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Blue Coat SGOS 4.x Upgrade Guide
18
Upgrade Behavior
As BWM is a new feature, upgrade issues are restricted to previously existing bandwidth
configuration that will now be subsumed into the BWM configuration.
BWM does not replace the older bandwidth limiting features currently available in Streaming (max
streaming, max Real and max MMS). It complements it.
BWM replaces the bandwidth-limiting configuration in Access Logging. Related BWM classes are
automatically created based on the older Access Log bandwidth configuration and placed under the
class "
access-log-logname,” where logname is the name of the log.
Downgrade Behavior
If downgraded, the access log behaves as previously configured.
Documentation References
Chapter 10, “Bandwidth Management,” in the Blue Coat ProxySG Configuration and Management Guide.
Compression
In SGOS 4.x, Blue Coat offers both HTTP compression and SOCKS compress.
• HTTP Compression is an algorithm that reduces a file size but does not lose any data. When you
use compression depends upon three resources: server-side bandwidth, client-side bandwidth,
and ProxySG CPU. If server-side bandwidth is more expensive in your environment than CPU,
then you should always request compressed content from the origin content server (OCS).
However, if CPU is comparatively expensive, the ProxySG should instead be configured to ask the
OCS for the same HTTP compressions that the client asked for and to forward whatever the server
returns.
The default configuration assumes that CPU is costlier than bandwidth. If this is not the case, you
can change the ProxySG behavior.
• SOCKS compression is supported for TCP/IP tunnels, which can compress the data transferred
between the branch (downstream proxy) and main office (upstream proxy), reducing bandwidth
consumption and improving latency.
When SOCKS compression is used in conjunction with the new Blue Coat Endpoint Mapper
(EPMapper) proxy, the Endpoint Mapper proxy accelerates Microsoft RPC traffic (applications
that use dynamic port numbers) between branch and main offices, automatically creating TCP
tunnels to ports where RPC services are running.
Upgrade Behavior
Prior to SGOS 4.x, the HTTP proxy did not cache objects if the server sent compressed content. With
HTTP compression and variant object support, objects are now cached regardless of its encoding (if all
other conditions allows caching).
With variant object support, multiple copies of the same object (variants) might exist in the cache, and
that might affect object carrying capacity of the disk.
On-box compression and decompression can significantly affect CPU and RAM usage. This will
directly affect the capacity of the box.