Question

c) Suppose an application generates chunks of 60 bytes of data every 20 msec, and each chunk gets encapsulated in a TCP segment and then an IP datagram. What percentage of each datagram will be overhead, and what percentage will be application data?

d) What is network address translation? Briefly explain with an example.

Answer 1

c) TCP and IP are 20bytes each which makes of 40 bytes

And the data chunks to be added is 60 bytes which makes total of 100 total bytes

then the over head is 40 of the 100 total ,which is 40%.

40% (20 TCP byte+ 20 IP byte + 60 byte data chunk =100 bytes;100/40=40%).

d)Network address translation which is also called as NAT is a process in which one or more local IP address space into another by modifying network address information in the IP packets when they are in transit across a routing device. It was used to avoid the need to assign a new address to every host when a network was moved, but could not route the networks address space. One Internet-routable IP address of a NAT gateway can be used for an entire private network and generally operates on router or firewall.

Example:

The below diagram shows the working of NAT,
when Host PC 172.168.20.10 wants to communicate with the outside and the destination web server IP is
192.100.20.2. It will send a data packet to the gateway router with NAT for communication. The gateway router reads the source IP address of the packet and checks in the table whether the packet meets the condition for translation. The gateway router maintains an access control list which locates the authenticate hosts for the internal network translation purposes. It translate's the inside local IP address into an inside global IP address as 192.100.10.25. Then it stores in the NAT table and the gateway router will route the packet to the destination. When the web server of the Internet responds back to the request, the packet will respond back to the global IP address 192.100.10.25 of the router. The gateway router will again check in the NAT table to find out the translated IP address with respect to the global address. It translate to the inside local address and then the data packet is delivered to host PC address 172.168.20.10. If a search is not found in the table then it is discarded.