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| -rw-r--r-- | _sfp/sfp-standard.md | 2 |
1 files changed, 1 insertions, 1 deletions
diff --git a/_sfp/sfp-standard.md b/_sfp/sfp-standard.md index 54111e5..6825ace 100644 --- a/_sfp/sfp-standard.md +++ b/_sfp/sfp-standard.md @@ -13,7 +13,7 @@ With the need to increase the heat dissipation characteristics of the modules (i The Ethernet signals are all very similar, but there are some differences between Base-X and MMI. The media-independent interface (MMI) was defined in the IEEE 802.11u standard, was originally defined as a standard interface to connect a Fast Ethernet MAC block (i.e. CPU, switch) to a PHY chip (i.e. twisted pair, fiber optic, etc.) in a standardised way. The main advantage is that the MMI can be used without redesigning or replacing the MAC hardware. Thus any MAC may be used with any PHY, independent of the network signal transmission media[^ethernet]. The main difference is the physical media over which the frames are: -- *Base-X* is based on the Ethernet PHYsical Layer and this standard uses the 8B/10B coding, and *MMI* is based on the Ethernet MAC Device (the device that actually makes and receives Ethernet frames)[^ethernet]. +- *Base-X* is based on the Ethernet PHYsical Layer (level 1) and this standard uses the 8B/10B coding (or other encodings as specified in the EEPROM), and *MMI* is based on the Ethernet MAC Device (level 2, the device that actually makes and receives Ethernet frames)[^ethernet]. - In *Base-X*, auto-negotiation is limited to flow-control (and duplex, which is not really used since it's always full-duplex), and in *MII*, auto-negotiation (AN) also allows the PHY to indicate to the MAC the post-PHY link speed. Even though the MAC-to-PHY SGMII link is always 1000Mbps, it supports 10, 100 and 1000Mbps past the PHY and the MAC need to know this to space out the bits properly (e. g. if the external link is 100Mbps, each bit on the SGMII link is sent 10 times)[^ethernet]. The MII can be used to connect a MAC to an external PHY using a pluggable connector, or directly to a PHY chip on the same PCB. In the first case it is also used in SFP connectors, for example to allow connections between two MAC blocks without passing through a PHY (i.e. passive DAC). |