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(G)ELS - (G)ELS - Ethernet Ethernet VLAN-label Switching (ELS) VLAN-label Switching (ELS)
Benchmarking Carrier Ethernet Technologies Workshop
Session MII.1
Krakow, PolandApril 30, 2008
Dimitri Papadimitriou<[email protected]>
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Evolution of Ethernet paradigmsTwo main scalability concerns: VLAN ID space - can not be solved with Provider bridges (IEEE 802.1ad) MAC address space & learning - (hierarchical) hash-based table lookup (=> simple but limited MAC table size due to memory consumption & non-deterministic lookup time)
Main “networking” concern: Loop avoidance (STP) - can not be solved with STP 802.1d or RSTP 802.1w Convergence time of STP - idem
Main performance concern: STP “blocks” network trunks - not solved with MSTP 802.1s
Spanning Tree Protocol (STP)(VLAN-)Bridges
Multiple STP (MSTP)Provider Bridges (PB)
Multiple STP (MSTP)Provider Backbone Bridges
(PBB)
Ethernet LAN/MAN bridging branch
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Ethernet MAC and Ethernet v2
Ethernet 802.3 MAC Frame
Ethernet v2 Frame
Preamble SDDestination
AddressSource Address Length Information Pad FCS
7 1 6 6 2 4
64 to 1518 bytesSynch Startframe
• MAC address (6 bytes) is either • Single address (0x0….)• Group address (broadcast = 111...111)
• MAC addresses are defined • on local (0) or global (1) basis (second bit)• 246 possible global addresses
Preamble SDDestination
AddressSource Address Type Information Pad FCS
7 1 2 4
64 to 1518 bytesSynch Startframe
6 6
No TTL (time to live) => impossible to detect
looping Ethernet MAC frames
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Spanning Tree Protocols: Count-to-infinity
Spanning tree: a connected, acyclic subgraph (no cycles) containing all the vertices of a graph
Minimum spanning tree (aka shortest spanning tree): a weighted graph which contains all of the graph's vertices
Count-to-infinity problem (as for any other Distance-Vector routing protocol)
Temporary forwarding loop (cycle) that con persist for O(10s)
(R)STP does not provide for fast convergence (and no - known - suitable technique to improve distance vector convergence properties)
Note: steiner tree = a minimum-weight tree connecting a designated set of vertices, called terminals, in an undirected, weighted graph or points in a space. The tree may include non-terminals.
Source: Dictionary of Algorithms and Data Structures [online], Paul E. Black, ed., U.S. National Institute of Standards and Technology. 17 July 2006.
Root Root unreachablecycle
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Evolution of Ethernet paradigms: PBB
Two main scalability concerns: VLAN ID space - solved: S-VID (12 bits) -> I-SID (24bits) MAC address space & learning - solved: MAC-in-MAC tunneling (MAC learning still required)
Main “networking” concern: Loop avoidance (STP) - not solved Convergence time of STP - not solved
Main performance concern: STP “blocks” network trunks - not solved
Spanning Tree Protocol (STP)(VLAN-)Bridges
Multiple STP (MSTP)Provider Bridges (PB)
Multiple STP (MSTP)Provider Backbone Bridges
(PBB)
Ethernet LAN/MAN Bridging branch
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Ethernet Transport technologies
Switching Bridging
Ethernet • ELS: Ethernet VLAN-label switching (link local label): VLAN ID Label
• PBB-TE: Provider Backbone Bridges - Traffic engineering (domain wide label): DA_MAC + VLAN ID Label
Evolution of both Ethernet control and forwarding paradigm
• Legacy: VLAN Bridged Ethernet (MSTP)
Provider bridges: IEEE 802.1q/.1adPBB Provider Backbone Bridge: IEEE 802.1ah
• Shortest Path Bridging: IEEE 802.1aq ( link-state)
Evolution of Ethernet control paradigm only
Shim header (sub-layer)
• Legacy: Ethernet Pseudo-wire over MPLS Packet Switched Network (PSN)
Routing bridges (Rbridges)
Ethernet packet-switched technology with two possible variants: Ethernet Bridging: 802.1ah (PBB), 802.1aq (SPB) Ethernet Switching (ongoing efforts):
MAC + VID based (domain-wide labels): 802.1Qay (PBB-TE) VID based (link-local labels): Ethernet VLAN label switching
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Problem statement
Management
Spanning Tree, Learning, FilteringForwarding Plane Ethernet Control (MSTP)
Provisioning(Policy, etc)
Provisioning(Forwarding Components)
Existing IEEE 802.1 forwarding components and their control does not fulfil requirements associated to Carrier Ethernet metro (and core) networks
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Evolution of control and forwarding paradigms: Ethernet VLAN-label Switching (ELS)
Spanning Tree Protocol (STP)(VLAN-)Bridges
Multiple STP (MSTP)Provider Bridges (PB)
Multiple STP (MSTP)Provider Backbone Bridges
(PBB)
Ethernet Bridging branch (Distance
vector)
Ethernet Switching branch (Link State
routing)
S-VID (encapsulation) +
Constraint-based switched data paths
Link-local labels
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Ethernet LER (E-LER) function: take an incoming Ethernet MAC frame, add or remove the label (encoded in the TAG field)
Ethernet LSR (E-LSR): take incoming labelled Ethernet MAC frame and perform label swap (VID in VID out) => forwarding independent of destination MAC address
Ethernet: point-to-point and point-to-multipoint data paths
Ethernet VLAN-label Switching (ELS) - Overview
Ethernet 802.1ad Switch
E-LSR E-LSR E-LSR
Source Dest
Router
S-VID swapS-VID push S-VID popEthernet
LSP
Ethernet MAC frame
Ethernet MAC frame
Eth. PHYEth. PHY Ethernet 802.1ad Switch
Ethernet 802.1ad Switch
Router
PHY
MAC header + S=VID
Payload (Eth, X, Y)
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Ethernet VLAN-label Switching (ELS) - Framing
Ethernet Frame Format
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ // +-+-+-+-+-+-+-+-+-+| MAC_DA | MAC_SA | S-TAG | C-TAG | ET| Payload | CRC |+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ // +-+-+-+-+-+-+-+-+-+
IEEE 802.1 TAG format
Oct: 1 2 3 4+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+| TPID | TCI |+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
bit: 8 1 8 1 8 1 8 1
TPID (16 bits): TAG Protocol IdentificationTCI (16 bits): TAG Control Information
S-VLAN TAG Control Information (TCI)
Oct: 1 2 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ PCP (3 bits): Priority Code Point | PCP |D| S-VID | D (1 bits): Drop Eligible Indicator (DEI) bit+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ S-VID (12 bits): S-VLAN Identifier
bit: 8 7 6 5 4 3 2 1 8 7 6 5 4 3 2 1
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Traffic engineering adapt traffic routing to network conditions with joint traffic and resource-oriented performance objectives
Effectively control usage of available network resources (put traffic where unused capacity is)
Efficiently re-/direct selected traffic flows from IGP shortest path onto an alternative path
Rapidly redistribute traffic in response to changes in network topology
Performance objectives (provisioning and recovery) Resource-oriented Traffic-oriented: packet loss, delay (and variation)
Approaches Proactive (longer-term): anticipating traffic changes Reactive/adaptive (shorter-term): responsive to traffic
changes
ELS Control Paradigm: Traffic Engineering
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Use RequestConstraints
Explicit Route Representation
(GMPLS) RSVP-TE Signaling
Traffic engineeringDatabase (TEDB)
Traffic engineeringDatabase (TEDB)
Routing table
(GMPLS) OSPF-TE
Operations performed by a LSP head-end (G)MPLS-TE capable node
Constrained-SPF Computation
1 2
3
6
4
5(GMPLS) OSPF-TE ExtensionsDistributed (piggybacked) using Opaque Link State Advertisements (LSA) & encoded as Link sub-TLVMetrics: Unreserved Bandwidth, Maximum Reservable Bandwidth, TE Metric, Resource Class and ISCD (Max. LSP Bandwidth, Switching Cap., LSP Enc. Type)
(1) Store information from IGP flooding in the Link State DB (LSDB)
(2) Store traffic engineering information in the TE Link State DB (TEDB)
(3) Examine user defined constraints for the incoming connectivity requests (=> QoS routing)
(4) Path computation for the data path (LSP) through the TE link topology (=> Policy routing)
(5) Representation of the computed path as an Explicit Route (=> Source routing)
(6) Pass Explicit Route to (GMPLS) RSVP-TE engine for signaling
Constrain-based Routing (Policy-based + QoS source routing)
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Ethernet VLAN-Label Switching (ELS)
S-VID Label (link local)
Positioning ELS
Ethernet (Untagged, C-/S-VID)
Shim (I-SID)
Ethernet + B-VID
Provider Backbone Bridges (PBB)
Provider Backbone Bridges (PBB-TE)
Ethernet (Untagged, C-VID)
[Ethernet] + S-VID
Ethernet (Untagged, C-/S-VID)
Shim (CW + PW label)
PSN Tunnel (MPLS)
Ethernet PW over MPLSMPLS Label (link local)
PayloadPayloadPayload
IEEE: PBB/PBB-TEEthernet VLAN-label
Switching (ELS)Ethernet PW over
MPLS
4k LSP per port (max.)
LSP merging
Unique payload type per LSP
Encapsulating LSP can not be merged (as PW labels are node specific)
PBB: same issues as for any other 802.1 based technologyPBB-TE: Single domain (MAC unicity) and no multicast support (single VID space segmentation)
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Positioning ELS vs PBB-TE (1)
ELS (Ethernet VLAN-label
Switching)Provider Backbone Bridges (PBB-
TE)
Paradigm
Ethernet frame forwarding independent from destination MAC address (no learning)
Constraint-based routing
Add traffic engineering capabilities to PBB networks
Connection ID encoded in the data frame
Label encoding S-VID (12 bits) B-VID + B-MAC DA (requires MAC-in-MAC)
Label semantic Link local Domain wide
Hierarchy Single level Single level
PathUnidirectional, Bi-directional P2P
Unidirectional: MP2P (merge), P2MP (multicast)
Unidirectional, Bi-directional P2P
Unidirectional MP2P (multiplexing requires SA MAC lookup =/= classical label merging)
No P2MP data path support
Provisioning
RecoveryControl-plane based (GMPLS RSVP-TE)
Management or optionally control-plane based (GMPLS RSVP-TE)
Data plane linear protection based on (ongoing efforts on ring protection)
Load balancing No (in order delivery) No (in order delivery)
OAMBFD, Ping, Traceroute
ETH OAM (based on Y.1731)
ETH OAM (based on Y.1731)
CC/CV OAM requires SA MAC lookup
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Router
Frame Filtering
I-SID
B-VID
B-DA
IP/MPLS
ETH + S-VID
Router
PWoMPLS LER
IP/MPLS
ETH+S-VID
IP/MPLS
ETH
IP/MPLS
ETH
Ethernet LSR
Ethernet Transport
Ethernet Transport
Positioning ELS vs PBB-TE (2)
PB (BCB)
VLAN label Switching
Ethernet Label Switching <B-DA, B-
VID>
S-VID Label Switching
Frame forwarding independent of MAC
address
Same Ethernet MAC address
space
Disjoint Ethernet MAC address
spaces
ETH PHY
PBB (BEB)
IP/MPLS
ETH + S-VID
IP/MPLS
ETH + S-VID
B-SA
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Positioning ELS vs Ethernet PW over PSN (1)
Ethernet Label Switching (ELS)
Ethernet (Untagged, C-VID)
[Ethernet] + S-VID
Ethernet (Untagged, C-/S-VID)
Shim (CW + PW label)
PSN Tunnel (MPLS)
Ethernet Pseudo-Wires (PW)
Connectivity Service
Network Emulation & Adaptation
Network PE-to-PE Connection
Data link layer
Ethernet P2P, P2MP, MP Segment
Pseudo-Wire (PW) label
MPLS/T-MPLS
Network Intermediate Trunks MPLS Tunnel/T-MPLS Tunnel
Ethernet MAC/PPP-HDLC
Ethernet PW over PSN
Client Payload Outside scope
Physical layer Ethernet PHY/SONET-SDH
Ethernet Transport
Ethernet P2P, P2MP Segment
Ethernet Path (PE-to-PE) Append S-VID to Ethernet frames
IP, IP/MPLS, etc.
Ethernet PHY/SONET-SDH
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Router
PWoMPLS LER
IP/MPLS
PW
ETH
MPLS
MPLS
DLL
IP/MPLS
ETH
IP/MPLS
ETH
MPLS LSR
Router
PWoMPLS LER
IP/MPLS
ETH+S-VID
IP/MPLS
ETH
IP/MPLS
ETH
Ethernet LSR
Ethernet (connectivity) Service
Ethernet Transport
Positioning ELS vs Ethernet PW over PSN (2)
MPLS Label Switching
VLAN label Switching
MPLS Label Switching
Same Ethernet MAC address
space
Disjoint Ethernet MAC address
spaces
ETH PHY
S-VID Label Switching
Frame forwarding independent of MAC
address
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Resolving the Ethernet Paradox
Ethernet Paradox Ethernet evolves as intra-domain aggregation technology for metro & core
networks (by better adapting transport to Ethernet as MPLS is adapted to IP)
Ethernet forwarding plane Ethernet switching technology e.g. ELS Moving Ethernet "networking" properties (linked to LAN / campus networks)
toward metro-aggregation networks - but also core - definitely transform intrinsic nature of Ethernet
Ethernet routing paradigm (control) use of unified control e.g. GMPLS
Consequences Ethernet control:
From distance vector routing protocol (spanning tree protocol) to link state routing protocol
As IP routing evolved from RIP (distance vector) to OSPF (link state) Ethernet forwarding:
Ethernet forwarding without specific mechanisms suitable/dedicated for LAN (campus, enterprise, etc.) environments
Mechanisms fitting specific needs of aggregation
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Router
IP/MPLS
Optical
ETH
IP/MPLS
ETH
IP/MPLS
ETH
Router
IP/MPLS
ETH+S-VID
IP/MPLS
ETH
IP/MPLS
ETH
Ethernet LSR
Ethernet (connectivity) between routers using OWS network
ELS and Architectural evolution: IP over Optics IP over Carrier Ethernet
Optical Switching
VLAN label Switching
Optical Switching
S-VID VLAN Label Switching (802.1ad)
Same Ethernet MAC address space + Same admin domain
Disjoint Ethernet MAC address
spaces+ Service boundary
ETH PHY
Ethernet (connectivity) between routers using carrier Ethernet switching network
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Architectural evolution: IP over Optics IP over Carrier Ethernet
IP routers traffic aggregation (level 1) networking (single peering point), IP fast re-routing (not MPLS), and multi-topology routing, and
BFD (OAM) Carrier Ethernet: robust, resilient, flexible and cost-effective traffic aggregation (level 2) Optical equipment/switching: (internal long distance) connectivity
IP router
Carrier Ethernet
Optical
Domain boundary
Long distance, Ethernet switch interconnection
Domain boundary IP router
ETH PHY ETH PHY ETH PHY
ETH PHY ETH PHY
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Tomorrow’s situation
< 5,5 km < 50 km < 100 km < O(100 km)
O(10) nodes
LargeCO
RegionalPOP
Ethernet aggregation
Ethernet metro switch
Core
Metro-Aggregation
Metro Access
First Mile
< 10 nodes
IP edge routers
CustomerPremises
IP Access router
IP Access router
SP1..i-1
SPi…n
Internet
Ethernet aggregation
Ethernet core switch
100GbE
100GbE
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Conclusion: Evolution of Ethernet control and forwarding paradigms
Forwarding component
control
Provisioning(TE data paths, re-routing, etc)
Management
Forwarding Plane Unified Ethernet Control (e.g. GMPLS)
The ultimate goal toward Carrier Ethernet …
Provisioning(Forwarding Components)
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Several issues for further investigation
Ethernet Forwarding Plane Ethernet label space and scalability ( Label/LSP merging ?) - specific
to link-local label switching based Ethernet forwarding Ethernet CoS mechanisms (DSCP to Ethernet PCP mapping DCP ?) -
common Ethernet multicast traffic (connectivity and adaptation) - common
Ethernet Control - common Unified traffic engineering (including fast re-routing) lighter protocol
suite(*) ? Adaptive traffic engineering and resource allocation including
Bandwidth Constraint Models (BCM) Lightweight measurement/monitoring capabilities including
performance
(*) fundamental issue: developing, deploying and operating metro Ethernet using unified
control must remain time-, resource- and cost-efficient (prevent over-engineering)
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