eetp bbt week2 final

8/16/2019 EETP BBT Week2 Final

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Broadband Technology(BB) Jumpering, LAN

2 JUMPERING ARRANGEMENT AT MDF FOR NEW &EXISTING CUSTOMER, LAN, NETWORKING

COMPONENTS & WLAN

STRUCTURE

2.1 INTRODUCTION

2.2 OBJECTIVE

2.3 MDF

2.4 LINE PARAMETERS

2.5 ISO MODEL

2.6 LAN ARCHITECTURE2.7 LAN TOPOLOGIES

2.8 MEDIA ACCESS CONTROL

2.9 LOGICAL LINK CONTROL

2.10 BASIC NETWORKING COMPONENTS

2.11 WIRELESS LAN

2.12 SUMMARY

2.13 SELF ASSESSMENT QUESTIONS

2.14 REFERENCES AND SUGGESTED FURTHER READINGS

2.1 INTRODUCTION

Main Distribution Frame (MDF) is a point of flexibility, where cables coming from customerside are to be connected to the telephone exchange equipment. MDF also provides means tohouse safety devices such as Gas Discharge Tube, Fuses etc. for protecting costly telephoneexchange equipment from surge voltage etc. Jumpering for a broadband customer has to bedone at MDF broadband Main Distribution Frame (MDF), as voice & data is coming fromcustomer premises on a common cable pair up to DSLAM. Splitter at DSLAM separates voice& data. Voice then is to be sent towards Telephone exchange. For this, jumpering is to bechanged in case of an existing landline customer (requesting add-on Broadband service). In caseof new broadband customer, the jumpering is to be directly done at Broadband MDF. The OSIis the reference model which acted as reference theoretical model for developing a workingmodel of Internet in the form of TCP/IP protocol suite. Established in 1947, the

EETP/BSNL Gold Certification Course/Ver.02/Jan ’2015 Page 1 of 19

For Restricted Circulation


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International Standards Organization (ISO) is a multinational body dedicated to worldwideagreement on international standards. An ISO standard that covers all aspects of networkcommunication is the Open Systems Interconnection (OSI) model (ISO/IEC 7498-1). An open system is a model that allows any two different systems to communicate regardlessof their underlying architecture. Vendor-specific protocols close off communication

between unrelated systems. The purpose of the OSI model is to open communication between different systems without requiring changes to the logic of the underlyinghardware and software. The OSI model is not a protocol: it is a model for understandingand designing a network architecture that is flexible, robust and interoperable. Networkingmeans interconnection of computers. These computers can be linked together for different

purposes and using a variety of different cabling types. The basic reasons why computers need to be networked are : ♦ to share resources (files, printers, modems, fax machines etc.)♦ to share application software (MS Office, Adobe Publisher etc.)♦ increase productivity (makes it easier to share data amongst users)

2.2 OBJECTIVES

The main objectives of this chapter are to understand: -

Termination of wiring in MDF

ADSL Subscriber Line Parameter

ISO Model Layered Architecure Layers of OSI Model The concept of Computer LAN

LAN Architecture

LAN Topology Various components of LAN

2.3 MDF: MAIN DISTRIBUTION FRAME

MDF is a distribution frame on one part of which the external trunk cables enteringa facility terminate, and on another part of which the internal user subscriber linesand trunk cabling to any intermediate distribution frames terminate. MDF is a cablerack that interconnects and manages the telecommunications wiring between itselfand any number of IDFs (Intermediate distribution frame), which connects internal

lines to the MDF. For example, an enterprise that encompasses a building withseveral floors may have one centralized MDF on the first floor and one IDF on eachof the floors that is connected to the MDF. A distribution frame is a passive device which terminates cables, allowing arbitraryinterconnections to be made. For example, the Main Distribution Frame (MDF) locatedat a telephone central office terminates the cables leading to subscribers on the onehand, and cables leading to active equipment (such as DSLAMs and telephone switches)on the other. Service is provided to a subscriber by manually wiring a




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twisted pair (called a jumper wire) between the telephone line and the relevant DSLor POTS line circuit as per diagram given below.

Following steps will be done for extending broadband connectivity to thecustomer premises for an existing & a new customer:-

For Existing Customer:-

1. Disconnect jumper wire between exchange side & a line side.2. Reconnect the jumper wire from the exchange side to the exchange side

tag bock of the DSLAM & line side to the line side tag block of theDSLAM. as shown in the above diag.

For New Customer:- Connect the jumper wire from the exchange side to the exchange side tag bock ofthe DSLAM & line side to the line side tag block of the DSLAM as shown in the

below diagram

Wiring of DSLAM port with inbuilt splitter

Wiring of DSLAM port with external splitter at MDF tag block

2.4 ADSL LINE CHARACTERISTICS

This appendix describes electrical line characteristics and considerations while deployingDSL service.

DC Loop Resistance

The subscriber line DC loop resistance value per kilometer for wires (with different corediameter) differs usually with a maximum limit:

The DC loop resistance for 0.32 mm core diameter should not be more than 470 /Km.




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The DC loop resistance for 0.4 mm core diameter should not be more than 290 /Km(typical value: 270 /Km).

The DC loop resistance for 0.5 mm core diameter should not be more than 190 /Km.

There may be subscriber lines with mixed core diameters in practice.

Insulation Resistance

Insulation resistance is the ratio of the DC voltage (U) imposed between cable cores (or between cores and ground) to the leakage current (I) that pass the core. Low insulationresistance causes current leakage, heavy loss of energy and signal attenuation. Also, withlow insulation resistance, line is more vulnerable to external ground-wire noise andcommon-mode interference.

The requirements for activating the ADSL service include insulation resistance between Line Aand Line B; and the Line A/B-to-ground insulation resistance should be higher than 5 M .

Wire-to-Wire Capacitance

Wire-to-wire capacitance indicates high-frequency transmission capability of line. Thegreater the wire-to-wire capacitance is, the greater the high-frequency signal attenuation is.The magnitude of wire-to-wire capacitance is also related to the core diameter and thelength of lines. For the line with core diameter of 0.32 mm, the length may be estimatedaccording to the capacitance value of 40 nF/Km; for line with core diameter of 0.4 mm and0.5 mm, the length may be estimated according to the capacitance value of 50 nF/Km.

Cross Talk

Crosstalk is a disturbance caused by the electric or magnetic fields of onetelecommunication signal affecting a signal in an adjacent circuit. In the ADSL service, theservices such as ISDN, POTS and ADSL on other adjacent line pairs in the same bundle ofcables can affect ADSL. For the ISDN and POTS services, the main crosstalk noise is thenear-end crosstalk (NEXT).

For the ADSL, as the frequency division modulation (FDM) is used and the frequency bands occupied by the uplink and downlink signals are separate, the crosstalk noise ismainly the influence of the far-end crosstalk (FEXT).

Line Attenuation

At present, DMT modulation mode is adopted for ADSL with the working frequencyranging from 26 KHz to 1,104 KHz. Line attenuation is in direct proportion to the distance.The greater the carrier frequency is, the greater the line attenuation is. As the line frequencyincreases (exceeding 300 KHz), frequency can be regarded as in direct proportion to thesquare root of the carrier frequency. The bigger the twisted-pair cable diameter is, the lessthe attenuation is, and the farther the transmission distance is.

The following are the requirements for activating the ADSL services:




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i. The attenuation values per kilometer (dB/Km) under normal temperature of the cable pairs of different core diameters stipulated in the industry specification YD322-96 areshown in Table 1.

T A B L E 1 – A T T E N U A TI O N V A L U E S P E R K I LO M E T E R

Core Attenuation at 150 KHz Attenuation at 1,024 KHz Diameter (dB) (dB)

Polyolefin (mm)

insulation 0.32 16.8 33.5 cable in

0.4 12.1 27.3 solid core 0.5 9.0 22.5

0.6 7.2 18.5

Core Attenuation at 150 KHz Attenuation at 1,024 KHz Diameter

Filled (dB) (dB) (mm) polyolefin 0.32 16.0 33.1 insulation

0.4 11.7 23.6 cable in solid core 0.5 8.2 18.6

0.6 6.7 15.8

ii. The DAC bits of the ADSL transmitter determine the maximum SNR as 78 dB to 84 dBafter quantification. Considering the error rate requirements after decoding at the

receive side, the SNR must be larger than 14.5 db; considering the encoding gain for theADSL system, the ADSL service cannot be activated if the line attenuation of the sub-channel is larger than 70 dB.

Idle Channel Noise

Idle channel noise is noise present in a communication channel when no signals are applied.The channel conditions and terminations must be stated for idle-channel noisemeasurements to be meaningful. Idle channel noise is usually caused due to the backgroundnoise of adjacent lines and is an important parameter for calculating the S/N, which directlyreflects the quality of transmission performance and the length of transmission distance.

Line Impedance

If the line characteristic impedance does not match the ADSL equipment port impedance, orthe impedance is not continuous when twisted pair cables with different line widths areconnected, mismatched impedance will be caused and signal reflection will be generated.Reflected signals will cause loss of signal energy and extra interference in the line, thusaffecting line stability.




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The requirements for activating the ADSL service: The nominal feature impedance of linesis 100 . The error should not be over 10%.

2.5 ISO MODEL

The Open Systems Interconnection model is a layered framework for the design of networksystems that allows for communication across all types of computer systems. It consists ofseven separate but related layers, each of which defines a segment of the process of movinginformation across a network. Understanding the fundamentals of the OSI model provides asolid basis for exploration of data communication.

2.5.1.1 WAN protocol architecture

The OSI model is built of seven ordered layers: Physical (layer 1), Data link (layer 2), Network (layer 3), Transport (layer 4), Session (layer 5), Presentation (layer 6), andApplication (layer 7). The Control is passed from one layer to the next, starting at the application layer in onestation, and proceeding to the bottom layer, over the channel to the next station and back upthe hierarchy. During the process data is encapsulated from the higher layer to the lowerlayer and reverse is performed at the other end.

2.5.1.1 WAN protocol architecture

In OSI reference model there seven layers of protocols. Each layer provides services to thelayer above it. There are in all seven layers of in OSI. They are:

1. Physical Layer: It is the lower most layer of the OSI reference model. It is layer which isresponsible for direct interaction of the OSI model with hardware. The hardware providesservice to the physical layer and it provides service to the datalink layer.

The physical layer defines electrical and physicalspecifications for devices. In particular, it defines therelationship between a device and a transmissionmedium, such as a copper or fiber optical cable. Thisincludes the layout of pins, voltages, line impedance,cable specifications, signal timing, hubs, repeaters,network adapters, host bus adapters (HBA used in storagearea networks) and more. The major functions and services performed by the

physical layer are: Establishment and termination of a connection to a

communications medium.

Participation in the process whereby thecommunication resources are effectively sharedamong multiple users. For example, contentionresolution and flow control.

Modulation or conversion between the representation of digital data in user equipmentand the corresponding signals transmitted over a communications channel. These are




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signals operating over the physical cabling (such as copper and optical fiber) or over aradio link.

2. Datalink Layer: There may be certain errors which may occur at the physical layer. If possible, these errors are corrected by the datalink layer. The datalink layer provides theway by which various entities can transfer the data to the network.

The data link layer provides the functional and procedural means to transfer data betweennetwork entities and to detect and possibly correct errors that may occur in the physicallayer. Originally, this layer was intended for point-to-point and point-to-multipoint media,characteristic of wide area media in the telephone system. Local area network architecture, which included broadcast-capable multi-access media, wasdeveloped independently of the ISO work in IEEE Project 802. IEEE work assumedsublayer-ing and management functions not required for WAN use. In modern practice,only error detection, not flow control using sliding window, is present in data link protocolssuch as Point-to-Point Protocol (PPP), and, on local area networks, the IEEE 802.2 LLClayer is not used for most protocols on the Ethernet, and on other local area networks, its

flow control and acknowledgment mechanisms are rarely used. Sliding window flowcontrol and acknowledgment is used at the transport layer by protocols such as TCP, but isstill used in niches where X.25 offers performance advantages. The ITU-T G.hn standard, which provides high-speed local area networking over existing

wires (power lines, phone lines and coaxial cables), includes a complete data link layerwhich provides both error correction and flow control by means of a selective repeat SlidingWindow Protocol. Both WAN and LAN service arrange bits, from the physical layer, into logical sequences

called frames. Not all physical layer bits necessarily go into frames, as some of these bitsare purely intended for physical layer functions. For example, every fifth bit of the FDDI bitstream is not used by the layer.

2.5.1.2 WAN protocol architectureConnection-oriented WAN data link protocols, in addition to framing, detect and maycorrect errors. They are also capable of controlling the rate of transmission. A WAN datalink layer might implement a sliding window flow control and acknowledgment mechanismto provide reliable delivery of frames.

2.5.1.3 IEEE 802 LAN architecturePractical, connectionless LANs began with the pre-IEEE Ethernet specification, which isthe ancestor of IEEE 802.3. This layer manages the interaction of devices with a sharedmedium, which is the function of a media access control (MAC) sub-layer. Above thisMAC sub-layer is the media-independent IEEE 802.2 Logical Link Control (LLC) sub-layer, which deals with addressing and multiplexing on multi-access media. While IEEE 802.3 is the dominant wired LAN protocol and IEEE 802.11 the wireless LAN

protocol, obsolete MAC layers include Token Ring and FDDI. The MAC sub-layer detects but does not correct errors.

3. Network Layer: It does not allow the quality of the service to be degraded that wasrequested by the transport layer. It is also responsible for data transfer sequence from sourceto destination.




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The network layer provides the functional and procedural means of transferring variablelength data sequences from a source host on one network to a destination host on a differentnetwork (in contrast to the data link layer which connects hosts within the same network),while maintaining the quality of service requested by the transport layer. The network layer

performs network routing functions, and might also perform fragmentation and reassembly,and report delivery errors. Routers operate at this layer, sending data throughout the

extended network and making the Internet possible. This is a logical addressing scheme – values are chosen by the network engineer. The addressing scheme is not hierarchical. The network layer may be divided into three sublayers:

1) Subnetwork access – that considers protocols that deal with the interface to networks, such as X.25;

2) Subnetwork-dependent convergence – when it is necessary to bring the level of atransit network up to the level of networks on either side

3) Subnetwork-independent convergence – handles transfer across multiple networks.

It manages the connectionless transfer of data one hop at a time, from end system to ingressrouter, router to router, and from egress router to destination end system. It is notresponsible for reliable delivery to a next hop, but only for the detection of erroneous

packets so they may be discarded. A number of layer-management protocols belong to the network layer. These includerouting protocols, multicast group management, network-layer information and error, andnetwork-layer address assignment. It is the function of the payload that makes these belongto the network layer, not the protocol that carries them.

4. Transport Layer: The reliability of the data is ensured by the transport layer. It alsoretransmits those data that fail to reach the destination.

The transport layer provides transparent transfer of data between end users, providingreliable data transfer services to the upper layers. The transport layer controls the reliabilityof a given link through flow control, segmentation/desegmentation, and error control. Some

protocols are state- and connection-oriented. This means that the transport layer can keeptrack of the segments and retransmit those that fail. The transport layer also provides theacknowledgement of the successful data transmission and sends the next data if no errorsoccurred. Although not developed under the OSI Reference Model and not strictly conforming to theOSI definition of the transport layer, the Transmission Control Protocol (TCP) and the UserDatagram Protocol (UDP) of the Internet Protocol Suite are commonly categorized as layer-4 protocols within OSI.

5. Session Layer: The session layer is responsible for creating and terminating the connection. Management of such a connection is taken care of by the session layer.

The session layer controls the dialogues (connections) between computers. It establishes,manages and terminates the connections between the local and remote application. It providesfor full-duplex, half-duplex, or simplex operation, and establishes checkpointing, adjournment,termination, and restart procedures. The OSI model made this layer responsible for gracefulclose of sessions, which is a property of the Transmission Control Protocol, and also for sessioncheck pointing and recovery, which is not usually used in the Internet Protocol Suite. Thesession layer is commonly implemented explicitly in application




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environments that use remote procedure calls. On this level, Inter-Process communicationhappen (SIGHUP, SIGKILL, End Process, etc.).

6. Presentation Layer: This layer is responsible for decoding the context (syntax andsemantics) of the higher level entities.

The presentation layer establishes context between application-layer entities, in which thehigher-layer entities may use different syntax and semantics if the presentation service provides a mapping between them. If a mapping is available, presentation service data unitsare encapsulated into session protocol data units, and passed down the stack. This layer provides independence from data representation (e.g., encryption) by translating

between application and network formats. The presentation layer transforms data into theform that the application accepts. This layer formats and encrypts data to be sent across anetwork. It is sometimes called the syntax layer. The original presentation structure used the Basic Encoding Rules of Abstract Syntax

Notation One (ASN.1), with capabilities such as converting an EBCDIC-coded text file toan ASCII-coded file, or serialization of objects and other data structures from and to XML.

7. Application Layer: Whichever software application that implements socket programming will communicate with this layer. This layer is closest to the user.

The application layer is the OSI layer closest to the end user, which means that both the OSIapplication layer and the user interact directly with the software application. This layerinteracts with software applications that implement a communicating component. Suchapplication programs fall outside the scope of the OSI model. Application-layer functionstypically include identifying communication partners, determining resource availability, andsynchronizing communication. When identifying communication partners, the applicationlayer determines the identity and availability of communication partners for an applicationwith data to transmit. When determining resource availability, the application layer mustdecide whether sufficient network or the requested communication exist. In synchronizingcommunication, all communication between applications requires cooperation that ismanaged by the application layer. Some examples of application-layer implementations alsoinclude: On OSI stack:

FTAM File Transfer and Access Management Protocol X.400 Mail Common Management Information Protocol (CMIP)

2.6 LAN ARCHITECTURE

Networking means interconnection of computers. These computers can be linked togetherfor different purposes and using a variety of different cabling types. The basic reasons why computers need to be networked are : ♦ to share resources (files, printers, modems, fax machines etc.)♦ to share application software (MS Office, Adobe Publisher etc.)♦ increase productivity (makes it easier to share data amongst users)




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Small networks are often called Local Area Networks (LAN). A LAN is a network allowingeasy access to other computers or peripherals. The typical characteristics of a LAN are : ♦ physically limited distance (< 2km)♦ high bandwidth (> 1mbps)♦ inexpensive cable media (coaxial or twisted pair)♦ data and hardware sharing between users♦ owned by the user

The factors that determine the nature of a LAN are : ♦ Topology♦ Transmission medium♦ Medium access control technique

The layered protocol concept can be employed to describe the architecture of aLAN, wherein each layer represents the basic functions of a LAN. LAN protocols areconcerned primarily with the lower layers of the OSI model.

The lowest layer of the IEEE 802 reference model corresponds to the physical layer of theOSI model, and includes the following functions : ♦ Encoding/ decoding of signals♦ Preamble generation/ removal (for synchronisation)♦ Bit transmission/ reception

The physical layer of the 802 model also includes a specification for the transmissionmedium and the topology. Generally, this is considered below the lowest layer of the OSImodel. However, the choice of the transmission medium and topology is critical in LANdesign, and so a specification of the medium is included.

Above the physical layer are the functions associated with providing service to theLAN users. These comprise : ♦ Assembling data into a frame with address and error-detection fields for onward

transmission.♦ Disassemble frame, perform address recognition and error detection duringreception. ♦ Supervise and control the access to the LAN transmission medium.♦ Provide an interface to the higher layers and perform flow control and error control.

The above functions are typically associated with OSI layer 2. The last function notedabove is grouped in to a logical link control (LLC) layer. The functions in the first three

bullet items are treated as a separate layer, called medium access control (MAC). Theseparation is done for the following reasons:

♦ The logic and mechanism required to manage access to a shared-access medium isnot found in the conventional layer-2 data link control.♦ For the same LLC, different MAC options may be provided.




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2.7 LAN TOPOLOGIES

The common topologies for LANs are bus, tree, ring, and star. The bus is a special case ofthe tree, with only one trunk and no branches.

Bus and Tree Topologies

Bus and Tree topologies are characterised by the use of a multi-point medium. For the busall stations attach, through appropriate hardware interfaces known as a Tap , directly to alinear transmission medium, or bus. Full-duplex operation between the station and the tap

permits data to be transmitted onto the bus and received from the bus. A transmission fromany station propagates throughout the length of the medium in both directions and can bereceived (heard) by all other stations. At each end of the bus is a terminator, to avoidreflection of signals.

Tap Flow of data Terminating

Resistance

Station

Fig. (a) Bus

Head-end

Fig. (b) Tree

The tree topology is a generalisation of the bus topology. The transmission medium is a branched cable with no closed loops. The tree layout begins at a point known as the head-end , where one or more cable start, and each of these may have branches. The branches in turn may have additional branches. Transmission from any station propagates throughoutthe medium and can be received (heard) by all other stations.




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Ring Topology

In the ring topology, the network consists of a set of repeaters joined by point-to point linksin a closed loop. The repeater is a comparatively simple device, capable of receiving dataon one link and transmitting them, bit by bit, on the other link as quickly as they are

received, with no buffering at the repeater. The links are unidirectional, i.e. data istransmitted in one direction (clockwise or counter-clockwise).

Each station is attached to the network at a repeater and can transmit data onto the networkthrough that repeater.

Ring

Star Topology

In the Star type topology, each station is directly connected to a common central node.Typically, each station attaches to a central node, referred to as the star coupler, via two

point-to point links, one for transmission in each direction.

In general, there are two alternatives for the operation of the central node :

One method is for the central node to operate in a broadcast fashion. The transmission of a frame from one station to the Central Node is retransmitted in all of the outgoing links. Inthis case, although the arrangement is physically a star, it is logically a bus; a transmissionfrom any station is received by all other stations, and only one station at a time maytransmit (successfully).

Another method is for the central node to act as a frame switching device. An incoming frame is buffered in the node and then retransmitted on an outgoing link to the destination station.

Central Hub,

Switch/ Repeater




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2.8 MEDIUM ACCESS CONTROL

All LANs consist of a collection of devices that have to share the network’ s transmissioncapacity. Some means of controlling access to the transmission medium is needed to

provide for an orderly and efficient use of that capacity. This is the function of mediumaccess control (MAC) protocol.

The MAC layer receives a block of data from the LLC layer and is responsible for performing functions related to medium access and for transmitting the data. MACimplements these functions, by making use of protocol data unit at its layer; in this case, thePDU is referred to as a MAC frame. In general, the fields of this frame are :

♦ MAC control : This field contains any protocol control information needed for the functioning of the MAC protocol. For example, a priority level could be indicated here.

♦ Destination MAC Address : The destination physical attachment point on the LAN for this frame.

♦ Source MAC address : The source physical attachment point on the LAN for thisframe. ♦ LLC : The LLC Data from the next higher layer. ♦ CRC : The cyclic redundancy check field ( also known as the frame check sequence,

FCS, field). This is an error-detecting code, as we have seen in HDLC and other datalink control protocols

MAC

MAC Destination Source LLC PDU CRC Frame control MAC MAC

Generic MAC Frame format.

In most of the data link control protocols, the data link protocol entity is responsible notonly for detecting errors using the CRC, but for recovering from those errors by re-transmitting damaged frames. In the LAN protocol architecture, these two functions aresplit between the MAC and LLC layers. The MAC layer is responsible for detecting errorsand discarding any frames that are in error. The LLC layer optionally keeps track of whichframes have been successfully received and retransmits unsuccessful frames.

2.9 LOGICAL LINK CONTROLLLC is concerned with the transmission of a link-level protocol data unit (PDU) betweentwo stations, without the necessity of an intermediate switching node. LLC has twocharacteristics not shared by most other link control protocols : ♦ It must support the multi-access, shared-medium nature of the link.♦ It is relieved of some details of link access by the MAC layer.




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2.10 BASIC NETWORK COMPONENTS

There are a number of components which are used to build networks. An understandingof these is essential in order to support networks.

Network Adapter Cards A network adapter card plugs into the workstation, providing the connection to the network.Adapter cards come from many different manufacturers, and support a wide variety of cablemedia and bus types such as - ISA, MCA, EISA, PCI, PCMCIA.

New cards are software configurable, using a software programs to configure the resourcesused by the card. Other cards are PNP (plug and Play), which automatically configure theirresources when installed in the computer, simplifying the installation. With an operatingsystem like Windows 95, auto-detection of new hardware makes network connectionssimple and quick.

Cabling Cables are used to interconnect computers and network components together. There are 3main cable types used today :

♦ twisted pair♦ coaxial♦ fibre optic

The choice of cable depends upon a number of factors like : ♦ cost♦ distance♦ number of computers involved♦ speed♦ bandwidth i.e. how fast data is to be transferred

REPEATERS Repeaters extend the network segments. They amplify the incoming signal received fromone segment and send it on to all other attached segments. This allows the distancelimitations of network cabling to be extended. It does not give any more bandwidth or allowto transmit data faster.

Repeaters also allow isolation of segments in the event of failures or fault conditions. Arepeater works at the Physical Layer by simply repeating all data from one segment toanother.

Summary of Repeater features : ♦ increases traffic on segments♦ have distance limitations♦ limitations on the number of repeaters that can be used♦ propagate errors in the network♦ cannot be administered or controlled via remote access♦ cannot loop back to itself (must be unique single paths)




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no traffic isolation or filtering is possible

BRIDGES Bridges interconnect Ethernet segments. Most bridges today support filtering andforwarding, as well as Spanning Tree Algorithm. The IEEE 802.1D specification is thestandard for bridges.

During initialisation, the bridge learns about the network and the routes. Packets are passedonto other network segments based on the MAC layer. Each time the bridge is presentedwith a frame, the source address is stored. The bridge builds up a table which identifies thesegment to which the device is located on. This internal table is then used to determinewhich segment incoming frames should be forwarded to.

The diagram above shows two separate network segments connected via a bridge. Note thateach segment must have a unique network address number in order for the bridge to be ableto forward packets from one segment to the other.

Bridges work at the Media Access Control sub-layer of the Data Link layer of the OSI model.

Summary of Bridge features : ♦ operate at the MAC layer (layer 2 of the OSI model)♦ can reduce traffic on other segments♦ broadcasts are forwarded to every segment♦ most allow remote access and configuration♦ often SNMP (Simple Network Management Protocol) enabled♦ loops can be used (redundant paths) if using spanning tree algorithm♦ small delays may be introduced♦ fault tolerant by isolating fault segments and reconfiguring paths in the event offailure ♦ not efficient with complex networks♦ redundant paths to other networks are not used (would be useful if the major path being

used♦ was overloaded)♦ shortest path is not always chosen by the spanning tree algorithm

ROUTERS In an environment consisting of several network segments with differing protocols andarchitectures, a bridge may not be adequate for ensuring fast communication among all ofthe segments. A network this complex needs a device which not only knows the address ofeach segment, but also determine the best path for sending data and filtering broadcasttraffic to the local segment. Such a device is called a router.

Routers work at the Network layer of the OSI model. This means they can switch and route packets across multiple networks. They do this by exchanging protocol-specific information between separate networks. Routers read complex network addressing information in the packet and, because they function at a higher layer in the OSI model than bridges, they haveaccess to additional information.

Routers can provide the following functions of a bridge : ♦ Filtering and isolating traffic♦ Connecting network segments




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Routers have access to more information in the packet than bridges, and use thisinformation to improve packet deliveries. Routers are used in complex network situation

because they provide better traffic management than bridges and do not pass broadcasttraffic. Routers can share status and routing information with one another and use thisinformation to bypass slow or malfunctioning connections.

How Routers Work

The routing table found in routes contain network addresses. However, host addresses may be kept depending on the protocol the network is running. A router uses a table to determinethe destination address for incoming data. The table lists the following information :

♦ All known network addresses♦ How to connect to other networks♦ The possible path between those routers♦ The cost of sending data over those paths

The router selects the best route for the data based on cost and available paths.

Summary of Router features : ♦ use dynamic routing♦ operate at the protocol level♦ remote administration and configuration via SNMP♦ support complex networks♦ the more filtering done, the lower the performance♦ provides security♦ segment the networks logically♦ broadcast storms can be isolated♦ often provide bridge functions also♦ more complex routing protocols used (such as RIP, IGRP, OSPF)

Hubs & Switches There are many types of hubs. Passive hubs are simple splitters or combiners that groupworkstations into a single segment, whereas active hubs include a repeater function and arethus capable of supporting many more connections.

Nowadays, with the advent of 10BaseT, hub concentrators are being very popular. These arevery sophisticated and offer significant features which make them radically different from theolder hubs which were available during the 1980's. These 10BaseT hubs provide each client

with exclusive access to the full bandwidth, unlike bus networks where the bandwidth is shared.Each workstation plugs into a separate port, which runs at 10 Mbps and is for the exclusive useof that workstation, thus there is no contention to worry about like in Ethernet.

In standard Ethernet, all stations are connected to the same network segment in busconfiguration. Traffic on the bus is controlled using CSMA (Carrier Sense Multiple Access)

protocol, and all stations share the available bandwidth.




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10BaseT Hubs dedicate the entire bandwidth to each port (workstation). The W/S attach tothe Hub using UTP. The Hub provides a number of ports, which are logically combinedusing a single backplane, which often runs at a much higher data rate than that of the ports.

Ports can also be buffered, to allow packets to be held in case the hub or port is busy. And, because each workstation has its own port, it does not contend with other workstations for

access, having the entire bandwidth available for its exclusive use.

The ports on a hub all appear as one Ethernet segment. In addition, hubs can be stacked orcascaded (using master/ slave configurations) together, to add more ports per segment. Ashubs do not count as repeaters, this is a better solution for adding more workstations thanthe use of a repeater.

Hub options also include an SNMP (Simple Network Management Protocol) agent. Thisallows the use of network management software to remotely administer and configure thehub.

The advantages of the newer 10 BaseT hubs are : ♦ Each port has exclusive access to its bandwidth (no CSMA/ CD)♦ Hubs may be cascaded to add additional ports♦ SNMP managed hubs offer good management tools and statistics♦ Utilise existing cabling and other network components♦ Becoming a low cost solution

2.11 WIRELESS LAN

A wireless local area network (LAN) utilizes radio frequency (RF) as an alternative for awired LAN. Wireless LANs transmit and receive data over the air, without the use of anycable, combining the benefits of data connectivity and user mobility.

Need for Wireless LAN

The widespread reliance on networking in business and the explosive growth of the Internetreveal the benefits of shared data and shared resources. With wireless LANs, users canaccess shared information and resources without looking for a place to plug in, and networkmanagers can set up networks without installing or moving wires. Wireless LANs provideall the functionality of wired LANs with the following benefits:

Mobility: Wireless LANs can provide users with access to real-time information and resources anywhere in their organization through designated access points. This freedom to"roam" increases employee productivity as they move throughout the building.

Installation Speed and Simplicity: Installing a wireless LAN system can be fast and easy and eliminates the need to pull cable through walls and ceilings.

Installation flexibility: Wireless technology allows the network to go where wires cannot go.

Scalability: Configurations for wireless LANs are easily changed and range from peer-to- peer networks suitable for a small number of users to full infrastructure networks of




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thousands of users that enable roaming over a broad area. Adding a user to the network is assimple as equipping a PC or laptop with a wireless LAN adapter card or USB device.

How do Wireless LANs Work?

Wireless LANs use radio airwaves to communicate information from one point to another

without relying on any physical connection. Radio waves are often referred to as radiocarriers because they simply perform the function of delivering energy to a remote receiver.The data being transmitted is superimposed (modulated) on the radio carrier so that it can

be accurately extracted at the receiving end.

In a typical wireless LAN configuration, a transmitter/receiver device, called an access point(AP), connects to the wired network from a fixed location using standard cabling. The access

point serves as a communications "hub" that receives, buffers, and transmits data between thewireless clients and the wired LAN. A single access point can support a small group of usersand can function within a range of less than one hundred to several hundred feet. The access

point (or antenna attached to the access point) is usually mounted high but may be mountedessentially anywhere that is practical as long as the desired radio coverage is obtained.

End users access the wireless LAN through wireless LAN adapters. These aremostly implemented as PC cards in notebook computers, PCI cards in desktop computers oras USB devices. Wireless LAN adapters provide an interface between the client networkoperating system (NOS) and the airwaves via an antenna

2.12 SUMMARY

Jumpering rearrangement in case of existing landline customer (requesting add-onBroadband service) to Broadband MDF and fresh jumpering in case of new broadbandcustomer is required as the data traffic is to be separated from voice at DSLAM. OSI modelis reference model which clearly mentions the independent functions of each layer. This hasresulted in developments in different layered areas irrespective of the functionality in otherlayers. Networking components are very essential for developing a network. They providemeans & ways to lay networks as per actual requirements.

2.13 SELF ASSESSMENT QUESTIONS

a) What are the different layers in OSI model?b) What are the advantages of having layered OSI architecture?c) What is the importance of physical layer?d) Explain the Transport layer function.e) Explain the function of transport layer

f) What do you mean by LAN topologies?g) Why media access control is required in LANs?h) How LAN components are useful in developing networks?i) What is MDF?

j) What is the purpose to install MDF in telephone exchanges?k) What are line parameters?




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2.14 REFERENCES AND SUGGESTED FURTHER READINGS

Andrew S. Tanenbaum, D. J. (2010). Computer Networks (5th Edition). RFC - Internet Official Protocol Standards. (n.d.).

Stallings, W. (2010). Data and Computer Communications (9th Edition). http://en.wikipedia.org/

Website www.bsnl.co.in Website www.datanetwork.bsnl.co.in Wi-Fi security by Stewart S Miller WPA & 802.11i by William A Arbaugh Wireless home networking for dummies


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