Multi-segment Pseudowires in Passive Optical Networks

Ruobin Zheng, robin@huawei.com Hongyu Li, lihy@huawei.com

•  Objective

•  MPLS to Access and Challenges

•  PW support in GPON systems

•  Summary

Contents

Page 3

Objective

  The objective of this draft is to provide the information of PW support in current GPON systems for mobile backhaul. �

Page 4

Scenario of GPON for 2G and 3G mobile backhaul

  According to the Technical Specification of “MPLS in Mobile Backhaul Networks Framework and Requirements” from IP/MPLS Forum 20.0.0, GPON is considered as a alternative for 2G and 3G mobile backhaul.

  With PW extension to ONU, e2e MPLS tunnel can be built between CSG and MASG for mobile backhaul.

  OLT don’t need to be aware of TDM/ATM/SDH services and don’t need to support physical interfaces of E1/T1, NxDS0, POS/SDH, ATM, …

HDLC TNL

HDLC TNL

Mobile Aggregation Site Gateway

IP TNL

ATM TNL TDM TNL

IP TNL

ATM TNL

TDM TNL

Aggregation network

BS

Access network

xDSL, microwave,

Leased Line, GPON,

Pt-to-pt fiber

Access Node

Cell Site Gateway

Edge Node

IP/MPLS Core

mobile networ

k

Iur/R3

Abis A

Iub

Iub/R6/R2

Iub

Radio Contoller

Iu-CS Iu-PS

MPLS transport network

Gb Iu-PS

Iu-CS A Gb Abis MSC 3G

SGSN 3G SGSN 2G

MSC 2G

Abis Abis

Edge Node

Edge Node

Edge Node

Iub/R6/R2

R3 CSN WiMAX

R3

Source from “IP/MPLS Forum 20.0.0” �MPLS “edge”

Page 5

  Complexity   ONU is very cost-sensitive to routing protocols and dynamic label allocation

  Is routing protocol necessary in GPON?

  Provisioning difficulties

  When MS-PW is implemented in a PON, there may be a very large number of PW T-PEs. If PW labels on ONUs are

provision d by NMS directly, it requires a network manager touching each ONU once for each PW, and there may be

very many PWs. This makes provisioning a heavy burden for the network manager.

  Additionally, there must be a concern that the configuration at the ONU and the OLT will be inconsistent because for

any PW, both the ONU and the OLT must be configured.

  ONTs may not be able to support SNMP.

Challenges for MPLS to GPON for mobile backhaul

3G core

RNC Node B

Native MPLS

MPLS “edge”

IP node

Routing

LSP label allocation

ISIS or OSPF

LDP LDP

PE P PE

PW label allocation targeted LDP

LDP

ISIS or OSPF

P

MS-PW

LDP

ISIS or OSPF

OLT ONU

IP static route RIPv2

  Native MPLS requires IP routing and routers

everywhere �

S-PE

Page 6

PHY

MPLS backbone

BS CSG

ONU S-PE

Access Metro/Core

TDM/ATM/ETH

PW

GEM

PW

MPLS MPLS LSP

LINK

GEM port

PHY

GEM

PHY

MPLS

LINK

PHY PHY

PW

OLT

GEM port Spoke MPLS Hub

Network reference model for MS-PW over GPON

PW

  Network is partitioned into access segments and Metro/Core segments in a hub & spoke topology.   The OLT is recommended as a S-PE so that PWs can be optimized within each segments. “PW over GEM” is

recommended as per ITU-T G.984.3 in access segments providing generic transport of TDM/ATM/ETH traffic.   All PW segments are of the same technology, which is packet encapsulated. It is only the tunneling technology

that changes at the S-PE. �

Page 7

MS-PW ONU AR(OLT)

IP node

3G core

RNC Node B

MASG

Routing

LSP label allocation

ISIS or OSPF

OMCI LDP

T-PE P T-PE

PW label allocation targeted LDP

LDP

ISIS or OSPF

P S-PE

LDP

OMCI

  Simplify MPLS /PW operation in GPON by introducing semi-static configuration using extensions to

OMCI as per G.988   No routing protocol and dynamic label

allocation protocol needed in the access network �

MS-PW over GPON

ISIS or OSPF

PWE3/MPLS “edge”

Label Provisioning for PW over GPON

  The ONT management and control interface (OMCI) is a management channel between the OLT and the ONUs.

  G.984.4 and G.988 extends the functions that can be configured using OMCI to include MPLS and MPLS PW termination points at an ONT. This allows seamless integration of MPLS and MPLS PW services with a PON.

  Making use of a GPON management protocol (OMCI) helps to   reduce the labor of configuration   simplify and speed up the PW provision procedure to a great extent   avoid the potential inconsistence or mismatch between ONUs and OLT   notify to S-PE (which is the OLT) of the status of the AC at the T-PE (which is the ONU).

  It can be applied when SNMP is not support by ONTs.

Page 8

  There is a trend that operators are deploying MPLS and PWE3 in access networks, especially

in an access network of G-PON or NG-GPON.   However, IP routing and routing protocol challenge the scalability and complexity of the

access network (e.g. PON).   With OMCI for PW operation and PW over GPON, no need for full IP/MPLS stack in GPON

ONUs. Thus keep PON simple and cost-effective.

Summary

PON

Access router (OLT)

NG-GPON

ONU

MPLS edge

Aggregation network � MPLS in GPON

BS BS

Data Plane

PW over GPON for multiple services

Management Plane

OMCI for label provisioning

Thank you

Page 10

  G.984.4 and G.988 extends the functions that can be configured using OMCI to include MPLS and MPLS PW termination points at an ONT. This allows seamless integration of MPLS and MPLS PW services with a PON.

Dynamic Control Plane of native MPLS

PE Auto-Discovery

Signaling for PW

VPN

Pro

toco

ls

T-LDP

BGP-AD

Signaling for LSP

Multicast signaling

Tunn

el L

SP P

roto

cols

Topology Discovery

Physical links Ethernet, etc.

mLDP or PIM

LDP

IGP(ISIS/OSPF)

Node Registration

Semi-static PW configuration

Semi-static LSP configuration

Tree Topology

Physical links

PON or Eth. OMCI

Semi-static Label Provisioning

One Simplification

for all

One Simplification for All The ONT management and control interface (OMCI) is a management channel between the OLT and the ONUs that supports Ethernet, equipment, subscriber interface, and subscriber feature management.

OMCI specifies the managed entities of a protocol-independent management information base (MIB) module that models the resources and services in an ONU. Through standardized OMCI signalling, OLT builds up its management bonds with ONUs automatically.

OMCI is standardized in G.984.4 and G.988.

Page 11

SNMP-based Provisioning vs. OMCI-based Provisioning   Problems of SNMP-based provisioning

  When MS-PW is implemented in a PON, there may be a very large number of PW T-PEs. If PW labels on ONUs are provision d by NMS directly, it requires a network manager touching

each ONU once for each PW, and there may be very many PWs. This makes provisioning a heavy burden for the network manager.

  Additionally, there must be a concern that the configuration at the ONU and the OLT will be inconsistent because for any PW, both the ONU and the OLT must be configured.

  ONTs may not be able to support SNMP.   Benefit of OMCI-based provisioning

  reduce the labor of configuration   simplify and speed up the PW provision procedure to a great extent

  When using OMCI to provision PWs on ONU, the network manager only needs to send all configurations to the OLT, which will send all parameters to ONUs automatically through OMCI. There is no need to touch each ONU.

  avoid the potential inconsistence or mismatch between ONUs and OLT   Through standardized OMCI signalling, OLT builds up its management bonds with ONUs

automatically.   OMCI can act as a signaling mechanism between ONU and OLT, which enables the ONU to

notify AC status to OLT.   It can be applied when SNMP is not support by ONTs.

Page 12

Multi-service support in GPON systems

•  Multi-service support means multiple transport modes in current GPON system. •  high OPEX: operational difficulty and management complexity •  high cost of access router (NG-OLT) with a whole bunch of physical interfaces: E1/T1, NxDS0, POS/SDH, ATM, ETH …

GPON MAC

SDH ETH IP MPLS TDM

GEM GEM GEM GEM GEM

Service layer ATM

GEM

TDM

PW

ATM Service layer ETH …

GEM GPON MAC

•  The trend is that PW layer functions as an uniform transport layer for multiple services. •  OMCI is extended for semi-static configuration of PWs. •  It can greatly reduce the operational difficulty and management complexity and keeps ONU simple and cost-effective.