Information Technology Reference
In-Depth Information
Network A
Network B
Internet
gateway
Transport
TCP
TCP
Network
IP
IP
IP
Convertor to
Ethernet,
Token Ring,
FDDI
modem
Data link
Ethernet,
Token Ring,
FDDI
modem
Ethernet,
Token Ring,
FDDI
modem
Physical
Figure 23.2
Internet gateway layers
23.4 Internet datagram
The IP protocol is an implementation of the network layer of the OSI model. It adds a data
header onto the information passed from the transport layer, the resultant data packet is
known as an internet datagram. The header contains information such as the destination and
source IP addresses, the version number of the IP protocol and so on. Figure 23.3 shows its
format.
1
2
3
4
5
6
7
8
9
10 11 12 13 14 15 16
Version
Header length
Type of service
Total length
Identification
Fragment offset
0
D
M
Time-to-live
Protocol
Header checksum
Source IP address
Destination IP address
Options
Data (less than 64 kB)
Figure 23.3
Internet datagram format and contents
