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Introduction
The Fast Ethernet speed and duplex configuration process is often taken for granted. Most of the time when an Ethernet cable is connected between two Ethernet devices, a link is automatically established with matching speed and duplex ttings. However, if there is a mismatch with either or both of the ttings, the result is either no link or poor network performance. An understanding of the speed and duplex detection mechanisms will help to resolve the tting conflicts.
This application note provides a quick overview of how speed and duplex ttings are determined and configured for Fast Ethernet devices. First, a brief introduction to some key configuration components, auto negotiation, parallel detection, and force mode, will be prented. A discussion of configuration modes will follow. And last, link results for all combinations of configuration modes between two Ethern
种树英文et devices will be provided.
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All M icrel Fast Ethernet PHYs and switches with integrated PHYs support auto negotiation and parallel detection. In addition, all of the devices, except for the KS8997, support force mode. Configuration Components
Fast Ethernet speed and duplex configurations are determined using three key components: auto negotiation, parallel detection, and force mode.
Auto Negotiation
The auto-negotiation protocol, defined in ction 28 of the IEEE 802.3u specification, allows two Ethernet devices to exchange information about their capabilities over a link gment. Speed and duplex capabilities are two parameters conveyed using the protocol.
海滩冲浪>论文开题报告模板An Ethernet device advertis its speed and duplex capabilities to its link partner using Fast Link Pul (FLP) signals. FLPs are bursts of Normal Link Pul (NLP) signals. A NLP is ud for link detection in 10BASE-T systems, and is shown in Figure 1. The protocol enables an Ethernet device and its link partner to lect the highest priority tting among their common capabilities.
All of Micrel’s Fast Ethernet Switches/PHYs support and adverti the following speed and duplex capabilities, listed from highest priority to lowest priority:
100BASE-TX / Full Duplex
100BASE-TX / Half Duplex
10BASE-T / Full Duplex
10BASE-T / Half Duplex
If there is no common capability detected at either end of the link, then no link will be made.
Detail information on the auto-negotiation process can be found in the IEEE 802.3u specification, in Ethernet textbooks, and at network technology and equipment vendors’ websites.
Parallel Detection
The parallel detection mechanism operates on the PHY’s receive side and works in conjunction with the auto-negotiation protocol to determine the speed of link partners that do not support auto negotiation. Speed detection is achieved by listening for the following characteristic signals:
Normal Link Pul signals
100BASE-TX Idle Pattern
NLP signals indicate the link partner is in 10BASE-T mode, and hence the local Ethernet device will t its port to 10BASE-T mode and establish link accordingly. Figure 1 shows the NLP waveform, which is measured differentially across a 100Ωtermination at the near end.
The prence of 100BASE-TX Idle Pattern indicates the link partner is in 100BASE-TX mode, and hence the local Ethernet device will t its port to 100BASE-TX mode and establish link accordingly. Figure 2 shows the 100BASE-TX Idle Pattern waveform, which is measured differentially across a 100Ω termination at the near end.
Figure 1. Normal Link Pul
Figure 2. 100BASE-TX Idle Pattern
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Parallel detection is limited to identifying only the speed of link partners that do not support auto negotiation. If a non-negotiating, fixed speed link partner is t to full duplex mode, the local auto-negotiating Ethernet device will be unable to obtain its link partner’s duplex tting. Here, the IEEE specification calls for the auto-negotiating device to t its port to half duplex mode. The duplex mismatch that results from this scenario will produce frame errors, late collisions, and dropped frames. All of which can have a vere impact on network performance.
The auto negotiation and parallel detection process flow is depicted in Figure 3.
前马Force Mode
Force mode, also referred to as manual configuration, provides the option to t the speed and duplex mode of operation manually to a pre-determined configuration. This can be beneficial for tho applications that require the bandwidth to be limited to a maximum of 10Mbps, or maintained at 100Mbps. Here, force mode is ud to prevent a link partner from linking with the local Ethernet device if there is a speed difference.场面描写
All Micrel Fast Ethernet PHYs and Switches support force mode, except the KS8997. Force mode is enabled by disabling auto negotiation and lecting the desired speed and duplex mode of operation.
Depending on the device, force mode can be configured through strapping pins or via registers. Registers are accesd using an EEPROM or one of the management interfaces. More details on the programming options can be found in each device’s datasheet.
Configuration Modes
A local device and its link partner can each be t to either auto-negotiation (AN) mode or force mode. Over a link gment, this produces three different combinations of configuration modes: AN-AN, AN-force, and force-force. AN-AN
In this mode, both the local device and its link partner are configured as auto-negotiating devices. FLPs are ud to convey each device’s speed and duplex capabilities to the other. Link will be t to the highest priority tting among their common capabilities. If there is no common capability between the two devices, no link will be made. AN-Force
In this mode, the local device and its link partner are each configured to different configuration modes. One is in AN mode, while the other is in force mode. Due to the configuration mode differences, auto negotiation will fail and parallel detection will be ud to detect the speed of the non-negotiating device. The auto-negotiating device will link at the speed of the non-negotiating devi
ce, and t its port to half duplex mode, as required by the IEEE specification. If the non-negotiating device is t to full duplex mode, there will be a mismatch in duplex tting. As a result, network performance will be impacted verely.
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In this mode, both the local device and its link partner have their speed and duplex modes configured manually to pre-determined ttings. Link is established if both devices are t to the same speed. If there is a mismatch in duplex tting between the devices, network performance will be impacted verely. Therefore, for proper operation, the speed and duplex ttings need to be the same for both devices.
Link Results
The three matrices in Figures 4 through 6 depict the link results for all combinations of auto-negotiated and force mode ttings between a local Ethernet device and its link partner.
Figure 3. Auto Negotiation and Parallel Operation
Figure 4. Link Status (LD with LP in Auto-Negotiation Mode)
