Networking Topologies & Models

Physical and Logical Topologies

• Every network has a physical and logical topology

Physical topologies

• The physical topology represents the physical layout of the network


• Bus
◇ Host devices are connected to one centralized cable or hardware device by twisted pair wiring
◇ Network data travel is bi-directional, which means that data can collide
• Full Mesh
◇ All devices are connected to each other for redundancy. This network is the most reliable
◇ It is also the most expensive and difficult to set up
◇ You can create a partial mesh topology as an alternative
• Star
◇ A central device connects to network and host devices using twisted pair wiring
• Ring
◇ All devices are connected using a single cable and data is routed through each device
◇ The data travels in a single direction until it reaches its intended target
◇ This topology averts network collisions, but is susceptible to failure if a single node fails
• Dual Ring
◇ Two rings enable data to be sent in opposite directions, creating redundancy
◇ If one ring fails, the other continues to transmit data


Logical topologies

• The logical topology is a virtual representation of how the physical topology operates, and is not necessarily identical to the physical topology
• For example, a network's physical topology might be laid out in the form of a star topology, but its logical operation functions like a ring topology


Network Wiring and Cables

Types of wires

• These wires are typically twisted together in pairs to reduce interference
• Types: Shielded and Unshielded


Network cable categories

Cable ratingFrequencyData PerformanceChannel length limitMax data speedLength limit at maxNotes
Cat 5e100 MHz100 MBS100 m1 GBPS100 mCan handle 1G Ethernet
Cat 6250 MHz1 GBPS100 m10 GBPS37 mCan handle 10G Ethernet for a length up to 55 meters depending on cabling quality and installation practices
Cat 6a500 MHz10 GBPS100 m10 GBPS100 m

• A network engineer cannot run cables to an unlimited length. Resistance in the wires causes the signal to degrade past the maximum length, which causes data loss
• Hardware devices called repeaters are sometimes needed to connect cables to repeat and strengthen the signal that is being sent

Straight and crossover network cables




This table reveals certain patterns
• Use a crossover cable to connect identical device types, except in the case of hub-switch and router-workstation connections. Router-workstation connections are uncommon
• Use a straight cable to connect different device types


The OSI Reference Model

• To understand how data is processed through the network, you need to understand the communication model
• Open System Interconnection (OSI ) is created by Organization for Standardization (ISO) in 1984. The OSI model is a tool used to describe how network data packets are transported through the network
• In the OSI model there are seven layers


LayerNameFunctionExample protocolsFormatNetwork hardware
7ApplicationInterface between software applications and the networkTelnet, HTTP, FTP, SSHData
6PresentationHandles encryption, message formatting, and compressionASCII, JPEG, PNGData
5SessionManages applications and establishes, maintains, and terminates user connectionsOperating systems, schedulingData
4TransportProvides reliable or best-effort data delivery with optional error and flow controlTCP, UDPSegments
3NetworkProvides logical end-to-end network addressing and routingIPPacketsRouter
2Data LinkUses MAC addresses to access network devices. Provides error detection but no correction.802.3, 802.2, HDLC, FDDI, PPP, Frame relayFramesSwitch, Bridge
1PhysicalBit stream. Specifies voltage, wire speed, and cable pin outsEAI/TIA, V.35BitsHub, Repeater, NIC


• When data is being prepared, headers are added at each layer. This is called encapsulation
• Removing the headers is called de-encapsulation


The TCP/IP Suite

• Another prevalent network communication model is the TCP/IP suite, also known as the TCP/IP Stack or IP Stack
• There are 4 layers In the TCP/IP Suite


• The TCP/IP Stack is sometimes presented as a 5-layer model because layer 1 ("Physical") and layer 2 ("Data Link") are split rather than combined into one layer ("Network Access")

LayerNameFunctionExample protocolsFormatNetwork hardware
4ApplicationProvides network services to applications via services and protocols. Sockets and port numbers are used to differentiate the path and sessions on which applications operate. Message formatting and compression is provided.Telnet, HTTP, FTP, SSH, JPG, Operating Systems SchedulingData
3TransportProvides reliable or best-effort data delivery with optional error and flow controlTCP, UDPSegments
2InternetProvides logical end-to-end network addressing and routing.IPPacketsRouter
1Network AccessEncapsulates IP packets into frames for transmission. Maps IP addresses to physical hardware addresses (MAC addresses) and uses protocols for physical data transmission.802.3, 802.2, HDLC, FDDI, PPP, Frame RelayFrames, BitsSwitch, Bridge, Hub, Repeater, NIC