WAN Optimization Techniques: Accelerating Remote Network Performance
High latency and limited bandwidth don't have to cripple your remote offices. Learn techniques to maximize WAN performance without expensive upgrades.
The WAN Challenge
Wide Area Networks connect geographically dispersed locations, but they bring inherent challenges: higher latency due to distance, limited bandwidth compared to LANs, and packet loss from traversing multiple networks. Applications designed for local networks often perform poorly across WAN links.
The Impact of Latency
TCP's round-trip handshakes amplify latency impact. A file transfer over a 100ms WAN link can be 10x slower than the same transfer on a 1ms LAN, even with identical bandwidth.
Core Optimization Techniques
Data Deduplication
Identify and eliminate redundant data in transit. If the same file section was sent before, reference the cached copy instead of resending. Can reduce traffic by 60-90% for repetitive data.
Compression
Compress data before transmission, decompress on arrival. Works best for text-based protocols. Already-compressed data (images, video) sees minimal benefit.
Protocol Optimization
Modify how protocols behave over WAN. Reduce round trips by batching requests, use local acknowledgments, and optimize TCP window sizes for high-latency links.
Caching
Store frequently accessed data locally. Web caching, file caching, and application-level caching all reduce WAN traffic and improve response times.
TCP Optimization
TCP wasn't designed for high-latency links. Standard TCP behaviors that hurt WAN performance:
| Behavior | Problem | Solution |
|---|---|---|
| Small initial window | Slow start on every connection | Increase initial congestion window |
| Small receive window | Can't fill the pipe | TCP window scaling |
| Packet loss = congestion | Backs off on any loss | Loss-tolerant congestion control |
| Sequential acks | High latency for each round trip | Selective acknowledgments (SACK) |
# Linux TCP tuning for high-latency links # Increase buffer sizes sysctl -w net.core.rmem_max=16777216 sysctl -w net.core.wmem_max=16777216 sysctl -w net.ipv4.tcp_rmem="4096 87380 16777216" sysctl -w net.ipv4.tcp_wmem="4096 65536 16777216" # Enable window scaling and SACK sysctl -w net.ipv4.tcp_window_scaling=1 sysctl -w net.ipv4.tcp_sack=1
Application-Specific Optimization
Different applications benefit from different techniques:
| Application | Primary Issue | Best Approach |
|---|---|---|
| File shares (SMB/CIFS) | Chatty protocol, many round trips | Protocol optimization, caching |
| Backup software | Large data volumes | Deduplication, compression |
| Web applications | Multiple small objects | Caching, object prefetching |
| Database replication | Synchronous writes | Local ack, write pipelining |
WAN Optimization Appliances
Dedicated WAN optimization appliances sit at each site and transparently optimize traffic between locations:
How They Work
Traffic passes through appliances at each end. They maintain synchronized data caches, intercept protocols, and apply optimization techniques transparently to endpoints.
Deployment Models
In-path (inline with traffic), out-of-path (traffic redirected via policy), or virtual appliances running in cloud or hypervisors.
Note: WAN optimization appliances add complexity and cost. Consider them for sites with expensive WAN links or severe application performance issues, not as a default deployment.
SD-WAN and Modern Alternatives
Software-Defined WAN has absorbed many WAN optimization functions:
- -Path selection: Route traffic over the best available path (MPLS, broadband, LTE) based on real-time conditions.
- -Application awareness: Identify applications and apply appropriate policies automatically.
- -Forward error correction: Add redundancy to overcome packet loss without retransmission.
- -Packet duplication: Send critical packets over multiple paths for reliability.
Measuring Optimization Effectiveness
Track these metrics to validate your WAN optimization efforts:
| Metric | What It Shows |
|---|---|
| Data reduction ratio | Bytes sent vs. bytes on wire after optimization |
| Application response time | End-user perceived performance improvement |
| WAN throughput | Effective bandwidth achieved vs. link capacity |
| Connection setup time | Impact of protocol optimization |
Quick Wins Without Appliances
Before investing in optimization appliances, try these free improvements:
Tune TCP on Servers
Increase buffer sizes and enable window scaling on file servers and application servers accessed over WAN.
Enable Compression in Applications
Many applications support built-in compression. Enable it for database replication, backup software, and web servers.
Deploy Local Caching
Branch office file caches (like BranchCache or DFS-R) keep frequently accessed files local without WAN optimization appliances.