GEM Port and Priority Mapping

Hi,

GEM Port:

The smallest traffic channel in GPON. The GPON Encapsulation Method (GEM) frames are transmitted between the OLT and the ONU/ONT. The GEM port is the virtual connection used to identify the service traffic. Each GEM port beans one kind of service traffic.
 

 
Each GEM port is identified by the port-ID uniquely. The ALLLOC_ID ranges from 0-4095. I is allocated by OLT i.e.a T_CONT and can only be used by one ONT per PON interface on the OLT

The following section describes the GEM frame structure based on the mapping of the Ethernet service in GPON mode.

• The GPON system parses Ethernet frames and maps data intoGEM payloads for transmission.

• Header information is automatically encapsulated into GEMframes.

• The mapping format is clear and has good compatibility.

Hello,

1. The concept of gem frames in GPON is that the GPON protocol runs between the GPON module of the ONU and the GPON module of the OLT. The data inside is encapsulated in the gem frame. The gemport-ID is used to identify the gem frame header.

   
   

2. Priority mapping. I wonder if you are talking about the one in ONT-lineprofile? Generally, there are several types of gem mapping, vlan-> gemport and pri-> gemport, which are to map the service flow from the LAN side to the corresponding gemport.

Thanks

Hi,

GEM is a protocol which used to carry the service traffic in GPON technology and its like Ethernet protocol in LAN Technology. The advantage of GEM protocol is capable to carry any of the protcol stack which using for communication incuding IP, Ethernet, MPLS, TDM etc.

Typically GEM is using to map the service traffic in the particular GPON Line profile. Service traffic are differentiated with VLANs and VLANs are mapping to GEM ports. Each GEM ports can carry multiple service traffic and limited up to 8 VLANs.

For differentiate the service traffic priority to the ONT, priority mapping can be configured in GEM Ports based on the service VLANs. Before configuring the priority mapping to GEM port, you should change the "GEM Mapping Mode" to "VLAN+Priority" for enabling VLAN based priorty mapping under the GEM Port. So the traffic priroty will be effective between OLT & ONT upstream direction traffic only. 

Traffic profile is an another option to configure the proiority mapping to the each gpon traffic in any direction.

Regars,

Manu M