WAN Optimization Techniques
Data deduplication can operate at two levels; the file or block level. File deduplication eliminates duplicate files as above mentioned, but this is not the most efficient means of deduplication. Block deduplication looks further within a file and saves only the unique iterations of each block contained in the file. The individual chunks of data are processed using types of hash algorithms such as MD5 or SHA-1 (common VPN Authentication methods). The use of either the MD5 or SHA-1 process generates a unique number for each block which is then stored in an index. If and when the file is updated, only the changed data is saved and the index updated. If only a few bytes of the document or presentation are changed, then only the changed blocks are saved and these changes do not mean an entirely new file. This type or WAN optimization technique makes block deduplication far more efficient. That being said, block deduplication takes more processing power and will require a more robust hardware platform and uses a much larger index to track the individual pieces of file that changed.
The use of data deduplication is often used in conjunction with other forms of WAN optimization techniques such as compression. Together these WAN optimization techniques can be very effective at optimizing the use of storage space as well as the reduction of WAN traffic between multiple sites accessing the same resource materials.
With more and more corporations/users coming online it is apparent that there is a great need of TCP congestion control. For every segment that is sent out, this segment is stored in a queue and awaits the acknowledgment of the segment. Should the segment acknowledgement not be received within the default time the segment would be transmitted once again.
When TCP transmits a segment the initial sender of the segment starts a timer (much like a TTL time for DNS) which logs and calculates how long it took for an acknowledgment for that segment to return from the receiving client. If an acknowledgement is returned before the time reaches zero the timer is reset. If an acknowledgement for the segment does not return within the timeout period, the sender will once again send the segment and double the retransmission timer value for each consecutive timeout (up to 64 seconds). If there are network problems such as flopping ISP lines or high latency lines (i.e.: satellite connections) segments may take a high amount of time to be successfully transmitted before the sender eventually times out the segment and generates an error. Crucial to TCP is the measurement of the round trip time between two communicating TCP hosts (referred to as the RTT or Round Trip Time). The round trip time may vary during the TCP connection as network traffic patterns fluctuate and as routes become available or unavailable due to latencies experienced on the line.
Different TCP WAN optimization techniques exist:
IE: Tahoe, Reno, New Reno are a few of the most common WAN optimization techniques
Forward Error Correction
This WAN optimization technique handles packet loss by adding additional loss-recovery packets for every “N” packet that are sent. This would reduce the packet transmission in congested WAN connections. This WAN optimization technique is used for controlling errors in data transmission over unreliable or noisy communication channels which exist with cheaper low-end ISP connections.
Other WAN Optimization techniques also exist to attempt to remedy the network performance issues that exist in today’s modern Network infrastructures.