ITHELPDESK

What is bit synchronization? Determining the boundary (start and end) of signal cell is known as clock or bit synchronization. Why bit and frame synchronization techniques are used? Bit and frame synchronization techniques are used to make sure that  the signals sent from one host of the communication can be rightly decoded by the receiver. Uses of Synchronization techniques To guide the receiver in finding where data blocks start and end. To determine the time interval at which the sampling result is more accurate (with least errors). Data Transmission modes Asynchronous transmission Asynchronous transmission is a transmission in which there is no synchronization of sender and receiver clocks.  In this mode, each transmission element (character or byte) is treated independently. The receiver need to determine the boundary (starting and  ending) of each byte or character.  This mode is used whenever data has to be transferred in irregular intervals of time. Applic

NAT – Network Address Translation NAT definition: NAT is a method used to translate private IP addresses into a public IP address when the devices in the local network need to communicate through the internet. NAT allows a host that does not have a valid, registered, globally unique IP address to communicate with other hosts through the internet. Why NAT (Network Address Translation) is used? To extend the life of IPV4 as the network layer protocol of the internet by saving the IPV4 public address space. NAT saved the remaining unused IPV4 public address space by allowing the private addresses to communicate through the internet using one or few public address space. Instead of assigning 500 public IPs to the devices used in a company, one or two public address is sufficient for them to communicate through the Internet. Hosts in a LAN will use private IP addresses (free to use) to communicate with them. They use the purchased public address only when it is required to com

Number Keyword Description Attention Required 0 Emergency System down or unusable Severe 1 Alert Immediate  action required Severe 2 Critical Critical event Important 3 Error Error event Important 4 Warning Warning event Important 5 Notification Normal (but notable) Worth to get notified, but not to worry 6 Informational Normal (only informational) To inform the admin. 7 Debug All messages as requested by user debug Debug Cisco Syslog protocol Severity levels – Points to remember ·          Syslog messages are required to know the normal events or critical events happening in a cisco switch or router. ·          Severity level’s lowest number i.e. ‘0’ resembles the highest severity or importance. ·          The higher the number, the less important i

What is a Multimeter? Multimeter is a combination of different kind of testing meters including an ammeter, ohmmeter and voltmeter which helps to detect the correct operation or failure of various types of components. Multimeter consists of an analog or digital display, 2 probes and a selector switch. Multimeters are used to measure resistance, amperes and voltages. Beginners should prefer auto-ranging digital multimeters than buying analog multimeters for safety purposes. How to use a multimeter safely? Multimeters should not be used over maximum voltages mentioned in the multimeter. Filter capacitors in power supplies should be discharged before testing. Disconnect the input power before making resistance or diode test. Don’t attempt to repair or service the multimeter. Don’t touch the metal probes , while testing for currents and voltages. Always turn off the power and disconnect the probes before replacing the batteries or fuse in multimeters. A computer will not

Media Access method is nothing but a cable access method, which defines a set of rules to any NIC (Network Interface Card) for how to put data on and retrieve it from a network cable. Media Access Methods: CSMA/CD -  Carrier Sense Multiple Access with Collision Detection CSMA/CA – Carrier Sense Multiple Access / Collision Avoidance Token Passing or Token Ring Polling CSMA/CD (IEEE 802.3) In CSMA/CD method, every computer can transmit at any time. Hence, this method is a contention-based method. Detects collision after transmitting data. Efficient in medium-sized networks (less collisions) Ethernet (Mostly Wired LAN) works on IEEE 802.3 CSMA/CD standard. How collision occurs in CSMA/CD? How collision is detected in CSMA/CD? Step by step process: Carrier Sense: NICs that use CSMA/CD listen or sense the cable whether there is a carrier signal indicating that the network is currently being used. If the node hears a signal, it waits for a random period of time.  If no

Basics of NIC (Network Interface Card) NIC (Network Adapter)  is a physical interface between computer and cabling. NIC receives, translates, sends, and controls the flow of data. NICS translates the digital signals (data) from the computer into electrical or optic signals to make them flow through Ethernet or Fiber-optic cables. The NIC configuration consists things like a manufacturer’s MAC address, IRQ address, base I/O port address, base memory address etc.,    The proper NIC drivers should be installed to make the NICs to work efficiently. Always Install the latest NIC drivers from the device manufacturer’s website. Usually a green LED link light glows solid when plugged into the network. It indicates that there is a basic electrical connection to the network. NIC is also known as Network interface controller, Network adapter or LAN adapter. Ethernet connection uses RJ45 to connect to the NIC .(RJ stands for Registered Jack). Every manufacturer develop the

Ensure that the computer screen is disconnected from power. Wipe the screen gently with a dry cotton cloth to remove the dust. Avoid using tissue papers, paper towels etc., Prepare or buy a screen cleaning solution.  Screen cleaning solution = 50% of Distilled water (50%) + 50% of Vinegar or Isopropyl alcohol (Either Vinegar or Isopropyl alcohol, don’t use both). Fill the prepared cleaner solution into a spray bottle. Spray a small amount of cleaning solution onto the microfiber cloth or Lint-free cloth(Eye-glass cleaning cloth). Do not spray more solution as the excess moisture will affect the screen’s display performance. Also do not spray the solution directly onto the monitor. Wipe the screen slowly in small circular motions throughout the screen. Avoid scraping the stains but allow the cleaner to dissolve them. Repeat the cleaning process for tough spots. Wipe off the excess moisture with a dry cloth. Allow monitor to get dry before connecting the power cable.

Cisco Syslog Message Format Seq.No: Timestamp:  %Facility-Severity-Mnemonic:  Description Example 00011: Sep.15 20:36:15.072: %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet 0/0, changed state to up ·          Seq. No: Allows the host to use the number as an identifier for the message and also to detect whether there were any gaps in the messages that were received.       Note: Seq.No: is not enabled by default. To enable it, service sequence-numbers global                                 configuration command should be used. ·          Timestamp: Shows Date and time of the event. Timestamp can be disabled using no service timestamps global configuration command. ·          Facility:   Facility on the device that generated the log message. ·          Severity: There are 8 severity levels from 0 to 7. The lower the number, the more severe the event that caused the message. ·          Mnemonic: Text string that uniquely shows the message type.

Cisco devices try to notify administrators when major or minor events take place in the connected network.  This notifications or messages are called Syslog messages. Cisco devices can be configured to show Real-time messages and stored log messages. Real-Time Messages Real-time messages for Console users By default, Cisco IOS displays log messages to console users for all severity levels of messages. Because of the default logging console global configuration command. Real-time messages for Telnet and SSH users             By default, Cisco IOS has global configuration command – logging monitor that tells IOS to allow the sending of log messages to all logged users.       But, that default configuration is not sufficient to allow the user to view the log messages. terminal monitor EXEC command should be issued by the user during the login session to inform IOS that this terminal session would like to receive log messages. Stored Log Messages Aft