What is LTE?

Long-Term Evolution (LTE) is a cellular wireless broadband standard that Versa appliances use for internet connectivity, most often as a backup WAN circuit at branches without a wired connection. Configured as hot standby or cold standby, it lets SD-WAN traffic fail over to cellular when primary links go down.

Key takeaways

• LTE serves as a primary, hot-standby, or cold-standby WAN circuit.
• Hot standby monitors the LTE path continuously; cold standby stays down.
• SD-WAN forwarding profiles set circuit priority so LTE activates only when needed.
• VOS devices expose LTE interfaces as vni-0/100 and vni-0/101.
• Versa recommends avoiding FEC on LTE links to limit data plan usage.

On this page: Why it matters · How it works · Types · LTE & Versa · FAQ

Why is LTE important?

Not every branch has a reliable wired connection. Construction sites, pop-up retail locations, kiosks, and remote offices often have no MPLS or broadband option, or the wired circuit takes weeks to provision. LTE closes that gap: riding the commercial cellular network, a branch can be online within minutes of installing a SIM, with no trenching or installation queue.

LTE also matters for resilience. Wired links fail – fiber cuts, DSL noise, provider outages – and a branch with no backup path goes dark. An LTE circuit configured as hot standby or cold standby gives SD-WAN a fallback path that keeps tunnels, internet breakout, and management traffic alive until the primary link recovers. Because LTE plans are billed by usage, architects treat it as insurance: present everywhere continuity matters, engineered to carry as little day-to-day traffic as possible.

What is LTE?

Long-Term Evolution is the 4G cellular standard most mobile carriers use for broadband data, defined by the 3GPP standards body as the evolution path from earlier GSM and UMTS networks. On a VOS edge device, an LTE modem with an active SIM presents itself as a WAN interface – typically vni-0/100 or vni-0/101 – and Versa treats it like any other WAN link, participating in SLA monitoring and traffic steering.

What sets LTE apart is its circuit-media type. Each WAN interface is tagged Ethernet, DSL, LTE, T1, or T3, and SD-WAN forwarding profiles use that tag to decide when a path should carry traffic – for example, preferring wired circuits over LTE whenever both ends have one available. That tagging lets the same policy framework treat LTE as a full WAN member or a link of last resort.

Types of LTE

Versa supports three roles for an LTE circuit. Primary WAN link treats LTE like any wired transport – actively carrying traffic and load-balancing, useful where no wired option exists. Hot standby mode keeps the LTE interface up and continuously SLA-monitored, so failover is instantaneous when a primary link goes down or breaches its SLA; the tradeoff is that probe traffic itself consumes data plan credits. Cold standby mode keeps the interface administratively down until every primary wired interface fails, so no data is used until failover – but the switchover is not instantaneous, since the SIM must register on the mobile network first.

The choice between hot and cold standby trades failover speed against data cost. Administrators tune it further with circuit priorities, an “avoid connections” list that excludes LTE from scavenger traffic, and a lowered management-traffic priority.

LTE & Versa

VOS edge devices configure LTE behavior through SD-WAN forwarding profiles and circuit priorities, letting administrators define when a path through LTE should be preferred, avoided, or used only as a last resort – including asymmetric cases where a non-LTE branch must not route toward a remote branch’s LTE interface if a wired alternative exists. Internet breakout over LTE is tuned through BGP local preference: workflow templates advertise a default route from each WAN transport virtual router, and lowering the LTE-sourced route’s preference keeps it a backup rather than an active path. IP SLA monitor groups detect when wired interfaces go down and trigger cold-standby activation automatically. Versa recommends against Forward Error Correction on LTE links, since FEC adds overhead the link can’t absorb. The Consolidated SD-WAN Design Guide and Versa SD-WAN Design Guide cover LTE within the broader transport design; LTE Transport Modes is the dedicated configuration reference.

Frequently asked questions

What is the difference between LTE hot standby and cold standby modes?

Hot standby keeps the LTE interface up and SLA-monitored, so failover is instantaneous, but probe traffic consumes data plan credits even while idle. Cold standby keeps the interface administratively down until all primary links fail, using no data until then, but failover takes longer while the SIM registers.

Why does LTE cost more than other WAN transport options?

LTE data plans are billed by usage through a mobile carrier, unlike flat-rate wired circuits, so every byte – including SLA probes – carries a cost. Versa deployments typically configure LTE as backup and tune monitoring and priorities to minimize what crosses the cellular link.

What is circuit media type in Versa SD-WAN?

Circuit media is a configuration attribute on each WAN interface – Ethernet, DSL, LTE, T1, or T3 – identifying the transport type. SD-WAN forwarding profiles use it, with circuit priorities, to decide which path traffic should prefer, avoid, or fall back to.

Can LTE serve as a branch’s primary WAN link, not just a backup?

Yes. VOS edge devices treat LTE like any other WAN link, so it can carry SD-WAN VPN traffic, direct internet access, and management traffic as a primary circuit – common at branches, such as pop-up locations or kiosks, with no wired option at all.

Why does Versa recommend against Forward Error Correction on LTE links?

FEC adds duplicate or recovery packets to protect against loss, increasing traffic on a link that’s already capacity- and cost-constrained. Wireless networks also tend to drop many consecutive packets at once, a loss pattern FEC isn’t effective at recovering from.

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