Core: Transport technologies

WAN and last-mile transport selection

Miro Kosut

Miro Kosut

— 2 min read
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Requirement / business driver

Choose the access / transport methods for sites and the WAN, balancing bandwidth, cost, availability/SLA, latency, and reach across very different site profiles.

Options

Leased line / private circuit, MPLS access or Metro Ethernet, broadband (xDSL / DOCSIS / FTTx), cellular (4G / 5G, incl. fixed-wireless and backup), satellite (high-latency GEO vs lower-latency LEO), and point-to-point microwave / wireless bridge.

Comparison

access-transport-matrix

Tradeoffs

Private circuits / MPLS buy SLA and low latency at high cost; broadband is cheap but best-effort; cellular gives wide reach and fast/temporary deployment with data-cap and variability caveats; satellite reaches anywhere but adds latency (GEO) or cost (LEO).

Recommendation / justification

Pick by site profile and combine for resilience: HQ/DC on leased/MPLS, branches on broadband or Metro-E with cellular/broadband backup, remote sites on cellular or LEO satellite. The design rule is diverse transports over diverse paths (mind SRLG / fate-sharing - a "backup" down the same conduit isn't one). These transports are exactly the underlays an SD-WAN design / WAN transport architecture selection stitches together.

What would change this (mid-scenario twist)

  • Remote / no fibre -> cellular or LEO satellite.
  • Pure cost -> broadband primary with cellular backup.
  • High availability mandate -> dual diverse transports + diverse entrance.

Validation checks

  • Real path / transport diversity (not shared fibre or shared upstream)?
  • Does each transport meet the app latency budget, and is backup automatic?

IPv6 / dual-stack note

Confirm native IPv6 on each transport - broadband/cellular vary, and CGNAT on v4 may push you toward v6 for reachability.

Spaced repetition

The core design rule for WAN transport resilience is [...].

The core design rule for WAN transport resilience is diverse transports over diverse physical paths (avoid shared fate / SRLG).

A "redundant" second circuit fails to add resilience when [...].

A "redundant" second circuit fails to add resilience when it shares the same conduit/fibre/upstream (fate-sharing).

For a remote site with no fibre needing lower latency than GEO satellite, a modern option is [...].

For a remote site with no fibre needing lower latency than GEO satellite, a modern option is LEO satellite (or 5G fixed-wireless).

Sources

  • Cisco Press, Optimal Routing Design (WAN); SD-WAN design guides.

domain: Core · blueprint-ref: Core 1.4 Cellular and broadband (transport) / 1.1 Ethernet (Metro) · type: design-decision · status: complete · tags: [core, core/transport, tradeoff/cost, tradeoff/operability]

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