!LTE Equipment Evaluation Considerations Selection Criteria

7/30/2019 !LTE Equipment Evaluation Considerations Selection Criteria

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INDUSTRY INSIGHTS

LTE Equipment Evaluation:

Considerations and Selection Criteria

Questions for Operators

What is the maximum packets

per second rate that can be

encrypted/decrypted without

packet loss?

What is the average packet size

required by the network today?

What PPS will be required to

handle future network traffic

needs?

Recommended Criteria

Maximum encrypted packets

per second

Throughput (Gbps) for

encrypted traffic at several

packet sizes

Average packet size used for

capacity calculations

Additional equipment needed

to sustain line rate

throughput at a future

average packet sizes.

Higher Performance Requirements

Unfamiliar LTE equipment, increased architecture complexity with small cells, Wi-Fi

integration, network sharing arrangements, rising subscriber traffic and new OTT

applications all have created an unpredictable traffic environment for network

operators. A number of operator network outages have recently been publicized,

symptoms of network vulnerabilities not previously foreseen by the operator

despite diligent planning and testing. These outages and the higher uncertainty

regarding the likelihood of further traffic incidents illustrate how vital it is to

incorporate additional performance requirements for all LTE network elements.

As the #1 deployed LTE security aggregation equipment provider, Stoke has

encountered and overcome specific challenges arising from the new architecture

and traffic patterns. The following questions, considerations and recommendations

for operators evaluating LTE network equipment have evolved from this

deployment experience.

What is the maximum encrypted PPS?

Network engineers most often refer to the performance of network devices by

using the speed of the interfaces expressed in gigabits per second (Gbps).

Although this is useful and important information, Gbps alone does not adequately

cover other, perhaps more, important network device performance metrics.

For LTE network aggregation equipment, where encryption/decryption is needed

and the device is under a high network load, maximum encrypted Packets per

Second(PPS) should also be included in performance evaluations.

The maximum encrypted PPSdefines the equipments packet processing and

forwarding limits for encrypted (e.g., IPsec) packets. As packets get smaller, the

packet arrival rate increases and more packets must be simultaneously forwarded

by the equipment in a given period. Additionally, when IPsec is added, the

equipment must also manage the processor heavy encryption or decryption duties


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Stoke, Stoke Session Exchange and the Stoke logo are trademarks of Stoke, Inc. Copyright 2012 Stoke, Inc. All rights reserved. Lit# 150-0013-001 2

1Assumes ESP/AES128/SHA1

When the incoming packet

arrival rate (packets per second)

exceeds the processing limits ofthe equipment, packets will be

dropped or delayed, causing

retransmission, latency, or jitter."

before forwarding them.

Equipment with a higher maximum encrypted PPS can encrypt/decrypt higher

arrival rates of incoming packets and forward them more quickly, without

introducing latency or dropping packets.

Why is maximum PPS an important metric?

Both Gbps and PPS are performance metrics that impact scalability and cost, and

should be known by the operator. By identifying the maximum PPS, operators can

better understand how the equipment will perform under the full range of peak

traffic conditions and packet sizes found in the network, and how quickly network

equipment will need to be augmented to sustain network throughput as average

traffic characteristics change.

If the incoming packet arrival rate of the packets exceeds the PPS processing limits

of the equipment, packets will be dropped or delayed, causing retransmission,

latency, or jitter. Overall throughput will decline and additional capacity required.

Calculation of Theoretical PPS Standard 10 GigE Interface

The theoretical maximum packets per second can be quickly calculated from Gbps,

for a given packet size. In Figure 1, the theoretical packets per second are

calculated for a 64 byte packet, assuming eight 10GigE interfaces at full capacity

delivering traffic at 80 Gbps, including encryption and other overhead. Figure 1 is

simply a mathematical calculation on theoreticalmaximum and does not include

other equipment design limitations that can impact the actual packets per second

that an operator would achieve.

Gigabits per Second 80

GigaBytes per Second (Gbps/8) 10

Packet Size (Bytes) 64

Preamble + InterFrame Gap (Bytes) 20

IPsec Overhead (Bytes) 58

Total Bytes per Packet 142

Total Packets per Second (millions) 70

Theoretical Packets per Second

Figure 1. Example PPS calculation, assuming 64B encrypted packet at 80 Gbps.1

Figure 2 uses the above formula to calculate PPS at multiple packet sizes, both

encrypted and clear. As shown in Figure 2, at 80 Gbps, the maximum theoretical

PPS at 64 byte encrypted packets is 70 million. At 1,518 byte encrypted packets,

only 6 million PPS rate is possible. The impact of IPsec overhead is also clearly

illustrated. If all 80 gigabits delivered packets were 64 byte packets, 119 million


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2Theoretical IPSec PPS calculated on 80GigE pipe consisting of 100% of given packet size, with 78B added for encryption (58), IFG (12), and preamble (8). For example:

80,000,000,000 / ((64 + 20+58) * 8) = 70.4 million PPS for 64 byte (payload) packet. For clear channel, IFG and preamble overhead only are added 20 bytes.

" the smaller the packets, the

higher the PPS rate, and

therefore, the more packets need

to be forwarded by the

equipment."

could be delivered per second if clear (not encrypted), compared to 70 million

encrypted.

Figure 2. Theoretical packets per second by packet size, in 80 Gbps2

As can be seen, the smaller the packets, the higher the PPS rate, and therefore, the

more packets need to be forwarded by the equipment.

Example #1: Encrypted PPS Calculation - 17 Gbps Security blade

Most published data sheets for network nodes state a maximum throughput at a

specific packet size, but do not provide the maximum encrypted packets per

second (PPS) rate or Gbps for multiple packet size. However, by applying the

mathematical calculation described previously, the maximum PPS rate at different

packet sizes can be estimated, given the published Gbps and packet size for the

equipment.

For example, a security blade data sheet for a large infrastructure provider lists a

maximum throughput of 80 Gbps (8x10 GigE ports) and the maximum encrypted

(IPsec) throughput of 17 Gbps, assuming a 512 byte average packet size. Using

the published 17 Gbps as a starting point, Figure 3 shows the calculation for the

maximum encrypted PPS.

Security Blade Example #1

Max. ThroughputMax. IPsec

Throughput

Average

Packet Size

Calculated Maximum

Encrypted PPS


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3ExampleGbps calculation: 3.6 M packets * (384 Bytes + 78B)* 8/1,000,000,000 = 13.3 Gbps

"If the average packet size of the

network traffic is smaller than the

average packet size published in

equipment datasheets, then

operators need to adjust

equipment needed for theexpected capacity requirements

accordingly."

80 Gbps 17 Gbps 512 Bytes 3.6 million*

*Calculation: 17,000,000,000 / ((512+20+58) * 8) = 3,601,694

Figure 3. Maximum Encrypted PPS estimated from maximum throughput.

At 17 Gbps maximum IPsec throughput and 512 byte packets, the maximum

throughput possible is 3.6 million PPS, including encryption and other overhead.

What is the average packet size required in the network today?

Operators must evaluate network equipment capacity limits using the average

packet size needed by the network, not published by the vendor. If the average

packet size of the network traffic is smaller than the average packet size published

in equipment datasheets, then operators need to adjust equipment needed for the

expected capacity requirements accordingly.

Every operator network is different and average packet sizes can vary even within a

single network. The example following uses the same security blade parameters

and shows the impact on throughput if the average packet size is 384B, 256B, or

64B, rather than the 512 average assumed on the datasheet.

Example #2: 17 Gbps Security blade Throughput by Packet Size

Using the security blade example in Figure 2 with a maximum throughput of 17

Gbps and a maximum PPS of 3.6M, Figure 4 converts the 3.6M PPS to Gbps, at

three additional average packet sizes.


Maximum Encrypted

PPSAverage Packet Size

Estimated

Throughput3

3.6 Million

512 Bytes 17 Gbps

384 Bytes 13.3 Gbps

256 Bytes 9.6 Gbps

64 Bytes 4.1 Gbps

Figure 4. Conversion of maximum PPS to Gbps, by packet size.

If the average packet size needed by the network is actually 384 bytes instead of

512 bytes, then the security blade only provides 13.3 Gbps of capacity, not the 17

Gbps maximum.

Example #3: 17 Gbps Security Blade - Capacity Implications of 384B Average

Figure 5 shows that the throughput and available capacity of the security blade

(assuming 3.6M PPS, 17 Gbps@512 B packet), will decline 35% when the actual

network average packet size is 384, not 512 bytes.



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4Source: Journal of Network and Computer Applications, Application classification using packet size distribution and port association.

"As more real-time services are

used in LTE networks, average

packet size carried by the

network will be smaller. Network

aggregation nodes will need

ultra-fast encryption/decryption

to minimize latency and prevent a

poor user experience."

PPS Average Packet Size Throughput Capacity Impact

3.6 M512 Bytes 17 Gbps -

384 Bytes 13.3 Gbps 35%

Figure 5. Example - Decline in capacity with actual average packet size of 384B

In order to sustain the original 17 Gbps throughput, an additional blade (or

chassis) would need to be added.

If the actual network average packet size is different than the average used to

calculate published Gbps, or if it changes over time, additional equipment can, of

course, be added to augment throughput capacity. However, adding equipment

increases costs for equipment as well as for power, space, and maintenance.

Clearly, PPS and throughput by packet size are important metrics for accurate

network dimensioning.

What PPS rate will future network traffic require?

Increase in demand, changes in mix of device types and applications used, as well

as integration of voice will increase peak loads and decrease average packet size.

This in turn, increases the packet arrival rate or packets per second that network

equipment needs to process.

With VoLTE and other real time services, any performance delays in the network

are very noticeable by the subscriber. Therefore, the latency requirements for real-

time services are higher than for browsing or file downloads. As more real-time

services are used in LTE networks, average packet size carried by the network will

be smaller. Network aggregation nodes will need ultra-fast encryption/decryption

to minimize latency and prevent a poor user experience. Figure 6 shows typical

packet sizes for mobile applications.

Mobile Broadband Applications4 Typical Packet Sizes

VoIP / VoLTE 64B

Video Streaming (mobile) 256B

Web Browsing (HTTP) 384B

File Download/share 512-1,518B

Figure 6. Typical packet sizes for common applications.

Mobile network traffic, of course, includes a mix of all of these applications, and

the average network traffic composition is unlikely to ever be only one application

type. However, mobile broadband traffic can surge or spike on any number ofevents or applications, making peak traffic at any specific location at any given

time quite different than the typical network average. Equipment that provides

higher PPS can provide additional insurance against such extreme network


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5Source: Allot Mobile Trends Report

"When voice traffic is increased

by an additional 7% of total

traffic, average packet size drops

25%"

conditions.

Will VoLTE decrease average packet size?

VoLTE is a small part of mobile broadband traffic today, but the shift to

incorporate voice is happening quickly. Over the last year, VoLTE has seen usage

growth rates of 101%, and most operators expect to offer VoLTE in the next 1-2

years.5 VoLTE does not need to be a large percentage of the total traffic to have

an impact on average packet size. When voice traffic is increased by just anadditional 7% of total traffic, average packet size drops 25%, from 512 to 384

bytes (Figure 7).

Figure 7. 7% more voice decreases average packet size by 25%

Operators planning for near term scalability will have to consider the additional

capacity requirements that VoLTE will have on LTE aggregation nodes and other

equipment.

Recommended Evaluation Criteria

As operators prepare RFPs or conduct other LTE equipment evaluations, they

should include packets per second as part of their evaluative criteria and carefully

consider how well the equipment will perform and scale under future network

traffic conditions, such as changes in average packet size.

Figure 8 illustrates the performance impact of maximum packets per second rate

as packets get smaller, using the security blade example. If the average packet

size decreases from 512 to 384, throughput declines 35%. The performance limits


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6In RFC 2544, the IETF recommends that seven standard frame sizes (64, 128, 256, 512, 1024, 1280 and 1518 byte) be tested multiple times, for a specified length of time.

This is because all these frame sizes are used in the network and so the results for each must be known. http://www.ietf.org/rfc/rfc2544.txt

"As operators prepare RFPs or

conduct other LTE equipment

evaluations, they should include

packets per second as part of

their evaluative criteria"

of the equipment can be defined at 64 bytes, where throughput declines as 75%.

Figure 8. Maximum PPS reveals the performance limits of the equipment.

To fully evaluate the scalability and performance of LTE security gateway

equipment, the following specifications should be requested from vendors:

Maximum (encrypted/IPsec) packets per second

Throughput (Gbps) for encrypted traffic at several packet sizes, including

the highest (1518B), lowest (64B) and midrange (512B)6

Average packet size used by vendor for quoted throughput and PPS

capacity numbers

Additional equipment needed to sustain line rate throughput at a smaller

packet size.

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!LTE Equipment Evaluation Considerations Selection Criteria