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10- WIN- COMP- VI- REV- ACN

VIEWS: 1 PAGES: 25

									  Rajendara Mane College of Engineering and Technology, AMBAV (Devrukh) -415804
                                       University of Mumbai
                 Computer Engineering Sem-V I(Rev) Winter 2010(10-WIN-COMP-VI-REV-ACN)
                                Advanced Computer Network

Q.1 a] Describe how is the TCP/IP protocol stack organized compared to ISI/OSI protocol stack. (05
Marks)

Ans:- Diagram 1 Mark

       Description 4 Marks




Q.1 b] Differentiate between Bridge, Router and Gateway. (05 Marks)
Ans:- Any 2 difference between bridge, router and gateway 05 Marks

Bridge:- physical and data link layer function
Router:- physical, data, network function
Gateway:- five layer function


Q.1 c] what is difference between data plane and control plane in ATM?
Ans:- Any 2 Difference carry 5 marks

Data plane:- It is used for transferring user information along with associated control such as flow
control, error control etc.
Control plane:- It is supposed to perform the call control and connection control functions.


Q.P. Code GT7557                         Page 1 of 25              Prepared by: - Prof. A. B. Yadav
  Rajendara Mane College of Engineering and Technology, AMBAV (Devrukh) -415804
                                       University of Mumbai
                 Computer Engineering Sem-V I(Rev) Winter 2010(10-WIN-COMP-VI-REV-ACN)
                                  Advanced Computer Network

Q.1 d] Discuss the functions of SONET layers. (05 Marks)

Ans:- Diagram 1Mark

        Function of each layer carry 1 Mark (04*01=04)




Path Layer
The path layer is responsible for the movement of a signal from its optical source to its optical
destination. At the optical source, the signal is changed from an electronic form into an optical form,
multiplexed with other signals, and encapsulated in a frame. At the optical destination, the received
frame is demultiplexed, and the individual optical signals are changed back into their electronic forms.
Path layer overhead is added at this layer.
Line Layer
The line layer is responsible for the movement of a signal across a physical line. Line layer overhead is
added to the frame at this layer. STS multiplexers and add/drop multiplexers provide line layer
functions.
Section Layer
The section layer is responsible for the movement of a signal across a physical section. It handles
framing, scrambling, and error control. Section layer overhead is added to the frame at this layer.
Photonic Layer
The photonic layer corresponds to the physical layer of the OSI model. It includes physical
specifications for the optical fiber channel, the sensitivity of the receiver, multiplexing functions, and so
on.

Q.2a] Describe the Routing Information Protocol in detail with its message header And types.(10 Marks)

Ans:-   RIP 4 Marks

        Message Header diagram 1 Mark

        Explanation 4 Marks

        Types 1 Mark


Q.P. Code GT7557                           Page 2 of 25                   Prepared by: - Prof. A. B. Yadav
   Rajendara Mane College of Engineering and Technology, AMBAV (Devrukh) -415804
                                          University of Mumbai
                    Computer Engineering Sem-V I(Rev) Winter 2010(10-WIN-COMP-VI-REV-ACN)
                                     Advanced Computer Network




      •   Command - Indicates whether the packet is a request or a response. The request asks that a router send
          all or part of its routing table. The response can be an unsolicited regular routing update or a reply to a
          request. Responses contain routing table entries. Multiple RIP packets are used to convey information
          from large routing tables.
      •   Version number - Specifies the RIP version used. This field can signal different potentially incompatible
          versions.
      •   Zero - This field is not actually used by RFC 1058 RIP; it was added solely to provide backward
          compatibility with prestandard varieties of RIP. Its name comes from its defaulted value: zero.
      •   Address-family identifier (AFI) - Specifies the address family used. RIP is designed to carry routing
          information for several different protocols. Each entry has an address-family identifier to indicate the
          type of address being specified. The AFI for IP is 2.
      •   Address - Specifies the IP address for the entry.
      •   Metric - Indicates how many internet work hops (routers) have been traversed in the trip to the
          destination. This value is between 1 and 15 for a valid route, or 16 for an unreachable route.

RIP

The Routing Information Protocol (RIP) is an intradomain routing protocol used inside an autonomous system. It
is a very simple protocol based on distance vector routing. RIP implements distance vector routing directly with
some considerations:

1. In an autonomous system, we are dealing with routers and networks (links). The routers have routing tables;
networks do not.

2. The destination in a routing table is a network, which means the first column defines a network address.

Q.P. Code GT7557                               Page 3 of 25                    Prepared by: - Prof. A. B. Yadav
  Rajendara Mane College of Engineering and Technology, AMBAV (Devrukh) -415804
                                       University of Mumbai
                 Computer Engineering Sem-V I(Rev) Winter 2010(10-WIN-COMP-VI-REV-ACN)
                                  Advanced Computer Network

3. The metric used by RIP is very simple; the distance is defined as the number of links (networks) to reach the
destination. For this reason, the metric in RIP is called a hop count.

4. Infinity is defined as 16, which means that any route in an autonomous system using RIP cannot have more
than 15 hops.

5. The next-node column defines the address of the router to which the packet is to be sent to reach its
destination. Figure shows an autonomous system with seven networks and four routers. The table of each
router is also shown. Let us look at the routing table for Rl. The table has seven entries to show how to reach
each network in the autonomous system. Router Rl is directly connected to networks 130.10.0.0 and 130.11.0.0,
which means that there are no next-hop entries for these two networks. To send a packet to one of the three
networks at the far left, router Rl needs to deliver the packet to R2. The next-node entry for these three
networks is the interface of router R2 with IP address 130.10.0.1. To send a packet to the two networks at the
far right, router Rl needs to send the packet to the interface of router R4 with IP address 130.11.0.1.




Q.2 b] Write a code for connection oriented client server program using c++/java Assume suitable
libraries. Using socket programming for establishing connection. (10 Marks)



Ans:- Socket use 3 Marks

        Library use 2 Marks

Q.P. Code GT7557                            Page 4 of 25                   Prepared by: - Prof. A. B. Yadav
  Rajendara Mane College of Engineering and Technology, AMBAV (Devrukh) -415804
                                     University of Mumbai
               Computer Engineering Sem-V I(Rev) Winter 2010(10-WIN-COMP-VI-REV-ACN)
                              Advanced Computer Network

       Program 5 Marks




Q.3 a] Using block diagram describe a typical unidirectional dense wavelength division multiplexing
(DWDM) transmission system? What are the advantages and disadvantages of DWDM. (10 Marks)

Ans:- Diagram 2 Marks

       Explanation 4 Marks

       Advantage 2 Marks

       Disadvantage 2 Marks




Q.P. Code GT7557                      Page 5 of 25                Prepared by: - Prof. A. B. Yadav
  Rajendara Mane College of Engineering and Technology, AMBAV (Devrukh) -415804
                                       University of Mumbai
                 Computer Engineering Sem-V I(Rev) Winter 2010(10-WIN-COMP-VI-REV-ACN)
                               Advanced Computer Network




DWDM Hardware:

   1. DWDM multiplexer/demultiplexer

   2.   Add/drop Multiplexer

   3. Cross connect

   4. Optical amplifier

   5. Regenerator

Advantage:-

   1. Capacity to support 160 wavelengths means that over 1Tbps of traffic can be carried.

   2. Each wavelength can be different traffic type such as SONET, gigabit Ethernet or IP over PPP
      and can operate at different speed. Bandwidth flexibility.

   3. Optical amplifiers provide cost saving by amplifying all wavelength instead of requiring an
      optical amplifier for each fiber.

Disadvantage:-

   1. Some fiber plants not suitable for DWDM .

   2. DWDM system can be extremely difficult to troubleshoot, manage, and provision.

   3. Vendor interoperability issue exist.




Q.P. Code GT7557                        Page 6 of 25                Prepared by: - Prof. A. B. Yadav
   Rajendara Mane College of Engineering and Technology, AMBAV (Devrukh) -415804
                                        University of Mumbai
                  Computer Engineering Sem-V I(Rev) Winter 2010(10-WIN-COMP-VI-REV-ACN)
                                  Advanced Computer Network



Q.3 b] Explain functions of ATM adaptation layers. Explain in detail the AAL1 and AAL2 layes. (10
Marks)

Ans:- Function 2 Marks

        Diagram of AAL1 1 Mark

        Explanation of AAL1 3 Marks

        Diagram of AAL2 1 Mark

        Explanation AAL2 3 Marks

Application Adaptation Layer
The application adaptation layer (AAL) was designed to enable two ATM concepts. First, ATM must
accept any type of payload, both data frames and streams of bits. A data frame can come from an upper-
layer protocol that creates a clearly defined frame to be sent to a carrier network such as ATM. A good
exampre is the Internet. ATM must also carry multimedia payload. It can accept continuous bit streams
and break them into chunks to be encapsulated into a cell at the ATM layer. AAL uses two sublayers to
accomplish these tasks. Whether the data are a data frame or a stream of bits, the payload must be
segmented into 48-byte segments to be carried by a cell. At the destination, these segments need to be
reassembled to recreate the original payload. The AAL defines a sublayer, called a segmentation and
reassembly (SAR) sublayer, to do so. Segmentation is at the source; reassembly, at the destination.

AALI AALI supports applications that transfer information at constant bit rates, such as video and
voice. It allows ATM to connect existing digital telephone networks such as voice channels and T lines.
Figure shows how a bit stream of data is chopped into 47-byte chunks and encapsulated in cells. The CS
sublayer divides the bit stream into 47-byte segments and passes them to the SAR sublayer below. Note
that the CS sublayer does not add a header. The SAR sublayer adds 1 byte of header and passes the 48-
byte segment to the ATM layer. The header has two fields: Sequence number (SN). This 4-bit field
defines a sequence number to order the bits. The first bit is sometimes used for timing, which leaves 3
bits for sequencing (modulo 8). Sequence number protection (SNP). The second 4-bit field protects the
first field. The first 3 bits automatically correct the SN field. The last bit is a parity bit that detects error
over all 8 bits. AAL2 Originally AAL2 was intended to support a variable-data-rate bit stream, but it has
been redesigned. It is now used for low-bit-rate traffic and short-frame traffic such as audio (compressed
or uncompressed), video, or fax. A good example ofAAL2 use is in mobile telephony. AAL2 allows the
multiplexing of short frames into one cell




Q.P. Code GT7557                            Page 7 of 25                   Prepared by: - Prof. A. B. Yadav
  Rajendara Mane College of Engineering and Technology, AMBAV (Devrukh) -415804
                                       University of Mumbai
                 Computer Engineering Sem-V I(Rev) Winter 2010(10-WIN-COMP-VI-REV-ACN)
                                 Advanced Computer Network




AAL1




AAL2

The CS layer overhead consists of five fields: Channel identifier (CID). The 8-bit CID field defines the
channel (user) of the short packet. Length indicator (LI). The 6-bit LI field indicates how much of the
final packet is data. Packet payload type (PPT). The PPT field defines the type of packet. User-to-user
indicator (UUI). The UUI field can be used by end-to-end users. Header error control (HEC). The last 5
bits is used to correct errors in the header. The only overhead at the SAR layer is the start field (SF) that
defines the offset from the beginning of the packet.


Q.P. Code GT7557                          Page 8 of 25                   Prepared by: - Prof. A. B. Yadav
  Rajendara Mane College of Engineering and Technology, AMBAV (Devrukh) -415804
                                       University of Mumbai
                 Computer Engineering Sem-V I(Rev) Winter 2010(10-WIN-COMP-VI-REV-ACN)
                                 Advanced Computer Network

Q.4 a] Explain the Autonomous system concept and explain EGP in detail. (10 Marks)

Ans:- Concept of Autonomous system 3 Marks

        EGP diagram 1 Mark

        Explanation 6 Marks



Autonomous system:-

        Group of networks under one administrative authority
        Free to choose internal routing update mechanism
        Connects to one or more other autonomous systems


EGP:-

        Originally a single protocol for communicating routes between two autonomous systems
        Now refers to any exterior routing protocol
        Solves two problems
                Allows router outside a group to advertise networks hidden in another autonomous system
                Allows router outside a group to learn destinations in the group


        The most popular (virtually the only) EGP in use in the Internet
        Current version is BGP-4
        Allows two autonomous systems to communicate routing information
        Supports CIDR (mask accompanies each route)
        Each AS designates a border router to speak on its behalf
        Two border routers become BGP peers




Q.P. Code GT7557                          Page 9 of 25                  Prepared by: - Prof. A. B. Yadav
  Rajendara Mane College of Engineering and Technology, AMBAV (Devrukh) -415804
                                       University of Mumbai
                 Computer Engineering Sem-V I(Rev) Winter 2010(10-WIN-COMP-VI-REV-ACN)
                                  Advanced Computer Network



Q.4 b] Explain different Traffic descriptors used in ATM. (05 Marks)

Ans:- Each carry 1 Mark



   1. Peak cell rate (PCR):- 1/T in units of cell per second where T is the minimum intercell spacing.
   2. Call delay variation (CDV):- This traffic parameter normally cannot specified by the user but is set by the
      network.
   3. Sustainable cell rate (SCR):- is the maximum average rate that a bursty on-off traffic source that can be
      sent at peak rate.
   4. Maximum burst size (MBS):- is the maximum of cell that can be sent at peak rate.


   Q.4 c] Explain the naming scheme used in SNMP.(05 Marks)

   Ans:-       Diagram 2 Marks

               Explanation 3 Marks




The tree structure starts with an unnamed root. Each object can be defined by using a sequence of integers
separated by dots. The tree structure can also define an object by using a sequence of textual names separated
by dots. The integer-dot representation is used in SNMP. The name-dot notation is used by people. For example,
the following shows the same object in two different notations:

       iso.org.dod.internet.mgmt.mib-2 ... 1.3.6.1.2.1
Q.P. Code GT7557                           Page 10 of 25                   Prepared by: - Prof. A. B. Yadav
  Rajendara Mane College of Engineering and Technology, AMBAV (Devrukh) -415804
                                       University of Mumbai
                 Computer Engineering Sem-V I(Rev) Winter 2010(10-WIN-COMP-VI-REV-ACN)
                                 Advanced Computer Network

The objects that are used in SNMP are located under the mib-2 object, so their identifiers always start with
1.3.6.1.2.1.

Q.5 a] what is main function of DVMRP? How does it differ from RIP and OSPF? (10 Marks)

Ans:- Function 5 Marks

       Difference 5 marks

The Distance Vector Multicast Routing Protocol (DVMRP) is used to share information between routers
to transport IP Multicast packets among networks. It is based on the RIP protocol to forward packets: the
router generates a routing table with the multicast group that it has knowledge with its corresponding
distance (number of devices -routers- in the middle to reach it). When a multicast packet is received by a
router, it is forwarded by router's interfaces specified in the routing table. The DVMRP protocol uses
IGMP messages to exchange information with other routers.



Q.5 b] List different queuing models. Explain one in detail.

Ans:- List 2 Marks

       Explanation 8 Marks

Queuing theory provides a mathematical basis for understanding and predicting the behavior of
communication networks.
Basic Model




Major parameters:
– interarrival-time distribution
– service-time distribution
– number of servers
– queueing discipline (how customers are taken from the queue, for example, FCFS)
Q.P. Code GT7557                          Page 11 of 25                 Prepared by: - Prof. A. B. Yadav
  Rajendara Mane College of Engineering and Technology, AMBAV (Devrukh) -415804
                                       University of Mumbai
                 Computer Engineering Sem-V I(Rev) Winter 2010(10-WIN-COMP-VI-REV-ACN)
                                  Advanced Computer Network

– number of buffers, which customers use to wait for service
_ A common notation: A/B/m, where m is the number of servers and A and B are chosen from
– M: Markov (exponential distribution)
– D: Deterministic
– G: General (arbitrary distribution)

M/M/1 Queueing Systems
-Interarrival times are exponentially distributed, with average arrival rate l.
-Service times are exponentially distributed, with average service rate m.
_There is only one server.
_The buffer is assumed to be infinite.
_The queuing discipline is first-come-firstserve (FCFS).


Q.6 a] what is RSVP? What are features of RSVP? How RSVP works? Give its frame format. (10 Marks)

Ans:- RSVP basic 2 Marks

       Features 2 Marks

       Working 4 Marks

       Frame format 2 Marks

The Resource Reservation Protocol (RSVP) is a network-control protocol that enables Internet
applications to obtain special qualities of service (QoSs) for their data flows. RSVP is not a routing
protocol; instead, it works in conjunction with routing protocols and installs the equivalent of dynamic
access lists along the routes that routing protocols calculate. RSVP occupies the place of a transport
protocol in the OSI model seven-layer protocol stack. RSVP originally was conceived by researchers at
the University of Southern California (USC) Information Sciences Institute (ISI) and Xerox Palo Alto
Research Center. The Internet Engineering Task Force (IETF) is now working toward standardization
through an RSVP working group. RSVP operational topics discussed in this chapter include data flows,
quality of service, session startup, reservation style, and soft state implementation.




Q.P. Code GT7557                           Page 12 of 25                  Prepared by: - Prof. A. B. Yadav
  Rajendara Mane College of Engineering and Technology, AMBAV (Devrukh) -415804
                                       University of Mumbai
                 Computer Engineering Sem-V I(Rev) Winter 2010(10-WIN-COMP-VI-REV-ACN)
                                 Advanced Computer Network




RSVP Data Flows

In RSVP, a data flow is a sequence of messages that have the same source, destination (one or more),
and quality of service. QoS requirements are communicated through a network via a flow specification,
which is a data structure used by internetwork hosts to request special services from the internetwork. A
flow specification often guarantees how the internetwork will handle some of its host traffic.

RSVP supports three traffic types: best-effort, rate-sensitive, and the delay-sensitive. The type of data-
flow service used to support these traffic types depends on QoS implemented. The following sections
address these traffic types and associated services. For information regarding QoS, refer to the
appropriate section later in this chapter.

Best-effort traffic is traditional IP traffic. Applications include file transfer, such as mail transmissions,
disk mounts, interactive logins, and transaction traffic. The service supporting best-effort traffic is called
best-effort service.

Rate-sensitive traffic is willing to give up timeliness for guaranteed rate. Rate-sensitive traffic, for
example, might request 100 kbps of bandwidth. If it actually sends 200 kbps for an extended period, a
router can delay traffic. Rate-sensitive traffic is not intended to be run over a circuit-switched network;
however, it usually is associated with an application that has been ported from a circuit-switched
network (such as ISDN) and is running on a datagram network (IP).

An example of such an application is H.323 videoconferencing, which is designed to run on ISDN
(H.320) or ATM (H.310) but is found on the Internet. H.323 encoding is a constant rate or nearly
constant rate, and it requires a constant transport rate. The RSVP service supporting rate-sensitive traffic
is called guaranteed bit-rate service.


Q.P. Code GT7557                           Page 13 of 25                  Prepared by: - Prof. A. B. Yadav
  Rajendara Mane College of Engineering and Technology, AMBAV (Devrukh) -415804
                                       University of Mumbai
                 Computer Engineering Sem-V I(Rev) Winter 2010(10-WIN-COMP-VI-REV-ACN)
                                 Advanced Computer Network

Delay-sensitive traffic is traffic that requires timeliness of delivery and varies its rate accordingly.
MPEG-II video, for example, averages about 3 to 7 Mbps depending on the amount of change in the
picture. As an example, 3 Mbps might be a picture of a painted wall, although 7 Mbps would be required
for a picture of waves on the ocean. MPEG-II video sources send key and delta frames. Typically, one
or two key frames per second describe the whole picture, and 13 or 28 frames describe the change from
the key frame. Delta frames are usually substantially smaller than key frames. As a result, rates vary
quite a bit from frame to frame. A single frame, however, requires delivery within a frame time or the
CODEC is unable to do its job. A specific priority must be negotiated for delta-frame traffic. RSVP
services supporting delay-sensitive traffic are referred to as controlled-delay service (non-real time
service) and predictive service (real-time service).

RSVP Data Flows Process

RSVP data flows are generally characterized by sessions, over which data packets flow. A session is a
set of data flows with the same unicast or multicast destination, and RSVP treats each session
independently. RSVP supports both unicast and multicast sessions (where a session is some number of
senders talking to some number of receivers), whereas a flow always originates with a single sender.
Data packets in a particular session are directed to the same IP destination address or a generalized
destination port. The IP destination address can be the group address for multicast delivery or the unicast
address of a single receiver. A generalized destination port can be defined by a UDP/TCP destination
port field, an equivalent field in another transport protocol, or some application-specific information.

RSVP data distribution is handled via either multicasts or unicasts. Multicast traffic involves a copy of
each data packet forwarded from a single sender toward multiple destinations. Unicast traffic features a
session involving a single receiver. Even if the destination address is unicast, there might be multiple
receivers, distinguished by a generalized port. Multiple senders also might exist for a unicast destination,
in which case, RSVP can set up reservations for multipoint-to-point transmission.

Each RSVP sender and receiver can correspond to a unique Internet host. A single host, however, can
contain multiple logical senders and receivers, distinguished by generalized ports.

RSVP Quality of Service (QoS)

In the context of RSVP, quality of service (QoS) is an attribute specified in flow specifications that is
used to determine the way in which data interchanges are handled by participating entities (routers,
receivers, and senders). RSVP is used to specify the QoS by both hosts and routers. Hosts use RSVP to
request a QoS level from the network on behalf of an application data stream. Routers use RSVP to
deliver QoS requests to other routers along the path(s) of the data stream. In doing so, RSVP maintains
the router and host state to provide the requested service.




Q.P. Code GT7557                          Page 14 of 25                 Prepared by: - Prof. A. B. Yadav
    Rajendara Mane College of Engineering and Technology, AMBAV (Devrukh) -415804
                                           University of Mumbai
                     Computer Engineering Sem-V I(Rev) Winter 2010(10-WIN-COMP-VI-REV-ACN)
                                    Advanced Computer Network




RSVP Message Header Fields

RSVP message-header fields are comprised of the following:



    •    Version---4-bit field indicating the protocol version number (currently version 1).
    •    Flags---4-bit field with no flags currently defined.
    •    Type---8-bit field with 6 possible (integer) values, as shown in table

value Message Type
1       Path
2       Reservation-request
3       Path-error
4       Reservation-request error
5       Path-teardown
6       Reservation-teardown
7       Reservation-request acknowledgment

 Checksum---16-bit field representing a standard TCP/UDP checksum over the contents of the RSVP
message, with the checksum field replaced by zero.
 Length---16-bit field representing the length of this RSVP packet in bytes, including the common
header and the variable-length objects that follow. If the More Fragment (MF) flag is set or the fragment
offset field is non-zero, this is the length of the current fragment of a larger message.

Q.P. Code GT7557                           Page 15 of 25                 Prepared by: - Prof. A. B. Yadav
  Rajendara Mane College of Engineering and Technology, AMBAV (Devrukh) -415804
                                        University of Mumbai
                  Computer Engineering Sem-V I(Rev) Winter 2010(10-WIN-COMP-VI-REV-ACN)
                                 Advanced Computer Network

 Send TTL---8-bit field indicating the IP time-to-live (TTL) value with which the message was sent.
 Message ID---32-bit field providing a label shared by all fragments of one message from a given
next/previous RSVP hop.
More Fragments (MF) Flag---Low-order bit of a 1-byte word with the other 7 high-order bits specified
as reserved. MF is set on for all but the last fragment of a message.
 Fragment Offset---24-bit field representing the byte offset of the fragment in the message


Q.6 b] Explain TCP segment header format. (10 Marks)
Ans:- Diagram 2 Marks
       Explanation 8 Marks




Header Format:-

The segment consists of a 20- to 60-byte header, followed by data from the application

Program. The header is 20 bytes if there are no options and up to 60 bytes if it

contains options.



1. Source port address. This is a 16-bit field that defines the port number of the application program in
the host that is sending the segment. This serves the same purpose as the source port address in the UDP
header.

Q.P. Code GT7557                          Page 16 of 25                 Prepared by: - Prof. A. B. Yadav
  Rajendara Mane College of Engineering and Technology, AMBAV (Devrukh) -415804
                                       University of Mumbai
                 Computer Engineering Sem-V I(Rev) Winter 2010(10-WIN-COMP-VI-REV-ACN)
                                  Advanced Computer Network

2. Destination port address. This is a 16-bit field that defines the port number of the Application
program in the host that is receiving the segment. This serves the same purpose as the destination port
address in the UDP header.

3. Sequence number. This 32-bit field defines the number assigned to the first byte of data contained in
this segment. As we said before, TCP is a stream transport protocol. To ensure connectivity, each byte to
be transmitted is numbered. The sequence number tells the destination which byte in this sequence
comprises the first byte in the segment. During connection establishment, each party uses a random
number generator to create an initial sequence number (ISN), which is usually different in each
direction.

4. Acknowledgment number. This 32-bit field defines the byte number that the receiver of the segment
is expecting to receive from the other party. If the receiver of the segment has successfully received byte
number x from the other party, it defines x + I as the acknowledgment number. Acknowledgment and
data can be piggybacked together.

5. Header length. This 4-bit field indicates the number of 4-byte words in the TCP header. The length of
the header can be between 20 and 60 bytes. Therefore, the value of this field can be between 5 (5 x 4
=20) and 15 (15 x 4 =60).

6. Reserved. This is a 6-bit field reserved for future use.

7. Control. This field defines 6 different control bits or flags as shown in Figure.




8.Window size. This field defines the size of the window, in bytes, that the other party must maintain.
Note that the length of this field is 16 bits, which means that the maximum size of the window is 65,535
bytes. This value is normally referred to as the receiving window (rwnd) and is determined by the
receiver. The sender must obey the dictation of the receiver in this case.

9. Checksum. This 16-bit field contains the checksum. The calculation of the checksum for TCP follows
the same procedure as the one described for UDP. However, the inclusion of the checksum in the UDP
Q.P. Code GT7557                         Page 17 of 25               Prepared by: - Prof. A. B. Yadav
  Rajendara Mane College of Engineering and Technology, AMBAV (Devrukh) -415804
                                      University of Mumbai
                Computer Engineering Sem-V I(Rev) Winter 2010(10-WIN-COMP-VI-REV-ACN)
                                Advanced Computer Network

datagram is optional, whereas the inclusion of the checksum for TCP is mandatory. The same
pseudoheader, serving the same purpose, is added to the segment. For the TCP pseudoheader, the value
for the protocol field is 6.

10. Urgent pointer. This l6-bit field, which is valid only if the urgent flag is set, is used when the
segment contains urgent data. It defines the number that must be added to the sequence number to obtain
the number of the last urgent byte in the data section of the segment. 11. Options. There can be up to 40
bytes of optional information in the TCP header.

Q.7 Write short note on any two of following. (20 Marks) Each carry 10 Marks

A] MIB:-

Ans:- Diagram 2 Marks

       Explanation 8 Marks

Management Information Base (MIB)
The Management Information Base, version 2 (MIB2) is the second component used in network
management. Each agent has its own MIB2, which is a collection of all the objects that the manager can
manage. The objects in MIB2 are categorized under 10 different groups: system, interface, address
translation, ip, icmp, tcp, udp, egp, transmission, and snmp. These groups are under the mib-2 object in
the object identifier tree.




The following is a brief description of some of the objects:
sys This object (system) defines general information about the node (system), such as the name,
location, and lifetime.
if This object (inteiface) defines information about all the interfaces of the node including interface
number, physical address, and IP address.
at This object (address translation) defines the information about the ARP table.
ip This object defines information related to IP, such as the routing table and the IP address.
icmp This object defines information related to ICMP, such as the number of packets sent and received
and total errors created.

Q.P. Code GT7557                         Page 18 of 25                Prepared by: - Prof. A. B. Yadav
  Rajendara Mane College of Engineering and Technology, AMBAV (Devrukh) -415804
                                       University of Mumbai
                 Computer Engineering Sem-V I(Rev) Winter 2010(10-WIN-COMP-VI-REV-ACN)
                                 Advanced Computer Network

tcp This object defines general information related to TCP, such as the connection table, time-out value,
number of ports, and number of packets sent and received.
udp This object defines general information related to UDP, such as the number of ports and number of
packets sent and received.
snmp This object defines general information related to SNMP itself.


B] Queue management algorithms.

Ans:- List carry 2 Marks

        Each Algorithm carry 4 Marks(04*02=08)

   1.   FIFO algorithm
   2.   Priority algorithm
   3.   Weighted algorithm
   4.   Hybrid algorithm

C] IP multicasting

Ans:- Diagrams 2 Marks

        Explanation 8 Marks

The great bulk of TCP/IP communications uses the Internet Protocol to send messages from one source
device to one recipient device; this is called unicast communications

. This is the type of messaging we normally use TCP/IP for; when you use the Internet you are using
unicast for pretty much everything. For this reason, most of my discussion of IP has been oriented
around describing unicast messaging.

IP does, however, also support the ability to have one device send a message to a set of recipients. This
is called multicasting. IP multicasting has been “officially” supported since IPv4 was first defined, but
has not seen widespread use over the years, due largely to lack of support for multicasting in many
hardware devices. Interest in multicasting has increased in recent years, and support for multicasting was
made a standard part of the next generation IP version 6 protocol. Therefore, I felt it worthwhile to
provide a brief overview of IP multicasting. It's a large and very complex subject, so I will not be getting
into it in detail—you'll have to look elsewhere for a full description of IP multicasting. (Sorry, it was
either a brief summary or nothing; maybe I'll write more on multicasting in the future.)

The idea behind IP multicasting is to allow a device on an IP internetwork to send datagrams not to just
one recipient but to an arbitrary collection of other devices. IP multicasting is modeled after the similar
function used in the data link layer to allow a single hardware device to send to various members of a
Q.P. Code GT7557                          Page 19 of 25                 Prepared by: - Prof. A. B. Yadav
  Rajendara Mane College of Engineering and Technology, AMBAV (Devrukh) -415804
                                      University of Mumbai
                Computer Engineering Sem-V I(Rev) Winter 2010(10-WIN-COMP-VI-REV-ACN)
                                Advanced Computer Network

group. Multicasting is relatively easy at the data link layer, however, because all the devices can
communicate directly. In contrast, at the network layer, we are connecting together devices that may be
quite far away from each other, and must route datagrams between these different networks. This
necessarily complicates multicasting when done using IP (except in the special case where we use IP
multicasting only between devices on the same data link layer network.)

There are three primary functions that must be performed to implement IP multicasting: addressing,
group management, and datagram processing / routing.

Multicast Addressing

Special addressing must be used for multicasting. These multicast addresses identify not single devices
but rather multicast groups of devices that listen for certain datagrams sent to them. In IPv4, 1/16th of
the entire address space was set aside for multicast addresses: the Class D block of the original
“classful” addressing scheme.

The vast majority of traffic on IP internetworks is of the unicast variety: one source device sending to
one destination device. IP also supports multicasting, where a source device can send to a group of
devices. Multicasting is not used a great deal on the Internet as a whole at the present time, mainly due
to lack of widespread hardware support, so most of our focus in looking at IP is on unicast. Multicast is
useful in certain circumstances, however, especially as a more efficient alternative to broadcasting. I
include one summary topic on multicasting for your perusal, and also want to briefly discuss here IP
addressing issues related to multicasting.

The “classful” IP addressing scheme sets aside a full one-sixteenth of the address space for multicast
addresses: Class D. Multicast addresses are identified by the pattern “1110” in the first four bits, which
corresponds to a first octet of 224 to 239. So, the full range of multicast addresses is from 224.0.0.0 to
239.255.255.255. Since multicast addresses represent a group of IP devices (sometimes called a host
group) they can only be used as the destination of a datagram; never the source.

Multicast Address Types and Ranges

The 28 bits after the leading “1110” in the IP address define the multicast group address. The size of the
Class D multicast address space is therefore 228 or 268,435,456 multicast groups. There is no
substructure that defines the use of these 28 bits; there is no specific concept of a network ID and host
ID as in classes A, B and C. However, certain portions of the address space are set aside for specific
uses.




  Range Start Address Range End Address Description


Q.P. Code GT7557                         Page 20 of 25                 Prepared by: - Prof. A. B. Yadav
    Rajendara Mane College of Engineering and Technology, AMBAV (Devrukh) -415804
                                      University of Mumbai
                Computer Engineering Sem-V I(Rev) Winter 2010(10-WIN-COMP-VI-REV-ACN)
                                Advanced Computer Network


    224.0.0.0           224.0.0.255           Reserved for special “well-known” multicast addresses.
    224.0.1.0           238.255.255.255       Globally-scoped (Internet-wide) multicast addresses.
    239.0.0.0           239.255.255.255       Administratively-scoped (local) multicast addresses.




i

D] X.25

Ans:- Diagram 4 Marks

        Explanation 6 Marks

X.25 network devices fall into three general categories: data terminal equipment (DTE), data circuit-
terminating equipment (DCE), and packet-switching exchange (PSE). Data terminal equipment devices
are end systems that communicate across the X.25 network. They are usually terminals, personal
computers, or network hosts, and are located on the premises of individual subscribers. DCE devices are
communications devices, such as modems and packet switches, that provide the interface between DTE
devices and a PSE, and are generally located in the carrier's facilities. PSEs are switches that compose
the bulk of the carrier's network. They transfer data from one DTE device to another through the X.25
PSN.




Q.P. Code GT7557                        Page 21 of 25                Prepared by: - Prof. A. B. Yadav
  Rajendara Mane College of Engineering and Technology, AMBAV (Devrukh) -415804
                                      University of Mumbai
                Computer Engineering Sem-V I(Rev) Winter 2010(10-WIN-COMP-VI-REV-ACN)
                                Advanced Computer Network




Packet Assembler/Disassembler

The packet assembler/disassembler (PAD) is a device commonly found in X.25 networks. PADs are
used when a DTE device, such as a character-mode terminal, is too simple to implement the full X.25
functionality. The PAD is located between a DTE device and a DCE device, and it performs three
primary functions: buffering (storing data until a device is ready to process it), packet assembly, and
packet disassembly. The PAD buffers data sent to or from the DTE device. It also assembles outgoing
data into packets and forwards them to the DCE device. (This includes adding an X.25 header.) Finally,
the PAD disassembles incoming packets before forwarding the data to the DTE. (This includes
removing the X.25 header.)

X.25 Session Establishment

X.25 sessions are established when one DTE device contacts another to request a communication
session. The DTE device that receives the request can either accept or refuse the connection. If the
request is accepted, the two systems begin full-duplex information transfer. Either DTE device can
terminate the connection. After the session is terminated, any further communication requires the
establishment of a new session.

X.25 Virtual Circuits

A virtual circuit is a logical connection created to ensure reliable communication between two network
devices. A virtual circuit denotes the existence of a logical, bidirectional path from one DTE device to
another across an X.25 network. Physically, the connection can pass through any number of
intermediate nodes, such as DCE devices and PSEs. Multiple virtual circuits (logical connections) can
be multiplexed onto a single physical circuit (a physical connection). Virtual circuits are demultiplexed
at the remote end, and data is sent to the appropriate destinations.


Q.P. Code GT7557                         Page 22 of 25                Prepared by: - Prof. A. B. Yadav
  Rajendara Mane College of Engineering and Technology, AMBAV (Devrukh) -415804
                                       University of Mumbai
                 Computer Engineering Sem-V I(Rev) Winter 2010(10-WIN-COMP-VI-REV-ACN)
                                  Advanced Computer Network

Packet-Layer Protocol

PLP is the X.25 network layer protocol. PLP manages packet exchanges between DTE devices across
virtual circuits. PLPs also can run over Logical Link Control 2 (LLC2) implementations on LANs and
over Integrated Services Digital Network (ISDN) interfaces running Link Access Procedure on the D
channel (LAPD).

The PLP operates in five distinct modes: call setup, data transfer, idle, call clearing, and restarting.

Call setup mode is used to establish SVCs between DTE devices. A PLP uses the X.121 addressing
scheme to set up the virtual circuit. The call setup mode is executed on a per-virtual-circuit basis, which
means that one virtual circuit can be in call setup mode while another is in data transfer mode. This
mode is used only with SVCs, not with PVCs.

Data transfer mode is used for transferring data between two DTE devices across a virtual circuit. In this
mode, PLP handles segmentation and reassembly, bit padding, and error and flow control. This mode is
executed on a per-virtual-circuit basis and is used with both PVCs and SVCs.

Idle mode is used when a virtual circuit is established but data transfer is not occurring. It is executed on
a per-virtual-circuit basis and is used only with SVCs.

Call clearing mode is used to end communication sessions between DTE devices and to terminate SVCs.
This mode is executed on a per-virtual-circuit basis and is used only with SVCs.

Restarting mode is used to synchronize transmission between a DTE device and a locally connected
DCE device. This mode is not executed on a per-virtual-circuit basis. It affects all the DTE device's
established virtual circuits.

Four types of PLP packet fields exist:

   •   General Format Identifier (GFI) - Identifies packet parameters, such as whether the packet
       carries user data or control information, what kind of windowing is being used, and whether
       delivery confirmation is required.
   •   Logical Channel Identifier (LCI) - Identifies the virtual circuit across the local DTE/DCE
       interface.
   •   Packet Type Identifier (PTI) - Identifies the packet as one of 17 different PLP packet types.
   •   User Data - Contains encapsulated upper-layer information. This field is present only in data
       packets. Otherwise, additional fields containing control information are added.




Q.P. Code GT7557                           Page 23 of 25                  Prepared by: - Prof. A. B. Yadav
  Rajendara Mane College of Engineering and Technology, AMBAV (Devrukh) -415804
                                      University of Mumbai
                Computer Engineering Sem-V I(Rev) Winter 2010(10-WIN-COMP-VI-REV-ACN)
                                Advanced Computer Network




   Flag - Delimits the beginning and end of the LAPB frame. Bit stuffing is used to ensure that the flag
pattern does not occur within the body of the frame.
   Address - Indicates whether the frame carries a command or a response.

Q.P. Code GT7557                        Page 24 of 25                 Prepared by: - Prof. A. B. Yadav
  Rajendara Mane College of Engineering and Technology, AMBAV (Devrukh) -415804
                                        University of Mumbai
                  Computer Engineering Sem-V I(Rev) Winter 2010(10-WIN-COMP-VI-REV-ACN)
                                Advanced Computer Network

    Control - Qualifies command and response frames and indicates whether the frame is an I-frame, an
S-frame, or a U-frame. In addition, this field contains the frame's sequence number and its function (for
example, whether receiver-ready or disconnect). Control frames vary in length depending on the frame
type.
   Data - Contains upper-layer data in the form of an encapsulated PLP packet.
   FCS - Handles error checking and ensures the integrity of the transmitted data




   References:-

1. B. A. Forouzan, “TCP/IP Protocol Suite”, Tata McGraw Hill edition, Third Edition.

2. A.S.Tanenbaum, ”Computer Networks”, Pearson Education, Fourth Edition.

3. Darren Sphon “ Data Network Design “ Tata McGraw Hill edition




Q.P. Code GT7557                         Page 25 of 25                Prepared by: - Prof. A. B. Yadav

								
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