Basics of Computer Networking

by Dinesh Thakur Category: Communication Networks

The notion of quality of service, or QoS, concerns certain characteristics of a network connection under the sole of the network service provider liability.

A QoS value applies to the whole of a network connection. It must be identical at both ends of the connection, even if it is supported by several interconnected subnetworks each offering different services.

by Dinesh Thakur Category: Communication Networks

• Bluetooth is, with the infrared, one of the major wireless technologies developed to achieve WPAN. Bluetooth is a wireless LAN technology used to connect devices of different functions such as telephones, computers (laptop or desktop), notebooks, cameras, printers and so on. Bluetooth is an example of personal area network.
• Bluetooth project was started by SIG (Special Interest Group) formed by four companies  IBM, Intel, Nokia and Toshiba for interconnecting computing and communicating devices using short-range, lower-power, inexpensive wireless radios.
• The project was named Bluetooth after the name of Viking king – Harald Blaatand who unified Denmark and Norway in 10th century.
• Nowadays, Bluetooth technology is used for several computer and non computer application:

1. It is used for providing communication between peripheral devices like wireless mouse or keyboard with the computer.
2. It is used by modern healthcare devices to send signals to monitors.
3. It is used by modern communicating devices like mobile phone, PDAs, palmtops etc to transfer data rapidly.
4. It is used for dial up networking. Thus allowing a notebook computer to call via a mobile phone.
5. It is used for cordless telephoning to connect a handset and its local base station.
6. It also allows hands-free voice comml1nication with headset.
7. It also enables a mobile computer to connect to a fixed LAN.
8. It can also be used for file transfer operations from one mobile phone to another.
9. Bluetoothusesomnidirectionalradio waves that can through wallsor othernon-metalbarriers.

Bluetooth devices have a built-in short range radio transmitter. The rate provided is 1Mbps and uses 2.4 GHz bandwidth.

Bluetooth is that when the device is with in the scope of a other devices automatically start the transfer information without the user noticing. small network between the devices is created and the user can accessed as if there were cables.

Bluetooth Architecture

Bluetooth architecture defines two types of networks:

1. Piconet

2. Scattemet

1. Piconet

• Piconet is a Bluetooth network that consists of one primary (master) node and seven active secondary (slave) nodes.

• Thus, piconet can have upto eight active nodes (1 master and 7 slaves) or stations within the distance of 10 meters.

• There can be only one primary or master station in each piconet.

• The communication between the primary and the secondary can be one-to-one or one-to-many.


• All communication is between master and a slave. Salve-slave communication is not possible.

• In addition to seven active slave station, a piconet can have upto 255 parked nodes. These parked nodes are secondary or slave stations and cannot take part in communication until it is moved from parked state to active state.

2. Scatternet

• Scattemet is formed by combining various piconets.

• A slave in one piconet can act as a master or primary in other piconet.

• Such a station or node can receive messages from the master in the first piconet and deliver the message to its slaves in other piconet where it is acting as master. This node is also called bridge slave.

• Thus a station can be a member of two piconets.

• A station cannot be a master in two piconets.


Bluetooth layers and Protocol Stack

• Bluetooth standard has many protocols that are organized into different layers.

• The layer structure of Bluetooth does not follow OS1 model, TCP/IP model or any other known model.

• The different layers and Bluetooth protocol architecture.

                 Bluetooth layers and protocol architecture

Radio Layer

• The Bluetooth radio layer corresponds to the physical layer of OSI model.

• It deals with ratio transmission and modulation.

• The radio layer moves data from master to slave or vice versa.

• It is a low power system that uses 2.4 GHz ISM band in a range of 10 meters.

• This band is divided into 79 channels of 1MHz each. Bluetooth uses the Frequency Hopping Spread Spectrum (FHSS) method in the physical layer to avoid interference from other devices or networks.

• Bluetooth hops 1600 times per second, i.e. each device changes its modulation frequency 1600 times per second.

• In order to change bits into a signal, it uses a version of FSK called GFSK i.e. FSK with Gaussian bandwidth filtering.

Baseband Layer

• Baseband layer is equivalent to the MAC sublayer in LANs.

• Bluetooth uses a form of TDMA called TDD-TDMA (time division duplex TDMA).

• Master and slave stations communicate with each other using time slots.

• The master in each piconet defines the time slot of 625 µsec.

• In TDD- TDMA, communication is half duplex in which receiver can send and receive data but not at the same time.

• If the piconet has only no slave; the master uses even numbered slots (0, 2, 4, ...) and the slave uses odd-numbered slots (1, 3, 5, .... ). Both master and slave communicate in half duplex mode. In slot 0, master sends & secondary receives; in slot 1, secondary sends and primary receives.

• If piconet has more than one slave, the master uses even numbered slots. The slave sends in the next odd-numbered slot if the packet in the previous slot was addressed to it.

• In Baseband layer, two types of links can be created between a master and slave. These are:

1. Asynchronous Connection-less (ACL)

• It is used for packet switched data that is available at irregular intervals.

• ACL delivers traffic on a best effort basis. Frames can be lost & may have to be retransmitted.

• A slave can have only one ACL link to its master.

• Thus ACL link is used where correct delivery is preferred over fast delivery.

• The ACL can achieve a maximum data rate of 721 kbps by using one, three or more slots.

2. Synchronous Connection Oriented (SCO)

• sco is used for real time data such as sound. It is used where fast delivery is preferred over accurate delivery.

• In an sco link, a physical link is created between the master and slave by reserving specific slots at regular intervals.

• Damaged packet; are not retransmitted over sco links.

• A slave can have three sco links with the master and can send data at 64 Kbps.

Logical Link, Control Adaptation Protocol Layer (L2CAP)

• The logical unit link control adaptation protocol is equivalent to logical link control sublayer of LAN.

• The ACL link uses L2CAP for data exchange but sco channel does not use it.

• The various function of L2CAP is:

1. Segmentation and reassembly

• L2CAP receives the packets of upto 64 KB from upper layers and divides them into frames for transmission.

• It adds extra information to define the location of frame in the original packet.

• The L2CAP reassembles the frame into packets again at the destination.

2. Multiplexing

• L2CAP performs multiplexing at sender side and demultiplexing at receiver side.

• At the sender site, it accepts data from one of the upper layer protocols frames them and deliver them to the Baseband layer.

• At the receiver site, it accepts a frame from the baseband layer, extracts the data, and delivers them to the appropriate protocol1ayer.

3. Quality of Service (QOS)

• L2CAP handles quality of service requirements, both when links are established and during normal operation.

• It also enables the devices to negotiate the maximum payload size during connection establishment.

Bluetooth Frame Format

The various fields of blue tooth frame format are:

                 Bluetooth Frame Format

1. Access Code: It is 72 bit field that contains synchronization bits. It identifies the master.

2. Header: This is 54-bit field. It contain 18 bit pattern that is repeated for 3 time.

The header field contains following subfields:

(i) Address: This 3 bit field can define upto seven slaves (1 to 7). If the address is zero, it is used for broadcast communication from primary to all secondaries.

(ii)Type: This 4 bit field identifies the type of data coming from upper layers.

(iii) F: This flow bit is used for flow control. When set to 1, it means the device is unable to receive more frames.

(iv) A: This bit is used for acknowledgement.

(v) S: This bit contains a sequence number of the frame to detect retransmission. As stop and wait protocol is used, one bit is sufficient.

(vi) Checksum: This 8 bit field contains checksum to detect errors in header.

3. Data: This field can be 0 to 2744 bits long. It contains data or control information coming from upper layers

by Dinesh Thakur Category: Communication Networks

We are talking of Wireless LAN (WLAN) that is to say, "Wireless LAN", not to be confused with WAN course. Also referred Radio LAN (WLAN) if the communication medium is the radio (not light infrared for example).The stations of the wireless network can communicate directly with each other, we called Ad Hoc network type, or via relay terminals called APs (Access Points, PA) then it is an infrastructure network. the second type is by far the most common in business.

by Dinesh Thakur Category: Communication Networks

Gigabit Ethernet or GbE, is the penultimate evolution of Ethernet standard. Several improvements have been made for it to Fast Ethernet at 100 Mbit/s.

When the IEEE approved the fast Ethernet standard, fast Ethernet provided 10 time’s higher bandwidth and other new features such as full-duplex operation and auto-negotiation. It established Ethernet as a scalable technology. Now, with the emerging Gigabit Ethernet standard, it is expected to scale even further. An industry consortium called the Fast Ethernet Alliance pushed the Fast Ethernet standard. In March 1996, the IEEE 802.3 committee approved the 802.3z Gigabit Ethernet Standardization project. At that time, as many as 54 companies expressed their intentions to participate in the standardization project. The Gigabit Ethernet Alliance was formed in May 1996 by 11companies. They are 3Com Corp., Bay Networks Inc., Cisco Systems Inc., Compaq Computer Corp., Granite Systems Inc., Intel Corporation, LSI Logic, Packet Engines Inc., Sun Microsystems Computer Company, UB Networks, and VLSI Technology.

by Dinesh Thakur Category: Communication Networks

Fast Ethernet is the name of the extension to 100 Mbit/s Ethernet network to 10 Mbit/s. This is the IEEE 802.3u working group that is at the origin. Access technique is the same as in the Ethernet Version 10 Mbit/s, but at a speed multiplied by 10. transported frames are identical. This increase in speed may conflict with the wiring system and the possibility or not there such important transit flows.

by Dinesh Thakur Category: Communication Networks

The parity check method is used fro error detection. It is also known as VRC method.

(a) In this method, a redundant bit called parity bit is added to each data.

by Dinesh Thakur Category: Communication Networks

• In all practical situations, the transmission of data needs to be bi-directional. This is called as full-duplex transmission.

• We can achieve this full duplex transmission i.e. by having two separate channels-one for forward data transfer and the other for separate transfer i.e. for acknowledgements.

by Dinesh Thakur Category: Communication Networks

• In sliding window method, multiple frames are sent by sender at a time before needing an acknowledgment.

• Multiple frames sent by source are acknowledged by receiver using a single ACK frame.

by Dinesh Thakur Category: Communication Networks

• In this method of flow control, the sender sends a single frame to receiver & waits for an acknowledgment.

• The next frame is sent by sender only when acknowledgment of previous frame is received.

by Dinesh Thakur Category: Communication Networks

Hamming code is technique developed by R.W. Hamming for error correction. This method corrects the error by finding the state at which the error has occurred.

by Dinesh Thakur Category: Communication Networks

Cyclic Redundancy Check (CRC) An error detection mechanism in which a special number is appended to a block of data in order to detect any changes introduced during storage (or transmission). The CRe is recalculated on retrieval (or reception) and compared to the value originally transmitted, which can reveal certain types of error. For example, a single corrupted bit in the data results in a one-bit change in the calculated CRC, but multiple corrupt bits may cancel each other out.

by Dinesh Thakur Category: Communication Networks

When data is being transmitted from one machine to another, it may be possible that data become corrupted on its, way. Some of the bits may be altered, damaged or lost during transmission. Such a condition is known as error.

by Dinesh Thakur Category: Communication Networks

The pair of twisted is the simplest transmission medium. it consists of one or more pairs of electrical son arranged spiral. This type of support is suitable for transmission both analog and digital.

by Dinesh Thakur Category: Communication Networks

Signal: A signal is the variation of an electrical current or another physical magnitude that is used to transmit information. For example, in telephony, there are different signals, consisting of a continuous or intermittent tone, a characteristic frequency, which allows the user to know in which situation the call located.

by Dinesh Thakur Category: Communication Networks

Computers are digital in nature. Computers process, store, and communicate information in binary form, i.e. in the combination of 1s and 0s which has specific meaning in computer language. A binary digit (bit) is an individual 1 or O. Multiple bit streams are used in a computer network.

by Dinesh Thakur Category: Communication Networks

Analog is best explained by the transmission of signal such as sound or human speech, over an electrified copper wire. In its native form, human speech is an oscillatory disturbance in the air. Which varies in terms of its volume or power (amplitude) and its pitch or tone (frequency)? Analogous variations in electrical or radio waves are created in order to transmit the analog information signal for video or audio or both over a network from a transmitter (TV station or CATV source) to a receiver (TV set, computer connected with antenna). At the receiving end an approximation (analog) of the original information is presented.

by Dinesh Thakur Category: Communication Networks

Definition Data Transmission: When we enter data into the computer via keyboard, each keyed element is encoded by the electronics within the keyboard into an equivalent binary coded pattern, using one of the standard coding schemes that are used for the interchange of information. To represent all characters of the keyboard, a unique pattern of 7 or 8 bits in size is used. The use of 7 bits means that 128 different elements can be represented, while 8 bits can represent 256 elements. A similar procedure is followed at the receiver that decodes every received binary pattern into the corresponding character.

by Dinesh Thakur Category: Communication Networks

Data communication refers to the exchange of data between a source and a receiver via form of transmission media such as a wire cable. Data communication is said to be local if communicating devices are in the same building or a similarly restricted geographical area.

by Dinesh Thakur Category: Communication Networks

Open System Interconnection (OSI) model, an ISO standard for worldwide communication Networks that defines a networking framework for implementing protocols in seven layers. Layering the communications process means breaking down the communication process into Smaller and Easier to handle interdependent categories. The convention and rules used in such communications are collectively known as Layer protocolOpen Systems Interconnection (OSI) model is developed by ISO (International organization for standardization) in 1984. ISO is the organization dedicated to defining global communication and standards.

by Dinesh Thakur Category: Communication Networks

Transmission media is a pathway that carries the information from sender to receiver. We use different types of cables or waves to transmit data. Data is transmitted normally through electrical or electromagnetic signals.


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Dinesh ThakurDinesh Thakur holds an B.C.A, MCSE, MCDBA, CCNA, CCNP, A+, SCJP certifications. Dinesh authors the hugely popular blog. Where he writes how-to guides around Computer fundamental , computer software, Computer programming, and web apps. For any type of query or something that you think is missing, please feel free to Contact us.