When the Card Terminal and the Phone Line Compete: Prioritising Traffic Across Retail Stores

Retailers keep voice and card payments reliable by classifying store traffic, marking calls and payments as top priority at the store router, separating guest WiFi, and adding a second connection path with automatic failover through SD-WAN.

TL;DR

• A store's internet link carries card terminals, POS, phone calls, video meetings, signage, CCTV & guest WiFi at the same time. Without rules, they all compete equally.
• Voice breaks first. The ITU recommends keeping one-way delay under 150 milliseconds for conversation, and a call needs very little bandwidth but a steady path.
• Quality of Service (QoS) marks each traffic type so the store router sends calls and payments first.
• SD-WAN adds application-aware routing and sub-second failover to a second circuit or 4G/5G, so a single line fault doesn't take the tills or phones down.

Which traffic competes on a store's connection?

A typical store connection carries at least eight kinds of traffic, each behaving differently. Card payments send small amounts of data that must arrive every time. Calls send a constant stream that breaks up with small delays. CCTV uploads send large bursts that can fill the line for minutes.

The list in most multi-site retailers looks like this: card terminals, cloud POS or ERP, loyalty app transactions, store phones and contact centre calls, Microsoft Teams or Zoom meetings, digital signage content, CCTV uploads, and customer WiFi. Stock sync and back-office file transfers join them overnight or, if nobody has scheduled them, at 11am on a Saturday.

Traffic prioritisation is the practice of classifying network traffic by type and giving the most time-sensitive classes first access to the connection. It decides which traffic waits when the line is full.

Why do phone calls fail first when a store connection is busy?

Phone calls fail first because voice is real-time. A delayed email arrives a second late and nobody notices. A delayed voice packet is useless by the time it arrives, so the listener hears a gap, an echo or a robotic voice.

The International Telecommunication Union's G.114 recommendation sets 150 milliseconds of one-way delay as the limit for most conversational applications. Jitter (variation in delay) and packet loss do as much damage as raw delay. A G.711 call uses 64 kbps of audio payload plus packet overhead, a fraction of a basic broadband line. What a call needs is low, consistent delay.

A bad line also changes behaviour. If a store phone line is choppy, staff stop answering it, customers ring the contact centre instead, and head office sees call volume rise with no obvious cause. For retailers adding AI to calls, clean audio matters too, since transcription and speech recognition depend on what actually arrives.

Martin Browne, CTO and CX Chief Technologist at DigitalWell, puts the case for protecting voice plainly:

"Voice isn't going away. Voice is still the preferred channel for high value complex interactions requiring empathy, understanding." Martin Browne, CTO and CX Chief Technologist, DigitalWell

How should a retailer rank its store traffic?

Rank traffic by what the business loses if it's delayed, then set rules to match. The table below is a starting point most multi-site retailers can adapt.

The labels in the "typical handling" column come from the IETF's RFC 4594, which defines standard service classes. It assigns telephony to the Expedited Forwarding class, the highest-priority treatment most routers support.

How do you prioritise voice and cloud traffic in practice?

Work through these steps site by site. Start with one store that has a known problem, then turn the result into a template for every site.

1. Measure what's on the line. Capture a week of traffic at a busy store, including a Saturday. Note which applications peak and when.
2. Agree the classes. Use a short list, like the table above. Five to seven classes is easier to manage than twenty.
3. Mark traffic at the edge. Configure the store router or firewall to identify each application and tag it with the right priority.
4. Reserve bandwidth for voice and payments. Give both a guaranteed slice that bulk traffic can't take, even when the line is full.
5. Separate customer WiFi. Put it on its own network segment with a bandwidth cap, so shoppers streaming video can't slow the tills.
6. Add a second path. A second broadband circuit or 4G/5G backup keeps payments and calls running if the primary line fails.
7. Monitor delay, jitter and loss per site. Averages across the estate hide the one store with a problem. Alert on each site's numbers.
8. Test before peak. Run the rules under load before Black Friday and the January returns rush, when a fault costs the most.

Does QoS work over normal broadband?

QoS works on the parts of the network you control: the store's LAN, the router and the upload queue onto the internet line. Public internet carriers generally don't honour priority markings between your store and the destination. On a busy broadband line, the store router's upload queue is usually where congestion happens, so local QoS still solves most in-store problems.

For the rest of the path, the options are a private network or smarter path selection. MPLS is a carrier-managed private network with guaranteed quality of service end to end. It suits voice-heavy sites such as a central contact centre. SD-WAN runs over internet circuits and picks the best available path for each application, moment by moment.

Many retailers use both: MPLS or a dedicated line for head office and the contact centre, SD-WAN over broadband for stores.

What does SD-WAN add for multi-site retailers?

SD-WAN (software-defined wide area network) is a managed layer that sits above a site's internet or MPLS circuits and decides, application by application, which path each type of traffic takes. It turns the prioritisation rules above into one central policy for every store.

DigitalWell's SD-WAN service uses FortiGate appliances at each site, with dual internet circuits and optional 4G/5G backup. If the primary link degrades, traffic fails over in under a second, handled locally by the appliance. Application-aware routing sends Microsoft 365 and Zoom traffic direct to the cloud by the fastest path, while sensitive traffic follows the most secure route.

Three details matter for retail estates:

• One policy for every store. Appliances are managed centrally, so a new store opens with the same rules as the other 50.
• The best circuit per site. DigitalWell sources connectivity from over 20 last-mile operators across Ireland, rather than one carrier's footprint.
• Security at the edge. Encryption, network segmentation and documented SLAs are part of the managed service, which helps when a PCI DSS assessor or cyber insurer asks how the card network is separated.

How does separating guest WiFi help with PCI DSS?

The PCI Data Security Standard applies to every system that stores, processes or transmits cardholder data, and to anything connected to them. Segmenting the network doesn't make a retailer compliant by itself. It's the standard way to shrink the number of systems in scope, which makes each assessment smaller and cheaper.

Putting customer WiFi, signage and CCTV on separate segments from card terminals does two jobs at once. It limits PCI DSS scope, and it stops the busiest non-critical traffic from sharing a queue with payments.

What does this look like across a real store estate?

Insomnia, the coffee chain with over 170 shops across Ireland and the UK, had recurring WiFi and broadband problems affecting in-store operations. DigitalWell carried out site assessments and rolled out high-speed WiFi, DSL and new routers across more than 76 locations. The design includes automated backup if a fixed line fails. The Insomnia case study reports faster card payments, more reliable loyalty transactions and better staff access to cloud systems.

"Customers can now enjoy an improved experience in our stores, with fast, seamless payments and reliable Wi-Fi, while staff also benefit from improved access to the company's cloud resources." Conor Ward, Head of IT, Insomnia

Where do voice services fit in the store network?

Prioritisation protects calls on the way out of the store; the voice service carries them the rest of the way. DigitalWell's Intelligent Network puts managed WAN, carrier-grade SIP trunking and the AI Voice Network under one contract, so one party owns call quality from the store router to the carrier. Smart Workplace then puts store managers, area teams & head office on one phone platform, and the Retail page shows how the pieces fit a store estate.

Frequently Asked Questions

Do small stores need traffic prioritisation?

Yes, often more than large ones. A small store usually has a single broadband line with limited upload speed, so one CCTV upload or a busy guest WiFi can fill it. Basic QoS on the store router is a low-cost fix.

How much bandwidth does a store phone call need?

Very little. A G.711 call uses 64 kbps of audio payload plus packet overhead. Poor call quality usually comes from delay, jitter and packet loss when other traffic fills the queue.

Is MPLS better than SD-WAN for voice?

MPLS gives guaranteed quality of service end to end, which suits voice-heavy sites like a central contact centre. For stores, SD-WAN over dual internet circuits is usually the better fit on cost and flexibility. Many retailers combine the two.

How do I know if call problems are caused by the network?

Check delay, jitter and packet loss at the affected store during the problem times. If they spike when the line is busy, the network is the cause. Per-site monitoring shows this without anyone on site.

Key Takeaways

• Every store link carries payments, calls, cloud apps, video, CCTV and guest WiFi at once. Prioritisation decides who waits when it's full.
• Voice needs a steady path: under 150 ms one-way delay, with low jitter and loss.
• A short list of traffic classes, marked at the store router, fixes most in-store call and payment problems.
• Separating guest WiFi and signage from card terminals protects performance and reduces PCI DSS scope.
• SD-WAN turns the rules into one central policy across the estate, with sub-second failover to a second circuit or 4G/5G.

Dropped calls or slow terminals in some of your stores? Book a network review with DigitalWell and we'll measure what's competing on your store connections before recommending a fix.