technical white paper for atm-eth iwf
TRANSCRIPT
Technical White Paper for ATM-ETH IWF
Huawei Technologies Co., Ltd.
Technical White Paper for ATM-ETH IWF
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
Technical White Paper for ATM-ETH IWF
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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.
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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
Technical White Paper for ATM-ETH IWF
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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.
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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)
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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
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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
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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.
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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.
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Technical White Paper for ATM-ETH IWF
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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.
Technical White Paper for ATM-ETH IWF
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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