why do we need ip address if we have mac address?

Ip address(network address) is just use for transfering informatiom from one network to an other.travelling of information among networks uses ip addresses.

Mac addresses(physical addresses) is actually uses for distrubution of information.so, the summay is:-

1) carring of information from one network to another.

2) distrubtion of information(resources) is based upon mac address.

example:-

Network A , Network B and Network C are three networks.all network are having 5 nodes(client).if i want to send information to node 3 for network B.

Solution:-

1) first i send infomation to network by the help of IP address of that network(Network B).Ip addresses are unique on network layer(this is the fact).

2)after that i will send infomation to node 3 of network B by the help of mac address which is unique at layer 2(DLL).

IP address (network address) is just used for transferring information from one network to another network. Travelling of information among networks uses IP addresses. It is used to identity the network and host. 

A MAC address (physical addresses) is used for distribution of information with in the network segment. The Ethernet uses MAC address to transfer data between hosts. When its used with IP network, the IP address is resolved using ARP protocol to find the MAC address of the end device and the data is transmitted. 

Port numbers are used by the TCP/UDP protocol to isolate the traffic which is multiplexed and sent by the user application. For example, the user device, can open multiple applications at the same time like, multiple web browsers, email and FTP. To identify the data individually the port number are used.