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Multimedia
is a term used to define many types of data and many types of transmission.
Types include: text, graphics, sound, still images, moving graphics, and
motion pictures. Networks used to deliver multimedia must support real-time
data transfer of continuous media. Unlike other data types transfered
on the network, Multimedia is sensitive and cannot handle transit
delays of even a fraction of a second.
The majority of today's network multimedia applications require less
than 10 Mbps for operation, so Ethernet is still an acceptable LAN medium.
The problem with Ethernet is that the 10 Mbps is usually shared or divided
amongst many users. Giving each desktop much less than 10Mbps.
In many cases, lack of bandwidth
is not caused by a slow LAN cabling, but rather by an inefficient LAN
design and segmentation.
A considerable amount of bandwidth can be gained by using switches
to resegment the campus LAN environment.
Here are 3 campus examples:
- One school has all 100 users on a shared ethernet
10BaseT network. Maybe a 16 port hub at the center that serves several
other hubs in the halls. In this design, the average bandwidth per
user is dropped down to100 Kbps. This network will not be able to
successfully serve multimedia applications to users.
- The next school replaces the shared hub at the center
with a 16 port switch. Then each hub or user connected to the switch
gets a dedicated 10 Mbps, which yields an average of 1 Mbps or more
for each of the 100 users on the network. Based on this network design,
this school can run medium quality video applications.
- The final school has a network designed with stacked
switches that allows each device to connect directly back to the central
switch. Each user has a dedicated l0-Mbps connection to the LAN. With
10 Mbps of bandwidth per user, this campus can easily support high-quality
network multimedia applications.
When using LAN switches to design networks to support
multimedia applications, it is important to remember the following design
constraints:
- Multicast
packets are basically equivalent to broadcast packets.
- Switches flatten the network and cause broadcast
packets (and multicast packets) to be flooded throughout the network.
- Virtual LANs (VLANs)
can be used to control the size and scope of the broadcast domain
and, therefore, the networks on which multicast packets are sent.
- Routers are required to allow VLANs to communicate
with each other and to control the spread of multicast packets.
Ethernet | Multimedia
| Switching | Router
| VLAN | Layer 2 v Layer
3 | ATM | Resources
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