Google云计算解决方案2_背景知识概述.ppt

? Spinnaker Labs, Inc. Ports Within an IP address, a port is a sub-address identifying a listening program Allows multiple clients to connect to a server at once ? Spinnaker Labs, Inc. Example: Web Server (1/3) The server creates a listener socket attached to a specific port. 80 is the agreed-upon port number for web traffic. ? Spinnaker Labs, Inc. Example: Web Server (2/3) The client-side socket is still connected to a port, but the OS chooses a random unused port number When the client requests a URL (e.g., “”), its OS uses a system called DNS to find its IP address. ? Spinnaker Labs, Inc. Example: Web Server (3/3) Server chooses a randomly-numbered port to handle this particular client Listener is ready for more incoming connections, while we process the current connection in parallel What makes this work? Underneath the socket layer are several more protocols Most important are TCP and IP (which are used hand-in-hand so often, they’re often spoken of as one protocol: TCP/IP) Even more low-level protocols handle how data is sent over Ethernet wires, or how bits are sent through the air using 802.11 wireless… ? Spinnaker Labs, Inc. IP: The Internet Protocol Defines the addressing scheme for computers Encapsulates internal data in a “packet” Does not provide reliability Just includes enough information for the data to tell routers where to send it ? Spinnaker Labs, Inc. TCP: Transmission Control Protocol Built on top of IP Introduces concept of “connection” Provides reliability and ordering ? Spinnaker Labs, Inc. Why is This Necessary? Not actually tube-like “underneath the hood” Unlike phone system (circuit switched), the packet switched Internet uses many routes at once ? Spinnaker Labs, Inc. Networking Issues If a party to a socket disconnects, how much data did they receive? … Did they crash? Or did a machine in the middle? Can someone in the middle intercept/modify our data? Traffic congestion makes switch/router topology important for efficient throughp