University:
York University
Course:
AP/ITEC 1610 | Introduction to Computer Programming
Academic year:

2023
Views:

96

Pages:

3
Author:

Nick T.

Packets: Packet switching: Host breaks application layer messages into packets. Network forwards packets from one router to the next across links on the path from source to destination. Forwarding/Switching: The local action of moving arriving packets from a router's input link to an appropriate router output link. Routing: Global action of determining source-destination paths taken by packets using routing algorithms. Store-and-Forward: Entire packet must arrive at a router before it can be transmitted to the next link. Queueing loss: If the arrival rate to a link exceeds the transmission rate of the link, packets will queue to be transmitted on the output link. If the memory buffer fills up, packets may be dropped. Four Sources of Delay: Nodal processing: Check bit errors, determine output link Queueing delay: Time packets wait at link Transmission delay: Packet length / link transmission rate Propagation delay: Length of physical link / propagation speed Throughput: The rate at which bits are being sent from sender to receiver. Client-Server Paradigm: Server: Always on, permanent IP address, often in data centers. Clients: Contact/communicate with server, intermittent connection, dynamic IP addresses, don't communicate directly with each other (e.g., HTTP). Peer-Peer Architecture: No always-on server, end systems directly communicate. Self-scalability. Changing IP addresses. Example: P2P file sharing. Sockets: Process sends/receives from its socket. Once info out the socket, it is the transport infrastructure's work. Addressing Processes: Process identifier includes IP address and port numbers associated. Example: HTTP server - 80. TCP: Reliable transport. Flow and congestion control. Connection-oriented. No timing, min throughput guarantee, security. ServerSocket-socket(AF_INET, SOCK_STREAM). UDP: Unreliable data transfer. No reliability, flow control, congestion control, timing, throughput guarantee, security, or connection set-up. No handshake. Sender explicitly attaches receiver IP and port#. Receiver extracts sender IP and port. AF_INET, SOCK_DGRAM. Web and HTTP: Application layer protocol defines: Types of messages exchanged Message syntax Semantics: Meaning of info in different fields Rules for sending and responding HTTP: Hypertext transfer protocol The web's application layer protocol Client-server model Uses TCP Stateless: Server maintains no info about past client requests Persistent vs. Non-Persistent Connections: Non-persistent: TCP connection opened Max 1 object sent TCP connection closed Persistent: TCP connection opened Multiple objects sent over single connection TCP connection closed Response Time: Response time = 2RTT + file transmission time Persistent connections cut response time in half Request Message General Format: Request line Header lines Body Status Codes: 200 OK 301 Moved Permanently 400 Bad Request 404 Not Found 505 HTTP Version Not Supported Other Request Messages: POST: Send input GET: HEAD: Requests headers only PUT: Uploads file/object