Video summary

Redes de Computadores - Topologías Físicas y Lógicas LAN/WAN - Fernando Pereñíguez

Main summary

Key takeaways

Technology

Physical vs. logical topology (core distinction)

  • Physical topology: how devices are physically deployed and installed (placement, cabling layout, interconnection hardware).
  • Logical topology: what network relationships exist from the traffic/communication perspective—how networks/subnets are actually interconnected and interpreted.

Example given: A physically hub/switch-based layout with a router can represent multiple logical networks, such as:

  • separate subnets for classrooms (e.g., classrooms 1–3)
  • a subnet for administrative management
  • a department server network

So, the logical diagram may differ from the physical diagram.

WAN topology concepts

At the physical level, WAN deployments may use three common connection types:

  1. Point-to-point
  2. Star (central interconnection device)
  3. Mesh
    • Complete mesh: all devices interconnect with all others
    • Partial mesh: devices connect only to some neighbors

At the logical level for WANs, the video states that the topology is effectively point-to-point:

  • Two devices communicate directly over the connection.
  • Logical addressing and Medium Access Control (MAC) are simpler because only one other device is effectively “at the other end.”

LAN topology concepts

LAN topologies are richer at the physical level, including:

  • Star topology
  • Extended star (two stars linked together; two concentrators/hubs connected)
  • Bus topology (shared transmission medium such as coaxial cable)
  • Ring topology (shared ring medium)

Despite physical differences, at the logical level in LANs:

  • the network acts as a shared medium
  • when one device transmits, others can “hear” it—creating a need for access control rules to avoid collisions

Access control methods on shared media

The video highlights two logical access-control approaches for LAN shared media:

1. Contention-based access (best-effort / “BEF”)

  • A device listens for the medium.
  • If free, it transmits.
  • If a collision happens, it stops, waits a defined time, then retries.
  • Examples mentioned: Ethernet-like ECN networks and Wi‑Fi (typical contention-based access).

2. Controlled access (turn-taking)

  • Devices follow a turn-taking system.
  • Common in ring-based media: a token circulates.
  • The device holding the token may transmit; otherwise it passes the token onward.
  • Examples/technologies mentioned:
    • Token Ring (IEEE 802.5)
    • FDDI (fiber distributed data interface)

Key takeaway / conclusion

  • WAN logical topologies are typically point-to-point, leading to simpler MAC behavior.
  • LAN logical topologies are typically shared media, requiring collision avoidance via either:
    • contention-based access (e.g., Wi‑Fi, Ethernet variants)
    • controlled access with token/turn-taking (e.g., Token Ring, FDDI)

Main speaker/source

  • Fernando Pereñíguez

Original video