Optimizing for Mobile Clients in BIG-IP LTM
Optimizing mobile client performance involves configuring the correct TCP profiles and settings to account for the unique characteristics of mobile networks (3G, 4G, LTE). Mobile networks can be prone to higher packet loss, variable latency, and lower bandwidth compared to wired connections, which means fine-tuning TCP settings is crucial for better performance.
1. "tcp-cell-optimized" Profile
Purpose: Designed specifically for mobile networks (particularly 3G and 4G), improving performance for mobile clients.
Key Features:
Best suited for smaller files (less than 1MB).
Optimized for mobile network conditions like variable bandwidth and high latency.
More efficient than profiles like mptcp-mobile-optimized for smaller file transfers.
When to Use:
Use this profile when dealing with mobile clients (especially in 3G and 4G networks) and optimizing file transfer performance for smaller-sized content.
2. "tcp-mobile-optimized" Profile
Purpose: A more conservative profile to start with when optimizing TCP for mobile environments, balancing performance and reliability.
Key Features:
Proxy Buffer Settings:
Set Proxy Buffer Low to Proxy Buffer High minus 64 KB.
If Proxy Buffer High is less than 64 KB, set the buffer size to 32 KB.
Send Buffer Size: Ranges from 64 KB to 350 KB, depending on the network’s characteristics.
In networks with higher packet loss, smaller buffer sizes typically perform better.
Congestion Control Algorithms:
Illinois Congestion Control Algorithm:
More aggressive than other algorithms, suitable for small object sizes.
However, for objects greater than 1 MB, the goodput might decrease.
High-loss networks may see lower goodput and higher retransmissions.
Woodside Congestion Control Algorithm:
Uses timestamps to determine transmission.
If timestamps are unavailable on the network, avoid using this algorithm.
Rate Pace Setting:
Enabling this setting improves goodput and prevents bursty traffic behavior on egress traffic.
Reduces loss recovery for most congestion algorithms, except Illinois.
3. Packet Loss Optimization
Packet Loss Ignore Rate:
For 4G LTE networks, set this to 0.
For 3G networks, set this to 2500.
If the Packet Loss Ignore Rate is greater than 0, the number of retransmitted bytes and SACKs (Selective Acknowledgments) might increase significantly.
Packet Loss Ignore Burst:
When the Packet Loss Ignore Rate is greater than 0, set Packet Loss Ignore Burst to > 0.
Higher Packet Loss Ignore Burst increases the chance of unnecessary retransmissions, so it should be used cautiously.
4. Initial Congestion Window Size
Initial Congestion Window Size is multiplied by the Maximum Segment Size (MSS), which is typically 1460 bytes.
Increasing this value from 0 to 10 or 16 helps in reducing the Round-Trip Time (RTT) by allowing faster initial data transmission.
Summary of Key TCP Optimizations for Mobile Clients
Parameter
Recommended Setting
Description
Profile to Use
tcp-cell-optimized or tcp-mobile-optimized
Use tcp-cell-optimized for small files (<1MB). tcp-mobile-optimized for a conservative approach.
Proxy Buffer Sizes
Proxy Buffer Low = Proxy Buffer High - 64 KB
Adjust buffer sizes based on network conditions to optimize mobile performance.
Send Buffer Size
64K - 350K
Choose based on network conditions; smaller buffers perform better with packet loss.
Congestion Control Algorithm
Illinois (Aggressive) or Woodside
Illinois is aggressive and works well for smaller objects but may perform poorly for larger ones. Woodside relies on timestamps (avoid if not supported).
Rate Pace
Enabled
Helps prevent burst traffic behavior and improves goodput.
Packet Loss Ignore Rate
0 for 4G LTE, 2500 for 3G
Helps manage retransmissions based on packet loss behavior.
Packet Loss Ignore Burst
> 0 if Packet Loss Ignore Rate > 0
Set to higher values cautiously to avoid unnecessary retransmissions.
Initial Congestion Window Size
Increase from 0 to 10 or 16
Reduces RTT and improves initial performance.
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