GarrettCom 6KQE manual Frame Buffering and Flow Control

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Magnum 6KQE Managed Edge Switch Installation and User Guide

02/09

2.2.2Frame Buffering and Flow Control

Magnum 6KQE’s are store-and-forward switches. Each frame (or packet) is loaded into the Switch’s memory and inspected before forwarding can occur. This technique ensures that all forwarded frames are of a valid length and have the correct CRC, i.e., are good packets. This eliminates the propagation of bad packets, enabling all of the available bandwidth to be used for valid information.

While other switching technologies (such as "cut-through" or "express") impose minimal frame latency, they will also permit bad frames to propagate out to the Ethernet segments connected. The "cut-through" technique permits collision fragment frames (which are a result of late collisions) to be forwarded which add to the network traffic. Since there is no way to filter frames with a bad CRC (the entire frame must be present in order for CRC to be calculated), the result of indiscriminate cut-through forwarding is greater traffic congestion, especially at peak activity. Since collisions and bad packets are more likely when traffic is heavy, the result of store-and-forward operation is that more bandwidth is available for good packets when the traffic load is greatest.

When the Magnum 6KQE Switch detects that its free buffer queue space is low, the Switch sends industry standard (full-duplex only) PAUSE packets out to the devices sending it packets to cause “flow control”. This tells the sending devices to temporarily stop sending traffic, which allows the traffic to catch-up without dropping packets. Then, normal packet buffering and processing resumes. This flow-control sequence occurs in a small fraction of a second and is transparent to an observer.

Another feature implemented in the Magnum 6KQE Switches is a collision- based flow-control mechanism (when operating at half-duplex only). When the Switch detects that its free buffer queue space is low, the Switch prevents more frames from entering by forcing a collision signal on all receiving half-duplex ports in order to stop incoming traffic.

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Contents Managed Edge Switch GarrettCom, Inc Contacting GarrettCom, IncElectrical Safety requirements Canadian Emissions StatementTable of Contents IntroductionTroubleshooting Appendix B DC Power InputNetwork Standards and Compliance, hardware Technical SpecificationsPerformance Maximum 10 Mbps Ethernet Segment LengthsAlarm Relay Contacts Fiber Multi-mode connector types supportedFiber Single-mode connector types Management Console connectorDual DC Power Input Optional AC Power Supply InternalPower Consumption 6KQE MountingConfiguration Options Ordering InformationWww . GarrettCom . com Inspecting the Package and Product Product Description Magnum 6KQE Managed Edge Switch Packet Prioritization, 802.1p QOS Frame Buffering and Flow Control Managed Network Software for Magnum 6KQE Web-browser, at ftp//ftp.garrettcom.com„ Fiber Ports Built-In Features and Benefits„ Managed switching for high performance Ethernet LANs „ MNS-6K-SECURE optional, for extra securityApplications Example 1 Magnum 6KQE Switch for an Industrial Application 5a The industrial factory floor application with Magnum 6KQEMagnum 6KQE Managed Edge Switch Installation and User Guide Www . GarrettCom . com Locating Magnum 6KQE Switches Media Ieee Standard Connector Connecting Ethernet MediaConnecting Twisted Pair CAT3, CAT5, UTP or STP Connecting Twisted Pair CAT5e or better, UTP or STP Connecting Single-Mode Fiber OpticSee .2 for the SFP’s available for the 6KQE Connecting Fiber Optic Cable to SFP TransceiversGigabit SFP Small Form-factor Pluggable Transceivers Mounting Dimensions for 6KQE with metal brackets DIN-Rail Mounting the Magnum 6KQE Powering the Magnum 6KQE Managed Edge Switch 5a Alarm Contacts DB-9 Console port connector Connecting the Console Terminal to Magnum 6KQEPin Signal Description 1 RS-232 DB-9 Console port Serial port pin assignmentsAddress Learning Switching FunctionalityFiltering and Forwarding Auto-CrossMDIX and Auto-negotiation, for RJ-45 ports Flow-control, Ieee 802.3x standard 6KQE Modules Power Budget Calculations for 6KQE Modules with Fiber MediaMagnum 6KQE Managed Edge Switch Port Modules 1 6KQE Module LED designations 2 6KQE Base Unit LED designations 3 6KQE4-RJ45, 4 x 10/100Mb RJ45 Slot C6KQE4-1MMRJ, 1 x Mtrj / 3 x RJ45 Slot C 5 6KQE4-2MMRJ, 2 x Mtrj / 2 x RJ45 Slot C 6 6KQE4-3MMRJ, 3 x Mtrj / 1 x RJ45 Slot A, Slot C6KQE4-1MLC, 1 x LC / 3 x RJ45 Slot C 10 6KQE4-xSLC, LC Singlemode 20km / RJ45 Module 8 6KQE4-2MLC, 2 x LC / 2 x RJ45 Slot C9 6KQE4-3MLC, 3 x LC / 1 x RJ45 Slot A, Slot C 11 6KQF-xSLCL, LC Singlemode 40km / RJ45 Module12 6KQE-2GCU, 1GCU Gigabit RJ45 Copper ports Slot D 13 6KQE-2GSFP, 1GSFP Gigabit SFP Fiber ports Slot D6KQEP-48VDC, Base Unit w/PoE Power-pass-through PoE LEDs SummaryWhen Calling for Assistance Before Calling for AssistanceReturn Material Authorization RMA Procedure No Problem FoundShipping and Packaging Information B2.0 12, 24, -48, 125 and 250VDC POWER, Theory of Operation Fig B1.0 Location of chassis ground Power ConsumptionStandard 6KQE DC Power Input Terminal Block -, GND, + B3.0 Applications for DC Powered Ethernet Switches B4.0 6KQE, 12, 24, -48, 125 and 250VDC InstallationB4.1 UL Requirements for DC-powered units B5.0 OperationAppendix C Internal DC Dual-Source Power Input Option C2.0 Magnum 6KQE, with DC Dual-Source optionC3.0 DUAL-SOURCE OPTION, Theory of Operation C6.0 Ordering Information for Dual Source Power Example Magnum 6KQE-48VDC Dual-Src-48V