UNI Identifier Service Attribute: A text string is used to uniquely identify this UNI in the CEN.
MEF 10.3
Physical Layer Service Attribute: The Physical Layer for each physical link implementing the UNI MUST be one of the PHYs listed in IEEE Std 802.3 – 2012 [3] but excluding 1000BASE-PX-D and 1000BASE-PX-U.
The Physical Layer MUST operate in full duplex mode.
Service Frame Format Service Attribute: A service frame must have the format of a MAC frame as defined by IEEE Std 802.3-2012. Frames with invalid format or frames that are less than 64 bytes must be discarded.
MEF 10.2
Physical Layer Service Attribute: The UNI speed can be 10 Mbps, 100 Mbps, 10/100 Mbps with Autonegotiation, 1 Gbps or 10 Gbps. The Mode MUST be set to Full Duplex.
All PHYs defined by IEEE 802.3-2005 that support Full Duplex transmission at the above speeds are supported.
MAC Layer Service Attribute: The MAC layer/frame formats defined in IEEE 802.3-2005 must be used with the exception that the information field MAY be larger than 1500 bytes.
UNI Maximum Frame Size Service Attribute: This attribute indicates the maximum allowable length for a service frame at the UNI. The value must be at least 1522 bytes.
Notes:
- MEF 6.2 recommends that the value be ≥ 1600 bytes.
- It is generally recommended that UNIs support envelope frames as defined in IEEE Std 802.3-2012 clauses 1.4.184 and 3.2.7. This requires support for frames of length 2000 bytes.
If a frame is dropped because it exceeds the MFS, it is not counted against the Frame Loss Ratio performance attribute.
Each EVC has an EVC Maximum Frame Size Service Attribute, and the value of that attribute must be less than or equal to the minimum UNI Maximum Frame Size Service Attribute at all of the UNIs associated by the EVC.
UNI Maximum Transmission Size Service Attribute: This attribute indicates the maximum allowable length for a service frame at the UNI. The value must be at least 1522 bytes.
The UNI MTU Size (and the EVC MTU Size) is a key service attribute. Some Service Providers offer a larger MTU size for their subscribers. For example, when using FCoE (Fiber-Channel over Ethernet) the MTU size would need to be set to slightly above 2,048 bytes.
If a frame is dropped because it exceeds the MTU, it is not counted against the Frame Loss Ratio performance attribute.
Each EVC has an EVC Maximum Transmission Uni Service Attribute, and the value of that attribute must be less than or equal to the minimum UNI Maximum Transmission Size Service Attribute at all of the UNIs associated by the EVC.
These topics are cover in more depth here: Bundling and Service Multiplexing
Service Multiplexing Service Attribute: A UNI can be defined to terminate exactly one service or multiple Ethernet Services. If the Service Multiplexing attribute has the value ENABLED then multiple Ethernet Services can terminate at the UNI. If Service Multiplexing has the value DISABLED, then only one Ethernet Service can terminate at the UNI.
If Service Multiplexing is allowed at the UNI, the there needs to be a way to associate incoming frames with specific services. The MEF services use the Customer Edge VLAN ID (CE-VLAN ID) as the way to do this. The next two parameters define some attributes of how the CE-VLAN IDs can be mapped to services.
Bundling Service Attribute: If the Bundling attribute has the value ENABLED then multiple CE-VLAN IDs can be associated with an Ethernet Service at the UNI. If the Bundling attribute has the value DISABLED then each Ethernet Service at the UNI can be associated with only one CE-VLAN ID.
All-to-One Bundling Service Attribute: This is a special case of bundling in which, when enabled, all CE-VLAN IDs are mapped to one Ethernet Service. If All-to-One Bundling is ENABLED there there can be only one service on the UNI and it must be a Private Service. If All-to-One Bundling is DISABLED then there can be one or more Virtual Private Services on the UNI.
CE-VLAN/EVC Map Service Attribute: This attribute is used associate the CE-VLAN ID in the C-tag of a service frame with an EVC in the CEN. If All-to-One Bundling is ENABLED at the UNI, then, in effect, all VLAN values are mapped to a single EVC. If All-to-One Bundling is DISABLED, then each valid CE-VLAN ID can be mapped to, at most, one EVC. Service Frames containing CE-VLAN IDs that are not mapped to an EVC are discarded at the UNI. The structure and encoding of the map is not specified, so the map can visualized in several ways.
CE-VLAN ID for Untagged and Priority tagged Service Frames: If a UNI has All-to-One Bundling ENABLED, then all Service Frames (data service frames, not necessarily L2CP service frames) including untagged and priority-tagged frames (see definitions in the next paragraph) are mapped to one EVC at the UNI.
- Untagged, i.e. when the Ether-type (also known as the TPID) is not 0x8100), there is no C-tag
- Priority-tagged, i.e. when the Ether-type is 0x8100 but the VLAN ID field contains 0 (the C-tag is used just to set the priority field)
If All-to-One Bundling is DISABLED at the UNI, then frames are mapped to EVCs based on their CE-VLAN ID. But what is there is no CE-VLAN ID (i.e., untagged or priority-tagged)? These frames must be assigned a CE-VLAN ID so that they can be subsequently mapped to an EVC. This is the purpose of this attribute. For example, if the value of this attribute is "17" then an untagged Service Frame would be associated with CE-VLAN 17. Whichever EVC has CE-VLAN ID 17 mapped to it would receive the untagged (or priority tagged) frame. Note that it is still allowable to also have service frames that are explicitly tagged with 17 although it is more common to choose a value that is not used in other service frames.
Note that if the CE-VLAN that is configured for this attribute is not mapped to an EVC, then untagged and priority tagged Service Frames will be dropped.
Mapping Example
In this example, there are three EVCs on the left hand UNI. Each EVC has one CE-VLAN ID mapped to it. In addition, the UNI has CE-VLAN ID for untagged and priority tagged frames set to 17 (see #10 on UNI Attributes (MEF 10.2)), so those frames are mapped to EVC 3.
| CE-VLAN-ID | EVC |
|---|---|
| 47 | EVC 1 |
| 1343 | EVC 2 |
17 | EVC 3 |
Maximum Number of EVCs Service Attribute: This attribute defines the maximum number of EVCs that the UNI can support. It MUST have a value of at least one. It can be set to a value higher than the number of EVCs defined on a UNI in order to support future service growth.
This attribute is typically tied to UNI speed. MEF 13 defines a recommended minimum number of EVCs that a UNI-N should be able to support as specified below:
- 10/100 Mbps UNI — 8 EVCs
- 1 Gbps UNI — 64 EVCs
- 10 Gbps UNI — 512 EVCs
Ingress Bandwidth Profile per UNI Service Attribute: An Ingress Bandwidth Profile can be specified on the UNI. If an Ingress Bandwidth Profile is specified on the UNI then no Ingress Bandwidth Profiles can be specified on that UNI at the EVC or Class-of-service (CoS) level.
Egress Bandwidth Profile per UNI Service Attribute: Similarly, an Egress Bandwidth Profile can be specified on the UNI and, if specified, no other Egress Bandwidth Profiles can be specified on that UNI at the EVC or Class-of-service level.
Notes:
- UNIs that are associated by an Ethernet Private Line service may not have an ingress or an egress bandwidth profile. See section on Bandwidth Profiles.
- A service frame can traverse only one bandwidth profile at an external interface. Since a per-UNI bandwidth profile applies to all frames at the UNI, no other bandwidth profiles (i.e. per EVC or per CoS) may be used at a UNI with a per UNI bandwidth profile.
UNI Layer 2 Control Protocol Processing Service Attribute:
In MEF 6.2, this attribute is a list of L2CPs that are peered by CEN. If a protocol is not in the list then it is either discarded or passed to the EVC and tunneled based on the L2CP Address Set Service Attribute defined in MEF 45. L2CP is processing is described in more detail here: UNI Attributes - L2CP Processing (MEF 10.3 & MEF 45).
UNI Layer 2 Control Protocol Processing Service Attribute: As indicated in MEF6.1, this attribute contains a list of protocols and for each protocol one of four alternatives for processing Layer 2 Control Protocol (L2CP) frames is indicated:
- Discard the frame
- Peer the frame, i.e., deliver the frame to a protocol processing entity in the CEN to process and possibly respond to the frame.
- Pass to EVC, i.e., present the frame to the EVC (only allowed for UNIs with All-to-One Bundling ENABLED so there can be only one EVC) which can decide to discard the frame or tunnel it through the CEN to the other UNIs in the EVC based on the attributes of the EVC.
- Peer and Pass to EVC, i.e., some Service Frames carrying the Layer 2 Control Protocol are processed by the CEN as a peer while other Service Frames carrying the Layer 2 Control Protocol are passed to the EVC. The method for identifying that a Service Frame is to be peered or passed to the EVC MUST be specified for each service.
L2CP Processing is described in more detail here: UNI Attributes - L2CP Processing (MEF 10.2)
Synchronous Mode Service Attribute: This attribute is a link with one entry for each link composing the UNI (see next attribute). The value for each entry can be ENABLED or DISABLED. If ENABLED then the CEN (actually the bits transmitted by the CEN) can be used as a synchronous Ethernet clock source on the physical link. If ENABLED, the CEN must specify the clock quality using the Ethernet Synchronous Messaging Channel (ESMC) messages.
Number of Links Service Attribute: A UNI can be implemented with one or more physical links. This attribute indicates the number of links that compose the UNI. If the value is 2 then the UNI Resiliency attribute is used to define the protection mechanism. Protection mechanisms for UNIs with more than two links are not defined at this time.
UNI Resiliency Service Attribute: This attribute must have one of the following three values:
- none if the number of links composing the UNI is 1
- 2-Link Aggregation if the number of links composing the UNI is 2
- other is the number of links composing the UNI is greater than 2
Link OAM Service Attribute: This attribute can be ENABLED or DISABLED. If ENABLED, then each link composing the UNI must support the Active DTE mode capabilities of the IEEE Std 802.3-2012 Link OAM protocol (clause 57.2.9).
UNI MEG Service Attribute: This attribute can be ENABLED or DISABLED. If ENABLED, the CEN must provide, at the UNI, the functions specified in section 7.9 of MEF 30.1. This primarily requires supporting a MEP on the UNI MEG. The mechanism for specifying the required values (e.g. the MEG Level) can be specified through an Implementation Agreement.
E-LMI Service Attribute: This attribute can be ENABLED or DISABLED. If ENABLED, the CEN must, at the UNI-N, meet the mandatory requirements for E-LMI specified in MEF 16.