The paper “ Network Traffic and Performance” is an actual variant of a lab report on information technology. Although scheduling techniques work well in managing packet flows through a network system, they suffer a common problem during periods of congestion. Since buffer space is a finite resource, under very heavy loads all space will be allocated and new arrivals must be discarded indiscriminately regardless of different classes of service. A ‘ maildrop’ is a problem with TCP/IP networks with potentially serious consequences. For instance, all mission or business-critical traffic is dropped at the input port regardless of whether or not low-priority traffic is currently enqueued.
When packets are discarded, TCP goes into a slow-start phase. Since packets are dropped indiscriminately, many sessions are affected. While this relieves the congestion, it is effectively like pulling on the emergency brake every time you approach a red light. Since many TCP sessions may be affected, and all go into slow-start, this results in a situation called global synchronization, where the dramatic oscillation of both congestion and low utilization occurs, rather than a graceful easing off. Congestion is likely to be caused by one or more bursty traffic sources.
Since packets are discarded during the congestion period, those sources are unfairly penalized. Therefore, a ‘ maildrop’ is effectively biased against senders (Kenyon 2002:503). For TCP this kind of bursty packet loss is particularly damaging, leading to overall inefficiency in TCP throughput for all network users. Furthermore, this problem cannot be addressed by simply increasing the memory available for queues, especially if the traffic profile is self-similar. The chaotic nature of self-similar traffic means that traffic is likely to burst beyond resource limits.
We, therefore, need a way to intelligently pre-empt congestion that backs off senders gracefully (Kenyon 2002:503). The key to this problem is to split traffic and allow each device to deal with a fair proportion of the overall traffic. The first issue to address is whether to do this on a per-packet basis or on a flow basis. The per-packet mechanism, for instance ‘ round robin’ is likely to result in fairer resource allocation but is also more likely to result in problems with retransmissions if end systems cannot re-sequence packets.
It may also be harder to debug and generate accounting data. If the load is to be spread among firewalls, state synchronization may rely on flow being handled deterministically where the flow or session goes in via one interface and returns through that interface rather than session being asymmetrical (Kenyon 2002: 504). Load-sharing server clusters, fronted by a proxy server, are a common technique used on inter-networks, as they offer both resilience and scalable performance. There are a number of algorithms available to iterate new sessions fairly between servers in a group.
The load can be distributed non-intelligently or intelligently, based on cost, delay, server status, and other factors. Therefore, it is useful to consider two environments for server load sharing. The case where the proxy server is local to the servers and the case where the proxy server is remotely located (Kenyon 2002:504). Basically, there are two approaches we can use to monitor session load on server pool members, non-intrusive and intrusive. Non-intrusive algorithms use simple heuristic techniques to distribute requests. On the other hand, intrusive algorithms require protocol interaction between each member of the server group and the proxy server, so that real-time status information can be passed between them.
Forouzan Behrouz and Fegan Sophia Chung, 2002, TCP/IP Protocol Suite, Published 2002 McGraw-Hill Professional, ISBN: 0072460601
Kenyon Tony, 2002, Data Networks: Routing, Security, and Performance Optimization, Published 2002 Digital Press, ISBN:1555582710
Orebaugh Angela, Ramirez Gilbert, Burke Josh, Wright Joshua, Pesce Larry, and Beale Jay, 2007, Wireshark & Ethereal Network Protocol Analyzer Toolkit, Published 2007 Syngress, ISBN:1597490733
Oodan, Antony, Ward Keith, Savolainen Catherine, Daneshmand Mahmoud, Hoath Peter, 2003, Telecommunications Quality of Service Management, Institution of
Electrical Engineers, Published 2003 IET, ISBN:0852964242
Sitaram Dinkar and Dan Asit, 1999, Multimedia Servers: Applications, Environments, and Design, Published 1999 Morgan Kaufmann, ISBN: 1558604308