background image
Tech Note #22: Asynchronous Transfer Mode (ATM)  Addresses
©
1998 Bionic Buffalo Corporation; All Rights Reserved.
       14 September 1998
http://www.tatanka.com
Page 
8 of 12
A VPCI is 16 bits long, longer than a VPI. This reflects the fact that, with cross-connects, the
number of VPCIs may easily exceed the number of unique VPIs.
A VPCI identifies a Virtual Path Connection (VPC), which can be considered a sequence of
individual Virtual Path Links (VPLs). Each of the VPLs of the VPC has its own VPI. Since the
VPI changes upon entry to and exit from a switch (that is, the virtual path is re-numbered), a
VPL generally extends only over the physical link from one switch to the next.
VP
VP
VP
VPL
VPL
VPL
VPL
VPI

VPI
 
VPI
!
VPI
"
VPC
The corresponding entity for channels is a Virtual Channel Link (VCL), which has its own
VCI. Accordingly, VCLs change when paths are terminated or the channel is switched from one
path to another. A sequence of VCLs from one user to another is a Virtual Channel Connection
(VCC), identified by a Virtual Channel Connection Identifier (VCCI).
VP
VP
VP
VCL
VCL
VCL
VCI

VCI

VCI
 
VCI
!
VCC