diff options
| -rw-r--r-- | _sfp/ont-wo-mac.md | 10 | ||||
| -rw-r--r-- | _sfp/sfp-standard.md | 4 |
2 files changed, 7 insertions, 7 deletions
diff --git a/_sfp/ont-wo-mac.md b/_sfp/ont-wo-mac.md index b1e6faf..cf2212d 100644 --- a/_sfp/ont-wo-mac.md +++ b/_sfp/ont-wo-mac.md @@ -9,10 +9,10 @@ PON technologies unlike Ethernet are not P2P but one-to-many with two device typ The OLT provides an integrated access box for Passive Optical Networks. OLTs are typically chassis with one or more line cards inside, and on each line card there is one or more PON transceiver, usually in SFP form factor. Each line card is connected to a secondary switch that provides line card aggregation to the Ethernet uplinks. OLTs are often a mixture of Layer 2 and Layer 3 switching with traffic shaping on a per-customer, per-service basis[^tibit]. -The communication within the SFP PON transceiver is neither MMI nor Ethernet, outside [SFP standards](/sfp-standard.md), but rather it is an *equivalent electrical symbols of optical transmission* (which is simply the input/output of the [BOSA](/bosa-tosa-rosa.md)) that for simplicity's sake we call **PON RAW communication** (also referred to as SFP w/o PON MAC). All the PON management part is left to the line card itself. Each equivalent electrical symbol of optical transmission is a separate dialect, distinct from other dialects. Furthermore, as one can easily guess, this communication is not standard and is not within the signalling standards ([^sfprate],[^sfprate2],[^sfpplusstandard]) but it is compliant with some portions of the MSA [^sfpstandard],[^sfpplusstandard],[^sfpplusmi]. This requires extreme compatibility between ONT and transreciver. This design choice is made for several reasons: -- *size*: the size of an OLT w/o PON MAC is very similar to that of an MMI or Ethernet transceiver, and the size of an OLT with the integrated PON MAC far exceeds that of the standard SFP form factor +The communication within the SFP PON transceiver is neither MII nor Ethernet, outside [SFP standards](/sfp-standard.md), but rather it is an *equivalent electrical symbols of optical transmission* (which is simply the input/output of the [BOSA](/bosa-tosa-rosa.md)) that for simplicity's sake we call **PON RAW communication** (also referred to as SFP w/o PON MAC). All the PON management part is left to the line card itself. Each equivalent electrical symbol of optical transmission is a separate dialect, distinct from other dialects. Furthermore, as one can easily guess, this communication is not standard and is not within the signalling standards ([^sfprate],[^sfprate2],[^sfpplusstandard]) but it is compliant with some portions of the MSA [^sfpstandard],[^sfpplusstandard],[^sfpplusmi]. This requires extreme compatibility between ONT and transreciver. This design choice is made for several reasons: +- *size*: the size of an OLT w/o PON MAC is very similar to that of an MII or Ethernet transceiver, and the size of an OLT with the integrated PON MAC far exceeds that of the standard SFP form factor - *dissipative heating capacity*: the dissipative heating capacity of an OLT with PON MAC is higher than a normal transceiver, such as a 1 or 10 Gbps Ethernet link. -- *duplication*: there is a double `MAC` → `MMI` conversion (`MMI` → `MAC` → `PHY` → `MAC` → `OLT CPU`) +- *duplication*: there is a double `MAC` → `MII` conversion (`MII` → `MAC` → `PHY` → `MAC` → `OLT CPU`) - *repairability*: since lasers often have a shorter lifetime than other ICs, it is good to be able to change only the transceiver Despite this, there is a vendor that sells OLT SFP with PON MAC[^tibit]. The following pictures show an OLT SFP with PON MAC part and a transreciver without PON MAC. It is interesting to see that the latter is much longer and requires an additional heatsink. @@ -40,7 +40,7 @@ graph TD end; subgraph CS[Cage SFP] E --> |I2C| Controller; - C --> |MMI on Tx - Rx| MAC; + C --> |MII on Tx - Rx| MAC; Controller[Controller I2C] --> Switch; MAC --> Switch; end; @@ -69,7 +69,7 @@ graph TD For utility reasons all SFPs w/o PON MAC are not illustrated on Hack GPON as they are not modifiable like ONT with MAC (they require two inter-compatible devices). -In particular, the SFP ONU of the AVM Fritz!Box 5530/5590 belongs in this category, and that the above-mentioned devices are not compatible with any other SFP using MMI/Ethernet/Fibre Channel, while for example the FreeBox or IliadBox supports both ONU w/o PON MAC and some SFP with MAC. +In particular, the SFP ONU of the AVM Fritz!Box 5530/5590 belongs in this category, and that the above-mentioned devices are not compatible with any other SFP using MII/Ethernet/Fibre Channel, while for example the FreeBox or IliadBox supports both ONU w/o PON MAC and some SFP with MAC. In general, these devices do not have enough customisation to allow the required parameters to be changed other than the GPON Serial Number and GPON Ploam Password. This means that in most scenarios these devices with ONT w/o MAC are not flexible enough to be used as a replacement for an ISP-provided ONT. diff --git a/_sfp/sfp-standard.md b/_sfp/sfp-standard.md index 6825ace..89375f9 100644 --- a/_sfp/sfp-standard.md +++ b/_sfp/sfp-standard.md @@ -10,10 +10,10 @@ The organisation that developed SFPs (MSA SFP) has always been very cautious abo After the SFP standard entered the market, in the early 2000s Ethernet and Fibre Channel, the MSA SFP also started to standardise signalling, starting with [^sfprate] and [^sfprate2] which define a list of admissible standard signalling limited to the capabilities of the current form factor SFP. With the need to increase the heat dissipation characteristics of the modules (in order to increase speeds) and to allow some additions to the EEPROM, an additional standard, called SFP+[^sfpplusstandard],[^sfpplusmi],[^xenpak_xfp], was developed, which contains all the aforementioned improvements. The 16GFC, 20GFC signalling for Fibre Channel and the 10 Gbps and 2.5 signalling for Ethernet were also included in the updated [^sfprate] and [^sfprate2] standard. Some of these are also included in [^sfpplusstandard] locking the SFP+ standard to a tenth of signalling, all other signals should fall under the SFP standard[^sfpstandard], but they can use the extended SFP+ management interface[^sfpplusmi]. -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 Ethernet signals are all very similar, but there are some differences between Base-X and MII. The media-independent interface (MII) 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 MII 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 (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]. +- *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 *MII* 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). |