1. TCP/IP TCP/IP LAYERED PROTOCOL TCP/IP'S APPLICATION LAYER TRANSPORT LAYER NETWORK LAYER NETWORK ACCESS LAYER (DATA LINK LAYER)

2. TCP/IP Layered protocol The TCP/IP protocol suite predates the OSI Reference Model by about a decade. Despite this, the TCP/IP protocol suite can (very generally) be mapped to the model. TCP/IP has fewer layers than the seven layers used in the OSI RM. Most descriptions of TCP/IP define four functional levels in the protocol architecture. In the OSI RM, data is passed down the stack when it is being sent to the net, and up the stack when it is being received from the network. Each layer in the stack adds control information (header) to ensure proper delivery. Each layer treats all of the information it receives from the layer above as data and encapsulated with its own header. When data is received, the opposite happens. Each layer strips off its header before passing the data on to the layer above.

3. TCP/IP’s application layer Layers 5,6,7 of the OSI RM. TELNET ( a terminal emulation protocol), FTP ( a file transfer protocol), TFTP (Trivial File Transfer Protocol ), SMTP ( simple mail transfer protocol), UNIX "r" commands, such as rlogin, rsh, rcp (remote Copy), rdate (cheking date from other host), are user application services and correspond roughly to the Application, Presentation, and session layers ( layers 7,6,5) of the OSI Reference Model.

4. Transport layer The TCP/IP Transport layer protocols ensure that packets arrive in sequence and without error, by exchanging acknowledgments of data reception, and re-transmitting lost packets. This type of communication is known as "end-to-end" or "host- to-host". Two types of transport protocols at this level: TCP ( Transport Control Protocol ) UDP ( User Datagram Protocol )

5. TCP protocol TCP enables applications to communicate with each other although connected by a physical circuit. TCP sends data in a form that appears to be transmitted in a character-by-character fashion, rather than as discreet packets. This transmission consists of starting point, which opens the connection. It consists of an ending point, which closes the connection. TCP attaches a header onto the transmitted data. This header contains a large number of parameters that help processes on the sending machine connect to peer processes on the receiving machine. TCP confirms that a packet has reached its destination by establishing an end-to-end connection between sending and receiving hosts. TCP is therefore considered a "reliable, connection-oriented" protocol

6. UDP protocol UDP, the other Transport layer protocol, provides datagram delivery service. UDP is an unreliable, (no ACK), connectionless datagram protocol. It does not provide any means of verifying that connection was ever achieved between receiving and sending hosts. As UDP eliminates the processes of establishing and verifying connections, applications that send small amounts of data use it rather than TCP. Applications that fit a "query-response" model are also excellent candidates for using UDP. Simplex broadcast messages uses UDP.

7. Network layer Also known as the Internet Layer. Accepts and delivers packets for the network. It includes the powerful  Internet protocol (IP),  the ARP protocol, and  the ICMP protocol.

8. IP protocol IP protocol and its associated routing protocols are possibly the most significant of the entire TCP/IP suite. IP is responsible for: IP addressing: The IP addressing conventions are part of the IP protocol. Host-to-host communication: IP determines the path a packet must take, based on the receiving host's IP address. Packet formatting: IP assembles packets into units known as IP datagrams. Fragmentation: If a packet is too large for transmission over the network media, IP on the sending hosts breaks the packet into smaller fragments. IP on the receiving host reconstructs the fragments into the original packet.

9. ARP Protocol The Address Resolution Protocol (ARP) assists IP in directing datagrams to the appropriate receiving host by mapping the IP address (32 bits long) to unique physical Ethernet address (48 bits long). Example: 137.207.192.55 decimal (89 CF C0 37) hex ====>00:00:at:10:fc:15

10. RARP Protocol RARP translates addresses, but in the opposite direction. It converts physical Ethernet addresses to IP addresses. Example: 00:00:a7:10:fc:15 ====> 137.207.192.55 decimal (89 CF C0 37) hex The RARP protocol really has nothing to do with routing data from one system to another. It helps configure diskless systems (workstation with no local disk, or an X- terminal) by allowing workstations to learn their IP addresses. A diskless station has no disk to read its IP address from TCP/IP configuration file. However, every system knows its physical address because it is encoded in the Ethernet interface card (LAN adapter). The diskless Xterminal uses the Ethernet broadcast facility to ask which IP address maps to its physical Ethernet address. When a server on the network sees the request, it looks up the Ethernet address in the ether file (table) and if it finds a match, the server replies with the X- terminal's (or the workstation's) IP address.

11. ICMP Protocol Internet Control Message Protocol (ICMP) is the protocol responsible for detecting network error conditions and reporting on them. ICMP reports on:  Flow control: When datagrams arrive too fast for processing, the receiver sends message to the sender to stop sending.  Connectivity failure: When a destination host can't be reached.  Redirection: Which tells a sending host to use another router.  Checking remote hosts: ping server ===> server is alive.

12. Network Access Layer ( Data Link Layer) It provides error control and framing of the datagram. It ensures the reliable delivery of data across the underlying physical network. It encompasses the function of the physical layer by specifying the characteristics of the hardware to be used for the network. In this layer TCP/IP describes hardware standards such as IEEE802.3, the specification for Ethernet network media, and RS- 232, the specification for standard pin connector for PPP communication link.