**Introduction to Computer Networking 200 Essential Questions and Answers
1. What is a Link?
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A link refers to the connectivity between two devices. It includes the type of cables and protocols used in order for one device to be able to communicate with the other.
2. What are the layers of the OSI reference model?
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There are 7 OSI layers: Physical Layer, Data Link Layer, Network Layer, Transport Layer, Session Layer, Presentation Layer and Application Layer.
3. What is backbone network?
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A backbone network is a centralized infrastructure that is designed to distribute different routes and data to various networks. It also handles management of bandwidth and various channels.
4. What is a LAN?
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LAN is short for Local Area Network. It refers to the connection between computers and other network devices that are located within a small physical location.
5. What is a node?
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A node refers to a point or joint where a connection takes place. It can be computer or device that is part of a network. Two or more nodes are needed in order to form a network connection.
6. What are routers?
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Routers can connect two or more network segments. These are intelligent network devices that store information in its routing table such as paths, hops and bottlenecks. With this info, they are able to determine the best path for data transfer. Routers operate at the OSI Network Layer.
7. What is point to point link?
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It refers to a direct connection between two computers on a network. A point to point connection does not need any other network devices other than connecting a cable to the NIC cards of both computers.
8. What is anonymous FTP?
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Anonymous FTP is a way of granting user access to files in public servers. Users that are allowed access to data in these servers do not need to identify themselves, but instead log in as an anonymous guest.
9. What is subnet mask?
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A subnet mask is combined with an IP address in order to identify two parts: the extended network address and the host address. Like an IP address, a subnet mask is made up of 32 bits.
10. What is the maximum length allowed for a UTP cable?
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A single segment of UTP cable has an allowable length of 90 to 100 meters. This limitation can be overcome by using repeaters and switches.
11. What is data encapsulation?
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Data encapsulation is the process of breaking down information into smaller manageable chunks before it is transmitted across the network. It is also in this process that the source and destination addresses are attached into the headers, along with parity checks.
12. Describe Network Topology
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Network Topology refers to the layout of a computer network. It shows how devices and cables are physically laid out, as well as how they connect to one another.
13. What is VPN?
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VPN means Virtual Private Network, a technology that allows a secure tunnel to be created across a network such as the Internet. For example, VPNs allow you to establish a secure dial-up connection to a remote server.
14. Briefly describe NAT.
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NAT is Network Address Translation. This is a protocol that provides a way for multiple computers on a common network to share single connection to the Internet.
15. What is the job of the Network Layer under the OSI reference model?
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The Network layer is responsible for data routing, packet switching and control of network congestion. Routers operate under this layer.
16. How does a network topology affect your decision in setting up a network?
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Network topology dictates what media you must use to interconnect devices. It also serves as basis on what materials, connector and terminations that is applicable for the setup.
17. What is RIP?
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RIP, short for Routing Information Protocol is used by routers to send data from one network to another. It efficiently manages routing data by broadcasting its routing table to all other routers within the network. It determines the network distance in units of hops.
18. What are different ways of securing a computer network?
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There are several ways to do this. Install reliable and updated anti-virus program on all computers. Make sure firewalls are setup and configured properly. User authentication will also help a lot. All of these combined would make a highly secured network.
19. What is NIC?
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NIC is short for Network Interface Card. This is a peripheral card that is attached to a PC in order to connect to a network. Every NIC has its own MAC address that identifies the PC on the network.
20. What is WAN?
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WAN stands for Wide Area Network. It is an interconnection of computers and devices that are geographically dispersed. It connects networks that are located in different regions and countries.
21. What is the importance of the OSI Physical Layer?
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The physical layer does the conversion from data bits to electrical signal, and vice versa. This is where network devices and cable types are considered and setup.
22. How many layers are there under TCP/IP?
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There are four layers: the Network Layer, Internet Layer, Transport Layer and Application Layer.
23. What are proxy servers and how do they protect computer networks?
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Proxy servers primarily prevent external users who identifying the IP addresses of an internal network. Without knowledge of the correct IP address, even the physical location of the network cannot be identified. Proxy servers can make a network virtually invisible to external users.
24. What is the function of the OSI Session Layer?
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This layer provides the protocols and means for two devices on the network to communicate with each other by holding a session. This includes setting up the session, managing information exchange during the session, and tear-down process upon termination of the session.
25. What is the importance of implementing a Fault Tolerance System? Are there limitations?
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A fault tolerance system ensures continuous data availability. This is done by eliminating a single point of failure. However, this type of system would not be able to protect data in some cases, such as in accidental deletions.
26. What does 10Base-T mean?
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The 10 refers to the data transfer rate, in this case is 10Mbps. The word Base refers to base band, as oppose to broad band. T means twisted pair, which is the cable used for that network.
27. What is a private IP address?
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Private IP addresses are assigned for use on intranets. These addresses are used for internal networks and are not routable on external public networks. These ensures that no conflicts are present among internal networks while at the same time the same range of private IP addresses are reusable for multiple intranets since they do not “see” each other.
28. What is NOS?
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NOS, or Network Operating System, is specialized software whose main task is to provide network connectivity to a computer in order for it to be able to communicate with other computers and connected devices.
29. What is DoS?
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DoS, or Denial-of-Service attack, is an attempt to prevent users from being able to access the internet or any other network services. Such attacks may come in different forms and are done by a group of perpetuators. One common method of doing this is to overload the system server so it cannot anymore process legitimate traffic and will be forced to reset.
30. What is OSI and what role does it play in computer networks?
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OSI (Open Systems Interconnect) serves as a reference model for data communication. It is made up of 7 layers, with each layer defining a particular aspect on how network devices connect and communicate with one another. One layer may deal with the physical media used, while another layer dictates how data is actually transmitted across the network.
31. What is the purpose of cables being shielded and having twisted pairs?
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The main purpose of this is to prevent crosstalk. Crosstalks are electromagnetic interferences or noise that can affect data being transmitted across cables.
32. What is the advantage of address sharing?
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By using address translation instead of routing, address sharing provides an inherent security benefit. That’s because host PCs on the Internet can only see the public IP address of the external interface on the computer that provides address translation and not the private IP addresses on the internal network.
33. What are MAC addresses?
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MAC, or Media Access Control, uniquely identifies a device on the network. It is also known as physical address or Ethernet address. A MAC address is made up of 6-byte parts.
34. What is the equivalent layer or layers of the TCP/IP Application layer in terms of OSI reference model?
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The TCP/IP Application layer actually has three counterparts on the OSI model: the Session layer, Presentation Layer and Application Layer.
35. How can you identify the IP class of a given IP address?
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By looking at the first octet of any given IP address, you can identify whether it’s Class A, B or C. If the first octet begins with a 0 bit, that address is Class A. If it begins with bits 10 then that address is a Class B address. If it begins with 110, then it’s a Class C network.
36. What is the main purpose of OSPF?
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OSPF, or Open Shortest Path First, is a link-state routing protocol that uses routing tables to determine the best possible path for data exchange.
37. What are firewalls?
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Firewalls serve to protect an internal network from external attacks. These external threats can be hackers who want to steal data or computer viruses that can wipe out data in an instant. It also prevents other users from external networks from gaining access to the private network.
38. Describe star topology
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Star topology consists of a central hub that connects to nodes. This is one of the easiest to setup and maintain.
39. What are gateways?
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Gateways provide connectivity between two or more network segments. It is usually a computer that runs the gateway software and provides translation services. This translation is a key in allowing different systems to communicate on the network.
40. What is the disadvantage of a star topology?
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One major disadvantage of star topology is that once the central hub or switch get damaged, the entire network becomes unusable.
41. What is SLIP?
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SLIP, or Serial Line Interface Protocol, is actually an old protocol developed during the early UNIX days. This is one of the protocols that are used for remote access.
42. Give some examples of private network addresses.
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10.0.0.0 with a subnet mask of 255.0.0.0 172.16.0.0 with subnet mask of 255.240.0.0 192.168.0.0 with subnet mask of 255.255.0.0
43. What is tracert?
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Tracert is a Windows utility program that can used to trace the route taken by data from the router to the destination network. It also shows the number of hops taken during the entire transmission route.
44. What are the functions of a network administrator?
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A network administrator has many responsibilities that can be summarize into 3 key functions: installation of a network, configuration of network settings, and maintenance/troubleshooting of networks.
45. Describe at one disadvantage of a peer to peer network.
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When you are accessing the resources that are shared by one of the workstations on the network, that workstation takes a performance hit.
46. What is Hybrid Network?
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A hybrid network is a network setup that makes use of both client-server and peer-to-peer architecture.
47. What is DHCP?
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DHCP is short for Dynamic Host Configuration Protocol. Its main task is to automatically assign an IP address to devices across the network. It first checks for the next available address not yet taken by any device, then assigns this to a network device.
48. What is the main job of the ARP?
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The main task of ARP or Address Resolution Protocol is to map a known IP address to a MAC layer address.
49. What is TCP/IP?
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TCP/IP is short for Transmission Control Protocol / Internet Protocol. This is a set of protocol layers that is designed to make data exchange possible on different types of computer networks, also known as heterogeneous network.
50. How can you manage a network using a router?
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Routers have built in console that lets you configure different settings, like security and data logging. You can assign restrictions to computers, such as what resources it is allowed access, or what particular time of the day they can browse the internet. You can even put restrictions on what websites are not viewable across the entire network.
51. What protocol can be applied when you want to transfer files between different platforms, such between UNIX systems and Windows servers?
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Use FTP (File Transfer Protocol) for file transfers between such different servers. This is possible because FTP is platform independent.
52. What is the use of a default gateway?
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Default gateways provide means for the local networks to connect to the external network. The default gateway for connecting to the external network is usually the address of the external router port.
53. One way of securing a network is through the use of passwords. What can be considered as good passwords?
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Good passwords are made up of not just letters, but by combining letters and numbers. A password that combines uppercase and lowercase letters is favorable than one that uses all upper case or all lower case letters. Passwords must be not words that can easily be guessed by hackers, such as dates, names, favorites, etc. Longer passwords are also better than short ones.
54. What is the proper termination rate for UTP cables?
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The proper termination for unshielded twisted pair network cable is 100 ohms.
55. What is netstat?
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Netstat is a command line utility program. It provides useful information about the current TCP/IP settings of a connection.
56. What is the number of network IDs in a Class C network?
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For a Class C network, the number of usable Network ID bits is 21. The number of possible network IDs is 2 raised to 21 or 2,097,152. The number of host IDs per network ID is 2 raised to 8 minus 2, or 254.
57. What happens when you use cables longer than the prescribed length?
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Cables that are too long would result in signal loss. This means that data transmission and reception would be affected, because the signal degrades over length.
58. What common software problems can lead to network defects?
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Software related problems can be any or a combination of the following:
- client server problems
- application conflicts
- error in configuration
- protocol mismatch
- security issues
- user policy and rights issues
59. What is ICMP?
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ICMP is Internet Control Message Protocol. It provides messaging and communication for protocols within the TCP/IP stack. This is also the protocol that manages error messages that are used by network tools such as PING.
60. What is Ping?
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Ping is a utility program that allows you to check connectivity between network devices on the network. You can ping a device by using its IP address or device name, such as a computer name.
61. What is peer to peer?
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Peer to peer are networks that does not reply on a server. All PCs on this network act as individual workstations.
62. What is DNS?
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DNS is Domain Name System. The main function of this network service is to provide host names to TCP/IP address resolution.
63. What advantages does fiber optics have over other media?
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One major advantage of fiber optics is that is it less susceptible to electrical interference. It also supports higher bandwidth, meaning more data can be transmitted and received. Signal degrading is also very minimal over long distances.
64. What is the difference between a hub and a switch?
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A hub acts as a multiport repeater. However, as more and more devices connect to it, it would not be able to efficiently manage the volume of traffic that passes through it. A switch provides a better alternative that can improve the performance especially when high traffic volume is expected across all ports.
65. What are the different network protocols that are supported by Windows RRAS services?
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There are three main network protocols supported: NetBEUI, TCP/IP, and IPX.
66. What are the maximum networks and hosts in a class A, B and C network?
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For Class A, there are 126 possible networks and 16,777,214 hosts For Class B, there are 16,384 possible networks and 65,534 hosts For Class C, there are 2,097,152 possible networks and 254 hosts
67. What is the standard color sequence of a straight-through cable?
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orange/white, orange, green/white, blue, blue/white, green, brown/white, brown.
68. What protocols fall under the Application layer of the TCP/IP stack?
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The following are the protocols under TCP/IP Application layer: FTP, TFTP, Telnet and SMTP.
69. You need to connect two computers for file sharing. Is it possible to do this without using a hub or router?
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Yes, you can connect two computers together using only one cable. A crossover type cable can be use in this scenario. In this setup, the data transmit pin of one cable is connected to the data receive pin of the other cable, and vice versa.
70. What is ipconfig?
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Ipconfig is a utility program that is commonly used to identify the addresses information of a computer on a network. It can show the physical address as well as the IP address.
71. What is the difference between a straight-through and crossover cable?
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A straight-through cable is used to connect computers to a switch, hub or router. A crossover cable is used to connect two similar devices together, such as a PC to PC or Hub to hub.
72. What is client/server?
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Client/server is a type of network wherein one or more computers act as servers. Servers provide a centralized repository of resources such as printers and files. Clients refers to workstation that access the server.
73. Describe networking.
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Networking refers to the inter connection between computers and peripherals for data communication. Networking can be done using wired cabling or through wireless link.
74. When you move the NIC cards from one PC to another PC, does the MAC address gets transferred as well?
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Yes, that’s because MAC addresses are hard-wired into the NIC circuitry, not the PC. This also means that a PC can have a different MAC address when the NIC card was replace by another one.
75. Explain clustering support
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Clustering support refers to the ability of a network operating system to connect multiple servers in a fault-tolerant group. The main purpose of this is the in the event that one server fails, all processing will continue on with the next server in the cluster.
76. In a network that contains two servers and twenty workstations, where is the best place to install an Anti-virus program?
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An anti-virus program must be installed on all servers and workstations to ensure protection. That’s because individual users can access any workstation and introduce a computer virus when plugging in their removable hard drives or flash drives.
77. Describe Ethernet.
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Ethernet is one of the popular networking technologies used these days. It was developed during the early 1970s and is based on specifications as stated in the IEEE. Ethernet is used in local area networks.
78. What are some drawbacks of implementing a ring topology?
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In case one workstation on the network suffers a malfunction, it can bring down the entire network. Another drawback is that when there are adjustments and reconfigurations needed to be performed on a particular part of the network, the entire network has to be temporarily brought down as well.
79. What is the difference between CSMA/CD and CSMA/CA?
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CSMA/CD, or Collision Detect, retransmits data frames whenever a collision occurred. CSMA/CA, or Collision Avoidance, will first broadcast intent to send prior to data transmission.
80. What is SMTP?
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SMTP is short for Simple Mail Transfer Protocol. This protocol deals with all Internal mail, and provides the necessary mail delivery services on the TCP/IP protocol stack.
81. What is multicast routing?
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Multicast routing is a targeted form of broadcasting that sends message to a selected group of user, instead of sending it to all users on a subnet.
82. What is the importance of Encryption on a network?
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Encryption is the process of translating information into a code that is unreadable by the user. It is then translated back or decrypted back to its normal readable format using a secret key or password. Encryption help ensure that information that is intercepted halfway would remain unreadable because the user has to have the correct password or key for it.
83. How are IP addresses arranged and displayed?
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IP addresses are displayed as a series of four decimal numbers that are separated by period or dots. Another term for this arrangement is the dotted decimal format. An example is 192.168.101.2
84. Explain the importance of authentication.
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Authentication is the process of verifying a user’s credentials before he can log into the network. It is normally performed using a username and password. This provides a secure means of limiting the access from unwanted intruders on the network.
85. What do mean by tunnel mode?
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This is a mode of data exchange wherein two communicating computers do not use IPSec themselves. Instead, the gateway that is connecting their LANs to the transit network creates a virtual tunnel that uses the IPSec protocol to secure all communication that passes through it.
86. What are the different technologies involved in establishing WAN links?
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Analog connections - using conventional telephone lines; Digital connections - using digital-grade telephone lines; switched connections - using multiple sets of links between sender and receiver to move data.
87. What is one advantage of mesh topology?
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In the event that one link fails, there will always be another available. Mesh topology is actually one of the most fault-tolerant network topology.
88. When troubleshooting computer network problems, what common hardware-related problems can occur?
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A large percentage of a network is made up of hardware. Problems in these areas can range from malfunctioning hard drives, broken NICs and even hardware startups. Incorrectly hardware configuration is also one of those culprits to look into.
89. What can be done to fix signal attenuation problems?
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A common way of dealing with such a problem is to use repeaters and hub, because it will help regenerate the signal and therefore prevent signal loss. Checking if cables are properly terminated is also a must.
90. How does dynamic host configuration protocol aid in network administration?
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Instead of having to visit each client computer to configure a static IP address, the network administrator can apply dynamic host configuration protocol to create a pool of IP addresses known as scopes that can be dynamically assigned to clients.
91. Explain profile in terms of networking concept?
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Profiles are the configuration settings made for each user. A profile may be created that puts a user in a group, for example.
92. What is sneakernet?
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Sneakernet is believed to be the earliest form of networking wherein data is physically transported using removable media, such as disk, tapes.
93. What is the role of IEEE in computer networking?
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IEEE, or the Institute of Electrical and Electronics Engineers, is an organization composed of engineers that issues and manages standards for electrical and electronic devices. This includes networking devices, network interfaces, cablings and connectors.
94. What protocols fall under the TCP/IP Internet Layer?
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There are 4 protocols that are being managed by this layer. These are ICMP, IGMP, IP and ARP.
95. When it comes to networking, what are rights?
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Rights refer to the authorized permission to perform specific actions on the network. Each user on the network can be assigned individual rights, depending on what must be allowed for that user.
96. What is one basic requirement for establishing VLANs?
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A VLAN is required because at switch level there is only one broadcast domain, it means whenever new user is connected to switch this information is spread throughout the network. VLAN on switch helps to create separate broadcast domain at switch level. It is used for security purpose.
97. What is IPv6?
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IPv6 , or Internet Protocol version 6, was developed to replace IPv4. At present, IPv4 is being used to control internet traffic, but is expected to get saturated in the near future. IPv6 was designed to overcome this limitation.
98. What is RSA algorithm?
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RSA is short for Rivest-Shamir-Adleman algorithm. It is the most commonly used public key encryption algorithm in use today.
99. What is mesh topology?
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Mesh topology is a setup wherein each device is connected directly to every other device on the network. Consequently, it requires that each device have at least two network connections.
100. What is the maximum segment length of a 100Base-FX network?
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The maximum allowable length for a network segment using 100Base-FX is 412 meters. The maximum length for the entire network is 5 kilometers.
101. Define Network?
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A network is a set of devices connected by physical media links. A network is recursively is a connection of two or more nodes by a physical link or two or more networks connected by one or more nodes.
102. What is a Link?
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At the lowest level, a network can consist of two or more computers directly connected by some physical medium such as coaxial cable or optical fiber. Such a physical medium is called as Link.
103. What is a node?
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A network can consist of two or more computers directly connected by some physical medium such as coaxial cable or optical fiber. Such a physical medium is called as Links and the computer it connects is called as Nodes.
104. What is a gateway or Router?
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A node that is connected to two or more networks is commonly called as router or Gateway. It generally forwards message from one network to another.
105. What is point-point link?
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If the physical links are limited to a pair of nodes it is said to be point-point link.
106. What is Multiple Access?
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If the physical links are shared by more than two nodes, it is said to be Multiple Access.
107. What are the advantages of Distributed Processing?
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a. Security/Encapsulation b. Distributed database c. Faster Problem solving d. Security through redundancy e. Collaborative Processing
108. What are the criteria necessary for an effective and efficient network?
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a. Performance It can be measured in many ways, including transmit time and response time. b. Reliability It is measured by frequency of failure, the time it takes a link to recover from a failure, and the network’s robustness. c. Security Security issues includes protecting data from unauthorized access and viruses.
109. Name the factors that affect the performance of the network?
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a. Number of Users b. Type of transmission medium c. Hardware d. Software
110. Name the factors that affect the reliability of the network?
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a. Frequency of failure b. Recovery time of a network after a failure
111. Name the factors that affect the security of the network?
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a. Unauthorized Access b. Viruses
112. What is Protocol?
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A protocol is a set of rules that govern all aspects of information communication.
113. What are the key elements of protocols?
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The key elements of protocols are a. Syntax It refers to the structure or format of the data, that is the order in which they are presented. b. Semantics It refers to the meaning of each section of bits. c. Timing Timing refers to two characteristics: When data should be sent and how fast they can be sent.
114. What are the key design issues of a computer Network?
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a. Connectivity b. Cost-effective Resource Sharing c. Support for common Services d. Performance
115. Define Bandwidth and Latency?
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Network performance is measured in Bandwidth (throughput) and Latency (Delay). Bandwidth of a network is given by the number of bits that can be transmitted over the network in a certain period of time. Latency corresponds to how long it takes a message to travel from one end off a network to the other. It is strictly measured in terms of time.
116. Define Routing?
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The process of determining systematically hoe to forward messages toward the destination nodes based on its address is called routing.
117. What is a peer-peer process?
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The processes on each machine that communicate at a given layer are called peer-peer process.
118. When a switch is said to be congested?
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It is possible that a switch receives packets faster than the shared link can accommodate and stores in its memory, for an extended period of time, then the switch will eventually run out of buffer space, and some packets will have to be dropped and in this state is said to congested state.
119. What is semantic gap?
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Defining a useful channel involves both understanding the applications requirements and recognizing the limitations of the underlying technology. The gap between what applications expects and what the underlying technology can provide is called semantic gap.
120. What is Round Trip Time?
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The duration of time it takes to send a message from one end of a network to the other and back, is called RTT.
121. Define the terms Unicasting, Multiccasting and Broadcasting?
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If the message is sent from a source to a single destination node, it is called Unicasting. If the message is sent to some subset of other nodes, it is called Multicasting. If the message is sent to all the m nodes in the network it is called Broadcasting.
122. What is Multiplexing?
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Multiplexing is the set of techniques that allows the simultaneous transmission of multiple signals across a single data link.
123. Name the categories of Multiplexing?
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a. Frequency Division Multiplexing (FDM) b. Time Division Multiplexing (TDM) i. Synchronous TDM ii. ASynchronous TDM Or Statistical TDM c. Wave Division Multiplexing (WDM)
124. What is FDM?
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FDM is an analog technique that can be applied when the bandwidth of a link is greater than the combined bandwidths of the signals to be transmitted.
125. What is WDM?
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WDM is conceptually the same as FDM, except that the multiplexing and demultiplexing involve light signals transmitted through fiber optics channel.
126. What is TDM?
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TDM is a digital process that can be applied when the data rate capacity of the transmission medium is greater than the data rate required by the sending and receiving devices.
127. What is Synchronous TDM?
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In STDM, the multiplexer allocates exactly the same time slot to each device at all times, whether or not a device has anything to transmit.
128. List the layers of OSI
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a. Physical Layer b. Data Link Layer c. Network Layer d. Transport Layer e. Session Layer f. Presentation Layer g. Application Layer
129. Which layers are network support layers?
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a. Physical Layer b. Data link Layer and c. Network Layers
130. Which layers are user support layers?
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a. Session Layer b. Presentation Layer and c. Application Layer
131. Which layer links the network support layers and user support layers?
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The Transport layer links the network support layers and user support layers.
132. What are the concerns of the Physical Layer?
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Physical layer coordinates the functions required to transmit a bit stream over a physical medium. a. Physical characteristics of interfaces and media b. Representation of bits c. Data rate d. Synchronization of bits e. Line configuration f. Physical topology g. Transmission mode
133. What are the responsibilities of Data Link Layer?
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The Data Link Layer transforms the physical layer, a raw transmission facility, to a reliable link and is responsible for node-node delivery. a. Framing b. Physical Addressing c. Flow Control d. Error Control e. Access Control
134. What are the responsibilities of Network Layer?
Answer (Click to show)
The Network Layer is responsible for the source-to-destination delivery of packet possibly across multiple networks (links). a. Logical Addressing b. Routing
135. What are the responsibilities of Transport Layer?
Answer (Click to show)
The Transport Layer is responsible for source-to-destination delivery of the entire message. a. Service-point Addressing b. Segmentation and reassembly c. Connection Control d. Flow Control e. Error Control
136. What are the responsibilities of Session Layer?
Answer (Click to show)
The Session layer is the network dialog Controller. It establishes, maintains and synchronizes the interaction between the communicating systems. a. Dialog control b. Synchronization
137. What are the responsibilities of Presentation Layer?
Answer (Click to show)
The Presentation layer is concerned with the syntax and semantics of the information exchanged between two systems. a. Translation b. Encryption c. Compression
138. What are the responsibilities of Application Layer?
Answer (Click to show)
The Application Layer enables the user, whether human or software, to access the network. It provides user interfaces and support for services such as e-mail, shared database management and other types of distributed information services. a. Network virtual Terminal b. File transfer, access and Management (FTAM) c. Mail services d. Directory Services
139. What are the two classes of hardware building blocks?
Answer (Click to show)
Nodes and Links.
140. What are the different link types used to build a computer network?
Answer (Click to show)
a. Cables b. Leased Lines c. Last-Mile Links d. Wireless Links
141. What are the categories of Transmission media?
Answer (Click to show)
a. Guided Media i. Twisted - Pair cable 1. Shielded TP 2. Unshielded TP ii. Coaxial Cable iii. Fiber-optic cable b. Unguided Media i. Terrestrial microwave ii. Satellite Communication
142. What are the types of errors?
Answer (Click to show)
a. Single-Bit error In a single-bit error, only one bit in the data unit has changed b. Burst Error A Burst error means that two or more bits in the data have changed.
143. What is Error Detection? What are its methods?
Answer (Click to show)
Data can be corrupted during transmission. For reliable communication errors must be deducted and Corrected. Error Detection uses the concept of redundancy, which means adding extra bits for detecting errors at the destination. The common Error Detection methods are a. Vertical Redundancy Check (VRC) b. Longitudinal Redundancy Check (VRC) c. Cyclic Redundancy Check (VRC) d. Checksum
144. What is Redundancy?
Answer (Click to show)
The concept of including extra information in the transmission solely for the purpose of comparison. This technique is called redundancy.
145. What is VRC?
Answer (Click to show)
It is the most common and least expensive mechanism for Error Detection. In VRC, a parity bit is added to every data unit so that the total number of 1s becomes even for even parity. It can detect all single-bit errors. It can detect burst errors only if the total number of errors in each data unit is odd.
146. What is LRC?
Answer (Click to show)
In LRC, a block of bits is divided into rows and a redundant row of bits is added to the whole block. It can detect burst errors. If two bits in one data unit are damaged and bits in exactly the same positions in another data unit are also damaged, the LRC checker will not detect an error.
147. What is CRC?
Answer (Click to show)
CRC, is the most powerful of the redundancy checking techniques, is based on binary division.
148. What is Checksum?
Answer (Click to show)
Checksum is used by the higher layer protocols (TCP/IP) for error detection
149. List the steps involved in creating the checksum.
Answer (Click to show)
a. Divide the data into sections b. Add the sections together using 1’s complement arithmetic c. Take the complement of the final sum, this is the checksum.
150. What are the Data link protocols?
Answer (Click to show)
Data link protocols are sets of specifications used to implement the data link layer. The categories of Data Link protocols are
- Asynchronous Protocols
- Synchronous Protocols a. Character Oriented Protocols b. Bit Oriented protocols
151. Compare Error Detection and Error Correction?
Answer (Click to show)
The correction of errors is more difficult than the detection. In error detection, checks only any error has occurred. In error correction, the exact number of bits that are corrupted and location in the message are known. The number of the errors and the size of the message are important factors.
152. What is Forward Error Correction?
Answer (Click to show)
Forward error correction is the process in which the receiver tries to guess the message by using redundant bits.
153. What is Retransmission?
Answer (Click to show)
Retransmission is a technique in which the receiver detects the occurrence of an error and asks the sender to resend the message. Resending is repeated until a message arrives that the receiver believes is error-freed.
154. What are Data Words?
Answer (Click to show)
In block coding, we divide our message into blocks, each of k bits, called datawords. The block coding process is one-to-one. The same dataword is always encoded as the same codeword.
155. What are Code Words?
Answer (Click to show)
“r” redundant bits are added to each block to make the length n = k + r. The resulting n-bit blocks are called codewords. 2^n - 2^k codewords that are not used. These codewords are invalid or illegal.
156. What is a Linear Block Code?
Answer (Click to show)
A linear block code is a code in which the exclusive OR (addition modulo-2) of two valid codewords creates another valid codeword.
157. What are Cyclic Codes?
Answer (Click to show)
Cyclic codes are special linear block codes with one extra property. In a cyclic code, if a codeword is cyclically shifted (rotated), the result is another codeword.
158. Define Encoder?
Answer (Click to show)
A device or program that uses predefined algorithms to encode, or compress audio or video data for storage or transmission use. A circuit that is used to convert between digital video and analog video.
159. Define Decoder?
Answer (Click to show)
A device or program that translates encoded data into its original format (e.g. it decodes the data). The term is often used in reference to MPEG-2 video and sound data, which must be decoded before it is output.
160. What is Framing?
Answer (Click to show)
Framing in the data link layer separates a message from one source to a destination, or from other messages to other destinations, by adding a sender address and a destination address. The destination address defines where the packet has to go and the sender address helps the recipient acknowledge the receipt.
161. What is Fixed Size Framing?
Answer (Click to show)
In fixed-size framing, there is no need for defining the boundaries of the frames. The size itself can be used as a delimiter.
162. Define Character Stuffing?
Answer (Click to show)
In byte stuffing (or character stuffing), a special byte is added to the data section of the frame when there is a character with the same pattern as the flag. The data section is stuffed with an extra byte. This byte is usually called the escape character (ESC), which has a predefined bit pattern. Whenever the receiver encounters the ESC character, it removes it from the data section and treats the next character as data, not a delimiting flag.
163. What is Bit Stuffing?
Answer (Click to show)
Bit stuffing is the process of adding one extra 0 whenever five consecutive Is follow a 0 in the data, so that the receiver does not mistake the pattern 0111110 for a flag.
164. What is Flow Control?
Answer (Click to show)
Flow control refers to a set of procedures used to restrict the amount of data that the sender can send before waiting for acknowledgment.
165. What is Error Control ?
Answer (Click to show)
Error control is both error detection and error correction. It allows the receiver to inform the sender of any frames lost or damaged in transmission and coordinates the retransmission of those frames by the sender. In the data link layer, the term error control refers primarily to methods of error detection and retransmission.
166. What is Automatic Repeat Request (ARQ)?
Answer (Click to show)
Error control is both error detection and error correction. It allows the receiver to inform the sender of any frames lost or damaged in transmission and coordinates the retransmission of those frames by the sender. In the data link layer, the term error control refers primarily to methods of error detection and retransmission. Error control in the data link layer is often implemented simply: Any time an error is detected in an exchange, specified frames are retransmitted. This process is called automatic repeat request (ARQ).
167. What is Stop-and-Wait Protocol?
Answer (Click to show)
In Stop and wait protocol, sender sends one frame, waits until it receives confirmation from the receiver (okay to go ahead), and then sends the next frame.
168. What is Stop-and-Wait Automatic Repeat Request?
Answer (Click to show)
Error correction in Stop-and-Wait ARQ is done by keeping a copy of the sent frame and retransmitting of the frame when the timer expires.
169. What is usage of Sequence Number in Relaible Transmission?
Answer (Click to show)
The protocol specifies that frames need to be numbered. This is done by using sequence numbers. A field is added to the data frame to hold the sequence number of that frame. Since we want to minimize the frame size, the smallest range that provides unambiguous communication. The sequence numbers can wrap around.
170. What is Pipelining ?
Answer (Click to show)
In networking and in other areas, a task is often begun before the previous task has ended. This is known as pipelining.
171. What is Sliding Window?
Answer (Click to show)
The sliding window is an abstract concept that defines the range of sequence numbers that is the concern of the sender and receiver. In other words, he sender and receiver need to deal with only part of the possible sequence numbers.
172. What is Piggy Backing?
Answer (Click to show)
A technique called piggybacking is used to improve the efficiency of the bidirectional protocols. When a frame is carrying data from A to B, it can also carry control information about arrived (or lost) frames from B; when a frame is carrying data from B to A, it can also carry control information about the arrived (or lost) frames from A.
173. What are the two types of transmission technology available?
Answer (Click to show)
(i) Broadcast and (ii) point-to-point
174. What is subnet?
Answer (Click to show)
A generic term for section of a large networks usually separated by a bridge or router.
175. What are the possible ways of data exchange?
Answer (Click to show)
(i) Simplex (ii) Half-duplex (iii) Full-duplex.
176. What are the types of Transmission media?
Answer (Click to show)
Signals are usually transmitted over some transmission media that are broadly classified in to two categories. a) Guided Media: These are those that provide a conduit from one device to another that include twisted-pair, coaxial cable and fiber-optic cable. A signal traveling along any of these media is directed and is contained by the physical limits of the medium. Twisted-pair and coaxial cable use metallic that accept and transport signals in the form of electrical current. Optical fiber is a glass or plastic cable that accepts and transports signals in the form of light. b) Unguided Media: This is the wireless media that transport electromagnetic waves without using a physical conductor. Signals are broadcast either through air. This is done through radio communication, satellite communication and cellular telephony.
177. What is Project 802?
Answer (Click to show)
It is a project started by IEEE to set standards that enable intercommunication between equipment from a variety of manufacturers. It is a way for specifying functions of the physical layer, the data link layer and to some extent the network layer to allow for interconnectivity of major LAN protocols. It consists of the following:
- 802.1 is an internetworking standard for compatibility of different LANs and MANs across protocols.
- 802.2 Logical link control (LLC) is the upper sublayer of the data link layer which is non-architecture-specific, that is remains the same for all IEEE-defined LANs.
- Media access control (MAC) is the lower sublayer of the data link layer that contains some distinct modules each carrying proprietary information specific to the LAN product being used. The modules are Ethernet LAN (802.3), Token ring LAN (802.4), Token bus LAN (802.5).
- 802.6 is distributed queue dual bus (DQDB) designed to be used in MANs.
178. What is Protocol Data Unit?
Answer (Click to show)
The data unit in the LLC level is called the protocol data unit (PDU). The PDU contains of four fields a destination service access point (DSAP), a source service access point (SSAP), a control field and an information field. DSAP, SSAP are addresses used by the LLC to identify the protocol stacks on the receiving and sending machines that are generating and using the data. The control field specifies whether the PDU frame is a information frame (I - frame) or a supervisory frame (S - frame) or a unnumbered frame (U - frame).
179. What are the different type of networking / internetworking devices?
Answer (Click to show)
- Repeater: Also called a regenerator, it is an electronic device that operates only at physical layer. It receives the signal in the network before it becomes weak, regenerates the original bit pattern and puts the refreshed copy back in to the link.
- Bridges: These operate both in the physical and data link layers of LANs of same type. They divide a larger network in to smaller segments. They contain logic that allow them to keep the traffic for each segment separate and thus are repeaters that relay a frame only the side of the segment containing the intended recipent and control congestion.
- Routers: They relay packets among multiple interconnected networks (i.e. LANs of different type). They operate in the physical, data link and network layers. They contain software that enable them to determine which of the several possible paths is the best for a particular transmission.
- Gateways: They relay packets among networks that have different protocols (e.g. between a LAN and a WAN). They accept a packet formatted for one protocol and convert it to a packet formatted for another protocol before forwarding it. They operate in all seven layers of the OSI model.
180. What is ICMP?
Answer (Click to show)
ICMP is Internet Control Message Protocol, a network layer protocol of the TCP/IP suite used by hosts and gateways to send notification of datagram problems back to the sender. It uses the echo test / reply to test whether a destination is reachable and responding. It also handles both control and error messages.
181. What are the data units at different layers of the TCP / IP protocol suite?
Answer (Click to show)
The data unit created at the application layer is called a message, at the transport layer the data unit created is called either a segment or an user datagram, at the network layer the data unit created is called the datagram, at the data link layer the datagram is encapsulated in to a frame and finally transmitted as signals along the transmission media.
182. What is difference between ARP and RARP?
Answer (Click to show)
The address resolution protocol (ARP) is used to associate the 32 bit IP address with the 48 bit physical address, used by a host or a router to find the physical address of another host on its network by sending a ARP query packet that includes the IP address of the receiver. The reverse address resolution protocol (RARP) allows a host to discover its Internet address when it knows only its physical address.
183. What is the minimum and maximum length of the header in the TCP segment and IP datagram?
Answer (Click to show)
The header should have a minimum length of 20 bytes and can have a maximum length of 60 bytes.
184. What is the range of addresses in the classes of internet addresses?
Answer (Click to show)
Class A 0.0.0.0 - 127.255.255.255 Class B 128.0.0.0 - 191.255.255.255 Class C 192.0.0.0 - 223.255.255.255 Class D 224.0.0.0 - 239.255.255.255 Class E 240.0.0.0 - 247.255.255.255
185. What is the difference between TFTP and FTP application layer protocols?
Answer (Click to show)
The Trivial File Transfer Protocol (TFTP) allows a local host to obtain files from a remote host but does not provide reliability or security. It uses the fundamental packet delivery services offered by UDP. The File Transfer Protocol (FTP) is the standard mechanism provided by TCP / IP for copying a file from one host to another. It uses the services offered by TCP and so is reliable and secure. It establishes two connections (virtual circuits) between the hosts, one for data transfer and another for control information.
186. What are major types of networks and explain?
Answer (Click to show)
- Server-based network: provide centralized control of network resources and rely on server computers to provide security and network administration
- Peer-to-peer network: computers can act as both servers sharing resources and as clients using the resources.
187. What are the important topologies for networks?
Answer (Click to show)
- BUS topology: In this each computer is directly connected to primary network cable in a single line. Advantages: Inexpensive, easy to install, simple to understand, easy to extend.
- STAR topology: In this all computers are connected using a central hub. Advantages: Can be inexpensive, easy to install and reconfigure and easy to trouble shoot physical problems.
- RING topology: In this all computers are connected in loop. Advantages: All computers have equal access to network media, installation can be simple, and signal does not degrade as much as in other topologies because each computer regenerates it.
188. What is mesh network?
Answer (Click to show)
A network in which there are multiple network links between computers to provide multiple paths for data to travel.
189. What is difference between baseband and broadband transmission?
Answer (Click to show)
In a baseband transmission, the entire bandwidth of the cable is consumed by a single signal. In broadband transmission, signals are sent on multiple frequencies, allowing multiple signals to be sent simultaneously.
190. What is packet filter?
Answer (Click to show)
Packet filter is a standard router equipped with some extra functionality. The extra functionality allows every incoming or outgoing packet to be inspected. Packets meeting some criterion are forwarded normally. Those that fail the test are dropped.
191. What is virtual path?
Answer (Click to show)
Along any transmission path from a given source to a given destination, a group of virtual circuits can be grouped together into what is called path.
192. What is virtual channel?
Answer (Click to show)
Virtual channel is normally a connection from one source to one destination, although multicast connections are also permitted. The other name for virtual channel is virtual circuit.
193. What is logical link control?
Answer (Click to show)
One of two sublayers of the data link layer of OSI reference model, as defined by the IEEE 802 standard. This sublayer is responsible for maintaining the link between computers when they are sending data across the physical network connection.
194. Why should you care about the OSI Reference Model?
Answer (Click to show)
It provides a framework for discussing network operations and design.
195. What is the difference between routable and non- routable protocols?
Answer (Click to show)
Routable protocols can work with a router and can be used to build large networks. Non-Routable protocols are designed to work on small, local networks and cannot be used with a router.
196. What is MAU?
Answer (Click to show)
In token Ring , hub is called Multistation Access Unit(MAU).
197. Explain 5-4-3 rule.
Answer (Click to show)
In a Ethernet network, between any two points on the network, there can be no more than five network segments or four repeaters, and of those five segments only three of segments can be populated.
198. What is the difference between TFTP and FTP application layer protocols?
Answer (Click to show)
The Trivial File Transfer Protocol (TFTP) allows a local host to obtain files from a remote host but does not provide reliability or security. It uses the fundamental packet delivery services offered by UDP. The File Transfer Protocol (FTP) is the standard mechanism provided by TCP / IP for copying a file from one host to another. It uses the services offered by TCP and so is reliable and secure. It establishes two connections (virtual circuits) between the hosts, one for data transfer and another for control information.
199. What is the range of addresses in the classes of internet addresses?
Answer (Click to show)
Class A - 0.0.0.0 - 127.255.255.255 Class B - 128.0.0.0 - 191.255.255.255 Class C - 192.0.0.0 - 223.255.255.255 Class D - 224.0.0.0 - 239.255.255.255 Class E - 240.0.0.0 - 247.255.255.255
200. What is the minimum and maximum length of the header in the TCP segment and IP datagram?
Answer (Click to show)
The header should have a minimum length of 20 bytes and can have a maximum length of 60 bytes.