Saturday, June 25, 2011

Internship @ A Service Provider

The summer of 2011 was getting stressful than the last semester. As usual, i had a BIG to-do list. One of the task was sorta necessary and i was looking forward to it i.e. a 21 day internship, to be done as a part of our Bachelor of Engineering's course in Computer Science.
This year, BSNL a.k.a. Bharat Sanchar Nigam Limited (India's Largest Internet Service Provider) was hosting training for 2/3 year engineering students of Electronics/Electrical/Computer Science students. The RTTC (Regional Telecom Training Center) which is only one for a particular state was nearby my home. I initially joined their 4 weeks programme.

The RTTC is quite big, consisting of 3 floors, equipped with large lecture halls, conference rooms, seminar halls, a library, communication labs along with a separate MSC (Mobile Switching Center) and offices of the instructors (or rather employees of BSNL)

The first day, our mentor (more of a batch in-charge) T. D. Mishra, introduced himself and other senior employees present there. He handed over our schedule to us along with the timings. The four weeks were divided into separate units that include sessions, labs as well as visits to telephone exchanges. The lectures started with the overview of telecom networks and job opportunities for engineering students in the field of telecommunication. In the first week, we covered The PCM Principle along with Digital Switching. These topics demonstrate how every bit of your voice that u speak in your telephone reaches from point A to point B within no time via a huge network starting from the local loop(the line from your home which connects to the service provider's nearest exchange) to the ISP's switching modules, trunk lines (hopping from one exchange to the other) via copper or optical fibers to the correct exchange which further routes the signal to the nearest exchange the called person is connected to and finally transmitting it via another local loop to the correct telephone which decodes the signal back to comprehensible voice that the other person is able to hear and respond to in a similar manner.

Fun Fact: A mobile number generally is over 100 digits long! This includes all codes and identification numbers that can be used to pin-point a particular SIM card uniquely in the entire world. But when limited to within a country and considering the large amount of Service providers present, subscribers need to only remember 10 digits.

The second week was fun, conceptually as well as physically. We had a fiber optic systems session, coupled with SDH and DWDM concepts. Then two labs relating to fiber optics, where we understood how practically SDH systems are laid out in a large service provider's network, how they actually work and in what manner are they easy to troubleshoot.

Fun fact: A single optical fiber can be used to such an extent that it can facilitate simultaneous 1,25,000 calls via wavelength windows and loads of multiplexing. This is the reason why tariffs exist that reduce calls costs to only a few cents per minute.

Following this, the most interesting lab was where we got to join two optical fibers by fusion spilicing. The week ended with our first exchange visit where we got to enter all the rooms that stated "No Entry" or "Not Allowed" :-) including the MDF (Main Distribution Frame) Room, Switching and Power/Backup rooms.

Side View of MDF room (Click to view Full size image)
The third week seemed small to me, but it had great sessions, especially the GSM and CDMA parts as well as the visit to the Mobile Switching Center. I could not manage to get pictures of the inside of the MSC, but it was fascinating how it served millions of subscribers simultaneously.

Fun Fact: GSM is the most widely used mobile communication standard, because of which it is termed as "Global Systems for Mobile Communications"

(Click to view full size image)
Fig: A section of the MDF installed in an exchange. The mesh of wires terminating into vertical white boxes(called as modules) interconnect the subscriber's landline to the exchange's switching system
The final week was the best of them all as it included the concept of Intelligent Networks (seriously, that was a wow!), how SSP's, SCP's and SMP's work together in a secure manner to provide amazing services throughout the country. The last visit was to the biggest exchange in the city. Except for WiMAX, every other technology was implemented, including the 16Mbps-100Mbps fiber lines that provided high end connectivity to subscribers (IIRC it was implemented by using a HUAWEI box). Further, the exchange had separate 2G (more in number) and 3G racks (comparatively less in number) which were mostly implemented by Ericsson. The CDMA division was implemented by ZTE's BTS's (Base Trans-Receive Station, what is referred to as a "mobile tower" by the general public) and a software named Netnumen provided all possible controls for both physical and radio configurations. Amongst all these, the MSC's HLR's and VLR's were held in their own server racks (MSC is a collective term consisting of all mobile related registers). HLR or the "Home Location Register" (is populated with cell phone numbers local to a resident area) and VLR or the "Visitor Location Register" (temporary register, which is populated by roaming cellphone numbers) is an integral part of every MSC. By registers i mean to imply databases with focus on regular backups.

Fun Fact: BSNL's NIB (National Internet Backbone) consists of five Cisco 12416 routers interconnected in a mesh, each costing nearly 1 million dollars (~5 Crores INR)

The meaning of internship is not limited to going to a company and performing a task for a specified period of time, rather it involves regular learning, hands on experience along with the huge amount of life lessons that u get in a very short period of time. Special thanks to Mr. T.D. Mishra for sticking by me and answering even the most stupid question i had. After the completion of my training, everytime i move around and see cellphone towers(technically called as BTS's) it reminds me of my days at BSNL.

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