The transport layer accepts data from the session layer, breaks it into packets, and delivers the packets to the network layer. It provides end-to-end communication and ensures reliable delivery of data. The network interface layer sends and receives TCP/IP packets on the network medium. It encompasses the data link and physical layers of the OSI model. TCP/IP is independent of the specific network technology.

1. MC0087-INTERNETWORKING WITH TCP/IP
Que. 1 Discuss the functions of transport layer and Network Interface Layer?
Ans
Functions of transport layer: -
Transport layer accepts data from session layer breaks it into packets and delivers these packets to
the network layer. It is the responsibility of transport layer to guarantee successful arrival of data at
the destination device. It provides an end-to-end dialog that is the transport layer at the source
device directly communicates with transport layer at destination device.
Message headers and control messages are used for this purpose. It separates the upper layers from
the low level details of data transmission and makes sure an efficient delivery.
OSI model provides connection-oriented service at transport layer.
It is responsible for the determination of the type of service that is to be provided to the upper
layer. Normally it transmits packets in the same order in which they are sent however it can also
facilitate the transmission of isolated messages. There is no surety that these isolated messages are
delivered to the destination devices in case of broadcast networks and they will be in the same
order as were sent from the source.
Applications
Applications
Transport
TCP/UDP
Internetwork
IP
ICMP
ARP/RARP
Network Interface
And
Hardware
Network Interface
And
Hardware
Functions of transport layer

2. Network Interface Layer: -
The Network Interface Layer (also called the Network Access Layer) sends TCP/IP packets on the
network medium and receives TCP/IP packets off the network medium.
TCP/IP was designed to be independent of the network access method, frame format, and medium.
Therefore, you can use TCP/IP to communicate across differing network types that use LAN
technologies – such as Ethernet and 802.11 wireless LAN – and WAN technologies –such as Frame
Relay and Asynchronous Transfer Mode (ATM). By being independent of any specific network
technology, TCP/IP can be adapted to new technologies.
The Network Interface layer of the DARPA model encompasses the Data Link and Physical layers of
the OSI model. The Internet layer of DARPA model does not take advantage of sequencing and
acknowledgment services that might be present in the Data Link layer of the OSI model. The
Internet layer assumes an unreliable Network Interface layer and that reliable communication
through session establishment and the sequencing and acknowledgment of packets is the
responsibility of either the Transport layer or the Application layer.

3. Que. 2 Brief the following
a) ISDN
b) X.25
Ans
a) ISDN
The ISDN Basic Rate Interface (BRI) usually supports two B-channels with a capacity of 64 kbps
each, and a 16 kbps D-channel for control information. B-channels can be used for voice or data or
just for data in a combined way. The ISDN Primary Rate Interface (PRI) can support many
concurrent B-channel links and one 64 kbps D-channel. The PPP, LCP and NCP mechanisms are
particularly useful in this situation in reducing or eliminating manual configuration and facilitating
ease of communication between diverse implementations. The ISDN D-channel can also be use for
sending PPP packets when suitably framed, but is limited in bandwidth and often restricts
communication links to a local switch. PPP treats ISDN channels as bit- or octet-oriented
synchronous links. These links must be full duplex, but can be either dedicated or circuit-switched.
PPP presents an octet interface to the physical layer. There is no provision for sub-octets to be
supplied or accepted. PPP does not impose any restrictions regarding transmission rate other than
that of the particular ISDN channel interface. PPP does not require the use of control signals. When
available, using such signals can allow greater functionality and performance. The D-channel
interface requires NRZ encoding.
b) X.25
This topic describes the encapsulation of IP over X.25 networks, in accordance with ISO/IEC and
CCITT standards. IP over X.25 networks is documented by RFC 1356 (which obsoletes RFC 877).
RFC 1356 is a Draft Standard with a status of elective. The substantive change to the IP
encapsulation over X.25 is an increase in the IP datagram MTU size, the X.25 maximum data packet
size, the virtual circuit management, and the interoperable encapsulation over X.25 of protocols
other than IP between multi-protocol routers and bridges.
One or more X.25 virtual circuits are opened on demand when datagram arrive at the network
interface for transmission. Protocol Data Units (PDUs) are sent as X.25 complete packet sequences.
That is, PDUs begin on X.25 data packet boundaries and the M bit (more data) is used to fragment
PDUs that are larger than one X.25 data packet in length. In the IP encapsulation, the PDU is the IP
DATAGRAM. The first octet in the Call User Data (CUD) field (the first data octet in the call Request
packet) is used for protocol de-multiplexing in accordance with Subsequent Protocol Identifier
(SPI) in ISO/IEC TR 9577.

4. Que. 3 What are congestion? Mention two algorithms to overcome congestion?
Ans.
TCP is the popular transport protocol for best-effort traffic in Internet. However, TCP is not well-suited
for many applications such as streaming multimedia, because TCP congestion control
algorithms introduce large variations in the congestion window size (and corresponding large
variations in the sending rate). Such variability in the sending rate is not acceptable to many
multimedia applications. Hence, many multimedia applications are built over UDP and use no
congestion control at all.
The absence of congestion control in applications built over UDP may lead to congestion collapse on
the Internet. In addition, the UDP flows may starve any competing TCP flows. To overcome these
adverse effects, congestion control needs to be incorporated into all applications using the Internet,
whether at the transport layer or provided by the application itself. Furthermore, the congestion
control algorithms must be TCP-friendly, i.e. the TCP-friendly flows should not gain more
throughput than competing TCP flows in the long run. Thus, in recent years, many researchers have
focused on developing “TCP-friendly” transport protocols which are suitable for many applications
that currently use UDP.
The first step in answering these questions is to study the short-term and long-term behavior of
these algorithms. Although the goal of all TCP-friendly algorithms is to emulate the behavior of TCP
in the long term, these algorithms may have an adverse impact in the short-term on competing TCP
flows. Since TCP-friendly algorithms are designed for smoother sending rates than TCP, these
algorithms may react slowly to new connections that share a common bottleneck link.
Such a slower response may have a deleterious effect on TCP flows. For example, a TCP connection
suffering losses in its slow start phase may enter the congestion avoidance phase with a small
window, and consequently obtain lesser throughput than other competing flows.
In this paper, we analyze the reasons for this unfairness, and validate the analysis by simulations.
The rest of the paper is organized as follows. In Section II, we briefly overview the various TCP-friendly
congestion control algorithms proposed in literature. In Section III, we define the transient
behaviors studied in this paper, and analyze the expected transient behaviors of the various TCP-friendly
congestion control algorithms.
Few algorithms to overcome congestion
1) Transient behaviors evaluated in the paper
2) Equation-Based Congestion Control Algorithm
3) General AIMD-Based Congestion Control Algorithms
4) Binomial Congestion Control Algorithm

5. Que. 4 Differentiate between permanent and transient host groups?
Ans
IP multicasting is defined as the transmission of an IP datagram to a "host group", a set of zero or
more hosts identified by a single IP destination address. A multicast datagram is delivered to all
members of its destination host group with the same "best-efforts" reliability as regular uncast IP
datagram’s, i.e. the datagram is not guaranteed to arrive at all members of the destination group or
in the same order relative to other datagram’s
The membership of a host group is dynamic; that is, hosts may join and leave groups at any time.
There is no restriction on the location or number of members in a host group, but membership in a
group may be restricted to only those hosts possessing a private access key. A host may be a
member of more than one group at a time. A host need not be a member of a group to send
datagram’s to it.
A host group may be permanent or transient. A permanent group has a well-known,
administratively assigned IP address. It is the address, not the membership of the group that is
permanent; at any time a permanent group may have any number of members, even zero. A
transient group, on the other hand, is assigned an address dynamically when the group is created,
at the request of a host. A transient group ceases to exist, and its address becomes eligible for
reassignment, when its membership drops to zero.
The creation of transient groups and the maintenance of group membership information is the
responsibility of "multicast agents", entities that reside in internet gateways or other special-purpose
hosts. There is at least one multicast agent directly attached to every IP network or sub
network that supports IP multicasting. A host requests the creation of new groups, and joins or
leaves existing groups, by exchanging messages with a neighboring agent.
Multicast agents are also responsible for internetwork delivery of multicast IP datagram’s. When
sending a multicast IP datagram, a host transmits it to a local network multicast address which
identifies all neighboring members of the destination host group. If the group has members on
other networks, a multicast agent becomes an additional recipient of the local multicast and relays
the datagram to agents on each of those other networks, via the internet gateway system.

6. Que. 5 What is domain name resolution? Discuss the domain name resolution process?
Ans
Domain Name System: -
DNS is a way to resolve meaningful and easy-to-remember names to IP addresses. Because millions
of sites are connected to the Internet, maintaining one central list of the name to- IP-address
relationships across the Internet is unrealistic. The DNS system was designed to coordinate and
distribute the resolution load.
The two major tasks that DNS provides are: -
1) IP address resolution to hosts on the Internet, for local hosts
2) IP address resolution to hosts on the local network, for other hosts on the Internet
The domain name resolution process as under like: -
1) A user program issues a request such as the get host by name () system call (this particular
call asks for the IP address of a host by passing the host name) or the get host name ()
system call (which asks for a host name of a host by passing the IP address).
2) The resolver formulates a query to the name server. (Full resolvers have a local name cache
to consult first; stub revolvers do not.
3) The name server checks to see if the answer is in its local authoritative database or cache,
and if so, returns it to the client. Otherwise, it queries other available name servers, starting
down from the root of the DNS tree or as high up the tree as possible.
4) The user program is finally given a corresponding IP address (or host name, depending on
the query) or an error if the query could not be answered. Normally, the program will not
be given a list of all the name servers that have been consulted to process the query. Domain
name resolution is a client/server process .The client function (called the resolver or name
resolver) is transparent to the user and is called by an application to resolve symbolic high-level
names into real IP addresses or vice versa. The name server (also called a domain
name server) is the server application providing the translation between high- level
machine names and the IP addresses. The query/reply messages can be transported by
either UDP or TCP.

7. Que. 6 Differentiate between Simple Mail Transfer Protocol and Post Office Protocol?
Ans
Simple Mail Transfer Protocol: -
SMTP is a core Internet protocol used to transfer e-mail messages between servers (first defined in
RFC 821 in 1982)
This contrasts with protocols such as POP3 and IMAP, which are used by messaging clients to
retrieve e-mail. SMTP servers look at the destination address of a message and contact the target
mail server directly. Of course, this means the Domain Name Service (DNS) has to be configured
correctly otherwise mail could be handed to the wrong server - potentially a big problem because,
unless you have encrypted your messages, your e-mail will be in plain text!
SMTP was designed to be a reliable message delivery system. Reliable in this case means that a
message handled by SMTP is intended to get to its destination or generate an error message
accordingly.
This is not the same as a guaranteed delivery service, it just does its best. To guarantee delivery
requires all sorts of data exchanges that would add considerable communications overhead that
would be pointless for everyday purposes.
SMTP communications are transported by TCP to ensure reliable end-to-end transport. RFC 822
defines the format of SMTP messages.
Post Office Protocol: -
POP is short for Post Office Protocol, a protocol used to retrieve e-mail from a mail server.
Most e-mail applications (sometimes called an e-mail client) use the POP protocol, although some
can use the newer IMAP (Internet Message Access Protocol).
There are two versions of POP. The first called POP and second became a standard in the mid-80 s
and requires SMTP to send messages.
The newer version, POP3, can be used with or without SMTP.
Pop is short for point of presence, an access point to the Internet. ISPs have typically multiple POPs.
A point of presence is a physical location, either part of the facilities of a telecommunications
provider that the ISP rents or a separate location from the telecommunications provider that
houses servers, routers, ATM switches and digital/analog call aggregators.
Pop is short for Programmed Operator (POP), a pseudo-opcode in a virtual machine language
executed by an interpretive program. The Programmed Operator instructions provide the ability to
define an instruction set for efficient encoding by calling subprograms into primary memory.
POP is short for picture-outside-picture POP is a feature found on some televisions that allows the
user to divide the screen into two same-size pictures, enabling you to view a second program.
Compare with picture-in-picture (PIP).