Operation Manual

IP
SIP Software Release 6-0-0
J613-M0524-00
21
Protocol The high level protocol used to create the message
(analogous to the type field in an Ethernet packet)
Header checksum A checksum of the header
Source IP address 32-bit IP address of the sender
Destination IP address 32-bit IP address of the recipient
Options An optional field primarily used for network
testing or Debugging.
Padding All bits set to zero—used to pad the datagram
header to a length that is a multiple of 32 bits.
User data The actual data being sent.
Addressing
Internet addresses are fundamental to the operation of the TCP/IP internet.
Each packet must contain an internet address to determine where to send
the packet. Most packets also require a source address so that the sender of
the packet is known. Addresses are 32-bit quantities which are logically
divided into fields. They must not be confused with physical addresses
(such as an Ethernet address); they serve only to address Internet Protocol
packets.
Addresses are organised into five classes (see Table 12).
Table 12. Internet Protocol address classes and limits on numbers of
networks and hosts.
Class Maximum number of possible
networks
Maximum number of hosts
per network
A 127
16,777,216
B 16,384
65,536
C 2,097,152
255
D Reserved Class
E Reserved Class
Each class differs in the number of bits assigned to the host and network
portions of the address (see Figure 5).