Mobile Networks and Handoff Procedures

This assignment delves into the intricacies of mobile networks, particularly emphasizing handoff procedures. It explores scenarios involving ongoing calls transitioning between cells (A, B, C) with varying channel availability. The questions demand a deep understanding of how calls are maintained, potential call drops during handoffs, and strategies to prevent such interruptions. The assignment also touches upon the role of MSC, BSC, BTS, VLR, and HLR in managing mobile connections and user information.

MOBILE DATA NETWORK
Q.1: The following packets are transmitted in a SCTP session. The marked
packet is lost. What are the complete contents of the packet including the
SACK chunk from Node 2?
Ans.1 Mobile data network deals with the mobile IP and thus whenever we
move from one place to another, the mobile network keeps on changing or we
can say that the mobile network gets switched to the better station that
provides good service in that area and thus helps to maintain the connection
secure (Yuan & Buckman, 2006). The data over the network is transmitted in
the form of packets. The data is bind and provided over the network to be
transmitted at another end. The packets move accordingly to the specified IP
address. If any packet gets lost, it is due to the transmission error or various
other factors i.e. network congestion, due to packet loss the reliability of
network decreased as well as latency and throughput get affected. It also
affects the quality of service.
Request and reply both are necessary to go towards the next node and thus
every node request for the data and subsequently ask for the acknowledge to
move forward over that path and if in case that node did not provide the
actual information than the data over the node get cancelled and no further
processes can take place. The routes are decided depending upon the reverse
and forward links of the nodes connected to the available source and
destination unit medium and thus they are transmitted in actual data node
distribution. The data is further broadcasted to provide the available data
utility and thus helps to gain access to the best route to get to the destination.

Various protocols are used to provide the secure transmission of data over the
network and therefore SCTP provides a secure, reliable and message-oriented
transmission of data like TCP and UDP. It also provides congestion control
mechanism. It sends message in the form of chunks and thus provides a
sequence number to the streams of data so that the receiver can know which
the actual sequence of data transmitted is. To provide an easy implementation
and processing of data and provide desired results (Wang & Canny, 2006). The
data transmission with the help of SCTP is shown in the figure below, various
request are being made for the transmission of data. Chunks are the additional
data storage information that moves with SCTP protocol to provide the
reliability of data.
The data is transmitted from SCTP A to SCTP Z and thus sender sends the
actual amount of data that other party wants and thus starts the
communication. The SACK value is transmitted along with the actual data and
by checking the available resources that are with the SACK at SCTP A the
further SACK and DATA is transmitted that makes data executable. The SACK

value can further be taken as the acknowledgement of the available data files
and resources.
Q.2: A) is a table driven routing protocol suitable for high mobility scenarios?
Justify your answer with reasons.
B) Consider the topology shown below. Simulate the DSR protocol to
establish a path from node 1 to node 10. Find the paths found and the ratio
of the number of Route Request packets sent out in the network.
Ans.2 (a) The Ad-hoc network is analysed and established with the help of
table driven routing. Whenever a network topology changes the update
message is propagated to maintain simultaneous flow of data at different
nodes. Each node maintains multiple routing tables so that the information is
reliable and consistent throughout the network.
DSDV (Destination Sequenced Distance Vector) is usually suitable for small
networks. The criteria depend on time complexity. Dynamic Source Routing is
used for wireless network to establish the desirable path between various
nodes, this type of routing can be used up to a network of 100 nodes. The DSR
is also a self maintained thus; it is used to maintain all the faults themselves
without the intervention of user request. The data get configured by it and
each source helps to determine the route that it should follow to reach the
destination. The two basic things to keep in mind while talking about DSR is
that: - Route Discovery and Route Maintenance. Route Discovery helps to give
the best path from source to destination and Route Maintenance ensures that
the chosen best path should be loop free and thus there should not be any
traffic. The routes are decided to the specified nodes and thus all the data is
gathered at every nodes that provides the information to reach the

destination. The node 1 will get the information of the entire subsequent path
and will decide at which path to move forward.
Ans.2 (b) Ad-hoc on demand distance vector routing protocol is basically
developed for wireless mobile data communications. It is free to be operated
on mobile Ad-hoc network. The AODV routing protocol does not affect the
global nodes, the local network affects only the local nodes that are to be
available within the area interface. They also make use of sequence number to
indicate which route to be followed. Further, it helps for unicast and multicast
communications. The AODV protocol has expiry date for particular route which
expires if that route is not used. All the routes are maintained but the one that
used on regular basis are maintained periodically but the route that are not in
use they get expired and thus are not maintained for operation as they get
destroyed (McPherson, Smith-Lovin & Brashears, 2006). The unused route is
also called as STALE. The route table gives the entry of all the available routes
and thus specifies the lifetime for which particular route is valid.

The route can be changed depending upon the distance indicated in the path
so that the data packet can be reached on time and there can be no packet
loss. Here, source, destination and next-hop are addressed with the help of IP-
addressing and thus IP address is unique and every node will be represented as
new one. The various basic messages are: - PREQ- route request, RREP- route
reply, RERR- route error, HELLO- for link status monitoring. As soon as the
RREQ reaches the destination the communication gets started. There is a
provision that route must be included in header of packet before the actual
transmission started as that route helps to further generate the same data
resource entities. The sequence number feature is unique and new and thus it
helps to keep the track of all the available active nodes. It also helps to destroy
or delete the inactive cell and thus helps to get knowledge about the desired
cells and functionality.

Q.3: A) the Ad Hoc network shown below (including node Q) is currently
operating. The network is running the AODV routing protocol. Show the
steps required to route a packet from node N to node I. In particular, what
state is maintained at each node in the network?
B) What changes occur to the route, and how are these determined if node
Q drops out of the network?
Ans.3 No functionality loops should be formed while processing of data and
specific tasks of the cells. Routing loops creates faults and thus they are not
liable to function properly and thus the route with limited data and secure
transmission should be selected for better data transmission media. The
mobile host is movable thus the location of the user gets changed according to
the distinct locations. Due to advancement in internet, the task of processing
at fixed location overcome with new strategies. While mobility support router
sends various packets to mobile host so it is possible that the host is moving
from one place to another and thus, the network drop can take place and
disturbs the continuity of packets transmitted. Packet lost also results in
discarding of information and if you did not have duplicate copy or backup of
that data, the data gets lost permanently.
The data has to be gathered and provided to remote network so that it is
possible for different networking interface to get the information of the same.
The packets might have to be redirected to avoid further confusion of the data
interface so that all the packets should reach their location on time.
b) The route can be changed depending upon the distance indicated in the
path so that the data packet can be reached on time and there can be no
packet loss. If data packet Q gets lost then node has to define another route to

go there. It can chose route A-C-E-J-L-P to move forward to get the packet
there and thus has to be deduced to reach at specified point. Multiple data
packets can be transmitted over the transmission medium and thus makes the
transmission even better and reliable. Due to the failure of node Q the longer
path has to be taken and thus greater path value has to be taken to reach the
destination. The decisions are taken by the nodes it. Here, source, destination
and next-hop are addressed with the help of ip-addressing and thus ip address
is unique and every node will be represented as new one.
Different cells are available in the network and thus they ensure that all the
packets should be received sequentially. For example: the experiment of
making phone call with the help of tin cans and string, we can say like a guy C
holding that and let us consider that he is the cell tower. When A makes a call
to B, the cell tower C analyses and connects both according to the
requirements specified.
Q.4: Consider the scenario wherein a mobile host (MH) is communicating
with a fixed host (FH) through Mobility Support Router (MSR-1) using the
Indirect TCP (I-TCP) protocol. The MSR sends to the MH the packets P1, P2,
P3, P4 and P5 in that order. Packet P3 is dropped but packet P4 reaches the
MH causing it to generate the first duplicate acknowledgement (DUPACK).
Before this DUPACK packet arrives at the MSR it has already sent out packet
P5. Write down the sequence of steps that will be performed by the MSR and
MH to bring the system to a consistent state. (5 marks)
The MH now moves from MSR-1 to another cell (MSR-2). Detail the sequence
of step required to move the connection to the new MSR.

Ans. 4 There are various points that should be considered to prevent dropping
of calls:
The weather, climatic conditions, quality of phones, tower bandwidth, etc.
There are various types of bands used by a telephone like tri-band, etc. that
also affects the efficiency of call and results in call drop.
Further, the dead spots in the service areas can also results in network drop.
The dead spots are widely experienced while driving.
Clusters divide the network into multiple segments and it creates an illusion as
a single machine. Multiple computers are connected together to provide the
functioning of a single machine. Managing large machines is not easy therefore
multiple processors are collaborated.
Whenever we switch on our mobile phone to make a call it first scans all the
available networks within its range and finds the strongest one. The mobile
network analyses the same strong channel and it keeps on monitoring until the
network gets dropped to its minimum level before the network actually starts
to reboot. Every mobile network do this process to get the knowledge of all
available strong networks and it is efficient to use the one that maintains its
characteristics for a long duration of time. We can also analyse the signal level
as it is displayed on our phone screen and thus get to know which network is
better to use.
Cells is when a large area is divided into various small areas and thus it is done
in a hexagonal manner to provide frequency reuse as in circular cells the area
between the connected circles gets wasted which also reduces the frequency

of transmission and processing the data and the channel over which the data is
transmitted also get wasted. The distance can also be reused as the side
already get calculated must not have to be calculated further. Cell sectoring
increases the capacity and also helps to provide extra channels for the storage
of data. Various cell sectors are created according to the available degree to
form equal partitions. Sectoring the cells increasing the number of antennas at
each base station and thus reduces the trunk efficiency. The cost also increases
that is all the resources are to be considered for calculations. The coverage
area for specified groups in decreased and thus the handoffs increases rapidly.
The cells are prepared by keeping in mind about all the specified data utility
and thus all the records are gathered to achieve the specified task that must be
needed to look forward for the data growth. Cells are designed to utilize the
complete cell space and thus no part should be wasted. Therefore, the cells are
hexagonal in shape. The cell value A can be marked over different variation in
various 6 places to use the combined space and thus all the values are
satisfied.
Q.5: A mobile network is built with a cluster size of 12. Draw an example
cluster arrangement below centred on cell A.
Traffic in cell A increases such that the cell must be segmented using cell
sectoring. It is decided to use 6 sectors in the cell. Draw the additional sectors
and relabelled the cluster such that frequency reuse distances are not
violated.
Ans. 5 A connections must be established to a service provider before making
a call. Here a call is initiated in cell A and continues its progress in cell B with
the help of cell A the calling process goes on. Base station indicates a

stationary or we can say a fixed tower that consists of transmitters and
receivers to detect the following activities which are located at different
locations.
The phone call we make is converted into electrical signals, which is further
transmitted in the form of radio waves and before reaching the receiver end it
is again converted into your sound to reach your friend. Following process
takes place when a call is made: At first, a call initiation request along with
Mobile Identification Number (MIN), Electronic Serial Number (ESN) and the
dialled telephone number is sent on the reverse control channel. All this data is
received by the base station and further it is sent to the Mobile Switching
Control (MSC). The MSC helps to check the validity of the request by checking
the MIN with the stored data in the database. If it matched, the connection is
established by a third party with the help of Public Switched Telephone
Network (PSTN). The MSC plays an important part to manage the
communication, as it helps to maintain the power transmitted by the mobile
when it moves in and out of the network area.
Q. 6: A voice call was initiated in cell A. It is currently in progress in cell B, and
is continuing to use the channels from cell A. The mobile host moves so that

cell C is now the better base station. Cell C currently has no free channels.
Describe in detail under what circumstances the call can continue in cell C,
and when the call will be dropped. What reasonable steps could be
performed to avoid dropping such calls in the future?
A makes a call to B, the cell tower C analyses and connects both according to
the requirements specified. Following process takes place when a call is made:
At first, a call initiation request along with Mobile Identification Number (MIN),
Electronic Serial Number (ESN) and the dialled telephone number is sent on
the reverse control channel. The MSC makes request to base station to
transfer the mobile phone to the unused channel so that the communication
can be started without the call drop. All the requests are made to the base
station so that the transmitter and receiver are aware of what data is actually
operating over the connected stations. If a mobile phone that contains a call
moves from one base station to another base station that process is called as
handoff. Further, if a call is made and the executable voice channel is not free
then we get the message like network busy and this takes place when large
number of calls are made within the coverage area of single base station. It is
obvious that if single base station is used for operating of multiple call requests
then call dropping will take place more frequently and thus there results no
reliability and accuracy of call made.
All the mobile devices are connected to BTS (Antenna). BTS is connected to a
switching system called BSC. BSC is connected to main switching system called
MSC. MSC has its own VLR (Visitor Location Register) whenever we move from
one place to another VLR keeps the track of all the places we visit and thus it is
a temporary storage for the network information. There is also a main
database that is called as HLR (Home Location Register) where all the

information and documents are stored that we provide before we buy a SIM
card. Thus, VLR takes all the data from HLR whenever we roam from one state
to another or anywhere in the network area.
The route can be changed depending upon the distance indicated in the path
so that the data packet can be reached on time and there can be no packet
loss. If data packet Q gets lost then node has to define another route to go
there. It can chose route A-C-E-J-L-P to move forward to get the packet there
and thus has to be deduced to reach at specified point. Multiple data packets
can be transmitted over the transmission medium and thus makes the
transmission even better and reliable. Due to the failure of node Q the longer
path has to be taken and thus greater path value has to be taken to reach the
destination. The decisions are taken by the nodes it.
Reference
McPherson, M., Smith-Lovin, L., & Brashears, M. E., 2006, Social isolation in
America: Changes in core discussion networks over two decades. American
Sociological Review, 71, 353-375.
Wang, J., & Canny, J., 2006, End-user place annotation on mobile devices: A
comparative study. In Proceedings of the ACM CHI Conference on Human
Factors in Computing Systems (pp. 1493-1498). Montreal: ACM Press.

Yuan, L., & Buckman, R., 2006, Social networking goes mobile: MySpace,
Facebook strike deals with cell companies. The Wall Street Journal, p. D1.