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As we discussed earlier that apart from the OSI model, there is another network model known as TCP/IP protocol suite which was eventually developed prior to the OSI model. Hence, the layers in the TCP/IP model do not go with the layers discussed in the OSI model.

Architecture of TCP/IP Model

TCP/IP is a hierarchical protocol model made up of interactive modules, where each layer provides specific functionalities; but the modules are necessarily independent.

TCP/IP protocol suite was designed by defining only four layers, such as:

1.   Host-to-network.
2.   Internet Layer.
3.   Transport Layer.
4.   Application Layer.

TCP/IP model layers and protocols residing are discussed in the picture below,

tcp ip model, tcp ip layer
TCP IP model
Now from the above picture,

When TCP/IP is compared to OSI model, we can claim that the host-to-network layer is equivalent to the combination of physical layer and data link layer. The internet layer is equivalent to the network layer and IP. The transport layer goes for the same taking care of the duties of TCP and other protocols. But application layer is roughly doing the work of combined job of session layer, presentation and application layer.

Layers and Protocols of TCP/IP Model

1. Host-to-Network : The host-to-network layer defines the responsibilities of combined duty of Physical layer and Data link layer of OSI model. In this layer TCP/IP does not define any specific protocol, because supports all the standard and proprietary protocols of the underlying network. This layer may contain several local area network (LAN) or wide area network (WAN).

2. Network Layer (Internet layer) : In this layer, TCP/IP supports internetworking protocol i.e. IP which does the addressing part; in turn it uses four supporting protocols such as, ARP, RARP, ICMP, and IGMP.

  • ARP (Address Resolution Protocol): ARP is used to find the physical address (MAC Address) where its internet address (IP Address) is known. In other words, mapping from IP address to MAC address is done here.

  • RARP (Reverse Address Resolution Protocol) : RARP is exactly reverse of ARP. It’s used to find the internet address where physical address is known. In other words, mapping from MAC address to IP address is done here.

  • ICMP (Internet Control message Protocol) : ICMP uses a mechanism to send a notification back to the sender if any datagram related problem occurs. It also sends query and error reporting messages.

  • IGMP (Internet Group Message Protocol) : IGMP mainly facilitates the simultaneous transmission of a message to a group of recipients or receiver. 

3. Transport Layer: In this TCP/IP defines three major protocols, i.e. TCP, UDP and SCTP.

  • TCP (Transmission Control Protocol) : TCP provides full transport layer services to all applications. It’s reliable and stream transport protocol Here the term ‘stream’ means connection-oriented, means before transmission it supports to establish a strong connection between both ends to transmit data.

  • UDP (User Datagram Protocol) : UDP is the simpler form of TCP and SCTP, it’s a process-to-process protocol that only adds port addresses, checksum, error control and length information of the data. But its unreliable than TCP, and connection-less protocol.

  • SCTP (Stream Control Transmission Protocol) : SCTP provides the support of modern application such as, Voice over Internet. It’s a transport layer protocol that combines the best features of TCP and UDP.

4. Application Layer: Application layer in TCP/IP is equivalent to the combination of session layer, presentation layer and application layer of OSI model. Many protocols are defines in this layer like; HTTP, FTP, SMTP, SNMP etc will be discussed in the later posts.

Study Sessions

Q1. State the differences of how do TCP/IP model layers technically correlate to the OSI model layers?

Q2. Name the services are provided by the application layer in the internet model.

Q3. What are the differences between the protocols TCP and UDP in TCP/IP model?

Q4. What are the functionalities of ARP and RARP? Explain


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