1. Metro Ethernet Forum Layer 2 Services
Bob Klessig
Member of the Board and Co-Chair of the Technical Committee
Director of Engineering, Cisco Systems

2. Agenda
MEF Specifications Roadmap
Services Model
Traffic Management

3. MEF Services Technical Specifications
MEF 1.0 Ethernet Services Model, Phase1*
Technical descriptions of service features
MEF x.0 Traffic Management Specification, Phase1
Fractional Bandwidth and Performance
MEF x.0 Ethernet Services Definitions, Phase1
Specific service instances *

4. Agenda
MEF Specifications Roadmap
Services Model
Traffic Management

5. Services Model Customer Edge (e.g., router) (CE) Customer Edge (CE)
Metro Ethernet Network
Service Attributes
A service is what the CE sees.
The technology used inside the MEN is not visible.

6. User Network Interface
The demarcation point between Service Provider and Subscriber Responsibilities CE CE
Metro Ethernet Network
Dedicated to a single Subscriber
Based on Standard Ethernet PHYs for Phase 1, e.g.,
RJ45 Socket on Service Provider owned Ethernet switch
RJ45 plug on Service Provider owned cable
UNI
UNI

7. Service Frame
The Layer 2 protocol data unit exchanged between the CE and the MEN at the UNI
Standard Ethernet
With IEEE 802.1Q tag (up to 1522 bytes)
Without IEEE 802.1Q tag (up to 1518 bytes)
Includes everything but the preamble
More than 100 Million devices exist that are potential Customer Edge devices

8. Service Frame Transparency
Service Frames must be delivered from ingress UNI to egress UNI(s) transparently except possibly as follows:
Ingress Service Frame
Egress Service Frame*
Untagged
Tagged
Tagged w/ different value
*Frame Check Sequence recalculated

9. Each Service Instance is a Layer 2 VPN
Example showing a green service and a blue service.
Service Multiplexed UNI
Service Frames cannot leak in or out of a Service Instance
Multiple Service instances can exist at a UNI, called Service Multiplexing

10. Formal Service Instance Definition
Ethernet Virtual Connection (EVC)
Association of two or more UNIs
Service Frames can only be exchanged among the associated UNIs
A Service Frame sent into the MEN via a particular UNI MUST NOT be delivered out of the MEN via that UNI

11. Exactly two UNIs are associated.
Point-to-Point EVC
Exactly two UNIs are associated.

12. Multipoint-to-Multipoint EVC
Two* or more UNIs are associated
A broadcast or multicast ingress frame is typically replicated and delivered to all of the other UNIs
* A MP2MP EVC with two UNIs is different than a P2P EVC since additional UNIs can be added at any time.

13. Identifying an EVC at a UNI
CE-VLAN ID/EVC Map
Service Frame Format
Untagged* Priority Tagged* Tagged, VID = 1 Tagged, VID = Tagged, VID = 4094 Tagged, VID = 4095
CE-VLAN ID
EVC
Red Green Blue
CE-VLAN ID/EVC Map
*Untagged and Priority Tagged Service Frames have the same CE-VLAN ID and that value is configurable at each UNI. This is the behavior expected by an IEEE 802.1Q CE.

14. CE-VLAN ID Preservation
EVC Blue
EVC Blue
CE-VLAN ID 37
CE-VLAN ID/EVC Map for EVC must be identical at all UNIs in the EVC and
Priority Tagged in must be priority tagged out
Untagged in must be untagged out

15. All to One Bundling (Map)
Untagged* Priority Tagged* Tagged, VID = 1 Tagged, VID = Tagged, VID = 4094 Tagged, VID = 4095
CE-VLAN ID
EVC Red
CE-VLAN ID/EVC Map
Only one EVC at the UNI (no service multiplexing)
All CE-VLAN IDs map to this EVC – no need for coordination of CE-VLAN ID/EVC Map between Subscriber and Service Provider
EVC must have CE-VLAN ID Preservation

16. Using All to One Bundling
Disaster Recovery Service Provider
Branch HQ
Branch
Bridge or Router
Private Line Replacement
LAN Extension

17. One to One Map
Untagged Priority Tagged Tagged, VID = 1 Tagged, VID = Tagged, VID = 4094 Tagged, VID = 4095
CE-VLAN ID
EVC Red Blue
CE-VLAN ID/EVC Map
No more than one CE-VLAN ID is mapped to each EVC at the UNI
If CE-VLAN ID not mapped to EVC, ingress Service Frames with that CE-VLAN ID are discarded
Service Multiplexing possible
CE-VLAN ID Preservation not required
Subscriber and Service Provider must coordinate CE-VLAN ID/EVC Map

18. CE-VLAN ID Translation
EVC Blue
EVC Blue
CE-VLAN ID 156
CE-VLAN ID/EVC Map can be different at different UNIs in an EVC
Fine for CE routers
Problematic for CE bridges

19. Using One to One Map Internet Service Provider
CE-VLAN ID Preservation would constrain ISP
178  Blue 179  Yellow 180  Green
2000  Green
ISP Customer 3
2000  Blue
2000  Yellow
ISP Customer 1
ISP Customer 2
Frame Relay PVC Replacement
Router

20. Bundling (Map)
Untagged* Priority Tagged* Tagged, VID = 1 Tagged, VID = Tagged, VID = 4094 Tagged, VID = 4095
CE-VLAN ID
EVC Red Blue
CE-VLAN ID/EVC Map
More than one CE-VLAN ID is mapped to an EVC at the UNI
Service Multiplexing possible
CE-VLAN ID Preservation is required for EVC if multiple CE-VLAN IDs mapped to it
Subscriber and Service Provider must coordinate CE-VLAN ID/EVC Map

21. Feature Combinations and Uses
CE-VLAN ID/EVC Map Characteristic
EVC Type
Point-to-Point
Multipoint-to-Multipoint
All to One Bundling
Private Line replacement with Router or Bridge
LAN Extension with Router or Bridge
One to One Map
Frame Relay replacement with Router
Uses TBD
Bundling
Ethernet Line Service (E-Line)
Ethernet LAN Service (E-LAN)

22. Delivery of Service Frames
Broadcast
Deliver to all UNIs in the EVC but the ingress UNI
Multicast
Typically delivered to all UNIs in the EVC but the ingress UNI
Unicast
Typically delivered to all UNIs in the EVC but the ingress UNI if not learned
Otherwise, deliver to the UNI learned for the destination MAC address
Learning is important for Multipoint-to-Multipoint EVCs
Type of Service Frame determined from the destination MAC address

23. Handling Layer 2 Control Protocols
Need to worry about Layer 2 Control Protocols
Bridge
Bridging Example
Bridge
Bridge
Bridges will try to run Spanning Tree Protocol by exchanging Bridge Protocol Data Units (BPDUs)
If BPDUs are blocked, loop will result and Ethernet Service will be unusable
Solutions: Use routers or deliver Subscriber BPDUs

24. Options for Layer 2 Control Protocols
Discard
PDU from CE discarded by MEN
PDU never egresses from MEN
Peer
MEN peers with CE to run protocol
Tunnel
PDUs carried across MEN as if they were normal data
EVC is that associated with the CE-VLAN ID of the PDU, e.g., the Untagged CE-VLAN ID for most standard Layer 2 Control Protocols defined by IEEE 802

25. Agenda
Specifications Roadmap
Services Model
Traffic Management

26. Caveat
MEF Traffic Management work is still evolving and likely to change significantly.

27. Two Areas Covered by Traffic Management
Bandwidth Profile
How to buy just the bandwidth you need and have a predictable bill
Class of Service
Identifying the CoS for a Service Frame
Performance parameters that define a CoS

28. Bandwidth Profile Overview
Similar in concept to the traffic policing of Frame Relay
Bandwidth Profile is a characterization of the lengths and arrival times of Service Frames at the UNI
The level of compliance with the Bandwidth Profile is assessed for each ingress Service Frame
Green = full compliance
Yellow = partial compliance
Red = non-compliance
Delivery performance then based on compliance level

29. Bandwidth Profile Defined by Token Bucket Algorithm
Committed Information Rate
Excess Information Rate
“Green” Tokens
“Yellow” Tokens
Overflow
Overflow
Committed Burst Size
Excess Burst Size
C-Bucket
E-Bucket
If (Service Frame length less than C-Bucket tokens) declare green and remove tokens from C-Bucket
else if (Service Frame length less than E-Bucket tokens) declare yellow and remove tokens from E-Bucket
else declare red

30. Two Options for Algorithm
Option 1: Decoupled
Option 2: Coupled
“Green” Tokens
“Green” Tokens
Overflow
Overflow
C-Bucket
C-Bucket
“Yellow” Tokens
“Yellow” Tokens
Overflow
Overflow
E-Bucket
E-Bucket

31. Bandwidth Profile Parameters
Committed Information Rate (CIR) expressed as bits per second. CIR  0.
Committed Burst Size (CBS) expressed as bytes. CBS  0.
Excess Information Rate (EIR) expressed as bits per second. EIR  0
Excess Burst Size (EBS) expressed as bytes. EBS  0.
Coupling Flag (S). S = 0 or 1.

32. Detailed Algorithm (Extension of RFC 2697)*
Frame of length lj arrives at tj
Bc(tj) = min{CBS, Bc(tj-1) + CIR(tj – tj-1)} Be(tj) = min{EBS, Be(tj-1) + EIR(tj – tj-1) + Smax[0, Bc(tj-1) + CIR(tj – tj-1) – CBS]}
Yes
Declare frame green Bc(tj) = Bc(tj) - lj
lj ≤ Bc(tj) No
Yes
Declare frame yellow Be(tj) = Be(tj) - lj
lj ≤ Be(tj) No
Declare frame red
*Algorithm for “color blind” mode. A “color aware” version exists but requires some way to identify the color of the ingress Service Frame.

33. Three Ways to Apply Bandwidth Profile to a Service Frame
Per ingress UNI
Per EVC at the ingress UNI
Per CoS instance at the ingress UNI (see below for CoS identification)
Multiple methods can apply at a UNI but configuration must be such that only one Bandwidth Profile is applied to each ingress Service Frame

34. Bandwidth Profile Policing
Green
Deliver Service Frame with performance levels as per the Service Level Agreement for the CoS instance
Yellow
Deliver Service Frame but Service Level Agreement for the CoS instance does not apply
Red
Discard

35. Two Ways to Identify CoS Instance
EVC
All Service Frames mapped to the same EVC receive the same CoS
<EVC,set of user_priority values>
All Service Frames mapped to an EVC with one of a set of user_priority values receive the same CoS

36. Class of Service
A Class of Service is defined by three performance objectives
Frame Delay: P percentile of delay ≤ d msec
Frame Jitter: Definition TBD
Frame Loss: Percent of frames lost ≤ p%
Phase 1 will cover only Point-to-Point EVCs

37. “Ethernet for MAN-kind” www.MetroEthernetForum.org