Making streaming media available to internal ISA clients.

by Ricky M. Magalhaes [Published on 3 Jan. 2002 / Last Updated on 21 May 2013]

The streaming media filter enables secure network address translation (Secure NAT) and ISA Firewall clients to use streaming media protocols to access media streaming resources on the internet. In this tutorial I will outline what is involved in making streaming media filter available to internal ISA clients.

The streaming media filter enables secure network address translation (Secure NAT) and ISA Firewall clients to use streaming media protocols to access media streaming resources on the internet. In this tutorial I will outline what is involved in making streaming media filter available to internal ISA clients.

This process will help you create a system called live media streaming splitting. This means that when one ISA client streams media resources from a server then the media is streamed and stored locally on the internal network (WMT window media technologies Server) so that other clients accessing the same steaming media will benefit from local network bandwidth speeds. This method conservers bandwidth and has better streaming results giving client seamless integration with the client and fast media streaming access. Please Read my previous article Configuring live stream splitting for streaming application filters before continuing with this tutorial as configuring the Streaming filter is required for the system to work.

Please note: When packet filtering is enabled on ISA Server, all packets sent to the external interface are dropped unless they are explicitly allowed, by using IP packet filters, or by using access policies or publishing rules.

The following protocols are supported by ISA’s Media streaming splitting technologies.

  • MMS (Microsoft Windows Media) uses port 1755, when this port is used it makes the traffic faster because it is using pure MMS technology and has no HTTP overhead. MMS also works on port 80 but is slower because it is using http pragma command extensions. MMS uses Windows Media Player client to access steaming media resources. MMS is the ‘carrier’ of ASF (Advanced Streaming Format) Microsoft’s ® propriety streaming protocol. Its prime use is to carry live or pre-recorded multi media broadcasts, archived videos, sound tracks and live shows over the internet. MMS operates on top of UDP or TCP transport protocols, they are transport/network level, where as MMS exists and operates at the application level.
  • PNM (Progressive Networks protocol) uses port 7070, this protocol allows for backward compatibility with a RealPlayer 5.0 and below client. PNM protocol allows access and server publishing when serving large or high-quality files. “HTTP is not quite as robust as PNM and HTTP is best suited for those serving smaller files or not insistent upon the absolute best sound quality.” This is what the company that designed this protocol and client claim I and many others have not been able to find a difference between the two PNM and HTTP protocols when it comes to streaming.
  • RTSP (Real Time Streaming Protocol) uses port 554 for fast access and port 80 for slower access as before with MMS, RTSP is designed specifically for clips created and read with RealSystem G2 tools. It is an open standard protocol that supports SureStream files as well as SMIL, RealText, and RealPix files, which allows RealPlayer G2 and QuickTime 4 client access and server publishing capabilities.
Protocol
URL format
RTSP rtsp://domain/file.rm
PNM pnm://domain/file.rm
HTTP http://domain/ramgen/file.rm

This table will help you troubleshoot some of the problems you can encounter with Media streaming splitting technologies.

Note: the URL starts with the protocol to be used, then the domain name is addressed and then the respective file where the media content resides will be addressed. This content normally resides on a streaming server on that domain, and has either a virtual directory or a link to the streaming sever by other means.

 

Configuring live stream splitting for streaming application filters

 

Summary: When the stream splitting concept is fully understood it becomes a bandwidth saving tool. This tutorial has outlined the concepts and protocols making them clearer to you enabling you to understand the fundamentals behind the system.

 

The Author — Ricky M. Magalhaes

Ricky M. Magalhaes is a security specialist that has worked as a consultant and IT technical specialist for the past 8 years. He has been primarily responsible for implementation and design of Security, network architecture, communications, network infrastructure and Security R&D for many South African organizations that he works with. He is a windows 9x product specialist and has been working with the windows product since version win 3.11. He has also written articles on security for www.windowsecurity.com ; www.ISAserver.org ; www.governmentsecurity.com and many other well known security and technology websites.

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