Several organizations are planning or already using MPEG/DVB for
transmission of IP packets. The advantages over HDCL include:
* availability of low cost receivers, which are low cost
because of mass production for the consumer market. There are set top boxes
available in the $1000 range. DVB cards for PCs cost $200 to $300.
* security and program control provided by the conditional
access mechanism
* ability to filter local information from a large carrier.
Use of large carriers improves statistical multiplexing therby increasing
bandwidth efficiency.
* ability to use large carriers that saturate a transponder.
This picks up some power, allowing the use of smaller antennas or more less
impactive FEC.
* use of Reed-Solomon coding for improved signal processing.
To counter balance these benefits there is a disadvantage due to MPEG packet
overhead.
DVB uses fixed 188 byte cells, four of these bytes are overhead. There is
also a 16 byte overhead for section packing, if you use multiprotocol
encapsulation. Also, incomplete cells are padded, causing furthor loss. This
loss depends on packet size and could be quite substantial. Some vendors
will pack packets from the same service in an MPEG packet which minimizes
the impact of short packets. Packing, however, implies delay, because the
processor must wait some time to see if there is another packet ready to
transmit. So in the end it is a tradeoff of efficiency vs. delay. If you
want the packing feature you must make sure that both the encapsulator at
the uplink and the receiver support this feature.
Overall, the advantages of MPEG/DVB are quite significant, especially if you
can saturate a transponder using a single carrier.
Burt Liebowitz
> ----------
> From: Jon Mansey[SMTP:[email protected]]
> Sent: Saturday, April 10, 1999 9:58 PM
> To: [email protected]
> Subject: transports: MPEG vs HDLC
>
> Hi List,
>
> After the interesting discussion recently on BER, I want to throw another
> one out there.
>
> What are the lists opinions of MPEG/DVB as an IP transport over satellite,
> vs HDLC?
>
> Is there any published research comparing them?
>
> Im particularly interested in comparing 3 aspects, link performance,
> encapsulation and decapsulation overhead, and equipment requirements at
> each end.
>
> Jon.
> [email protected] Chief Science Officer
> ------------------------------------------------------------------
> "Low-cost & high-speed access to the US Internet via Satellite"
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> 1901 Main St. 2nd Floor tel (310) 382 3300
> Santa Monica, California 90405 fax (310) 382 3310
> ------------------------------------------------------------------
>
> "Unix IS user friendly... It's just selective about who its friends are."
>
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