CN march 3

Default Port Number for STTP

  • The default port number for Simple Text Transfer Protocol (STTP) is 80.

Overview of STTP Request Process

  • Client-Server Model:
    • A client (usually a web browser) requests information from a server.
    • Content such as HTML files, images, and JavaScript files are stored on the web server.
    • The client knows which server to contact through the domain name provided in the URL (e.g., http://full-container.domain).

URL Resolution to IP Address

  • When a client initiates a request using a domain name:
    • The client must first resolve this domain name into an IP address.
    • This process generally involves sending a DNS query (Domain Name System query) to a local DNS server to fetch the corresponding IP address of the domain, e.g., gong.com.
    • It is assumed there is always a local DNS resolver available for the client.

TCP Handshake and Connection Establishment

  • After the client receives the IP address:
    • The client must perform a TCP handshake to establish a connection with the web server.
    • This is an essential step for the TCP protocol, which operates at the transport layer.

Requesting Objects from the Web Server

  • Following the establishment of a TCP connection:
    • The client sends an HTTP request to the server for the desired objects (e.g., HTML files).

Terms and Definitions

  • Round Trip Time (RTT):

    • The time it takes for a signal to go to the destination and back.
    • RTT is an important metric in assessing response times during network requests.

  • Transmission Time:

    • This is the time it takes for the data packets to be sent from the source to the destination over the network.

Example Calculation of Delays

  • Scenario 1: Requesting an HTML Page with Zero Objects

    1. DNS Query: 1 RTT to contact the local DNS.
    2. TCP Connection: 1 RTT for the TCP handshake.
    3. HTTP Request and Response: 1 RTT to fetch the HTML page.
    • Total Delay: 3 RTT.

  • If the DNS needs to contact multiple servers (root DNS, TLD DNS, and authority):

    • Total Delay can extend to 4 RTT.

Nonpersistent vs. Persistent HTTP Connections

  • Nonpersistent Connection:

    • A new TCP connection is opened for every single object requested.
    • This means there will be round trips for TCP and HTTP for each object.

  • Persistent Connection:

    • The connection remains open for multiple requests, avoiding the need for repeated handshakes.
    • More efficient as less overhead is required for establishing new connections.

Efficiencies to Improve Load Time

  • Threading Concept: This allows multiple requests to be sent simultaneously to reduce overall load times.
  • Pipelining:
    • Persistent connections with pipelining allow clients to send multiple requests without waiting for the preceding responses.
    • This can greatly reduce load times as the delivery of multiple objects can occur instantly after being requested.

Connections and Their Effects on Response Time

  • In the case of parallel connections and different server object requests:

    • With five images requested from various domains, unique DNS queries are required for each.
    • A separate round trip must be counted for all additional DNS hops.

  • HTTP scenarios can depend on the number of objects and the type of connection (persistent vs. nonpersistent)

    • Nonpersistent connection per object typically incurs 2 RTTs (One for TCP, One for HTTP).
    • Persistent connections can reduce this overhead significantly due to their efficiency.

Caching Considerations

  • Caching can help minimize transmission delays by storing frequently accessed objects.

    • When a cached object is requested again, the client can bypass the server, reducing overhead.

  • Conditional GET Requests:

    • Rather than downloading all objects anew, they will check if the objects have changed since the last request, significantly reducing date transfer when no changes are detected.
    • For example, if 60% of objects in 50 requests are unchanged, they won’t incur additional transmission time, reducing the load on the server and enhancing speed.

Exam Preparation and Practice Questions

  • Students are encouraged to utilize resources & knowledge checks as they prepare.
  • Focused studying and collaboration with peers can enhance understanding.
  • Reminder: Utilize cheat sheets and allow for ample time to cover all concepts thoroughly.