180704 – Advanced Computer Network · 180704 - Advanced Computer Network (Question Bank) Sr. No....

180704 – Advanced Computer Network IMP Questions

Prepared by: Mayur Padia Darshan Institute of Engineering & Technology, Rajkot 1 | P a g e

Darshan Institute of Engineering & Technology, Rajkot Computer Engineering Department

BE Semester VIII

180704 - Advanced Computer Network (Question Bank)

Sr. No. Unit No Question

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1 12 Write short note on OSPF (open shortest path first) algorithm.

7 7 7 7 28

2 13 Write short note on Spanning tree protocol (STP). 7 7 7 7 28

3 2 Explain ATM reference model. OR Explain the ATM reference model and explain what are the various services provided by it.

7 7 7 21

4 4 Discuss protocols associated with layers of TCP/IP protocol suite. OR List and explain seven application layer protocol of TCP/IP protocol suite.

7 7 7 21

5 1 Explain SONET structure. OR Explain SONET Layered architecture and Frame format for SONET.

7 7 14

6 1 Explain optical networking with its benefits and drawbacks. 7 7 14

7 2 Explain ATM cell header format. 7 7 14

8 4 Explain classful IP addressing scheme. OR Explain IP Addressing using Classful and Classless Addresses.

7 7 14

9 5 Describe BGP (Border Gateway protocol) in detail. 7 7 14

10 7 Write a short note on SNMP(standard network management protocol).

7 7 14

11 11 List and explain five commands to configure router. 7 7 14

12 1 Describe DWDM in detail. OR Explain working of DWDM and network configuration in DWDM.

4 7 11

13 3 Explain architecture of X.25. 4 7 11

14 6 Describe the multiprotocol label switching’s (MPLS’s) working and operation?

4 7 11

15 12 Write short note on IGRP (Interior Gateway Routing Protocol)

7 4 11



1) Write short note on OSPF Algorithm. (GTU - Summer 13, Winter 13, Summer 14, Winter 14)

Open Shortest Path First (OSPF) is another Interior Gateway Protocol based on link-state routing.

Link-state routing uses Dijkstra’s Shortest Path First (SPF) algorithm for selecting the shortest path.

It is a routing protocol developed by Internet Engineering Task Force (IETF) for Internet Protocol (IP) networks.

OSPF was created because; the Routing Information Protocol (RIP) was increasingly incapable of serving large, heterogeneous internetworks.

OSPF being a SPF algorithm scales better than RIP.

It requires the following steps to update each and every link in the network: o Creation: Every node creates its Link-State Packet (LSP). o Distribution: LSPs are distributed to all the links. This is known as flooding. o Formation: Every link forms its shortest path tree to reach other links. o Calculation: A routing table is designed on the basis of the shortest path tree.

Important features of OSPF are as follows:

o This protocol is open. It means that anyone can implement it without paying license fees.

o OSPF is based on the SPF algorithm. o OSPF is a link-state routing protocol that calls for the sending of link-state advertisements (LSAs) to all

other routers within the same hierarchical area. o OSPF specifies that all the exchanges between routers must be authenticated. It allows a variety of

authentication schemes; even different areas can choose different authentication schemes. o OSPF include Type of service Routing. It can calculate separate routes for each Type of Service (TOS).

For example it can maintain separate routes to a single destination based on hop-count and high throughput.

o OSPF provides Load Balancing. When several equal-cost routes to a destination exist, traffic is distributed equally among them.

o OSPF allows supports host-specific routes, Subnet-specific routes and also network-specific routes.

o OSPF allows sets of networks to be grouped together. Such a grouping is called an Area. Each Area is self-contained; the topology of an area is hidden from the rest of the Autonomous System and from other Areas too. This information hiding enables a significant reduction in routing traffic.

o OSPF uses different message formats to distinguish the information acquired from within the network (internal sources) with that which is acquired from a router outside (external sources).

Four types of routers used in OSPF protocol are as follows:

Internal router: Refers to a router that has its entire links connected to the networks within the same area.

Area border router: Refers to the router at the border of an area.

Backbone router: Refers to the routers inside the central backbone area. A backbone area is interconnected with all the areas in an autonomous system. Backbone router can also work as an area border router.



Autonomous system boundary router: Refers to a router that has its links associated to another

autonomous system.

A 32-bit Identity Document (ID) is provided to each area inside an autonomous system known as area ID. The backbone area is always denoted with area ID 0.0.0.0

2) Write short note on Spanning tree protocol (STP). (GTU - Summer 13, Winter 13, Summer 14, Winter 14)

Spanning-tree protocol (STP) is a protocol used in switching network to create a loop-free topology.

STP is enabled by default on all VLANs on Catalyst switches.

STP switches send BPDU's (Bridge Protocol Data Units) to each other to form their topology databases.

BPDU's are sent out all ports every two seconds, are forwarded to a specific MAC multicast address. What causes a loop in a switched network?

When two switches connected via a single cable there will be no loops in switching network.

Loops occur when we add redundancy to avoid single point failure (means connecting two switches via

two or more cable to give back up in the case of a failure to one of the link).

When a loop is introduced into the network, highly destructive broadcast storm can develop within seconds and it will slow down or block off all other traffic.



How loop happening in below topology:

Computer A which is connected to switch A sends an ARP request because it's looking for the MAC address of a computer connected to switch B. An ARP request is a broadcast frame.

Switch A will forward this broadcast frame on all its interfaces, except the link where the frame originated from.

Switch B will receive both broadcast frames from switch A

Switch B will forward it out of every link except the interface where it originated from.

This means that the frame that was received on Interface fa0/1 will be forwarded on Interface fa0/2.

The frame that was received on Interface fa0/2 will be forwarded on Interface fa0/1. So a loop will occur in the network. Both switches will keep forwarding over and over until we disconnect on of the cable, or switch will crash due to overburden traffic.

So how STP blocks or prevent loop? STP enabled switch will block port if a loop exist and blocked port will be activated again if needed.

The STP Process To maintain a loop-free environment, STP performs the following functions: o A root Bridge is elected o Root Ports are identified o Designated Ports are identified. o If a loop exists, a port is placed in blocking state. If the loop is removed the blocked port is activated again.

If multiple loops exist in the switching environment, multiple ports will be placed in a blocking state.

Switches exchange BPDU's to perform the election process.

By default, all switches "believe" they are the Root Bridge, until a switch with a lower Bride ID is discovered. Root Bridge elections are a continuous process.



If a new switch with a lower Bridge ID is added to the topology, it will be elected as the new Root Bridge.

3) Explain the ATM reference model and explain what the various services are

provided by it. (GTU - Summer 13, Summer 14, Winter 14)

Asynchronous Transfer Mode (ATM) is an ITU-T standard for cell relay wherein information for multiple service types, such as voice, video, or data, is conveyed in small, fixed-size cells.

ATM networks are connection-oriented.

ATM integrates the multiplexing and switching functions, is well suited for busty traffic, and allows communications between devices that operate at different speeds.

ATM is designed for high-performance multimedia networking.

The most basic service building block is the ATM virtual circuit, which is an end-to-end connection that has defined end points and routes but does not have bandwidth dedicated to it.

Bandwidth is allocated on demand by the network as users have traffic to transmit.

ATM Reference Model

The ATM architecture uses a logical model to describe the functionality that it supports.

ATM functionality corresponds to the physical layer and part of the data link layer of the OSI reference model. The ATM reference model, as shown in Fig. below, consists of the following planes, which span through all layers: o Control – This plane is responsible for generating and managing signaling requests. o User – This plane is responsible for managing the transfer of data. o Management – This plane contains two components:

Layer management manages layer-specific functions, such as the detection of failures and protocol problems.

Plane management manages and coordinates functions related to the complete system. The ATM reference model consists of the following ATM layers:

1) Physical layer

2) ATM layer

3) ATM adaptation layer (AAL)



The ATM Physical Layer

The main functions of the ATM physical layer are as follows:

Cells are converted into a bit stream,

The transmission and receipt of bits on the physical medium are controlled,

ATM cell boundaries are tracked,

Cells are packaged into the appropriate types of frames for the physical medium. The ATM physical layer is divided into two parts: the physical medium-dependent (PMD) sub layer and the transmission convergence (TC) sub layer.

The PMD sub layer provides two key functions:

It synchronizes transmission and reception by sending and receiving a continuous flow of bits with associated timing information.

It specifies the physical media for the physical medium used, including connector types and cable.

The TC sub layer has four functions:

Cell allocation, it maintains ATM cell boundaries, allowing devices to locate cells within a stream of bits.

Generates and checks the header error control code to ensure valid data.

Cell-rate decoupling, maintains synchronization and inserts or suppresses idle (unassigned) ATM cells to adapt the rate of valid ATM cells to the payload capacity of the transmission system.

Transmission frame adaptation packages ATM cells into frames acceptable to the particular physical layer implementation.

ATM Layer

The ATM layer provides routing, traffic management, switching and multiplexing services.

It processes outgoing traffic by accepting 48-byte segment from the AAL sub layers and transforming them into 53-byte cell by addition of a 5-byte header.

Adaptation Layers

ATM adaptation layers allow existing packet networks to connect to ATM facilities.

AAL Protocol accepts transmission from upper layer services (e.g.: packet data) and map them into fixed-sized ATM cells.

These transmissions can be of any type, variable or fixed data rate.

At the receiver, this process is reversed and segments are reassembled into their original formats and passed to the receiving services.

Instead of one protocol for all types of data, the ATM standard divides the AAL layer into categories, each supporting the requirements of different types of applications.

There are four types of data streams that are identified: Constant-bit rate, variable bit-rate, connection oriented packet data transfer, connectionless packet data transfer.

In addition to dividing AAL by category (AAL1, AAL2 and so on), ITU-T also divides it on the basis of functionality.



Each AAL layer is actually divided into two layers: the convergence sub-layer and Segmentation and reassembly (SAR) sub-layer.

Convergence Sub layer: This layer wraps the user-service data units in a header and trailer which contain information used to

provide the services required. The information in the header and trailer depends on the class of information to be transported but

will usually contain error handling and data priority preservation information. Segmentation and reassembly Sub layer: This layer receives the convergence sub layer protocol data unit and divides it up into pieces which it

can place in an ATM cell. It adds to each piece a header which contains information used to reassemble the pieces at the

destination.

4) Discuss protocols associated with layers of TCP/IP protocol suite. (GTU - Summer 13, Winter 13, Winter 14)

A protocol suit consists of a layered architecture where each layer depicts some functionality which can be carried out by a protocol.

Each layer usually has more than one protocol options to carry out the responsibility that the layer adheres to.

TCP/IP is normally considered to be a 4 layer system.

The 4 layers are as follows: o Application layer o Transport layer o Network layer o Data link layer

Application layer

This is the top layer of TCP/IP protocol suite.

This layer includes applications or processes that use transport layer protocols to deliver the data to destination computers.

At each layer there are certain protocol options to carry out the task designated to that particular layer.

So, application layer also has various protocols that applications use to communicate with the second layer, the transport layer.

Some of the popular application layer protocols are:

a) HTTP (Hypertext transfer protocol) b) FTP (File transfer protocol) c) SMTP (Simple mail transfer protocol) d) SNMP (Simple network management protocol) etc.,



Transport Layer

This layer provides backbone to data flow between two hosts.

This layer receives data from the application layer above it.

There are many protocols that work at this layer but the two most commonly used protocols at transport layer are TCP and UDP.

TCP is used where a reliable connection is required while UDP is used in case of unreliable connections.

Network Layer

This layer is also known as Internet layer.

The main purpose of this layer is to organize or handle the movement of data on network.

By movement of data, we generally mean routing of data over the network.

The main protocol used at this layer is IP. ICMP (used by popular ‘ping’ command) and IGMP are also used at this layer.

Data Link Layer

This layer is also known as network interface layer.

This layer normally consists of device drivers in the OS and the network interface card attached to the system.

Both the device drivers and the network interface card take care of the communication details with the media being used to transfer the data over the network.

In most of the cases, this media is in the form of cables.

Some of the famous protocols that are used at this layer include ARP (Address resolution protocol), PPP (Point to point protocol) etc.



5) Explain SONET Layered architecture and Frame format for SONET. OR Write a

short note on SONET network. (GTU - Winter 13, Summer 14)

SONET is a standardized multiplexing protocol that transmits information over optical fiber using lasers or LEDs.

SONET uses synchronous transmission medium. [Synchronous: Defines that all digital transitions in the signals occur at precisely the same rate.]

In SONET network, the timing of all the equipment is handled by a single clock.

SONET-Layered Architecture

SONET follows a four-layered architecture model.

All the layers in SONET’s protocol stack are equivalent to the physical layer of OSI model.

In-band Operation, Administration, Maintenance, and Provisioning (OAMP) is one of the greatest benefits of SONET.

Layers Description

Path Information carried end-to-end

Transport

Pointer functions

Line Information carried for STS-n (Synchronous Transport Signal-n)

Manages interfaces from physical layer

Section

Information carried between adjacent network equipment

Synchronization

Channel multiplexing

Protection switching

Physical Photonic Interface

Physical fiber type, path and characteristics

The four layers of the SONET architecture are as follows:

Physical (or Photonic) layer: Signifies the type of optical fiber used as well as the characteristics of transmission medium

Section layer: Supports the physical integrity of the network and builds the SONET frames from either lower SONET interfaces or electrical interfaces.

Line layer: Manages Synchronous Transport Signal level n (STS-n) frame for adding or dropping user data and deals with the interfaces from the physical layer. The line layer also provides synchronization, channel multiplexing or de-multiplexing, and protection switching to the SONET network.

Path layer: Carries information end-to-end and looks after the actual data transport across the SONET network.



SONET Structure

The SONET structure follows a strict hierarchy, which maps to the electrical hierarchy followed in many countries.

The SONET structure is multiplexed to form higher speed transport circuits that provide an alternative to aggregate multiple DS1 and DS3 signaling schemes.

The structure of SONET is built around the following three basic devices:

o STS multiplexer and de-multiplexer: Refer to a Synchronous Transport Signal multiplexer (STS MUX) and Synchronous Transport Signal de-multiplexer (STS DMUX), respectively. STS MUX multiplexes (STS-1s) signals from multiple sources into an STS-n (where n=3, 12, 48, 192 …), whereas STS DMUX de-multiplexes an STS-n into different destination signals (STS-1s). The terms STS-1 and STS-n are used to show the hierarchy of signaling levels. Each STS level from STS-1 to STS-192 supports a certain bit rate.

o Regenerator: Refers to a repeater that receives an attenuated and distorted optical signal and regenerates it. Apart from working as a physical layer repeater, a SONET regenerator also functions at the data link layer. It replaces some of the existing header information with new information.

o Add/drop multiplexer: Refers to the equipment that adds signals coming from different sources into a given path or takes away a desired signal from a path and redirect it without de-multiplexing the entire signal.

The equipment used in the SONET structure is as follows:

Path Terminating Equipment (PTE): Refers to the user interface at Customer Premises Equipment (CPE). CPEs are the equipment at the user end that helps the user to connect to the telecommunication network, such as LAN, MAN, or WAN. Some of the CPEs are router, bridge, switch and hub.

Line Terminating Equipment (LTE): Refers to a terminal, switch, add/drop multiplexer, or cross-connect used in SONET.

Section Terminating Equipment (STE): Refers to a regenerator that interprets and modifies or creates Section Overhead. STE is linked to one or more LTEs.

Frame Format Structure

SONET uses a basic transmission rate of STS–1 that is equivalent to 51.84 Mbps.

Higher-level signals are integer multiples of the base rate.

For example, STS–3 is three times the rate of STS–1 (3 x 51.84 = 155.52 Mbps).

An STS–12 rate would be 12 x 51.84 = 622.08 Mbps.

SONET is based on the STS-1 frame.

STS-1 Frame Format is shown in Fig below.



STS-1 consists of 810 octets o 9 rows of 90 octets o 27 overhead octets formed from the first 3 octets of each row

9 used for section overhead 18 used for line overhead

o 87x9 = 783 octets of payload one column of the payload is path overhead - positioned by a pointer in the line overhead

o Transmitted top to bottom, row by row from left to right STS-1 frame transmitted every 125 us: thus a transmission rate of 51.84 Mbps.

The synchronous payload envelope can also be divided into two parts: the STS path overhead (POH) and the payload.

Transport overhead is composed of section overhead and line overhead.

The STS–1 POH is part of the synchronous payload envelope.

The first three columns of each STS–1 frame make up the transport overhead, and the last 87 columns make up the SPE.

SPEs can have any alignment within the frame, and this alignment is indicated by the H1 and H2 pointer bytes in the line overhead.

6) Explain optical networking with its benefits and drawbacks. (GTU - Summer 14, Winter 14)

Optical networking is based on optical technology, which uses lasers and fiber-optics media for the propagation of optical signals.

Light is an electromagnetic carrier wave, which is used to carry information through optical fibers in optical networking.

Benefits of Optical Networking

Low material cost: Signifies that fiber cables cost much cheaper than copper cables for the same transmission capacity.

Lightweight and small size: Specify that fiber cable is considerably smaller in size and lighter in weight than electrical cables to perform the same task.



High capacity: Refers to the property of optical fiber to transfer information at very high rate (up to 10 Gbps). This capacity of the optical fiber can be increased by sending many channels on a single fiber using WDM.

No electrical connection: Defines that optical fiber does not require any electrical connection to transmit light signal, whereas a coaxial cable requires a high-voltage electric connection to transmit electrical signal.

No electromagnetic interference: It means that optical signal cannot be distorted interfered by the other signals.

Long distance between repeaters: Shows the feature of optical signal that it loses its strength and picks up noise after travelling more distance than the electrical signal. It is estimated that in optical transmission system, repeaters are placed normally 40 km apart.

Better security: Ensures less possibility to tap optical fiber cable; as a result, an intruder experiences difficulty to tap an optical fiber transmission system. Even if tapping is done it is very easy to detect it.

Drawbacks of Optical Networking

Difficult to join cables: Refers to the problem of joining two ends of the optical fiber. The most commonly used technique for joining the two ends of an optical fiber is fusion splicing. In this technique, the two fiber ends are fused together by melting glass. Fusion splicing is a skilled task and requires precision equipment to make splices in a way that will ensure minimal loss of signal. Other technique is unreliable and causes a large amount of signal loss.

Difficult to bend cables: Refers to the problem of bending the optical fiber. When light travels along the fiber, it is reflected from the interface between core and cladding. The electromagnetic wave (light) resides in the fiber only in case the fiber is bent to a certain degree. However, if the fiber is bent more than a certain degree, the reflected light escapes.

Gamma radiation: Refers to the radiation that comes from Gamma rays, which can harm optical signals. Gamma radiation can cause some types of glass to emit light that results to interference. This radiation can also cause the glass to discolor and attenuate the signal.

Electrical fields: Refer to a very high voltage and influences some glass fibers in the same way as gamma rays do.

7) Explain ATM cell header format. (GTU - Winter 13, Winter 14)

ATM transfers information in fixed-size units called cells.

Each cell consists of 53 octets, or bytes as shown in Fig.

The first 5 bytes contain cell-header information, and the remaining 48 contain the payload (user

information).

Header 5 bytes

Payload 48 bytes

ATM Cell Format



Small, fixed-length cells are well suited to transfer voice and video traffic because such traffic is intolerant to delays that result from having to wait for a large data packet to download, among other things.

An ATM cell header can be one of two formats: UNI or NNI.

The UNI header is used for communication between ATM endpoints and ATM switches in private ATM

networks.

The NNI header is used for communication between ATM switches.

Unlike the UNI, the NNI header does not include the Generic Flow Control (GFC) field.

Additionally, the NNI header has a Virtual Path Identifier (VPI) field that occupies the first 12 bits, allowing for larger trunks between public ATM switches.

The following descriptions summarize the ATM cell header fields: o Generic Flow Control (GFC) - Provides local functions, such as identifying multiple stations that share a

single ATM interface. This field is typically not used and is set to its default value of 0 (binary 0000). o Virtual Path Identifier (VPI) - In conjunction with the VCI, identifies the next destination of a cell as it

passes through a series of ATM switches on the way to its destination. o Virtual Channel Identifier (VCI) - In conjunction with the VPI, identifies the next destination of a cell as

it passes through a series of ATM switches on the way to its destination. o Payload Type (PT) - Indicates in the first bit whether the cell contains user data or control data. If the

cell contains user data, the bit is set to 0. If it contains control data, it is set to 1. The second bit indicates congestion (0 = no congestion, 1 = congestion), and the third bit indicates whether the cell is the last in a series of cells that represent a single AAL5 frame (1 = last cell for the frame).

o Cell Loss Priority (CLP) - Indicates whether the cell should be discarded if it encounters extreme congestion as it moves through the network. If the CLP bit equals 1, the cell should be discarded in preference to cells with the CLP bit equal to 0.

o Header Error Control (HEC) - Calculates checksum only on the first 4 bytes of the header. HEC can correct a single bit error in these bytes, thereby preserving the cell rather than discarding it.



8) Explain IP Addressing using Classful and Classless Addresses. (GTU - Winter 13, Summer 14)

Classful Addressing

All IP addresses have a network and host portion.

In Classful addressing, the network portion ends on one of the separating dots in the address (on an octet boundary).

Classful addressing divides an IP address into the Network and Host portions along octet boundaries.

In the Classful addressing system all the IP addresses that are available are divided into the five classes A,B,C,D and E, in which class A,B and C address are frequently used because class D is for Multicast and is rarely used and class E is reserved and is not currently used.

The main disadvantage of Classful addressing is that it limited the flexibility and number of addresses that can be assigned to any device.

One of the major disadvantages of Classful addressing is that it does not send subnet information but it will send the complete network address.

The router will supply its own subnet mask based on its locally configured subnets.

As long as you have the same subnet mask and the network is contiguous, you can use subnets of a Classful network address.

Classless Addressing

Classless addressing uses a variable number of bits for the network and host portions of the address.

Classless addressing treats the IP address as a 32 bit stream of ones and zeroes, where the boundary between network and host portions can fall anywhere between bit 0 and bit 31.

Classless addressing system is also known as CIDR (Classless Inter-Domain Routing).

Classless addressing is a way to allocate and specify the Internet addresses used in inter-domain routing more flexibly than with the original system of Internet Protocol (IP) address classes.



CIDR (Classless Internet Domain Routing) defines arbitrarily-sized subnets solely by base address and number of significant bits in the address.

A CIDR address of 192.168.0.0/24 defines a block of addresses in the range 192.168.0.0 through 192.168.0.255, while 192.168.0.0/20 would define a network 16 times as large - from 192.168.0.0 through 192.168.15.255

9) Describe BGP (Border Gateway protocol) in detail. (GTU - Summer 13, Winter 14)

BGP (Border Gateway Protocol) is a protocol for exchanging routing information between gateway hosts (each with its own router) in a network of autonomous systems.

BGP is often the protocol used between gateway hosts on the Internet.

The routing table contains a list of known routers, the addresses they can reach, and a cost metric associated with the path to each router so that the best available route is chosen.

Hosts using BGP communicate using the Transmission Control Protocol (TCP) and send updated router table information only when one host has detected a change.

Only the affected part of the routing table is sent.

BGP-4 is the latest version.

BGP should be used under the following circumstances: o Multiple connections exist to external AS’s (such as the Internet) via different providers. o Multiple connections exist to external AS’s through the same provider, but connect via a separate CO

or routing policy. o The existing routing equipment can handle the additional demands.

BGP’s true benefit is in controlling how traffic enters the local AS, rather than how traffic exits it.

BGP Algorithm

BGP uses an algorithm that is neither a pure distance vector algorithm nor a pure link state algorithm.

Instead, it uses a modified distance vector algorithm, referred to as a "Path Vector" algorithm.

This algorithm uses path information to avoid traditional distance vector problems.

Each route within BGP pairs information about the destination with path information to that destination.

Path information (also known as AS_PATH information) is stored within the AS_PATH attribute in BGP.

The path information assists BGP in detecting AS loops, thereby allowing BGP speakers to select loop-free routes.

BGP uses an incremental update strategy to conserve bandwidth and processing power.

That is, after initial exchange of complete routing information, a pair of BGP routers exchanges only the changes to that information.

Such an incremental update design requires reliable transport between a pair of BGP routers in order to function correctly.

BGP solves this problem by using TCP for reliable transport.

In addition to incremental updates, BGP has added the concept of route aggregation so that information about groups of destinations that use hierarchical address assignment (e.g., CIDR) may be aggregated and sent as a single Network Layer Reachability (NLRI).



Finally, note that BGP is a self-contained protocol. That is, BGP specifies how routing information is exchanged, both between BGP speakers in different autonomous systems, and between BGP speakers within a single autonomous system.

Message header format

The following is the BGP version 4 message header format:

bit offset

0-15 16-23 24-31

0

Marker 32

64

96

128 Length Type

Marker: Included for compatibility, must be set to all ones.

Length: Total length of the message in octets, including the header.

Type: Type of BGP message. The following values are defined: o Open (1) o Update (2) o Notification (3) o KeepAlive (4) o Route-Refresh (5)

10) Write a short note on SNMP (standard network management protocol) (GTU - Winter 13, Winter 14)

Simple Network Management Protocol (SNMP), an application layer protocol, facilitates the exchange of management information among network devices, such as nodes and routers.

It comprises part of the TCP/IP suite.

System administrators can remotely manage network performance, find and solve network problems, and plan for network growth by using SNMP.

Instead of defining a large set of commands, SNMP places all operations in a get-request, get-next-request, get-bulk-request, and set-request format.

For example, an SNMP manager can get a value from an SNMP agent or store a value in that SNMP agent.

The SNMP manager can comprise part of a network management system (NMS), and the SNMP agent can reside on a networking device such as a router.

SNMP comprises of three parts—SNMP manager, SNMP agent, and MIBs.

SNMP manager is a network node that implements an SNMP interface that allows unidirectional (read-only) or bidirectional (read and write) access to node-specific information. Managed devices exchange node-specific information with the NMSs. Sometimes called network elements, the managed devices can



be any type of device, including, but not limited to, routers, access servers, switches, bridges, hubs, IP telephones, IP video cameras, computer hosts, and printers.

SNMP agent is a network-management software module that resides on a managed device. An agent has local knowledge of management information and translates that information to or from an SNMP-specific form.

A network management station (NMS) executes applications that monitor and control managed devices. NMSs provide the bulk of the processing and memory resources required for network management. One or more NMSs may exist on any managed network.

SNMPv3 provides the following security features: o Authentication - Verifying that the request comes from a genuine source o Privacy - Encrypting data o Authorization - Verifying that the user allows the requested operation o Access control - Verifying that the user has access to the objects that are requested

SNMP PDUs are constructed as follows:

IP header UDP header version community PDU-type request-id error-status

error-index

variable bindings

The seven SNMP protocol data units (PDUs) are as follows:

GetRequest - A manager-to-agent request to retrieve the value of a variable or list of variables. Desired variables are specified in variable bindings (values are not used). Retrieval of the specified variable values is to be done as an atomic operation by the agent. A Response with current values is returned.

SetRequest - A manager-to-agent request to change the value of a variable or list of variables. Variable bindings are spjnbbecified in the body of the request. Changes to all specified variables are to be made as an atomic operation by the agent. A Response with (current) new values for the variables is returned.

GetNextRequest - A manager-to-agent request to discover available variables and their values. Returns a Response with variable binding for the lexicographically next variable in the MIB.

GetBulkRequest - Optimized version of GetNextRequest. A manager-to-agent request for multiple iterations of GetNextRequest. Returns a Response with multiple variable bindings walked from the variable binding or bindings in the request.

Response - Returns variable bindings and acknowledgement from agent to manager for GetRequest, SetRequest, GetNextRequest, GetBulkRequest and InformRequest. Error reporting is provided by error-status and error-index fields.

Trap - Asynchronous notification from agent to manager. SNMP traps enable an agent to notify the management station of significant events by way of an unsolicited SNMP message.

InformRequest - Acknowledged asynchronous notification.



11) List and explain five commands to configure router.

(GTU - Summer 13, Winter 13) (Write any of the below 5 commands if asked)

Requirement Cisco Command

Set a console password to cisco Router(config)#line con 0 Router(config-line)#login Router(config-line)#password cisco

Set a telnet password Router(config)#line vty 0 4 Router(config-line)#login Router(config-line)#password cisco

Stop console timing out Router(config)#line con 0 Router(config-line)#exec-timeout 0 0

Set the enable password to cisco Router(config)#enable password cisco

Set the enable secret password to peter.

This password overrides the enable password and is encrypted within the config file

Router(config)#enable secret peter

Enable an interface Router(config-if)#no shutdown

To disable an interface Router(config-if)#shutdown

Set the clock rate for a router with a DCE cable to 64K

Router(config-if)clock rate 64000

Set a logical bandwidth assignment of 64K to the serial interface

Router(config-if)bandwidth 64 Note that the zeroes are not missing

To add an IP address to a interface Router(config-if)#ip addr 10.1.1.1 255.255.255.0

To enable RIP on all 172.16.x.y interfaces Router(config)#router rip Router(config-router)#network 172.16.0.0

Disable RIP Router(config)#no router rip

To enable IRGP with a AS of 200, to all interfaces Router(config)#router igrp 200 Router(config-router)#network 172.16.0.0

Disable IGRP Router(config)#no router igrp 200

Static route the remote network is 172.16.1.0, with a mask of 255.255.255.0, the next hop is 172.16.2.1, at a cost of 5 hops

Router(config)#ip route 172.16.1.0 255.255.255.0 172.16.2.1 5

Disable CDP for the whole router Router(config)#no cdp run

Enable CDP for the whole router Router(config)#cdp run

Disable CDP on an interface Router(config-if)#no cdp enable



12) Describe DWDM in detail. OR Explain working of DWDM and network

configuration in DWDM. (GTU - Summer 13, Summer 14)

In digital signal processing, DWDM (Dense Wavelength Division Multiplexing) is a technique for increasing the bandwidth of optical network communications.

DWDM allows dozens of different data signals to be transmitted simultaneously over a single fiber.

To keep the signals distinct, DWDM manipulates wavelengths of light to keep each signal within its own narrow band.

DWDM is a more cost-effective alternative to Time Division Multiplexing (TDM).

Working of DWDM

Some of the functions of the physical layer, such as combining the signal and transmitting the signal, are carried out by DWDM.

The preceding figure depicts the working of DWDM for four channels, where every optical channel takes up its own wavelength.

The system executes the following main functions:

Generating the signal: Implies that the source (a laser) must provide a steady light within a definite bandwidth. This steady light holds the digital data, which is modulated as analog signal. The line width of the signal must not go outside the allocated band. Depending on the width of the allocated band, the signal generation needs to be ideally performed so that the signal stays within the allocated band.

Combining the signals: Means that to combine the signals, DWDM systems make use of multiplexers. Some inborn signal loss is associated with multiplexing and demultiplexing of signals. This loss is based upon the number of channels in the DWDM system, but can be diminished with optical amplifiers, which enhance all the wavelengths at once without electrical conversion.

Transmitting the signals: Means that the signal needs to be optically amplified over a transmission link. The ability to amplify the mixed signal is one of the factors that make WDM possible. However, when multiple amplifiers are used in a long link, they create considerable difficulty (in the form of noise amplification) to the signal.

Transmitter#1

Transmitter#2

Transmitter#3

Transmitter#4

TERM

INA

L M

UX

TE

RM

INA

L M

UX

Receiver#1

Receiver#2

Receiver#3

Receiver#4

OPTICAL FIBER



Separating the received signals: Indicates that the multiplexed signals are taken apart at the receiving end. The following are the several possible methods that we can use for separating the signals at the receiving end: o Reflective gratings o Waveguide grating routers o Circulators with in-fiber Bragg gratings o Splitters with individual Fabry-Perot filters

Receiving the signals: Specifies that the receiver is reasonably straightforward and generally the same as a usual receiver. This is because the signals have been de-multiplexed before they arrive at the detector. The de-multiplexed signal is received by a photo-detector.

Network Configuration in DWDM

The factors such as distances, applications, protocols, access patterns, and legacy network topologies are responsible for network configuration in DWDM systems. The topology of the architecture can be any one of the following on the basis of the preceding factors: o Point-to-point topology: Connects locations within an enterprise o Ring topology: Connects inter-office equipment and is used for residential access o Mesh topology: Connects to the long-haul backbone network and is used for inter-Post Office Protocol

(POP) connections.

Point-to-Point Topologies

Point-to-point topologies can be implemented with or without OADM. These networks are characterized by ultra-high channel speeds (10 to 40 Gbps), high signal integrity and reliability, and fast path restoration. In long-haul networks, the distance between transmitter and receiver can be several hundred kilometers, and the number of amplifiers required between endpoints is typically less than 10. In the MAN, amplifiers are often not needed.



Ring Topologies

Rings are the most common architecture found in metropolitan areas and span a few tens of kilometers. The fiber ring might contain as few as four wavelength channels, and typically fewer nodes than channels. Bit rate is in the range of 622 Mbps to 10 Gbps per channel. Ring configurations can be deployed with one or more DWDM systems, supporting any-to-any traffic, or they can have a hub station and one or more OADM nodes, or satellites. At the hub node traffic originates, is terminated and managed, and connectivity with other networks is established. At the OADM nodes, one or more wavelengths is dropped off and added, while the others pass through transparently (express channels). In this way, ring architectures allow nodes on the ring to provide access to network elements such as routers, switches, or servers by adding or dropping wavelength channels in the optical domain. With increase in number of OADMs, however, the signal is subject to loss and amplification can be required.

Mesh Topologies

Mesh architectures are the future of optical networks. As networks evolve, rings and point-to-point architectures will still have a place, but mesh promises to be the most robust topology. This development will



be enabled by the introduction of configurable optical cross-connects and switches that will in some cases replace and in other cases supplement fixed DWDM devices. DWDM mesh networks, consisting of interconnected all-optical nodes, will require the next generation of protection. This means, among other things, that a data channel might change wavelengths as it makes its way through the network, due either to routing or to a switch in wavelength because of a fault. Mesh networks will therefore require a high degree of intelligence to perform the functions of protection and bandwidth management, including fiber and wavelength switching. The benefits in flexibility and efficiency, however, are potentially great. Fiber usage, which can be low in ring solutions because of the requirement for protection fibers on each ring, can be improved in a mesh design. Protection and restoration can be based on shared paths, thereby requiring fewer fiber pairs for the same amount of traffic and not wasting unused wavelengths.

13) Explain architecture of X.25. (GTU - Winter 13, Summer 14)

X.25 network devices fall into three general categories: data terminal equipment (DTE), data circuit-terminating equipment (DCE), and packet-switching exchange (PSE) as shown in Fig.

Data terminal equipment (DTE) devices are end systems that communicate across the X.25 network.

They are usually terminals, personal computers, or network hosts, and are located on the premises of individual subscribers.

Data communication Equipment (DCEs) are communications devices, such as modems and packet switches that provide the interface between DTE devices and a PSE, and are generally located in the carrier's facilities.

PSEs are switches that compose the bulk of the carrier's network. They transfer data from one DTE device to another through the X.25 PSN.

Figure above illustrates the relationships among the three types of X.25 network devices.

The basic idea behind the development of X.25 was to create a global PSN. When the X.25 architecture

was initially defined, the following three basic protocol levels or layers were present: o Physical level



o Link level o Packet level

All the three levels shown in the preceding figure are as follows: o Physical level:

Works with the physical interface between the nodes of the network.

Physical level operates between a DTE and the link that joins the DTE to the packet switching node.

The physical connector has 15 pins, but not all of them are used.

The DTE uses the T and C circuits to transmit data and control information respectively.

The DCE uses the R and I circuits for data and control information respectively.

The S circuit contains a signal stream emitted by the DCE to provide timing information so the DTE knows when each bit interval starts and stops.

The B circuit may also provide to group the bits into byte frames.

If this option is not provided the DCE and DTE must begin every control sequence with at least two SYN characters to enable each other to deduce the implied frame boundary.

o Link level:

Provides reliable transmission of information across the physical link.

Link level transfers the data traffic as a sequence of frames and uses a subset of High-Level Data Link Control (HDLC) known as Link Access Protocol Balanced (LAPB), which is a bit oriented protocol.

The functions performed by the link level include: Transfer of data in an efficient and timely fashion. Synchronization of the link to ensure that the receiver is in step with the transmitter. Detection of transmission errors and recovery from such errors Identification and reporting of procedural errors to higher levels, for recovery.

o Packet level:

This level governs the end-to-end communications between the different DTE devices.

Layer 3 is concerned with connection set-up and teardown and flow control between the DTE devices, as well as network routing functions and the multiplexing of simultaneous logical connections over a single physical connection.

PLP is the network layer protocol of X.25.

Packet level performs the following functions: o Establishing connection o Transferring data o Terminating data o Terminating a connection o Error and flow control

Information is transmitted in packets through virtual circuits using the X.25 packet level.



14) Describe the multiprotocol label switching’s (MPLS’s) working and operation? (GTU - Summer 13, Winter 13)

Multiprotocol Label Switching (MPLS) is a mechanism in high-performance telecommunications networks that directs data from one network node to the next based on short path labels rather than long network addresses, avoiding complex lookups in a routing table.

The labels identify virtual links (paths) between distant nodes rather than endpoints.

MPLS can encapsulate packets of various network protocols.

MPLS is a scalable, protocol-independent transport.

In an MPLS network, data packets are assigned labels.

Packet-forwarding decisions are made solely on the contents of this label, without the need to examine the packet itself.

This allows one to create end-to-end circuits across any type of transport medium, using any protocol.

The primary benefit is to eliminate dependence on a particular OSI model data link layer technology, such as Asynchronous Transfer Mode (ATM), Frame Relay, Synchronous Optical Networking (SONET) or Ethernet, and eliminate the need for multiple layer-2 networks to satisfy different types of traffic. MPLS belongs to the family of packet-switched networks.

How MPLS Works

The easiest way to see how MPLS operates is to follow a packet through the network.



Step 1

The network automatically builds routing tables as MPLS-capable routers or switches participate in interior gateway protocols, such as Open Shortest Path First (OSPF) or Intermediate System to Intermediate System (IS-IS), throughout the network.

Label Distribution Protocol 1 (LDP) uses the routing topology in the tables to establish label values between adjacent devices.

This operation creates Label Switching Paths (LSPs), pre-configured maps between destination endpoints. Step 2

A packet enters the ingress Edge Label Switching Router (LSR) where it is processed to determine which Layer 3 services it requires, such as Quality of Service (QoS) and bandwidth management.

Based on routing and policy requirements, the Edge LSR selects and applies a label to the packet header and forwards the packet.

Step 3

The LSR in the core reads the label on each packet replaces it with a new one as listed in the table and forwards the packet.

This action is repeated at all core and distribution “hops.” Step 4

The egress Edge LSR strips the label, reads the packet header and forwards it to its final destination. For enabling business IP services, the most significant benefit of MPLS is the ability to assign labels that have special meanings. Sets of labels can distinguish routing information as well as application type or service class. The label is compared to pre-computed switching tables in core devices that contain Layer 3 information, allowing each switch to automatically apply the correct IP services to each packet. Tables are pre-computed, so there is no need to analyze the packets again at every hop. This not only makes it possible to separate types of traffic, such as best-effort traffic from mission-critical traffic, it also renders an MPLS solution highly scalable. MPLS decouples packet-forwarding from IP header information because it uses different policy mechanisms to assign labels. This characteristic is essential to implementing advanced IP services such as QoS, Virtual Private Networks (VPNs) and traffic engineering.

15) Write short note on IGRP (Interior Gateway Routing Protocol) (GTU - Summer 13, Summer 14)

The Interior Gateway Routing Protocol (IGRP) is an advanced distance vector routing protocol.

Because it is a Cisco-developed routing protocol, only Cisco devices can utilize this protocol for routing purposes.

Like RIP, it, too, is a Classful protocol, meaning that it does not send the subnet mask with routing updates.

For this reason, it cannot support VLSMs.



IGRP Routing Updates

A router running IGRP sends an update broadcast every 90 seconds, by default.

When an update from the originating router is not received within three update periods (270 seconds), it declares a route invalid.

After seven update periods (630 seconds), which include the three update periods, the router removes the route from the routing table.

IGRP advertises three types of routes: o Interior— Routes between subnets in the network attached to a router interface. o System— Routes to networks within an autonomous system. The router derives system routes from

directly connected network interfaces and system route information provided by other IGRP-speaking routers.

o Exterior— Routes to networks outside the autonomous system that are considered when identifying a gateway of last resort. The router chooses a gateway of last resort from the list of exterior routes that IGRP provides. The router uses the gateway (router) of last resort if it does not have a better route for a packet and the destination is not a connected network. If the autonomous system has more than one connection to an external network, different routers can choose different exterior routers as the gateway of last resort.

IGRP Scalability Features

IGRP is an advanced distance vector protocol.

Several features distinguish it from other distance vector routing protocols, such as RIP: o Increased scalability – Improved for routing in larger networks compared to networks that use RIP,

IGRP can be used to overcome RIP's 15-hop limit. IGRP has a default maximum hop count of 100 hops, which can be configured to a maximum of 255 hops.

o Sophisticated metric – IGRP uses a composite metric that provides significant flexibility in route selection. By default, internetwork delay and bandwidth are used to arrive at a composite metric. Reliability, load, and MTU may be included in the metric computation as well.

o Multiple path support – IGRP can maintain up to six unequal-cost paths between a network source and destination, but only the route with the lowest metric is placed in the routing table. RIP, on the other hand, keeps only the route with the best metric and disregards the rest. Multiple paths can be used to increase available bandwidth or for router redundancy.

180704 – Advanced Computer Network · 180704 - Advanced Computer Network (Question Bank) Sr. No....

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