While much attention has been focused on LTE data rates, another important parameter, latency, has gone largely unnoticed. Yet, latency is critical to enable a number of applications particularly voice services (VoLTE). I review in this post some of the publicly reported results I found on LTE latency.
But first, I like to clarify that latency will depend on a number of parameter. It is a statistical measure and through the reported results, we sort of get a feel for what LTE can provide. Some of the parameters impacting latency include traffic and subscriber load, the type of traffic and the channel radio frequency condition.
LTE includes quality of service management with up to 9 classes of service. Conversational voice is very susceptible to delay and packet error loss, particularly for low bit-rate vocoders. Real-time gaming is another highly demanding application both in terms of delay budget and packet error rate.
|
QCI |
Resource Type |
Priority |
Packet Delay Budget |
Packet Error Loss Rate |
Example Services |
|
1 |
GBR |
2 |
100 ms |
10-2 |
Conversational Voice |
|
2 |
4 |
150 ms |
10-3 |
Conversational Video (Live Streaming) | |
|
3 |
3 |
50 ms |
10-3 |
Real Time Gaming | |
|
4 |
5 |
300 ms |
10-6 |
Non-Conversational Video (Buffered Streaming) | |
|
5 |
Non-GBR |
1 |
100 ms |
10-6 |
IMS Signalling |
|
6 |
6 |
300 ms |
10-6 |
Video (Buffered Streaming) TCP-based (e.g., www, e-mail, chat, ftp, p2p file sharing, progressive video, etc.) |
|
|
7 |
7 |
100 ms |
10-3 |
Voice, Video (Live Streaming) Interactive Gaming |
|
|
8 |
8 |
300 ms |
10-6 |
Video (Buffered Streaming) TCP-based (e.g., www, e-mail, chat, ftp, p2p file sharing, progressive video, etc.) |
|
|
9 |
9 |
I summarized below some of my findings. Unfortunately, most of these reported values were not qualified for the general conditions under which the measurements were taken.
| Reported Latency | Network / Reference | Comments |
| Average: 49 msecMin: 40 msec | AT&T Houston (Signals Research) | Latency measured to servers in the operators local market. |
| Average: 23 msecMax: 38 msec | TeliaSonera Finland (Epitiro) | These are reported as “Network Latency” and defined as “the time it takes for a network to respond.” I believe this measurement was done under very controlled conditions since they reported relatively stable average. |
| Average: 143 msecMin: 79 msec | Verizon (BTIG) | Tests were conducted in-building and near a window. |
According to LTE system specification and requirements, user plane latency is defined to be sub 10 msec for two way radio delay. Although this value excludes the latency to the core, the bulk of latency typically occurs on the air interface. Hence, there is much more room for improvements and optimization when it comes to LTE latency. In fact, I see this as a key issue and even failure of the LTE standard if latency is not improved. After all, LTE was designed with a 1 msec sub-frame to meet the low latency requirement. So far, this goal has not been achieved.
AT&T Houston LTE Network Latency Test Results (Source: Signals Research Group, LLC)
TeliaSonera Finland LTE Network Latency Test Results (Source: Epitiro)
Verizon LTE Network Test Results (Source: BTIG)
very good
Is PACKET DELAY Budget between UE ENB or ENBPDN
The main delay is between the UE and eNB. The delay to the core is generally small in comparison.
I agree,but im asking specifically about packet Delay Budget
The packet delay budget is end-to-end: it’s the total allowed for the application to run properly.