DSLAM Basics

The new evolution of xDSL is the VDSL2 as the replacement of ADSL2+.

Could anyone explain how this new technology at the access section of broadband network, will be deployed at the production field?

For example:
1) which will be the real access rates for the customers (in contrast of ADSL2+)?
2) will be needed new dslams or CPEs?
3) will be necessary to develop the FTTX or is this irrelevant for the Vdsl?
4) will be any change at the upper layers by the adoption of VDSL2 (ethernet first mile, no more ATM)
5) which other changes should be consider when an operator step forward from a ADSL2 to VDSL network?

1. Depends on distance from the DSLAM - generally you need to be within 1km to get near the best speeds.
2. Depends on the DSLAM - newer models (atleast Alcatel, Siemens and Huawei DSLAMs) are able to offer VDSL by just inserting a VDSL line card.
3. Depends on the scenerio - I spose you could run fibre into an apartment and offer VDSL2 from there.
4. AFAIK, atleast with the implementation I worked with, it is still ATM.
5. Provision more bandwidth between the DSLAM and edge aggregation is probably a good start.

Hi,

DSLAM stands for Digital Subscriber Line Access Multiplixer. It's primary function is to provide broadband connections to subscribers based upon various DSL flavours, e.g.;

ADSL - Asymetrical Digital subscriber Line
VDSL - Very High Speed DSL
SH.DSL - Symetrical High Speed DSL

DSLAMs are split in to 2 sides - Customer Side & Trunk Side.

Customer side is where the customer telephone lines are connected and trunk side is where the dslam connects to the ISP network.

On the customer side each line is configured to supply a data connection via DSL to the customer modem. Customer connections are always ATM over DSL - this means the customers ethernet frames (from their PC) are put in to ATM cells which are transmitted vis the DSL on their phone line to the DSLAM.

The trunk side can use various connections depending upon the make & model. Typically trunk connections are ATM, Ethernet or IP.

Trunk interfaces can include:

- STM1 155mb/s
- DS3 (Americas approx 34 Mb/s)
- E1 (European approx 2 Mb/s)
- Gigabit Ethernet 1000 Mb/s
- Fast Ethernet Mb/s

Depending on the trunk connection the DLSAM can make connections between the customer side and the trunk side in a number of ways:

1) ATM DSLAM
- Customer modem packages ethernet frames in to Atm Cells
- ATM cells are transmitted over the phone line using DSL
- DSLAM line card receives ATM cells and passes them to Control card
- Control card switched ATM cells via switching Fabric to trunk interface
- ATM cells are forwarded via ATM network to BRAS - Broadband Remote Access Server (edge router with radius/ authentication functions)

2) ETHERNET DSLAM
- Customer modem packages ethernet frames in to Atm Cells
- ATM cells are transmitted over the phone line using DSL
- DSLAM line card receives ATM cells and passes them to Control card
- Control card re-assembles ethernet frame from ATM cells
- Ethernet frames forwarded to VLAN based trunk interface based on connection table and on to BRAS

3) IP DSLAM
- Customer modem packages ethernet frames in to Atm Cells
- ATM cells are transmitted over the phone line using DSL
- DSLAM line card receives ATM cells and passes them to Control card
- Control card re-assembles ethernet frame from ATM cells
- IP Packets are removed from ethernet frames
- IP Packets are routed to VLAN based trunk interface based on routing table and on to BRAS

A typical network would look like this:

PC --> CPE --> DLSAM --(ATM / Ethernet network)-- -->BRAS --> WWW

(CPE = customer premisies equipment, or DSL Modem)

Please feel free to ask further questions, and please let state where you are in the world as the european implementation is different from the Asian implementation which is different from the Americas implementation

- Ranger

Great explanation Ranger! Just out of curiousity, I understand how a DSL (ADSL) process works, how about VDSL2? Would it be classed as an IP DSLAM whereby ATM cells are de-encapsulated at the DSLAM?

Or does it use another protocol (PTM? Ethernet over DSL?). Thanks!

Hi Ranger,

Can u please explain how to configure the ericcsion ip dslam(edn 312&edn 320) with commands. ie,one dslam connected with cpe and isp network. thanks in advance.....

Hi Ranger,
Read the complete thread. You are awesome. Just a quick q. Since you say that the Ethernet Frames from a customers PC are converted (by the modem, i presume) to ATM cells , why am i asked to change to a different modem when i choose to have IP DSLAM Internet. Any specific reasons?

Thanks in advance.

hi,

can anyone explain about gdmt,g.lite modulation in the ADSL technology...and then what is interleaving?