Metro Ethernet Forum Layer 2
Services
Bob Klessig
Member of the Board and Co-Chair of the
Technical Committee
Director of Engineering, Cisco Systems
bklessig@cisco.com
1
Agenda
• MEF Specifications Roadmap
• Services Model
• Traffic Management
2
MEF Services Technical
Specifications
MEF 1.0
Ethernet Services Model, Phase1*
MEF x.0
Traffic Management Specification, Phase1
Technical descriptions of service features
Fractional Bandwidth and Performance
MEF x.0
Ethernet Services Definitions, Phase1
Specific service instances
*http://www.metroethernetforum.org/PDFs/Standards/MEF-1.0.doc
3
Agenda
• MEF Specifications Roadmap
• Services Model
• Traffic Management
4
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.
5
User Network Interface
The demarcation point between Service
Provider and Subscriber Responsibilities
CE
CE
Metro
Ethernet
Network
UNI
UNI
• 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
6
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
7
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
Untagged
Tagged
Tagged w/ different value
*Frame Check Sequence recalculated
8
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
9
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
10
Point-to-Point EVC
Exactly two UNIs are associated.
11
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.
12
Identifying an EVC at a UNI
CE-VLAN ID/EVC Map
Service Frame Format
CE-VLAN ID
EVC
Untagged*
Priority Tagged*
Tagged, VID = 1
Tagged, VID = 2
.
.
.
Tagged, VID = 4094
Tagged, VID = 4095
1
2
.
.
.
4094
4095
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.
13
CE-VLAN ID Preservation
CE-VLAN ID
37
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
14
All to One Bundling (Map)
Untagged*
Priority Tagged*
Tagged, VID = 1
Tagged, VID = 2
.
.
.
Tagged, VID = 4094
Tagged, VID = 4095
CE-VLAN ID
EVC
1
2
.
.
.
4094
4095
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
15
Using All to One Bundling
Disaster Recovery
Service Provider
Branch
HQ
Bridge
or Router
Branch
Private Line
Replacement
LAN
Extension
16
One
to
One
Map
Untagged
Priority Tagged
Tagged, VID = 1
Tagged, VID = 2
.
.
.
Tagged, VID = 4094
Tagged, VID = 4095
•
•
•
•
•
CE-VLAN ID
EVC
1
2
.
.
.
4094
4095
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 CEVLAN ID are discarded
Service Multiplexing possible
CE-VLAN ID Preservation not required
Subscriber and Service Provider must coordinate CE-VLAN ID/EVC Map
17
CE-VLAN ID Translation
CE-VLAN ID
37
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
18
Using One to One Map
Internet
Service Provider
178  Blue
179  Yellow
180  Green
CE-VLAN ID Preservation
would constrain ISP
2000  Green
ISP
Customer 3
2000  Blue
2000  Yellow
ISP
Customer 1
Router
ISP
Customer 2
Frame Relay PVC
Replacement
19
Bundling
(Map)
Untagged*
Priority Tagged*
Tagged, VID = 1
Tagged, VID = 2
.
.
.
Tagged, VID = 4094
Tagged, VID = 4095
CE-VLAN ID
EVC
1
2
3
.
.
4094
4095
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
20
Feature Combinations and Uses
EVC Type
CE-VLAN ID/EVC
Map Characteristic
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
Uses TBD
Uses TBD
Ethernet Line Service
(E-Line)
Ethernet LAN Service
(E-LAN)
21
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
22
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
23
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
24
Agenda
• Specifications Roadmap
• Services Model
• Traffic Management
25
Caveat
MEF Traffic Management
work is still evolving and
likely to change significantly.
26
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
27
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
28
Bandwidth Profile Defined by Token
Bucket Algorithm
“Green”
Tokens
Committed
Information
Rate
Overflow
Committed
Burst Size
C-Bucket
“Yellow”
Tokens
Excess
Information
Rate
Overflow
Excess
Burst Size
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
29
Two Options for Algorithm
Option 1: Decoupled
Option 2: Coupled
“Green”
Tokens
“Green”
Tokens
Overflow
C-Bucket
Overflow
C-Bucket
“Yellow”
Tokens
“Yellow”
Tokens
Overflow
E-Bucket
Overflow
E-Bucket
30
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.
31
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]}
lj ≤ Bc(tj)
No
lj ≤ Be(tj)
No
Yes Declare frame green
Bc(tj) = Bc(tj) - lj
Yes Declare frame yellow
Be(tj) = Be(tj) - lj
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.
32
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
33
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
34
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
35
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
36
“Ethernet for MAN-kind”
www.MetroEthernetForum.org
37