SatLink VSAT User Guide
Publication no. 101557
Copyright © 2009 – STM Group, Inc.
Page 86 (160)
18.2 TCP Performance Enhancing Proxy (PEP)
Conditions particular to satellite communication severely constrict the performance of TCP and reduce
the end users experience of accessing the Internet over satellite. Large latency, elevated bit error rates,
and asymmetric bandwidth are all characteristics of satellite networks that result in degraded TCP
performance. Various TCP Performance Enhancing techniques are used to improve the performance of
the TCP protocol over satellite links. The TCP PEP implementation in the SatLink System makes use of a
TCP Performance Enhancing Server installed in the STM SatLink Hub and a PEP software client
embedded in the STM SatLink VSAT.
The STM SatLink VSAT embedded PEP client is an optional feature, which is enabled by entering a
license key. Use of the VSAT’s embedded PEP client is subject to the Network Operator/ISP supporting
the PEP functionality using a PEP server on the Hub side. It is possible for the Network Operator/ISP to
activate the embedded client software remotely from the Hub, thus requiring no end-user intervention.
Alternatively, an end-user can receive a license key from the Network Operator/ISP and activate the
functionality using the CLI command
sw license as shown in the example below.
Example:
# sw license pep mykeyforenablingpep
The PEP server in the Hub may be installed in two different modes.
1. Re-direct mode
2. Transparent mode
Re-direct mode is the default setting. The Network Operator/ISP should inform you if the Hub PEP server
is installed in transparent instead of re-direct mode.
When operating in re-direct mode, the IP address of the TCP PEP Server in the Hub must be configured
in the STM SatLink VSAT. If the VSAT is authorised to use PEP, this is normally performed remotely by
the SatLink Hub when the VSAT logs on to the network. Alternatively, the VSAT user can locally
configure the server address by means of the CLI command
ip pep server <ipaddr> using the PEP
Server IP address provided by the Network Operator/ISP.
To enable the PEP functionality, use the CLI command
ip pep enable [<mode>], where <mode>
can assume the values
redirect or trans. To verify that the PEP functionality has been enabled, type
ip pep show.
The CLI command sequence to configure and enable the PEP functionality is recapitulated below:
Example:
# sw license pep mykeyforenablingpep
# ip pep server 10.0.0.10
# ip pep enable redirect
# ip pep show
(to verify that the functionality is enabled)
PEP Status : enabled
PEP TCP Mode : Redirect Mode
PEP TCP Server Address : 137.133.81.40
Maximum Connections : 512
Current Connections : 178
Total Connections : 584928
Transp Connections : 0
Failed Connections : 0
Received Segments : 29411430
Out of sequence Segments : 12338
Duplicate Segments : 5843
Transmitted Segments : 25883165
Retransmitted Segments : 10849
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