Bluetooth 802.15.1

Bluetooth 802.15.1

1. Wireless network using uhf radio waves Invented by Ericson in 1994 
2. Operate in Ism band 2.4
3. Bluetooth uses a radio technology called frequency-hopping spread spectrum . The
   transmitted data are divided into packets and each packet istransmitted on one of the 79
   designated Bluetooth channels.
4. Gaussian frequency-shift keying (GFSK) modulation but 8dpsk technique may also be used.

Read More

Spraed spectrum methods FHSS and DSSS

Spread spectrum method used for digital tx over air

1. DSSS
2. FHSS

Fhss

• the data signal is modulated with a narrowband carrier signal that "hops" in a random but predictable sequence from frequency to frequency.
•  The signal energy is spread in time domain rather than frequency domain.
• This technique reduces interference because a signal from a narrowband system will only affect the spread spectrum signal if both are transmitting at the same frequency at the same time.

DSSS

•  Also known as direct sequence code division multiple access (DS-CDMA),
• Stream of information to be transmitted is divided into small pieces, each of which is allocated across to a frequency channel across the spectrum.
• Data signal is combined with high bit rate sequence also called chipping code ,divides the data according to a spreading ratio.
• The redundant chipping code helps the signal resist interference and also enables the original data to be recovered if data bits are damaged during transmission.

Read More

LLC and Mac

Llc

1. Logical link control layer is upper subleases of data link layer.
2. Provide multiplexing
3. Provide flow control and error management contribute like ARQ Automatically repeat request.
4. The LLC sublayer acts as an interface between the media access control (MAC) sublayer and the network layer .

•  The LLC sublayer follows the IEEE 802.2 Where's in network like 802.11 Mac layer controls the error and flow control. Like Csma/ca
• PPP can be considered as LLC protocols.
•  

Mac ( Media access control)

1. Sublayer of 2 layer
2. Control the addressing and channel access control.
3. Provide communication between shared network like ethernet
4. Acts as interface between llc and physical layer.

This channel may provide unicast , multicast or broadcast communication service.


Examples of common statistical time division multiplexing multiple access protocols for wired multi-
drop networks are:

• CSMA/CD (used in Ethernet and
• IEEE 802.3)
• Token bus (IEEE 802.4 )
• Token ring ( IEEE 802.5 )
• Token passing (used in FDDI)

Examples of common multiple access protocols that may be used

• CSMA/CA (used in IEEE 802.11 /
• WiFi WLANs )
• Slotted ALOHA
• Dynamic TDMA
• Reservation ALOHA (R-ALOHA)
• Mobile Slotted Aloha (MS-
• ALOHA)
• CDMA
• OFDMAs

Read More

802.11 WLAN

Wlan
A wireless local area network ( WLAN ) is a wireless computer network that links two or more devices using a wireless distribution method  within a limited area such as a home, school, computer laboratory, or office building.

Use 802.11 also called wifi


Wi-Fi

• Wi-Fi is a WLAN (Wireless Local Area
• Network) technology.
• The older variant of Wi-Fi, 802.11g speeds of up to
• 54Mbps

 802.11b (providing up to 11Mbps).

802.11n

The more recent standard is called 802.11n (offering speeds of up to150Mbps per channel or up to 600Mbps in total). It can be used in the 2.4 GHz or 5 GHz frequency bands, 

Wi-Fi 802.11ac

latest (so far) Wi-Fi ac standard. It allows for speeds of up to 500 Mbps per channel and over 1Gbps in total.  Wi-Fi 802.11ac operates only on the 5GHz band.

Wi-Fi is much faster than any data cellular network like GPRS, EDGE and even UMTS and HSDPA.

The range 

 is from 30 to 100 meters indoors
while outdoors  can cover about 650 meters.

Read More

List of Protocols of OSI layers

Protocols of Osi
Physical layer

• 802.11wifi
• DSL digital subscriber line.
• ADSL  Asynchronoues
• ISDN Integrated service for digital network.
• Ethernet
• Bluetooth 802.15

Data link layer protocols

• CDP Cisco discovery protocol
• Ethernet
• IEEE 802.11 WiFi
• IEEE 802.16 WiMAX
• PPP Point-to-Point Protocol
• PPTP Point-to-Point Tunneling Protocol
• ARP Address Resolution Protocol
• RARP Reverse Address
• Resolution Protocol
• ATM Asynchronous Transfer
• Mode

Network layer

• Tcp/ip ip protocols

Transport layer

• Tcp
• UDP User Datagram Protocol
• DCCP Datagram Congestion
• Control Protocol
• Ah authentication header over ip

Session layer

• NCP NetWare Core Protocol
• NFS Network File System
• SMB Server Message Block

Presntation layer

• TLS Transport Layer Security
• SSL

Application layer

• Adc
• Bittorrent
• DNS
• Dhcp Dynamic Host Configuration Protocol
• FTP HTTP HTTPS
• IMAP , Internet Message Access
• Protocol
• NNTP , Network News Transfer
• Protocol
• NTP , Network Time Protocol
• POP3 Post Office Protocol Version 3
• SMTP , Simple Mail Transfer
• Protocol
• Telnet , a remote terminal access
• protocol

Read More

TCp and UDP protocols

Tcp/udp

TCP/IP or UDP/IP (User Datagram Protocol )  are just protocols of Internet. They are in the 4th Layer of OSI. TCP or UDP are used to determine what kind of connection is to be established whether Connection-Oriented or Connection-Less.

Connection Oriented which uses TCP/IP: protocol is used when there is a need to establish a session and where lost packets have to be retransmitted if lost like when you use email, you dont want to send a mail with uncertainty of whether the mail will reach its destination or not and moreover with uncertainty of sending incomplete mail with lost packets.

Connectio-Less which: uses the UDP/IP protocol is used when you dont want waste time on establishing a connection and you don’t want to retransmit the lost packets as the latest packet is more necessary to reach the destination like when using chat, you dont want to resend the old packets or data later or else it will be like you are talking on some other topic and the earlier packet reaches later out of nowhere. Same can be said for buffering of a video.

Read More

GSM architecture Complete

Gsm archt.

1. The Mobile Station (MS)
2. The Base Station Subsystem (BSS )
3. The Network Switching Subsystem (NSS)
4. The Operation Support Subsystem (OSS)

MS

consists of the physical

equipment, such as the radio

transceiver, display and digital signal

processors, and the SIM card.

MS also provides access to the

various data services available in a

GSM network.dg Gprs and high speed data.

BSS

The BSS is composed of two parts:

• The Base Transceiver Station (BTS)
• The Base Station Controller (BSC)

BTS and the BSC communicate

across the interface,

enable operations between

components that are made by

different suppliers.

The radio components of a BSS may consist of

four to seven or nine cells. A BSS

may have one or more base stations.

The Base Transceiver Station (BTS ) :

The BTS hold the radio

transceivers that define a cell and

handles the radio link protocols with

the MS.

In a large urban area, a large

number of BTSs may be deployed.

A BTS is usually placed in the center of a cell.

Its transmitting power defines the size of a cell.

Each BTS has between 1 and 16 transceivers, depending on

the density of users in the cell 

Function

Encoding, encrypting,

multiplexing, modulating,

Uplink channel measurements

The Base Station Controller (BSC)

The BSC manages the radio resources

for one or more BTSs.

It handles radio channel setup, frequency hopping, and handovers.

The BSC is the connection between the mobile and the MSC.

 Also linked to the Public

Switched Telephone Network (PSDN) or ISDN.

It assigns and releases frequencies

and time slots for the MS.

The

function of the BSC is to allocate the

necessary time slots between the BTS

and the MSC.

Control of frequency hopping

Performing traffic concentration

to reduce the number of lines

from the MSC

Providing an interface to the

Operations and Maintenance

Center for the BSS

Reallocation of frequencies

among BTSs

Time and frequency

synchronization

Power management

Time-delay measurements of

received signals from the MS

NSS

The Network switching system (NSS),

the main part of which is the Mobile

Switching Center (MSC), performs the

switching of calls between the mobile

and other fixed or mobile network

users, as well as the management of

mobile services such as

authentication.

The switching system includes the

following functional elements:

The HLR is a database used for

storage and management of

subscriptions. The HLR is considered

the most important database, as it

stores permanent data about

subscribers, including a subscriber's

service profile, location information,

and activity status.

Mobile Services Switching Center

(MSC )

The central component of the

Network Subsystem is the MSC. The

MSC performs the switching of calls

between the mobile and other fixed

or mobile network users,

Visitor Location Register ( VLR)

The VLR is a database that contains

temporary information about

subscribers that is needed by the

MSC in order to service visiting

subscriber or raoming.

Authentication Center ( AUC )

The Authentication Center is a

protected database that stores a copy

of the secret key stored in each

subscriber's SIM card, which is used

for authentication and ciphering of

the radio channel.

Equipment Identity Register (EIR )

The Equipment Identity Register (EIR)

is a database that contains a list of

all valid mobile equipment on the

network, where its International

Mobile Equipment Identity (IMEI)

identifies each MS.

Read More

OFDMA, SDMA, PDMA, CSMA-DA, CSMA-CA Difference between GSM CDMA

Orthogonal frequencyvdivision multiplexing (OFDM)

• Access technique used in Long-Term Evolution (LTE) to accommodate multiple users in a given bandwidth

• Modulation method that divides a channel into multiple narrow orthogonal bands that are spaced so they don’t interfere with one another.
• DATA divided into many lower bit streams.
• Time slot bw each subchannel are used to package the data.
• This technique is very spectrally efficient, so it provides very high data rates. It also is less
• affected by multipath propagation effects.
• To implement OFDMA, each user is assigned a group of subchannels and related time slots.

Space division multiple access SDMA

• SDMA uses physical separation methods that permit the sharing of wireless channels.
• single channel may be used simultaneously if the users are spaced far enough from one another to avoid interference. Known as frequency reuse.
• Useful in gsm

Pdma polarization division multiple access (PDMA)

• One unique variation of SDMA, polarization division multiple access (PDMA), separates signals by using different polarizations of the antennas. 
• Two different signals then can use the same frequency, one transmitting a vertically polarized signal and the other transmitting a horizontally polarized signal.

CSMA-CD

• A unique and widely used method of multiple access is carrier sense multiple access with collision detection (CSMA-CD).
• used in Ethernet local-area networks (LANs). 
• It allows multiple users of the network to access the single cable for transmission. 
• All network nodes listen continuously. When they want to send data, they listen first and then transmit if no other signals are on the line. 
• If two or more transmissions occur simultaneously, a collision occurs.
• The network interface circuitry can detect a collision, and then the nodes will wait a random time before retransmitting.

Csma ca

variation of this method is called carrier sense multiple access with collision avoidance (CSMA-CA).

This method is similar to CSMA-CD. However, a special scheduling algorithm is used to determine the appropriate time to transmit over the shared channel.

 While the CSMA-CD technique is most used in

wired networks, CSMA-CA is the preferred method in wireless networks.

Differentiate between GSM and CDMA

GSM

- GSM uses multiple frequencies.

- Uses TDMA and FDMA for accessing

signals.

- The voice rate is 9.6 KBPS.

- Uses less bandwidth.

CDMA

- CDMA uses single frequency as

carrier.

- The voice rate is 14.4 KBPS.

- CDMA power control to access

method is better as Phased Locked

Loops are used.

- Follows soft handoff, hence call

handling is more efficient.

Read More

CDMA - Basic points

Cdma

• Use spread spectrum techniques.
• Every  channel uses full frequency channel.
• Conversation are encoded with pseudo random digital signal.
• Better capacity for data and vioce.
• Common tech in 3g umts and wcdma.
• Also in gps.
•  A spread spectrum technique spreads the bandwidth of the data uniformly for the same transmitted power.
• Code run at much higher speed than data.
• Data is bitwise xor with code.
• The separation of the signals is made by correlating the received signal with the locally generated code.  If the signal matches User code then the correlation function will be high and the system can extract that signal. If the user's code has nothing in common with the signalthe correlation then zero (thus eliminating the signal); this is referred to as cross-correlation .

Read More

FDMA - Basics

Fdma

• Divide channel into multiple bands.
• Users share the same frequency channel But use a single frequency.
• Between these feq glad band is used.
• Used in analog radio and analog cellular system. Can be used in digital too.
• Req high fiters
• Crosstalk may occur.
• No time problem and near far problem as in tdma and cdma.
• Also support demand assigned, freq assigned on temp basis.
• Tv sysyem.

Read More

TDMA-Main Points

Tdma

1. N users share same radio channel
2. But uses only particular slot
3. Only gsm technology
4. Data streams divided in frames which contains N slots.
5. Duplex mode
6. Bw is N times the Bw required to transmit for single user.
7. Less expansive and smaller
8. N down link it is simple - just multiplexing.
9. In unlink - hard as user has to be aligned in time.

Read More

Networking Basics and Types of Computer Networks

Computer networking is basically the way to connect different computer devices by using the different components mainly hardware and software across the large distances. Thus networking makes us to easily access the information, sends the information from one device to other devices and makes our life easier.

Basic benefits of Networking

There could be many benefits and advantages of connecting through networking but if we talk in basics there are some main basic benefits of computer networking which are as follows

Information or file sharing: It is the need of the modern technology that information should be easily accessible and easily transferable. It could be in any type, a signal, a file or a file or folder. If you want to send information from one computer to other then networking is the essential part.

Resource Sharing : In case you want to share your computer resources using computer networking such as printers, fax machines, Storage Devices, Webcam, Scanners, Modem and many more devices can be shared using computer networking.

Program sharing and remote services:
You can easily share and send any program from one computer to the other computer by using different techniques of networking and by using remote services you can access the resources far away from the actual computer

Different types of computer networks:

LAN (Local area network):

LAN is called as Local area network and as name suggests it is used to connect networking devices which are geographically close to each other. This type of networking include the examples such as a floor of a building, a building itself, or a campus environment.

WAN (Wide area networks)

Wide area network is used when the geographical locations are not that much close so that we can bind them together with the help of LAN, so we make use of wide area network in that case.

MAN (metropolitan area network)

A metropolitan area network (MAN) is considered the mixture of LAN and WAN to connect the devices in a particular geographical area.

Intranet:

Intranet is a network which is local to an organization. All the information that will be available is from that network only and to access that information; they would not need to rely on the other network. This network comprises the LAN, MAN and WAN too.

Extranet:

Extranet is bit wider that of intranet where some of the information or services can be accessible by the thirds party, so the data can be share to outside an oragnisation up to some extent.

Internet:

Internet is used when the information and resources are too made available to all the external and outside users.

VPN: Virtual private network

VPN is a kind of secured network that is used to provide a secure connection over internet or any other public network. VPN use the three way secure connection which include authentication, confidentiality and integrity to ensure that data is sent between two devices is not been tempered by others.

Read More