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. What are the possible ways of data exchange?(i) Simplex (ii) Half-duplex (iii) Full-duplex.

4. What is SAP?Series of interface points that allow other computers to communicate with the other layers of network protocol stack.

5. What is frame relay, in which layer it comes? Frame relay is a packet switching technology. It will operate in the data link layer.

6. What is terminal emulation, in which layer it comes?Telnet is also called as terminal emulation. It belongs to application layer.

7. What is Brouter?Hybrid devices that combine the features of both bridges and routers.

8. What is point-to-point protocol?A communications protocol used to connect computers to remote networking services including Internet service providers.

9. 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.

10. 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.

11. 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.

12. What are the types of Transmission media?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.

13. 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 LANprotocols.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.

14. 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).

15. What are the different types 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 recipient 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 enables them to determine which of the several possible paths the best for a particular transmission is.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.

16. 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.

17. 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.

18. 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.

19. 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.

20. What is the range of addresses in the classes of internet addresses? Class A 0.0.0.0 - 127.255.255.255Class B 128.0.0.0 - 191.255.255.255Class C 192.0.0.0 - 223.255.255.255Class D 224.0.0.0 - 239.255.255.255Class E 240.0.0.0 - 247.255.255.255

21. 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.

22. What is difference between baseband and broadband transmission?In a baseband transmission, the entire bandwidth of the cable is consumed by a singlesignal. In broadband transmission, signals are sent on multiple frequencies, allowing multiple signals to be sent simultaneously.

23. 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.

24. What is multicast routing?Sending a message to a group is called multicasting, and its routing algorithm is called multicast routing.

25. What is IGP (Interior Gateway Protocol)?It is any routing protocol used within an autonomous system.

26. 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.

27. 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).

28. What is Gateway-to-Gateway protocol?It is a protocol formerly used to exchange routing information between Internet core routers.

29. 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.

30. What is OSPF?It is an Internet routing protocol that scales well, can route traffic along multiple paths, and uses knowledge of an Internet's topology to make accurate routing decisions.

What Is a Network Protocol?Protocols serve as a language of communication among network devices. Network protocols like HTTP, TCP/IP, and SMTP provide a foundation that much of the Internet is built on. Find out more about these protocols and how they work.

FirewallsA network firewall guards a computer against unauthorized network access. Firewalls are one of the essential elements of a safe home or business network.

Networking Basics: EthernetEthernet is a physical and data link layer technology for local area networks (LANs). Ethernet is reliable and inexpensive, the leading standard worldwide for building wired LANs.

OSI model

Layer Function Protocols Network

ComponentsApplication

User Interface

used for applications specifically written to run over the network

allows access to network services that support applications;

directly represents the services that directly support user applications

handles network access, flow control and error recovery

Example apps are file transfer,e-mail, NetBIOS-based  applications           

DNS; FTP; TFTP; BOOTP; SNMP;RLOGIN; SMTP; MIME; NFS; FINGER; TELNET; NCP; APPC; AFP; SMB

Gateway

Presentation

Translation

Translates from application to network format and vice-versa

all different formats from all sources are made into a common uniform format that the rest of the OSI model can understand

responsible for protocol conversion, character conversion,data encryption / decryption, expanding graphics commands, data compression

sets standards for different systems to provide seamless communication from multiple

  Gateway

Redirector

protocol stacks

not always implemented in a network protocol

Session

"syncs and sessions"

establishes, maintains and ends sessions across the network

responsible for name recognition (identification) so only the designated parties can participate in the session

provides synchronization services by planning check points in the data stream => if session fails, only data after the most recent checkpoint need be transmitted

manages who can transmit data at a certain time and for how long

Examples are interactive login and file transfer connections, the session would connect and re-connect if there was an interruption; recognize names in sessions and register names in history

NetBIOS

Names Pipes

Mail Slots

RPC

Gateway

Transport

packets; flow control & error-

handling

additional connection below the session layer

manages the flow control of data between parties across the network

divides streams of data into chunks or packets; the transport layer of the receiving computer reassembles the message from packets

"train" is a good analogy => the data is divided into identical units

provides error-checking to guarantee error-free data delivery, with on losses or duplications

provides acknowledgment of successful transmissions; requests retransmission if some packets don’t arrive error-free

provides flow control and error-handling

TCP, ARP, RARP;

SPX

NWLink

NetBIOS / NetBEUI

ATP

Gateway

Advanced Cable Tester

Brouter

Network translates logical network address and names to their physical address (e.g.

IP; ARP; RARP, ICMP; RIP; OSFP;

Brouter

addressing; routing

computername ==> MAC address)

responsible for o addressingo determining routes for

sendingo managing network

problems such as packet switching, data congestion and routing

if router can’t send data frame as large as the source computer sends, the network layer compensates by breaking the data into smaller units. At the receiving end, the network layer reassembles the data

think of this layer stamping the addresses on each train car

IGMP;

IPX

NWLink

NetBEUI

OSI

DDP

DECnet

Router

Frame Relay Device

ATM Switch

Advanced Cable Tester

Data Link

data frames to bits

turns packets into raw bits 100101 and at the receiving end turns bits into packets.

handles data frames between the Network and Physical layers

the receiving end packages raw data from the Physical layer into data frames for delivery to the Network layer

responsible for error-free transfer of frames to other computer via the Physical Layer

this layer defines the methods used to transmit and receive data on the network. It consists of the wiring, the devices use to connect the NIC to the wiring, the signaling involved to transmit / receive data and the ability to detect signaling errors on the network media

Logical Link Control

error correction and flow control

manages link control and defines SAPs

802.1 OSI Model

802.2 Logical Link Control

Bridge

Switch

ISDN Router

Intelligent Hub

NIC

Advanced Cable Tester

Media Access Control

communicates with the adapter card

controls the type of media being used:

802.3 CSMA/CD (Ethernet)

802.4 Token Bus (ARCnet)

802.5 Token Ring

802.12 Demand Priority

Physical

hardware; raw bit stream

transmits raw bit stream over physical cable

defines cables, cards, and physical aspects

defines NIC attachments to hardware, how cable is attached to NIC

defines techniques to transfer bit stream to cable

IEEE 802

IEEE 802.2

ISO 2110

ISDN

Repeater

Multiplexer

Hubs

Passive Active

TDR

Oscilloscope

Amplifier

OSI Model Concepts

The standard model for networking protocols and distributed applications is the International Standard Organization's Open System Interconnect (ISO/OSI) model. It defines seven network layers. 

Short for Open System Interconnection, an ISO standard for worldwide communications that defines a networking framework for implementing protocols in seven layers. Control is passed from one layer to the next, starting at the application layer in one station, proceeding to the bottom layer, over the channel to the next station and back up the hierarchy.

Layer 1 - Physical

Physical layer defines the cable or physical medium itself, e.g., thinnet, thicknet, unshielded twisted pairs (UTP). All media are functionally equivalent. The main difference is in convenience and cost of installation and maintenance. Converters from one media to another operate at this level.

Layer 2 - Data Link

Data Link layer defines the format of data on the network. A network data frame, aka packet, includes checksum, source and destination address, and data. The largest packet that can be sent through a data link layer defines the Maximum Transmission Unit (MTU). The data link layer handles the physical and logical connections to the packet's destination, using a network interface. A host connected to an Ethernet would have an Ethernet interface to handle connections to the outside world, and a loopback interface to send packets to itself.

Ethernet addresses a host using a unique, 48-bit address called its Ethernet address or Media Access Control (MAC) address. MAC addresses are usually represented as six colon-separated pairs of hex digits, e.g., 8:0:20:11:ac:85. This number is unique and is associated with a particular Ethernet device. Hosts with multiple network interfaces should use the same MAC address on each. The data link layer's protocol-specific header specifies the MAC address of the packet's source and destination. When a packet is sent to all hosts (broadcast), a special MAC address (ff:ff:ff:ff:ff:ff) is used.

Layer 3 - Network

NFS uses Internetwork Protocol (IP) as its network layer interface. IP is responsible for routing, directing datagrams from one network to another. The network layer may have to break large datagrams, larger than MTU, into smaller packets and host receiving the packet will have to reassemble the fragmented datagram. The Internetwork Protocol identifies each host with a 32-bit IP address. IP addresses are written as four dot-separated decimal numbers between 0 and 255, e.g., 129.79.16.40. The leading 1-3 bytes of the IP identify the network and the remaining bytes identifies the host on that network. The network portion of the IP is assigned by InterNIC Registration Services, under the contract to the National Science Foundation, and the host portion of the IP is assigned by the local network administrators. For large sites, the first two bytes represents the network portion of the IP, and the third and fourth bytes identify the subnet and host respectively.

Even though IP packets are addressed using IP addresses, hardware addresses must be used to actually transport data from one host to another. The Address Resolution Protocol (ARP) is used to map the IP address to it hardware address.

Layer 4 - Transport

Transport layer subdivides user-buffer into network-buffer sized datagrams and enforces desired transmission control. Two transport protocols, Transmission Control Protocol (TCP) and User Datagram Protocol (UDP), sits at the transport layer. Reliability and speed are the primary difference between these two protocols. TCP establishes connections between two hosts on the network through 'sockets' which are determined by the IP address and port number. TCP keeps track of the packet delivery order and the packets that must be resent. Maintaining this information for each connection makes TCP a stateful protocol. UDP on the other hand provides a low overhead transmission service, but with less error checking. NFS is built on top of UDP because of its speed and statelessness. Statelessness simplifies the crash recovery.

Layer 5 - Session

The session protocol defines the format of the data sent over the connections. The NFS uses the Remote Procedure Call (RPC) for its session protocol. RPC may be built on either TCP or UDP. Login sessions uses TCP whereas NFS and broadcast use UDP.

Layer 6 - Presentation

External Data Representation (XDR) sits at the presentation level. It converts local representation of data to its canonical form and vice versa. The canonical uses a standard byte ordering and structure packing convention, independent of the host.

Layer 7 - Application

Provides network services to the end-users. Mail, ftp, telnet, DNS, NIS, NFS are examples of network applications.

The OSI Model Stack

The OSI model divides the complex task of computer-to-computer communications, traditionally called internetworking, into a series of stages known as layers. Layers in the OSI model are ordered from lowest level to highest. Together, these layers comprise the OSI stack. The stack contains seven layers in two groups:

Upper layers – 7. application 6. presentation 5. session

Lower layers - 4. transport 3. network 2. data link 1. physical

Benefits of the OSI Model

By separating the network communications into logical smaller pieces, the OSI model simplifies how network protocols are designed. The OSI model was designed to ensure different types of equipment (such as network adapters, hubs, and routers) would all be compatible even if built by different manufacturers. A product from one network equipment vendor that implements OSI Layer 2 functionality, for example, will be much more likely to interoperate with another vendor's OSI Layer 3 product because both vendors are following the same model.

The OSI model also makes network designs more extensible as new protocols and other network services are generally easier to add to a layered architecture than to a monolithic one.

What Is a MAC Address?The MAC address is a unique value associated with a network adapter. MAC addresses are also known as hardware addresses or physical addresses. They uniquely identify an adapter on a LAN.

MAC addresses are 12-digit hexadecimal numbers (48 bits in length). By convention, MAC addresses are usually written in one of the following two formats:

MM:MM:MM:SS:SS:SS

MM-MM-MM-SS-SS-SSThe first half of a MAC address contains the ID number of the adapter manufacturer. These IDs are regulated by an Internet standards body (see sidebar). The second half of a MAC address represents the serial number assigned to the adapter by the manufacturer. In the example, 00:A0:C9:14:C8:29

The prefix 00A0C9indicates the manufacturer is Intel Corporation.

MAC vs. IP AddressingWhereas MAC addressing works at the data link layer, IP addressing functions at the network layer (layer 3). It's a slight oversimplification, but one can think of IP addressing as supporting the software implementation and MAC addresses as supporting the hardware implementation of the network stack. The MAC address generally remains fixed and follows the network device, but the IP address changes as the network device moves from one network to another.

IP networks maintain a mapping between the IP address of a device and its MAC address. This mapping is known as the ARP cache or ARP table. ARP, the Address Resolution Protocol, supports the logic for obtaining this mapping and keeping the cache up to date.

DHCP also usually relies on MAC addresses to manage the unique assignment of IP addresses to devices.