Visitor
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7 Messages
Expecting 100Mbps upload but getting 20Mbps
I am expecting 100Mbps upload speed as advertised for my address on https://www.xfinity.com/broadband-labels, but I'm seeing uploads of 20 Mbps.
My download speed is fine.
I just signed up for service with my own 32x8 DOCSIS 3.0 modem on the list at https://www.xfinity.com/support/devices/#auth.
The automated troubleshooting shows no problem and the internet is otherwise fine.
What might be the issue?
BruceW
Gold Problem Solver
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25.9K Messages
5 months ago
All the devices approved for the new higher upload speeds are DOCSIS 3.1. See:
Also see the "All Compatible Devices" link near the bottom of https://www.xfinity.com/support/devices (at the moment it points to https://assets.xfinity.com/assets/dotcom/projects/cix-4997_compatible-devices/2024.04.03%20Full%20List%20of%20Compatible%20Devices.pdf, but this changes from time to time).
Realize that although Comcast calls some devices "Approved" and some "Recommended", for all but a few devices those designations only mean "approved/recommended for use with their Internet service", and not necessarily approved for the new upload speeds.
You need one of Comcast's newer rental gateways or one of the few retail devices shown in the "Next Gen Speed Tier" group with an upload speed rating in the "All Compatible Devices" PDF. Also see the Reddit link, which lists the approved retail devices as well as other requirements for faster upload speeds. Comcast could make all of this much clearer, but they have chosen not to do so.
Please be aware that there are 2 kinds of responses in this Forum: Replies and Comments. When you Comment on a post by scrolling down to "Comment on this post here...", I am notified of your response. But if you select Reply, I am NOT notified and may not be aware of your response.
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BruceW
Gold Problem Solver
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25.9K Messages
5 months ago
Comcast doesn't use multiple upstream QAM channels to deliver the new higher upload speeds, they use a single OFDMA channel. See, for example, the "Upstream Overview" and "OFDMA Upstream Overview" charts in https://forums.xfinity.com/conversations/your-home-network/upload-speed-being-throttled-from-200mbps-to-40mbps/660656ade5bf876df6460c12?commentId=66065783e5bf876df6460c16.
My (possibly incorrect) understanding is that DOCSIS 3.0 modems don't have OFDMA channels. For higher upload speeds DOCSIS 3.1 is required, and the device must be one Comcast approves for the purpose, and the other requirements listed in the Reddit article must be met.
Please be aware that there are 2 kinds of responses in this Forum: Replies and Comments. When you Comment on a post by scrolling down to "Comment on this post here...", I am notified of your response. But if you select Reply, I am NOT notified and may not be aware of your response.
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EG
Expert
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106K Messages
5 months ago
A current, single 256 QAM modulated, 6.4 MHz wide, 5.120 MSym/sec downstream cable channel supports a raw data rate of approximately 43 Mbps, and a real world throughput of approximately 38.1 Mbps.
38.1 X 32 = 1219.2 Mbps. That's a fairly good amount of bandwidth. But anything is possible.
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solarplex24
Visitor
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7 Messages
5 months ago
Are you recommending against folks purchasing a gig plan because they'll never max out the download stream?
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solarplex24
Visitor
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7 Messages
4 months ago
It looks like BruceW's reply is correct: only a handful of user-owned DOCSIS 3.1 modems can support Comcast's implementation of the 100 Mbps upload speed.
However, I'm not going to mark it as the accepted answer because
1) I see no "All Compatible Devices" link on https://www.xfinity.com/support/devices as suggested. Even so, the provided pdf link provided does NOT clearly say that "Next Gen" is required for 100 Mbps uploads.
2) Searching for the information on Comcast's pages does NOT definitively answer, and the webpages circle back on each other. For example, https://www.xfinity.com/support/devices points to https://www.xfinity.com/support/articles/upgraded-areas-leased-equipment-required-for-upload-speeds. The latter says, "See a full list of these retail devices [that support the higher upload speeds];" however, the link just points back to the devices page.
For those wanting more information for clarification:
The newly defined upload speeds are in new "Mid-Split" tiers as opposed to the original "Sub-Split" tiers (https://www.xfinity.com/networkmanagement). Sub-Split uses upstream frequencies of 5-42MHz and Mid-Split uses 5-85MHz, which allocates more frequencies for upload (and thus higher speeds).
Other posts make the claim Comcast is keeping QAM channels on the original 5-42MHz frequencies and reserving 42-85MHz for one OFDMA channel at about 40MHz in width. This looks like figure 31 in section 7.3.1.2 in the paper here:
https://www.nctatechnicalpapers.com/Paper/2021/2021-improving-upstream-efficiency/download
That paper also details in Section 4 that it's best to keep SC-QAM channels and OFDMA channels separate.
It would appear, then, that Comcast is keeping the Sub-Split frequencies as they are so all existing customers are otherwise unaffected. As OFDMA is much more efficient at transmission, it would make sense to use the newer technology in the newly unlocked frequencies for faster rates in the future. Also, as OFDMA was introduced with D3.1, only D3.1 modems would be able to participate in the implementation of the Mid-Split tier (D4.0 will be required to operate in the "Full Duplex" tier).
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ozisat
Visitor
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1 Message
3 months ago
I have the same issue. The difference is that I use the xfinity Gateway xFi. The signal levels look reasonable at a glance, but not sure if there's an issue with them.
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Xantoszz12
Contributor
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51 Messages
3 months ago
I don't believe this is the root cause as I was having this issue before switching to the new speed. If it is the cause then they need to give their customers the correct equipment. I was sent an XB7, went into the store and was told that XB7 was out of date and they gave me an XB8. Still having the issue almost 2 months later
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biodev_1
1 Message
2 months ago
During the pandemic, I worked in Madison, WI but lived in CA, commuting between. In both WI and CA, I would regularly get 1G/s download speeds. Both were on Comcast networks with my personal laptop. When it came to upload speeds, they were throttled to 20mbps in CA, but in WI, uploads were 1G/s. Similar deal when I visit family in WA. They have Comcast and are not throttled, but I still am in CA. So, if it really is that Comcast hasn't upgraded, it seems some of their networks have upgraded. Furthermore, if it is true that some security protocol is a problem for them to update, that's pathetic. I expect Comcast/Xfinity to be a leader in the field, not a laggard. My son has Google fiber and loves it. No hassles; full-speed uploads. Can't wait until it's available in my area. Xfinity's lack of action on this demonstrates they are not a good team player.
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