圖片來源：sdncentral.com
What is Carrier network(電信網路)?
在了解SDN與Carrier Network 的關係之前，讓我們先了解一下何謂Carrier Network (電信網路)，參考whatis.com的定義：
A carrier network is the proprietary network infrastructure belonging to a telecommunications service provider such as Verizon, AT&T or Sprint. Telecom carriers are authorized by regulatory agencies to operate telecommunications systems. Carrier networks are made up of large, complex configurations of hardware, interconnected to provide communications services to people spread over large geographic areas.
Specific device types served by a carrier network include
- telephony equipment
- CATV (community access television) receivers
- satellite television receivers
- mobile computing devices
- PCs (personal computers)
- certain specialized items such as medical and surveillance equipment.
由上面的描述我們可以知道電信網路的特色：
- 主要是網路傳輸的骨幹
- 由少數大廠把持(不管是設備規格和協定)
- 更換週期低，投資成本高
SDN in Carrier Networks
參考Broadcom SDN in Carrier Networks 的投影片，在WAN兩個Router的連線，邏輯上是使用IP Network，但是實體上是透過Carrier Networks 通常是光纖網路。
所以目前網路遇到的瓶頸與沒有效率的原因在於IP網路與實體傳輸網路是被分開設計與規劃的，此外實體傳輸網路(電信網路)，都是由特殊的設備廠，與特殊的通訊協定所壟斷。
此外在投影片中也有提到相較起來Package switch 又比 Circuit Switch 還貴 (相較於流量與承載量)，所以把這兩種網路合在一起是趨勢也是共同的目標。
在 Packet and Circuit Network Convergence 這篇文章中也有提：
However, service providers such as AT&T and Verizon are obliged to own and operate two distinct networks for IP and Transport. These networks are typically planned, designed and managed by separate divisions within the same organization, leading to substantial management overhead, functionality/resource duplication, and increased Opex.
在文章中他們認為，唯有從架構上去改變才有可能讓這兩種網路合併，而最後的解法就是SDN
To that end, we propose a converged architecture and control plane based on Software Defined Networking (SDN) and OpenFlow.
新的Unified Architecture of a Converged Packet-Circuit Network
這樣看起來一開始SDN的目標就是一魚多吃，除了把Network Virtualization化，方便搬運與管理，另一方面就是要解決Carrier Network 的問題....
hmm....這訊息量太大了....先記錄下來有機會再來好好研究吧...Orz...
[1] Huawei - Carrier SDN [中文版]
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