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Gary Kaiser

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In Part IV, we wrapped up our discussions on bandwidth, congestion and packet loss. In Part V, we examine the four types of processing delays visible on the network, using the request/reply paradigm we outlined in Part I. Server Processing (Between Flows) From the network's perspective, we allocate the time period between the end of a request flow and the beginning of the corresponding reply flow to server processing. Generally speaking, the server doesn't begin processing a request until it has received the entire flow, i.e., the last packet in the request message; similarly, the server doesn't begin sending the reply until it has finished processing the request. We sometimes refer to these delays between flows as "pure" processing delays, distinct from another type of intra-flow processing delay we call starved for data and discuss later. Server processing delays ... (more)

Understanding Application Performance on the Network | Part 1

As a network professional, one of your newer roles is likely troubleshooting poor application performance. For most of us, our jobs have advanced beyond network "health," towards sharing - if not owning - responsibility for application delivery. There are many reasons for this more justifiable than the adage that the network is first to be blamed for performance problems. (Your application and system peers feel they are first to be blamed as well.) Two related influencing trends come to mind: Increased globalization, coupled with (in fact facilitated by) inexpensive bandwidth me... (more)

Understanding Application Performance on the Network | Part 6

In Part V, we discussed processing delays caused by "slow" client and server nodes. In Part VI, we'll discuss the Nagle algorithm, a behavior that can have a devastating impact on performance and, in many ways, appear to be a processing delay. Common TCP ACK Timing Beyond being important for (reasonably) accurate packet flow diagrams, understanding "normal" TCP ACK timing can help in the effective diagnosis of certain types of performance problems. These include those introduced by the Nagle algorithm, which we will discuss here, and application windowing, to be discussed in Par... (more)

Understanding Application Performance on the Network | Part 2

When we think of application performance problems that are network-related, we often immediately think of bandwidth and congestion as likely culprits; faster speeds and less traffic will solve everything, right? This is reminiscent of recent ISP wars; which is better, DSL or cable modems? Cable modem proponents touted the higher bandwidth while DSL proponents warned of the dangers of sharing the network with your potentially bandwidth-hogging neighbors. In this blog entry, we'll examine these two closely-related constraints, beginning the series of performance analyses using the ... (more)

Understanding Application Performance on the Network | Part 4

We know that losing packets is not a good thing; retransmissions cause delays. We also know that TCP ensures reliable data delivery, masking the impact of packet loss. So why are some applications seemingly unaffected by the same packet loss rate that seems to cripple others? From a performance analysis perspective, how do you understand the relevance of packet loss and avoid chasing red herrings? In Part II, we examined two closely related constraints - bandwidth and congestion. In Part III, we discussed TCP slow-start and introduced the Congestion Window (CWD). In Part IV, we'... (more)