Link state routing is one of the routing techniques. It a simple technique and the operation done during this routing technique can be divided into five stages. Each router of a network
must follow the following operation.
The router of the network must discover its neighbor routers and get their network address.
- The router of the network must calculate the time delay to each of its neighbor router.
- The router of the network must create a packet having all information it has got form other routers.
- The router has to send this packet to other neighbor routers.
- Finally computation of shortest path to every neighbor routers has to be done.
The above five points are discussed below one by one.
GETTING ADDRESS OF NEIGHBOR ROUTERS:
When a router is started or booted its first job is to know about its neighbor router and also get their network address. A router does this job by sending a special packet named HELLO to its neighbor routers. The other routers of the network are expected to send a reply telling who they are.
CALCULATION OF TIME DELAY:
Each routers of the network must know or at least have an estimate of the delay to each of its neighbor routers. To calculate time delay between two routers a special packet ECHO is to be sent from first router to the second router, the second router has to send back the packet immediately. Now by measuring the round trip time and dividing it by two the delay can be calculated. The most accurate value of delay can be found by sending the packet n times and taking the average of round trip time.
CREATING THE PACKET HAVING ALL INFORMATION:
Once the router have collected all information which is needed for the exchange between routers, the router has to create a packet which all these information. The packet starts with the identity of the sender, followed by a sequence number and age and a list of neighbor routers.
The next step of link state routing is to distribute the packet to all its neighbors. Flooding technique is used to distribute the packets. Each packet is given a sequence number and it incremented for the next packet. When a packet comes in it is checked against the list of packets already seen. If the packet is new then it is forwarded to all other routers if it is a duplicate packet then it is discarded.
COMPUTATION OF SHORTEST PATH:
The final step of link state routing is to find the shortest routes. Construction of shortest path is accomplished by Dijkstra’s algorithm. The results of this algorithm
are stored in the routing tables and normal operations resumed.
URL also known as Uniform resource Locator of a website is an internet name of that website. It is a way to address data and information on the Internet. The URL of a site contains the following information.
- The URL contains the Internet name of the site which has the data and information.
- It contains the name of services used by the site for example HTTP and GOPHER.
- It contains the Internet port number of the service. If the port number is not given then it uses a commonly used value.
- And finally the locations of data or information in directory like structure.
The standard format of a website is given below. The structure of a URL is hierarchical and it follows from left to right.
Protocol service://server-name.domain-name.top-level-domain-name/directory-name/file name.html
Example of an URL is given below.
Protocol service : http
Server name : www
Domain name : bscshortnote
Top level domain name : com
Directory name : DECODE
File name : what-is-decoder-and-its-types.html
The range of frequencies that can pass through a transmission medium is called the bandwidth of that medium. A medium cannot allow to pass or to block all the ranges of frequencies. Thus the bandwidth is a range and is normally the difference of the maximum and minimum frequencies that can pass through that medium. Hence it can be calculated by the given formula.
Bandwidth of a medium = Maximum frequency – Minimum frequency
As for example, suppose a medium can allow passing the signals whose frequencies are between 2000 to 5000 Hz then what is the bandwidth of the medium?
Here, the maximum frequency of the signal is 5000 Hz and minimum frequency is 2000 Hz. Thus
Bandwidth of a medium (B)
= Maximum frequency – Minimum frequency
= 5000 – 2000