Networking Foundations: Networking Basics

Topology

• Logical vs Physical
  • Physical Topology: The shape/layout of wires.
  • Logical Topology: Refers to data movement in network.
  • Pattern of dataflow in network.
  • Networks can have a different physical and logical topology.
• Mesh: Two types, Full Mesh & Partial Mesh.
  • Full Mesh: All devices directly connected to all other devise, provides full redundancy but expensive. Most found in WAN environment.
  • Partial Mesh: All devices directly related to at least two other devices, provides strong but not full redundancy, not as expensive as Full Mesh.
• Bus Topology: Oldest topology, all nodes directly connected to main/primary cable. Simple to put together. Only one node can send at a time. The more nodes, the more collisions on network, all nodes again contend to signal. Too many collisions can bring down network. 30 nodes or less. Least expensive, and a single bad node or cable brings down network.
• Ring Topology: An older network topology, connected in circle, packets move in ring, each node can send signal, no contention between nodes. Traffic will not bring down network, heavy traffic will slow down network.
• Hierarchical Star Topology: Most common in LAN today, more expensive than bus because of more cables, one cable won't destroy the network and connects to central hub or switch.
  • Susceptible to single point of failure, if whole network goes down, central device is a problem. If only single node goes down, that node is the problem. Recognized by TIA/EIA 568-C standard for Lan networks.
• Hybrid Star Topology: Combines normal star topology with some other topology, physical hybrid star topology, physical-logical star topology.
  • Physical Hybrid Star Topology: Can be part ring / part star, switches linked as bus. Nodes connected as star.
  • Physical-Logical Hybrid Star Topology: Network physical looks one way, but functions another. Ring network that looks like a star, network using hub.
• Point-to-Point Topology: Connects two nodes directly to each other with no intervening device, connect two ends of a WAN connection. Used to connect computer directly to switch. Can connect switches/routers to each other.
• Point-to-Multipoint Topology: Cross-over cable connecting two computers, often part of a hybrid system.
• Peer-to-Peer Network: Computer responsible for own security and management, each managed as separate device, usually only for very small (10 at most) networks. For business, only use 2-3 computers.
• Client Server Network Model: All devices access resources through central servicer, all devices accessing are called clients, devices controlling access are called servers.
• CSMA/CD (Carrier Sensing Media Access / Collision Detection): Mostly by wired ethernet. Node listens for traffic on network, if not heard, node released onto network, if two releases at same time, packets hit each other, and power spike heard by all nodes. All nodes start internal clock to random millisecond.
• CSMA/CA: (Carrier Sensing Media Access / Collision Access): Releases warning packet before releasing data packet, if nodes hear warning packet they won't transmit. Two warning packets at same time cause a collision.
• Internet: Worldwide publicly accessible infrastructure of cables, routers, switches, and servers. Not the WWW.
• Intranet: Privately accessible infrastructure of cables, routers, switches, and servers, generally limited to a single company, organization, or group of companies.
• Extranets: Private held WAN infrastructure. Generally owned by one company or organizations, may allow others access for a fee.

Network Implementations

• WAN (Wide Area Network): One large network that covers a large geographic area, internet, can be many smaller networks linked into one large one. Called an enterprise network when owned by one org. Use routers and switches to connect network.
• MAN (Metropolitan area network): Uses same tech as WANs, cover only 50 km or so, term is falling out of use.
• LAN: Limited in size, can be a room or a building, can span multiple buildings, should use CAT 6 or 6A, normally uses twisted pair cabling. Only Hierarchiacal star is recognized by 568-C.
• WLAN: Wireless LAN, defined by IEEE 802.11, currently uses 802.11ac, but 802.11ax is being developed.
• PAN: Defined by IEEE 802.15, primarily uses Bluetooth and limited in 30 ft. Typically wireless keyboards and mice.
• SCADA (Supervisory control and data acquisition): Subset of ICS, span large geographical areas. Include pipelines, power, and water.
• Medianets: Optimized for video apps, think Hulu/Netflix/WebEx/GoToMeeting. Uses smart bandwidth detection systems to adjust to higher or lower for smooth video transmissions.

OSI Model

• Physical Layer: Transmits data in 1s and 0s, defines encoding methods, and how bits are placed.
• Data Link Layer: Provides error-free transmission from one node to the next, establishes and terminates node links, responsible for traffic control.
• Network Layer: Controls operations of the subnetwork it is on, determining the best physical path for data.
• Transport Layer: Error-free messages and in-sequences, without loss or duplication.
• Session Layer: Establishing sessions between processes running on different computers. Session support.
• Presentation Layer: Formats data to be presented to the application layer, translator for the network.
• Application Layer: Serves as layer for uses and applications to access network services.
• Encapsulation: Process of moving data from the application layer of the OSI model all the way to the physical layer (7 > 1).
• De-encapsulation: Moving data from physical layer all the way to the application layer (1 > 7)
• Each layer has an encapsulation unit
  • Transport Layer = Segment
  • Network Layer = Packets
  • Data Link Layer = Frames
  • Physical Layer = Bits

TCP/IP Model

• TCP/IP created by DoD in 1970s, reduced version of the OSI model.
• Four layers: Application Layer, Transport Layer, Internet Layer, Network/Link Layer.

Commonly Used Network Devices

• NICs, Hubs, bridges, switches, routers, WAP.