Blocked Call Vs Dropped Call

A Blocked Call and a Dropped Call are two very common terms used in telecommunications (Cellular Communications) world these days. These two are completely different phenomena, but the impact they create on a customer is the same, annoyance. In this post I am going to discuss what the differences between these two events are, and briefly explain how they can be handled by the mobile service provider.

Blocked Call:

A Blocked Call is an event that can occur only before the call is completed between the called and the calling parties. Completion of the call here implies the connection being complete for either party to exchange talks. Any call you place on a cellular network, the service provider has to find all the resources necessary to connect the call between the two parties. As I mentioned in my previous post about a wireless call, it is not wireless in entirety and it has to access the wire-line network in order to reach the destination cell phone. In case of a long distance call, a service provider should make sure that there is sufficient network capacity all through the intermediate network hops to carry the call from one end to the other.

If there is not sufficient capacity to carry the call through, this results in a blocked call. When you are in a stadium watching a Baseball match or a Cricket match, when you attempt to make a call, you might hear a voice recording saying “the network is currently busy please try after sometime” or the call may just give three beeps and not connect. This is mainly because of insufficient bandwidth availability (Wireless Channels or the Wire-Line Channels) compared to the number of people attempting to access the network. In one of my posts about Why Sprint Nextel has more dropped calls than AT&T and Verizon? I mentioned that Sprint has an advantage of selecting the higher frequency range of (1900 MHz). If Sprint can tackle the dropped calls issue by installing more cell sites to cover the same area as that of its competitors, this automatically provides higher number of wireless channels in the same geographical area thereby reducing the chances of blocked calls. It still has to build the backbone wire-line network to support the calls but for now let us assume that this matter has been taken care. As the customer base keeps increasing in a geographic area, AT&T and Verizon have to eventually invest to tackle the increasing capacity requests from the customers. But Sprint, already has the wireless network to handle increasing capacity which is definitely an advantage but this is not a great situation to be in. Gradual investment as the customer base grows is always a better situation to be in than investing heavily at once expecting the customer base to rise. So this is a catch 22 situation where the decision has to be made by the service provider depending on the traffic analysis and customer growth analysis made over the years.

This is where traffic management comes into picture. A traffic management team makes sure that the network is always ready to handle the calls at any moment of time including the busiest hour of the day. During events like American Idol or on auspicious days like Christmas Day, Mother’s Day, Father’s Day or New Years Day, the network has to be ready to handle the avalanche of calls that can hit the network. Even in events like the baseball matches, the service provider takes necessary actions to provide more wireless channels by process called Cell Sectoring or another process of turning on smaller and more cellular base station towers to cover the same area.

To summarize things, a Blocked Call is something which occurs before the connection is complete between the called party and the calling party. This phenomenon depends on the entire network, the wireless channels on the calling end, the wire-line backbone network, the wireless channels on the destination end.

Dropped Call:

This is an event that can occur only after the call is connected and the exchange of talks has started. This implies that the network has the capacity to handle this call and the resources necessary for the call have already been allocated to the call. In my previous post I mentioned about the various factors that influence and contribute towards dropping of a call. The dropped call is a result of improper R.F. planning or some of the natural phenomena that cellular signals undergo while travelling in the environment surrounding us. Even as the mobile moves from one coverage area to another coverage area, there might be a dead zone resulting in a dropped call. The co-channel interference also can influence a dropped call but this is more evident in GSM network than CDMA network. A blocked call only depends on the wireless part of the network, i.e. the wireless signal power on the calling side and the wireless signal power on the receiving side.

I tried to explain the difference between a Blocked Call and Dropped Call in simple terms and there might be something that you can add to understand the process better. Please add any comments or suggestions on the blog.

Thank you very much for reading the blog.

Sincerely,

Krishna Chaitanya Emani.

Wireless Communications: Is it Entirely Wireless?

Hello all,

The topic of this blog might be slightly confusing for people who are not familiar with the wireless communications and cellular communications. When you call a technology wireless communications, why should there be a question if it is really wireless? With little over and year experience in the wireless industry, I thought of sharing the knowledge that I gained during this experience.

When you make a call from your mobile phone to any other mobile phone in the same area, how do you think the call is connected? The simplest answer one can give is to say that the call goes from my mobile to the destination mobile and the call is completed. But what actually happens in between the mobile phones is a mystery to many people. Let me give a description of what actually happens when you call someone from your mobile phone. Before going to the details of the call flow, let me discuss few of the very terms used in mobile communications.

Base Station: A base station is a wireless receiver installed by the wireless service provider, which receives signals from various mobile devices in a pre-defined geographic area and processes them to complete the call.

Base Station Controller (BSC): A Base Station Controller coupled with the base station make a Base Station Subsystem. Number of base stations are connected to a base station controller which connects the calls to the Mobile Switching Center (MSC) which is described next.

Mobile Switching Center (MSC): This is more intelligent than the Base Station Controller and has far more responsibilities than the BSC. This is like the Switch used in the old telephone systems, which connect the calls between originating and destination telephones.

When you make a call from your mobile phone, the call goes to the local Base Station which is responsible for the calls in your geographic area. Then the call is sent to the BSC and then handed over to the MSC through a wire-line connection made between the Base Station and the BSC and then from the BSC to the MSC. A single MSC has many Base Stations Controllers connected to it and each MSC maintains a register of all the mobile users under each and every Base Station. When the call reaches the MSC, it checks for the location of the destination mobile phone number and transfers the call to the destination Base Station again on a wire-line connection. Then the call is handed off to the destination mobile phone over a wireless channel.

This is a simple case where the call is between two mobile phones belonging to the same Mobile Switching Center (MSC). Even in such a simple case, it is pretty clear that a wireless to wireless or a mobile to mobile call is not wireless in entirety. It is wireless only from our mobile phones to the closest Base Station and then goes a really strong wire-line network built by the mobile service providers. In a more complex case where the call has to travel longer distances, or has to jump from one MSC to another, it is still wireless only from the mobile to the base station and then it traverses the wire-line network over longer distances built between MSC. I will discuss about the various call flows later in my blog taking one scenario at a time.

Please let me know if you have any questions about the explanation I have given in the following blog.

Thanks,
Krishna C. Emani