Technical White Paper for ATM-ETH IWF

Technical White Paper for ATM-ETH IWF

Huawei Technologies Co., Ltd.


Copyright ©2007 Huawei Technologies Co., Ltd. Copyrights Reserved ihttp://www.huawei.com/cn/products/datacomm/

Table of Contents

1 Foreword.............................................................................................................................1

2 Core Technology.................................................................................................................2

2.1 Concept of 1483B............................................................................................................ 2

2.2 Concept of IWF and the Implementation......................................................................... 2

2.3 ATM Network Migration Solution..................................................................................... 3

2.4 Implementation of IWF QoS ............................................................................................ 4

3 Typical Application ..............................................................................................................6

3.1 Access to a Single BRAS Through IWF CCC ................................................................. 6

3.2 Access to a Single BRAS Through IWF PW ................................................................... 6

3.3 Access to Dual BRAS through IWF VPLS....................................................................... 7

3.4 IWF Multicast Service Deployment.................................................................................. 8

4 Summary ............................................................................................................................8

Appendix A Abbreviation..........................................................................................................10


Copyright ©2007 Huawei Technologies Co., Ltd. Copyrights Reserved 1http://www.huawei.com/cn/products/datacomm/

Technical White Paper for ATM-ETH IWF Abstract: With the development of Ethernet, ATM access network is stepping towards

Ethernet. The routers with IWF feature provide a perfect solution for making full

use of existent ATM network and devices (ATM DSLAM, ATM Switch, etc.). It

helps ATM network intercommunicate with Ethernet smoothly through multiple

carrier methods such as CCC, PW and VPLS.

Keywords: IWF, CCC, PW, VPLS, BRAS, 1483B, QoS

1 Foreword

ATM has a long history. Over the past two decades, ATM network has been fully

developed. Due to its robust QoS capability, the existent ATM network has carried many

importance services, such as IP, Voice, conference call, ISDN/DSL and etc. However,

with the fast development of IP technologies, particularly the seamless combination of IP

technology and Ethernet technology, the future of ATM technology has been shadowed.

The limitations of ATM have been exposed, as follows:

Due to the cell tax of ATM, its transmission efficiency is rather low.

Due to the segmentation and reassembly (SAR) of ATM, the capacity of core

network has been confined greatly; OC-48 SAR has limited functions. The

existing ATM networks have the common interfaces of 622M and 155M, and it is

hard to see interfaces of 2.5G or above.

ATM cannot keep up with the increase of IP services, and it is poor in terms of

multicast. Therefore, it is hard to deploy new services, particularly the popular

Triple Play/IPTV services.

Building ATM network is very costly, and the maintenance of devices is also

complex.

IP and Ethernet technologies have been widely used in the world due to their good

compatibility and scalability, and it is inevitable for ATM network to evolve into IP network

and Ethernet work. However, such a change should be smooth and gradual to protect

customers’ interests and make full use of existent network and devices. Also, Ethernet

has to carry the traditional ATM services and make both ATM network and Ethernet

intercommunicate, evolving the services and protecting the investment.



2 Core Technology

2.1 Concept of 1483B

RFC 1483 (Updated 2684) defines the encapsulation format of multi-protocol packet over

AAL5, including routing PDU and bridging PDU, namely, 1483R routing and 1483B

bridging. 1483R routing includes PPPoA and IPoA, but it often refers to IPoA.

1483B bridging mainly uses Ethernet encapsulation format including PPPoEoA and

IPOEOA. RFC 1483 defines two types of encapsulation:

VC Based multiplexing: A VC is used to transmit only one protocol packet. The

user needs to specify the packet format of PVC packet that often refers to

VC_MUX encapsulation.

LLC Encapsulation: The protocol number carried in the header identifies the

protocol type. A VC can be used to transmit multiple protocol packets. A SNAP

header is appended behind the header. It is called SNAP encapsulation.

VC_MUX is of non-frame encapsulation format while SNAP is of frame encapsulation

format, as shown in the following figure:

VC_MUX

Encapsulation pTag PDU

0xAA 0xAA 3 0x000000

SNAP

Encapsulation pTag DSAP SSAP Ctrl OUI

Ether

TypePDU

1483B Encapsulation Format

ATM interface/sub-interface configured in bridged mode supports Layer 2 packet

broadcast and MAC address learning. 1483B can implement all services like Ethernet,

including transparently transmitting VLAN, Layer 2/Layer 3 forwarding, access VPLS and

access L3 VPN.

2.2 Concept of IWF and the Implementation

Inter-Working Function (IWF) means that the ATM packets are translated into Ethernet

packets through QinQ mapping between 1483B-based ATM link and Ethernet link; that is,

map the VPI of ATM packets to external VLAN Tag, and VCI to internal VLAN Tag, thus

implementing the transmission of ATM packets over Ethernet links.

The Ethernet packets after translation are often carried by L2VPN. According to different


Copyright ©2007 Huawei Technologies Co., Ltd. Copyrights Reserved 3

carrying methods, IWF has the following two methods:

Local CCC mode: implement the cross connection of circuit between an ATM

interface and Ethernet sub-interface of the same router.

CCC local connection

PW mode: LSP, GRE or TE tunnel helps implement transparent transmission of

data packets over ATM and Ethernet links between peer PE routers.

PW mode

2.3 ATM Network Migration Solution

For the migration of ATM access network to Ethernet, both IWF and 1483B L2 forwarding

schemes can help.

(1) 1483B Layer 2 forwarding scheme

VPI and VCI are mapped to one-layer VLAN tag which is used to mark the

information about ATM DSLAM, but the user information is lost. After the PPPoE

authentication packets reach BRAS, BRAS will authenticate them according to the

user account and the device information (one layer of VLAN tag); it has the risk of

account faking for users under the same ATM DSLAM device.

(2) IWF scheme

VPI and VCI are mapped to double tags. The inner tag and the outer tag identify ATM

DALAM device information and user information respectively. After PPPoE

authentication packet reaches BRAS, BRAS can authenticate based on user account,

device information (the outer tag) and user information (the inner tag). In this way,

account embezzlement can be avoided in terms of security.

http://www.huawei.com/cn/products/datacomm/



ATM network migration solution

For both solutions, they all use a router to terminate the ATM packets so as to transmit the

packets over Ethernet, but IWF features better security and scalability. So IWF provided

by routers is more suitable for migration of ATM network to Ethernet.

2.4 Implementation of IWF QoS

ATM features robust QoS with strict differentiated level of QoS. This point should be noted

in converting ATM packets to Ethernet packet by IWF.

1) When the packet is out of the interface, ATM interface at the egress supports the

mapping from 802.1P or DSCP to 802.1P/EXP/DSCP. QoS information (CLP) of

ATM is not mapped.

2) In the ATM interface at the ingress, 1483B packet as ATM cells enters PVC. ATM

CLP is obtained by mapping based on the upper layer priority and ATM CLP is

filled in the cell header.

ATM Service CLP EXP DSCP 802.1p Service

CBR 0 5 5 (EF) 5 Voice (media stream)

0 7 7 (CS7) 7 Control VC (routing protocols, signaling stream)

Rt-VBR

1 6 6 (CS6) 6 Control VC (routing protocols, signaling stream)




0 4 4 (AF4 green) 4 Video stream

1 3 4 (AF4 yellow) 3 Video stream

0 3 3 (AF3 green) 3 VPN traffic

1 2 3 (AF3 yellow) 2 VPN traffic

0 2 2 (AF2 green) 2 Bandwidth assurance, data stream

Nrt-VBR

1 1 2 (AF2 yellow) 1 Bandwidth assurance, data stream

0 1 (AF1 green) Common data stream ABR

1 1

1 (AF1 yellow) 1

Common data stream

0 UBR

1 0 0 (BE) 0 Common data stream

0 OAM cell

1 5 5 (EF) 5 --

ATM IP Mapping Relationship

EXP DSCP 802.1p CLP

7 7 (CS7) 7 0

6 6 (CS6) 6 0

5 5 (EF) 5 0

4 4 (AF4 green) 4 0

3 4– 3 (AF4 yellow) 3 1

2 (AF2 green) 2 0 2

2 (AF2 yellow) 2 1

1 1 (AF1) 1 1

0 0 (BE) 0 1

IP ATM Mapping Relationship



3 Typical Application

3.1 Access to a Single BRAS through IWF CCC

In local CCC mode, accessing ATM traffic from DSLAM, 1483B encapsulation-based

traffic on a router is cross connected to the Eth-link. VPI is mapped to the external VLAN

tag and VCI the internal VLAN tag. The packet is transmitted from Ethernet interface to

the remote BRAS device for authentication. The BRAS device differentiates DSLAM users

according to both VLAN tags.

Access to a single BRAS through IWF CCC

3.2 Access to a Single BRAS through IWF PW

1483B traffic of ATM access can be transparently transmitted to remote Eth link through

PW (L2VPN in Martini or Kompella mode). During the transparent transmission, VPI is

mapped to the outer tag and VCI the inner tag. BRAS device differentiates the DSLAM

users according to both VLAN tags of packets.

Access to a single BRAS through IWF PW




3.3 Access to Dual BRAS through IWF VPLS

If active/standby protection of BRAS is necessary in network migration, namely, ATM

DSLAM is connected to two BRASs, use the following VPLS schema. In the schema, the

reliability becomes the focus of the design.

Access to dual-BRAS through IWF VPLS

H-VPLS model is used in network access, and two PWs are set up between UPE

and PE-AGG, namely service PW and management PW.

The traffic of 1483B enters through ATM DSLAM; UPE maps the VPI/VCI to

QinQ, and then the QinQ is connected to service PW of VPLS; at last, the traffic

will be authenticated at the remote BRAS after transparent transmission. The

returned traffic determines QinQ by using VSI+MAC; UPE maps the QinQ to

VPI/VCI, and then the traffic is forwarded to ATM DSLAM.

BFD is enabled on the link between UPE and NPE; both NPEs run BFD for

VRRP; the active and standby state of VRRP controls the Layer 2 and Layer 3

services, and determines whether the external route advertised should be

cancelled or not.

The link protection between UPE and PE-AGG is carried out by TE protection

group and BFD for LSP, and the protection for node is implemented by BFD for

VRRP over mVSI and the BFD between UPE and NPE jointly.

BFD for VRRP detection packets are transmitted between the management

sub-interfaces of QinQ of both NPEs, and they are carried by management PW

between UPE and PE-AGG; during the active/standby switchover, Layer 3

services request the UPE to switch the link by sending free ARP packets in

relevant PWs; Layer 2 services delete the relevant forwarding entries in VSI

through free ARP packets in PW monitored by UPE, finishing the switchover.




3.4 IWF Multicast Service Deployment

IWF multicast service deployment

Users have more and more demands for multicast services with the development of IPTV.

Because ATM DSLAM is poor in supporting multicast, it is hard for ATM customers to

deploy IPTV services. In the migration from ATM network to Ethernet, if ATM customers

have the demand for IPTV, duplicate the multicast VLAN to the PVC of users at a router.

This requires the router supports IWF and IGMP Snooping, and the ATM PVC type should

be added to multicast FIB.

Generally, ATM DSLAM is connected to the upstream through 155M/622M, so the

bandwidth is limited for IPTV service stream, and only few users could get IPTV services.

During the interim of ATM network migration, it is a reasonable policy to control the

number of IPTV service users. It is not suggested to deploy a large amount of multicast

services on ATM access network, and the customers can access it through Ethernet if

necessary.

4 Summary

The migration of ATM access network to Ethernet is a smooth process, and the routers

with IWF feature provide a perfect solution. It does not only implement both

communication between ATM network and Ethernet, but also ensure the QoS of services;

also, it provides many flexible and competitive solutions of CCC, PW and VPLS, without

any influence on the interests and investments of customers.




At present, ATM access network is the main part of carrier networks. The ATM-ETH IWF

solution and the devices provided by Huawei can bring more value for you.



Appendix A Abbreviation

Abbreviations/Acronyms English Name

AAL5 ATM Adaptation Layer 5

BRAS Broadband Remote Access Server

PDU Packet Data Unit

IWF Inter-Working Function

ATM Asynchronous Transfer Mode

CCC Circuit Cross Connect

PW Pseudo Wire

VPLS Virtulal Private LAN Service

VPI Virtual Path Identifier

VCI Virtual Channel Identifier

VC Virtual Circuit

PVC Permanent Virtual Circuit

QoS Quality of Service

VLAN Virtual Local Area Network

VPN Virtual Private Network

VSI Virtual Switch Instance

VRRP Virtual Router Redundancy Protocol

LSP Label Switched Path

UPE User Provider Edge

NPE Network Provider Edge

BFD Bi-directional Forwarding Detection

Technical White Paper for ATM-ETH IWF

Documents

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iwf feature

frame encapsulation

external vlan

internal vlan

local ccc

existent atm