Configuring Virtual Circuits Module 3

Module Overview After successfully completing this module, you should be able to: Define the purpose of rate monitoring Describe how an Ascend switch marks a frame as red, amber, or green Describe the purpose of graceful discard Configure a PVC Monitor a PVC for proper operation Manually define a PVC path Move a PVC end point Configure a Zero CIR PVC In this module we discuss several issues related to the Frame Relay Protocol. These topics will help you understand the basics of Frame Relay and its advantages when used for wide are networking. Upon completion of this module you will be able to identify the following: The relationship between Frame Relay switching over a Wide Area Network and Local Area Networking. The characteristics of Frame Relay. Virtual Circuit Service and the differences between a Permanent Virtual Circuit and a Switched Virtual Circuit . Addressing for a Permanent Virtual Circuit. The purpose and functions of Link Management for circuit management. The formatting of each frame passing through the Frame Relay network. Network management capabilities of Frame Relay. Multiprotocol encapsulation in a Frame Relay network.

Virtual Circuit Service Chicago Orlando New York DLCI 50 DLCI 25 DLCI 20 A PVC is a logical connection from one access point to another The Data Link Connection Identifiers (DLCIs) define the end points of the PVC Data follows the same path between source and destination, so packets are always in sequence

Customer Contracts: Rate Monitoring Rate monitoring done at ingress port A customer enters into a contract with a provider for certain levels of service The contract is implemented by monitoring the ingress port of the customer’s access line Important elements of the contract include Access Rate Committed Information Rate (CIR) Committed Burst Size (Bc) Excess Burst Size (Be)

Monitoring Customer Ingress Ports Bits 1536 Kb Bursts of Traffic from CPE into FR Network Bc +Be DE Bit Set Be Bc=CIR=512 T1 1 sec T2 1 sec T3 1 sec T0 Frame Relay traffic is typically “bursty,” with every transmission at line speed Ingress port traffic is sampled in measured time intervals On an Ascend switch, time interval is 1 second In each interval, customer may exceed CIR or Be

Rate Enforcement on an Ascend Switch (Bits) Red Frames DE Bit Set Bc +Be Be Amber Frames Bc=CIR Green Frames T0 Measurement Interval T1 On an Ascend switch, all frames at ingress port are categorized by color: green, amber, or red CIR and Be are used as color boundaries Color designator is stored in Frame Relay header Color determines order of discard at a congested port

Graceful Discard Graceful discard is a PVC parameter (Bits) Red Frames DE Bit Set Bc +Be Be Amber Frames Bc=CIR Graceful Discard Green Frames T0 T1 Graceful discard is a PVC parameter Applies to red frames received on ingress port If Graceful Discard = ON (default), then red frames are accepted into network If Graceful Discard = OFF, then red frames are discarded at ingress

Ascend’s VC Manager VC Manager is software entity that supports the ability to Add/delete PVCs Activate/deactivate PVCs Route/reroute PVCs Generate “keep-alive” packets across idle PVCs Maintain PVC traffic statistics CP holds master VC table, each IOP contains table of PVCs that begin/end on slot An entry in the VC table contains Description of the VC path (switch/Lport pairs) Forward/reverse bandwidth values

PVC Formation When a PVC is provisioned, the following occurs Switch with the higher internal IP address initiates the setup VC manager on IOP requests a path from OSPF OSPF returns path string (string of switch/Lport pairs) Calling IOP issues a Call Request PDU (Protocol Data Unit) Call Request routed through network Called IOP responds with Confirm PDU PVC becomes active

Adding a PVC 1. From map window, choose Administer => Cascade Parameters => Set All Circuits => Point-to-Point 2. Click on Add… to select logical end points Select logical end points

Setting PVC Attributes Every PVC has three three categories of configuration parameters: 1) Administrative 2) Traffic Type 3) User Preference

PVC Administrative Attributes Define DLCI end points Declare a circuit name

PVC Traffic Type Attributes Set CIR, Be, Bc

PVC User Preference Attributes Set graceful discard to desired setting (default = On)

PVC Templates Creates template containing this PVC’s administrative, traffic type, and user preference attributes Expedites PVC configuration

PVC Traffic Statistics (1) 1. From map window, choose Administer => Cascade Parameters => Set All Circuits => Point-to-Point 2. Select a circuit 3. Click on Statistics button Key to PVC end points Router Router Tx (A) (PVC) Tx (B) Rx (A) Rx (B)

PVC Traffic Statistics (2) Discards typically due to rate monitoring Indicator of congestion in FR network PVC utilization may exceed 100%

PVC QoS Statistics Packets lost between endpoint Lports Cumulative trunk delay

Manually Defined PVCs 1. This PVC has already been defined 3. Build new path by selecting each trunk segment and adding to path 2. Existing path of PVC (found by OSPF)

Moving Circuit End Points From map window, choose Administer => Cascade Parameters => Set All Circuits => Move Circuit Endpoint Existing Circuit End Point New Circuit End Point

Zero CIR PVCs When set to On: - CIR/Bc fixed at 0 - Be set to access rate - All frames in tagged amber

Module Summary A Permanent Virtual Circuit is a logical connection whose end points are Lports Rate monitoring parameters such as CIR, Bc, and Be determine the bandwidth requirements of a PVC All frames on an Ascend switch are classified as green, amber, or red A PVC has three levels of configuration attributes: Administrative, Traffic Type, and User Preferences A PVC can be moved by changing the location of its end points