State the functions performed by the Network layer and application layer in a TCP/I protocol.

Functions of the Network Layer:

1. Subnet Traffic Control: Network layer routers (network layer intermediate systems) can instruct a sending station to "throttle back" its frame transmission when the router's buffer fills up.
2. Logical-Physical Address Mapping: It translates logical addresses, or names, into physical addresses.
3. Subnet Usage Accounting: It has accounting functions to keep track of frames forwarded by subnet intermediate systems. 
4. Internetworking: One of the main responsibilities of the network layer is to provide internetworking between different networks. It provides a logical connection between different types of networks. It is because of this layer that we can combine various different networks to form a bigger network.
5. Logical Addressing: A large number of different networks can be combined together to form bigger networks or internetworks. In order to identify each device on the internetwork uniquely, the network layer defines an addressing scheme. Such an address distinguishes each device uniquely and universally.
6. Routing: When independent networks or links are combined together to create networks, multiple routes are possible from the source machine to the destination machine. The network layer protocols determine which route or path is best from source to destination. This function of the network layer is known as routing. Routes frames among networks.
7. Packetising: The network layer receives the data from the upper layers and creates its own packets by encapsulating these packets. The process is known as packetising. This packetising is done by Internet Protocol (IP) that defines its own packet format.
8. Fragmentation: Fragmentation means dividing the larger packets into small fragments. The maximum size for a transportable packet is defined by the physical layer protocol. For this, the network layer divides the large packets into fragments so that they can be easily sent on the physical medium. If it determines that a downstream router's maximum transmission unit (MTU) size is less than the frame size, a router can fragment a frame for transmission and reassembly at the destination station. 

Functions Application Layer: 

1. Network Virtual Terminal: It allows a user to log on to a remote host
2. File Transfer, Access, and Management (FTAM): This application allows a user to access files on a remote computer (to make changes or read data), to retrieve files from a remote computer, and to manage or control files on a remote computer.
3. Mail Service: This application provides the basis for e-mail forwarding and storage.
4. Remote Logins: This layer allows logging into a host that is remote.
5. Network Abstraction: Provides an abstraction of the underlying network to an end user and an application.
6. Directory Services: This application provides distributed database sources and access for global information about various objects and services.