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.