Networks

Defining a Network A computer network is a collection of computers and peripheral devices connected by communication links that allow the network components to work together. Networks allow for communication between people and the sharing of information between people, computers, and devices.

Networks in Today’s Society Common examples of networks: The Internet ATMs (connected to a bank) Printers (connected to one or more computers) Networks allow information (knowledge, opinions, culture, etc.) to be quickly spread across the globe. - Discussion: what other examples of networks can you think of? How have networks changed society?

Local and Remote Networks Personal Area Networks (PAN) connect computers and devices within a room Local Area Networks (LAN) connect computers and devices within a building Wide Area Networks (WAN) connects computers and devices between cities or countries - The internet is a collection of WANs. - Discussion: give examples of PANs, LANs, and WANs.

Wired vs Wireless Computers in wired networks are physically connected with wires or cables. Computers in wireless networks are connected via radio waves, satellites, etc. A cell network divides land into cells, each of which has a base station transceiver.

Remote Communication Remote communication allows two users or systems to communicate independent of their location. Examples include online storage, cloud computing, remote desktop, etc. - Discussion: how do you use the cloud in every day life?

Components of Network Communication Understand how media, medium, message are related

Communication Devices Common connection devices: Switches (links devices to create a network) Routers (links networks) Modem (converts analog data from telephone lines to the digital form used on computers) Cable modem (a digital modem used for high-speed Internet services) DSL (digital subscriber line. Transmits digital data over telephone wires) Network Medium Types: Twisted pair (copper wires) CAT 6 (standardized cable for Gigabit Ethernet) G3 (wireless connection used for PANs) Bluetooth (wireless technology standard for exchanging data over short distances) Fiber optic (a glass fiber that uses pulses of light to transmit data) - Switches are within a network; routers connect networks.

Network Operating Systems (NOS) The software that runs on a server. Enables the server to manage connections, security, and the storage and transfer of data Common NOS’s include: UNIX Microsoft Windows Server Mac OS X

Packets Data sent over a network is divided up into small chunks called packets. A packet consists of the data to be sent (called payload) a header with control information (such as source and destination addresses, sequencing information, and a checksum to check whether the packet arrives uncorrupted) - Dividing the data to be sent into tiny chunks enables it to be sent more easily across the network, instead of clogging it up. - However, it also means that individual chunks can get lost or be corrupted along the way. - To maintain order, packets have a header that gives identifying information about the packet, including the number of the packet and the total number of packets (so if you have received packets 1/3 and 2/3, you know that packet #3 is missing).

Protocols A protocol is a set of rules that govern the behavior of a network. These rules allow all hosts on a network to cooperate together. Examples of rules: Each packet shall be 100 bytes in size If a host is down, it will inform all other hosts on the network Examples of protocols: TCP/IP (provides reliable delivery) UDP (provides unreliable delivery) FTP (used to transfer files) HTTP, HTTPS (the foundation of the world wide web) - For any two systems to communicate, they must be using the same protocol. - TCP: checks that each packet arrives intact (using checksums) and sends requests back for ones that were corrupted or went missing. Ensures that every single packet eventually arrives. - UDP: used when getting the data fast is what’s most important. Each packet is only sent once—if one gets lost, it is not resent. This is used for streaming music and video, for which a few missing packets (that is, frames or soundbytes) will go unnoticed.

Protocol Stack A collection of protocols that governs the transfer of data across all levels of hardware and software. - The protocol stack is a collection of protocols that enable networks to interact with each other on different levels (on a spectrum of abstraction from software down to the nitty-gritty hardware). - It allows each level to ignore the levels beneath it—that is, on the highest level, the application thinks it is talking directly to the other host’s application. But in reality, the data is sent from the Application layer to the Transport layer all the way down to the Physical layer, transported across the network, and back up the stack to the Application layer of the other host. - Analogy: this works quite a bit like a corporation. The CEO of one company promises to send a file to the CEO of another company. But what he really does is hands it off to a vice president, who promises to do it, but hands it to a staff member, who hands it to an intern, who actually does the work. - The Application layer: the highest level of abstraction, which provides protocols that interface with human user interfaces (web browsers, email clients, etc.). - The Transport layer: divides the data into packets. Responsible for transferring data from one host to another. - The Network layer: responsible for transferring data through a network. (Includes addressing and packet-handling conventions.) - The Link layer: responsible for transferring data between adjacent network nodes. (Deals with a combination of hardware, software, and firmware. Protocol includes path selection conventions.) - The Physical layer: the lowest layer. Governs the lowest-level hardware. Transmits raw bits instead of packets. - Each layer handles a smaller problem. For example, the Network layer is concerned with transferring data through the whole network, but the Link layer is only concerned with getting data from one network node to the next. - Each layer of the protocol stack wraps the packet up with more control information. The Transport layer adds the port number; Network adds the source and destination IP addresses; Link adds the corresponding MAC addresses.

Careers and Educational Options in Network Administration Certifications: CIW CompTia Cisco Certified Network Associate (CCNA) Educational opportunities: A.S. or B.S. Network Administration Career opportunities: Network administrators / engineers / technicians Network security Network analysis

Network Simulation Three people are selected to be hosts; everyone else is a router. Two hosts write a two or three sentence message to send to the third host. The message is split up into packets using notecards: Five words to a packet Each packet also contains the name of the sender and the receiver, as well as the packet number. The routers transmit these packets to the receiving host. They may lose packets or corrupt them by scribbling out or rewriting part of the message. The receiving host must put the packets of each message in order and reply to them using the same method. If the receiving host is missing a packet or receives a corrupted packet, he/she sends a one-packet request for that packet to be re-sent. - The goal is to get all the packets (eventually) to the receiving host (Host 3). Host 3 will sort the packets into Host 1’ s message and Host 2’s message, put them in order, and read them. - Host 3 will then write a message back to each Host 1 and Host 2 and sent it back through the other way. - In real life, routers lose packets when their packet buffer is full. But for this activity, routers should arbitrarily choose whether or not a packet should be lost.