Friday, 26 January 2007

More from Zyxel

Following our previous discussions with Zyxel regarding CPE's we raised another raft of questions relating to "in use" scenarios, and steering of sessions from the DsLam chassis to our Bras's

We have had a number of responses back, but some are commercially sensitive so I have edited and the results are paraphrased below:


Q.
I still have a number of questions / clarifications regarding these points if I may.
Session Steering > Our intention is to have two Bras's behind the Dslam chassis. At this point they are are likely to be Cisco 7206's, but possibly something else. We want to attach each Dslam chassis to two Bras's for resilience and will provision either two switches or connect the chassis directly to two Bras's. Our question relates to how we steer the sessions to each Bras. Does it operate similar to multiple DHCP/BootP servers where the session is broadcast and the first to respond does, or so you map a port to an endpoint mac address etc. This is all related to resilience and if one Bras is down, we need to know how to steer the sessions, or if this is un-necessary as any Bras can respond.

Zyxel.
PPPoE session starts with broadcast just like DHCP. The first BRAS responds to a PPPoE request takes the control of this PPPoE session.
Two BRAS can backup each other just like DHCP servers without any configuration changes.

IES-5000 cannot support PPPoE relay, customer cannot define designate BRAS in the DSLAM.

Typically, customer can config max session number in a BRAS server. If the session of 1st BRAS reaches its threshold, it stops response to new request, and 2nd BRAS takes over.
For example, if the there are totally 2K subscribers, set max session number is 1K+ in each BRAS.

Another way is using PPPoE intermediate agent. DSLAM will insert DSLAM and port information in the PPPoE request packet. BRAS can using this information to decide to service this request or not.
It needs some configuration in the BRAS, but it is more secure.

Also if with the configuration if you have database with the MAC address of your client
You can configure your BRAS to respond for a specific MAC address.
For example, BRAS A responses to customer 1, 3, 5
BRAS B responses to customer 2, 4, 6


Q.
Zyxel indicated when we met them that sdsl.bis was approved for use in the UK under ANFP so long as appropriate .psd files were applied to the ports, limiting it to 3mb/s per port, rather than the 4 or so shown as potential. Do you know if this is correct, and are the .psd files available.

Zyxel.
Within the UK the ANFP is still dated as of August 2005 - I am pushing our contacts within the SP community, BT and the NICC to disclose information with regards to the changes. My current view is it that the new document will be produced in line with the launch of 21CN in July. I will forward all of the current documents that I have to you for your perusal and any updated ones that I get visibility of. I have a clearer picture from the other EU markets especially in Ireland where SHDSL.BIS and VDSL/2 will be defined by June 07 and I suspect that BT will follow suit. The issue remains on voice splitting on the mdf frame and the interference with the ADSL2+ circuits. I have a view as to which PSD and band plane will be used.


Q.
I note from the Zyxel website that the 48 port ADSL2+ card shows Annex M capability, but lists as "Maximum transmission rate up to 25Mbps/1.2Mbps for
ADSL2+ ". Surely if it is Annex M then it should be a 2.5Mbps upstream rate.
Can you confirm please.

Zyxel.
Yes, if you enable Annex M with a CPE that supports Annex M, you can get a upstream rate higher rate than 1.2M.
Typically, the rate is between 2M ~ 2.5M dependant on the CPE and quality of the local loop

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