Cabletron Systems BRIM-A6 User Manual

ATM networks use two different types of Virtual Channels – Permanent 
Virtual Channels (PVCs) or Switched Virtual Channels (SVCs). The 
difference between PVCs and SVCs exists in the channel set-up.

PVCs are pre-configured by an administration function, and are usually 
established for long term use. After setting-up this channel, nothing else is 
required by the network to transfer information between the two 
established points. This type of virtual channelling is established through 
a local or remote management interface.

SVCs use a signaling and network switching procedure to set up 
dynamically. In other words, SVCs establish “on the fly,” as needed for a 
particular service, are used to transmit on the short term, and then 
terminated. Each time a specific channel is established, a routing protocol 
comes into play providing LAN-style operation and management.

Existing PTM transmission technologies (Ethernet, Token Ring, FDDI) 
adhere to the International Organization for Standardization (ISO) Open 
System Interconnection (OSI) model. This seven layer model provides a 
consistent hierarchy of rules for developing system connection standards. 
In essence, OSI is a framework on which protocols for particular network 
types are based. It is important to note that the OSI model is different 
from the ATM model.

A user’s perception of how a network operates is that it provides a direct 
link to another device. In reality, the information that the user sees is 
routed through the layers represented in the following models. Each layer 
modifies the information a user is either sending or receiving, according 
to the standards or protocol established for each individual layer. 

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