Chapter 2: Term-End Examination, December- 2014
MCS-022: OPERATING SYSTEM CONCEPTS AND NETWORKING MANAGEMENT
Q.1. (a) Explain the collision avoidance mechanism of CSMA/CD. Also, differentiate between CSMA/CD and token passing access methods. 8
Answer:
Collision Avoidance Mechanism of CSMA/CD (Carrier Sense Multiple Access with Collision Detection):
CSMA/CD Overview: Carrier Sense Multiple Access with Collision Detection (CSMA/CD) is a network protocol used in Ethernet networks to manage access to the shared communication medium. The primary goal of CSMA/CD is to avoid collisions and maximize the efficient use of the network.
Collision Avoidance Mechanism: The collision avoidance mechanism in CSMA/CD involves the following steps:
1. Carrier Sensing:
Before transmitting data, a device using CSMA/CD listens to the network to determine if it is idle. It checks for the presence of a carrier signal, indicating ongoing transmissions by other devices.
2. Transmission Initiation:
If the network is idle, the device initiates the transmission of its data. It starts sending the frame onto the network.
3. Collision Detection:
While transmitting, the device continues to monitor the network for any collision. Collisions can occur when two or more devices attempt to transmit simultaneously, leading to a jumbled signal.
4. Jam Signal:
If a collision is detected, the transmitting devices stop transmitting and send a jam signal to alert other devices about the collision. The jam signal ensures that all devices on the network are aware of the collision.
5. Backoff and Retransmission:
After sending the jam signal, the devices that experienced the collision enter a random backoff period before attempting retransmission. This randomization reduces the likelihood of collisions happening repeatedly.
6. Retry Mechanism:
The devices attempt retransmission after the backoff period. If the network remains busy, the devices may go through multiple backoff and retry cycles until successful transmission.
Difference Between CSMA/CD and Token Passing Access Methods:
CSMA/CD (Carrier Sense Multiple Access with Collision Detection):
1. Nature:
CSMA/CD is a contention-based access method, where devices contend for access to the shared network medium.
2. Collision Handling:
CSMA/CD uses collision detection and resolution. If a collision occurs, devices involved in the collision stop transmitting, send a jam signal, and then enter a backoff period before retransmission.
3. Topology:
CSMA/CD is commonly used in bus and star topologies, where multiple devices share a common communication medium.
4. Efficiency:
As the number of devices on the network increases, the probability of collisions also increases, potentially impacting the efficiency of the network.
Token Passing:
1. Nature:
Token passing is a deterministic access method, where devices take turns accessing the network based on a token that circulates the network.
2. Collision Handling:
Token passing inherently avoids collisions because only the device holding the token can transmit. There is no contention for access, eliminating the need for collision detection.
3. Topology:
Token passing is commonly used in ring topologies, where devices are connected in a closed-loop, and a token circulates sequentially.
4. Efficiency:
Token passing can be more efficient in certain scenarios as it avoids contention and collisions. However, the efficiency may decrease as the network size increases due to the time it takes for the token to circulate.
In summary, CSMA/CD and token passing represent different approaches to managing access to a shared network medium. CSMA/CD relies on contention and collision detection, while token passing uses a deterministic token circulation method to control access. The choice between these methods depends on factors such as network topology, scalability requirements, and the likelihood of collisions in the network.
(b) Describe the concept and advantages of using EFS services in Windows 2000. 7
Answer:
Encrypting File System (EFS) Services in Windows 2000:
Concept of EFS: Encrypting File System (EFS) is a feature in Windows operating systems, including Windows 2000, that provides file-level encryption to protect sensitive data stored on NTFS (New Technology File System) volumes. EFS uses public key cryptography to secure files and folders, ensuring that only authorized users can access the encrypted content.
Advantages of EFS Services in Windows 2000:
1. Data Confidentiality:
EFS ensures the confidentiality of data by encrypting files and folders. Even if unauthorized users gain physical access to the storage media, they cannot read the encrypted content without the appropriate encryption keys.
2. User-Level Encryption:
EFS operates at the user level, allowing individual users to encrypt their own files. Each user has a unique set of encryption keys, providing a personalized security layer.
3. Seamless Integration with NTFS:
EFS seamlessly integrates with the NTFS file system, making it a native and efficient solution for securing files. Users can enable encryption on specific files or folders through the file properties in Windows Explorer.
4. Transparent Encryption and Decryption:
Once a user encrypts a file, EFS transparently encrypts and decrypts the file on the fly during read and write operations. Users don't need to manually decrypt files before accessing them; the process is seamless and automatic.
5. Scalability:
EFS is designed to scale with the needs of the organization. It can be implemented on individual workstations or across enterprise networks, providing flexibility in securing data at various levels.
6. Integration with Active Directory:
In a domain environment, EFS integrates with Active Directory, allowing administrators to manage encryption policies centrally. This enables efficient key recovery and simplifies the administration of EFS across a network.
7. Recovery of Encrypted Files:
Windows 2000 provides a mechanism for recovering encrypted files in case a user loses access to their private key. Authorized recovery agents can assist in recovering encrypted data, ensuring data accessibility in critical scenarios.
8. Selective Encryption:
EFS allows users to selectively encrypt specific files or folders based on their sensitivity. This granular control ensures that only the necessary data is encrypted, minimizing the impact on system performance.
9. Secure Key Storage:
EFS securely stores users' private encryption keys. These keys are protected with the user's logon credentials, ensuring that only authorized users can access their encrypted data.
10. File and Folder Sharing:
EFS supports secure sharing of encrypted files and folders among authorized users. As long as the recipient has the necessary permissions, they can access and work with the encrypted content.
11. Compliance and Regulation:
EFS helps organizations comply with security regulations and standards that mandate the protection of sensitive data. It provides a robust solution for encrypting data to meet legal and regulatory requirements.
EFS services in Windows 2000 offer a powerful and flexible solution for securing sensitive data at the file level. By leveraging encryption and key management, EFS enhances data confidentiality and provides administrators with the tools needed to implement and manage encryption policies across Windows networks.
(c) What option in Registry Management will be useful in tracking who accessed the registry, from where, and when? Also, write the steps for enabling this option. 5
Answer: In Windows, auditing registry access can be achieved using the "Audit Registry" option, which is a part of the Windows Security Policy settings. This option allows you to track who accessed the registry, from where, and when by generating audit events in the Windows Security Event Log.
Steps for Enabling Registry Access Auditing:
1. Access Local Group Policy Editor:
Press Win + R to open the Run dialog, type gpedit.msc, and press Enter. This opens the Local Group Policy Editor.
2. Navigate to Registry Audit Policy:
In the Local Group Policy Editor, navigate to the following path:
Computer Configuration -> Windows Settings -> Security Settings -> Advanced Audit Policy Configuration -> Object Access
3. Enable Audit Registry:
In the right pane, double-click on "Audit Registry" to open its properties.
4. Configure Auditing Settings:
Select the "Define these policy settings" option.
Check the boxes for "Success" and/or "Failure" based on your auditing requirements.
5. Configure Auditing for Specific Subcategories (Optional):
Click on the "Subcategories of Object Access...
