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Networks / Data Communications
Lecture Week Three
Now that we have covered most of the media types available for our networks Protocols that run over the top of the media and the standards they follow, the final topic here is choosing a design of a network by choosing media types and infrastructure that will best suit the needs of the business.
When to use hubs verses routers and switches is not always a clear-cut decision. In many cases the decision is made due to cost not necessarily best choice. For most office environments a hierarchical design with 10/100/1000 Mbps ...view middle of the document...
Now let’s talk about routing. What does this mean, routable, not routable? Why do I care? Imagine all of the data in the world going to all of the computers in the world. None of the data would get through because of all of the traffic and anyone would be able to see anyone else’s data. To prevent this we have devices called a Routers Bridges and switches.
The Router acts as a traffic cop. It looks at the address of where the data needs to go. It looks in its little guidebook (the routing table) and sends the data on its way. It does not let data pass unless the destination is on the other side of the Router. This keeps network traffic down to a minimum. A Router can be a hardware device or software. Most operating systems today have routing software built in. If your computer has two or more NICs, the computer can act as a Router.
At the network layer as we said, each host gets an IP address. This address is obtained by the network layer of the sending machine and made part of the header information of the network layer packet. The data is then sent along the wire. Each of the hosts on that wire sees the data; if the packet does not have its address, the host ignores the data. If your network has multiple segments there is usually a Router connecting the two segments together. Finally the packet of data gets to a Router. The Router reads the address and looks in its routing table to see if it knows which path to send the data on.
This is like the clerk in the mailroom. He/she reads the information on the envelope and places the package in the proper mailbox. If the clerk does not have the recipient on the list he/she will make some inquires; do you know this person? What department does (s)he work in? Once the determination is made, the clerk will enter that information into his/her address book for the future. This address book is the routing table. That’s great, anytime mail is sent to this new person the mail clerk knows what to do with it.
Oh great, there is another problem! There are two mail clerks and each have their own address books. The other mail clerk just received mail for this new person but the clerk does not have the new person in the address book. Can you think of a solution? How about making a deal with the other mail clerk. Anytime you find out about someone new you let me know and I will do the same.
Routers can be configured to do the same thing. This is called dynamic routing. There are also standards for how this is done. Routing tables in the routers are configured differently depending on the protocol. Many of the protocols are routable.
Many times there are multiple routes to the destination. In the routing table there is a parameter that gives the cost of each path. The term cost is not in dollars and cents, it is in value of the link. Part of the header information in an IP packet is a value called, time to live. This value is used to make sure a data...