Week 2 CST 311: Introduction to Computer Networks

In week 2, we learned about the principles of network applications, web and HTTP, DNS, peer-to-peer, and video streaming and content distribution networks. 

Network apps are services like email, web, text messaging, and P2P file sharing on the internet. They run on different end systems (phones, tvs, tablets) over a network. There are two application architectures: client-server, and peer-to-peer. In the client-server architecture, the server is a host who is always on, has a permanent IP address, and is usually located in a data center. The client communicates with the server, may be connected, have dynamic IP addresses, and usually do not communicate with one another. In P2P architecture, there is no server because the end systems/peers directly communicate by requesting services from other peers who also have dynamic IPs. For this, it scales with more users.

HTTP is the hypertext transfer protocol using the client-server model where the client initiates a TCP connection to the server, is accepted by the server, HTTP messages are exchanged between the client and server, and then the TCP connection is closed.

DNS is the Domain Name System or a distributed database of name servers that provides hostname to IP address translation, host aliasing, mail server aliasing, and load distribution. For example, if a client wants the IP for a website, the client queries the root server to find the “com” DNS server, then the “.com” DNS server to get the website DNS server. It will then query the website DNS server to get the IP address for the website.

In video streaming and content distribution networks, many users are involved. In video streaming, Dynamic Adaptive Streaming over HTTP (DASH) is used by the server to divide the video into encoded chunks, and the client measures the bandwidth and requests one chunk at a time based on the bandwidth. The CDN stores multiple copies of videos at geographically distributed sites and will either enter deep by pushing CDN servers to many access networks or bring home by having larger clusters in POPs near the access networks. The CDN stores copies of content at the nodes, a subscriber requests content, and then receives content from the nearby copy.