Chapter 8 _ Protocol Architecture _ Computer Networks

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Chapter 1- Introduction

Chapter 2- Transmission Media

Chapter 3-Encoding And

Modulating

Chapter 4- Digital Data

Communication

Chapter 5- MULTIPLEXING AND

SWITCHING

Chapter 6- SPREAD SPECTRUM

Chapter 7- ERROR DETECTION

AND CORRECTION

Chapter 8- PROTOCOL

ARCHITECTURE

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Chapter 8 : Protocol Architecture

Q. 1. Define Protocol architecture.

Ans.

Protocol architecture is the layered structure of hardware and software that supports theexchange of data between system and supports distributed applications, such as electronicmail and file transfer etc.

Q. 2. What is a Protocol?

Ans.

A protocol is a set of rules that governs data communications. A protocol defines what iscommunicated, how it is communicated and when it is communicated. The key elements oprotocol are

(a) Syntax: Syntax is defined as structure or format of data, meaning the order in whichthey are presented.

(b) Semantics: It refers to the meaning of each section of bits. It includes that how is aparticular pattern to be interpreted and when action is to be taken based on thatinterpretation.

(c) Timing: It includes two characteristics when data should be sent and how fast they canbe sent.

Q. 3. What do you mean by standards?

Ans.

Standards are very important factors in telecommunication technology and process. Theyprovide guidelines to manufactures, vendors, govt. agencies, etc. Data comm. standards

can be classified as following:

1. De facto: These are the standards that have not been approved by an organized bodybut have been adopted as standards through wider spread use.

2. De Jure : Those that have been legislated by an officially recognized body.

Q. 4. Name any four standards creation committees.

Ans.





1. International organization for standards (ISO)

2. American National standards Institute (ANSI).

3. Institute of electrical and electronics engineers (IEEE).

4. Electronic Industries Association (EIA).

Q. 5. Discuss simple protocol architecture?

Ans.

Instead of a single module for performing communications, there is a structured set omodules that implement the communication functions. The structure is referred to asprotocol architecture. The following figure suggests the way in which a file transfer facilitycould be implemented.

In this three modules are used.

1 .File transfer module: this module is responsible for making sure that the file transfecommands and data are reliably exchanged between systems. Hence file transfer modulecontains all of the logic that is unique to the file transfer applications, such as transmittingpasswords, file commands, and file records

2. Communications service modules: It is concerned with assuring that the twocomputer systems are active and ready for data transfer and for keeping track of data thaare being exchanged to assure delivery

3. Network access module: Because these tasks are independent of the type of networkthat is being used Therefore the logic for actually dealing with the network is placed in aseparate network access module. That way, if the network to be used is changed only thenetwork access module is affected

Q 6 What is the main communication agents’

Ans

The communication agents are those who help in transforming the information from oneplace to another place. in general communications can be said to involve three agents :-

1. Applications

2. Computers





3. Networks

Application execute on computers that typically support multiple simultaneous applications

Computers are connected to network and the data to be exchanged are transferred by thenetwork from one computer to another. Thus the transfer of data from one application toanother involves first getting the data to the computer in which the application resides andthen getting it to the intended application within the computer

Q. 7. Explain the Three layer model briefly.

Ans.

We can organize the communication task into three independent layers:

1. Network access layer: It is concerned with exchange of data between a computer andthe network to which it is attached. The sending computer must provide the network withthe address of destination computer, so that the network may route the data to theappropriate destination. The specific software used at the layer depends on the type onetwork to be used. Different standards have been developed for circuit switching, packeswitching, LAN’s and others.

2. Transport layer: Regardless of nature of applications that are exchanging data, thereis usually a requirement that data be exchanged reliably. That is we would like to beassured that all of the data arrive at the destination application and that the data arrived inthe same order in which they were sent. The mechanisms for providing reliability areindependent of nature of applications. Thus it makes sense to correct those mechanisms ina common layer shared by all applications this is referred to as transport layer.

3. Application layer: Application layer contains the logic needed to support the varioususer applications. For each different type of application such as file transfer, a separatemodule is needed that is peculiar to that application.

Fig. illustrates the simple architecture. It shows the three computers connected to anetwork. Each computer contains software at the network access and transport layers andsoftware at the application layer for one or more applications. For successfucommunication, every entity in overall system must have a unique address.

Q. 8. Define service access points?

Ans.

Each application on a computer must have a unique network address. This allows thenetwork to deliver data to the proper computer. Each application on a computer must havean address that is unique within that computer. This allows the transport Layer to suppor





multiple applications at each computer. These latter addresses are known as serviceaccess points (SAPs)

Q. 9. What is interface data unit (IDU)?

Ans.

The set of rules about the interface should be present for successful exchange o

information between two layers. The IDU consists of two parts:

(a) SDU (Service data unit)

(b) ICI (Interface control information)

Q. 10. Define service data unit (SDU).

Ans.

SDU is a part of IDU. The SDU is the information passed across the network to the peerentity and then up to layer (n + 1).

Q. 11. Define IC! (Interface control Unit).

Ans.

ICI contains the control information which is necessary to help the lower layer (n) to dothe necessary job.

Q. 12. What is PDU (Protocol Data Unit) ?

Ans.

In order to transfer the SDU, the layer n entity has to divide it into many smaller pieces

Each piece is given a header and sent as a separate PDU such as a packet

The PDU headers are used by the peer entities to carry out their peer protocol. Some

PDUs contain data while other PDUs contain the control information. The PDU headers wilidentify or differentiate between different types of PIJUs. They also provide sequencenumbers and counts. .

Q. 13. What are the Merits and demerits of Os! Reference model?

Ans.





Merits:

1. The protocols in OSI model are better hidden. So they can be easily replaced by newprotocols as the technology changes.

2. OSI model is truly a general model.

3. It distinguishes very clearly between the services, interfaces and protocols.

4. This, model supports connection oriented as well as connectionless services,

Demerits:

1. Sessions and presentation layers are not of much use.

2. This model was devised before the protocols were invented. So in real life there is aproblem of fitting protocol into model.

Q. 14. Write a short note on LAN.

Ans.

These networks connect computers and other information processing devices, which arelocated within a limited physical area, like office, classroom, building, factory, work siteetc. LANs are essentially a part of many organizations for providing telecommunicationsnetwork capabilities to the end users.

Most of LANs use a range of communication media, like twisted pair wire, coaxial cablewireless radio etc. which we have already learnt about to interconnect various micro-computers and work stations. For making this communication possible, every PC has thecircuit board known as “network interface card.” Most of LANs use a powerfumicrocomputer having a large hard disk, which is known as network server, which has anetwork operating system which controls telecommunications and the use and sharing o

network resources.

Q. 15. Write a short note on WANs.

Ans.

As most of the organizations are very widespread. Whose offices are not limited tobuilding, they may be spread throughout large city of metropolitan area. Thecommunication networks, which cover large geographic areas, are called wide area

networks. These networks have become quite necessary in the current era, where the dayto day activities of many business organizations are spread thought. WANs are used bymany companies for transmitting and receiving information among the workers, customersclients etc across cities, regions, countries etc. These networks usually have a globaconnectivity also.

Q. 16. Define Internet?

Ans.





As the business operations are becoming, global, where one has to have connectivity withglobal customers, other organization etc. This connectivity is done by connecting manyLANs using wide area networks. These inter connected networks are generally known asinter network or popularly known as Internet. We can define internet as a network onetworks, which connects different organizations, to share information, resource etc. Thesenetworks enable end users to communicate with other users on other LANs, so that onecan access the computing resources, organizations. These networks for their connectivityrely on inter networks processors like switches, routers hub gateways etc.

Q. 17. Write a short note on intranet.

Ans.

The basic goal of many organizations is to create connectivity between each and everybranches of the organization. The network which connects the various locations and givesconnectivity within the organization is called intranet. These networks are limited to theorganization for which they are setup. These intranets can be connected to other intranetsand extranets forming internet.

Intranets are designed to be open with security, whose web browsing to the end usersThere internal websites may be designed by company, its business, Units, departmentsworkgroups etc. For example, a marketing department may design an intranet website sothat anyone can know about their products and, services an. have detail information abouthem.

Q. 18. What is Extranet?

Ans.

There are those networks, which link some of the internets of the company with those oits business partners, customers, suppliers, consultants, etc., who cart access selectedintranet websites and company’s databases.

Most of the organizations establish private extranets among themselves, so that they can

be real business partners, who share information, resources etc. Instead of privateextranets, organizations can also use the internet, to establish network connectionsbetween them. Some organizations use virtual private networks (VPNs) to establish secureIntranets and Extranets.

Q. 19. Write down the difference between OSI and TCP/IP model.

Ans.





Q 20 Name any five standard creation committees

Ans.

1 International organization for standardization (ISO)

2 International Telecommunication Union— Telecommunication standards

3 American National standards institute (ANSI)

4 Institute of electrical and electronics engineers (II Fl)

5. Electronic industries Association (ElA).

Q. 21. Describe connection-oriented and connectionless services.

Ans.

Layers can offer two different types of service i.e. connection-oriented and connectionlesservices.

Connection-oriented service:

It is modelled after the telephone system. To talk to someone, you pick up the phone, diathe number, talk and then hang up. Similarly, to use a connection oriented networksystem, the service user first establishes a connection, uses the connection, and thenreleases the connection. The essential aspect of a connection is that it act like a tube, thesender pushes objects in at one end, and receiver takes them out in same order at theother end.

Connectionless service:

It is modelled after the postal system. Each message carries the lull destination addressand each one is routed through the system independent of all others. Normally, when twomessages are sent to the same destination, the first one sent will be the first one to arrive





Q. 22. Discuss the communication systems.

Ans.

Communication systems can be classified as

1. Simplex system

2. Half duplex system

3. Full duplex system.

1. Simplex system: ln these systems the information is communicated in only onedirection. For example the radio or TV broadcasting systems can only transmit, theycannot receive.

2. Half duplex systems: These systems are bi-directional, i.e. they can transmit as welas receive but not simultaneously. At a time these systems can either transmit or receivee.g. Tranreceiver .

3. Full duplex system: These are truly bi-directional systems as they allow thecommunication to take place in both the directions simultaneously. These systems transmias well as receive simultaneously, for example the telephone system.

Q.23 Explain the OSI Reference model.

Ans.

This standard model for network protocol was developed by international standardsorganisation (ISO) which was the major step in standardization on networkcommunications. This model is known as ISO-OSI (International standards organizationopen system interconnection) reference model, as it deals with connecting open systemi.e. the systems which are open for communication with other systems. This model serveas a standard model for network architecture. OSI model is divided into seven layers asfollows:

1. Physical layer: This layer is concerned with the transmission of raw bits, over thecommunication channel. This layer provides physical transmission of data of thecommunication media in the network. While designing this layer, it has to be made surethat when one computer sends a 1 bit, other competitor should receive it’ as a I bit, noonly as a 0 bit. Here the concerned issues largely deal with mechanical, electrical andprocedural interfaces. This layer is in the domain of electrical engineer.,

2. Data Link Layer: This layer is concerned with providing on error free Organization andtransmission of data into data frames transmit these frames sequentially and process theacknowledgment frames which are sent back by the receiver. As the physical layer isconcerned only with accepting and, transmission of bits without knowing structure of themit is up to data link layer to create and recognise the frame boundaries.





This task is done by attaching special bit patterns to the beginning and end of frames.

3. Network layer: This layer provides appropriate routing by establishing connectionamong the various subnets. This layer design is concerned with determination of routing odata packets across the source to the destination. When many packets are present in thesubnet, it creates congestion which has to be controlled by this layer.

When data has t be routed across different networks, the addressing of the data packedestinations, which poses great problems. The difference in protocols of networks may alsopose problems. All these problems have to be overcome, by this layer to allowheterogenous network to be interconnected.

4 Transport layer: This layer helps organization and transfer of data between the nodesThe basic function of this layer to accept the data from the session layer divide it intosmaller’ units, if needed, then send them to the network layer. This layer ensures that althe data pieces arrive correctly, at the receiving end. This layer also determines the typeof service to be provided to the session layer.

5. Session layer: This layer is concerned with establishment of sessions between twocomputers to establish connection. A session transmits the data like, transport layer, but iprovides useful enhanced service. This layer allows establishing connection to remotesystems. This layer determines which user has the turn for data transmission. It does iusing taken management technique, where tokens are given to data, the data whichposses the token can do a data transmission.

6. Presentation layer: This layer provides data transmission codes and formats. Thislayer is concerned with syntax and semantics of the information which is beingtransmitted. This layer handles the abstract data structures and conversion to the standardrepresentation. The data encryption compression etc. is used for data transmission, whoserepresentation is taken care of by this presentation layer.

7. Application layer: This layer provides communication services for user applicationsThis layer contains a large number of protocols which are commonly required transmissionof data. All the software required for interacting with incompatible hardware and softwareare available in this layer. This layer is also used for file transfer. This layer provides algeneral purpose and special purpose facilities.

Q. 24. Write down the Basic principles of OSI model.

Ans

1. Whenever, there is a need for different levels of data abstraction, a different layer hasto be created.

2. Every layer has well defined functions.

3. The functions of every layer should be based on international standard protocols.

4. The layers should have boundaries to minimize the flow of information across theinterfaces.

5. The total number of layers should be large enough so that functions which are distincshould not be performed by one layer.

Q. 25. What is Sliding Window Protocol?

Ans.





The principle advantage of using piggy backing over having distinct acknowledgemenframes is a better use of the available channel band width. The pack field in the frameheader casts only a few bits, whereas a separate frame would need a header, theacknowledgement and a checksum. In addition fewer frames sent means fewer “Framearrived” interrupts and perhaps fewer buffer in the receiver, depending on how thereceiver’s software is organized. In the next protocol to be examined, the piggy back fieldcasts only I bit in the frame header. If r and y costs more than a few bits, the next threeprotocols are more robust and continue to function even under pathological conditions. Althree belong to a class of protocols called sliding window protocols. The three differ amongthemselves of efficiency, complexity, and buffer requirements.

In all sliding window protocols, each out bound frame contains a sequence number ranging

from 0 up to some maximum. The maximum of usually 21. So the sequence number fitsnicely in n but field. The stop and wait sliding window protocol uses n = I restricting thesequence number to 0 and 1, but more sophisticated versions on use arbitrary n.

The essence of all sliding window protocol is that at any instant of time, the sendemaintains a set of sequence numbers. Corresponding to, frames it is permitted to send

These frames are said to fail within the sending window similarly, the receiver alsomaintains a receiving window corresponding to the set of frames, it is permitted to accepthe sender’s window and receiver’s window need not have the same lower and upper limitsor even have the same size. In some protocols they are fixed in size, but in other’ they cangrow or shrink as frames are sent and received.

Q. 26. What are the various networking devices?

Ans.

1. Repeaters it’s the property of signal that after travelling a particular distance it getsweakened, the property is called as attenuation. Hence a way should be there, by which aweakened signal should gain its original strength and is propagated further. This isachieved with the help of device called repeater. Before signal gets weakened, it is madepass through the repeater. One another device, which sounds similar to repeater, isamplifier, but the basic difference between them is that amplifiers are generally used fothe analog signals while repeaters for digital. Above all there is a difference between theirworking principles too, i.e. repeaters from the input signal extracts the data andregenerates it, in doing so the noise is eliminated at each interface but amplifiers onlyamplifies the incoming signal and let it pass, is also given the gain in same factor as data

signal is getting, leading to the poor signal quality.

2. Bridges. Bridges don’t care what protocol is being used on the network (TCP/IP, IPXApple Talk, etc.) since they operate at what’s called the data-link level. This is both abenefit and a curse; since they work at such a simple level, that they are able to operateat blindingly fast speeds, but since they will indiscriminately forward data, one has littlecontrol over their operation. This is where routers come in. l3ridges operate at link layerbut Routers work’ at the network layer.

3. Routers. Routers understand the protocols being used to carry the data over thenetwork. And since they understand the protocols, they can use rules to decide ‘hat to dowith a specific piece of data. Because of this, routers are useful in linking networks that areused for different purposes or by different organizations.

4. Gateways. They are the devices, which operate at Application Layer, so depending onthe type of applications various application gateways exist. Various types of gateways are ‘

Filtering gateways make routing decisions based on information in network packets. if apacket passes the security criteria, the gateway passes it through. Filtering gateways areeasy to build but difficult to configure securely. Because filters pass traffic directly from anuntrusted network, they are not as secure as other gateways.

Circuit-level gateways operate at the session level and require modified clients tocommunicate directly with the gateway, which appears to the outside host as the sessionoriginator.

Application-level gateways (proxies) operate at the application level,

• Negotiation each client/server connection made between a host on the trusted network





and a host outside. Like the circuit gateway, they never directly link trusted and untrustednetworks. Hosts inside the trusted network point their clients to the application gatewaywhich accepts client requests (e.g., HTTP, Telnet, or FIP) and relays them to an externadestination host as if the firewall were the requesting client.

Q. 27. Explain TCP/IP Protocol.

Ans.

This is most widely used protocol for networks throughout the world. This technology iadopted as the global standard of networking. This is combination of two basic protocolsthe transmission control and internet. This technology is used by the internet, internet andextranets. Many operating systems and networking software are coming up withcompatibility to this architecture. Currently most of the organizations are adopting thistechnology. This protocol consists of five basic layers which can be related to seven layersof ISO-OSI reference model.

According to TCP/IP reference model total functionality of communication process isdivided into four different layers

1. Internet layer

2. Transport layer3. Application layer

4. Host to network layer.

1. The Internet layer: This layer holds the whole architecture together. Its job is topermit hosts to inject packets into any network and have they travel independently to thedestination. They may arrive in a different order than they were sent, in which care it isthe job of higher layers to rearrange them, if in-order delivery is desired.

The internet layer defines an official packet format and protocol called internet protoco(IP). The job of internet layer is to deliver IP packets where they are supposed to goPacket routing is clearly the major issue here, as is avoiding congestion.

2. Transport layer: The layer above the internet layer is called transport layer. It is

designed to allow peer entities on the source and destination hosts to carry on aconversation, just as in the OSI transport layer. Two end to end transport protocols havebeen defined here. The first one TCP, is a reliable connection oriented protocol that allowsa byte stream originating one machine to be declined without error on any other machinein the internet.

The second protocol in this layer, UDP (User Datagram Protocol), is an unreliable,connectionless protocol for applications that do not want TCP’s sequencing or flow controand wish to provide their own, It is also used for one-short, client-server-type requesreply queries and applications in which prompt delivery is more important than accuratedelivery, such as transmitting speech or video.

3. The application layer: The TCP/IP model does not have session or presentationlayers. No need for them was perceived, so they were not included. Experience with an051 model has proven this view correct, they are of little be use to most applications. Ontop of transport layer is the application layer. It contains all the higher-level protocols. Theearly ones included virtual terminal (TELNET), file transfer (FTP), and electronic mai(SMTP). The virtual terminal protocol allows a user on one machine to log on to a distantmachine and work their. The file transfer protocol provides a way to move data efficientlyfrom one machine to another.

4. The Host to network layer: Below internet layer is a great void. The TCP/IP modedoes not really by much about what happens here, except to point out that the host has toconnect to the network using some protocol so it can send IP packets to it.

This protocol is not defined and varies from host to host and network to network.




Q. 28. Write a short note on Ethernet.

Ans.

Ethernet is the most widely used LAN Protocol. The original Ethernet was created in 1976Ethernet is designed to operate at 10 Mbps. Access to the network by a device is through acontention method (CSMA/CD). The Ethernet frame contains seven fields.

1. Preamble

2. Start frame delimiter (SFD)

3. Destination address (DA)

4. Source address

5. Length / type

6. Data

7. CRC

Each station on an Ethernet network has its own network interface card (NIC). The NIC fitsinside the station and provides the station with a 6 byte physical address. The Ethernetaddress is 6 bytes (48 bits) that is normally written in hexadecimal notation. In Ethernet asource address is always a unicast address and the destination address can be unicastmulticast or broadcast. There are the different categories of traditional

10 Base-T is Twisted-pair Ethernet.

Base-3 FL is the fiber link Ethernet.

Thick Ethernet uses a bus topology with an external transceiver connected via a tap to athick coaxial cable.

This Ethernet uses a bus topology with an internal transceiver or a point-to-pointconnection via an external transceiver.

10 base-T uses a physical star topology. The stations are connected to a hub with an

internal transceiver or an external transceiver.10 Base FL uses a star topology to connect stations to a hub. The standard is normallyimplemented using an external transceiver called fiber optic MAV.

LAN is divided into Bridges. A bridge can raise the bandwidth and separate the collisiondomains on an Ethernet LAN. A switch allows each station on an Ethernet.

LAN to have the entire capacity of the network to itself.

Chapter 8 _ Protocol Architecture _ Computer Networks

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