Cisco Systems CL-28826-01 Understanding ATM Management Protocols

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User Guide for Cisco Security Manager 4.4

OL-28826-01

Chapter 59 Configuring Router Interfaces

PVCs on Cisco IOS Routers

configuration on CBR may vary with different platforms. For more details, see Understanding the

CBR Service Category for ATM VCs at:

http://www.cisco.com/en/US/tech/tk39/tk51/technologies_tech_note09186a0080094e6a.shtml.

•Unspecified Bit Rate (UBR) This is a service class where the network management makes no Quality

of Service (QoS) commitment. It models the best-effort service that the Internet normally provides

and is suitable for applications tolerant to delay that do not require real-time responses. Examples

include email, fax transmission, file transfers, Telnet, LAN and remote office interconnections. For

more details, see Understanding the UBR Service Category for ATM Virtual Circuits at:

http://www.cisco.com/en/US/tech/tk39/tk51/technologies_tech_note09186a00800a4837.shtml.

•Unspecified Bit Rate (UBR+) Cisco provides a variant of the UBR service class called UBR+. The

main advantage of the UBR+ service class is that it allows an ATM end-system to signal a minimum

cell rate to an ATM switch in a connection request, and the ATM network attempts to maintain this

minimum as an end-to-end guarantee. For more details, see Understanding the UBR+ Service

Category for ATM VCs at:

http://www.cisco.com/en/US/tech/tk39/tk51/technologies_tech_note09186a0080094b40.shtml.

•Variable Bit Rate - Non-Real Time (VBR-nrt) This service class is used to transmit non-real-time

applications that are bursty in nature. The traffic characteristics are defined in terms of the Peak Cell

Rate (PCR), Sustained Cell Rate (SCR), and Minimum Burst Size (MBS). For more details, see

Understanding the VBR-nrt Service Category and Traffic Shaping for ATM VCs at:

http://www.cisco.com/en/US/tech/tk39/tk51/technologies_tech_note09186a0080102a42.shtml.

•Variable Bit Rate - Real Time (VBR-rt) This service class is used to transmit real-time data that is

sensitive to time delays, like compressed voice over IP and video conferencing. As with VBR-nrt,

VBR-rt traffic is defined in terms of a PCR, SCR, and MBS. For more details, see Understanding

the Variable Bit Rate Real Time (VBR-rt) Service Category for ATM VCs at:

http://www.cisco.com/en/US/tech/tk39/tk51/technologies_tech_note09186a0080094cd0.shtml.

You can use these service classes to define ATM quality of service (QoS) guarantees, such as traffic

shaping. Traffic shaping is the use of queues to constrain data bursts, limit peak data rate, and smooth

jitter so that traffic fits within the envelope defined by the traffic contract. ATM devices use traffic

shaping to adhere to the terms of the traffic contract.