Optical + Ethernet: Converging the Transport Network An Overview.

Optical + Ethernet:Converging the Transport Network

An Overview

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Trends

R&E Optical Networks Locally-managed fiber termination points Locally-organized peering relationships Locally-controlled layer-0/1/2 services

Ubiquitous Ethernet Most-requested client service interface Both point-to-point and virtual-LAN topologies Apps consuming bandwidth in Ethernet-sized increments

Unit of provisioning 100/1000/10000Mbps

Options: L2 WAN, Pseudowires, Converged


L2 WAN

Classical Bridged Network Transparent handoff to optical transponders Switches establish topology at L2

Deployment issues are many Wide-area spanning tree, ugh Limited VLAN tag space, or go 802.1ad/ah No Traffic Engineering, at mercy of STP

= L2 switch, 802.1q/ad/ah

= OADM, transponding only

= Ethernet service

Optical Core


Pseudowires

L2 Pseudowires over IP/MPLS Core Ethernet encapsulated in IP at PE routers Transport via IP/MPLS core, over optical WAN

VPLS-enabled Control Plane Full mesh of MPLS LSPs, PE-to-PE BGP/LDP assigns 802.1q flows to LSPs Optical layer setup manually or via GMPLS

= Multi-tenant unit (MTU)

= OADM, transponding only

= Ethernet service

IP/MPLS/Optical

= PE routers, MPLS + 802.1Q


Pseudowires (cont’d)

Benefits If IP/MPLS already built out, service type is additive

Update IP/MPLS PEs and MTUs with VPLS functionality; software for signaling, possible fw/hw for L2-in-IP encapsulation

Issues Several distinct control mechanisms

Manual or GMPLS control plane in optical transport IP/MPLS between PEs to establish full mesh of tunnels LDP/BGP between PE client ports, to map pseudowires to tunnels

Management complexity How to coordinate indications/actions/repairs across mechanisms?

Multiple encapsulations Ethernet, into IP, into perhaps something else, into optical, and out again

Many moving parts Control planes are complex enough, without having three of them


Converged

Converged Optical + Ethernet OADMs are adding L2 functionality Ethernet client interface, Optical transport

Unified Control Method Optical service established via GMPLS L2 tunnel within Optical service, also

established via GMPLS (PBB-TE/GELS)

= OADM + 802.1q/1ad/1ah

= Ethernet service

Optical Core

= Multi-tenant unit (MTU)


PBB-TE / GELS

GMPLS Control Plane for Ethernet Ethernet as just another transport technology

VLAN or VLAN+MAC becomes the GMPLS “label” Labels identify end-to-end path, distributed via signaling Ethernet services become regular GMPLS tunnels

Integrates Ethernet into GMPLS management framework Same tools (routing, signaling, pce) used by optical GMPLS Eliminates need for other control mechanisms (RSTP, etc)

Benefits Traffic Engineering for Ethernet – explicit control over path Unified Control – eases coordination among layers Automation – 802.1ad/ah forwarding tables populated via signaling

rather than manually

Two methods: “short-label” and “long-label”


“Short Label”

Hardware Optical DWDM transport L2-aware client interfaces

Able to switch L2 frames between ports Able to swap VLAN tags when transiting ports

Control Plane Optical tunnels setup via GMPLS; label is Lambda L2 tunnels also setup via GMPLS; label is VLAN tag

VLAN tag changes along service path – unique per-link only

OADM+L2

OADM+L2OADM+L2

OADM+L2

OADM+L2 OADM+L2

= Optical LSP, lambda A

= Optical LSP, lambda B

VLAN tag X

= L2 LSP, VLAN X

= L2 LSP, VLAN Y + Z

VLAN tag Y VLAN tag Z

= swap Y for Z

= add/remove VLAN


“Long Label”

Hardware Optical DWDM transport “L2-aware” client interfaces

Able to switch L2 frames between ports Able to encapsulate MAC-in-MAC (802.1ah)

Control Plane Optical tunnel setup via GMPLS; label is Lambda L2 tunnel also setup via GMPLS; label is VLAN + MAC

Local L2 forwarding tables provisioned with VLAN + MAC

OADM+L2

OADM+L2OADM+L2

OADM+L2

OADM+L2 OADM+L2

= Optical LSP, lambda A

= Optical LSP, lambda B

VLAN tag X

= L2 LSP, VLAN X + MAC A

= L2 LSP, VLAN Y + MAC B

VLAN tag Y

= forward per VLAN + MAC

MAC B

= add/remove VLAN + MAC

MAC A


Converged Approach

Benefits Fewer moving parts

Single element with optical transport and L2 capability Native transport for most-requested traffic

Single, unified control mechanism across all layers Unified control via GMPLS

Coexistence with existing 802.nnn infrastructure No dataplane changes for long-label; ships-in-the-night with regular PBB

Traffic Engineering for Ethernet services Explicit control over path taken; usual benefits

New deployments achieve greatest benefit; existing IP/MPLS less so

Issues Short label requires VLAN tag swapping

Older switches may not be capable of doing this Long label requires carrying 8-byte label in GMPLS signaling

Most implementations carry a 4-byte label; software only


Protocol Details

Signaling L2 Labels Define short-label, long-label formats Update label-related protocols objects in RSVP-TE:

Generalized Label, Label Request, Upstream Label, Suggested Label, Acceptable Label Set, Explicit Route, Record Route

TE Routing L2 Labels Advertise L2 Label availability into OSPF-TE

Range of available VLAN tags (short-label) VLAN+MAC pairs (long-label); under discussion

Hierarchical LSP setup Lambda LSP setup establishes optical service Lambda LSP forms L2SC FA-LSP, populates L2 TE database L2 LSP paths computed on L2 TE database, established thru FA-LSP


References

IEEE 802.1d – STP/RSTP (2004) 802.1q – VLAN 802.1s – Multi-STP 802.1ad – PB (Q-in-Q) 802.1ah – PBB (MAC-in-MAC) PBB-TE – under discussion

IETF draft-fedyk-gmpls-ethernet-pbt-01 (GELS)

Thank You

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Optical + Ethernet: Converging the Transport Network An Overview.

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