Atm Virtual Connections; Virtual Channel Connection; Virtual Path Connection; Atm Svcs - Juniper JUNOSE SOFTWARE 11.2.X - LINK LAYER CONFIGURATION GUIDE 7-7-2010 Configuration Manual

ATM Virtual Connections

ATM SVCs

ATM Adaptation Layer

Copyright © 2010, Juniper Networks, Inc.
A virtual connection (VC) defines a logical networking path between two endpoints in an
ATM network. ATM cells travel from one point to the other over a virtual connection. An
ATM cell is a package of information that is always 53 bytes in length, unlike a frame or
packet, which has a variable length. An ATM cell has a cell header and a payload. The
payload contains the user data.
The cell header includes an 8-bit virtual path identifier (VPI) and a 16-bit virtual channel
identifier (VCI).
An ATM network can have two types of VCs, depending on the addressing used to switch
the traffic:
Virtual channel connection (VCC)
Virtual path connection (VPC)

Virtual Channel Connection

A VCC uses all the addressing bits of the cell header to move traffic from one link to
another. The VCC is formed by joining a series of virtual channels (VCs), which are logical
circuits uniquely identified for each link of the network. On a VCC, switching is done based
on the combined VPI and VCI values.

Virtual Path Connection

A VPC uses the higher-order addressing bits of the cell header to move traffic from one
link to another. A VPC carries many VCCs within it. A VPC can be set up permanently
between two points, and then switched.
VCCs can be assigned within the VPC easily and quickly. The VPC is formed by joining a
series of virtual paths, which are the logical groups of circuits uniquely defined for each
link of the network. On a VPC, switching is done based on the VPI value only.
JunosE Software does not support configuration and monitoring of ATM switched virtual
circuits (SVCs) on the router.
The ATM Adaptation Layer (AAL) defines the conversion of user information into cells
by segmenting upper-layer information into cells at the transmitter and reassembling
them at the receiver. AAL1 and AAL2 handle intermittent traffic, such as voice and video,
and are not relevant to the router. AAL3/4 and AAL5 support data communications by
segmenting and reassembling packets.
E Series routers support the following AAL5 encapsulation types as specified in RFC
2684—Multiprotocol Encapsulation over ATM Adaptation Layer 5 (September 1999),
which replaces RFC 1483:
aal5snap—LLC/SNAP
aal5mux ip—VC-based multiplexing
Chapter 1: Configuring ATM
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