Triple-Play Service Deployment

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Chapter 6: Troubleshooting Video in the Headend
This is challenging for two reasons:
– MPEG-2 transport is a complex and vulnerable system which
works well provided that all the MPEG transport packets arrive
at the set top box in a specific order, and within a specific
window of time. This is a challenge in and of itself, even when a
relatively simple RF modulation is used for the distribution
network.
– An IP network by nature is not designed to deliver a high
QoS–even in a higher-layer transport. Rather, it is designed to
deliver static payload in a relatively unrestricted timeframe. It is
a best-effort delivery service. Higher-layer protocols and
intelligent hosting/routing can improve performance, but to a
certain extent these efforts are almost counter-intuitive to the
nature of IP transport.
As a result of these factors, triple-play service delivery essentially
requires the provider to maintain two transport networks: IP and
MPEG. The former is a familiar task, and although there are
additional test requirements with the advent of IPTV, they
primarily are enhancements to existing IP test practices. Because
MPEG-2 transport streams have a tight window for packet arrival,
any MPEG packet loss incurred by dropped IP Packets or excessive
spacing (from inter-frame delay or re-sequencing) in the IP
transport network will present significant risk to the program
quality. Buffering at a network node will allow for a certain window
for retransmissions and for delayed frames to catch up, but
buffering also contributes to latency. Once the program
presentation has begun, the stream is constrained to the much
smaller buffer of the set top box.Therefore, an operator can look to
monitor the IP jitter and IP packet loss over an Ethernet transport
segment to gauge the performance of that IP pipe specific to
video services. This enables monitoring of the threat-level to the
digital video programs from the IP transport over that leg of the IP
network. More sophisticated analysis will allow monitoring these
IP parameters on a per flow basis as opposed to the generic
performance of the entire IP pipe.