Dr Shivu_GAT_Computer Network_22ISE52_Module 4.pdf

COMPUTER NETWORKS (INTEGRATED)
(22ISE52 )
Module-4
Dr. Shivashankar
Professor
Department of Information Science & Engineering
GLOBAL ACADEMY OF TECHNOLOGY-Bengaluru
1/23/2025 1
Dr. Shivashankar, ISE, GAT
GLOBAL ACADEMY OF TECHNOLOGY
Ideal Homes Township, Rajarajeshwari Nagar, Bengaluru – 560 098
Department of Information Science & Engineering

Course Outcomes
After Completion of the course, student will be able to:
 Describe the Internet Protocol and network layer routing algorithms.
 Explain transport layer UDP and TCP protocols services.
 Describe and demonstrate of application layer protocol and its supporting
protocols.
 Discuss the wireless and mobile network covering IEEE 802.11 standard
 Describe the different network security algorithms.
Text Book:
1. James F Kurose and Keith W Ross, Computer Networking, A Top-Down
Approach, Sixth edition, Pearson,2017.
Reference Books:
1. Behrouz A Forouzan, Data and Communications and Networking, Fifth
Edition, McGraw Hill, Indian Edition
2. Larry L Peterson and Brusce S Davie, Computer Networks, fifth edition,
ELSEVIER
3. Andrew S Tanenbaum, Computer Networks, fifth edition, Pearson
4. Mayank Dave, Computer Networks, Second edition, Cengage Learning
1/23/2025 2

Module 4: Wireless and Mobile Networks
• A wireless network is a computer network that uses wireless data
connections between network nodes.
• Wireless networking allows homes, telecommunications networks, and
business installations to avoid the costly process of introducing cables into a
building, or as a connection between various equipment locations.
• Admin telecommunications networks are generally implemented and
administered using radio communication.
• This implementation takes place at the physical level (layer) of the OSI model
network structure.
• Examples of wireless networks include cell phone networks, wireless local
area networks (WLANs), wireless sensor networks, satellite communication
networks, and terrestrial microwave networks.
• There are many different wireless technologies, including Bluetooth, ZigBee,
LTE, and 5G. Wi-Fi is a specific wireless protocol defined by the Institute of
Electrical and Electronic Engineers (IEEE).
1/23/2025 3

Cont…
• A cellular network or mobile network is a telecommunications
network where the link to and from end nodes is wireless and the network is
distributed over land areas called cells, each served by at least one fixed-
location transceiver (such as a base station).
• These base stations provide the cell with the network coverage which can be
used for transmission of voice, data, and other types of content.
• A cell typically uses a different set of frequencies from neighboring cells, to
avoid interference and provide guaranteed service quality within each cell.
• This enables numerous portable transceivers (e.g., mobile
phones, tablets and laptops equipped with mobile broadband
modems, pagers, etc.) to communicate with each other and with fixed
transceivers and telephones anywhere in the network, via base stations, even
if some of the transceivers are moving through more than one cell during
transmission.
1/23/2025 4

Wireless links and Network characteristics
• A wireless link is a communication connection that transmits signals without
using physical wires. Wireless links can:
• Increase range: can increase the range of communication.
• Reduce power consumption: use less power than wired links.
• Improve reliability: can improve reliability.
• Reduce signal-to-noise: can reduce signal-to-noise requirements.
Wireless links typically use radio and microwave frequencies in the
electromagnetic spectrum. Some examples of wireless networks include:
Wi-Fi : A wireless network that uses radio waves to send signals.
Bluetooth: A short-range wireless connectivity
Mesh networking: multiple devices work together to maintain connectivity and
provide coverage.
Wireless ad hoc network: each node forwards messages on behalf of the other
nodes.
Fixed wireless: A method of delivering internet connectivity to households and
businesses over airwaves.
1/23/2025 5

Cont…
A number of important differences between a wired link and a wireless link
(Network Characteristics):
Decreasing signal strength:
Electromagnetic radiation attenuates as it passes through matter. Even
in free space, the signal will disperse, resulting in decreased signal
strength as the distance between sender and receiver increases.
Interference from other sources:
Radio sources transmission in the same frequency band will interfere
with each other.
In addition to interference from transmitting sources, electromagnetic
noise within the environment can result in interference.
Multipath propagation:
It occurs when portions of the electromagnetic wave reflect off objects
and the ground, taking paths of different lengths between a sender and
receiver.
Moving objects between the sender and receiver can cause multipath
propagation to change over time.
1/23/2025 6

Cont…
• Wireless links employ powerful CRC error detection codes and link-level
reliable-data-transfer protocols that retransmits corrupted frames because bit
errors are more common in wireless links.
• The host receives an electromagnetic signal that is a combination of a
degraded form of the original signal transmitted by the sender and
background noise in the environment.
• The Signal-to-noise ratio (SNR) is a relative measure of the strength of the
received signal and this noise.
• The SNR is typically measured in dB.
• It is 20*the ratio of the base-10 logarithms of the amplitude of the
receives signal to the amplitude of the noise.
• A larger SNR makes it easier for the receiver to extract the
transmitted signal from the background noise.
• Bit error rate : A metric used to measure the quality of a telecommunication
signal by quantifying the number of bits received incorrectly compared to the
total number of bits transmitted.
1/23/2025 7

Cont…
1. A transmitted bits are 1011100011 and received bits are 1010000010, calculate
the BER.
Solution:
Transmitted bits : 1011100011
Received bits : 1010000010
BER =
𝑁𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑏𝑖𝑡 𝑒𝑟𝑟𝑜𝑟
𝑇𝑜𝑡𝑎𝑙 𝑛𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑏𝑖𝑡𝑠
=
3
10
= 30%
2. if 2 bits are received incorrectly out of 9 transmitted bits, what is the BER?
Solution: BER =
𝑁𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑏𝑖𝑡 𝑒𝑟𝑟𝑜𝑟
𝑇𝑜𝑡𝑎𝑙 𝑛𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑏𝑖𝑡𝑠
=
2
9
= 22.2%
1/23/2025 8
Errors

Cont…
3. At the transmitter, the signal power is 23mW. The input SNR is 40 dB. The
channel offers 3 dB attenuation to the signal and the output noise is thrice the
input noise level. Determine the SNR at the output.
Solution:𝑆𝑁𝑅𝑖/𝑝 =
𝑆𝑖/𝑝
𝑁𝑖/𝑝
Calculation of Output Power Level
An attenuation of 3 dB equals halving the input transmission power. If the ratio of
two quantities on the linear scale is 1/2, it translates to -3 dB on the dB scale
which is indicated as attenuation. So, the output signal power is 23mW/2 =11.5
mW.
Calculation of Input Noise Level
The input SNR is 40 dB. This means that the input power level is 10000 times
greater than the input noise level.
10𝑙𝑜𝑔10
1000
1
= 40𝑑𝐵 =
23μ𝑊
𝑁𝑖/𝑝
= 10000
The input noise level - 𝑁𝑖/𝑝 is 2.3 μW.
In the question, it is given that the output noise is thrice the input noise. Thus, the output
noise level is 2.3μW x 3 = 6.9 μW.
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Cont…
𝑆𝑁𝑅0/𝑝=
𝑆𝑜/𝑝
𝑁𝑜/𝑝
Output signal power = 11.5mW
Output noise power = 6.9μW
The ratio of the output signal power to the output noise power gives the output SNR at
the receiver.
𝑆𝑁𝑅𝑜/𝑝 =
11.5𝑚𝑊
6.9μW
=1666.67
𝑆𝑁𝑅𝑜/𝑝 = 10𝑙𝑜𝑔10
𝑆𝑝
𝑁𝑝
= 10𝑙𝑜𝑔101666.67 = 32.22𝑑𝐵
Inference :
The input SNR is 40dB while the output SNR is 32.22dB. Due to the channel noise, the
output SNR has decreased by 8 dB.
However, the signal power is still large enough than the noise power to have a faithful
deletion and decoding at the receiver.
1/23/2025 10

Cont…
4. The initial SNR measured at the transmitter was 20dB. In order to combat the
channel conditions, the signal power was doubled prior to transmission. What is the
new SNR at the transmitter?
Soln − Initial SNR = 20 dB. Let SP denote the initial signal power and Sp’ denote the
new signal power such that Sp’ = 2SP. Let Np denote the noise power. Let us first find
convert the initial SNR to absolute value.
SNR = 10𝑙𝑜𝑔10
𝑆𝑝
𝑁𝑝
20dB = 10𝑙𝑜𝑔10
𝑆𝑝
𝑁𝑝
𝑙𝑜𝑔10
𝑆𝑝
𝑁𝑝
= 2;
𝑆𝑝
𝑁𝑝
= 102
=100
𝑆𝑝
𝑁𝑝
= 100 = 𝑆𝑝= 100𝑁𝑝
Let SNR’ denote the new SNR. We know that 𝑆𝑝’= 2𝑆𝑝
SNR’ = 10𝑙𝑜𝑔10
𝑆𝑝′
𝑁𝑝
= 10𝑙𝑜𝑔10
2𝑆𝑝
𝑁𝑝
, since 𝑆𝑝= 100𝑁𝑝
SNR’ = 10𝑙𝑜𝑔10
200𝑁𝑝
𝑁𝑝
= 10𝑙𝑜𝑔10200 ~23𝑑𝐵, 𝑡ℎ𝑒𝑟𝑒𝑓𝑜𝑟𝑒, 𝑡ℎ𝑒 𝑛𝑒𝑤 𝑆𝑁𝑅 𝑖𝑠 23𝑑𝐵
1/23/2025 11

Cellular Internet Access
• A cellular network is a communication network that uses radio waves to link
mobile devices to a central server or hub and each other.
• "Cellular" describes the network's topology, which is separated into regions
known as cells.
• Each cell's radio transceiver equipment is a component of a wider network
architecture.
• Cellular internet access, also known as mobile broadband, is a type of internet
connection that uses cellular networks to provide service.
• It's the most popular way to connect to the internet, and is available on
smartphones, tablets, and other mobile devices.
• Every base station is connected to the Mobile Switching Centre (MSC) to
create a call and mobility network by connecting mobile phones to wide area
networks.
• On the other hand, internet connectivity is achieved using wireless network
devices.
• Cellular networks rely on the availability of network ranges, while Wi-Fi has a
limited range.
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Important elements of a cellular network consist of
Cell sites, also known as base stations, are places outfitted with transceivers and
antennas to aid communication with mobile devices inside a particular cell. Every
cell location is linked to the main network infrastructure.
• Mobile Devices: These end-user gadgets employ radio frequency signals to
connect to cell sites, including cell phones and mobile phones.
• Centralized Network Infrastructure: This refers to the fundamental
components of the network that control communication between various
cells and establish connections with other networks, including the internet or
the Public Switched Telephone Network (PSTN).
• Switching Systems: These connect users to external networks and direct calls
and data amongst users inside the cellular network.
• Backhaul Network: The network that links various cell sites to the core
infrastructure is called the backhaul network. Between the cell sites and the
core network, it transports data.
• Improvements in data speed, capacity, and latency brought about by the
switch from 1G (first Generation) to 5G (fifth Generation) have made it
possible to use a variety of applications outside of traditional voice
communication, including mobile internet, video streaming, and the Internet
of Things (IoT).
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An Overview of Cellular Network Architecture
• Global System for Mobile communication (GSM) is a digital mobile network
that is widely used by mobile phone users in Europe and other parts of the
world.
• GSM uses a variation of Time Division Multiple Access (TDMA) and is the most
widely used of the three digital wireless telephony technologies: TDMA, GSM
and Code-division Multiple Access (CDMA).
• GSM digitizes and compresses data, then sends it down a channel with two
other streams of user data, each in its own time slot.
• It operates at either the 900 megahertz (MHz) or 1,800 MHz frequency band.
• GSM, together with other technologies, is part of the evolution of wireless
mobile telecommunications that includes High-Speed Circuit-Switched Data
(HSCSD), General Packet Radio Service (GPRS), Enhanced Data GSM
Environment (EDGE) and Universal Mobile Telecommunications Service
(UMTS).
• Europeans deployed GSM technology with great success in the early 1990s,
and since then GSM has grown to be the 800-pound gorilla of the cellular
telephone world, with more than 80% of all cellular subscribers worldwide
using GSM.
1/23/2025 14

Cont…
• First Generation (1G) systems were analog FDMA systems designed exclusively for
voice-only communication.
• These 1G systems are almost extinct now, having been replaced by digital 2G systems.
• The original 2G systems were also designed for voice, but later extended (2.5G) to
support data (i.e., Internet) as well as voice service.
• The 3G systems that currently are being deployed also support voice and data, but with
an ever increasing emphasis on data capabilities and higher-speed radio access links.
Cellular Network Architecture, 2G: Voice Connections to the Telephone
Network
• The term cellular refers to the fact that the region covered by a cellular
network.
• Each cell contains a Base Transceiver Station (BTS) that transmits signals to
and receives signals from the mobile stations in its cell.
• The coverage area of a cell depends on many factors, including the
transmitting power of the BTS, the transmitting power of the user devices,
obstructing buildings in the cell, and the height of base station antennas.
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Cont…
Figure 6.18: Components of the GSM 2G cellular network architecture
1/23/2025 16

Cont…
• GSM systems consist of 200-kHz frequency bands with each band supporting eight TDM
calls.
• GSM encodes speech at 13 kbps and 12.2 kbps.
• A GSM network’s Base Station Controller (BSC) will typically service several tens of base
transceiver stations.
• The role of the BSC is to allocate BTS radio channels to mobile subscribers, perform
paging (finding the cell in which a mobile user is resident), and perform handoff of
mobile users.
• The BSC and its controlled base transceiver stations collectively constitute a GSM base
station system (BSS).
• The Mobile Switching Center (MSC) plays the central role in user authorization and
accounting (e.g., determining whether a mobile device is allowed to connect to the
cellular network), call establishment and teardown, and handoff.
• A single MSC will typically contain up to five BSCs, resulting in approximately 200K
subscribers per MSC.
• A cellular provider’s network will have a number of MSCs, with special MSCs known as
GateWay MSCs connecting the provider’s cellular network to the larger public
telephone network.
1/23/2025 17

3G Cellular Data Networks: Extending the Internet to Cellular
Subscribers
• For faster data transfer speeds and mobile internet access compared to 2G:
• Data rates: 3G networks could achieve data rates of up to 2 Mbps.
• Communication technique: 3G networks used wide-band code division
multiple access (CDMA) to carry data.
• Frequency bands: 3G networks operated in the licensed cellular network
bands of 850 MHz and 1900 MHz.
• Mobile internet: 3G allowed users to access mobile internet, which made
smartphones possible.
3G Core Network
• The 3G core cellular data network connects radio access networks to the public
Internet. The core network interoperates with components of the existing cellular voice
network (in particular, the MSC).
• 3G data services is clear: leave the existing core GSM cellular voice network untouched,
adding additional cellular data functionality in parallel to the existing cellular voice
network.
• There are two types of nodes in the 3G core network: Serving GPRS Support Nodes
(SGSNs) and Gateway GPRS Support Nodes (GGSNs).
• Generalized Packet Radio Service(GPRS), an early cellular data service in 2G networks;
1/23/2025 18

Cont…
Fig.4.12: 3G system architecture.
1/23/2025 19

conti,..
3G Radio Access Network: The Wireless Edge
• The 3G radio access network is the wireless first-hop network that we see as a
3G user.
• The Radio Network Controller (RNC) typically controls several cell base
transceiver stations similar to the base stations that we encountered in 2G
systems (but officially known in 3G UMTS parlance as a “Node Bs”—a rather
non-descriptive name!).
• Each cell’s wireless link operates between the mobile nodes and a base
transceiver station, just as in 2G networks.
• The RNC connects to both the circuit-switched cellular voice network via an
MSC, and to the packet-switched Internet via an SGSN.
• Thus, while 3G cellular voice and cellular data services use different core
networks, they share a common first/last-hop radio access network.
• A significant change in 3G UMTS over 2G networks is that rather than using
GSM’s FDMA/TDMA scheme, UMTS uses a CDMA technique known as Direct
Sequence Wideband CDMA (DS-WCDMA) within TDMA slots; TDMA slots, in
turn, are available on multiple frequencies—an interesting use of all three
dedicated channel-sharing approaches.
1/23/2025 20

On to 4G: LTE
• 4G LTE stands for Long Term Evolution, or 4th generation LTE, is a mobile
technology that offers faster speeds and lower latency than previous
generations.
• Even 5G devices spend a good chunk of time on the older, more reliable
network.
• There are two main types of 4G: LTE and HSPA+ (High Speed Packet Access).
• LTE and is the best 4G solution, LTE can theoretically achieve speeds of up to
300 Mbps for download and 75 Mbps for upload, but again, it varies
depending on the network and the device.
• In comparison, HSPA+ speeds up to 168 Mbps for download and 22 Mbps for
upload.
• That said, 100Mbps can be more than good enough for most casual users and
is known for being much more battery efficient.
Evolved Packet Core (EPC) [3GPP Network Architecture 2012]:
 The EPC is a simplified all-IP core network that unifies the separate circuit-
switched cellular voice network and the packet-switched cellular data
network.
 The EPC allows multiple types of radio access networks, including legacy 2G
and 3G radio access networks, to attach to the core network.
1/23/2025 21

Cont…
LTE Radio Access Network:
• LTE uses a combination of Frequency Division Multiplexing (FDM) and Time Division
Multiplexing (TDM) on the downstream channel, known as Orthogonal Frequency
Division Multiplexing (OFDM).
• In LTE, each active mobile node is allocated one or more 0.5ms time slots in one or
more of the channel frequencies.
• By being allocated increasingly more time slots, a mobile node is able to achieve
increasingly higher transmission rates.
• Another innovation in the LTE radio network is the use of sophisticated Multiple-input,
Multiple Output (MIMO) antennas.
• The maximum data rate for an LTE user is 100 Mbps in the downstream direction and
50 Mbps in the upstream direction, when using 20 MHz worth of wireless spectrum.
• LTE-Advanced allows for downstream bandwidths of hundreds of Mbps by allocating
aggregated channels to a mobile node.
• An additional 4G wireless technology—WiMAX (World Interoperability for Microwave
Access)—is a family of IEEE 802.16 standards that differ significantly from LTE. Whether
LTE or WiMAX becomes the 4G technology.
1/23/2025 22

Comparison of Mobile Networks Generation
First generation - 1G
1980s: 1G delivered analog voice.
Second generation - 2G
Early 1990s: 2G introduced digital voice (CDMA).
Third generation - 3G
Early 2000s: 3G brought mobile data (e.g. CDMA2000).
Fourth generation - 4G LTE
• 2010s: 4G LTE ushered in the era of mobile broadband.
• 5G is used across three main types of connected services, including enhanced
mobile broadband, mission-critical communications, and the massive IoT.
• 5G mobile technology can usher in new immersive experiences such as VR
(Virtual Reality) and AR (Augmented Reality) with faster, more uniform data
rates, lower latency, and lower cost-per-bit.
• New 5G NR mobile network is backed up by a Gigabit LTE coverage
foundation, which can provide ubiquitous Gigabit-class connectivity.
• The new networks offer not only higher download speeds, with a peak speed
of 10 Gbit/s.
1/23/2025 23

Cont…
6G is the sixth generation of wireless networks and is expected to be available
around 2030.
Speed
6G networks are expected to be 100 times faster than 5G, with data rates
potentially measured in terabits per second.
Latency
6G networks are expected to have lower latency, with sub-millisecond latency for
extreme connectivity.
Reliability
6G networks are expected to be more reliable, with enhanced reliability through
simultaneous transmission, multiple wireless hops, and device-to-device
connections.
Intelligence
6G networks are expected to be more intelligent, with AI-powered interfaces and
distributed AI/ML.
New capabilities
Expected to support new capabilities such as real-time learning, distributed
computation, and sensing.
1/23/2025 24

Mobility Management
Principles
• From the network layer’s standpoint, how mobile is a user?
A physically mobile user will present a very different set of challenges to the network layer,
depending on how he or she moves between points of attachment to the network.
• How important is it for the mobile node’s address to always remain the same?
Must a laptop similarly maintain the same IP address while moving between IP networks? :
IP provides this transparency, allowing a mobile node to maintain its permanent IP address
while moving among networks.
• What supporting wired infrastructure is available?
Mobile user can connect—for example, the home’s ISP network, the wireless access
network in the office, or the wireless access networks lining the autobahn.
 In a network setting, the permanent home of a mobile node (such as a laptop or
smartphone) is known as the home network.
 Entity within the home network that performs the mobility management functions-the
mobile node is known as the home agent.
 The network in which the mobile node is currently residing- foreign (or visited)
network.
 The entity within the foreign network that helps the mobile node with the mobility
management functions - foreign agent.
 A correspondent is the entity wishing to communicate with the mobile node.
1/23/2025 25

Conti.
Figure 4.22: Initial elements of a mobile network architecture
1/23/2025 26

Addressing
• When a mobile node is resident in a foreign network, all traffic addressed to
the node’s permanent address now needs to be routed to the foreign network.
• When the mobile node leaves one foreign network and joins another, the new
foreign network would advertise a new, highly specific route to the mobile
node, and the old foreign network would withdraw its routing information
regarding the mobile node.
• One role of the foreign agent is to create a so-called care-of address (COA) for
the mobile node, with the network portion of the COA matching that of the
foreign network.
• There are thus two addresses associated with a mobile node, its permanent
address and its COA, sometimes known as a foreign address.
• The permanent address of the mobile node is 128.119.40.186.
• When visiting network 79.129.13/24, the mobile node has a COA of
79.129.13.2.
• A second role of the foreign agent is to inform the home agent that the mobile
node is resident in its (the foreign agent’s) network and has the given COA.
1/23/2025 27

Routing to a mobile node
The basic idea used for mobile routing on the internet and cellular network is for the
mobile hosts to tell the host at the home location.
Routing in a mobile ad-hoc network depends on many factors such as:
 Modeling of the topology,
 Selection of routers,
 Initiation of a route request,
 And serve as heuristics in finding the path effectively.
Indirect Routing to a Mobile Node
It is a method for sending packets to a mobile node that uses a third party, or home
agent, to forward the packet to the mobile node. This allows a mobile device to
maintain a permanent IP address while moving between networks.
Here are the steps involved in indirect routing to a mobile node:
 The correspondent node sends a packet to the mobile node's home network using
the mobile node's permanent address.
 The home agent (HA) intercepts the packet and sends it to the foreign agent (FA)
in the network the mobile node is currently visiting.
 The FA receives the packet and forwards it to the mobile node.
 The mobile node replies directly to the correspondent node.
1/23/2025 28

Cont…
Figure 4.23: Indirect routing to a mobile node
1/23/2025 29

Cont…
Indirect routing by listing the new network layer functionality required to
support mobility
A mobile-node–to–foreign-agent protocol:
The mobile node will register with the foreign agent when attaching to the
foreign network. Similarly, a mobile node will deregister with the foreign agent
when it leaves the foreign network.
• A foreign-agent–to–home-agent registration protocol:
The foreign agent will register the mobile node’s COA with the home agent. A
foreign agent need not explicitly deregister a COA when a mobile node leaves its
network, because the subsequent registration of a new COA, when the mobile
node moves to a new network, will take care of this.
• A home-agent datagram encapsulation protocol: Encapsulation and forwarding
of the correspondent’s original datagram within a datagram addressed to the
COA.
• A foreign-agent decapsulation protocol:
Extraction of the correspondent’s original datagram from the encapsulating
datagram, and the forwarding of the original datagram to the mobile node.
1/23/2025 30

Cont…
Figure 4.24: Encapsulation and decapsulation
1/23/2025 31

Direct Routing to a Mobile Node
• The indirect routing approach suffers from an inefficiency known as the
triangle routing problem—datagrams addressed to the mobile node must be
routed first to the home agent and then to the foreign network.
• Direct routing overcomes the inefficiency of triangle routing, but does so at
the cost of additional complexity.
• In the direct routing approach, a correspondent agent in the correspondent’s
network first learns the COA of the mobile node.
• This can be done by having the correspondent agent query the home agent,
assuming that (as in the case of indirect routing) the mobile node has an up-
to-date value for its COA registered with its home agent.
• It is also possible for the correspondent itself to perform the function of the
correspondent agent, just as a mobile node could perform the function of the
foreign agent.
Two important additional challenges:
 A mobile-user location protocol is needed for the correspondent agent to
query the home agent to obtain the mobile node’s COA.
 When the mobile node moves from one foreign network to another, how will
data now be forwarded to the new foreign network?
1/23/2025 32

Cont…
Figure 4.25 : Direct routing to a mobile user
1/23/2025 33

Mobile IP
• Mobile IP is a communication protocol (created by extending Internet
Protocol, IP) that allows users to move from one network to another with the
same IP address.
• It ensures that the communication will continue without the user’s sessions or
connections being dropped.
• Mobile IP works similarly, ensuring that even if our device changes its network
connection, it can still communicate without interruption.
• Mobile IP useful for mobile devices like smartphones, laptops, and tablets,
which frequently switch between different networks, such as Wi-Fi and
cellular.
• Mobile IP helps keep internet connections stable and reliable, making it easier
to stay connected while on the move.
The mobile IP standard consists of three main pieces:
1. Agent discovery: Mobile IP defines the protocols used by a home or foreign agent to
advertise its services to mobile nodes, and protocols for mobile nodes to solicit the
services of a foreign or home agent.
2. Registration with the home agent: Defines the protocols used by the mobile node
and/or foreign agent to register and deregister COAs with a mobile node’s home agent.
1/23/2025 34

Cont…
Indirect routing of datagrams: The standard also defines the manner in which
datagrams are forwarded to mobile nodes by a home agent, including rules for
forwarding datagrams, rules for handling error conditions, and several forms of
encapsulation.
Agent discovery
The process used by mobile nodes to determine their current network location
and identify mobility agents.
Home agent bit (H): Indicates that the agent is a home agent for the network.
Foreign agent bit (F): Indicates that the agent is a foreign agent for the network.
Registration required bit (R): Indicates that a mobile user in this network must
register with a foreign agent. In particular, a mobile user cannot obtain a care of
address in the foreign network (for example, using DHCP).
M, G encapsulation bits: Indicate whether a form of encapsulation other than IP-
in-IP encapsulation will be used.
Care-of address (COA) fields: A list of one or more care-of addresses provided by
the foreign agent. The mobile user will select one of these addresses as its COA
when registering with its home agent.
1/23/2025 35

Managing mobility in cellular Networks
• Mobility management is a set of protocols and mechanisms that enable users
to move around wireless networks without interruption.
• It's a key function in cellular networks that allows users to make calls, send
SMS messages, and use other mobile services.
• Mobility management is important for enabling continues access to wireless
networks and mobile services.
• It allows users to move across different wireless networks and continue their
application sessions without interruption.
• It also enables global roaming, which allows users to move into and use
different operators' networks.
• The home network maintains a database known as the Home Location
Register (HLR), which contains the permanent cell phone number and
subscriber profile information for each of its subscribers. Importantly, the HLR
also contains information about the current locations of. these subscribe.
• The HLR contains enough information to obtain an address in the visited
network to which a call to the mobile user should be routed-called as Gateway
Mobile services Switching Center (GMSC) is contacted by a correspondent
when a call is placed to a mobile user.
1/23/2025 36

Routing calls to a Mobile user
1. The correspondent dials the mobile user’s phone number. The leading digits in the number are
sufficient to globally identify the mobile’s home network. The call is routed from the
correspondent through the PSTN to the home MSC in the mobile’s home network. This is the first
leg of the call.
2. The home MSC receives the call and interrogates the HLR to determine the location of the mobile
user. In the simplest case, the Home Location Register (HLR) returns the Mobile Station Roaming
Number (MSRN), which we will refer to as the roaming number. If HLR does not have the roaming
number, it returns the address of the Visitor Location Register (VLR) in the visited network.
3. Given the roaming number, the home MSC sets up the second leg of the call through the network
to the MSC in the visited network. The call is completed, being routed from the correspondent to
the home MSC, and from there to the visited MSC, and from there to the base station serving the
mobile user.
1/23/2025 37
Figure 6.29 : Placing a call to a
mobile user: indirect routing

Handoffs in GSM
In cellular communications, the handoff is the process of transferring an active
call or data session from one cell in a cellular network or from one channel to
another.
There may be several reasons for handoff to occur, including (1) the signal
between the current base station and the mobile may have deteriorated to such
an extent that the call is in danger of being dropped, and (2) a cell may have
become overloaded, handling a large number of calls. This congestion may be
alleviated by handing off mobiles to less congested nearby cells.
Handoff in GSM is initiated by the old base station based on these
measurements, the current loads of mobiles in nearby cells, and other factors.
when a base station does decide to handoff a mobile user:
1. The old base station informs the visited MSC that a handoff is to be
performed and the BS (or possible set of BSs) to which the mobile is to be
handed off.
2. The visited MSC initiates path setup to the new BS, allocating the resources
needed to carry the rerouted call, and signaling the new BS that a handoff is
about to occur.
1/23/2025 38

Cont…
3. The new BS allocates and activates a radio channel for use by the mobile.
4. The new BS signals back to the visited MSC and the old BS that the visited MSC-to-new-
BS path has been established and that the mobile should be informed of the impending
handoff.
5. The mobile is informed that it should perform a handoff.
6. The mobile and the new BS exchange one or more messages to fully activate the new
channel in the new BS.
7. The mobile sends a handoff complete message to the new BS, which is forwarded up to
the visited MSC. The visited MSC then reroutes the ongoing call to the mobile via the new
BS.
8. The resources allocated along the path to the old BS are then released.
1/23/2025 39
Figure 6.31: Steps in accomplishing a
handoff between base stations with a
common MSC.

Wireless and Mobility: Impact on Higher-layer protocols.
Wireless: The transmission of signals over radio waves instead of wires. Wireless networks
are local area networks (LANs) that use radio waves to connect devices without cables.
Mobility: The ability to move freely or change quickly. Mobility typically refers to the
capability of devices or systems to be used while on the move.
If protocols such as TCP or UDP are used to provide transport-layer services to applications
in both wired and wireless networks, then the application layer should remain unchanged
as well.
1/23/2025 40
GSM element Comment on GSM element Mobile IP
element
Home system Network to which the mobile user’s
permanent phone number belongs.
Home network
Gateway mobile switching
center or simply home MSC,
Home location register
Home MSC: point of contact to obtain
routable address of mobile user
Home network
Visited system Network other than home system where
mobile user is currently residing
Visited network.
Visited mobile services
switching center, Visitor
location register
Visited MSC Foreign agent
Mobile station roaming number
or simply roaming number
Routable address for telephone call segment
between home MSC and visited MSC
Core of address

Dr Shivu_GAT_Computer Network_22ISE52_Module 4.pdf

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