Network design requirements

Network design connectivity requirements

Cisco has a detailed Cisco TelePresence Network Systems Design Guide to ensure that an organization’s IP network is ready—or can be made ready—for a Cisco TelePresence solution deployment. A major benefit of the Cisco TelePresence solution over competitive offerings is that the real-time, high-definition video and audio are transported over an organization’s converged IP network rather than a dedicated network (although dedicated networks are also supported).

The key enabling technology to accomplish this convergence is quality of service (QoS), matched with the service level requirements of real-time applications, such as Cisco TelePresence, which are defined by the following four parameters:  Bandwidth, Latency (delay), Jitter (variations in delay) and Packet loss.

Since every implementation of a Cisco TelePresence solution is different, and since every organization’s internal network is different, a Cisco Network Path Assessment (NPA) will be conducted before any Cisco TelePresence implementation begins. The NPA is three components:

• A methodology for surveying an organization’s network, comparing it against documented network design recommendations and best practices, to verify that the network meets the requirements for a successful Cisco TelePresence deployment.

• A checklist and tool set for measuring the network path between every Cisco TelePresence device and validating the required infrastructure services

• Documentation to be submitted to the Cisco TelePresence Systems Business Unit’s Experience & Order Assurance (EOA) department.

This process ensures Carlsberg a good working TelePresence environment with optimal end-user experience.

For the offered TX9000-series of TelePresence endpoints, the following requirements are defined for the most important four network parameters:  Bandwidth, Latency (delay), Jitter (variations in delay) and Packet loss:

TelePresence Bandwidth Requirements

Endpoint bandwidth requirements per location per system

Bandwidth values quoted above represent the average bit rate of all audio and video channels, as measured per second, including 5fps XGA presentation. Not including Layer 2-4 network overhead or optional features such as high frame rate / high resolution presentation channel, or secondary standard-definition interoperability channels.

TelePresence Jitter Requirements

Cisco TelePresence has a peak-to-peak jitter target of 10 ms. Jitter is defined as the variance in network latency. Thus, if the average latency is 100 ms and packets are arriving between 95 ms and 105 ms, the peak-to-peak jitter is defined as 10 ms. Measurements within the Cisco TelePresence codecs use peak-to-peak jitter.

Similar to the latency service level requirement, Cisco TelePresence codecs have built in thresholds for jitter to ensure a high quality user experience. Specifically, if peak-to-peak jitter exceeds 20 ms (which we call Jitter Threshold 1) for several seconds, then two things occur:

• A warning message appears at the bottom of the 65″ plasma display indicating that the network is experiencing congestion and that call quality may be affected.

• The TelePresence codecs downgrade to a lower level of motion handing quality within the given resolution

TelePresence Latency Requirements

Cisco TelePresence has a network latency target of 150 ms; this target does not include codec processing time, but purely network flight time.

There may be scenarios, however, where this latency target may not always be possible to achieve, simply due to the laws of physics and the geographical distances involved. Therefore, TelePresence codecs have been designed to sustain high levels of call quality even up to 200 ms of latency. Beyond this threshold (which we refer to as ‘Latency Threshold 1’) a warning message appears on the screen indicating that network conditions may be affecting call quality. Nonetheless, the call continues. If network latency exceeds 400 ms (which we refer to as ‘Latency Threshold 2’) another warning message appears on the screen and the call quality steadily degrades as latency increases. Visually, the call quality is the same, but aurally the lag time between one party speaking and the other party responding becomes unnaturally excessive.

A detailed document on the network requirements for Cisco TelePresence systems is available in .pdf- format and can be found here:

http://www.cisco.com/en/US/docs/solutions/Enterprise/Video/TelePresence_Network_Systems_2.0_DG.pdf