LTE not working on Sprint (Fix?) [11/16]

[MinceMan]

The following is my understanding of the problem. If any corrects or updates need to be made just post and I will update the OP.

Many N5 users are on Sprint noticing that they are not connecting to LTE. The key here is that the N5 is a single radio Triband LTE CDMA device. There is also a great post that explains everything here (thanks LordLugard) and technical pros and cons as well as nice information on the current state of the network are on post #8.

From the s4gru post:

In previous Sprint LTE phones, when a device was in Sprint LTE coverage it would park in both the LTE and CDMA Sprint networks at the same time. When a voice call came in, it would just go straight through to the device. And signal to the LTE network would be maintained the whole time while the call was active.

In contrast, a Sprint Triband LTE device can only stay on one technology at a time. CDMA or LTE, not both. So when a Sprint LTE Triband device is in Sprint LTE coverage it parks only in LTE. And doing so means it cannot transmit calls or text without Circuit Switched Fallback (CSFB) on the network side. CSFB and eCSFB (Enhanced Circuit Switched Fallback) are network controls that will allow a single mode/single path network to operate in two modes, both CDMA and LTE.

Here is how it works in the simplest way I can describe. When your Triband LTE device has an LTE signal, it cannot receive or make calls/texts on its own. It is just using LTE data happily. However, what if someone calls or texts you? How does it get through the CDMA network to your device? Via CSFB.

When the Sprint network tries to forward a call/text to your device but cannot see it via CDMA, it then checks for an LTE connection to your device. If it sees one, it tells your device to disconnect from LTE for a moment and reconnect to CDMA. Your device then jumps over to take the call or text on Sprint CDMA and the LTE session is interrupted. This happens very fast and seamlessly. Except for the loss of data availability. If it is just a text, the data session is only interrupted for fractions of a second and is likely not even noticed by the user...

...much of Sprint’s legacy network either doesn’t support Circuit Switched Fallback or doesn’t support it in cases where the legacy network equipment is by a different manufacturer than the new Network Vision equipment.

So in other words your N5 cannot get phone calls and texts when using LTE while on old crappy legacy towers so it keeps you on 3G.

Warning, I am not responsible for any problems following this advice or code causes. In fact I suggest you stop reading, close your browser and never come back to XDA.

But wait there's a fix!!!

Well not really... but kinda. Type *#*#4636#*#* into your phone dialer and then go to Phone information. From here you can set preferred network type. Choose LTE/GSM/CDMA auto (PRL) (in rare cases LTE only (PRL) maybe required). Now you will auto connect to LTE if it is available. The problem is that if your on a legacy tower you will not receive texts or phone calls when on LTE. It's easy enough to switch between LTE/CDMA auto (PRL) and LTE/GSM/CDMA auto (PRL) on the fly but that's no solution, it just builds the hatred in your blood.

Update - This app is not needed but will be left up. See update 2.

I've built a really simple app to help with this. All the app does is put the above code into your clipboard and launch your dialer. You can then just paste and it will launch the Tester/PhoneInfomation of your phone.
Full source here. The apk is also in the repo.

Update 2
No Dialer codes need. Just install this app and it will launch the activity you need. Credit to DMX31 for posting this link I this thread.

 

[Itchiee]

I haven't had any issues so far with LTE (sending texts, making and receiving calls) on my Nexus 5 and i'm in a spark launch city.
I'm not even going to pretend to understand half of what's being discussed because I don't care enough...

 

[musclehead84]

I have a lte tower right by my house and can't conext to lte on my n5. 4 other phones connect just fine cause it's a strong signal. Called sprint and they said it's a known problem. This is ridiculous. If it's not fixed by my 14 days it's going back. Can't stand not having lte

Sent from my SPH-L900 using xda premium

 

[H2Beg]

This problem effects me, so bad to the point I just sold my N5 and went back to my CM S3. Kudos if you're not having issues, but lots are. The hours on tech support and browsing forums searching for a fix is not worth the effort over a piece of plastic to me with no ETA on when all the towers will be upgraded. Probably months out in my particular area. Happily chugging along on LTE again, maybe I'll try the nexus again next year.

 

[graffix31]

Wait of the n5 is single band lte and sprint is changing their phones to single band to. Shouldn't this be a problem soon to go away?

Sent from my SPH-D710 using Tapatalk

 

[afazel]

It's only a problem in some markets. No issues where I am, for example, but in Chattanooga where I will be moving, the towers are only 4G accepted, not 3G/4G (from what I hear). This problem should be going away for anyone in completed 3G markets soon, and for markets that are not 3G accepted, Sprint should be ramping up the pace of the completions through vendor incentives.

Sent from my Nexus 5 using Tapatalk

 

[MinceMan]

Wait of the n5 is single band lte and sprint is changing their phones to single band to. Shouldn't this be a problem soon to go away?

Sent from my SPH-D710 using Tapatalk

I think that the key is them updating their towers. I don't know about where you live but that doesn't occur quickly in Raleigh North Carolina.

 

[lilotimz]

I think that the key is them updating their towers. I don't know about where you live but that doesn't occur quickly in Raleigh North Carolina.

The key is Network Vision 3G upgrades so the phone can talk to the eCSFB side of the network. Incumbent vendor regions that are mostly not affected are regions where Alcatel-Lucent took over Lucent and Ericsson took over Nortel. Those should be fine and if there are issues then it's really just a software update on the cell site.

In areas where there's non-incumbent equipment then it's a big deal. Areas taken over such as Motorola will have an issue. Then there are the Samsung vendor regions.

Every Samsung region is a non-incumbent region (except PR/VI) and are guaranteed to have issues because Samsung is replacing Nortel, Motorola (hard handoffs known for a while - see Chicago), and etc. According to the document I'll quote below the only mitigation for the eCSFB gaps are to actually quickly complete the network rollout / conversion and fire up NV 3G as soon as possible so Tri-Band devices can actually talk to the LTE core and 3G side.

Explains the apparent "lack" of work in Samsung markets but a huge number of sites physically completed. No time for acceptance / integration when you must complete as many sites as possible to mitigate the eCSFB gaps.

Sprint eCSFB Gap Issue Legal Approved Talking Points:

eCSFB Gap Talking Points

Sprint’s Network Vision Plan (Spectrum)

• Sprint’s Network Vision plan includes access to three spectrum bands, (1.9, 800 and 2.5), and LTE handsets with a single radio.
• Access to diverse spectrum assets allows Sprint to maximize capacity and coverage.

Current Sprint LTE Devices (2 Radios)

• Current Sprint LTE devices are Simultaneous Voice and LTE (SVLTE)—using two radios, one for voice and one for LTE data. This allows CDMA calls and LTE to operate at the same time.
• Dual Radio SVLTE devices can degrade the user’s quality of experience – two antennas may slow throughput at the cell edge and reduce battery life.

Future Sprint LTE Devices (1 Radio)

• CSFB and eCSFB (Circuit Switch Fall Back and enhanced Circuit Switch Fall Back) are features that enable single radio functionality in the handset.
  eCSFB Benefits:
• With eCSFB implementation, Sprint will be able to offer fast LTE data speeds and 3G voice supported on single radio devices. This provides a more cost effective option for Sprint’s long-term business plans to support additional spectrum bands.
• eCSFB is expected to improve handset battery life compared to SVLTE.

eCSFB Gap Issue – What you Need to know:

• Smart devices require eCSFB to “fall back” to 3G to accept a voice call if the user is connected to the LTE network.
• All markets need to be upgraded with eCSFB capability.
• eCSFB Gaps are only in non-incumbent markets where a site has 4G LTE and no 3G upgrade.
• 4G LTE integration with 3G is different by OEM type:
• Incumbent markets – LTE 4G only sites can communicate with either legacy 3G or NV 3G sites.
• Non-Incumbent – LTE 4G can only communicate with NV 3G sites; so individual sites need both NV upgrades.

LTE devices – Customer Experience

• When 4G LTE is deployed in a non-incumbent market on sites without upgrade to 3G service, there is a gap.
• Existing Devices – No Impact
• eCSFB Devices – Phone becomes 3G only device

Non-Launched Markets

• No coverage visible on Sprint.com maps but different experience for users with existing devices versus new eCSFB devices.

Launched Markets

• Sprint coverage tools will display LTE coverage. For new LTE smart device users this could be confusing since they would expect LTE and 3G coverage with the device they purchased, but would not experience LTE until the 3G network is upgraded.

Mitigation plan:

New LTE Markets

• When locking new LTE markets for announcement/ launch, eCSFB deployment status will be a factor in the analysis. New LTE markets will not be announced unless the eCSFB gap risk is low.
• Complete the build quickly in eCSFB gap impacted markets.

Acronyms
CSFB – Circuit Switch Fall Back. It allows for single radio devices. (ERC)
eCSFB – Enhanced Circuit Switch Fall Back Next generation CSFB. (ALU, STA)
SVLTE – Simultaneous Voice & LTE. Allows CDMA calls and LTE to operate simultaneously
Incumbent – An incumbent market is one in which the OEM stays the same as before Network Vision
Non-incumbent – A market in which the OEM changes as well as all of the equipment.
ERC - Ericsson
ALU – Alcatel Lucent
STA - Samsung
NV – Network Vision
OEM – Original Equipment Manufacturer (ERC, ALU, STA)
Gap – 4G LTE on sites without appropriate upgrades to 3G service
1.9 GHz Spectrum - Provides initial capacity and coverage for voice and data services.
800 MHz Spectrum - Improves coverage and in-building penetration for all services.
2.5 GHz Spectrum - Increases data capacity to support higher data demands and more users.

 

[squshy 7]

^^this. To the OP, this is only a temporary problem, as it is not in Sprint's future plan to keep any markets in a eCSFB gap. This is just an unfortunate side-effect of the rollout not being finished.

Sent from my Nexus 5 using XDA Premium 4 mobile app

 

[MinceMan]

^^this. To the OP, this is only a temporary problem, as it is not in Sprint's future plan to keep any markets in a eCSFB gap. This is just an unfortunate side-effect of the rollout not being finished.

Sent from my Nexus 5 using XDA Premium 4 mobile app

RANT:
Temporary yes but really what does that mean. I'm guessing maybe between 1-2 years? By the time it's fixed in my area I might not even have this phone any longer. Their network has been a mess for years and I'm paying good money for this crap.

 

[persibro]

Is this related to my data dropping completely by any chance? I can connect to 3G and 4G fine, but after a random amount of time the data connecting just disappears but I can still make calls and send texts.

The Nexus 5 is a great phone, but I'm finding this whole situation pretty frustrating so far.

 

[MinceMan]

Is this related to my data dropping completely by any chance? I can connect to 3G and 4G fine, but after a random amount of time the data connecting just disappears but I can still make calls and send texts.

The Nexus 5 is a great phone, but I'm finding this whole situation pretty frustrating so far.

I have not experienced that and it doesn't sound like the same problem to me...

 

[DXM31]

The easiest way(for me) to toggle between networks is this app
https://play.google.com/store/apps/details?id=de.mangelow.network&hl=en
No dialer codes needed.

 

[Cuppeerr]

So here's something that's happening to me. I'll send a message and it'll be stuck on sending. BUT. If I place a call and let it connect then hang up the text will go through fine. I'm in Dallas and have LTE almost everywhere but my house lol. Sometimes i'll get LTE upstairs at my house.

I can also remember doing this on my Evo 3D around September-November 2011

 

[LordLugard]

S4GRU Nails it..

This article from S4GRU says it all.

http://s4gru.com/index.php?/blog/1/...-due-to-circuit-switched-fallback-technology/

 

[chugger93]

This article from S4GRU says it all.

http://s4gru.com/index.php?/blog/1/...-due-to-circuit-switched-fallback-technology/

Lord: Thanks for that link. That was about the best, most comforting information I've read in a long time and helps to clarify the issue.

 

[LordLugard]

Lord: Thanks for that link. That was about the best, most comforting information I've read in a long time and helps to clarify the issue.

You're welcome.

 

[premo15]

This article from S4GRU says it all.

http://s4gru.com/index.php?/blog/1/...-due-to-circuit-switched-fallback-technology/

Interesting...Thanks for this. I wonder if lack of CSFB in one's market would be grounds for waiving the ETF...

Sent from my EVO LTE

 

[geoff2k]

But wait there's a fix!!!

Well not really... but kinda. Type *#*#4636#*#* into your phone dialer and then go to Phone information. From here you can set preferred network type. Choose LTE/GSM/CDMA auto (PRL). Now you will auto connect to LTE if it is available. The problem is that if your on a legacy tower you will not receive texts or phone calls when on LTE. It's easy enough to switch between LTE/CDMA auto (PRL) and LTE/GSM/CDMA auto (PRL) on the fly but that's no solution, it just builds the hatred in your blood.

When I go into *#*#4636#*#* and force LTE Only in Phone info, the radio indicator in the notification area shows me as having four bars of LTE, but the Current network indicator stays in the Searching for Service state and never progresses past this point.

I am however, able to run a ping test on that screen, and while both the "ping hostname" and "http client test" pass, the "ping ipaddr" test fails with "IP addr not reachable".

Is this what others are experiencing as well in markets where you have to force LTE?

 

[MinceMan]

@geoff2k Yes to all.

Sent from my Nexus 5 using XDA Premium 4 mobile app