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Aruba EdgeConnect: Path Conditioning


Today let’s take a deeper view of the Path Conditioning features. In our last article, briefly covered the Path Conditioning Feature of the Aruba EdgeConnect solution. Path Conditioning feature enables carrier-grade reliability over commodity links (Public Internet). Today we are going to cover it in detail. If you have not seen the last article, you can find it here…

The below picture will give you an idea of what are we talking about today and where this feature fits in the Traffic Handling techniques available in the Aruba SD-WAN solution.  

Figure 1: Path Conditioning in Relation to Traffic Handling Features

It becomes easy to explain the importance of Path Conditioning which includes Forward Error Correction (FEC) and Packet Order Correction (POC) when we know the factors that impact the network throughput.  Network throughput is the capacity of the network which defines how much data can be transferred from source to destination. Network latency, loss, and link speed can affect the network throughput.

Network link bandwidth can be controlled but latency and loss are always going to be there on the link. Typical International circuits can have up to 200 ms delays. Typically, an MPLS network has a loss between 0.1% to 0.5%. And if the traffic traverses the Internet Circuit this loss can be up to 1.0%. During peak hours you may experience more loss over the public Internet.

With these inherited path characteristics where packet loss and packets arriving out-of-order may cause problems in the network. Packet loss causes a slow response problem where the lost packet needs to be retransmitted. With this retransmission there comes another problem of congestion over the network.

In these scenarios, real-time applications such as voice and video can suffer, and we experience video freeze, pixelating, distortion, and call disconnections. Path Conditioning features overcome these two problems in the network. FEC addresses the packet loss problem and POC addresses the out-of-packet problem – we see less retransmission on the network and bandwidth is optimally used.

Forward Error Correction

Aruba EdgeConnect Enterprise Solution comes with FEC as a native feature to mitigate the effect of packet loss. FEC works by creating extra packets parallel to the original data stream which is called the parity packet. These parity packets are used by receiving EdgeConnect appliances at the destination to reconstruct the lost data if any during transmission.

Aruba SD-WAN solution uses the adaptive FEC approach in the network which means when there is high packet loss, the FEC parity packet to original data ratio is high and in normal conditions with no loss, less FEC parity packets. Link bonding policies such as “High Availability” heavily utilizes the FEC to ensure carrier-grade performance over any link.

To achieve this level of reliability 1:1 FEC is used here which means for every regular data there is one FEC parity packet over multiple links. During the transmission across multiple circuits may face packet loss but this extra parity packet helps to reconstruct the complete data stream.

It can easily be demonstrated during PoC, that physical links have packet drops but the Business Intent Overlay traffic doesn’t see any drop. This setting is generally turned on for Real-time applications like voice and video.

Figure 2: Forward Error Correction

Packet Order Correction

Today it is apparent that organizations are adopting hybrid connections (MPLS + Internet) at branches with different link speeds. With the Aruba EdgeConnect solution both links can be bundled together and utilized simultaneously.

Considering the fact both links have different characteristics, the packet at the destination may arrive out of order (some packets are delivered fast and others may be delayed during transmission).

In general, the side effect of the out-of-order packet is retransmission as the destination router can assume the packet is lost in between and need to be resent. This increases the high response time and sometimes transaction failure.

Packet Order Correction solves this problem by measuring the round-trip time, to assess how long to wait for packets to arrive and caching the out-of-order packets. When all packets arrive, the destination EdgeConnect appliance transmits the packets in the correct order to the destination.

Figure 3: Packet Order Correction

With these techniques, the Aruba EdgeConnect solution creates carrier-grade performance over any transport. We have heard about “Transport independence” and these features ensure “Performance over any Transport” both are different. If you do not agree please go to another article where we talked about how these two terms are not the same.




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