TCP/IP Interview Preparation Guide

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IP itself does not guarantee to deliver data correctly. It leaves
all issues of data protection to the transport protocol. Both TCP
and UDP have mechanisms that guarantee that the data they deliver
to an application is correct.

Using the IP layer the correct destination of the packet is identified and delivered. The Transport layer protocols(TCP/UDP/SCTP) check if the data delivered are correct using Check sum mechanism. However if the destination IP is not alive, the packet is hopped by decrementing the TTL field and when it becomes zero, the packet is lost and undelivered. If the Transport layer is UDP the source doesn't know of the failure in delivery of the packet

TCP/IP is a name given to the collection (or suite) of networking protocols that have been used to construct the global Internet. The protocols are also referred to as the DoD (dee-oh-dee) or Arpanet protocol suite because their early development was funded by the Advanced Research Projects Agency (ARPA) of the US Department of Defense (DoD).

The data unit of transport layer is "Segment".

IP layer PDU is "packet". So, data is send as packet.

Detecting crashed systems over TCP/IP is difficult. TCP doesn't require any transmission over a connection if the application isn't sending anything, and many of the media over which TCP/IP is used (e.g. Ethernet) don't provide a reliable way to determine whether a particular host is up. If a server doesn't hear from a client, it could be because it has nothing to say, some network between the server and client may be down, the server or client's network interface may be disconnected, or the client may have crashed. Network failures are often temporary (a thin Ethernet will appear down while someone is adding a link to the daisy chain, and it often takes a few minutes for new routes to stabilize when a router goes down) and TCP connections shouldn't be dropped as a result.

OSI - Open System Interconnection
TCP/IP - Transmission Control Protocol/ Internet Protocol

2^6=64 and 2^7=128
as per question, we need to accommodate 76 networks through fixed subnetting(ie VLSM is not asked for); so we need to use /23 mask which gives 128 subnets
No. of hosts per subnet = (2^9)-2 = 510

Subnet Address = 172.16.0.0
Subnet mask = 255.255.254.0
Valid subnets = 256-254 = 0,2,4,6...254

Subnet Example: for Subnet 0.0

First Host = 0.1
Last Host = 1.254
Broadcast = 1.255

PDU for Network Layer is: "Packet" and PDU for Data Link Layer is :"Frame"

128 bit in tcp ip

Each application running over TCP or UDP distinguishes itself from
other applications using the service by reserving and using a
16-bit port number. Destination and source port numbers are placed
in the UDP and TCP headers by the originator of the packet before
it is given to IP, and the destination port number allows the
packet to be delivered to the intended recipient at the
destination system.

IP really isn't very fussy about how its packets are transported.
The details of how an IP packet is carried over a particular kind
of network are usually chosen to be convenient for the network
itself. As long as the transmitter and receiver observe some
convention that allows IP packets to be differentiated from any
other data that might be seen by the receiver, then IP can be used
to carry data between those stations.

Ip is just a protocol which used to carry data,packets over the network in the manner which the n/w components can understand.
ip is a identity of n/w devices