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1 Click Here for Type Bulletin No: H Category: VersaMax To: 1/5, 2, 3, 4 Summary VersaMax CPUE05 Ethernet Loading Considerations Guidelines on how to determine if you are overloading the CPUE05's Ethernet capability. Introduction VersaMax CPUE05 Ethernet Network Bandwidth Usage Guidelines Communications Products Hardware Technology March 26, 2001 Objective This report outlines the performance limits of the IC200CPUE05 (CPUE05) and gives some basic guidelines for using Ethernet Global Data (EGD) and Service Request Transfer Protocol (SRTP). Scope This document applies to the initial release 2.10 of the VersaMax PLC CPUE05 and 10Mbps networks. Performance Limits Due to its multiple access (CSMA/CD) nature, an Ethernet network operates most effectively when the average network bandwidth usage is below 20%. As the average bandwidth usage climbs above 30%, an Ethernet network starts to experience rapid degradation of serviceability due to high probability of delays and collisions during transmission attempts. Two separate limts must be considered: Any given CPUE05 should be configured to utilize no more than 15% of the available network bandwidth The network to which CPUE05s are connected should utilize no more than 20% of the available bandwidth. Exceeding either of these limits may result in the following behavior: Timeout Errors may be logged when the CPUE05 cannot process requests within a specified timeout period. Missed EGD exchanges, unexpected automatic restarts of the Ethernet interface within the CPUE05, or runtime fatal errors at the Ethernet interface may occur. Receive Resources can be exhausted, causing the system to log errors for each packet that was dropped. The greater the degree of exceeding either or both of these limits, the more likely it is that the above behavior will be seen.

2 Page 2 of 5 VersaMax CPUE05 Ethernet Loading Considerations H Determining Network Bandwidth Utilization You can determine network bandwidth utilization either by measuring it or by calculating it. To measure bandwidth utilization, you need a monitoring device, such as a Network General Sniffer. To measure a particular CPUE05 s utilization, configure the monitoring device to capture traffic associated with that CPUE05. To measure total bandwidth utilization, capture all traffic on the network segment. For more detailed instructions, consult your monitoring device s documentation. The remainder of this document explains how to calculate network bandwidth utilization by a CPUE05 Calculating Network Bandwidth Utilization This section details the math behind calculating the Network Bandwidth Utilization. The Excel spreadsheet CPUE05 Network Bandwidth Worksheet.xls implements the calculations described in this chapter. This Application Bulletin and the CPUE05 Network Bandwidth Worksheet can be found on the Internet at Select Files and you will find a ZIP file which has both this bulletin and the worksheet. For the rest of this section, unicast i data transfers are assumed. For multicast ii EGD data transfers, the network bandwidth usage is identical to the Peer-to-Peer unicast case because no additional transfers are used to transmit data to multiple receivers. SRTP, on the other hand, can only perform unicast transfers. The following table lists the computed values for the network bandwidth required to perform one transfer of specific amounts of user data over Ethernet using SRTP vs. EGD. The connection set-up and teardown required by SRTP is not included here. Nor does it take into account retransmission. Note: Maximum SRTP transfer is 2048 data bytes and maximum EGD transfer is 1400 data bytes Table 1 Network Bandwidth Usage per Transfer by Protocol Data Size (bytes) Total Bytes Transferred (Data + Protocol Overhead) PLC-PLC SRTP Transfer EGD Network Bandwidth Usage for 1 Transfer (% of 1 second) PLC-PLC SRTP Transfer EGD % % % 0.011% % 0.027% % 0.048% % 0.089% % 0.12% N/A 0.21% N/A To estimate the network bandwidth requirement for an EGD exchange or an SRTP connection, take the appropriate entry in the preceding table or the next higher entry in the table if the appropriate entry is not listed. Then take the usage figure and multiply by the number of transfers per second for that particular exchange or SRTP connection. For example, to find out how much network bandwidth is required to produce a 512-byte EGD exchange at 100 ms production period, read off the appropriate table entry. In this case, it s 0.048% for an EGD exchange at 512 bytes for one transfer. A 100 ms production period corresponds to 10 transfers per second (1 second divided by 100 ms per transfer). The result is 10 times 0.048%, or 0.48%. i a unicast transfer is an Ethernet message directed to a particular IP address ii a multicast transfer is an Ethernet message directed to a multicast group IP address

3 Page 3 of 5 VersaMax CPUE05 Ethernet Loading Considerations H The exact amount of overhead in an EGD datagram over the network is 86 bytes. The next table demonstrates the relative efficiency of SRTP, which is a TCP iii -based mechanism, and EGD, which is based on UDP iv. It is based on the numbers shown in the preceding table. Table 2 Ratio of Network Bandwidth Usage by Protocol Data Size Ratio of Required Network Bandwidth (bytes) PLC-PLC SRTP Transfer EGD As demonstrated in the above tables, EGD requires less network bandwidth than SRTP. EGD requires far less bandwidth than the corresponding SRTP transfer because the consumers are completely passive, i.e. consumers do not generate any traffic over the network at all. In contrast, both the client and the server in an SRTP transfer must generate network traffic for acknowledgment. This overhead can impose a heavy penalty in situations where the assurance of delivery acknowledgment is not needed. In order to calculate your own utilization on a per data transfer basis, you can use the equations in Equations 1 and 2. NetworkExchangeSize = ExchangeDataSize in bytes + 86 ( Network Overhead) χ NetworkExchangeSize in bytes *8*1000 Utilization% = *100 10,000,000 * χ EGD Exchange Period in ms ρ Equation 1 - EGD Utilization Calculation - Since EGD Utilizes UDP and is limited to a single IP packet, the bandwidth utilization is a straightforward calculation. Record the size and production period for all Produced Exchanges. You need the Exchange size for any exchange. IF the SRTP Data Size in bytes is less than 1404 bytes, use: Network SRTP Data Size = SRTP Data Size in bytes ( Network Overhead IF the SRTP Data Size in bytes is greater than or equal to 1404 bytes, use: ) iii TCP Transmission Control Protocol, a connection-oriented reliable transport protocol iv UDP User Datagram Protocol, a best-effort connectionless unreliable transport protocol

4 Page 4 of 5 VersaMax CPUE05 Ethernet Loading Considerations H Network SRTP Data Size = SRTP Data Size in bytes + % χnetworksrtpdatasize *8*1000 *100 10,000,000* Utilization = χ SRTP Period in ms ρ 626 ( Network Overhead ) Equation 2 SRTP Utilization Calculation - The VersaMax CPUE05 can act as an SRTP server to requests from a remote client. Since SRTP uses TCP, it is slightly more complicated than EGD to calculate the Network Usage. The Network Overhead for SRTP will change depending on the amount of data being transmitted. Examples Using the equations above we can generate the following examples of maximum size configurations that limit the CPUE05 to 15% Network Utilization. Example 1 - Maximum EGD Exchanges Table 3 Maximum EGD Exchanges in a system containing only EGD to maintain <15% bandwidth usage. Size per Period of Exchange (ms) Exchange (bytes) So for example, if your application uses 256-byte exchanges, read the row in Table 3 for 500-byte exchanges. At a period of 50 ms, up to 16 exchanges are recommended. Example 2 - Maximum SRTP Connections Table 4 Maximum SRTP Connections in a system containing only SRTP to maintain <15% bandwidth utilization. Size per Connection Period of Transfers (ms) (bytes) So for example, if your application uses a 1000-byte connection, read the row in Table 4 for the 1400-byte connection. At a period of 50ms, up to 5 connections are recommended.

5 Page 5 of 5 VersaMax CPUE05 Ethernet Loading Considerations H Useful Tips Use no more than 15% of the available network bandwidth for the traffic on a single CPUE05. Use no more than 20% of the available network bandwidth for all traffic on the network. If your network is utilizing more than 20% of the available network bandwidth including the traffic on the CPUE05, GE Fanuc recommends that you use a Network Switch instead of a hub. Phone: - Fax:

Chapter 16 Networking

Chapter 16 Networking Outline 16.1 Introduction 16.2 Network Topology 16.3 Network Types 16.4 TCP/IP Protocol Stack 16.5 Application Layer 16.5.1 Hypertext Transfer Protocol (HTTP) 16.5.2 File Transfer