In LAN environments, switches provide direct 100 Mbps connections between each client computer and server - so if there is a performance bottleneck, it usually occurs at the server, not the network. Accessing applications across the WAN introduces a totally new bottleneck into the system, because WANs become congested, slow, and error-prone - significantly increasing application response times for remote office users. IT managers look to WAN optimization (sometimes referred to as network optimization) solutions to mitigate the negative effects of the WAN, such as low bandwidth, high latency, packet loss, or network contention.
WAN traffic actually traverses a series of network segments between the remote office and the data center. Each network segment is connected to the next by a network device, such as a router or switch, which receives and stores incoming network data packets and then retransmits the packets ("hops") to the appropriate next segment. Each hop adds latency, which hampers overall WAN performance. Application performance can be no better then the slowest link in the network.
As the network load increases, one or more of these segments can become overloaded. One recent contributing factor to increased network load has been the move to centralize mission-critical resources at the data center and enable application access to remote offices through Web-based portals. Gartner estimates that over 80 percent of corporate traffic is generated from remote offices, and over 75 percent of that WAN traffic is HTTP-based. This increased load on the enterprise network stresses remote access performance and increases application response times.
As congestion builds, the network devices transmitting over the saturated link start buffering packets for longer periods of time before transmitting data, leading to increased latency. If the network load continues to grow, then buffers will eventually overflow and network packets will be dropped according to preset policies, leading to further packet loss. Increases in packet loss dramatically decrease TCP throughput. For example, a 2 percent packet loss rate decreases the overall throughput of a TCP connection by 90 percent. Although TCP behaves reasonably well through a wide range of LAN and good WAN conditions, performance deteriorates rapidly under poor WAN conditions and directly affects application performance.
WAN bandwidth - the rate of transmitting data - is a primary, but not the only, source of network-induced application response latency (IART). For example, it takes 53 seconds to send 10 MB of data over an ideal T1 (1.5 Mbps) WAN connection, but only 0.8 seconds on a 100 Mbps LAN. That's nearly 70 times faster. Any application that needs to send or receive large amounts of network data will be subject to significantly increased latencies due to fundamental bandwidth restrictions. Adding more bandwidth to the enterprise network may help solve some latency issues but will have no real effect on network contention or packet loss, other factors in maintaining high-performing application delivery.
As applications are accessed simultaneously from remote offices across the WAN, the bandwidth is divided among the competing users. So, even though the office might use a high-speed T1 connection, each user is allotted a much smaller effective bandwidth. QoS and traffic prioritization can prevent low-priority traffic, such as personal Web surfing, from grabbing bandwidth when high-priority line-of-business (LOB) applications need the network. However, QoS does not help when multiple users are all running LOB applications, and network contention can negatively impact QoS services.
Given all these issues, the enterprise IT challenge is to cost-effectively deliver LAN-like performance over the WAN, especially for critical LOB applications that drive the business. The enterprise must find a way to make these otherwise sluggish Web applications responsive for remote office users - users who make up 80 percent of the enterprise work force.
Subscribe to our RSS News feed. (How to...)
Download the aCelera Virtual Appliance for Application Acceleration data sheet as a PDF document. 
documents require the Adobe Reader. Download the reader for free.
