SDN 程式語言 p4（SDN programming language P4）
行業趨勢，SND是未來. P4 是未來。
SDN is inevitably， and P4 is inevitably。
P4 = Programming Protocol-Independent Packet Processors
Cisco 感到壓力了。
OpFlex: An Open Policy Protocol White Paper
Cisco reveals OpenFlow SDN Killer
官網（org）：
p4 paper：
http://arxiv.org/pdf/1312.1719.pdf
ABSTRACT(摘要)
P4 is a high-level language for programming protocol-independent packet processors.
P4 屬於高階語言， 用來對 協議無關的網路包處理器 程式設計。
P4 works in conjunction with SDN control protocols like OpenFlow.
P4 用於SDN控制協議（如OpenFlow）
In its current form, OpenFlow explicitly specifies protocol headers on which it operates.
在目前格式，OpenFlow 明確指定了其要操作的協議頭。
This set has grown from 12 to 41 fields in a few years, increasing the complexity of the specification while still not providing the flexibility to add new headers.
隨著規範的複雜性的提高， 這個 set(語法集？) 已經從12個域增加到41個域， 但是仍然不能提供 靈活的增加新頭部。
In this paper we propose P4 as a strawman proposal for how OpenFlow should evolve in the future.
在這個論文中，我們建議P4作為一個稻草人提議，用來促進OpenFlow的進化。
We have three goals:
有3個目標
(1)Reconfigurability in the field（域可重構性）:
Programmers should be able to change the way switches process packets once they are deployed.
一旦部署，程式設計師能夠改變交換機處理包的方式。
(2) Protocol independence（協議無關）:
Switches should not be tied to any specific network protocols.
交換機不應該繫結任何網路協議。
(3) Target independence（目標無關）:
Programmers should be able to describe packet processing functionality independently of the specifics of the underlying hardware.
程式設計師能夠描述 與底層硬體規範無關的 包處理功能，
As an example, we describe how to use P4 to configure a switch to add a new hierarchical label.
例子 描述 P4 怎麼配置 交換機 增加一個新的分層標籤。