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Understanding TCP contd

Internet layer

Beneath the Transport layer is the Internet layer. Three key protocols reside in the Internet layer: Internet Protocol (IP), Address Resolution Protocol (ARP), and Internet Control Message Protocol (ICMP), along with two less-used protocols, Reverse Address Resolution Protocol (RARP) and Internet Group Management Protocol (IGMP).

Internet Protocol has been discussed above.

Address Resolution Protocol (ARP) matches IP address requests, such as www.netcomm.com.au, with a DNS number, such as 216.218.210.207. More info on Address Resolution is provided in the article About DNS (see below).

ICMP is part of the TCP stack that handles verification, correction and resend requests.

RARP and IGMP won't be detailed here.

The Data Link Layer

The next layer is the Data Link layer. Having been 'packetised' and 'addressed', the data is then 'encapsulated' in a format suitable for transmission across the network. 'Encapsulation' re-formats the data again into a format compatible with lower-level network protocols, and adds another layer of information to identify and demarcate data packets as they traverse the network. 'Encapsulation' places 'packets' within another type of packet, often called a data 'frame'.

Examples of a data-link-layer protocols include Ethernet, FDDI, Token Ring, and Wi-Fi.

The Physical Layer

The bottom layer of the stack is the layer on which network cards and card driver software operates. Among other things, Physical Layer services interface with the computer network hardware and provide another level of error correction code to ensure that data is transmitted correctly on the physical-link level.

Summary

This brief description has introduced

1. The concept of the TCP/IP Stack
   
2. Some essential attributes and applications of each network layer
   
3. Some key protocols belonging to each network layer
   

This article has introduced IP addressing and the main components of TCP. Of course, these are big topics, but the emphasis here is on getting just enough knowledge to start forming a meaningful idea of how they work. Once the idea of data packets being routed across networks by their IP addresses becomes familiar, a lot of things about the Internet become a lot easier to grasp.

The next article in this brief series will introduce DNS - the Domain Name System.

For further resources, check the Books page.

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