QOS in LTE & Troubleshooting Issue

Quality of Service (QoS) Parameters in LTE

Quality of Service (QoS) ensures that different types of traffic (e.g., voice, video, web browsing) get the appropriate priority and network resources. In LTE, QoS is controlled using various parameters. Let's go through them one by one with examples and troubleshooting scenarios.

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1️⃣ QCI (QoS Class Identifier)

📌 Definition:

• QCI is a numeric identifier (1 to 9) that defines the priority, delay, and packet loss characteristics for a data flow.
• Each QCI value corresponds to a specific service type (e.g., VoLTE, video streaming).

✅ Example of QCI:

QCI	Priority	Delay (ms)	Packet Loss	Service Type
1	High	100	10^-2	VoLTE (Real-time voice)
5	Medium	300	10^-6	IMS Signaling
9	Low	No guarantee	No guarantee	Best Effort (Web Browsing, Email)

📌 Troubleshooting Issue:

• If VoLTE calls are dropping, check whether QCI 1 is properly configured in the network.
• If video streaming is buffering, check whether the correct QCI (6 or 8) is assigned to the data session.

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2️⃣ ARP (Allocation and Retention Priority)

📌 Definition:

• ARP defines whether a bearer should be established (Allocation) and maintained (Retention) during network congestion.
• A higher ARP value (e.g., 1) means higher priority to get resources in congested conditions.

✅ Example of ARP:

ARP Value	Priority	Example Use Case
1	Highest	Emergency services, Police communication
5	Medium	Business-critical applications (VoLTE, Video Calls)
15	Lowest	Best effort internet browsing

📌 Troubleshooting Issue:

• If emergency calls are failing, check if ARP 1 is assigned to emergency bearers.
• If VoLTE calls are not getting priority, verify that ARP for VoLTE is higher than best-effort data (ARP 5 vs. ARP 15).

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3️⃣ GBR (Guaranteed Bit Rate)

📌 Definition:

• GBR defines a minimum guaranteed bandwidth for a bearer, ensuring that the service always gets a dedicated share of network resources.
• Used for real-time services like VoLTE, video calls, and gaming.

✅ Example of GBR:

Service	GBR (Mbps)
VoLTE	0.1
Video Call	1.5

📌 Troubleshooting Issue:

• If VoLTE calls are experiencing poor quality, check if GBR is correctly set (e.g., 0.1 Mbps for VoLTE).
• If video calls are lagging, verify that GBR is allocated in the network (e.g., 1.5 Mbps for video calls).

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4️⃣ NON-GBR (Non-Guaranteed Bit Rate)

📌 Definition:

• Non-GBR does not guarantee a minimum bandwidth. It allows best-effort traffic based on network availability.
• Used for web browsing, file downloads, background applications.

✅ Example of Non-GBR:

Service	GBR Required?	Traffic Type
Web Browsing	❌ No	Best Effort
Email	❌ No	Best Effort
YouTube (Basic)	❌ No	Best Effort

📌 Troubleshooting Issue:

• If YouTube streaming buffers, check if it's running on a non-GBR bearer instead of a GBR bearer.
• If users experience slow web browsing, network congestion may be affecting non-GBR bearers.

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5️⃣ MBR (Maximum Bit Rate)

📌 Definition:

• MBR defines the maximum bit rate a user or bearer can consume.
• Prevents one user from taking excessive bandwidth.

✅ Example of MBR:

Service	MBR (Mbps)
VoLTE	0.2
Video Call	2.0

📌 Troubleshooting Issue:

• If a user complains about slow speeds, check whether MBR is restricting their data rate.
• If video calls are getting poor quality, verify if MBR is high enough (e.g., 2 Mbps for HD video calls).

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6️⃣ APN-AMBR (Access Point Name - Aggregate Maximum Bit Rate)

📌 Definition:

• APN-AMBR limits the total data rate for all bearers under the same APN (e.g., Internet APN, Corporate APN).
• It applies across all bearers rather than a single session.

✅ Example of APN-AMBR:

APN	APN-AMBR (Mbps)
Internet	100
Corporate	10

📌 Troubleshooting Issue:

• If all data applications (web, video, downloads) are slow, check if APN-AMBR is too low for the Internet APN.
• If users in a corporate network complain about slow speeds, verify whether Corporate APN-AMBR is limiting them (e.g., 10 Mbps cap instead of 50 Mbps).

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7️⃣ UE-AMBR (User Equipment - Aggregate Maximum Bit Rate)

📌 Definition:

• UE-AMBR defines the total maximum data rate that a single UE (device) can achieve, across all bearers.
• Helps in controlling per-user data consumption.

✅ Example of UE-AMBR:

User Plan	UE-AMBR (Mbps)
Premium User	500
Standard User	100
Basic User	10

📌 Troubleshooting Issue:

• If a premium user is experiencing slow speeds, check if UE-AMBR is capped at 100 Mbps instead of 500 Mbps.
• If normal users complain about slow speed, verify if UE-AMBR is too restrictive (e.g., 10 Mbps for basic users).

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🎯 Summary Table of LTE QoS Parameters

QoS Parameter	Definition	Example	Troubleshooting
QCI	Defines traffic priority, delay, and loss	QCI 1 for VoLTE, QCI 9 for browsing	VoLTE call drops? Check QCI 1 is assigned
ARP	Decides bearer priority during congestion	ARP 1 for emergency, ARP 15 for best effort	Emergency calls fail? Ensure ARP 1 is assigned
GBR	Guaranteed bandwidth for real-time traffic	VoLTE (0.1 Mbps), Video Call (1.5 Mbps)	Poor VoLTE quality? Check if GBR is set correctly
Non-GBR	Best-effort traffic without guaranteed bandwidth	Web browsing, file downloads	Slow web? Network congestion affecting non-GBR
MBR	Limits max bit rate per bearer	VoLTE (0.2 Mbps), Video Call (2 Mbps)	Slow speeds? Check if MBR is restricting throughput
APN-AMBR	Limits total speed for all bearers under an APN	Internet APN (100 Mbps), Corporate APN (10 Mbps)	All apps slow? APN-AMBR may be too low
UE-AMBR	Limits total speed for a device	Premium (500 Mbps), Standard (100 Mbps)	Premium users slow? Check UE-AMBR limits

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🔹 Key Takeaways

✔ QCI controls service quality (VoLTE vs. browsing).
✔ ARP ensures emergency calls get priority.
✔ GBR guarantees bandwidth for real-time services.
✔ MBR, APN-AMBR, and UE-AMBR control max speeds for users and APNs.

💡 If VoLTE fails, check QCI, GBR, ARP.
💡 If data is slow, check APN-AMBR, UE-AMBR, MBR.