TCP Optimization Enhancements for a Better Mobile Experience

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Published July 12, 2017

According to the Cisco Visual Networking Index 2017, mobile video traffic accounted for 60 percent of total mobile data traffic in 2016. All told, mobile video is expected to increase nine-fold between 2016 and 2021, accounting for 78 percent of total mobile data traffic by 2021.

Given the anticipated growth, it’s clear that providing customers with a great video experience will be critical for mobile operators to stay competitive and profitable. But it won’t be easy.

The Trouble with TCP

The mobile network deployment of WiFi, 3G, 4G, and 5G aims to give subscribers a higher-quality experience for mobile broadband, while providing operators an opportunity to create and customize revenue streams. However, to maintain a competitive advantage, mobile operators will need to evolve their Transmission Control Protocol (TCP) optimization practices to deliver faster network services as mobile data traffic increases.

While most applications use TCP to communicate with the services they need, it was originally designed to establish connections and deliver data between clients and servers—not to support services like voice and video. Moreover, TCP is optimized for accurate delivery rather than timely delivery and can incur seconds-long delays while waiting for out-of-order messages or retransmissions of lost messages. Thus, TCP is not ideal for real-time applications such as voice and video. Sporadic packet loss caused by network congestion can drastically slow transfer rates. This means reduced loading speeds, degraded voice quality, and poor video streaming experiences for users.

What TCP Optimization Actually Does

TCP optimization solutions need to be flexible enough to handle the varying network conditions of WiFi, 3G, 4G, future 5G, and handover scenarios between these network types. TCP optimization techniques need to handle congestion, lower latency, integrate with policy awareness and user control, and support high scalability to approach Cisco’s 2021 predictions.

To support the varying network conditions and overcome inherent protocol limitations, F5’s BIG-IP platform uses these adaptive TCP optimization-specific functions:

  • Rate Pacing: This controls the flow of packets across the network to avoid overpowering buffers downstream. Without rate pacing, packets are sent immediately and consecutively. By knowing the speed at which different flows are being sent and received, the TCP stack can control how quickly to send new packets, improving the distribution across flows. Pacing the flow rate allows the buffers to adjust without being overfilled, preventing inconsistent traffic behaviors and packet loss due to network congestion. BIG-IP products constantly monitor network buffers—sending packets at rates that prevent buffer bloat by proactively adjusting the pace of delivery during heavy traffic, thereby avoiding congestion. Once traffic lightens up again, BIG-IP products enable quicker speeds to maximize the use of available bandwidth.
  • Programmable TCP Tuning: Operators can change TCP parameters based on network conditions, such as a user roaming across multiple radio access types. For example, when a UE roams from 3G to 4G, the BIG-IP product detects the change in RAT type and automatically adjusts window sizes up or down before responding.
  • Dynamic Auto-Tuning: BIG-IP products can modify TCP parameters dynamically as network conditions change. Operators establish thresholds that, when triggered, cause BIG-IP products to automatically update the applicable buffer sizes (for example, when a user is roaming from 3G to 4G).
  • Aggressive TCP Loss Recovery: In low round trip time (RTT) networks, recovering packet loss using retransmission timeouts (RTOs) reduces network performance significantly. BIG-IP products implement a new, more aggressive, TCP loss recovery algorithm that can retransmit missing PDUs multiple times during the loss recovery period. This approach prevents lengthy RTOs and correspondingly improves performance.
  • Multipath TCP (MPTCP) Full Mesh and Congestion Control: This enables a device to use multiple paths during a TCP session, allowing multiple client-side flows to connect to a single server-side flow. Particularly relevant for mobile devices, this means that connections are seamlessly passed across WiFi and macro 3G/4G networks. When one path fails, MPTCP allows the session to continue to work over an alternative path, yielding fewer dropped communications. MPTCP also improves the use of network resources through higher throughput and improved network resilience.


Properly handled, TCP optimization provides reliable, consistent services and application delivery while dramatically improving performance across networks to deliver a better user experience. Users gain faster browsing and quicker access to content, with uncompromised quality of service.

All of this makes TCP optimization an effective (and necessary) means for mobile operators to maintain a strong competitive advantage via reduced loading times for applications and subscribers. Through the advantages described above, the BIG-IP platform lets operators adapt in real-time to the variable conditions of mobile networks—latency, packet loss, congestion, etc.—fully utilizing available bandwidth and accelerating application traffic.

Further Reading

To learn more about F5’s TCP optimization capabilities, visit our Data Traffic Management solution page.