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What is Signal and also explain about signal propagation?

In electronics, a signal is an electric current orelectromagnetic field used to convey data from one placeto another. The simplest form of signal is a direct current (DC) that is switched on and off; this is theprinciple by which the early telegraph worked. More complex signals consist of an alternating-current(AC) or electromagnetic carrier that contains one or more data streams.Data is superimposed on a carrier current or wave by means of a process called modulation. Signal

modulation can be done in either of two main ways:analogand digital. In recent years, digital modulationhas been getting more common, while analog modulation methods have been used less and less. There arestill plenty of analog signals around, however, and they will probably never become totally extinct.Except for DC signals such as telegraph and baseband, all signal carriers have a definable frequency orfrequencies. Signals also have a property calledwavelength, which is inversely proportional to thefrequency.In some information technology contexts, a signal is simply "that which is sent or received," thusincluding both the carrier and the data together.In telephony, a signal is special data that is used to set up or control communication. See signaling

Signal Propagation:

A radio system transmits information to the transmitter. The information is transmitted through an

antenna which converts the RF signal into an electromagnetic wave. The transmission medium forelectromagnetic wave propagation is free space.

Transmission range: receiver receives signal with an error rate low enough to be able to

communicate

Detection range: transmitted power is high enough to detect the transmitter, but high error rate

forbids communication

Interference range: sender interferes with other transmissions by adding to the noise.

Radio waves exhibit three fundamental propagation behavior

Ground wave (< 2 MHz) : waves with low frequency follow earths surface

can propagate long distances

Used for submarine communication or AM radio

Sky wave (2-30 MHz) : waves reflect at the ionosphere and bounce back and forth

between ionosphere and earth , travelling around the world

Used by international broadcast and amateur radio

Line of Sight (> 30 MHz) : emitted waves follow a straight line of sight

allows straight communication with satellites or microwave links on the ground

used by mobile phone system, satellite systems

2. What is antenna? Explain briefly about various types of antenna?

An electrical conductor or system of conductors used for radiating electromagnetic energy into

space or for collecting electromagnetic energy from the space. An integral part of a wireless

system

Radiation Patterns: Antenna radiates power in all directions, but typically does not radiate equally in all

directions. Ideal antenna is one that radiates equal power in all direction

called an isotropic antenna

all points with equal power are located on a sphere with the antenna as its center

Omnidirectional Antenna

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Produces omni directional

radiation pattern of equal strength in all directions

Vector A and B are of equal length

Directional Antenna:

Radiates most power in one axis (direction), radiates less in other direction, vector B is longerthan vector A : more power radiated along B than A

directional along X

Dipole Antenna:

Half-wave dipole or Hertz, antenna consists of two straight collinear conductor of equal lengthLength of the antenna is half the wavelength of the signal.

Quarter-wave antenna:

Quarter-wave or marconi antenna, has a veritcal conductor of, length quarter of the wavelengthof the signal

Sectorized Antenna:

Several directional antenna, combined on a single pole, to provide sectorized antenna

each sector serves receivers, listening it its direction

3. Explain Multipath Propagation in Detail?

Wireless signal can arrive at the receiver through different pahs

LOS

Reflections from objects

DiffractionOccurs at the edge of an impenetrable body that is large compared to the wavelength of the signal.

Multipath Propagation (source: Stallings)

Inter Symbol Interference (ISI)

in multipath (source: Stallings)

Effect of Multipath Propagation:

Multiple copies of the signal may arrive with different phases. If the phases add destructively, the

signal level reduces relative to noise.Inter Symbol Interference (ISI)

4. What is multiplexing? Discuss in detail about different types in Meltiplexing?

A fundamental mechanism in communication system and networks

Enables multiple users to share a medium

For wireless communication, multiplexing can be carried out in four dimensions: space, time,

frequency and code

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Space division multiplexing:

Channels are assigned on the basis of space (but operate on same frequency)

The assignment makes sure that the transmission do not interfere with each (with a guard band in

between)

Frequency Division Multiplexing:

Frequency domain is subdivided into several non-overlapping frequency bands Each channel is assigned its own frequency band (with guard spaces in between)

Time Division Multiplexing:

A channel is given the whole bandwidth for a certain amount of time

All senders use the same frequency, but at different point of time

Frequency and time division multiplexing:

A channel use a certain frequency for a certain amount of time and then uses a different

frequency at some other time

Used in GSM systems

Code division multiplexing:

separation of channels achieved by assigning each channel its own code

guard spaces are realized by having distance in code space (e.g. orthogonal codes)

transmitter can transmit in the same frequency band at the same time, but have to use different

code

Provides good protection against interference and tapping

but the receivers have relatively high complexity

has to know the code and must separate the channel with user data from the noise

composed of other transmission

has to be synchronized with the transmitter

5. What is modulation? Explain in detail.

Process of combining input signal and a carrier frequency at the transmitter

Digital to analog modulation

necessary if the medium only carries analog signal

Analog to analog modulation

needed to have effective transmission (otherwise the antenna needed to transmit original

signal could be large)

permits frequency division multiplexing

Amplitude Shift Keying (ASK)

ASK is the most simple digital modulation scheme

Two binary values, 0 and 1, are represented by two different amplitude

In wireless, a constant amplitude cannot be guaranteed, so ASK is typically not used

Frequency Shift Keying (FSK) The simplest form of FSK is binary FSK

assigns one frequency f1 to binary 1 and another frequency f2binary 0

Simple way to implement is to switch between two oscillators one with f1 and the other with f2

The receiver can demodulate by having two bandpass filter

Phase Shift Keying (PSK)

Uses shifts in the phase of a signal to represent data

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Shifting the phase by 1800 each time data changes: called binary PSK

The receiver must synchronize in frequency and phase with the transmitter

Quadrature Phase Shift Keying (Q-PSK)

Higher bit rate can be achieved for the same bandwidth by coding two bits into one phase shift.

450 for data 11

1350

for data 10 2250 for data 00

3150 for data 01

6. What is spread spectrum. Explain Direct sequence and frequency hopping spread spectrum?

Spread Spectrum

Spreading the bandwidth needed to transmit data

Spread signal has the same energy as the original signal, but is spread over a larger

frequency range

provides resistance to narrowband interference

Direct Sequence Spread Spectrum

Takes a user bit sequence and performs an XOR with, what is known as, chippingsequence

Each user bit duration tb

chipping sequence has smaller pulses tc

If chipping sequence is generated properly it may appear as random noise

sometimes called pseudo-noise (PN)

tb/tc is known as thespreading factor

determines the bandwidth of the resultant signal

Used by 802.11b

Frequency Hopping Spread Spectrum

Total available bandwidth is split into many channels of smaller bandwidth and guard spaces Transmitter and receiver stay on one of these channels for a certain time and then hop to another

channel

Implements FDM and TDM

Pattern of channel usage : hopping sequence

Time spent on a particular channel: dwell time

Slow hopping

Transmitter uses one frequency for several bit period

systems are cheaper, but are prone to narrow band interference

Fast hopping

Transmitter changes frequency several times in one bit period

Transmitter and receivers have to stay synchronized within smaller tolerances

Better immuned to narrow band interference as they stick to one frequency for a very

short period

Receiver must know the hopping sequence and stay synchronized with the transmitter

Used by bluetooth

7. Explain in detail about Cellular wireless networks.

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A cellular networkis a radio network distributed over land areas called cells, each served by at least one

fixed-location transceiverknown as a cell site orbase station. When joined together these cells provide

radio coverage over a wide geographic area. This enables a large number of portable transceivers

(e.g., mobile phones,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.

Cellular networks offer a number of advantages over alternative solutions:

increased capacity

reduced power use

larger coverage area

reduced interference from other signals

An example of a simple non-telephone cellular system is an old taxi driver's radio system where the taxi

company has several transmitters based around a city that can communicate directly with each taxi.

In a cellular radio system, a land area to be supplied with radio service is divided into regular shaped

cells, which can be hexagonal, square, circular or some other irregular shapes, although hexagonal cells

are conventional. Each of these cells is assigned multiple frequencies (f1 -f6) which have

correspondingradio base stations. The group of frequencies can be reused in other cells, provided that the

same frequencies are not reused in adjacent neighboring cells as that would cause co-channel interference.

The increased capacity in a cellular network, compared with a network with a single transmitter, comes

from the fact that the same radio frequency can be reused in a different area for a completely different

transmission. If there is a single plain transmitter, only one transmission can be used on any given

frequency. Unfortunately, there is inevitably some level ofinterference from the signal from the other

cells which use the same frequency. This means that, in a standard FDMA system, there must be at least a

one cell gap between cells which reuse the same frequency.

In the simple case of the taxi company, each radio had a manually operated channel selector knob to tune

to different frequencies. As the drivers moved around, they would change from channel to channel. The

drivers know which frequency covers approximately what area. When they do not receive a signal from

the transmitter, they will try other channels until they find one that works. The taxi drivers only speak one

at a time, when invited by the base station operator (in a sense TDMA).

http://en.wikipedia.org/wiki/Radiohttp://en.wikipedia.org/wiki/Transceiverhttp://en.wikipedia.org/wiki/Cell_sitehttp://en.wikipedia.org/wiki/Base_stationhttp://en.wikipedia.org/wiki/Mobile_phonehttp://en.wikipedia.org/wiki/Pagerhttp://en.wikipedia.org/wiki/Taxicabhttp://en.wikipedia.org/wiki/Cellular_radiohttp://en.wikipedia.org/wiki/Radio_base_stationhttp://en.wikipedia.org/wiki/Co-channel_interferencehttp://en.wikipedia.org/wiki/Channel_capacityhttp://en.wikipedia.org/wiki/Co-channel_interferencehttp://en.wikipedia.org/wiki/Frequencyhttp://en.wikipedia.org/wiki/Time_division_multiple_accesshttp://en.wikipedia.org/wiki/Radiohttp://en.wikipedia.org/wiki/Transceiverhttp://en.wikipedia.org/wiki/Cell_sitehttp://en.wikipedia.org/wiki/Base_stationhttp://en.wikipedia.org/wiki/Mobile_phonehttp://en.wikipedia.org/wiki/Pagerhttp://en.wikipedia.org/wiki/Taxicabhttp://en.wikipedia.org/wiki/Cellular_radiohttp://en.wikipedia.org/wiki/Radio_base_stationhttp://en.wikipedia.org/wiki/Co-channel_interferencehttp://en.wikipedia.org/wiki/Channel_capacityhttp://en.wikipedia.org/wiki/Co-channel_interferencehttp://en.wikipedia.org/wiki/Frequencyhttp://en.wikipedia.org/wiki/Time_division_multiple_access

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Example of frequency reuse factor or pattern

Unit IV

1. What are the requirements of a mobile IP?

Mobile IP (orIP mobility) is an Internet Engineering Task Force (IETF) standard

communicationsprotocol that is designed to allow mobile device users to move from one network to

another while maintaining a permanent IP address.

The requirements of mobile IP:

Mobile IP allows a node to change its point of attachment to the Internet without needing to change its IPaddress. This is not simply a configuration simplification, but can facilitate continuous application-levelconnectivity as the node moves from point to point.

A possible solution to this problem would be to distribute routes through the network to declare the node'snew location and to update the routing tables so that packets can be correctly dispatched. This might, atfirst, seem attractive, but it is a solution that scales very poorly since it would be necessary to retain host-specific routes for each mobile host. As the number of mobile hosts in the Internet increases (and thegrowth of web access from mobile devices such as cell phones and palm-tops is very rapid), it wouldbecome impractical to maintain such tables in the core of the Internet.

The solution developed by the IETF involves protocol extensions whereby packets targeted at a mobilehost are sent to its home network (as if the host were not mobile) and passed to a static (nonmobile) nodecalled the node'shome agent. The mobile host registers its real location with the home agent, which isresponsible for forwarding the packets to the host.If the mobile host is at home (attached to its home network), forwarding is just plain old IP forwarding,but if the host is roving, packets must be tunneled across the Internet to a care-ofaddress where the hosthas registered its attachment to aforeign agent. At the care-of address (the end of the tunnel) the packetsare forwarded to the mobile host. This is illustrated in Figure 10.1 .

Note that this tunneling process is only required in one direction. Packets sent by the mobile host may berouted through the network using the standard IP procedures.

It is worth observing that although mobile IP can be used to address any IP mobility issue, its use withinwireless LANs and mobile phone networks might be better served by linklayer (i.e., sub-IP) procedures

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such as link-layer handoff. These processes are typically built into the link-layer mechanisms and involveless overhead than mobile IP. Such processes do, however, require that the mobile host remains logicallyconnected within the IP subnet to which its address belongs -- it becomes the responsibility of the linklayer to maintain connections or virtual connections into that subnet.

An alternative to tunneling in mobile IP might be to use source routing within IP. IPv4 has been enhanced

with optional extensions to support source routing. However, since the source routing extensions to IPv4are a relatively new development and are in any case optional, many (or even most) deployed IPv4 nodesdo not support them. This means that they are not a lot of use for developing mobile IP services overexisting IPv4 networks. They may be of more use in new networks that are being constructed for the firsttime since the Service Providers can insist on these extensions from their equipment vendors.

Figure 10.1 If the mobile node is away from home, IP traffic is sent to a home agent and tunneledacross the Internet to a foreign agent for delivery to the mobile node.

IPv6 offers some alternatives to tunneling for mobile IP by using the routing extension header. In thisway the mobile node can establish communications with its home agent and then use information learnedto directly route packets to the destination, bypassing the home agent. Since this feature is built into IPv6and so supported by all IPv6 implementations, it makes IPv6 a popular option for mobile IP deployments.

The main requirement for a mobile IP is that the mobile IP has to be compatible with all lower layer used

for standard, non mobile, IP. Mobile IP should remain invisible to higher layers and applications. The end

systems enhanced by the implementation of mobile IP must be able to communicate with the fixed

systems since in current situation fixed systems are in huge amount and working in all over the world.

The effects of mobility include higher delay and low bandwidth so there is also a requirement forbandwidth aware applications. The mobility could cause huge routing advertisements that could possibly

flood the whole network so special care regarding efficiency is required.

2. What are the entities in mobile IP?

Mobile IP Functional Entities

Mobile IP introduces the following new functional entities:

Mobile node (MN) Host or router that changes its point of attachment from one network to another network

while maintaining all existing communications by using its IP home address.

Home agent (HA) Router or server on the home network of a mobile node. The router intercepts datagrams that

are destined for the mobile node. The router then delivers the datagrams through the care-of address. The home

agent also maintains current information on the location of the mobile node.

Foreign agent (FA) Router or server on the foreign network that the mobile node visits. Provides host routing

services to the mobile node. The foreign agent might also provide a care-of address to the mobile node while the

mobile node is registered.

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Mobile IP enables routing of IP datagrams to mobile nodes. The home address of the mobile node

always identifies the mobile node regardless of where the mobile node is attached. When away from

home, a care-of address is associated with the mobile node's home address. The care-of address

provides information about the current point of attachment of the mobile node. Mobile IP uses a

registration mechanism to register the care-of address with a home agent.

The home agent redirects datagrams from the home network to the care-of address. The home agent

constructs a new IP header that contains the care-of address of the mobile node as the destination IP

address. This new header encapsulates the original IP datagram. Consequently, the home address of

the mobile node has no effect on the routing of the encapsulated datagram until the datagram arrives

at the care-of address. This type of encapsulation is called tunneling. After the datagram arrives at

the care-of address, the datagram is de-encapsulated. Then the datagram is delivered to the mobile

node.

The following figure shows a mobile node that resides on its home network, Network A, before the

mobile node moves to a foreign network, Network B. Both networks support Mobile IP. The mobile node

is always associated with the home address of the mobile node, 128.226.3.30.

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Mobile Node Residing on Home Network

The following figure shows a mobile node that has moved to a foreign network, Network B. Datagrams

that are destined for the mobile node are intercepted by the home agent on the home network,

Network A. The datagrams are encapsulated. Then, the datagrams are sent to the foreign agent on

Network B. The foreign agent strips off the outer header. Then the foreign agent delivers the datagram

to the mobile node that is located on Network B.

Mobile Node Moving to a Foreign Network

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The care-of address might belong to a foreign agent. The care-of address might be acquired by the

mobile node through the Dynamic Host Configuration Protocol (DHCP) or the Point-to-Point Protocol

(PPP). In the latter situation, a mobile node has a colocated care-of address.

Mobility agents (home agents and foreign agents) advertise their presence by using agent

advertisement messages. Optionally, a mobile node can solicit an agent advertisement message. The

mobile node uses any mobility agent that is attached locally through an agent solicitationmessage. A

mobile node uses the agent advertisements to determine whether the mobile node is on the home

network or a foreign network.

The mobile node uses a special registration process to inform the home agent about the current

location of the mobile node. The mobile node is always listening for mobility agents advertising their

presence. The mobile node uses these advertisements to help determine when the mobile node moves

to another subnet. When a mobile node determines that the mobile node has moved its location, the

mobile node uses the new foreign agent to forward a registration message to the home agent. The

mobile node uses the same process when the mobile node moves from one foreign network to another

foreign network.

When the mobile node detects that it is located on the home network, the mobile node does not use

mobility services. When the mobile node returns to the home network, the mobile

nodederegisters with the home agent.

3. Explain tunneling and encapsulation in mobile IP.Once a mobile node on a foreign networkhas completed a successful registration with its home agent, theMobile IP datagram forwarding process described in the general operation topic will be fully activated.The home agent will intercept datagrams intended for the mobile node as they are routed toits home network, and forward them to the mobile node. This is done by encapsulating the datagrams andthen sending them to the node's care-of address.

Mobile IP Data Encapsulation TechniquesEncapsulation is required because each datagram we intercept and forward needs to be resent over thenetwork to the device's care-of address. In theory, the designers might conceivably have done this by justhaving the home agent change the destination address and stick it back out on the network, but there arevarious complications that make this unwise. It makes more sense to take the entire datagram and wrap itin a new set of headers before retransmitting. In ourmail analogy, this is comparable to taking a letterreceived for our traveling consultant and putting it into a fresh envelope for forwarding, as opposed to justcrossing off the original address and putting a new one on.

The default encapsulation process used in Mobile IP is called IP Encapsulation Within IP, defined in RFC2003 and commonly abbreviated IP-in-IP. It is a relatively simple method that describes how to take an IPdatagram and make it the payload of another IP datagram. In Mobile IP, the new headers specify how tosend the encapsulated datagram to the mobile node's care-of address.

In addition to IP-in-IP, two other encapsulation methods may be optionally used:Minimal EncapsulationWithin IP, defined in RFC 2004, and Generic Routing Encapsulation (GRE), defined in RFC 1701. Touse either of these, the mobile node must request the appropriate method in its RegistrationRequest andthe home agent must agree to use it. If foreign agent care-of addressing is used, the foreign agent alsomust support the method desired.

The Mobile IP Data Delivery Tunnel

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The encapsulation process creates a logical construct called a tunnel between thedevice that encapsulatesand the one that decapsulates. This is the same idea of a tunnel used in discussions of virtual privatenetworks (VPNs), IPSec tunnel mode, or the various other tunneling protocols used for security. Thetunnel represents a conduit over which datagrams are forwarded across an arbitrary internetwork, with thedetails of the encapsulated datagram (meaning the original IP headers) temporarily hidden.

In Mobile IP, the start of the tunnel is the home agent, which does the encapsulation. The end of thetunnel depends on what sort of care-of address is being used:

Foreign Agent Care-Of Address: The foreign agent is the end of the tunnel. It receives

encapsulated messages from the home agent, strips off the outer IP header and then delivers thedatagram to the mobile node. This is generally done using layer two, because the mobile nodeand foreign agent are on the same local network, and of course, the mobile node does not have itsown IP address on that network (it is using that of the foreign agent.)

Co-Located Care-Of Address: The mobile node itself is the end of the tunnel and strips off the

outer header.

Normally, the tunnel described above is used only for data grams that have been sent to themobile node and captured by the home agent. When the mobile nodes wants to send a datagram,it doesn't tunnel it back to the home agent; this would be needlessly inefficient. Instead it justsends out the datagram directly using whateverrouterit can find on its current network, whichmay or may not be a foreign agent. When it does this, it uses its own home address as the sourceaddress for any requests it sends. As a result, any response to those requests will go back tothe home network. This sets up a triangle of sorts for these kinds of transactions:

1. The mobile node sends a request from the foreign network to some third party devicesomewhereon the internetwork.

1. The third party device responds back to the mobile node. However, this sends the reply back tothe mobile node's home address on its home network.

1. The home agent intercepts the response on the home network and tunnels it back to the mobile

node.The reverse transaction would be pretty much the same, just in the reverse order. In that case the thirdparty (Internet) device would send a request to mobile node, which would be received and forwarded bythe home agent. The mobile node would reply back directly to the Internet host.

Mobile IP Encapsulation and Tunneling

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This example illustrates how a typical request/reply message exchange in Mobile IP results in a triangleof communication. In step #1, the mobile node sends a request to a remote server somewhere on theInternet. It uses its own home address as the source for this request, so in step #2 the reply goes back tothe home agent. Step #3 consists of the home agent tunneling the reply back to the mobile node.

4.Describe Dynamic host configuration protocol

DHCP (Dynamic Host Configuration Protocol) is a communications protocol that lets networkadministrators centrally manage and automate the assignment of Internet Protocol ( IP) addresses in anorganization's network. Using the Internet Protocol, each machine that can connect to the Internet needs aunique IP address, which is assigned when an Internet connection is created for a specific computer.Without DHCP, the IP address must be entered manually at each computer in an organization and a new

IP address must be entered each time a computer moves to a new location on the network. DHCP lets anetwork administrator supervise and distribute IP addresses from a central point and automatically sendsa new IP address when a computer is plugged into a different place in the network.

DHCP is an extension of an earlier network IP management protocol, Bootstrap Protocol ( BOOTP).DHCP is a more advanced protocol, but both configuration management protocols are commonly usedand DHCP can handle BOOTP client requests. Some organizations use both protocols, but understandinghow and when to use them in the same organization is important. Some operating systems, includingWindows NT/2000, come with DHCP servers. A DHCP or BOOTP client is a program that is located in(and perhaps downloaded to) each computer so that it can be configured

The Dynamic Host Configuration Protocol (DHCP) is an auto configuration protocol used on IPnetworks. Computers that are connected to IP networks must be configured before they can communicatewith other computers on the network. DHCP allows a computer to be configured automatically,eliminating the need for intervention by a network administrator. It also provides a central database forkeeping track of computers that have been connected to the network. This prevents two computers fromaccidentally being configured with the same IP address.

In the absence of DHCP, hosts may be manually configured with an IP address. Alternatively IPv6 hostsmay use stateless address auto configuration to generate an IP address. IPv4 hosts may use link-localaddressing to achieve limited local connectivity.

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In addition to IP addresses, DHCP also provides other configuration information, particularly the IPaddresses of local caching DNS resolvers. Hosts that do not use DHCP for address configuration may stilluse it to obtain other configuration information.

There are two versions of DHCP, one forIPv4 and one forIPv6. While both versions bear the same nameand perform much the same purpose, the details of the protocol for IPv4 and IPv6 are sufficientlydifferent that they can be considered separate protocols.

Description of the communication steps

1. The client broadcasts a DHCPDISCOVER.2. Each server may respond with a DHCPOFFERmessage.3. The client receives one or more DHCPOFFERmessages from one or more servers and chooses

one server from which to request configuration parameters.The client broadcasts a DHCPREQUEST message.

4. Those servers not selected by the DHCPREQUEST message use the message as notification thatthe client has declined that server's offer.The server selected in the DHCPREQUEST message commits the responds witha DHCPACKmessage containing the configuration parameters for the requesting client.

5. The client receives the DHCPACKmessage with configuration parameters. At this point, theclient is configured.If the client receives a DHCPNAKmessage, the client restarts the configuration process.

6. The client may choose to relinquish its lease on a network address by sendinga DHCPRELEASE message to the server (e.g. on shutdown).

7. The server receives the DHCPRELEASE message and marks the lease as free.

5. Explain routing in IPv6.

Internet Protocol version 6 (IPv6) is a version of the Internet Protocol (IP) that is designed tosucceed Internet Protocol version 4 (IPv4). The Internet operates by transferring data in smallpackets thatare independently routed across networks as specified by an international communications

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protocol known as the Internet Protocol. Each data packet contains two numeric addresses that are thepacket's origin and destination devices. Since 1981, IPv4 has been the publicly used Internet Protocol, andit is currently the foundation for most Internet communications. The Internet's growth has created a needfor more addresses than IPv4 has. IPv6 allows for vastly more numerical addresses, but switching fromIPv4 to IPv6 may be a difficult process.

IPv6 was developed by the Internet Engineering Task Force(IETF) to deal with the long-anticipated IPv4address exhaustion, and is described in Internet standard document RFC 2460, published in December1998.[1]Like IPv4, IPv6 is an Internet Layerprotocol forpacket-switched internetworking and providesend-to-end datagram transmission across multiple IP networks. While IPv4 allows 32 bits for an InternetProtocol address, and can therefore support 232 (4,294,967,296) addresses, IPv6 uses 128-bit addresses, sothe new address space supports 2128(approximately 340 undecillion or 3.41038) addresses. This expansion allows for many more devices and users on the internet as well as extraflexibility in allocating addresses and efficiency for routing traffic. It also eliminates the primary needfornetwork address translation (NAT), which gained widespread deployment as an effort to alleviateIPv4 address exhaustion.

Routing is the process of forwarding packets between connected network segments. For IPv6-based

networks, routing is the part of IPv6 that provides forwarding capabilities between hosts that are locatedon separate segments within a larger IPv6-based network.

IPv6 is the mailroom in which IPv6 data sorting and delivery occur. Each incoming or outgoing packet iscalled an IPv6 packet. An IPv6 packet contains both the source address of the sending host and thedestination address of the receiving host. Unlike link-layer addresses, IPv6 addresses in the IPv6 headertypically remain the same as the packet travels across an IPv6 network.

Routing is the primary function of IPv6. IPv6 packets are exchanged and processed on each host by usingIPv6 at the Internet layer.

Above the IPv6 layer, transport services on the source host pass data in the form of TCP segments orUDP messages down to the IPv6 layer. The IPv6 layer creates IPv6 packets with source and destinationaddress information that is used to route the data through the network. The IPv6 layer then passes packets

down to the link layer, where IPv6 packets are converted into frames for transmission over network-specific media on a physical network. This process occurs in reverse order on the destination host.

IPv6 layer services on each sending host examine the destination address of each packet, compare thisaddress to a locally maintained routing table, and then determine what additional forwarding is required.IPv6 routers are attached to two or more IPv6 network segments that are enabled to forward packetsbetween them.

IPv6 routers

IPv6 network segments, also known as links or subnets, are connected by IPv6 routers, which are devicesthat pass IPv6 packets from one network segment to another. This process is known as IPv6 routing and isshown in the following illustration.

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IPv6 routers provide the primary means for joining together two or more physically separated IPv6network segments. All IPv6 routers have the following characteristics:

IPv6 routers are physically multihomed hosts.

A physically multihomed host is a network host that uses two or more network connection

interfaces to connect to each physically separated network segment.

IPv6 routers provide packet forwarding for other IPv6 hosts.

IPv6 routers are distinct from other hosts that use multihoming. An IPv6 router must be able toforward IPv6-based communication between networks for other IPv6 network hosts.

You can implement IPv6 routers by using a variety of hardware and software products, including acomputer running a member of the Windows Server 2003 family with the IPv6 protocol. Routers that arededicated hardware devices running specialized software are common. Regardless of the type of IPv6routers that you use, all IPv6 routing relies on a routing table to communicate between network segments.

Routing tables

t passes the packet to a protocol layer above IPv6 on the local host.

It forwards the packet through one of its attached network interfaces.

It discards the packet.

IPv6 searches the routing table for the route that is the closest match to the destination IPv6 address. Themost specific to the least specific route is determined in the following order:

1. A route that matches the destination IPv6 address (a host route with a 128-bit prefix length).

2. A route that matches the destination with the longest prefix length.

3. The default route (the network prefix ::/0).

Unit VExplain traditional TCP.The Transmission Control Protocol/Internet Protocolis the main protocol suite used with the Internet.This allows users to share and distribute information across the local network. Large enterprises,however, usually have several sites situated in different areas of the same country and more recently,different countries as well. To connect sites that are situated within the same country, companies leasetransmission lines between those sites, from the public carriers such as British Telecom. This formsa Wide Area Network(WAN). To connect sites that are situated in other countries, companies usedifferent types of communication, for example satellites, optic fibres across land and / or sea etc. Thenetworks that are formed from this type of communication are calledInternetworks or justInternets.

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TCP/IP consists of a suite or a layeredstackof two core protocols and they arethe internetand transportprotocols. The Internet Protocol (IP) provides a number of core functions thatassist the process of internetworking across dissimilar networks. These are:

1.Addressing. There are three types of address used with the current version of the internet protocol(IPv4), unicast,broadcastand multicast. Unicast addressing is used when a packet of information

ordatagram is to be sent to a single destination. Broadcast addressing is used when a message is to bedelivered to every host on a destination LAN. A multicast address is used to deliver a datagram to aspecific set of hosts, called a multicast group. This type of addressing is called IP Multicast. Hosts canjoin a multicast group at anytime and receive the datagrams that are sent to the group.

2. Fragmentation and reassembly. If the datagrams sent by a host are larger than the packet sizes used bya particular part of the internet, the datagrams will have to be fragmented into smaller chunks so that theycan be transmitted. When these smaller packets are received, they have to be reassembled into the originalsized packet, so that they can be used.

3. Routing. This is used to determine which subnets, within the internet, the datagrams must travto get tothe destination host. This could involve travelling over several different LANs or WANs.4. Error reporting. This consists of several functions that will detect errors, for example the process ofreassembly could cause several packets to be discarded, and report them back to the IP in the source host.

The transport protocols are designed to sit on ``top of'' the internet protocol mentioned above. Theyprovide two modes of operation, connection-orientedorconnectionless. A connection-oriented protocolcreates a connection between the transmitter and the receiver before the data is actually transmitted. Thisis also known as a reliable transport service since the data is guaranteed to get to the destination.

The Transmission Control Protocol(TCP) is an example of this type of service.A connectionless protocol, as the name suggests, does not form a connection and therefore can notguarantee that the data will be delivered. This mode of operation reduces the overhead associated witheach message transfer because no network connection is established prior to the transmission. TCP/IPprovides a connectionless protocol called the User Datagram Protocol(UDP).

When users want to transmit information over the internet, using an internet-aware application, theinformation is first passed to the transport protocol layer. This layer will determine the type of deliverymechanism, e.g. TCP or UDP, to use. The information is then passed to the internet protocol layer, whichattaches extra information, for example the destination host address etc.

When a host receives information from the internet, the internet protocol will carry out several tests onthe packets of information received. For example error reporting, which could result in the re-transmission of particular packets, reassembly of packets etc. The information is then passed to thetransport protocol layer which strips off any information to do with the delivery mechanism.

2.Explain classical TCP improvementsE.g. HTTP (used by web services) typically uses TCP

a. Reliable transport between client and server requiredTCP

b. Steam oriented, not transaction oriented

c. Network friendly: time-out congestion slow down transmission

Well known TCP guesses quite often wrong in wireless and mobile networksd. Packet loss due to transmission errorse. Packet loss due to change of network

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Resultf. Severe performance degradation

Transport protocols typically designed forg. Fixed end-systemsh. Fixed, wired networks

Research activities

i. Performancej. Congestion controlk. Efficient retransmissions

TCP congestion controll. packet loss in fixed networks typically due to (temporary) overload situations

m. router have to discard packets as soon as the buffers are fulln. TCP recognizes congestion only indirect via missing acknowledgements, retransmissions

unwise, they would only contribute to the congestion and make it even worseslow-start algorithm as reaction.

TCP slow-start algorithm

sender calculates a congestion window for a receiver

start with a congestion window size equal to one segment

exponential increase of the congestion window up to the congestion threshold, then linearincrease

missing acknowledgement causes the reduction of the congestion threshold to one half of

the current congestion window

congestion window starts again with one segment

TCP fast retransmit/fast recovery

TCP sends an acknowledgement only after receiving a packet

if a sender receives several acknowledgements for the same packet, this is due to a gap in

received packets at the receiver

however, the receiver got all packets up to the gap and is actually receiving packets

therefore, packet loss is not due to congestion, continue with current congestion window

(do not use slow-start)Influences of mobility on TCP-mechanisms

TCP assumes congestion if packets are dropped

typically wrong in wireless networks, here we often have packet loss due to transmission

errors

furthermore, mobility itself can cause packet loss, if e.g. a mobile node roams from one

access point (e.g. foreign agent in Mobile IP) to another while there are still packets in

transit to the wrong access point and forwarding is not possible

The performance of an unchanged TCP degrades severely

however, TCP cannot be changed fundamentally due to the large base of installation in

the fixed network, TCP for mobility has to remain compatible

the basic TCP mechanisms keep the whole Internet together Indirect TCP or I-TCP segments the connection

no changes to the TCP protocol for hosts connected to the wired Internet, millions of

computers use (variants of) this protocol

optimized TCP protocol for mobile hosts

splitting of the TCP connection at, e.g., the foreign agent into 2 TCP connections, no real

end-to-end connection any longer

hosts in the fixed part of the net do not notice the characteristics of the wireless part

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Indirect TCP II: Advantages

no changes in the fixed network necessary, no changes for the hosts (TCP protocol)necessary, all current optimizations to TCP still work

transmission errors on the wireless link do not propagate into the fixed network simple to control, mobile TCP is used only for one hop between, e.g., a foreign agent and

mobile host therefore, a very fast retransmission of packets is possible, the short delay on the mobile

hop is known Disadvantages

loss of end-to-end semantics, an acknowledgement to a sender does now not any longermean that a receiver really got a packet, foreign agents might crash

higher latency possible due to buffering of data within the foreign agent and forwardingto a new foreign agent

Transparent extension of TCP within the foreign agent

buffering of packets sent to the mobile host

lost packets on the wireless link (both directions!) will be retransmitted immediately by

the mobile host or foreign agent, respectively (so called local retransmission)

the foreign agent therefore snoops the packet flow and recognizes acknowledgementsin both directions, it also filters ACKs

changes of TCP only within the foreign agent

Snooping TCP II: Data transfer to the mobile host

FA buffers data until it receives ACK of the MH, FA detects packet loss via duplicated

ACKs or time-out

fast retransmission possible, transparent for the fixed network

Data transfer from the mobile host

FA detects packet loss on the wireless link via sequence numbers, FA answers directly

with a NACK to the MH

MH can now retransmit data with only a very short delay Integration of the MAC layer

MAC layer often has similar mechanisms to those of TCP

thus, the MAC layer can already detect duplicated packets due to retransmissions and

discard them

Problems

snooping TCP does not isolate the wireless link as good as I-TCP

snooping might be useless depending on encryption schemes

3.Write short notes on WAP.

WAP (Wireless Application Protocol) is a specification for a set of communication protocols tostandardize the way that wireless devices, such ascellular telephones and radio transceivers, can be usedfor Internet access, including e-mail, the World Wide Web, newsgroups, and instant messaging. WhileInternet access has been possible in the past, different manufacturers have used different technologies. Inthe future, devices and service systems that use WAP will be able to interoperate.

The WAP layers are:

Wireless Application Environment (WAE)

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Wireless Session Layer (WSL) Wireless Transport Layer Security (WTLS) Wireless Transport Layer (WTP)

The WAP was conceived by four companies: Ericsson, Motorola, Nokia, and Unwired Planet (nowPhone.com). The Wireless Markup Language (WML) is used to create pages that can be delivered usingWAP.

There are other approaches to an industry standard besides WAP, including i-Mode

Short for the WirelessApplicationProtocol, a secure specification that allows users to access informationinstantly via handheld wireless devices such as mobile phones, pagers, two-way radios, smartphones andcommunicators.

WAP supports most wireless networks. These include CDPD, CDMA, GSM, PDC, PHS, TDMA, FLEX,ReFLEX, iDEN, TETRA, DECT, DataTAC, and Mobitex.WAP is supported by all operating systems. Ones specifically engineered for handheld devices includePalmOS, EPOC, Windows CE, FLEXOS, OS/9, and JavaOS.

WAPs that use displays and access the Internet run what are called microbrowsers--browsers with smallfile sizes that can accommodate the low memory constraints of handheld devices and the low-bandwidth constraints of a wireless-handheld network.

Although WAP supports HTML and XML, the WML language (an XML application) is specificallydevised for small screens and one-hand navigation without a keyboard. WML is scalable from two-linetext displays up through graphic screens found on items such as smart phones and communicators.

WAP also supports WMLScript. It is similar to JavaScript, but makes minimal demands on memoryand CPU power because it does not contain many of the unnecessary functions found in other scriptinglanguages.

Because WAP is fairly new, it is not a formal standard yet. It is still an initiative that was started byUnwired Planet, Motorola, Nokia, and Ericsson.

Wireless Application Protocol (WAP) is an open internationalstandard. A WAP browseris acommonly used web browserfor small mobile devices such as cell phones.

Before the introduction of WAP, mobile service providers had extremely limited opportunities to offerinteractive data services, but needed interactivity to support Internet and Web applications such as:

Emailby mobile phone

Tracking of stock-market prices

Sports results

News headlines

Music downloads

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