HD Link Installation & Operation Manual
2 – Functional Design
Version 2, April 2010
2-4
Harris Corporation
Intraplex Products
Access
control
Police
And
Shape
Analog
or AES
Audio
Scheduling
Management Plane
(HTTP, SNMP, FTP, Telnet)
IP Layer
(Routing, tunneling, proxy ARP)
HD stream
(UDP/TCP)
One or more
channels of analog
or
AES audio
Figure 2-1. HD Link STL IP Gateway Architecture
2.2.5.2 Data Bandwidth Management
The network layer moves the various types of data across the link in the most efficient way. The
integrated IP gateway manages the available bandwidth and allocates it appropriately among these
traffic types:
●
Audio for the FM and, depending on component locations, the HD program(s)
●
IP data for the I2E or E2X HD Radio signal
●
Other IP data, such as control and management and even LAN traffic
As traffic from different sources converge on the IP gateway’s data plane, the gateway’s architecture
must support functionalities that filter unwanted Ethernet traffic, police and shape the incoming
Ethernet traffic, and finally prioritize traffic so that the low-priority traffic does not interfere with the
media-related traffic. To achieve this support, a committed traffic rate is allocated to the various
Ethernet traffic sources and to the digitized audio channels. The traffic from the audio source(s) is well
controlled and constant; it therefore does not require metering or policing. However, the Ethernet
traffic may be bursty or variable in rate, and it needs to be handled carefully.
Each IP stream (whether HD media or control traffic) entering the gateway’s Ethernet interface(s)
should first pass through an access control function, which only passes packets whose IP source and
destination address pair are configured as valid connection endpoints. This method prevents unwanted
traffic from a local subnet, including broadcast packets (that is, packets addressed to multiple
recipients), to enter the HD Link system and eat away at bandwidth that is allocated for the legitimate
media to be transported. Once the Ethernet traffic has passed access control, it needs to be prioritized
as either High or Low priority, based on either the physical port through which it has entered, 802.1p
priority, or the IP DiffServ code point.
A policing and shaping function ensures
●
Any excess Ethernet traffic entering the system via a lower-priority port, such as general LAN
traffic, is discarded, thus preventing such traffic from interfering with the transport of the critical
audio and HD streams.
●
The smoothing function accommodates instantaneous bursts of the HD’s media stream across the
allocated air bandwidth. Without this smoothing function, the transmission of instantaneous bursts
in the HD IP stream requires far greater air bandwidth.
Finally, a scheduling function should ensure that the strict priority is followed when queuing packets
for transport across the HD Link system.