CCDE SD-WAN Design Part 13: Best WAN Underlay Technologies for Enterprise Branch Connectivity

CCDE Enterprise Case Study Part 13 – Choosing the Best SD-WAN Underlay Technologies

As Jacobs evaluates a migration toward a modern SD-WAN architecture, one of the most critical design decisions involves selecting the correct WAN underlay technologies.

An SD-WAN overlay is only as good as the physical transport beneath it.

🎯 Core Design Objective

Jacobs wants to:

• Reduce MPLS dependency
• Improve scalability
• Reduce operational costs
• Improve cloud performance
• Maintain low latency for Jaystore
• Retain business-critical resiliency

Table of Contents

• 1. Question Overview
• 2. Correct Answer Analysis
• 3. Why 5G Is Optimal
• 4. Why MPLS Still Matters
• 5. Understanding Latency Requirements
• 6. Why Broadband Is Suboptimal
• 7. Why 4G/LTE Is Not Ideal
• 8. Recommended Hybrid Architecture
• 9. SD-WAN Configuration Examples
• 10. WAN Performance Mathematics
• 11. Machine Learning and WAN Analytics
• 12. Related Articles

1. Question Overview

The correct answers are:

Technology	Result
5G	Correct
MPLS Primary Circuit	Correct

This creates a:

$$ Hybrid\\ SD\\text{-}WAN\\ Architecture $$

where:

• MPLS provides deterministic enterprise transport
• 5G provides low-latency Internet transport

2. Correct Answer Analysis

Why 5G Is Correct

5G provides:

• Low latency
• Rapid deployment
• Flexible bandwidth
• High availability
• Cloud-friendly transport

Most importantly:

$$ Latency_{5G} \approx 10ms $$

which satisfies the:

$$ Jaystore < 20ms $$

requirement.

Why MPLS Is Still Correct

MPLS already exists and provides:

• QoS guarantees
• Deterministic routing
• Stable latency
• Enterprise SLA support

The SD-WAN migration strategy is therefore:

$$ MPLS + Internet\\ Overlay $$

instead of:

$$ Internet\\ Only $$

3. Why 5G Is Optimal for Jacobs

The Jaystore application is the single most important technical constraint in this design scenario.

The application becomes unstable when:

$$ Latency > 20ms $$

Estimated Technology Latency Comparison

Technology	Typical Latency	Suitable?
5G	10ms	Excellent
MPLS	5-15ms	Excellent
Broadband	20-50ms	Variable
4G/LTE	50-70ms	Poor

Latency Budget Formula

$$ Application\\ Success = Latency + Jitter + Loss < SLA $$

Additional Benefits of 5G

• Rapid deployment
• No fiber dependency
• Cloud-native Internet access
• Easy branch scalability
• Excellent backup transport

Why Modern SD-WAN Loves 5G

Modern enterprise WAN architectures increasingly use:

$$ 5G + SD\\text{-}WAN $$

because 5G offers:

• Carrier diversity
• Lower provisioning delays
• Better mobility support
• Improved DIA performance

4. Why MPLS Still Matters

Many engineers incorrectly assume:

$$ SD\\text{-}WAN = MPLS\\ Removal $$

This is not true.

SD-WAN is fundamentally:

$$ Transport\\ Agnostic $$

meaning it can use:

• MPLS
• Internet
• 5G
• LTE
• Broadband

simultaneously.

💡 Critical CCDE Insight

The best SD-WAN designs do NOT remove MPLS immediately.

They:

• Preserve business-critical SLAs
• Reduce WAN cost gradually
• Introduce Internet transports incrementally

Why Jacobs Should Keep One MPLS Circuit

Reason	Explanation
QoS	Jaystore and VoIP require low latency
Predictability	MPLS provides stable forwarding
SLA support	Carrier-backed guarantees
Migration safety	Reduces operational risk

5. Understanding the Latency Requirement

The most important architectural clue in this scenario is:

Jaystore does not function well above 20ms latency.

This dramatically affects WAN design decisions.

TCP Performance Formula

$$ TCP\\ Throughput \propto \frac{Window\\ Size}{RTT} $$

As latency increases:

• TCP efficiency decreases
• Application responsiveness degrades
• User experience worsens

Why This Matters

Jaystore was developed:

• Inside a LAN environment
• Without WAN optimization awareness
• Without cloud-native optimization

This is extremely common in legacy enterprise applications.

6. Why Broadband Is Suboptimal

Broadband Internet circuits:

• Can work well for SD-WAN
• Are cost-effective
• Are easy to deploy

However:

$$ Broadband\\ Latency = Variable $$

and:

$$ Broadband\\ Jitter = Variable $$

which creates risk for:

• VoIP
• Jaystore
• Real-time traffic

💡 Important Design Principle

Broadband is acceptable for:

• SaaS
• General Internet browsing
• Backup transport

but may not satisfy:

$$ Strict\\ Application\\ SLA $$

7. Why 4G/LTE Is Not Ideal

4G/LTE suffers from:

• Higher latency
• Variable congestion
• Carrier oversubscription
• Reduced stability

Typical LTE Characteristics

Metric	Typical Value
Latency	50-70ms
Jitter	High
Packet Loss	Variable

Voice Quality Formula

$$ MOS \propto \frac{1}{Latency + Loss + Jitter} $$

LTE therefore becomes unsuitable for:

• Real-time voice
• Latency-sensitive applications
• Legacy TCP applications

8. Recommended Hybrid SD-WAN Architecture

The optimal enterprise design for Jacobs is:

$$ MPLS + 5G + SD\\text{-}WAN $$

Recommended Store Connectivity

Store Type	Recommended Connectivity
Jacobs Stores	MPLS + 5G
Toolmate Stores	MPLS + 5G
Independent Stores	5G SD-WAN

Recommended Traffic Engineering Strategy

Application	Preferred Path
Jaystore	MPLS
VoIP	MPLS
Office 365	5G Internet DIA
General Internet	5G Internet DIA

9. SD-WAN Configuration Examples

Application-Aware Routing Policy

policy

 app-route-policy JAYSTORE

  sequence 10

   match application jaystore

   action accept

    set preferred-color mpls

5G Transport Configuration

vpn 0

 interface Cellular0/2/0

  ip address dhcp

  tunnel-interface

   encapsulation ipsec

MPLS Transport Configuration

vpn 0

 interface GigabitEthernet0/0

  ip address 10.10.10.1/30

  tunnel-interface

   color mpls

10. WAN Performance Mathematics

Latency Equation

$$ Latency = Propagation + Serialization + Queuing + Processing $$

Bandwidth Delay Product

$$ BDP = Bandwidth \times RTT $$

Packet Loss Impact

$$ Effective\\ Throughput \propto \frac{1}{\sqrt{Loss}} $$

Application SLA Formula

$$ SLA = Latency + Loss + Availability + Jitter $$

11. Machine Learning and WAN Analytics

Modern SD-WAN solutions increasingly use:

• AI-driven path optimization
• Predictive congestion analysis
• Anomaly detection
• Application behavior analytics

Useful machine learning concepts:

• Time Series Forecasting Beginners Guide
• How to Evaluate and Ensure Your Data
• Stationary vs Nonstationary Data

12. Related Articles

CCDE Enterprise Case Study Series

• Part 1 – Enterprise Architecture
• Part 2 – Business Drivers
• Part 6 – DMVPN Architecture
• Part 8 – SD-WAN Design
• Part 11 – Self-Managed SD-WAN
• Part 12 – SD-WAN Planes Explained
• CCDE SD-WAN Design Part 14: Internet Circuit Upgrade Requirements Before MPLS Migration

Related CCIE Technical Articles

• Reliable BGP Peering and Physical Connectivity
• Complete MPLS QoS Configuration Lab
• Complete MPLS L3VPN Configuration Lab
• Optimizing OSPF Timers for Faster Convergence

Final Conclusion

The best underlay design for Jacobs is:

$$ MPLS + 5G $$

because this solution provides:

• Low latency
• Application stability
• Business resiliency
• Cloud optimization
• Operational flexibility

The architecture successfully balances:

$$ Performance + Cost + Scalability + Reliability $$

which is the ultimate goal of enterprise SD-WAN transformation.