Section E: Troubleshooting the streaming media configuration

About this section

This section describes common problems you might have while deploying your streaming media cache and provides troubleshooting recommendations.

If you are experiencing poor streaming performance

The following table lists the actions you can take to improve your client's playback experience.

Corrective action	Where to find more information
Purchase a streaming license that allows more bandwidth	If you suspect that throughput is a problem
Check your auto-negotiation and duplex settings	If clients are buffering, switching to lower bit rates, or failing If you cannot determine the cause of network congestion
Revert your network to a simple configuration	If you cannot determine the cause of network congestion
Check your hardware	If reverting your network configuration did not improve streaming If you suspect your switch is the problem If you suspect your switch is the problem
Configure all network devices (including firewalls) for UDP traffic	If you are experiencing excessive packet loss
Check RealPlayer settings	If RTSP clients are failing If clients are failing in an IP spoofing deployment
Verify that no other clients are monopolizing UDP	If clients are buffering
Check the appliance configuration and media properties	If NetCache is not caching or splitting content

If you suspect that throughput is a problem

Verify that you have a streaming license installed that allows the expected performance. Three levels of MMS and RealSystem licensing are available-- Standard, Pro, and Ultra. These licenses are throughput-based and are available for the C2100 only.

If clients are buffering, switching to lower bit rates, or failing

If you configure the streaming media cache's NIC for auto-negotiation, ensure that any connecting devices are also configured for auto-negotiation. If some devices are not configured for auto-negotiation or do not auto-negotiate properly, your duplex settings will be inconsistent and network conditions will deteriorate. See If clients are failing in an IP spoofing deployment for duplex configuration details.

If you cannot determine the cause of network congestion

If you are experiencing packet loss and client failures and cannot determine the source of the problem, revert the network to a basic configuration. Configure clients, servers, streaming media caches, and switches to 100Base-T full duplex and test client playback. This simple configuration should enable you to incrementally increase the complexity of your network configuration so that you can determine the problem.

If reverting your network configuration did not improve streaming

If you have reverted your network to a clean configuration and still cannot determine the problem, the problem might lie with faulty hardware. Check your cables and connections and replace any hardware that you suspect might be faulty.

If you are experiencing excessive packet loss

Network configurations that use the NetCache appliance's Gigabit Ethernet NIC to deliver streaming data to 100Base-T clients can be problematic. If you have a switch with a Gigabit Ethernet interface connected to the NetCache appliance and a 100Base-T interface connected to clients, the switch will drop packets if the buffer cannot manage the traffic. This appears to be a limitation of current switch technology.

If you suspect your switch is the problem

To determine if a switch is the cause of your network difficulties, collect the port statistics to determine if the switch is dropping packets. If the number of packets entering the switch is greater than the number of packets leaving the switch, the switch is dropping packets. To fix the problem, test a different type of switch on your network.

If you are experiencing difficulties with streaming QuickTime traffic

If you want to stream Apple QuickTime content using the UDP transport protocol and your firewall blocks UDP traffic, you must configure the firewall to allow UDP traffic to the NetCache appliance for the port range specified in the UDP Port Range option.

The UDP Port Range option is located on the Streaming - RTSP page in the Appliance Manager (Setup tab > Streaming > RTSP).

If you do not allow UDP traffic, your clients will attempt to use HTTP. To allow HTTP-encapsulated QuickTime streaming, you must allow TCP port 80 and TCP port 7070.

If RTSP clients are failing

PNA (Progressive Networks Audio) is a RealNetworks proprietary protocol used for backwards compatibility with RealSystem 3.0 through 5.0. The NetCache streaming media caching and splitting features do not support the use of PNA. Therefore, ensure that the PNA proxy setting in the RealPlayer is not configured to point to the streaming media cache.

Note
NetCache proxies all HTTP-encapsulated PNA requests.

If clients are failing in an IP spoofing deployment

If you enable IP spoofing for RTSP, RealPlayers will not be able to use UDP and will either fail over to TCP (if the player has been configured to fail over) or fail. Therefore, if you must enable IP spoofing for RTSP, ensure that the RealPlayer failover option is enabled.

If clients are buffering

When testing your streaming media configuration, ensure that no other clients are using UDP to receive data. If other clients on the network are using UDP, they will monopolize the available bandwidth in congested networks.

If clients are failing to receive HTTP encapsulated streams

Using HTTP encapsulation for streaming media creates multiple GET and POST connections between the client and the NetCache appliance. If the deployment includes a switch for load balancing, there is no guarantee that all requests from the same player will be redirected to the same NetCache appliance. This means that some of the requests the player makes while playing a stream could be sent to the wrong NetCache appliance. The client, expecting a request, drops the connection, and the occurrence is not logged.

If NetCache is not caching or splitting content

If the NetCache appliance is not caching or splitting content, verify that

Your Streaming Cacheability Substring option (Setup tab > Streaming > Splitting and Caching Behavior) values are not prohibiting caching.
Your hierarchy rules are not preventing splitting or caching.
The RTSP media does not contain the following headers:
- Pragma: no-cache
- Cache-Control: private
- Cache-Control: no-cache
The media has an X-MEIPort header.
The RealNetworks streams do not require RealServer authentication. RealSystem Server authenticated streams cannot be cached. For more information, see Noncacheable streaming media content.

If you see abnormal connection termination

When the appliance is under extreme memory load, it will terminate connections that are fetching data from origin servers and live splitting connections to conserve memory.

Note
The appliance will try to avoid terminating connections that are serving data directly from the cache and connections that are just being proxied (these connections use less memory).

The following message in the Streaming details log indicates that connections are being dropped because of memory pressure:

SERVER_DATA_PRIVATE_LOW_MEMORY

To rectify the problem, you might need to upgrade to an appliance with more capacity.