Multiple Simultaneous Connections

In order to open multiple simultaneous connections to a web site, the browser must be capable of and configured for HTTP 1.1 connections. HTTP 1.1 brings the ability for a browser (or agent) to connect to a web server many times with the objective of increasing performance as prior to this standard HTTP 1.0 (and earlier) required that connections were opened and closed for every new request, Kurose & Ross (2010). This could be compared with a single lane road versus a motorway with three or more lanes, although in this example traffic cannot change lanes during a journey, the throughput is much increased allowing more vehicles to reach their destination than would have been possible in a single lane.

Most modern browsers can be configured to open multiple simultaneous connections to a web site, assuming that the web site in question resides on a web server that supports this, however many browsers do not have this enabled by default. Certainly when examining Mozilla Firefox 4, Internet Explorer 8, Opera 11 and Chrome 10 browsers on my system, only Opera 11 and Internet Explorer 8 had HTTP 1.1 enabled by default. Chrome 10 reported, in The Chromium Projects (2011), that they have decided to move towards a new open source “SPDY” protocol with the same aims of HTTP 1.1.: to make the web faster. In short, it seems that the browser making community are not agreed on HTTP 1.1 implementation.

This lack of agreement is due to the many different systems and uses of web servers and clients in the application layer today. Despite the lack of implementation in the browser market, the W3C (1999) stated that “HTTP implementations SHOULD implement persistent connections” due to the advantages of persistent over non-persistent connections. The main disadvantage of persistent connections, albeit still a performance increase over non-persistent connections, is that there may be a waste of network resources if the browser has completed its requests with the web server and the there is a long time out before the server closes the connection (as recommended by the W3C (1999)). The advantages of multiple simultaneous connections are many, largely around network performance and reporting as without the need to open a new connection on every new request and close when complete, which is processor and bandwidth heavy in comparison to the transmission of data, memory, bandwidth and latency is much improved. Add to this the ability to pipeline requests (again if enabled) then the browser can make multiple requests without the need to wait for a response and the ability for errors to be reported in the same connection then the result should be that performance should be enhanced further and errors reduced.


Kurose & Ross (2010) Computer Networking: A Top-Down Approach (Fifth Edition). Addison Wesley.

The Chromium Projects (2011) SPDY: An experimental protocol for a faster web [Online]. Available at (Accessed 17 Apr 2011).

W3C (1999) Hypertext Transfer Protocol — HTTP/1.1: 8.1 Persistent Connections [Online]. Available at (Accessed 17 Apr 2011).