Network Functions Virtualization(NFV) - Part 1

Network Virtualization is getting popular these days and is very trending technology in network space. Before getting into the concept of NFV, let me say something about hypervisors which play an important role in NFV.

What are these hypervisors ?

Hypervisor is a computer software or firmware on which several virtual machines are run.

Hypervisors create an environment for guest operating systems and make them believe that the hardware resources is dedicated to them.  But in reality there will be only one set of hardware resources and all the guest operating systems (so called virtual machines) will be sharing that hardware with the help of hypervisors.

History :

The term hypervisor was first coined by IBM way long back in 1956.IBM wanted to run an additional operating system on Mainframe computers and there were some limitations with the supervisor code to run multiple instances of the operating system. IBM tackled the problem by adding another layer in the architecture on top of supervisor and that became Hypervisor.

The hypervisor installed on the server hardware(host) controls the guest operating system running on the host machine. Its main job is to cater to the needs of the guest operating system with respect to hardware resources, and effectively manage them so that the instances of multiple operating systems do not interrupt one another.

There are 2 types of Hypervisors:-

Type 1 Hypervisor which directly run on the system hardware. This type of hypervisor is also called as bar metal hypervisor.

Type 2 Hypervisor: This runs on operating system of the host. Above Hypervisor the guest operating system will run.

GPON

What is GPON ?
GPON is an optical network technology used to realise FTTH concept.
Before going to GPON, let me quickly brief about FTTH.

What is FTTH?
FTTH (Fibre to the Home) is a way of delivering the communication signal over optical fibre from operators switching equipment to customer premises (home or business office). In the past this was done with the help of copper infrastructure like Coaxial or twisted pair cables. FTTH replaces the conventional copper to Fibre.
FTTH offers all the services like Voice, Video (Cable TV), High speed Internet from single CPE device.
GPON is a very popular technology used across the world, to realize FTTH solutions.


So What GPON is all about?
GPON stands for Gigabit Passive Optical Network.
ITU-T G.984 defines the standards for GPON

GPON is a successor of ATM based Passive Optical Network (APON) and Broadband based passive optical Network (BPON) which offered 622Mbps of downstream bandwidth and 155Mbps upstream bandwidth.

GPON provides much higher bandwidth compare to its predecessors i.e. 2.448 Gbps downstream bandwidth and 1.244 Gbps upstream bandwidth.

Where GPON is used?
It is used in the access network.


Elements of GPON Network.
GPON Network consists of an central office node OLT (Optical Line Terminal), ONT (Optical Network Terminal) present at customer premises, and a splitter between OLT & ONT

OLT acts as an interface between Service provider network and Customer Equipment.

GPON architecture eliminates the need of active elements between OLT and ONT thereby greatly reducing the cost and making it easier to maintain.

Features of GPON
A single optical fibre can carry multiple customer traffic from OLT to ONT in a TDM fashion.

GPON protocol permits a splitting of large customers split ratios up to 1:128. However, in practice the PONs are deployed with 1:32 split ratio. i.e. 32 customers' traffic is carried in a single fibre.

Both downstream and upstream traffics are carried in same fibre on 2 wavelengths i.e. 1490 nm for downstream traffic and 1310nm for upstream traffic.

The Maximum between OLT and ONT is 60 km


Why GPON is a passive network technology?
Before getting into this, let us know the concept of passive and active network.

Active networks consist of elements that require electrical power for working. Some of the active network elements are switch, router, multiplexers, etc. The customer traffic is managed and directed to the specific destination with the help of these active network elements.

In case of Passive Networks, passive elements like optical splitters are used to separate the customer traffic.

Since GPON uses optical splitters which is a passive element, the technology is called Passive optical Networks.

What is the advantage?
GPON offers low cost solution for high data rate customer application with minimal maintenance.
Quick Snapshot

GPON -                          Gigabit Passive Optical Network
ITU -T Standard -           G.984
Predecessor -                 APON ( ATM based Passive Optical Network) / BPON(Broadband                                          based Passive Optical Network) with 622Mbps of downstream 

                                     and 155Mbps of upstream bandwidth. 

GPON bandwidth -          2.448Gps downstream 

                                     1.244Gbps Upstream
Advancement in GPON-   XGPON( ITU-T G.987) / 10Gbps downstream & 2.5Gbps Upstream                                       WDM PON