How Telcos Mobile Network Work ?


Hello everyone! This is your hungry sysadmin, and today we're on a journey into the fascinating world of Telco's in Nepal. Buckle up, because we're diving deep into the technical tapestry that connects us all, orchestrated by the telecom giants - NTC (Nepal Telecom) and NCELL. Mobile networks have become an integral part of our daily lives, enabling us to connect, communicate, and access information on the go. Behind the scenes, a complex interplay of technologies, protocols, and physical infrastructure ensures the seamless functioning of various services such as mobile data, phone calls, SMS, international connectivity, and on-net/off-net scenarios. In this detailed blog, we will unravel the functions of each component, delving into the technologies that power our mobile experiences.

IMG Reference:

User Authentication and Registration:

At the heart of every mobile network is the process of user authentication and registration. The Subscriber Identity Module (SIM) card, a small but powerful chip embedded in our mobile devices, holds the key to securing our identity on the network. This authentication process involves cryptographic algorithms such as A3 and A8, ensuring that only authorized users gain access.

Behind the scenes, the Mobile Switching Center (MSC), the Authentication Center (AuC), and the Home Location Register (HLR) collaborate to verify user credentials. SS7, a sophisticated signaling protocol, facilitates the exchange of messages during the registration process, allowing the network to keep track of the user's location through the Visitor Location Register (VLR).

Mobile Data Usage:

When we engage with mobile data services, a cascade of technologies and components comes into play. Our mobile devices communicate with the nearest cell tower, initiating a data transmission journey through the Radio Access Network (RAN) and eventually reaching the Packet Data Serving Node (PDSN) in the core network.

Advanced technologies such as LTE and 5G NR govern this process, employing Orthogonal Frequency Division Multiple Access (OFDMA) and Single Carrier Frequency Division Multiple Access (SC-FDMA) for efficient downlink and uplink data transmission. These protocols, combined with the ubiquitous TCP/IP suite, form the backbone of the internet connectivity that empowers our mobile data experience.

Making a Phone Call:

Initiating and receiving phone calls involve a symphony of components within the mobile network. The call setup process is orchestrated by the Mobile Switching Center (MSC), which manages call routing, setup, and potential handovers. Voice data, encoded into packets, travels through the Radio Access Network (RAN), ensuring a continuous and high-quality conversation.

Different generations of mobile network technologies, from GSM and CDMA to LTE and 5G NR, contribute to the evolution of voice communication. Real-time Transport Protocol (RTP) steps in to facilitate the smooth transportation of audio data, while the choice between circuit-switching (2G, 3G) and packet-switching (4G, 5G) technologies shapes the dynamics of the voice call.

SMS (Short Message Service):

The simplicity of Short Message Service (SMS) belies the sophisticated mechanisms involved in its delivery. From our mobile devices, SMS messages embark on a journey facilitated by the Short Message Service Center (SMSC), which stores and forwards these messages. The Home Location Register (HLR) plays a crucial role in managing user profiles and SMS-related information.

Underneath the surface, protocols such as Short Message Peer-to-Peer (SMPP) and Mobile Application Part (MAP) ensure the seamless exchange and delivery of SMS messages. This store-and-forward mechanism allows for asynchronous communication, contributing to the ubiquity and reliability of text messaging.

International Calls:

Breaking through borders, international calls introduce a layer of complexity to the mobile network architecture. The Mobile Switching Center (MSC) navigates the call through international gateways, connecting domestic networks to their global counterparts. Undersea cables or satellite links form the physical infrastructure for international data transmission, highlighting the importance of global connectivity.

Protocols like ISDN User Part (ISUP) and Session Initiation Protocol (SIP) come into play during international calls, managing call setup, teardown, and signaling across different network domains. The advent of Voice over Internet Protocol (VoIP) further transforms the landscape, leveraging the internet for international voice communication.

On-Net and Off-Net Calls:

The distinction between on-net and off-net calls defines the scope of communication within and between different mobile networks. Internal gateways facilitate on-net communication, often characterized by lower costs and superior quality. In contrast, off-net calls traverse interconnection points, bringing together the intricate interplay of diverse networks.

Session Initiation Protocol (SIP) emerges as a common thread, powering both Voice over Internet Protocol (VoIP) communication and traditional circuit-switched calls. Interconnection agreements, defining the terms of engagement between networks, underscore the collaborative nature of the telecommunications industry.

Call Termination and SMS Delivery:

As a phone call concludes or an SMS reaches its destination, the Mobile Switching Center (MSC) and Short Message Service Center (SMSC) orchestrate the final acts of these communication processes. Call termination involves the release of resources, updating location information in the Visitor Location Register (VLR), and signaling the end of the call. Meanwhile, SMS delivery culminates in the successful forwarding of the message to the recipient's device.

Protocols like ISDN User Part (ISUP) govern the teardown of calls, ensuring the efficient release of resources within the network. Short Message Peer-to-Peer (SMPP) continues to play a pivotal role in SMS delivery, contributing to the reliability of this ubiquitous messaging service.

Billing and Records:

Behind the scenes, billing systems and call detail records (CDRs) meticulously record every interaction within the mobile network. Billing systems collect usage data from various network elements, while CDRs store information about calls, data usage, and SMS. The Authentication, Authorization, and Accounting (AAA) servers authenticate users and track their usage patterns for billing purposes.

Protocols such as RADIUS (Remote Authentication Dial-In User Service) and Diameter Protocol form the backbone of these billing and accounting processes. They ensure that users are accurately billed based on their subscription plans and usage patterns, contributing to the financial sustainability of the mobile network infrastructure.

Fallback and Handovers:

In the dynamic world of mobile communication, fallback mechanisms and handovers ensure uninterrupted service, even in the face of network challenges. Fallback mechanisms involve the adjustment of network parameters, such as reducing data speed or changing modulation schemes, to adapt to degraded conditions. Handovers, managed by network elements like the eNodeB in LTE or gNodeB in 5G, facilitate seamless connectivity as users move within the network.

Protocols like X2 and S1 Handover Procedures in LTE and 5G NR define the intricate processes of handing over a user's connection from one cell to another. In legacy technologies, Handover (HO) signaling protocols manage the transition between different cell towers, ensuring a smooth and continuous user experience.

Physical Infrastructure and Wireless Communication Components:

The physical infrastructure of a mobile network forms the bedrock upon which the wireless communication ecosystem is built. Cell towers, equipped with antennas, transceivers, and baseband processing units, create the radio coverage that blankets geographic areas. Backhaul networks, comprising fiber optic cables, microwave links, or satellite connections, provide the backbone for data transmission between cell towers and the core network.

Core network elements, including the Mobile Switching Center (MSC), Home Location Register (HLR), Visitor Location Register (VLR), Short Message Service Center (SMSC), and international gateways, serve as the nerve center of the mobile network. These elements manage the intricacies of call routing, user authentication, and the delivery of various services.

Wireless components, from the cellular modems embedded in mobile devices to the Subscriber Identity Module (SIM) cards that store user-specific information, play a pivotal role in facilitating wireless communication. The Radio Access Network (RAN), responsible for managing radio communication between mobile devices and the core network, ensures the seamless flow of data and voice across the network.

Base Transceiver Stations (BTS):

At the core of wireless connectivity stand Base Transceiver Stations (BTS). Positioned strategically across Nepal, these towers interface mobile devices with the telecom network, utilizing GSM, CDMA, and LTE technologies to transmit and receive signals. Their role is pivotal in ensuring seamless connectivity across diverse terrains, from urban centers to remote mountainous regions.

Mobile Switching Center (MSC):

The central intelligence of the telecom network, the Mobile Switching Center (MSC), orchestrates call routing, signaling, and network functionality. When a call is initiated, the MSC undergoes a complex process. It authenticates users through the Home Location Register (HLR) and Visitor Location Register (VLR), determining routing based on whether the call is on-net or off-net. The evolution to packet-switched networks, epitomized by technologies like VoLTE, is facilitated by the MSC's intricate coordination.

Satellite Communication:

In the majestic landscapes of Nepal, where mountains might play hide and seek with signals, satellite communication takes the stage. Earth stations establish a celestial link with communication satellites, extending connectivity to even the most remote areas. It's a dance involving modulation schemes, error correction algorithms, and satellite footprints, ensuring that every corner of the country stays connected.

Routing and Switching Mechanisms:

Let's understand the magic behind on-net and off-net calls. Imagine an on-net call within the same provider, say from one NTC subscriber to another. The MSC efficiently manages signaling and voice data, ensuring a smooth connection. Now, an off-net call, where an NTC user dials an NCELL subscriber, involves an intricate exchange of signals at interconnection points. It's like a relay race with signaling protocols such as SS7 guiding the call through different provider landscapes.


Our phone call wouldn't be complete without meeting the Home Location Registery (HLR) and Visitor Location Registery (VLR). These databases store subscriber information and play a crucial role in call authentication and routing.

HLR: A centralized repository storing subscriber profiles and subscription details. It uses MAP (Mobile Application Part) protocol, which ensures secure and reliable communication between the MSC and HLR.

VLR: A temporary database in the MSC containing information about subscribers currently within its coverage area. MAP is also employed for communication between the MSC and VLR, facilitating seamless subscriber authentication and call routing.


In conclusion, the world of mobile networks is a fascinating tapestry of technologies, protocols, and infrastructure that work in harmony to deliver the communication services we often take for granted. From the intricate dance of user authentication and registration to the dynamic handovers and fallback mechanisms that sustain connectivity, every component has a crucial role to play.

As we continue to witness the evolution of mobile technologies, from the early days of GSM to the advent of 5G, the landscape of mobile communication undergoes constant transformation. This comprehensive exploration serves as a guide to understanding the underlying complexities, demystifying the magic that happens behind the scenes every time we make a call, send a text, or access the internet on our mobile devices. The mobile network, a technological marvel in its own right, weaves together the threads of connectivity that have become an indispensable part of our modern lives.

Bonus Content

Example Scenario: Making a Call from NTC to NCELL

1. Initiating the Call:

You, the caller, decide to make a call from your NTC (Nepal Telecom) number to a friend using NCELL's network.

2. Base Transceiver Station (BTS):

Your call journey begins at the Base Transceiver Station (BTS) closest to you. This tower picks up your signal and prepares to transmit it to the network.

3. Mobile Switching Center (MSC) - NTC's Side:

The BTS hands over your call to the Mobile Switching Center (MSC) within NTC's infrastructure. The MSC authenticates your call by communicating with the Home Location Register (HLR), where your subscriber information is stored.

4. Interconnection Point:

Since your call is heading to a different network (NCELL), it reaches an interconnection point where NTC's and NCELL's networks meet.

5. Signaling and SS7 Protocol:

At this point, signaling protocols, such as Signaling System 7 (SS7), come into play. SS7 is the backbone of telecommunication signaling, and it facilitates the exchange of information between networks. The interconnection points use SS7 to communicate and decide how to route your call across networks.

6. Visitor Location Register (VLR) - NTC's Side:

NTC's MSC communicates with the Visitor Location Register (VLR) to get information about the recipient's current location and subscription details.

7. Routing to NCELL's MSC:

Based on the SS7 signaling exchange, your call is routed to NCELL's MSC. This might involve additional hops through various network elements, including Gateway MSCs and international gateways if applicable.

8. Visitor Location Register (VLR) - NCELL's Side:

NCELL's MSC contacts its Visitor Location Register (VLR) to authenticate the recipient and determine their current location.

9. Routing to the Recipient:

Once authenticated, the call is further routed within NCELL's network, heading toward the nearest Base Transceiver Station.

10. Recipient's Device Rings:

The recipient's device, connected to NCELL's network, receives the call, and your friend's phone starts ringing.

11. Voice Data Transmission:

If your friend answers, the voice data is transmitted between the devices using protocols like Real-Time Transport Protocol (RTP) to ensure a smooth conversation.

12. Call Termination:

After the call ends, signaling is exchanged again between the networks, ensuring proper termination of the call session.

Lastly, Thank you readers, I love you dherai dherai. Stay tuned for more interesting blogs...

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