2.12 Web Browsing via GPRS
2.12.1 Impact of Delay on the Web-Browsing Experience
While a high bandwidth connection is certainly one of the most important factors for a good web-browsing experience, the round-trip delay (RTD) time of the connection must also not be underestimated (11, 12). The RTD time is defined in this context as the time it takes to receive a response to a transmitted frame. This RTD can be measured, for example, with the ping command. The following example shows how delay impacts the web-browsing experience. When requesting for a new page, the following delays are experienced before the page can be downloaded and displayed:
- The URL has to be converted into the IP address of the web server that hosts the requested page. This is done via a DNS query that causes a delay of one RTD of the connection.
- Once the IP address of the server has been determined, the web browser needs to establish a TCP connection. This is done via a three-way handshake. During this handshake, the client sends a synchronization packet to the server, which is answered by a synchronization-ack packet. This in turn is acknowledged by the client by sending an acknowledgment packet. As three packets are sent before the connection is established, the whole operation causes a delay of 1.5 times the RTD of the connection. As the first packet containing user data is sent right after the acknowledgment packet, the time is, however, reduced to approximately a single RTD time.
- Only after the TCP connection ...