But it also creates challenges for small cell backhaul due to the requirements for low latency and monitoring end-to-end network performance.

For EPC networks utilizing the X2 interface, performance assurance is required both between the small cells themselves, and from the aggregation router to the small cells. This requirement drives the need for an active TWAMP generation capability: again, not just a passive reflector (see Figure 3). Operators will need this generation capability in their Layer 3 testing mechanisms to be able to verify performance between small cells. And since it is a more dynamic network with the X2 interface, operators need to be aware of more subtle changes in the network so that they can track performance trends and raise alarms before their subscribers notice a service problem.

[Figure 3. Generator and Reflector Techniques in Layer 3 Testing]

Source: Accedian

Based on the timestamps, it is possible to calculate:

• Delay (2-way) if only the generator timestamps

• Delay (1-way) if both generator and reflector timestamp

• Delay variation (Jitter)

This method can also be used to calculate:

• Frame loss (dropped packets)

• Connectivity faults (broken network)

Solution: inject the performance assurance capability into the small cell

Given that backhaul for small cells has some fundamentally different requirements compared to macro network, traditional performance assurance methods need to be adapted accordingly. For a deployment of small cells, it will not be possible to install performance-monitoring instruments at each cell site or send expensive field personnel to hundreds of sites to check that the backhaul links are operating properly before issuing a “birth certificate” before service launch. So, how can an operator measure and gather critical KPIs – such as delay, delay variation, frame loss and availability – across the small cell backhaul network?

The answer is to have standards-based performance assurance software agents reside in the small cells themselves or other network elements, such as a small cell router or demarcation device. This ensures that the backhaul to the small cells will be ready at launch and can be monitored during commercial operation. Since the small cell supplier adds this software, operators do not need to install any additional hardware or software at the cell site or send a technician to turn up a service, accelerating deployment times and saving equipment and operating costs. This solution also saves valuable space at the small cell site, because the software has zero footprint.

If an operator’s small cell vendor does not include the test and performance monitoring software agents, then those capabilities can be added to the small cell via a Smart SFP device. Just like the software-based solution, the Smart SFP device supports monitoring standards such as Y.1731 and TWAMP so that one-way and two-way measurements can be taken across the backhaul network. This hardware-based solution is cost effective because the Smart SFP device is compact and easy to install, so an operator need only send someone capable to plug in the Smart SFP and Fiber to install it.