Well, the downlink bandwidth isn't really shared, but separated.DVB is a multicast service, just like each DStv subscriber tunes their satellite receiver to the same frequency, and picks up the same transmission broadcast on that frequency. DVB subscribers will tune their DVB receivers to the provider-specified frequency.While they will all be in the same multicast group, their streams of data are separated from each other by the provider's DVB encapsulator, using two methods:o A PID [Programme Identification]o MAC addressThe PID is equivalent to a DLCI on frame relay technology. The MAC address is the Burned-In-Address [BIA] of the DVB card installed in your DVB receiver. The provider then configures their DVB encapsulator to route all traffic encapsulated with PID xx to MAC address xxxx.xxxx.xxxx.xxxx. Your DVB receiver will then receive this traffic, along with other multicast traffic [since multicast is just an intelligent form of broadcast], but will only de-encapsulate datagrams whose headers bear the PID and the MAC address for your circuit.This is sort of the same way you get several channels on the same satellite downlink stream. Each channel could have a separate PID, on the same frequency.Information still comes down at 45Mbps for each subscriber, so there is no oversubscription to satellite bandwidth. Even so, additional transponders can be acquired to increase capacity. The providers implement several other security techniques to ensure MAC addresses are not spoofed. It's a pretty safe and secure WAN connection method.Regards,Mark Tinka - CCNA
Network Engineer
Africa Online Uganda
5th Floor, Commercial Plaza
7 Kampala Rd,
Tel: +256-41-258143
Fax: +256-41-258144
E-mail: mtinka at africaonline.co.ug
Web: www.africaonline.co.ug
-----Original Message-----
From: owner-afnog at afnog.org [mailto:owner-afnog at afnog.org]On Behalf Of Eric stevance
Sent: Thursday, March 20, 2003 6:24 PM
To: afnog at afnog.org
Subject: RE: VSAT Access ProvidersMark,Thank you for this clear sumary of this technology!This is exactly what we use in Mali in C-Band.
We see more and more solution Ku, bandwidth share uplink and downlink as a very very low cost. In fact there is so many tarrif.Any suggestion or experiences regarding those service. I understand it is sharing bandwidth, but any experience will be welcome.Thank you,
Eric-----Message d'origine-----
De : owner-afnog at afnog.org [mailto:owner-afnog at afnog.org]De la part de Mark Tinka
Envoyé : jeudi 20 mars 2003 14:26
À : Alamicha Chapuma; pademmy at yahoo.com
Cc : afnog at afnog.org
Objet : RE: VSAT Access ProvidersKu is a cheaper transmission frequency, but is very prone to rain fade, heavy cloud cover and storms. Usually, the size of your satellite antenna will dictate the degree of signal loss you experience during bad weather.C-band has been more native, and is much more stable than Ku band. However, satellite service providers have higher running costs on C-band, and as such, may, at times, pass these costs ont to the client. On a weather scale, only a very heavy, and I mean very heavy storm could take a signal out, albeit it's very unlikely. High level humidity can also present some signal deterioration, although not full blown loss of service.DVB [Digital Video Broadcast] is the wave of the future on satellite transmisson techniques. DVB was meant to replace MPEG, as MPEG required more bandwidth to transmit video and audio. DVB can include several streams of media and protocols, independent of each other and using different mapping techniques to land at their destination. This is the same technology used by Pay-TV satellite companies such as Multichoice and DStv. It's purely a multicast service.On the same technology, you can include IP, voice and audio. Each stream/session is encapsulated in the DVB stream, independently journeying it's way to the correct destination within the frequency.Currently, DVB is being used as a downlink service only. A DVB receiver is required, running DVB-compliant protocol software to de-encapsulate the transmission. A normal 75ohm coaxial cable should suffice for that. Then, to your network, it connects via a 10/100Mbps fast ethernet interface. The DVB units can run either proprietory or general purpose software, such as Linux. Either way, they deliver.What this means is you can have an uplink provided by another company, say your ISP, at 64Kbps or more, and a dedicated DVB satellite downlink with capacity of up to 45Mbps. The DVB receiver can already support this, as the DVB card supports up to 45Mbps and higher, and the LAN interface supports up to 100Mbps. So, you really have no problems when it comes to expansion and growth in terms of Internet downlink bandwidth.Alternatively, you can have the DVB on the same satellite as your uplink. The uplink would still have to be a normal SCPC [Single Channel Per Carrier] link, although new technology is now even making that more efficient.I'd recommend you take a normal SCPC link for the uplink, and a DVB for the downlink. You may have to check with your provider whether they support DVB. The satellite provider [like PanAmSat] may support, but the IP provider may not.If initial cots outlay is a factor, then you can rent a leased-line or frame relay WAN connection to a local ISP, but setup a DVB downlink for you downlink capacity. That way, you only get to pay your ISP for a one-way, assymetric uplink service.Regards,Mark Tinka - CCNA
Network Engineer
Africa Online Uganda
5th Floor, Commercial Plaza
7 Kampala Rd,
Tel: +256-41-258143
Fax: +256-41-258144
E-mail: mtinka at africaonline.co.ug
Web: www.africaonline.co.ug
-----Original Message-----
From: owner-afnog at afnog.org [mailto:owner-afnog at afnog.org]On Behalf Of Alamicha Chapuma
Sent: Thursday, March 20, 2003 5:13 PM
To: pademmy at yahoo.com
Cc: afnog at afnog.org
Subject: Re: VSAT Access ProvidersI am new to VSATs - which system is best and why ? I gather the DVB can be with either KU-band or C-Band - correct?Please clarify !Alamicha Chapuma----- Original Message -----From: Paul Ademola AjayiTo: Alamicha ChapumaSent: Wednesday, March 19, 2003 7:05 PMSubject: Re: VSAT Access ProvidersHi,
What type of system do want? is it a KU-band, C-band or a DVB system which is very good and cost effective.
you can try verestar VSAT solution at verestar.com and emperion VSAT solution.
Paul Ademola Ajayi
Systems/Network Engineer
Orbit Wireless Internet Services
Plot 32, No. 6 Birabi Street, Off Presidential Hotel
G.R.A. Phase I Port Harcourt, Rivers State, Nigeria.
Tel.:234-84-573479Mobile:234-803-324-7220
E-mail: ajayi4u at hotmail.com OR pademmy at yahoo.com
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