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TCP/IP 39
• A universal data packet is built, consisting of a header and a data field. The header
consists, amongst others, of the address of the sender and of the destination. The data
packet is hardware independent and is encapsulated again on the local network before
it can be transported.
• The IP protocol does not check if the data have been sent correctly and it also does not
provide confirmation- or correction mechanisms: send-it and pray.
• The IP header is at least 20 bytes long. When using the options field, the header can be
60 bytes maximum. A header check sum is created.
The Internet Protocol(IP) is applicable to the network level (layer 3 of the OSI model). This
layer is responsible for the presentation and transportation of information over different networks.
Uniform addressing is required to realise this: the IP address.
This functionality is not required for as long as the information transfer takes place within the
same network. The connection of different networks takes place by means of routers. When
different networks are bundled into a bigger entity, each network should also be identifiable
with an address. Each network will therefore get a unique network address. With this network
address, every participant also gets a unique address number within this network address.
Uniform addressing is based on this principle. This address is defined on the IP layer and is
called IP address.
3.2.2 The IP address
General
An IP address consists of 32 bits, 4 bytes, represented as 4 decimals separated by a dot.
Figure 3.3: The IP address
Every network gets a name (Net ID) and every network participant gets a unique number
within this network (Host ID). Net ID and Host ID together form the IP address. The network
name is then the IP address whereby the Host ID is equal to zero.