NKN is a hierarchical network divided into three basic layers - Core (Level 1), Distribution (Level 2), and Edge (User Level). Depending on the type of connectivity required by the user organization, geographical presence, and the location of Points of Presence (PoP) of NKN, (belonging to Core and Distribution), connectivity would be provided to the institutes. NKN backbone will typically have 18 Core PoPs and around 25 Distribution PoPs across the country.
The NKN design uses a consortium of bandwidth providers for realising NKN since no single vendor has the geographical spread necessary for creating a pan India network and connecting underserved areas. The NKN backbone will be created by multiple bandwidth providers and the edges can be provided by any service provider, if the interface and feature set are in conformance with NKN design.
The Core PoPs will be connected as per the figure 2. Distribution PoPs can connect to different core PoPs using links from different National Long Distance service providers (NLDs), and form the NKN Backbone. Each of the Core PoPs will have last mile from a different NLD. This would ensure high availability at the PoP level. The proposed Core Backbone for NKN is shown in the figure 2. These PoPs shall be interconnected using multiple links from different NLDs to form a Mesh network. Besides, an additional design parameter that is considered is to keep the maximum number of hops between any two PoPs under 4-5.
Over and above, it is also proposed that apart from using λs from existing NLDs, the four legacy Metros, namely, New Delhi, Mumbai, Chennai & Kolkata will also be connected using Dark Optical Fibre. This would further boost the data transfer capacity by several orders of magnitude. Suitable equipments to handle and sustain these speeds would be provisioned at the respective PoPs.
In the next layer or level, Core PoPs will be connecting to distribution PoPs, which are basically in the State Capitals or cosmopolitan cities. Here, the distribution PoPs are also referred as PoP Level 2. The interconnected NKN with CORE and Distribution will logically appear as depicted in the figure below. Each of the distribution PoPs shall be connecting to Core PoPs using preferably more than one links from different NLDs. Each of the Core PoPs shall be providing connectivity to institutes in the respective region or city. Given the high speed nature of the network, NKN design suggests that the last mile connectivity – between NLDs and NKN PoP sites - would also be on a ring for ensuring no single point of failure at each of the PoP. It would be also ensured that there would not be sharing of connectivity media in any form between the different NLDs at each PoP.
From the NKN PoPs, end user institutions are directly connected. These connections are referred to as Edge connectivity or the Last Mile. In large cities it may so happen that NKN will have multiple PoPs. When multiple PoP locations are there in the same city, design should be such that they are economically utilised from the point of view of end users, NLDs, and long distance link investment and management. For example, in a city with Dual PoPs, the interconnection between the NKN PoPs and the end users will be as shown in the figure. In such scenarios, institutes that can demonstrate the need for extremely high availability can be provided with the last mile from different NLDs to the two different NKN PoPs. Institutes in such cities with 1 Gbps bandwidth would be connecting using Optical Fiber Cable (OFC) with in-built protection by the NLD, and the remote end will be terminated on both the NKN PoPs; one of the NKN PoPs will act as the Primary or active link; in case of primary link failure, the secondary NKN PoP would become active. Both the NKN PoPs will also be connected using high capacity protected links. This would also be helpful in making User Site level redundancies in NKN.
The end user institutions connecting to respective PoPs (Core or Distribution) will have the option to operate at speeds from 100 Mbps - 1 Gbps per connection. As far as possible, the last mile connection to the respective institute shall be on a Protected link. In other words, link protection would be built by the NLD itself for the institute. Multiple such links from the institute, with different bandwidths (1 Gbps or 100 Mbps) will also be possible.
While there are multiple ways by which one can achieve connectivity to various organisations/ institutes, NKN design chooses the best in terms of availability, technology, and future proofing. Interesting thing to note here however is that NKN does not stop with mere connectivity! NKN ensures that multiple choices are available to the users for running various services, because, it is the services that are to be run on the network that makes the difference. NKN takes ownership of delivering the packets end to end as per the requirements of the applications.