COM FACTS

Facts on COM
1. What are the two types of transmission technology available?
(i) Broadcast and (ii) point-to-point
2. What is subnet?
A generic term for section of a large networks usually separated by a bridge or router.
3. Difference between the communication and transmission.
Transmission is a physical movement of information and concern issues like bit polarity,
synchronisation, clock etc.
Communication means the meaning full exchange of information between two communication
media.
4. What are the possible ways of data exchange?
(i) Simplex (ii) Half-duplex (iii) Full-duplex.
5. What is SAP?
Series of interface points that allow other computers to communicate with the other layers of
network protocol stack.
6. What do you meant by "triple X" in Networks?
The function of PAD (Packet Assembler Disassemble) is described in a document known as X.3.
The standard protocol has been defined between the terminal and the PAD, called X.28; another
standard protocol exists between the PAD and the network, called X.29. Together, these three
recommendations are often called "triple X"
7. What is frame relay, in which layer it comes?
Frame relay is a packet switching technology. It will operate in the data link layer.
8.What is terminal emulation, in which layer it comes?
Telnet is also called as terminal emulation. It belongs to application layer.
9. What is Beaconing?
The process that allows a network to self-repair networks problems. The stations on the network
notify the other stations on the ring when they are not receiving the transmissions. Beaconing is
used in Token ring and FDDI networks.
10. What is redirector?
Redirector is software that intercepts file or prints I/O requests and translates them into network
requests. This comes under presentation layer.
11. What is NETBIOS and NETBEUI?
NETBIOS is a programming interface that allows I/O requests to be sent to and received from a
remote computer and it hides the networking hardware from applications.
NETBEUI is Net BIOS extended user interface. A transport protocol designed by Microsoft and IBM
for the use on small subnets.
12. What is RAID?
A method for providing fault tolerance by using multiple hard disk drives.
13. What is passive topology?
When the computers on the network simply listen and receive the signal, they are referred to as
passive because they don’t amplify the signal in any way. Example for passive topology - linear
bus.
14. What is Brouter?
Hybrid devices that combine the features of both bridges and routers.
15. What is cladding?
A layer of a glass surrounding the center fiber of glass inside a fiber-optic cable.
16. What is point-to-point protocol
A communications protocol used to connect computers to remote networking services including
Internet service providers.
17. How Gateway is different from Routers?
A gateway operates at the upper levels of the OSI model and translates information between two
completely different network architectures or data formats
18. What is attenuation?
The degeneration of a signal over distance on a network cable is called attenuation.
19. What is MAC address?
The address for a device as it is identified at the Media Access Control (MAC) layer in the network
architecture. MAC address is usually stored in ROM on the network adapter card and is unique.
20. Difference between bit rate and baud rate.
Bit rate is the number of bits transmitted during one second whereas baud rate refers to the
number of signal units per second that are required to represent those bits.
baud rate = bit rate / N
where N is no-of-bits represented by each signal shift.
21. What is Bandwidth?
Every line has an upper limit and a lower limit on the frequency of signals it can carry. This limited
range is called the bandwidth.
22. What are the types of Transmission media?
Signals are usually transmitted over some transmission media that are broadly classified in to two
categories.
23. 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.
24. What is Project 802?
It is a project started by IEEE to set standards to 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 nonarchitecture-
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.
25. What is Protocol Data Unit?
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).
26. What are the different type of networking / internetworking devices?
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.
27. What is ICMP?
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.
28. What are the data units at different layers of the TCP / IP protocol suite?
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.
29. What is difference between ARP and RARP?
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.
30. What is the minimum and maximum length of the header in the TCP segment and IP
datagram?
The header should have a minimum length of 20 bytes and can have a maximum length of 60
bytes.
31. What is the range of addresses in the classes of internet addresses?
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
32. What is the difference between TFTP and FTP application layer protocols?
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 offer 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.
33. What are major types of networks and explain?
· Server-based network
· Peer-to-peer network
Peer-to-peer network, computers can act as both servers sharing resources and as clients using
the resources.
Server-based networks provide centralized control of network resources and rely on server
computers to provide security and network administration
34. What are the important topologies for networks?
· 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.
35. What is mesh network?
A network in which there are multiple network links between computers to provide multiple paths
for data to travel.
36. What is difference between baseband and broadband transmission?
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.
37. Explain 5-4-3 rule?
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.
38. What MAU?
In token Ring , hub is called Multistation Access Unit(MAU).
39. What is the difference between routable and non- routable protocols?
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
40. Why should you care about the OSI Reference Model?
It provides a framework for discussing network operations and design.
41. What is logical link control?
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.
42. What is virtual channel?
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.
43. What is virtual path?
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.
44. What is packet filter?
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.
45. What is traffic shaping?
One of the main causes of congestion is that traffic is often busy. If hosts could be made to
transmit at a uniform rate, congestion would be less common. Another open loop method to help
manage congestion is forcing the packet to be transmitted at a more predictable rate. This is
called traffic shaping.
46. What is multicast routing?
Sending a message to a group is called multicasting, and its routing algorithm is called multicast
routing.
47. What is region?
When hierarchical routing is used, the routers are divided into what we will call regions, with each
router knowing all the details about how to route packets to destinations within its own region, but
knowing nothing about the internal structure of other regions.
48. What is silly window syndrome?
It is a problem that can ruin TCP performance. This problem occurs when data are passed to the
sending TCP entity in large blocks, but an interactive application on the receiving side reads 1 byte
at a time.
49. What are Digrams and Trigrams?
The most common two letter combinations are called as digrams. e.g. th, in, er, re and an. The
most common three letter combinations are called as trigrams. e.g. the, ing, and, and ion.
50. Expand IDEA.
IDEA stands for International Data Encryption Algorithm.
51. What is wide-mouth frog?
Wide-mouth frog is the simplest known key distribution center (KDC) authentication protocol.
52. What is Mail Gateway?
It is a system that performs a protocol translation between different electronic mail delivery
protocols.
53. What is IGP (Interior Gateway Protocol)?
It is any routing protocol used within an autonomous system.
54. What is EGP (Exterior Gateway Protocol)?
It is the protocol the routers in neighboring autonomous systems use to identify the set of
networks that can be reached within or via each autonomous system.
55. What is autonomous system?
It is a collection of routers under the control of a single administrative authority and that uses a
common Interior Gateway Protocol.
56. What is BGP (Border Gateway Protocol)?
It is a protocol used to advertise the set of networks that can be reached with in an autonomous
system. BGP enables this information to be shared with the autonomous system. This is newer
than EGP (Exterior Gateway Protocol).
57. What is Gateway-to-Gateway protocol?
It is a protocol formerly used to exchange routing information between Internet core routers.
58. What is NVT (Network Virtual Terminal)?
It is a set of rules defining a very simple virtual terminal interaction. The NVT is used in the start
of a Telnet session.