Network Devices

Mask

If the network address is given, we can find the block and the range of addresses in the block.  What about the reserves? If an address is given, can we find the given address (the beginning address in the block). This is important because to route a packet to the correct network, a router needs to extract a network address from the destination address (a host address) in the packet header.

One way we can find the network address to first find the class of the address and the net ID. We then set the host ID to zero to find the network address. For example, if the address is 134.45.78.2 is given, we can immediately say that the address belong to class B. the net ID is 134.45 (2 bytes)  and the network address is 134.45.0.0.

The above method is feasible if we not subnetted the network; that is, if we have not divided the network into subnetworks. A general procedure that can be used involves a mask to find the network address from a given address.

A mask is a 32 bits binary number that gives first address in the block (the network address). When bit-wise ANDed with an address in the block.

AND Operation

Masking uses the bit-wise AND operation defined in computer science. The operation is applied bit by bit to the address and the mask.

The UDP is process to process protocol that adds only port address, check-sum error control and length information to the data from the upper layer.

The TCP provides full transport layer services to application. TCP is a reliable stream transport protocol. The term stream in this context means connection-oriented: a connection must be established between both ends of a transmission before either can transmit data.

The application layer in TCP/IP is equivalent to the combined session, presentation and application layer in the OSI model. Many protocols are defined at this layer.

The transport layer is represented in TCP/IP by two protocols, TCP and UDP. The IP is a host-to-host protocol; UDP and TCP are transport level protocols. IP can deliver a packet form one physical device to another. UDP and TCP are responsible for delivery of a message from a process to another process (running programs) 

Physical and Data link Layer

At the physical and data link layer, TCP/IP does not define any specific protocol. It support all of the standard and proprietary protocol which LAN, MAN and WAN.

Network Layer

At the network layer TCP/IP supports the internetworking protocol which contains four supported protocols: ARP, RARP, ICMP and IGMP

The internetworking protocol (IP) is the transmission mechanism used by TCP/IP protocol. It is un reliable and connectionless datagram protocol- a best-effort delivery service. The term best-effort means that IP provides no error checking or tracking.

The Address Resolution Protocol (ARP) is used to associate an IP address with the physical address. ARP is used to find the physical address of the node, when its internet address is known.

The (RARP) allows a host to discover its internet address when it known only its physical address. It is used when a computer is connected to the network for the first time or when a diskless computer is booted.

The ICMP is a mechanism used by hosts and gateways to send notification datagram problems back to the sender.

The IGMP used to facilitate the simultaneous transmission of the message to a group of recipients.