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Chapter 7 Server Output Data Format 7-9
7.7 Differences Among Different Types of
Links
The following are distinctions among the ways a Sun MediaCenter server handles
video output over Fast Ethernet or ATM links:
■ As described in this chapter, MPEG streams are encapsulated in UDP/IP packets
and then in Ethernet packets, when sent over Fast Ethernet links. Over ATM,
MPEG streams can be encapsulated in AAL5 ATM packets or in IP packets for
subsequent encapsulation in AAL5 packets.
■ A Sun MediaCenter server can treat multiple Fast Ethernet links as a single
virtual pipe or as individual interfaces. In the virtual pipe (called “load sharing”)
case, the server performs load balancing over multiple Fast Ethernet links. The
first requested bit stream is directed over the first link. The next bit stream is sent
over the next link, and so on, in round-robin fashion. By contrast, multiple ATM
links are always addressed individually. A result of this is that an MSM client
could, potentially, reach the bandwidth limit on a given ATM link before the
server’s bandwidth limit was reached. In such a situation, the server stops
accepting new requests to ensure timely servicing of existing requests. This
situation of a single filled-up link causing a pausing of admissions could not
occur on a Fast Ethernet server on which load sharing was in effect.
■ How an MSM client specifies a destination differs among the different output
types of the Sun MediaCenter server. For a Fast Ethernet model and for ATM
servers that use Classical IP over ATM, the MSM client specifies a destination
without regard to a specific interface. For ATM server that uses MPEG over AAL
5, the MSM client specifies a given ATM interface on the server, as well as a
virtual circuit number that identifies the destination.
■ By default, links used for video output are not available to TCP/IP traffic. As
used by a Sun MediaCenter server, network interfaces used for video output are
one-way, from server to destination. However, you can configure an ATM link to
share bandwidth between two-way, TCP/IP traffic and video output traffic.
Follow the instructions for Classical IP configuration over AAL5/ATM in the
SunATM SBus Cards Manual.
7.8 References
[1] SAA Audio-visual Multimedia Service (AMS) Implementation Agreement, ATM
Forum/95-0012R5, August 7-11, 1995.