Cisco Cisco ASR 5500
Mobile Video Gateway Overview
Features and Functionality ▀
MVG Administration Guide, StarOS Release 17 ▄
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Figure 15. TCP Link Monitoring System Flow
The TCP link monitoring feature calculates the RTT (Round Trip Time) and estimates the link bandwidth based on the
downlink data sent towards the UE and the current congestion conditions. It then collects this information at the system
level to report to the bulk statistics collection server.
downlink data sent towards the UE and the current congestion conditions. It then collects this information at the system
level to report to the bulk statistics collection server.
Note that the throughput calculation for the TCP link excludes duplicate, out-of-order, and retransmitted packets.
Functional Overview
The key functions of the TCP link monitoring feature are bandwidth estimation and system-level TCP statistical
logging.
logging.
Bandwidth Estimation
Because mobile devices are served by a variety of TCP variants, either from the OS or from the Mobile Video
Gateway’s TCP proxy, the TCP link monitoring feature employs an independent bandwidth estimation technique
proposed by TCP Westwood+ (see “Performance Evaluation of Westwood+ TCP Congestion Control” by Mascolo, et
al).
Gateway’s TCP proxy, the TCP link monitoring feature employs an independent bandwidth estimation technique
proposed by TCP Westwood+ (see “Performance Evaluation of Westwood+ TCP Congestion Control” by Mascolo, et
al).
Westwood+ estimates bandwidth by calculating the ratio of the number of bytes of acknowledged TCP payload over
every RTT. This rate sample is then filtered by a weighted moving average to derive a per-flow average bandwidth
estimate for every RTT interval.
every RTT. This rate sample is then filtered by a weighted moving average to derive a per-flow average bandwidth
estimate for every RTT interval.
Statistical Logging
Statistical logging of TCP traffic supports two types of plots: histogram and time-series.