Network Architecture (Design)

Network design can be described with how it is administered

• centrally administered : a client/server network
• Certain computers on the network are designated as servers
• Servers require special operating system, such as Windows Server instead of XP or Vista
• Servers control network administration such as access to devices
• The other computers are clients
• locally administered (distributed) : a peer-to-peer (P2P) network
• all computers and devices are attached to the network
• no special operating system needed
• each administers its own affairs
• Consider printers on the network
  • A regular printer is attached to one computer using USB, and that computer controls access to it
  • A "network ready" printer attaches directly to the network using Ethernet (RJ-45), and is accessed directly by any computer on the network

The same terms are also used to describe network communication techniques:

• Client/Server communication is when server holds information and client knows the server by name to request it
• Most well-known example of client/server communication is web browser (client) requesting web pages from web server (server)
• Peer-to-peer communication is when information is distributed among peer computers and the information seeker does not know who has it
• Most well-known example of P2P communication is probably LimeWire. File sharing application where files are distributed among all LimeWire users

Network can be described by the distances of its geographic coverage

• LAN : Local Area Network, limited to a building or campus. Usually uses Ethernet protocols
• MAN : Metro Area Network, covers a metropolitan area. Just starting to pop up. May use WiMax
• WAN : Wide Area Network, covers a nation or world. Describes the Internet

Network Transmission Media

• Coaxial cable : used for Cable modem, also original cable for Ethernet
• Twisted Pair cable : used to wire an Ethernet LAN
• Fiber Optic cable : very thin transparent plastic cable that carries light signals instead of electricity
• wireless : wireless signals are carried through the atmosphere and outer space. Different services use different wave bandwidths

Typical Home Network

• Most home networks use P2P structure with Ethernet communication
• All networked devices must have a NIC : Network Interface Card to control network communications
• The NIC has an RJ-45 jack, aka LAN or Ethernet jack
• All devices connect to network either wirelessly or using twisted pair cable with RJ-45 connected to their NIC.
• Multiple devices can be attached to extension modules called hubs, switches and routers
• The network has one cable that attaches to DSL or Cable modem, which is the network's gateway to the Internet

More information about Ethernet

• P2P network structure and communication protocols
• First developed by Bob Metcalfe in the 1970s
• Nearly all LANs now use it (this was not always the case)
• The structure is called a "bus", basically a common highway for all data to follow (like the bus between the Memory Unit and the CPU)
• All devices attach to the common bus
• Data are transmitted in packets
• When a device needs to transmit a packet, it checks to be sure the line is "clear" then transmits
• When multiple devices transmit at about the same time, their packets may collide!
• If collision occurs, the devices each wait a random amount of time and try again.
• This is like the old fashioned telephone "party lines"! We had one on the farm when I was a kid
• If the phone rang, you listened for "your ring". Different houses had different ring patterns.
• If you wanted to use the phone, you picked up the receiver and if you heard someone talking you hung up and tried later
• Ethernet network is extended using hubs, switches and routers
• Hubs are simply junction boxes
• Switches are smarter and turn the "party lines" into "private lines"
• Routers are smarter still. They are switches that can communicate with both the Internet and the Ethernet

Wireless Access Points and Routers

• Wireless Access Points and Wireless Routers are two devices that allow wireless connection to the LAN
• Wireless Access Point allows multiple WiFi-enabled devices to connect through one shared wired connection
• Wireless Router combines both the Wireless Access Point with a wired LAN router (definition above)
• Most consumer Wireless Routers can connect up to 4 wired devices plus however many WiFi-enabled devices you want
• Thus a Wireless Router can be used both to extend a wired LAN and to permit wireless access to the LAN
• A device with WiFi NIC, such as a laptop, communicates with the access point or router to establish network connection
• WiFi range limited to a couple hundred feet and is affected by surfaces such as wall that come between the devices.
• Most laptops have both a WiFi NIC and an Ethernet NIC, so can connect either wirelessly or with a cable
• Note: You are not permitted to operate Wireless Access Points and Wireless Routers in Otterbein residence halls (www.otterbein.edu/its/wireless)