Wired and Wireless Local Area Networks: Key Concepts
LAN Overview
LANs provide user access to the network; typically multiple wired and wireless LANs connected by backbone networks.
Two core LAN technologies: wired Ethernet (IEEE 802.3) and wireless Ethernet (IEEE 802.11, Wi‑Fi).
Goal: quick recall of fundamental components, standards, topologies, and common design considerations.
LAN Components
Common devices: NICs, network circuits, hubs/switches/access points, network operating system (NOS).
Client and server basics assumed from earlier chapters.
Network Interface Card (NIC)
NIC = LAN adapter that enables wired or wireless communication.
Operates on physical and data link layers of the OSI model.
Each NIC has a unique 48‑bit MAC address, stored in ROM.
Typical connectors: RJ‑45, BNC; LEDs indicate activity.
Connection media: CAT5/6 (twisted pair), co‑ax, fiber; wireless via antenna.
Network Circuits and Cabling
Physical links between devices use copper (UTP/STP) or fiber; sometimes mixed.
UTP is low‑cost and common; STP used where electrical interference exists; fiber supports higher capacity and longer runs.
Wireless LANs use RF in 2.4 or 5 GHz bands; range limited by walls and interference.
Typical ideal range: ~ for wireless transmission; real range shorter in practice.
Hubs, Switches, and Access Points
Hub: physical layer device; CSMA/CD; can be Active, Passive, or Intelligent (hybrid, sometimes acts like a router/bridge).
Switch: forwards frames based on MAC addresses; operates mainly at the data link layer; reduces collisions; supports cut‑through or store‑and‑forward switching.
Access Point (AP): wireless device that bridges wired and wireless networks; provides SSID, security, and mobility features; often supports PoE; enables guest networks and mesh options.
Network Operating Systems (NOS)
NOS = software platform to manage network devices/services and users.
Key features: network management, authentication/access control, file/print sharing, directory services (e.g., AD/LDAP), security, backups, monitoring, scalability, redundancy.
NOS examples: Windows Server, Linux (Ubuntu/CentOS/Red Hat), Novell NetWare (historical), Cisco IOS, macOS Server.
NOS client software runs on end devices (Windows, Linux, macOS) to access resources; examples include Samba, CUPS, Bonjour, SSH clients, FTP clients, VPN clients, and management tools.
Ethernet and Wireless Ethernet (Wi‑Fi) Basics
Wired Ethernet: backbone for data transfer; standardized as IEEE 802.3; hardware at layer 1/2.
Wireless Ethernet (Wi‑Fi): IEEE 802.11 family; uses RF; often integrated into Ethernet LANs via APs.
Ethernet types: 10, 100, 1000, 10G, 40G, 100G varieties (e.g., 10Base‑T, 100Base‑T, 1000Base‑T, 10GbE, 40GbE, 100GbE).
Wireless types share a central AP/star topology with RF bus characteristics; speeds depend on standard and channel conditions.
Wireless Ethernet (Wi‑Fi) Details
Topology: physical star with central AP; logical bus (shared RF channel).
MAC: CSMA/CA with optional RTS/CTS to reduce collisions; uses backoff (DCF) and contention windows; interframe spacing (IFS).
SSID: network name; authentication/encryption via WPA2/WPA3 (avoid WEP).
Security best practices: strong passwords, up‑to‑date firmware, firewall, network segmentation, IDS/IPS, logging.
Roaming: devices switch between APs with minimal disruption.
Standards overview (backward compatible): 802.11a (5 GHz), 802.11b (2.4 GHz, up to 11 Mbps), 802.11g (2.4 GHz, up to 54 Mbps), 802.11n (2.4/5 GHz, up to 600 Mbps), 802.11ac (5 GHz, multiple Gbps), 802.11ad/ay (60 GHz variants), 802.11ax (Wi‑Fi 6, high efficiency), 802.11ad/802.11ay features and White‑Fi concepts are mentioned in broader context.
Wireless Frame Layout (802.11)
Wireless data frame adds four address fields (Address1–Address4) plus a sequence control field.
Transmission involves APs; destination/source addressing reflects wireless topology.
Fragmentation is handled at the data link layer (unlike traditional Ethernet where it’s done by higher layers).
MAC Protocols and Channel Access
CSMA/CD (Ethernet) vs CSMA/CA (Wi‑Fi).
RTS/CTS to reserve the channel and reduce collisions in Wi‑Fi environments.
Channel selection, backoff, and IFS govern how devices access the RF medium.
IEEE 802.11 Standards: Quick References
802.11a: 5 GHz, high data rates, shorter range.
802.11b: 2.4 GHz, up to 11 Mbps.
802.11g: 2.4 GHz, up to 54 Mbps, backward compatible with b.
802.11n: 2.4/5 GHz, up to 600 Mbps (MIMO).
802.11ac: 5 GHz, multi‑Gbps, wider channels, beamforming.
802.11ad/ay (WiGig/White‑Fi): 60 GHz and extended high‑speed short‑range variants; very high speeds, short range.
802.11ax (Wi‑Fi 6): up to >1–10 Gbps in practice, improved efficiency for dense environments (OFDM/OFDMA, TWT).
Wireless Security Best Practices (Summary)
Use WPA2/WPA3; avoid WEP; prefer CCMP over TKIP.
Strong, unique passwords; consider PSK vs enterprise authentication (802.1X).
Regular firmware updates; enable built‑in firewall; consider MAC filtering as supplemental.
Hide SSID selectively; enable firewall/VPN; segment networks; monitor logs.
Topologies (Overview)
Bus: single shared channel; simple but a single fault can disrupt the network.
Star: all hosts connected to a central device; fast, scalable, fault may be centralized on the hub.
Ring: each host connects to two neighbors; a ring of connections with a potential single point of failure at any link.
Mesh: many interconnections; full mesh vs partial mesh; robust and scalable but cabling can be costly.
Tree (Hierarchical): multi‑level structure with access, distribution, and core layers; common in LANs.
Hybrid: blends multiple topologies; common in WANs and large networks; tradeoffs between reliability, complexity, and cost.
Improving LAN Performance (Key Techniques)
Hardware upgrades: multi‑core CPUs, more RAM, SSDs for storage; virtualization to consolidate servers.
Virtualization: run multiple VMs per physical server for better resource utilization and isolation.
Load balancing: distribute traffic across multiple servers to improve throughput and fault tolerance.
Caching: store frequently accessed data to reduce load on servers/databases.
CDNs: distribute content across geographically distributed servers to reduce latency.
Regular monitoring and tuning to identify bottlenecks.
Improving Circuit Capacity and Reducing Demand
Increase circuit speeds (e.g., upgrade 100 Mbps to 1 Gbps; upgrade to higher‑speed WAN links).
Segment the network with switches and VLANs; in wireless, deploy APs on different channels to reduce interference.
Move heavy data/tasks to off‑peak times when possible.
Client caching and local processing to reduce network load.
Consider topology changes (e.g., more backbones, redundant paths).
SOHO and E‑commerce Network Design (Overview)
SOHO: assess needs, number of users, device types; ensure reliable internet, security, and ergonomics.
E‑commerce edge: design for high availability, scalable hosting, CDN use, secure payments, and robust security controls.
Wireless in SOHO: balance coverage, security, QoS, and ease of management; provide training on security practices.
Designing the Data Center (High‑Level)
Needs assessment: data volumes, compute/storage needs, growth plans.
Physical and environmental: location, access control, proximity to risk sources, cooling and humidity control.
Power and redundancy: reliable power, PDUs, generators, UPS/backup power.
Networking: high‑speed switches/routers, redundancy, fiber/copper cabling, clean cable management.
Security: firewalls, IDS/IPS, access controls, regular audits.
Documentation and testing: diagrams, configurations, hardware specs; test failover and performance.
E‑commerce and Digital Experience (Overview)
Digital storefront design for desktop and mobile; fast hosting; CDN integration; scalable architecture.
Security for payments, inventory, and customer data; encryption and threat monitoring.
Customer experience: optimized checkout, search, recommendations, and responsive support channels.
Security and Best Practices (Final Note)
Security is a design requirement, not an afterthought: update software, enforce strong authentication, segment networks, monitor activity, and train users.
Regular audits, backups, and recovery planning are essential for resilience.
Documentation, proper cable/asset management, and clear change control underpin reliable networks.