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VSAT technology and installation >> iDirect Forum: hubs and terminals >> TDM

Message started by nkast on Jan 20th, 2010 at 10:52am

Title: TDM
Post by nkast on Jan 20th, 2010 at 10:52am

I understand outbound fromt the HUB is TDM traffica and inbound is TDMA.

Why we cant apply TDM to the outbound traffic?


Title: Re: TDM
Post by Eric Johnston on Jan 20th, 2010 at 11:07am
The question does not make sense to me.

The high speed outbound continuous carrier from the hub, is received at all remote sites.  Within the data stream are various packets, joined end to end without any interruption of the timed data stream, intended for particular remote sites. The remote sites recognise and extract such packets to forward to their attached customer PC.  Such an outbound carrier is called TDM (time division multiplex) since the data stream comprises packets that have come from various internet servers and are being multiplexed together in time sequence before transmission of the composite data stream from the hub.  

The return link carrier slot from the remotes to the hub is an intermittent operation.  The remote sites transmit occasional bursts, all on the same frequency, but only one site at a time to avoid interference.  This is called TDMA, time division multiple access.  A site typically transmits as burst when a mouse is clicked or series of bursts when a long file is being sent.

Is there an alternative to TDMA for the inbound ?.
Yes.  You can use SCPC type modems.  Each remote site has a permanent continuous carrier to the hub.  This is ideal for voice, GSM backhaul, large business, ISP or internet/phone booth cafe.   Traffic is not subject to congestion by other people or FAP and you have steady dedicated bit rates 24/7.   Use iDirect 5000 series modems or Comtech CDM570.

Best regards, Eric.

Title: Re: TDM
Post by dot on Jan 20th, 2010 at 3:09pm
In actual fact if you added an iSCPC link (iDirect's SCPC product) you would effectively have TDM out and a TDM return. This can run alongside other star topology remotes that use the TDMA method for their return channels and it will all be managed by the same NMS. iDirect has announced that they will release SCPC return channels in an on-demand or as-required fashion in the near future as well. Bear in mind that the iDirect platform is IP-based and all the interfaces are Ethernet.

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