Digital Signal Processing Reference
In-Depth Information
IP addresses can be constant, or temporary. This is best illus-
trated by example: an organization or corporation may have
a unique, constant IP address, used to communicate over the public
IP network. However, within the corporation there's a private IP
network not intended to be accessible to outsiders, whichmay have
hundreds or thousands of different computers or devices with IP
addresses. Using dynamic host reconfiguration protocol (DHCP),
a router within the corporation can assign temporary IP addresses
to these nodes on the private network. Certain ranges of IP
addresses are designated for use by DHCP. These addresses are
assigned whenever a computer tries to connect to the private
network. The dynamically assigned addresses need only to be
unique within the private network
other private networks can use
the same range of addresses within their own private network. A
function in the router bridging the private network to the external
network, called network address translation (NAT), is used to
translate between the address space of the public internet and the
DHCP-assigned addresses within the private network.
Routers are the key components that allow anyone to transmit
data to anyone else over the internet. Routers are distributed
throughout the IP networks
e
they examine the headers, and,
using the destination address, forward the packets towards their
destinations. Since the packet may pass though many routers,
each router must decide how best to forward the packet to get it
closer to its destination. This is done by maintaining large routing
tables, and monitoring the status of various network connections
for traffic levels, and sometimes by determining priority for
a given packet.
e
Version (4 bytes)
Header length (4 bytes)
Service Type (8 bytes)
Total length (16 bytes)
Fragmentation control (16 bytes)
Time to live (8 bytes)
Protocol Identifier (8 bytes)
Header Checksum (16 bytes)
Source IP Addr (32 bytes)
Destination IP Addr (32 bytes)
Data (1- 65515 bytes)
Figure 18.1. IP packet formatting.
