读书笔记： 《Content Networking Fundamentals》

在生活的各个方面，需求导致新的创造和发明，网络计算也是一样，它的发展伴随着不断增长的用户需求：更加丰富的内容，更多的带宽，更多的可靠性。要完成这些要求，首先你必须解决以下四个方面：

Scalability and Availability

Bandwidth and Response Times

Customization and Prioritization

Security, Auditing, and Monitoring

Scalability and Availability

Scaling the Application

content networking 可以为应用提供未来增长的可扩展空间，而不需要改变应用工作的方式，只需要微小的改变网络架构。包括以下的服务：

• Content edge delivery Positioning application content away from the origin server, and in closer proximity to clients, scales the application by offloading requests to the content network. 将内容放在更加接近用户的地方。

• Enhanced content delivery with IP multicast, stream-splitting, and resource reservation IP multicast and stream-splitting scales the network by avoiding replication of identical flows over the same network link, thus minimizing end-to-end bandwidth consumption of content delivered to a large number of users. Resource reservation scales the application by manipulating network parameters to expedite application traffic delivery.通过组播和流分割技术，避免通过同样的网络连接（？)复制同样的内容，这样最小化了大量用户的端到端的带宽消耗。资源预留可以加快应用的通信传输。

• Content transformation and prioritization Transformation provides conversion of content within the network without further burdening of origin servers. Prioritization enables custom network delivery of application traffic.

• Flash crowd protection Protection against sudden, but valid, traffic spikes directed toward an application is important to maintaining service levels to customers. 需要在突发的大流量下维持服务水平。

Increasing Application Availability

包括以下部分：

• Content switching Increases availability by replicating origin server content across numerous identical systems, either within the same data center or across globally distributed data centers. 在多个相同系统复制原始服务器的内容，他们可以在同一个数据中心或者是跨全球的数据中心

• Session redundancy Session redundancy provides failover from one network device, such as a firewall or load balancer, to an identical device without dropping existing TCP connections. 在网络设备(firewall or LB)失效切换的时候不丢失已有的tcp连接。

• Router redundancy Protocols, such as Hot Standby Router Protocol (HSRP) and Virtual Router Redundancy Protocol (VRRP), provide router gateway redundancy by having two routers or load balancers share a virtual IP (VIP) and MAC address for clients to use as their default gateway. If either fails, the other will take over within seconds.

• IP routing redundancy Dynamic IP routing protocols, such as OSPF, EIGRP, and IS-IS, provide availability within a routing domain by maintaining multiple paths to each network in the routing table.

• Layer 2 switching redundancy Spanning tree and Cisco Etherchannel provides Layer 2 redundancy in a switched environment.

读书笔记： 《Content Networking Fundamentals》

从下面的内容里面，我感觉Content Networking总的概念就是，对于传统的基于包交换的网络，传输层是完全内容无关的，内容的感知是内容产生者的责任，Content Networking 就是对于整个网络层次，都是内容感知（content-awareness）的。

内容网络涵盖了网络处理各方面的元素，从下面的图片，我们可以看到3个层次：

Originator：内容生产者（or an origin server）为clients请求提供内容, 内容可以是live video, 文件下载传输还有动态的静态的数据，交互式多媒体内容。应用包括e-learning, corporate communications, e-commerce, hosting services, and enterprise client/server applications, among many others.

Network infrastructure：这层分发content, 包括一些协议和概念，such as TCP/IP and Ethernet, plus the content networking services and intelligent network services discussed in this book.

Recipient：请求content的client，可以是PC桌面软件不如浏览器，视频播放器等，也可以是TV/PDA/IP Phone等。

图片：Relationship Between Recipient, Network, and Originator Content Network Entities

传统的网络是基于包交换的，Originator 和 Recipient 之间互相所知的很少，除了一些name service等信息。基本上，过去的网络设备都是和应用无关的，最近几年，认识到网络增值应用中新的和日益增加的需求，不断加入新的网络软件来实现内容网络技术。满满的，现有的网络设备不断的扩展性的应用协议和智能网应用服务。也产生了新的基于内容的设备。

内容的网络化，可以大致的定义为不仅仅是内容的Originator是内容感知（content-awareness）的，而是网络的3个层面都是内容感知的。其实一般来说，Content Networking是一个有些模糊的概念。