Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Dynamic Host Configuration Protocol wikipedia , lookup
Cross-site scripting wikipedia , lookup
Remote Desktop Services wikipedia , lookup
List of wireless community networks by region wikipedia , lookup
TV Everywhere wikipedia , lookup
Zero-configuration networking wikipedia , lookup
Video on demand wikipedia , lookup
Routing in delay-tolerant networking wikipedia , lookup
Content-control software wikipedia , lookup
Technologies for Building Content Delivery Networks Pei Cao Cisco Systems, Inc. [email protected] What are Content Delivery Networks • A centrally managed network of devices that collectively facilitate the delivery of content to end users • Solve network bandwidth bottleneck • Solve server throughput bottleneck CDN Categories • Network Infrastructure: – Single ISP – Overlay networks – Enterprise premise • Content types: – Static images and texts – Multimedia content: audio and video streams – Dynamic HTML and XML pages • Customers: – Content providers – Enterprise Technology Components • Content distribution – Placing the content to the devices • Request routing – Steer users to a delivery node that is close • Content delivery – Protocol processing, access control, QoS mechanisms • Resource accounting – Logging and billing Content Distribution • Goal: position content objects into delivery devices • Different content types use different techniques – Static images and texts: pulled & cached, or pushed – Multimedia contents: usually pre-positioned – Dynamic pages: requires prior setup Distribution Mechanisms • HTTP request for pulling – Example: standard HTTP reverse proxy • FTP of tar files – Some equipment vendors use this technique • Rate limited tree-form replication – Example: Cisco’s “Soda” algorithm Distribution Mechanisms using Multicast • Application-level reliable multicast – Example: Inktomi’s Fast-Forward • Unreliable IP multicast with file-level error correction – Example: Digital Fountain, multicast-ftp • Unreliable IP multicast – Example: RealNetworks Content Consistency Mechanisms • Expiration times or TTL • Renaming in the HTML file • Web Cache Invalidation Protocol (WCIP) – Nodes receive invalidations when objects change – Objects are organized into channels – Nodes subscribe to a channel to receive invalidation Request Routing • Goal: steer the client such that it fetches the content from a close node • Methods – DNS selection – HTTP redirection – Transparent interception Overview of Request Arrival Process How a request for www.xyz.com/index.html arrives at 1.2.3.4: DNS server 1. what is IP addr of www.xyz.com? Client 6. 1.2.3.4 Router 2. where is name server Root NS of xyz.com? 3. NS record: 1.2.3.1 4. what is IP of www.xyz.com? xyz.com IP: 1.2.3.1 NS 5. A record:1.2.3.4 7. GET /index.html s w i t c h Server IP: 1.2.3.4 DNS selection • Basic idea: xyz.com’s NS returns node close to client • How to become xyz.com’s NS? – Rewrite URLs (aka Akamizer) – Take a subdomain cdn.xyz.com and put all content there • Accuracy limited to client’s name server – Only suitable for ISP or overlay networks – Not suitable for some enterprise or cable networks HTTP Redirection • Basic idea: web server tells client to go somewhere else – Returns “302 redirect … 1.2.4.5/index.html…” • Mostly used for multimedia objects – These objects are usually put together in an index file (.sml or .asx) and clients fetch the index file via HTTP before streaming • Accuracy is at individual client level – More suitable for enterprise and cable networks Transparent Interception • Router and switch along the request path can send the request elsewhere • Mostly used for distributed data centers front-ended with L7 switches – Example: Cisco’s CSS11k WebNS Algorithms for Request Routing • Map-based – Create a map of the Internet based on AS domains, pick the node with the shortest hop count to client – Or, set up coverage zones mapping a node to a collection of subnets • Racing-based – Let the delivery nodes all race to the client with A-records – Winner is selected by client automatically The Boomerang Algorithm • Cisco’s research published in WCW’01 – xyz.com’s NS server forwards lookup of www.xyz.com to all delivery nodes – Delivery nodes all send “A record” response with its own IP address to the client – The one that reaches the client first wins – NS server times the forwarding so that lookup message arrives at all nodes around the same time – Use “simulated annealing” for scalability Interaction between Content Distribution and Request Routing • Don’t route request to a node that doesn’t have the content! • Particularly important for large streaming contents – Such content are usually pre-positioned to ensure high-bandwidth playbacks • Nodes need to report its content acquisition status to the “request router” Content Delivery • Goal: serve content to each client at desired quality of service • Supported protocols – – – – HTTP Microsoft MMS Open standard RTP/RTSP RealNetworks RTP/RTSP • Usually part of the larger CDN system Content Access Control • Content object attributes – “Publication date” and “Expiration date” – ACL based on user/group/IP • User authentication – HTTP basic – Microsoft NTLM for enterprise environment – other schemes • Media Rights Management QoS of Content Delivery • Server QoS – Server needs to make sure it has enough CPU and disk to service the stream at specified bit rate • Network QoS – Interoperate with routers via DiffServ bits • Coordination with request router – delivery devices should communicate load information to the “Request Router” Resource Accounting • Mining the log files – Log file aggregation: all device sending log files to a central location – Local mining: analyzing the log file at each delivery device • Real-time statistics – Real-time statistics on throughput/latency based on domain, content type or any HTTP header – Example: Cisco CSS switch billing MIB Cisco’s CDN Products • • • • Content Distribution Manager (CDM) Content Router (CR) Content Engine (CE) CSS switch Summary • Main components of building a CDN: – – – – Content distribution Request routing Content Delivery Resource accounting • A CDN system requires the four components to work in concert with each other! • Cisco is the only vendor that provide the full solution!