Introduction to Network Concepts

Introductory Network Concepts, Network Standards, and the OSI Model

1. There are many reasons for a company to network its computers, some are as follows; Share software, information with others on networks, cheaper than buying individual software and hardware for each standalone especially if the software often offers deals for amount being purchased, e-mail between network users, and flexible access from any computer on the network. 2. Two fundamental network models are peer-to-peer(P2P) or Client/Server. In a P2P network, every computer can communicate directly with every other computer, and no computer on this network has more authority than another. On a client/server network every computer acts as a client or a server. 3. There are 3 types of networks depending on how much territory they cover, they are LANs, MANs, and WAN networks. LAN networks cover a small area like one building or one office. MANs cover multiple buildings like a handful of government offices surrounding a state capital. A WAN network is one that connects two or more geographically distinct LANs and MANs. 4. A server is a computer on the network that manages shared resources. 5. A client is a computer on the network that requests resources or services from another computer on a network. 6. A NIC or Network Interface Card is the device that enables a workstation to connect to the network and communicate with other computers. 7. A NOS or Network Operating System is the software that runs on a server and enables the server to manage data, users, groups, security, applications, and other networking functions. 8. A segment is part of a network. Usually it is composed of a group of nodes that share the same communications channel for all their traffic 9. A protocol is a standard method or format for communication between network devices. Protocols ensure that data are transferred whole, in sequence, and without error from one node on the network to another. 10. A data packet is discrete unit of information sent from one node on a network to another. 11. The organization which today is known as ISO began in 1926 as the International Federation of the National Standardizing Associations (ISA). This organization focused heavily on mechanical engineering. It was disbanded in 1942 during the Second World War but was re-organized under the current name, ISO, in 1946. 12. OSI is a standard industry model used to describe how data from a piece of software moves from one computer, through a network, to another computer. All tasks involved in doing this are split up into 7 layers.

Each layer is more or less independent of the other layers in the sense that the contents of each layer, the actual design of the tasks that make up each layer, can vary but the interface between one layer and the next is fixed. This allows:

- The layers to be designed and tested separately from other layers.
- Any layer can be changed without affecting any of the other layers.
- Successful communication to take place, as long as everyone uses the OSI model - before the OSI model successful data communication between different hardware and software was practically impossible.

The seven layers are:
Layer 7 - Application Layer - Deals with setting up headers on the packets to be sent.

Layer 6 - Presentation Layer - Sets the format of the data and any encryption used.

Layer 5 - Session Layer - Defines how data transmission will be started, controlled and finished.

Layer 4 - Transport Layer - Responsible for the ordering and reassembly of packets.

Layer 3 - Network Layer - Deals with the delivery of data packets.

Layer 2 - Data Link Layer - Concerned with getting error-free connections across networks

Layer 1 - Physical Layer - Deals with the physical characteristics of the hardware such as voltages, pin assignments in plugs, etc. 13. The data link layer is responsible for providing node-to-node communication on a single, local network. To provide this service, the data link layer must perform two functions. It must provide an address mechanism that enable messages to be delivered to the correct nodes. Also, it must translate messages from upper layers into bits that the physical layer can transmit. When the data link layer receives a message to transmit, it formats the message into a data frame (packets). 14. A packet is the PDU - protocol delivery unit at layer 3 (network layer) of the networking OSI model. You may have heard them referred to as ip packets. This is the organization of your data at layer 3

A frame is the PDU of layer 2 (data link) of the OSI model.
At layer 2, packets get encapsulated into frames so that they can be transferred over different media to the end destination. Still the same data...it could be split up differently due to varying window size, but there are a few different details added into the frame header. 15. Layer 4 usually uses segments, layer 3 are packets, layer 2 are frames. Layer 4 uses either tcp (SYN and ACKS) and UDP (connectionless) with port numbers