This topic presents in a very simplified way all the main concepts that should be understood by those who know LTE.
LTE Voice Services
LTE Voice Services enable high-quality voice calls by transmitting voice as data, integrating both voice and internet services into the same network. Traditionally, networks used Circuit-Switched (CS) channels exclusively for voice and Packet-Switched (PS) channels for data. In LTE, voice and data are handled together, with voice treated as data packets over the Packet-Switched (PS) network. This allows for clear, uninterrupted calls and efficient resource use. When LTE-only networks can’t handle voice directly, they use CS Fallback, which temporarily switches to older networks that support CS channels. Additionally, Single Radio Voice Call Continuity (SRVCC) is used when a call started in LTE moves into areas with only 3G or 2G coverage, allowing the call to continue seamlessly on the older network. Together, these features ensure reliable voice service wherever you go.
In LTE, voice services work like a modern city where both calls (voice) and data (internet) share the same roads. In the past, there were separate roads for each: one dedicated to voice calls, called Circuit-Switched (CS), and another for data, called Packet-Switched (PS). In LTE, everything now travels together on the same roads, with calls treated as small data packages. If the LTE city can’t handle a call directly, it uses CS Fallback, like taking an older road outside the city, which supports voice traffic and keeps the call going. And when someone is moving through the LTE city and enters an area with only older network roads, Single Radio Voice Call Continuity (SRVCC) steps in, seamlessly guiding the call from the LTE city roads to the older network roads without any stops or interruptions. Together, these features ensure you can keep talking, no matter where you go.
LTE Voice Services as roads with both cars and buses, symbolizing data and voice services traveling together. Paths lead to the modern LTE city with mixed traffic, while older roads branch off, representing CS Fallback and SRVCC.
Skip to: Roadmap to LTE
- Voice Services Introduction
- CS Fallback (CSFB)
- Voice over IP (VoIP)
- VoIP Protocol Stack
- Header Compression
- Voice over LTE via Generic Access (VoLGA)
- Single Radio Voice Call Continuity (SRVCC)
- Radio Resource Management
- TTI Bundling
- Semi-Persistent Scheduling
Voice Services Introduction
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LTE Voice Services enable high-quality voice communication over LTE networks. Unlike older networks that relied on separate circuits for voice and data, LTE combines everything into a single, efficient data network. This shift allows voice calls to be handled similarly to data, enhancing clarity and connectivity without compromising speed.
Imagine LTE as a busy city with roads that help cars (data) and buses (voice calls) travel smoothly. In this city, Voice Services are like special bus routes made just for voice calls. They make sure people can talk to each other clearly and quickly, just like riding a bus to get somewhere faster than walking.
LTE Voice Services with a clear route for voice calls, represented by special bus routes, showing efficient and clear communication within LTE Voice Services in a city setting.
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LTE Voice Services 
CS Fallback
CS Fallback (Circuit-Switched Fallback) is a solution for LTE networks that don’t fully support native voice services. When a user makes or receives a call, the LTE network temporarily switches to a legacy 3G or 2G network to handle the call. This allows voice calls to work on LTE-capable devices, even if full LTE voice support isn’t available. It is a temporary measure that allows LTE devices to switch back to older 2G or 3G networks for voice calls. This happens when LTE coverage is insufficient, ensuring continuous voice service even when 4G signals are weak.
Sometimes, when the LTE city doesn’t have enough resources to handle voice calls, it calls on an older part of the network, like using a different road outside the city. This is called CS Fallback. It’s like when a bus can’t go on a certain street and has to switch to an older road that’s still open for travel. CS Fallback is like switching to these older roads to make sure you can still reach your friends, even if the trip takes a bit longer.
LTE CS Fallback, showing the LTE city with modern data and voice roads, along with an older road symbolizing the switch to 2G/3G networks for voice calls. The phone has a thought bubble indicating it’s using CS Fallback for a voice call, with both buses (voice) and cars (data) traveling through the city.
- Search Forum LTE CS Fallback (CSFB)
Voice over IP (VoIP)
VoIP, or Voice over IP, is the technology that makes voice calls possible over data networks. In LTE, VoIP is the underlying technology that converts voice into data packets, which are then transmitted over the LTE network. This approach allows for faster, more flexible voice communication and aligns voice services with internet-based data handling. This means using data connections to carry voice signals, resulting in better quality and efficiency.
VoIP is like converting your voice into tiny letters that travel through the city roads as packages, instead of calling over an old-fashioned phone line. These packages carry bits of your conversation across LTE, so you can talk to someone on the other end without any interruption.
VoIP concept within LTE Voice Services, showing the voice converted into data packets moving through the LTE city roads.
- Search Forum VoIP concept within LTE Voice Services
VoIP Protocol Stack
The VoIP Protocol Stack is the layered set of technologies that manage how voice data is prepared, sent, and received in LTE networks. It ensures that voice packets are efficiently routed, reliably delivered, and received in the correct order, supporting clear, stable calls over LTE’s data network. It involves several layers that handle everything from voice encoding to error correction.
The VoIP Protocol Stack is like the instructions on how to deliver those little voice packages in the right order, so they make sense when they reach the listener. It’s like stacking your letters in the correct order and making sure none are lost along the way. This is like a stack of boxes that pack up your voice to send it over the internet. Each box in the stack has a job, like packing, labeling, and making sure it arrives safely at the other end.
LTE Voice Services - VoIP Protocol Stack, showing how each layer organizes, encodes, routes, and delivers voice data efficiently in LTE networks. The concept represents each layer as part of a neatly stacked process, ensuring data reliability and clear communication.
- Search Forum LTE VoIP Protocol Stack
Header Compression
In LTE voice services, header compression reduces the size of data packets by compressing repetitive information at the beginning of each packet. This helps save bandwidth and speeds up transmission, making voice services more efficient and freeing up network resources. It is a technique used to reduce the size of VoIP data packets. By compressing headers, we save bandwidth, making voice transmission more efficient and conserving network resources.
When the voice packages travel in the city, they have “headers” or labels to help identify them, but sometimes these labels are big. Header Compression is like using shorter labels to save space, so more packages can fit on each road. This helps keep traffic moving smoothly. Imagine shrinking all your letters to fit into smaller envelopes. Header Compression is about making our voice messages smaller so they travel faster and use less space on the internet roads.
Header compression in LTE Voice Services, showing data packets with large headers becoming smaller as they move along the city roads, representing how header compression saves space and allows forsmoother traffic flow in the network.
- Search Forum LTEHeader Compression
Voice over LTE via Generic Access (VoLGA)
VoLGA, or Voice over LTE via Generic Access, allows LTE networks to offer traditional voice services over LTE by connecting to existing network infrastructure. This means users can access voice services over LTE even if native VoLTE support isn’t available, bridging the gap in voice compatibility. VoLGA extends LTE’s capabilities by allowing voice services over the LTE network through a generic access method. This means it can support voice calls even in areas where traditional circuit-switched methods aren’t viable.
VoLGA is a bit like using a bridge that lets the LTE city connect to other, older neighborhoods that don’t have modern roads yet. This way, voice calls can work over LTE even if the newer roads aren’t fully built for voice calls, letting the city cover more areas. Like a special pass to use certain roads in our LTE city. VoLGA is like having a VIP pass to make sure our voice calls can go through special lanes, even when regular roads are busy.
Voice over LTE via Generic Access (VoLGA) in an LTE city setting, as a bridge connecting the LTE city to an older network area, symbolizing how VoLGA enables voice calls over LTE even when the LTE network isn’t fully equipped for voice. Cars and special buses (representing data and voice calls) move smoothly across the bridge, with a “VIP pass” sign indicating VoLGA’s special access for voice calls over this connection.
- Search Forum LTE Voice over LTE via Generic Access (VoLGA)
Single Radio Voice Call Continuity (SRVCC)
Single Radio Voice Call Continuity (SRVCC) is a feature that ensures uninterrupted voice calls when moving from an LTE network to a 3G or 2G network. If LTE coverage weakens, SRVCC seamlessly hands the call over to the older network without dropping the connection, providing continuous voice service in areas with mixed coverage. SRVCC ensures seamless transition of voice calls from LTE to older networks like 3G or 2G, without dropping the call. This is crucial for maintaining call quality and continuity as users move between different network types.
SRVCC is like a bus route that seamlessly crosses between the LTE city and other areas. If the bus is in LTE city and it loses signal, it can continue the route without stopping by moving onto an older road. This keeps the call from getting “lost” when coverage changes. Imagine you’re on a call while walking through different parts of the city. SRVCC makes sure your call doesn’t drop when you move from a new LTE road to an older one, like magic!
LTE Voice Services with SRVCC as the smooth transition from LTE to older networks, ensuring continuous call connectivity.
- Search Forum LTE Single Radio Voice Call Continuity (SRVCC)
Radio Resource Management
Radio Resource Management in LTE voice services efficiently allocates network resources to ensure clear, uninterrupted calls. It balances the demand for data and voice traffic, optimizing the way LTE resources are used for both voice calls and other network activities. It manages how radio frequencies and channels are allocated for voice services. It optimizes the use of available spectrum to ensure efficient and high-quality voice calls.
Radio Resource Management is like a traffic control team that makes sure buses and cars have enough room to move without crashing or causing traffic jams. It helps balance the needs of voice and data, so everyone gets where they need to go without delays. Just like traffic lights control cars, Radio Resource Management controls the radio signals in our LTE city. It helps manage who talks when, so everyone can have a clear conversation without traffic jams.
City roads with cars and buses represent data and voice traffic, guided by traffic lights symbolizing LTE signal management, ensuring smooth flow and clear communication.
- Search Forum LTE Radio Resource Management in LTE voice services
TTI Bundling
TTI Bundling is a technique that improves voice quality in weak signal areas by grouping multiple data transmissions together. This redundancy increases the chances that the voice data will be received correctly, making it ideal for maintaining call quality in challenging coverage conditions. TTI Bundling groups multiple Transmission Time Intervals (TTIs) together, improving the reliability of voice transmissions, especially in poor network conditions. This technique helps maintain call quality even when signals are weak.
TTI Bundling is like sending a convoy of buses together on the road, so if one gets stuck or delayed, there are others right behind it. This keeps the voice call steady even in rough traffic conditions, like when the signal is weak. You can also think of TTI Bundling as putting several letters into one envelope. It makes sure your voice messages stay together and get to their destination, even if the roads are a bit bumpy.
TTI Bundling in LTE Voice Services, showing a convoy of buses traveling together along a road with some rough patches, symbolizing grouped data transmissions to maintain stability in weak signal conditions. The buses represent voice packets sent in bulk to ensure reliability, even when the connection is challenging. This analogy helps to convey how TTI Bundling works to keep voice quality steady.
- Search Forum LTE TTI Bundling
Semi-Persistent Scheduling
Semi-Persistent Scheduling (SPS) is used in LTE voice services to allocate network resources more efficiently by keeping a reserved data channel for recurring activities like voice, reducing the need for frequent scheduling requests. This approach helps save battery life and network resources while supporting stable, continuous voice communication. It also minimizes delays and ensures smoother, more consistent voice call quality.
Semi-Persistent Scheduling is like giving a bus its own dedicated lane that stays open every time it needs to pass. This makes sure the bus can keep moving without waiting, so the voice call remains smooth and doesn’t have to keep “restarting” its path through the city. Like having a reserved lane on the road just for you. SPS makes sure your voice has a special path to travel on, reducing traffic delays and making your calls smooth and steady.
Semi-Persistent Scheduling (SPS) in LTE Voice Services, as a bus on a dedicated lane to illustrate the reserved data channel for smooth voice transmission, along with cell towers indicating LTE connectivity.
- Search Forum LTE Semi-Persistent Scheduling (SPS)
That’s it. 
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