CPS (Calls Per Second) is a measurement of how many calls a VoIP or telecommunications system can initiate or process in one second.

In simple terms:

CPS measures the rate at which calls are generated or accepted by a VoIP system, carrier, SIP trunk, or termination route.

CPS is particularly important for wholesale VoIP carriers, call centers, predictive dialers, CCaaS platforms, CPaaS providers, and telecom operators handling high volumes of simultaneous call attempts.

How Does CPS Work?

Suppose a call center sends:

10 calls every second

Its traffic rate is:

10 CPS

If the system maintains that rate for one minute:

10 × 60 = 600 call attempts per minute

CPS measures the rate of call attempts, not the number of calls that remain connected at the same time.

A simplified traffic flow looks like:

Call Center / Customer
↓
SIP Platform
↓
Carrier / SBC
↓
Wholesale Route
↓
Destination Carrier

Each part of the network may have its own CPS limitation.

CPS vs Concurrent Calls

CPS and concurrent calls are different measurements.

CPS = how quickly calls are initiated.

Concurrent Calls = how many calls are active at the same time.

For example:

A customer may generate:

20 CPS

while maintaining:

500 concurrent calls

These two metrics are related but measure different aspects of network capacity.

A simple relationship can be estimated as:

Concurrent Calls ≈ CPS × Average Call Duration

For example:

10 CPS × 60-second average duration ≈ 600 concurrent calls

This is an approximation rather than a guaranteed capacity calculation because real traffic patterns vary.

Why Is CPS Important in Wholesale VoIP?

CPS is a critical capacity metric when carriers exchange high-volume voice traffic.

A route may support thousands of concurrent calls but still have a relatively low CPS limit.

For example:

Route A

• CPS: 20
• Concurrent Calls: 500

Route B

• CPS: 50
• Concurrent Calls: 1,000

If a customer suddenly sends calls at 40 CPS, Route A could become a bottleneck even though it has substantial concurrent-call capacity.

This is why carriers should evaluate both CPS and concurrent call capacity when purchasing or selling wholesale routes.

CPS in Call Centers

CPS is especially important for call centers and predictive dialers.

A large call center may generate hundreds or thousands of call attempts very quickly.

For example:

50 CPS

means the system attempts approximately:

3,000 calls per minute

and potentially:

180,000 call attempts per hour

if the rate were sustained continuously.

Actual traffic will normally fluctuate rather than remain constant.

If the upstream carrier cannot handle the requested CPS, calls may be rejected, delayed, or rate-limited.

What Happens When CPS Is Too High?

Sending traffic above a route’s supported CPS can create several problems:

• SIP requests may be rejected
• Calls may receive temporary failure responses
• Call setup may become slower
• Traffic may experience congestion
• ASR can decline
• Customers may experience inconsistent call performance
• SBCs or gateways may become overloaded
• Carrier routing systems may apply throttling

For this reason, carriers normally establish a CPS limit for each customer, trunk, route, or destination.

CPS Limits in Wholesale VoIP

A wholesale carrier may assign different CPS limits depending on:

• Customer
• Destination
• Route
• Supplier
• SIP trunk
• IP address
• Account
• Traffic profile
• Available capacity
• Contractual limits

For example:

Destination	CPS Limit	Concurrent Calls
Australia	20 CPS	500
Bangladesh	15 CPS	300
Singapore	30 CPS	600
Japan	25 CPS	500

These limits can vary significantly between carriers and routes.

A customer should confirm the permitted CPS and concurrent-call capacity before sending high-volume traffic.

CPS and ASR

CPS can indirectly affect ASR (Answer-Seizure Ratio).

Suppose a route normally performs well at:

10 CPS

but a customer increases traffic to:

50 CPS

If the route does not have sufficient capacity, congestion or call rejection may occur.

This could result in a lower ASR.

Therefore, when increasing CPS, carriers should monitor:

• ASR
• ACD
• PDD
• SIP response codes
• Concurrent calls
• Packet loss
• Route capacity

CPS and PDD

CPS can also affect PDD (Post Dial Delay).

When a network becomes overloaded, call signaling may take longer to process.

For example:

Normal traffic:
10 CPS → PDD 1.2 seconds

High traffic:
30 CPS → PDD 3.5 seconds

If the increase is caused by capacity constraints, the carrier may need to investigate the route, SBC, gateway, or upstream supplier.

CPS and Route Capacity

A carrier should not evaluate a voice route only by its price.

A more complete route evaluation includes:

Rate + CPS + Concurrent Calls + ASR + ACD + PDD + CLI + Reliability

For example:

Route	Rate	CPS	ASR	PDD
Route A	$0.010	50	88%	1.2 sec
Route B	$0.008	20	84%	1.8 sec
Route C	$0.006	5	60%	4.5 sec

Route C may have the lowest price, but its limited CPS and weaker performance could make it unsuitable for a high-volume customer.

CPS in SIP

In a SIP-based network, CPS generally refers to the rate at which SIP call attempts are generated or processed.

For example, a customer sending:

25 SIP INVITEs per second

is generating approximately:

25 CPS

The actual definition can vary depending on the platform and monitoring system, so carriers should clarify whether CPS refers to incoming call attempts, outgoing attempts, accepted calls, or another specific measurement.

CPS vs Call Attempts Per Second

CPS is commonly used to mean Calls Per Second, but the exact measurement should be confirmed between interconnected carriers.

For example, one platform may calculate CPS based on:

SIP INVITEs received

while another may calculate it based on:

Calls accepted for processing

These differences can produce different reported CPS values.

Clear measurement definitions are particularly important when negotiating capacity between wholesale carriers.

CPS and Carrier Interconnection

When establishing a new SIP interconnection, carriers should discuss capacity requirements before launching traffic.

Important questions include:

• What is the maximum CPS?
• What is the maximum concurrent call capacity?
• Is CPS per customer or per IP?
• Is CPS applied per destination?
• Can CPS be increased on request?
• What happens when the limit is exceeded?
• Are burst rates allowed?
• Is additional capacity available?
• Is there automatic rate limiting?

This helps prevent unexpected call failures when traffic volumes increase.

How Can Carriers Increase CPS Capacity?

Increasing CPS may require additional infrastructure or capacity from one or more parties.

Possible approaches include:

• Increasing SBC capacity
• Adding additional SIP trunks
• Adding carrier interconnections
• Increasing upstream route capacity
• Distributing traffic across multiple suppliers
• Implementing load balancing
• Increasing permitted CPS limits
• Using route redundancy
• Optimizing routing policies

The appropriate solution depends on where the capacity constraint exists.

CPS and Traffic Bursts

CPS does not always remain constant.

A customer may normally send:

5 CPS

and suddenly increase to:

30 CPS

for several seconds.

This is called a traffic burst.

A carrier may therefore distinguish between:

Sustained CPS — the normal call rate maintained over a period.

Burst CPS — a temporary increase above the normal traffic rate.

When purchasing wholesale termination, customers should ask whether the supplier supports burst traffic and what limits apply.

Common CPS Questions

What does CPS stand for in VoIP?

CPS stands for Calls Per Second. It measures the rate at which call attempts are generated or processed.

What is a good CPS?

There is no universal “good” CPS. The required capacity depends on the customer, destination, traffic profile, call duration, and carrier infrastructure.

Is CPS the same as concurrent calls?

No. CPS measures the rate of new call attempts, while concurrent calls measure the number of active calls at a given time.

Why is CPS important for call centers?

Call centers and predictive dialers can generate large numbers of calls very quickly. Sufficient CPS capacity helps prevent call rejection, throttling, and congestion.

Can high CPS reduce ASR?

Yes. If traffic exceeds available network or route capacity, calls may be rejected or delayed, potentially reducing ASR.

Can CPS affect PDD?

Yes. Excessive traffic can create signaling or processing congestion, which may increase PDD.

Is CPS the same for every destination?

No. CPS capacity can vary by destination, carrier, route, customer, SIP trunk, and infrastructure.

Can a carrier increase my CPS?

Usually, CPS can be increased if additional capacity is available, but the carrier may need to adjust routing, infrastructure, trunk configuration, or commercial limits.

Best Practices for Managing CPS

Wholesale carriers and high-volume customers should:

• Define CPS limits before sending traffic
• Monitor CPS continuously
• Monitor concurrent calls alongside CPS
• Watch for traffic bursts
• Monitor ASR and PDD when CPS increases
• Confirm destination-specific capacity
• Establish route failover
• Avoid exceeding agreed capacity
• Scale SIP and SBC infrastructure as traffic grows
• Coordinate capacity increases with upstream carriers

For high-volume VoIP operations, CPS is not simply a technical number—it is an important part of capacity planning, route quality management, and carrier interconnection.