Network - Basics

Network - 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.

Link - 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.

Node - 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.

Gateway or Router - 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.

Point-Point link - If the physical links are limited to a pair of nodes it is said to be point-point link.

Multiple Access - If the physical links are shared by more than two nodes, it is said to be Multiple Access.

Factors that affect the performance of the network?

Number of Users, Type of transmission medium, Hardware, and Software

Protocol - A protocol is a set of rules that govern all aspects of information communication.

Key elements of protocols - 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.

Bandwidth - 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 - Latency corresponds to how long it t5akes a message to travel from one end of a network to the other. It is strictly measured in terms of time.

When a switch is said to be congested - 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.

Broadcasting - If the message is sent to all the m nodes in the network it is called Broadcasting.

Layers of OSI

a. Physical Layer

·         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

b. Data Link Layer

·         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

c. Network Layer

·         The Network Layer is responsible for the source-to-destination delivery of packet possibly across multiple networks (links).

• a.       Logical Addressing
• b.      Routing

d. Transport Layer

·         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

e. Session Layer

·         The Session layer is the network dialog Controller. It establishes, maintains and synchronizes the interaction between the communicating systems.

• a.       Dialog control
• b.      Synchronization

f. Presentation Layer

·         The Presentation layer is concerned with the syntax and semantics of the information exchanged between two systems.

• a.       Translation
• b.      Encryption
• c.       Compression

g. Application Layer

·         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

What are the categories of Transmission media?

• a.       Guided Media
•                     I.            Twisted - Pair cable

• a.       Shielded TP
• b.      Unshielded TP
•                     I.            Coaxial Cable
•                   II.            Fiber-optic cable

• b.      Unguided Media
•                      i.            Terrestrial microwave
•                    ii.            Satellite Communication

What are the types of errors?

• 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.

What is Error Detection? What are its methods?

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

Redundancy - The concept of including extra information in the transmission solely for the purpose of comparison. This technique is called redundancy.

Checksum - Checksum is used by the higher layer protocols (TCP/IP) for error detection

Encoder - 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.

Decoder

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.

Framing - 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.

Pipelining - In networking and in other areas, a task is often begun before the previous task has ended. This is known as pipelining.

Subnet - A generic term for section of a large networks usually separated by a bridge or router.

Difference between the communication and transmission.

Transmission is a physical movement of information and concern issues like bit polarity, synchronization, clock etc.

Communication means the meaning full exchange of information between two communication media.

Possible ways of data exchange? (i) Simplex (ii) Half-duplex (iii) Full-duplex.

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.

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 an 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.

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   -   255.255.255.255

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.

Logical link control - One of two sub layers of the data link layer of OSI reference model, as defined by the IEEE 802 standard. This sub layer is responsible for maintaining the link between computers when they are sending data across the physical network connection.

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.

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.