User`s guide

USER’S GUIDE
70 SFVRA Connection Manager
OTHER
Other Access options allow for the configuration of compression and the Callback feature.
C
OMPRESSION
Compression allows a CyberSWITCH to compress outgoing data and decompress incoming data.
This allows user devices on the WAN to initiate a connection to the system over the switched digital
network and transmit and receive compressed data, thereby decreasing transmission time.
The system data compression capability allows the system to negotiate compression algorithms
with a remote user. This compression can be done using some proprietary bridging protocols and
also the PPP CCP protocol.
After successfully negotiating compression, data is compressed by a peer and transmitted to the
system. The system decompresses the data, processes the addressing information contained in the
user data, and transmits the data as required. The converse is also true, the system can receive data
coming from a WAN or LAN and it compresses the data before transmitting it to a peer. The net
effect is to increase interconnect bandwidth by decreasing transmission time. If negotiation for
compression fails, data is transmitted uncompressed.
The compression software algorithm implemented is STAC-LZS. This algorithm is used in all of
STAC’s data compression products. This software version is fully compatible with STAC’s data
compression compressor chips including the multi-tasking features. STAC-LZS data compression
is performed by replacing redundant strings in a data stream with shorter tokens. The STAC-LZS
uses a compression history, or sliding window, as opposed to a structured dictionary. This allows
greater flexibility and a greater number of possible string comparisons during compression
process. The compression history automatically discards old information as new information is
processed. Both the user device and system must perform compression using the STAC-LZS data
compression algorithm. The peer and remote compression algorithms must be synchronized, this
is accomplished by negotiating compression at channel connect time. Once this has been
accomplished compressed data can be transmitted. If a transmission problem should ever occur the
problem is detected and compression re-synchronized by the execution of a pre-defined protocol.
C
ALLBACK
In order to maximize security and centralized billing, calls can be required to be made from the
central site to the remote site. This feature implements call back. In this process, the remote device
calls in to the central site and is authenticated. SFVRA-CONN will verify that the user satisfies the
configured call restriction, bandwidth and group requirements. If the user is validated, SFVRA-
CONN will instruct the CyberSWITCH to disconnect the call. The “CyberSWITCH Callback”
message will be logged as the reason for disconnection. The CyberSWITCH will then be instructed
to reconnect to the user, based on the load leveling feature, at which time the user is authenticated
again. The load leveling feature distributes outgoing Callback calls evenly among
CyberSWITCHES within a CyberSWITCH - User Group. If the user does not have any current calls,
SFVRA-CONN will examine all CyberSWITCH systems within the same group as the user. If a