Types Of Network Topology | Computer Network

What is Topology ?


Topology defines the structure of the network of how all the components are interconnected to each other. There are two types of topology: physical and logical topology.

Physical topology is the geometric representation of all the nodes in a network.

                                        OR

The way in which devices are interconnected to form a network is called network topology.

1. Bus Topology

Bus topology is a network type in which every computer and network device is connected to single cable. It transmits the data from one end to another in single direction. No bi-directional feature is in bus topology.

->The bus topology is designed in such a way that all the stations are connected through a single cable known as a backbone cable.

->The nodes are connected to the channel via drop lines.

->The bus topology is mainly used in 802.3 (ethernet) and 802.4 standard networks.


->The most common access method of the bus topologies is CSMA (Carrier Sense Multiple Access).



Advantages of Bus topology -

1. Low-cost cable: In bus topology, nodes are directly connected to the cable without passing through a hub. Therefore, the initial cost of installation is low.

2. Easy to install and maintain

3. Can be extended easily



Disadvantages of Bus topology -


1. If the common cable fails, then the whole system will crash down.

2. Extensive cabling: A bus topology is quite simpler, but still it requires a lot of cabling.





2. Ring Topology


In ring topology each terminal is connected to exactly two nodes, giving the network a circular shape. Data travels in only one pre-determined direction.

fig:  A ring topology comprises of 4 stations connected with each forming a ring..

The following operations takes place in ring topology are :

->One station is known as monitor station which takes all the responsibility to perform the operations.

->To transmit the data, station has to hold the token. After the transmission is done, the token is to be released for other stations to use.

->When no station is transmitting the data, then the token will circulate in the ring.

->There are two types of token release techniques : Early token release releases the token just after the transmitting the data and Delay token release releases the token after the acknowledgement is received from the receiver.

Advantages of Ring Topology

1. Very high transmission speeds possible

2. It is a more reliable network because the communication system is not dependent on the single host computer.

3. The possibility of collision is minimum in this type of topology.

Disadvantages of Ring Topology

1. Troubleshooting is difficult in this topology.

2. Failure of single node brings down the whole network

3. Star Topology

​

In star topology, all the devices are connected to a single hub through a cable. This hub is the central node and all others nodes are connected to the central node. The hub can be passive ​in nature i.e. not intelligent hub such as broadcasting devices, at the same time the hub can be intelligent known as active ​hubs. Active hubs have repeaters in them.

Advantages of Star topology

1. If N devices are connected to each other in star topology, then the number of cables required to connect them is N. So, it is easy to set up.

2. Each device require only 1 port i.e. to connect to the hub.

Disadvantages of Star topology

1. Failure of central node brings down the whole network.

2. Cost of installation is high.

4. Tree Topology

-> Tree topology combines the characteristics of bus topology and star topology.

-> A tree topology is a type of structure in which all the computers are connected with each other in hierarchical fashion.

-> The top-most node in tree topology is known as a root node, and all other nodes are the descendants of the root node.

-> There is only one path exists between two nodes for the data transmission. Thus, it forms a parent-child hierarchy.

Advantages of Tree Topology

1. Existing network can be easily expanded

2. Error detection: Error detection and error correction are very easy in a tree topology.

3. Limited failure: The breakdown in one station does not affect the entire network.

4. Point-to-point wiring: It has point-to-point wiring for individual segments.

Disadvantages of Tree Topology

1. Difficult troubleshooting: If any fault occurs in the node, then it becomes difficult to troubleshoot the problem.

2. High cost: Devices required for broadband transmission are very costly.

3. Insecure network.

5. Mesh Topology

-> In mesh topology, every device is connected to another device via particular channel.

-> It does not contain the switch, hub or any central computer which acts as a central point of communication.

-> The Internet is an example of the mesh topology.

-> Mesh topology is mainly used for wireless networks.

-> Mesh topology can be formed by using the formula:

Number of cables = (n*(n-1))/2;

Where n is the number of nodes that represents the network.

fig:  Every device is connected with another via dedicated channels. These channels are known as links.

1. If suppose, N number of devices are connected with each other in mesh topology, then total number of ports that is required by each device is ​ N-1. In the Figure 1, there are 5 devices connected to each other, hence total number of ports required is 4.

2. If suppose, N number of devices are connected with each other in mesh topology, then total number of dedicated links required to connect them is NC2 i.e. N(N-1)/2. In the Figure 1, there are 5 devices connected to each other, hence total number of links required is 5*4/2 = 10.

Advantages of Mesh Topology

1. It is robust.

2. Provides security and privacy.

3. Communication is very fast between the nodes.

Disadvantages of Mesh Topology

1. Installation and configuration is difficult.

2. Cost of maintenance is high.

6. Hybrid Topology 

-> The combination of various different topologies is known as Hybrid topology.

-> A Hybrid topology is a connection between different links and nodes to transfer the data.

-> When two or more different topologies are combined together is termed as Hybrid topology and if similar topologies are connected with each other will not result in Hybrid topology. For example, if there exist a ring topology in one branch of ICICI bank and bus topology in another branch of ICICI bank, connecting these two topologies will result in Hybrid topology.

Advantages of Hybrid Topology

1. Reliable

2. Flexible

3. Effective

Disadvantages of Hybrid Topology

1. Costly Hub

2. Complex Design

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What is Gigabit Ethernet in Computer Network

Gigabit Ethernet (GBE)


-> Gigabit Ethernet is a version of the Ethernet technology broadly used in local area networks (LANs) for transmitting Ethernet frames at 1 Gbps. It is used as a backbone in many networks, particularly those of large organizations. Gigabit Ethernet is an extension to the preceding 10 Mbps and 100 Mbps 802.3 Ethernet standards. It supports 1,000 Mbps bandwidth while maintaining full compatibility with the installed base of around 100 million Ethernet nodes.


-> Gigabit Ethernet usually employs optical fiber connection to transmit information at a very high speed over long distances. For short distances, copper cables and twisted pair connections are used.


-> Gigabit Ethernet is abbreviated as GbE or 1 GigE.



-> Gigabit Ethernet was developed by Dr. Robert Metcalf and introduced by Intel, Digital and Xerox in the early 1970s. It quickly became a larger LAN technology system for information and data sharing worldwide. In 1998, the first Gigabit Ethernet standard, labeled 802.3z, was certified by the IEEE 802.3 Committee.


-> Gigabit Ethernet is supported by five physical layer standards. The IEEE 802.3z standard incorporates 1000 BASE-SX for data transmission via multimode optical fiber. 

In addition, the IEEE 802.3z includes 1000 BASE-LX over single-mode fiber and 1000 BASE-CX via copper cabling for transmission. These standards use 8b/10b encoding, but the IEEE 802.3ab, known as interface type 1000BASE-T, uses a different encoding sequence for transmission over twisted pair cable.


Gigabit Ethernet offers the following benefits over regular 10 to 100 Mbps Ethernet:

1. Transmission rate is 100 times greater


2. Offers full-duplex capacity that can provide virtually doubled bandwidth
    
3. Offers cumulative bandwidth for faster speed by employing gigabit server adapters and switches
    
4. Quality of service (QoS) features reduced latency problems and offers better video and audio services
    
5. Highly affordable to own
    
6. Compatible with existing installed Ethernet nodes
    
7. Transfers a large amount of data quickly

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ATM ( Asynchronous Transfer Mode ) in Computer Network

What is ATM ?


Asynchronous transfer mode (ATM) is a switching technique used by telecommunication networks that uses asynchronous time-division multiplexing to encode data into small, fixed-sized cells. This is different from Ethernet or internet, which use variable packet sizes for data or frames. ATM is the core protocol used over the synchronous optical network (SONET) backbone of the integrated digital services network (ISDN). 


-> B-ISDN is the low-level MAC(Media Access control) protocol for transferring the actual data.



ATM was designed with an aim to provide:-

1. High speed data rate.
2. Low error rate between two or more switching centers.
3. Digital voice and videos.
4. Low operating cost.



Features of ATM:-

1. Flexibility and versatility of voice, videos and images can be transmitted simultaneously over a single or integrated corporate network.

2. Higher transmission capability.

3. It provides support for virtual networks.




ATM Bit Rates:-

ATM supports four different types of bit rate:


1. Constant bit rate (CBR)

CBR traffic is derived from the source, where the information is transmitted at a constant rate. 

Example: Telephonic speech without silencer.



2. Variable Bit Rate (VBR)

Variable traffic is derived from a variable source. 

Example: Compressed voice or video with silence suppression.



3. Available Bit Rate (ABR)

When a carrier has allocated the necessary bandwidth on the links to carry CBR traffic and minimum VBR is guaranteed. 
The ABR is the mechanism to share the remaining bandwidth fairly between the links.



4. Unspecified Bit Rate (UBR)

1. In UBR, there is no guarantee about the bandwidth traffic delay and loss. The control of flow in UBR can be provided from the end device.
  
2. The protocol which performs the operation of braking frames into the cells is known as ATM Adaptation Layer (AAL).
    
3. Cells carrying speech and video must be received in the order they were sent. This is known as preserving data integrity and it is a function of ATM layer.
    
4. Any link which preserves the order of data entering and leaving is known as channel.
    
5. In ATM protocols, an end-to end connection is established before traffic and starts to flow. Then ,the traffic follows the same path through the network to achieve a true quality of service.

    
6. The connection-less services are implemented with the help of AAL.




ATM Architecture -

1. Physical Layer - 

This layer corresponds to physical layer of OSI model. At this layer, the cells are converted into bit streams and transmitted over the physical medium. This layer has two sub layers: PMD sub layer (Physical Medium Dependent) and TC (Transmission Convergence) sub layer.



2. ATM layer -

-> ATM layer provides the routing information to the data cells.
    
-> ATM interfaces with the AAL and the Physical layer.
    
-> Functions of ATM layer are under the network management, signaling  and OAM protocol.



3. ATM Adaptation Layer -

-> AAL provides the flexibility of a single communication process to carry the multiple types of traffic such as data, voice, video and multimedia.
    

-> AAL is divided into two major parts.
    

-> Upper part of the AAL is called as the convergence sublayer. Its task is to provide the interface to the application. The lower part of the AAL is called as the segmentation and reassembly (SAR) sublayer. It can add headers and trailers to the data units given to it by the convergence sublayer to form cell payloads.

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What is Fiber Channel ? - Definition From Codevidyalay

Fiber Channel (FC) 


1. A fiber channel (FC) is a computer networking technology that is used to transfer data between one or more computers at very high speeds. It was initially designed for supercomputers but is now commonly implemented in storage networking server environments as a replacement to small computer system interface (SCSI) and other serial storage technology.


2. Fiber channel is used in a server environment to transfer bulk data between interconnected storage servers or clusters at very high data transfer rates (DTR). It can transfer data in excess of 1 Gbps and reach speed up to 4 Gbps.


3. Fiber channel based data transfer is usually achieved by using a FC port on a computer or server and a FC-specific switch, which is known as the fabric. The port and switch can be connected using standard coaxial cables or through fiber optic cables.


4. The signals transmitted from a FC port can be propagated to substantial distances, reaching several kilometers in length with high-speed mediums.

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Fiber Distributed Data Interface (FDDI) | Computer Network

Fiber Distributed Data Interface (FDDI) -



1. Fiber Distributed Data Interface, FDDI is a standard developed by ANSI (American National Standards Institute) for transmitting data on optical fiber cables. FDDI supports transmission rates of 100 megabits per second on token-passing networks.

                                    
2. Fiber distributed data interface (FDDI), which is an optical data communication standard used for long distance networks provides communication with fiber optic lines up to 200 kilometers at a speed of 100 megabit per second (Mbps). FDDI has dual primary and secondary communication rings. The primary ring works alongside the network, and the secondary ring remains idle and available for backup.


3. FDDI was later extended to FDDI-2 for long distance voice and multimedia communication. Organizations use this medium for voice and video conferences, online lectures, news and other multimedia.

4. FDDI networks, which are designed for geographically large-scaled organizations that support thousands of end users, operates in the OSI model's physical and media access control (MAC layers).


5. FDDI also is used by single and multi-mode fiber optic, which have different communication mechanisms. Multi-mode fiber optic uses a lead generation device, whereas single-mode fiber optic uses laser for data transmission only.

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What is Token Ring ? - Definition From Codevidyalay

Token Ring


A token ring network is a local area network (LAN) topology where nodes/stations are arranged in a ring topology. Data passes sequentially between nodes on the network until it returns to the source station. To prevent congestion and collision, a token ring topology uses a token to ensure that only one node/station on the line is used at a time, thereby easily denoting media users of its activity.


-> A token is a special frame of 3 bytes that circulates along the ring of stations

-> A token ring LAN is physically wired as a star topology but configured as a ring topology.

-> The token ring LAN system was standardized by the Institute of Electrical and Electronics Engineers as IEEE 802.5.


-> In the mid-1980s, token ring LAN speeds were standardized between 4 and 16 Mbps.




Token Passing Mechanism in Token Ring

If a station has a frame to transmit when it receives a token, it sends the frame and then passes the token to the next station; otherwise it simply passes the token to the next station. Passing the token means receiving the token from the preceding station and transmitting to the successor station. 

The data flow is unidirectional in the direction of the token passing. In order that tokens are not circulated infinitely, they are removed from the network once their purpose is completed. This is shown in the following diagram -

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LAN Protocol Architecture

LAN Architecture primarily focuses on the protocols used by LAN devices to share transmission media.

It best described in terms of layering of protocols that organize basic functions of LAN.

1. Physical media access control (MAC)

2. Logical link control (LLC)

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Differences Between HDLC and PPP

High-level Data Link Control (HDLC) -


HDLC (High-level Data Link Control) is a WAN protocol intended to perform the encapsulation of the data in the data link layer. The encapsulation of the data means to change the format of the of the data. SDLC is the predecessor of the HDLC which stands for the Synchronous Data Link Control protocol. Both SDLC and HDLC protocol are developed by IBM and submitted to the ANSI and ISO for the acceptance as the international standards.


The HDLC protocol follows the bit-oriented concept and uses bit stuffing for achieving data transparency. Here bit oriented approach signifies that the single bit is used to present the control information. The frame structure of HDLC contains the address, control, data, checksum and flag fields. The default encapsulation protocol in the Cisco devices is the HDLC. The Cisco proprietary HDLC only works when the devices in both of the ends of the link are of cisco. Standard HDLC can have different devices in the ends.


Frame format for the bit-oriented protocols-

Point-to-Point Protocol (PPP) -

PPP (Point-to-Point Protocol) is also a WAN protocol, but there are several enhancements made in the PPP protocol after HDLC. Priorly, the PPP protocol is not proprietary, which means that it can be used with two different type of devices without committing changes over the format of the data.



There are several features of PPP, which are discussed below.


1. To clearly identify the start and end of the frame, the framing method is used on the asynchronous data. It is also beneficial in the detection of the errors.

2. A link control protocol is used for enabling the network lines, testing them, terminate them when no longer used. This link control protocol is basically helpful in handling the synchronous and asynchronous circuits, and byte and bit-oriented encodings.


3 .It can select the NCP (Network Control Protocol) for each supported network layer.


Frame format for the PPP -

The PPP frame contains two flag fields, a protocol filed to determine the type of packet residing in the payload, and a payload field which can variate. However, the rest of the fields are the same as the HDLC protocol.





Differences Between HDLC and PPP


1. The HDLC is a bit-oriented protocol while PPP is byte-oriented as well as bit oriented because it can be sent over the dial-up modem lines and also true bit-oriented HDLC.

2. Only synchronous media can be used in HDLC. In contrast, PPP can work with synchronous and asynchronous media.

3. No link authentication is provided in HDLC, whereas it is provided in PPP.

4. PPP can dynamically assign and frees up the IP address according to the use. As against, this not the case in HDLC.

5. Interoperability between the non-cisco devices in HDLC is not achievable. However, this limitation of HDLC is eliminated from the PPP protocol.



Conclusion

Between HDLC and PPP, the PPP protocol performs better than HDLC because there is no compulsion of using the Cisco devices in both the ends, which means these are interoperable. PPP also supports multiple protocols and support authentication.

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Bit and Byte Oriented Protocols | Computer Network

Bit Oriented Protocol -


->A synchronous communications protocol requiring only a single bit to communicate a command signal to the target station. Bit-oriented protocols transmit information without regard to character boundaries and thus handle all types of information images. 


->Bit-oriented protocols are much less overhead-intensive, as compared to byte-oriented protocols, also known as character-oriented protocols. Bit-oriented protocols are usually full-duplex (FDX) and operate over dedicated, four-wire circuits. 


->Examples include Synchronous Data Link Control (SDLC) and the High-Level Data Link Control (HDLC). 


->A communications protocol that uses individual bits within the byte as control codes, such as IBM's SDLC. 


Note –    High-Level Data Link Control(HDLC) is a bit-oriented protocol.




Byte Oriented Protocol -


->A text-oriented synchronous communications protocol that handles only full bytes or characters of text, thereby requiring an entire byte to communicate a command signal to the target station. Control characters are embedded in the header and trailer of each data byte or block. 

->As byte oriented protocols are overhead-intensive, they are used exclusively in older computer protocols at the Data Link Layer. 

->Byte-oriented protocols generally are synchronous and half-duplex (HDX) in nature, and operate over dial-up, two-wire circuits. 


->Bisynchronous Communications (BSC) is an example of a byte oriented protocol. 

->A communications protocol that uses control codes made up of full bytes. The bisynchronous protocols used by IBM and other vendors are examples.


Note –   Point-to-Point Protocol (PPP) is a byte-oriented protocol.

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