A wide pipe on a wide-area network won’t solve delays caused by TCP

The price of bandwidth on local-area and wide-area networks may be dropping, but a trend towards server consolidation and the use of chatty network protocols means some applications have slow response times, even on wide pipes, according to some industry experts.Vendors are responding with application acceleration hardware and software, which includes caching and other technologies designed to reduce repetitive queries across networks.

The trend towards server consolidation has increased the time required for basic business applications such as e-mail, said Joe Skorupa, research vice-president for enterprise network services and infrastructure at the Stamford, Conn.-based Gartner Group Inc.

For example, he said, when a user sends an e-mail with an attachment to 100 colleagues in a wide-area network where every branch has a server, the attachment crosses the network once. But if the company has only one server in a centralized location, then that attachment would traverse the network 100 times. Moreover, he said, some network protocols such as Common Internet File System (CIFS) and Microsoft Corp.’s MAPI require hundreds of trips to open files or messages, which increases response times when servers and clients are located on different continents.

“Things that used to take seconds now take minutes or tens of minutes,” he said.

CIFS was designed for local-area networks, not for networks with multiple sites, said Ameet Dhillon, director of product management for Seattle-based F5 Networks Inc., which makes application delivery controllers.

“It was designed in the mid-80s,” he said of CIFS. “It’s a very chatty protocol. There’s a lot of back and forth.”

F5’s WANJet appliance uses F5’s transparent data reduction technology, which stores local images of files transferred across networks.

Dhillon describes TDR as “very high-speed pattern matching,” which is different from caching because TDR stores bytes, rather than files.

Other vendors offering application acceleration products include Sunnyvale, Calif.-based Juniper Networks Inc., which manufactures the WX products designed to improve application response times over wide-area networks.

The WX products address the latency problems caused by TCP, said Mike Banic, director of product marketing for Juniper’s application products group.

TCP windows are 64 Kilobytes in size and hosts have to receive acknowledgement from recipients before sending more data.

“You send that first 64K of data and the host sits there waiting for the acknowledgement before it sends more, and the link is underutilized,” he said.

He cited as an example a customer in India who was using a 155 Mbps link, but only got about 30 Mbps of bandwidth from it because of the limitations of TCP.

“The devices that we deploy detect the language of the network,” he said. “As we see repeated patterns, we will remove them and replace them with a label that points to an entry in the dictionary of the device and that has a dramatic reduction on the amount of traffic that’s sent over the WAN.”

Banic said Juniper’s WX products can also be used on satellite networks, which are especially prone to packet loss.

“If there’s a single packet error, we don’t have to re-transmit a whole window of data, which would really slow the performance of TCP.”

Another protocol that tends to slow network traffic is secure sockets layer (SSL), said Andrew McKinney, director of technical services for Toronto-based Richardson Partners Financial Ltd.

“Any application that’s SSL-based will have that encryption and decryption – overhead that you wouldn’t have with a traditional application,” McKinney said.

Richardson Partners, an investment advisor company with branch offices in Montreal and Winnipeg, uses SSL to encrypt sensitive information sent among its workers. The firm is using eight SG appliances, manufactured by Sunnyvale, Calif.-based Blue Coat Systems Inc.

SGs are designed to be installed either at Internet gateways or at the edge of networks to accelerate applications such as file services, e-mail and streaming audio and video.

McKinney said Richardson uses the SGs primarily for filtering, caching and to control “non-essential business traffic,” such as streaming audio and video.

“As we saw bandwidth being used more and more, we wanted to be ahead of the curve and not wait for it to be a problem,” McKinney said.

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