Shaping

Wan optimization

Citrix WANscaler (Branch repeater)

One of the unique features that comes with the WANscaler, is the ability to optimize within the ICA protocol. This device can put QOS on the four virtual channels within the ICA protocol. With the latest version 5.5.1 it is even possible to cache the information so that when the data is already been send the next client requesting the information wil get it from cache and will not be send across the WAN link. This technique has the ability to recognize bit patterns that have been send before.

WAN optimization techniques appropriate for virtualized applications include:

Compression and caching – There are a variety of techniques that can be used to reduce network payloads and thereby reduce bandwidth consumption and user response time. Compression generally involves replacing repetitive data patterns of various lengths by small tokens. Locally caching copies of frequently accessed data and graphics eliminates much of the redundancy in WAN traffic, reducing bandwidth consumption and user response time. Another form of caching is de-duplication, whereby only the changes in previously transmitted data objects are sent over the WAN. Compression, caching and de-duplication benefit streamed and hosted application usage where there is a high degree of traffic redundancy.

Protocol optimization – The inefficiencies of TCP, CIFS, HTTP and MAPI over WAN links with high latency and low bandwidth can be mitigated with protocol optimization techniques. TCP protocol optimization involves making changes to the standard error handling and flow control behaviors (window size and slow start) to improve network efficiency and help mitigate latency issues. TCP optimization benefits both streamed and hosted applications. Reducing both chattiness and payloads, as shown for CIFS in Figure 2, optimizes inefficient application protocols. Application protocol optimization is especially important for streamed applications that make use of native application protocols (i.e., CIFS, HTTP, MAPI) instead of a more efficient protocol such as ICA or RDP.

Quality of Service (QoS) – Prioritizing WAN traffic can ensure that critical application traffic is given higher priority service, reducing the effects of additional latency due to congestion and resulting packet drops. WAN traffic from both types of virtual applications can benefit significantly from QoS. For hosted application virtualization, QoS is even more valuable if it can differentiate among and prioritize different virtual channel types used within the delivery protocol (e.g., the screen refresh virtual channel vs. printing virtual channel).