IP insure the errors control and can ask to repeat a certain packet if it is corrupted.

Easy to use:

This protocol is implemented in almost all the existing platforms.

By using a software tool, you can configure a computer in seconds.

Multi purpose:

You can use it to connect to the Internet web.

You can transfer files, enter and browse web sites.

You can use it to videoconferences, to access remote computers, to talk to a friend connected on the network…

Very fast:

The always-improving technologies allow nowadays to be connected at speeds over one Mega Hertz.

The fast Ethernet connection is about to become a standard with all providers.

It means that every user can transfer data very quickly (30kbps and more), use the network to phone and to view videos.

Data format

0	1	2	3	4	5	6	7	8	9	10	11	12	13	14	15	16	17	18	19	20	21	22	23	24	25	26	27	28	29	30	31
Source Port																Destination Port
Sorting number
Request acknowledgement
Data shift				reserved						URG	ACK	PSH	RST	SYN	FIN	Window
Checksum																Emergency pointer
Options																						Fill in
Data

Signification des différents champs:

• Source Port (16 bits): number related to the source computer application.
• Destination Port (16 bits): Number related to the destination computer application.
• Sorting number (32 bits): when the flag SYN is set to 0, this number is the first segment word one’s.
  When SYN is set to 1, the value is set to the initial number used to synchronize the sequence numbers (ISN)
• Acknowledgement request number (32 bits): It is set to the number of the next expected segment.
• Data shift (4 bits): allows repeating the beginning of data. It is essential here because of the variable width of data.
• Reserved (6 bits): may be used in the future.
• Flags (6x1 bit):
• URG: if set to 1, urgent data packet treatment.
• ACK : if set to 1, it is an acknowledgement reception packet.
• PSH (PUSH): if set to 1, the following packet uses the PUSH method.
• RST: if set to 1, the connection is reset.
• SYN: it indicates a connection demand.
• FIN: if set to 1, the connection is interrupted.
• Window (16 bits): words number that the receiver wants to have without acknowledgement.
• Checksum: allows controlling the integrity of the packet.
• Emergency pointer (16 bits): Indicates the emergency level for packet treatment.
• Options: Misc. options
• Fill in: the remaining space is filled in with zeros to fit an n per 32 bits length.