R&S M3SR 4100 Series, Руководство по эксплуатации

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Operating Manual 6175.4760.02 – 01 5.39
M3SR Series 4100 IP over Air (IPoA)
destination port 35002 is mapped to the Text Message Services and treated with its respec-
tive priority. Therefore, the above listed UDP ports cannot be used by customer-specific ap-
plications and pose a restriction to the complete IP transparency of IPoA as described in
”Basics of IP over Air (IPoA)” on p. 5.32 (of course the restriction only applies when the be-
fore-mentioned services are configured). IP data not mapping to any of the configured ser-
vices (default IP data) is sent with lowest priority. This results in noticeable performance
degradation (data rate/ delay) for default IP data, when many of the mentioned (higher prior-
ity) IP services are enabled.
IPoA provides additional user services (User2 to 4) that can be enabled and configured in
R&S RNMS3000 to match the specific needs of a given network topology and customer ap-
plications. If your applications do not allow a data mapping based on protocol and port, IPoA
provides the possibility to map the data according to the TOS (Type Of Service) byte in the
IP header as an alternative. Please contact the Rohde & Schwarz Customer Support for fur-
ther information.
Feedback Messages
In order to allow a flow control for user data sent over the radio network, the IPoA protocol
generates ICMP (Internet Control Message Protocol) source quench messages when its
send buffer reaches a specific use level (upper threshold). Also when a packet is dropped
due to an exhausted send buffer, a source quench message is generated. As long as the use
level does not fall below a 2
nd
specific use level (lower threshold), each obtained packet is
answered with an ICMP source quench message destined to the originator. The ICMP
source quench implementation complies with RFC792 (request for commands). The origina-
tor of the IP data shall use the source quench messages to implement a flow control mech-
anism that is to reduce its data rate upon reception of source quench messages, and
eventually slowly increase the data rate later. Such a behaviour greatly reduces the risk of
packet drop due to full send queues inside the IPoA protocol.
Table 5.5 provides an overview of the internally allocated buffer space available for transmis-
sion and the upper and lower thresholds for the source quench messages.
Table 5.5 Send Buffer and Thresholds
The send buffer size varies among the waveforms due to their maximum data rates support-
ed, thus a fast waveform like OFDM (only R&S M3TR) possesses a larger send buffer when
compared to a slow waveform like SECOM-H.
Waveform Send buffer [Kbyte] Upper threshold [%] Lower threshold [%]
SECOM-V
(only R&S M3TR) 315 70 50
SECOM-H 39.4 70 50
OFDM
(only R&S M3TR) 630 70 50
ALE-3G / xDL 129 70 50