User guide

Video Services provided by ADSL Network Engineering
Telesyn Service Guide (Optimizing Video Services)
3-6
• bandwidth for Electronic Programming Guide (EPG) and emergency action channels
• bandwidth for data.
Maximum Number of STBs per Port Based on Minimum Downstream Rate Supported - Formula
The following formula can be used to determine how many set tops can be supported on a given line:
min downstream rate =
((1+ATM Overhead)*(Total Minimum Encoded Stream+Guaranteed Data Rate+(Voice BW*Num-
ber of Phones))*Number of STBs
Maximum Number of STBs per Port Based on Minimum Downstream Rate Sup-
ported
For example, with an ATM Overhead of .13, if an encoder is creating video at a combined 3.5Mbps with an EPG
channel of 360 Kbps, while using 2 set top boxes and guaranteeing 128K of Internet traffic, the result is:
(1.13*(3498 Kbps + 256 Kbps + (0)))*2
Take the result and round up to the nearest multiple of 32kbps for the minimum train rate. This result of rounding
up should be identified as the Minimum Downstream Rate. In this example then, the actual value to use is 8512
Kbps.
In this example this rate is required to serve (2) STBs and the required internet connection speed. Any loop that
can not consistently and reliably train to at least this value cannot support 2 STBs.
Note: Refer to Table 3-2 for a spreadsheet being used to capture these values, notes, and
calculations.
3.2.4.2.2 Maximum Number of STBs per ADSL service module
Each SM in the Telesyn product is serviced by a 100Meg Ethernet connection to the central fabric controller
(CFC) card. This 100Meg connection rate is completely independent of the rate that any given ADSL loop on
the ADSL trains up.
Operational rules must be put into place to assure that there is always enough bandwidth available to provide
video to all subscribers (100% non-blocking).
To stay below this limit the operator must assure that the total number of STBs connected to a single ADSL SM
is less than the engineered maximum.
Note: The 7000 product line can limit the number of multicast streams that are allowed on a given
ADSL16 card, preventing any deterioration of video quality by preventing additional channels
to be joined once the card's capacity has been reached.
Maximum Number of STBs per ADSL16 Card Based on Minimum Downstream Rate Supported - For-
mula
The calculation is:
Max # of STBs allowed on an ADSL16 = int(100Meg / ([Maximum burst rate of any multicast channel]+(Data
allowance)))