Hi,
Can someone explain how cable modems chooses upstreams?
Say I have 2 logical channels on an upstream port, the first with 10dB SNR threshold, the other 20dB. If the upstream have 30dB SNR or more, modems are all using the 10dB. Why any of them not using the speedier modulation on 20dB?
Christian
, but here is a link that might help. http://docsis.org/node/607 If you figure it out, please update this post.
Thanks,
Eric
what does your config look like? hop action roll back, spec mgmt should be set for them to return. load balance on the ports set as well?
~Carl
Carl,
My config file is pretty empty (only down/up speed and DOCSIS 2.0 Mode enabled).
I don't use the Upstream Channel ID TLV.
I've no idea what's a "hop action roll back" nor how to set "load balance on the ports".
Can you give any literature?
This what I've found so far:
CM-SP-RFI2.0-I11-060602.pdf
[STRONG]8.1.2.6 Logical Upstream Channels[/STRONG]
There are 4 distinct types of logical upstream:
• Type 1: DOCSIS 1.x upstreams that support no DOCSIS 2.0 TDMA features.
• Type 2: Mixed upstreams that support DOCSIS 1.x and DOCSIS 2.0 TDMA bursts.
• Type 3A: DOCSIS 2.0 TDMA only upstreams that cannot support DOCSIS 1.x CMs.
• Type 3S: S-CDMA upstreams that support only CMs operating in S-CDMA mode.
All valid logical upstreams fall into one of these 4 categories.
[STRONG]11.2.2 Obtain Upstream Parameters[/STRONG]
The CM MUST determine whether it can use the upstream channel from the channel description parameters. If
the channel is not suitable, the CM MUST try other channels until it finds a usable channel.
Before attempting initial ranging on an upstream, the CM categorizes the available upstreams into the following
types based on the UCD for each channel:
1. With a UCD (MAC management message type 2) offering DOCSIS 1.x burst descriptors only.
2. With a UCD (MAC management message type 2) offering both DOCSIS 2.0 TDMA and DOCSIS 1.x burst
descriptors.
3. With a UCD (MAC management message type 29) for a DOCSIS 2.0 Only Upstream.
The CM MUST have non-volatile storage in which channel ID of the last upstream on which the CM
successfully completed registration is stored. If multiple upstreams are available, the CM MUST attempt to use
the one that matches this stored channel ID. [STRONG]If none of the available upstreams match that stored ID, or if the CM
is unable to successfully complete initial ranging on the matching channel, then the CM MUST preferentially
select upstream channels in the following order. Type 3 channels are first, followed by type 2 channels, and type
1 channels are last. The CM MUST NOT begin initial ranging on a type 1 or type 2 upstream until it has allowed
sufficient time, at least the UCD Interval (refer to Annex B), to determine if a type 3 upstream is available. If
initial ranging fails on a type 3 upstream, the CM MUST ensure that it has allowed sufficient time to detect any
other type 3 upstreams that are available before moving on to a type 2 or type 1 upstream[/STRONG]. Of course, once the
CM has waited enough time to ensure that it knows about any available type 3 upstreams, it will also know about
any available type 2 upstreams and it MUST try them in preference to any type 1 upstreams.
---------------------------
I'm using 2 logical channels on each of my ports:
Type 2: TDMA-ATDMA
Type 3S: S-CDMA
Type 2 is the low SNR (10dB), Type 3S is the high SNR (24dB).
This way, if there is noise, my modems will use the low SNR channel, they do, but stick to it.
When the noise is over, all modems should go back to the high SNR channel, no way, even after reset.
I don't understand why my modems don't use Type 3S exclusively, the majority fall for Type 2.
If I remove the Type 2 channel, they all happily use S-CDMA.
Thanks
Christian