The backbone of a network may be an architectural issue, but the network is the backbone of the organization. Keeping it running while upgrading and planning future requirements is some challenge. Network managers often leave their jobs for lighter work, such as nuclear physics.
Back in the 1970s, who would have thought every user would have a desktop computer? In the 1980s, who would have thought every desktop computer would eventually be connected to a network? Now it's the 1990s and the networks are already starting to weather. Time to plan for the 21st century.
Many agencies and departments have a need for an immediate increase in bandwidth and a future need for quality of service (QoS). Ever-increasing databases, multimedia requirements and intranets are devouring current bandwidth, while future videoconferencing and interactive dataconferencing require guaranteed fluid motion. That's QoS. Your mission is to figure out how to implement them both economically -- on shrinking budgets today and on questionable budgets tomorrow. What fun.
For some time, I have predicted that the whole networking infrastructure will change some time in the future. I think it ultimately will go back to dumb terminals and centralized processing with an optical fiber to everybody's desk. Network management will be a breeze. Needless to say, don't hold your breath, because nobody has figured this out yet. Of course, you could say "Freedman told me so," and maybe we could start a movement. Got a spare fiber?
Following are the major trends.
THE OSI MODEL
In order to understand networking, it is essential to become thoroughly familiar with the protocol stack in the OSI model. Once thought to become a worldwide communications system, the OSI model never came to pass, but still serves as an excellent teaching tool.
In a nutshell, the concept is that whatever is to be transmitted in the sending machine is passed from the application (top layer) to each layer of software below in the stack. Each layer adds its own header or encapsulates it in some manner and passes it on to the next one. At the bottom (layer 1), it goes out onto the cable. At the receiving machine, the processes start at the bottom and work their way back up the stack.
The layers of importance for this article are layers 2 and 3. Layer3 is the network layer, which adds the network address of the destination station. If the destination machine is not directly attached to the subnetwork or domain of the user, then the address of the closest router is used. Layer 3 is concerned with protocols such as IPX, IP, DECnet, AppleTalk and APPN. Closely associated with layer 3 is layer 4, which is the transport layer. For example, TCP is layer 4, and IP is layer 3.
Layer 4 is responsible for sequencing the packets and ensuring that everything sent is received properly. Layer 4 is implemented within the client and server, but unless there is a gross conversion of the protocol, layer 4 data is not dealt with by internetworking devices such as routers.
Layer 2 is the data link layer, also known as the MAC layer, which is actually Ethernet, Token Ring, FDDI and ATM (asynchronous transfer mode). Layer 2 provides the access method for creating the packets that are transmitted.
ROUTERS AND ROUTING
Routers have been an essential component in networking for more than a decade. Routers are used to convert traffic from LANs to WANs and vice versa, as well as to filter traffic within LANs for security and broadcast containment. Broadcasts occur when the address of a user or service is not known. Clients and servers may come online and announce themselves. Sometimes, servers continually announce themselves. In all cases, the broadcast has to reach all possible networks and stations that might be able to respond.