What is meant by multi-destination routing?

- So many routing algorithms have been devised to aid in routing under different conditions.
- Effective routing algorithms have been developed that are capable of routing the messages from one source node to a number of receiving nodes i.e., the multiple destination nodes.
- These algorithms are termed as the multi – destination routing algorithms and the process is therefore called as the multi – destination routing.
- This type of routing has been developed for the minimization of the cost of the network i.e., NC (network cost).
- Network cost can be defined as the sum of all the links’ weights that consist of the routing path.
- There are many heuristic algorithms available for determining the NC min path.
- This problem falls under the category of the NP – complete problems.
- Heuristics are available for the traveling salesman problem and MST (minimum spanning tree) variations.
- Global information is used by both of them.
- Another set of such heuristics is available that uses only shortest paths for reaching the destinations.
- The best worst case performance is exhibited by the MST algorithm.
- However, one study revealed that effectiveness of the simpler heuristics is higher.
- The network cost (NC) is often compared with the destination cost (DC).
- Destination cost is the sum of the cost of all the shortest paths that lead to the destination.
- A scheme of algorithms has been developed for trading off between these two costs i.e., the NC and DC.  
- The sender of the transmitted data cannot be taken as a single node in a network where the cooperative communication is supported.
- This asks for the re-investigation of the traditional link concept.
- Any routing scheme thus depending up on this link concept needs to be reconsidered.
- Also, the potential performance gain resulting because of the cooperative communication needs to be exploited.

- Routing often gets complicated for some networks where the selection of the paths is no longer the job of a single entity.
- Rather, a number of entities are involved in the selection of the paths.
- Multiple entities can even select specific parts of a path.
- If these selected paths are chosen by the entities for their own objectives optimization then it can lead to inefficiency or serious complications in the network since they may or may not conflict with the other entities’ objectives.
- This would become clear from the following example, consider traffic moving in a system of roads.
- Now here each driver selects a path that would minimize only his/her traveling time.
- In this kind of routing, there are longer equilibrium routes (i.e., longer than the optimal.) for almost all other drivers.
- This is often termed as the Braess paradox.
- Another example is of the routing the AGVs (automated guided vehicles) by a model on some terminal.
- For prevention of the simultaneous usage of the infrastructure’s same part reservations are made. - This is called as the context – aware routing.
- The internet is divided in to a number of divisions which are nothing but Ass i.e., the autonomous system like ISPs.
- All these systems have control over the routes that lie in their own network at various different levels.

Following steps are involved in multi – destination routing:
1. The BGP protocol is used for selecting the AS – level paths.
2. A sequence of autonomous systems is produced by the BGP protocol via which the packet flow will take place.
3. The neighboring Ass offer multiple paths for each of the AS from which it can choose. Paths are selected based up on the relationships between the neighboring systems.
4. Each selected path refers to multiple corresponding router level paths.

Sliding Window Protocols? – Part 1

- There are many types of data transmission protocols of which one type is the packet based data transmission protocols. 

- These protocols have a feature called the sliding window protocol.

- The sliding window protocols are a great help wherever the in-order delivery of the data packets demand reliability. 

- For example, the Data link layer of the TCP (transmission control protocol) model and OSI model demand such reliability and thus use window sliding protocol. 

- According to the concept of the sliding window protocols, a consecutive number which is unique is assigned to each and every portion of the transmission i.e., the packets.

- These numbers are used by the receiver for placing the packets it will receive in their correct order. 

- Also, with the help of these numbers, the missing packets can be identified and the duplicate packets can be removed. 

- One problem regarding the sliding window protocols is that it has kept no limits for the size of these numbers that are required. 

- An unlimited number of data packets can be allowed to be communicated at any instant of time if limits are placed on the number of packets involved in transmission or reception. 

- By this, we mean using the sequence numbers of fixed size. 

- By term window we refer to the transmission side. 

- It actually represents the logical boundary or limit of the number of packets that the receiver has to acknowledge. 

- The transmitter has to be informed by the receiver for each ACK (acknowledgement) packet regarding the maximum size or the window boundary of the current receiver buffer. 

- For reporting the window size of the received buffer, a 16 bit field is used in the TCP header. 

- The maximum limit or boundary of the window that we can have is 2¹⁶ i.e., 64 KB. 

- When operating in the slow start mode, the counting of the transmitter begins with a low packet count.

- Gradually, the number of packets involved increases in every transmission after the ACK packet has been received. 

- Whenever it receives an ACK packet, the window slides logically by one packet for the transmission of a new packet. 

- On reaching the window threshold, one packet is sent by the transmitter for every one packet of ACK received. 

- Suppose the limit of the window is 10 packets and the transmitter is in slow start mode. 

- Then, first one packet will be transmitted followed by another two. 

- Between these two transmissions, it will send an ACK packet also. 

- This process will continue until the limit of 10 has reached. 

- After crossing the limit, the transmission is restricted to one i.e., for every ACK packet received only one data packet is transmitted. 

- When viewed during simulation, it seems as if the window is shifting by distance of one packet whenever an ACK packet is received. 

- For avoiding the traffic congestion, the sliding window protocol works up a great deal.

- In this way the application layer would not have to worry about transmission the next set of data packets. 

- It can continue to do so since the sliding windows of the packet buffer will be implemented on both the sides i.e., the receiver’s and the sender’s side by the TCP. 

-However, the network traffic influences the window size dynamically to a great extent. 

- In order to achieve the highest possible throughput, care should be taken for not forcing the transmitter to stop the transmission before one RTT or round trip delay time by the sliding window protocol. 

- The bandwidth delay product of the links in the communication should be less than the limit of the data amount that can be sent before sending ACK packet. - If this condition is not met, the links’ effective bandwidth will be limited by the protocol. 

What is the difference between HTTP and HTTPS?

HTTP is quite a common language with us and stands for hyper text transfer protocol. This is actually an application protocol that has been developed exclusively for the hyper media, collaborative and distributed information systems. 

The foundation of the data communication is entirely based upon www or World Wide Web.  

Now what is HTTPS? HTTPS is nothing but HTTP secure! This one is much more secure than usual hyper text transfer protocol. And like HTTP, it is also a quite popular communication protocol for a much secure communication over a network of computers. It is quite popular with internet. 

If you see it technically, it is actually not a protocol in itself but rather a layered form of HTTP along with SSL/ TLS protocol. This allows the security capabilities of the SSL/ TLS to be added to the HTTP.  In this article we hold up to discuss the differences between the two i.e., the HTTP and HTTPS.

Difference #1:

- The transmission and receiving of the information across a computer network or internet is solely the responsibility of the HTTP.   

- HTTPS holds the responsibility of exchanging confidential information among the servers and also since the access to such information has to be secured to prevent it from any un- authorized access.

Difference #2:

-The transmission of HTTP takes place through a wire via PORT 80(TCP) but it is not at all secure! Some can easily interfere in the communication between your system and the server. 

- HTTPS is a creation of the NetScape and it comes as a built in thing with the netscape browser that uses it for the encryption and decryption of the user’s requests.

- HTTPS is actually HTTP working over the layer of netscape’s secure socket layer (SSL). 

- Unlike regular HTTP, HTTPS transmission takes place through a wire via PORT 443 for carrying out interactions between the lower layer TCP/ IP. 

- SSL or secure socket layer makes use of a 40 bit key size for encrypting the RC4 streams algorithm. 

- Therefore an adequate degree of encryption is possible for commercial exchange.

Difference #3:

- HTTPS being so very secure finds its use in shopping/ commercial sites and login pages. 

- HTTPS though being a standard secure protocol transmits the data over world wide web just like HTTP with the only difference being in the form in which data is transmitted i.e., the encrypted form. 

- When you put https:// instead of http:// you are asking the server to establish a secure connection path. 

- The server makes it a point that the secure and non secure connections are kept separately. 

- When the address in the address bar of the web browser that you are using, starts with http://, it simply means that your requests are being communicated over regular un-secure “HTTP” language.

- It is basically the letter ‘S’ that makes all the difference between HTTP and HTTPS. 

Difference #4:

- Most of the requests of the clients are processed via HTTP. The client in turn gets a response from the server on the completion of a request in the form of a web page. 

- In HTTPS the information is highly encrypted which means that no can have a clue of what you are looking for. 

This type of secure communication is commonly prevalent in those areas wheer security is quite mandatory like the following:

1. E- mails
2. Banking web sites
3. Payment gateways and so on.

To get an HTTPS connection, the server requires a public key trusted and signed certificate.

What are different control flow defects?

Flow of control is the dynamic aspect of any program. Whenever there is a flow of control in a program, the program is said to be active or responsive. The execution of a software program, system or application depends pretty much on the flow of control and data. Flow of control is needed to maintain data links between the different components of the software system or application.

The control flow makes use of some predefined special codes. These codes are transmitted via a band over the communications channel preferably primary. These codes are of 2 types namely:


1. XON: it stands for “transmit on” and
2. XOFF: it stands for “transmit off”.

Because of these two codes, the flow of control is sometimes referred to as the “XON/ XOFF control flow”.

NOTE : Flow of control in a software system or application is totally different from the flow of control in the hardware system. Like any other process, the flow of control also experiences some defects.

MECHANISM OF CONTROL FLOW
In order to understand these defects it is necessary that you understand the mechanism of this process.
- One of the ends of the data link sends the code XON to the other end if this end is ready to intake data.
- If this end is not able to receive data it sends off the XOFF code to the other end.
- The other on getting this code immediately stops the data transmission and resumes once again when the other end is ready to accept the data and sends a XON code.

DIFFERENT CONTROL FLOW DEFECTS
- The ends of the data links sometimes become unresponsive to the intake or transmission of data.
- These kinds of problems are an indication of the defects in data linkage.

To make you understand the control flow defects let us see a detailed example:

- Say you connect your computer to printer whose performance speed is relatively slow when compared to the speed of the computer.
- When you want to take out a print, the computer starts by sending the data to be printed to the printer.
- Since the speed of the printer is slower than the computer, it lags behind i.e., it is unable to handle the incoming volume of data from the computer.

- Ultimately it reaches a stage where it memory is overflowing with the data.
- Now what the printer will do in such a situation? It sends a XOFF code to the computer to stop this data transmission.
- It again sends a XON code to the computer once it has received the whole previously transmitted data and is ready to receive the data again.
- XON and XOFF have a specialty that they can be used by the data links in both the directions.
- In some cases it happens that the data links are not able to employ these codes from either direction.
- This is again a defect in the control flow.
- The flow control is usually used for devices having old technology i.e., the devices which are not compatible with the modern software.
- The devices are unable to accept any more incoming data because their output rate is limited.

REMOVAL OF DEFECTS
- Removal of defects in the flow of control is very necessary.
- It is important since the flow of control is very crucial for the well execution of the software system or application.
- Tests should be undertaken to identify these defects.
- Once the defects have been identified, they should be assigned priority on the basis of the severity they can cause.
- The defects should be validated and resolves as soon as possible.

Sliding Window Protocols

These protocols comes under the data link layer.data link layer. It provides services to the network layer. It’s a bidirectional protocol. It means sender deletes the frames when it gets the acknowledgment.

The essence of all sliding window protocols is that at any instant of time, the
sender maintains a set of sequence numbers corresponding to frames it is permitted
to send. These frames are said to fall within the sending window. Similarly,
the receiver also maintains a receiving window corresponding to the set of frames
it is permitted to accept. The sender’s window and the receiver’s window need
not have the same lower and upper limits or even have the same size.



The sequence numbers within the sender’s window represent frames that have
been sent or can be sent but are as yet not acknowledged. When new packet from network layer comes in to send, it is given highest no and the upper edge of window is advanced by 1. When the acknowledgment comes in, lower edge of the window is advanced by 1.

Since frames currently within the sender’s window may ultimately be lost or
damaged in transit, the sender must keep all these frames in its memory for possible
retransmission. The receiving data link layer’s window corresponds to the frames it may accept. When a frame whose sequence number is equal to the lower edge of the window is received, it is passed to the network layer, an acknowledgment is generated, and the window is rotated by one.

Types of sliding window protocols

- One-Bit sliding window protocols.
- Go Back N sliding window protocols.
- Selective Repeat sliding window.

Network Interface Cards (NIC)

A Network Interface Card (NIC) provides the hardware interface between a computer and a network. A NIC technically is network adapter hardware in the form factor of an add-in card. Networked computers communicate with each other using a given protocol or agreed-upon language for transmitting data packets between the different machines, known as nodes. The network interface card acts as the liaison for the machine to both send and receive data on the LAN.
Some NIC cards work with wired connections while others are wireless. Most NICs support either wired Ethernet or WiFi wireless standards. In new computers, many NICs are now pre-installed by the manufacturer. NICs can be differentiated by their type of connectivity to the computer itself.

- 10/100 Ethernet : These cards are networking cards that are used most frequently in the home or small office setting. They are capable of speeds up to 10 or 100 megabits per second.
- Gigabit Ethernet :These NICs provide network transfer speeds of up to one Gigabit per second.
- Fiber Optics : These NICs use fiber optic cabling to reach speeds of 10 gigabits per second currently, with a specification under review to push this limit to 100 gigabits per second.
- Wireless NICs : These NICs provide the same networking capabilities as their wired counterparts, however, they have their own transfer capabilities. Speeds of 54 Mb/s are the most commonly available to wireless NICs without teaming several NICs together to combine bandwidths.
- Wireless Dongles : There is a wireless networking device used by individual machines that have access to a main computer that is connected to a wireless router. This wireless router allows the user to install wireless dongles instead of entire routers with each additional machine on the network.