Network Working Group A. Farrel Internet-Draft Huawei Technologies Intended status: Informational H. Endo Expires: January 12, 2012 Hitachi, Ltd. R. Winter NEC Y. Koike NTT M. Paul Deutsch Telekom July 11, 2011 Handling MPLS-TP OAM Packets Targeted at Internal MIPs draft-farrel-mpls-tp-mip-mep-map-04 Abstract The Framework for Operations, Administration and Maintenance (OAM) within the MPLS Transport Profile (MPLS-TP) describes how Maintenance Entity Group Intermediate Points (MIPs) may be situated within network nodes at the incoming and outgoing interfaces. This document describes a way of forming OAM messages so that they can be targeted at MIPs on incoming or MIPs on outgoing interfaces, forwarded correctly through the "switch fabric", and handled efficiently in node implementations where there is no distinction between the incoming and outgoing MIP. The material in this document is provided for discussion within the MPLS-TP community in the expectation that this idea or some similar mechanism will be subsumed into a more general MPLS-TP OAM document. This document is a product of a joint Internet Engineering Task Force (IETF) / International Telecommunication Union Telecommunication Standardization Sector (ITU-T) effort to include an MPLS Transport Profile within the IETF MPLS and PWE3 architectures to support the capabilities and functionalities of a packet transport network. Status of this Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at http://datatracker.ietf.org/drafts/current/. Farrel, et al. Expires January 12, 2012 [Page 1] Internet-Draft Internal MIP Handling July 2011 Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." This Internet-Draft will expire on January 12, 2012. Copyright Notice Copyright (c) 2011 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Farrel, et al. Expires January 12, 2012 [Page 2] Internet-Draft Internal MIP Handling July 2011 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 2. Requirements notation . . . . . . . . . . . . . . . . . . . . 5 3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 6 4. Summary of the Problem Statement . . . . . . . . . . . . . . . 7 5. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 5.1. Rejected Partial Solution . . . . . . . . . . . . . . . . 12 6. Possible Solutions . . . . . . . . . . . . . . . . . . . . . . 14 6.1. ID-based Solution . . . . . . . . . . . . . . . . . . . . 14 6.2. Using an ACH reserved bit . . . . . . . . . . . . . . . . 15 7. Security Considerations . . . . . . . . . . . . . . . . . . . 17 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 18 9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 19 10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 20 10.1. Normative References . . . . . . . . . . . . . . . . . . . 20 10.2. Informative References . . . . . . . . . . . . . . . . . . 20 Appendix A. Previously considered solutions . . . . . . . . . . . 21 A.1. GAL TTL . . . . . . . . . . . . . . . . . . . . . . . . . 21 A.2. A separate channel type for the out-MIP . . . . . . . . . 21 A.3. Decrement TTL once per MIP . . . . . . . . . . . . . . . . 21 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 22 Farrel, et al. Expires January 12, 2012 [Page 3] Internet-Draft Internal MIP Handling July 2011 1. Introduction The Framework for Operations, Administration and Maintenance (OAM) within the MPLS Transport Profile (MPLS-TP)(the MPLS-TP OAM Framework, [I-D.ietf-mpls-tp-oam-framework]) distinguishes two configurations for Maintenance Entity Group Intermediate Points (MIPs) on a node. It defines per-node MIPs and per-interface MIPs, where a per-node MIP is a single MIP per node in an unspecified location within the node and per-interface MIPs are two (or more) MIPs per node on both sides of the forwarding engine. In-band OAM messages are sent using the Generic Associated Channel (G-ACh) [RFC5586]. OAM messages for the transit points of pseudowires (PWs) or Label Switched Paths (LSPs) are delivered using the expiration of the MPLS shim header time-to-live (TTL) field. OAM messages for the end points of PWs and LSPs are simply delivered as normal. OAM messages delivered to end points or transit points are distinguished from other (data) packets so that they can be processed as OAM. In LSPs, the mechanism used is the presence of the Generic Associated Channel Label (GAL) in the Label Stack Entry (LSE) under the top LSE [RFC5586]. In PWs, the mechanism used is the presence of the PW Associated Channel Header (PWACH) [RFC4385]. In case multiple MIPs are present on a single node, these mechanisms alone provide no way to address one particular MIP out of the set of MIPs. This document describes a way of forming OAM messages so that they can be targeted at incoming MIPs and outgoing MIPs, forwarded correctly through the "switch fabric", and handled efficiently in node implementations where there is no distinction between the incoming and outgoing MIP. The material in this document is provided for discussion within the MPLS-TP community in the expectation that this idea or some similar mechanisms will be subsumed into a more general MPLS-TP OAM document. This document is a product of a joint Internet Engineering Task Force (IETF)/International Telecommunication Union Telecommunication Standardization Sector (ITU-T) effort to include an MPLS Transport Profile within the IETF MPLS and PWE3 architecture to support the capabilities and functionalities of a packet transport network. Note that the acronym "OAM" is used in conformance with [RFC6291]. Farrel, et al. Expires January 12, 2012 [Page 4] Internet-Draft Internal MIP Handling July 2011 2. Requirements notation The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119]. Farrel, et al. Expires January 12, 2012 [Page 5] Internet-Draft Internal MIP Handling July 2011 3. Terminology In this document we use the term in-MIP (incoming MIP) to refer to the MIP which processes OAM messages before they pass through the forwarding engine of a node. An out-MIP (outgoing MIP) processes OAM messages after they have passed the forwarding engine of the node. The two together are referred to as internal MIPs. Farrel, et al. Expires January 12, 2012 [Page 6] Internet-Draft Internal MIP Handling July 2011 4. Summary of the Problem Statement Figure 1 shows an abstract functional representation of an MPLS-TP node. It is decomposed as an incoming interface, a cross-connect (XC), and an outgoing interface. As per the discussion in [I-D.ietf-mpls-tp-oam-framework], MIPs may be placed in each of the functional interface components. ------------------------ |----- -----| | MIP | | MIP | | | ---- | | ----->-| In |->-| XC |->-| Out |->---- | i/f | ---- | i/f | |----- -----| ------------------------ Figure 1: Abstract Functional Representation of an MPLS-TP Node Several distinct OAM functions are required within this architectural model such as: o CV between a MEP and a MIP o traceroute over an MPLS-TP LSP and/or an MPLS-TP PW containing MIPs o OAM control at a MIP o data-plane loopback at a MIP o diagnostic tests The MIPs in these OAM functions may equally be the MIPs at the incoming or outgoing interfaces. Per-interface MIPs have the advantage that they enable a more accurate localization and identification of faults and targeted performance monitoring or diagnostic test. In particular, the identification of whether a problem is located between nodes or on a particular node and where on that node is greatly enhanced. For obvious reasons, it is important to narrow the cause of a fault down quickly to initiate a timely, and well-directed maintenance action to resume normal network operation. The following two figures illustrate the fundamental difference of using per-node and per-interface MEPs and MIPs for OAM. Figure 2 depicts OAM using per-interface MIPs and MEPs. For reasons of Farrel, et al. Expires January 12, 2012 [Page 7] Internet-Draft Internal MIP Handling July 2011 exposition we assume that these are located on the incoming interfaces. Figure 3 on the other hand shows the same basic network but for OAM operations per-interface maintenance points are configured. Customer| Operator's administrative | Customer Domain | Domain | Domain ------> |<--------------------------------------->| <------ CE1 | PE1 P1 PE2 | CE2 | <--------> <--------> <--------> | +---+ | +-+ +-+ +-+ +-+ +-+ +-+ +-+ +-+ +-+ | +---+ | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | +---+ | +-+ +-+ +-+ +-+ +-+ +-+ +-+ +-+ +-+ | +---+ | In FW Out In FW Out In FW Out | | | FWD LSP | o-------------------------- > | | V-------------*-------------V | | MEP1 MIP1 MEP2 | BWD LSP | <---------------------------o | | V-------------*-------------V | | MEP1' MIP1' MEP2'| (S1)<============> (S2)<==========================> Figure 2: Example of OAM relying on per-node MIPs and MEPs To illustrate the difference between these two modes of operation, we use fault detection as an example. Consider the case where the client traffic between CE1 and CE2 experiences a fault. Also assume that an on-demand CV test between PE1 and PE2 was successful. The scenario in Figure 2 therefore leaves the forwarding engine(FW) of PE2, the out-going interface of PE2, the transmission line between PE2 and CE2 or CE2 itself as a potential location of the fault as on- demand CV can only be performed on segment S2. The per-interface model in Figure 3 allows more fine-grained OAM operations to be performed. At first, CV on segment S'4 and in addition CV on segment S'5 can help to rule out e.g. the forwarding engine of PE2. This is of course only a single example, and other OAM functions and scenarios are trivially conceivable. The basic message is that with the per-interface OAM model, an operator can configure smaller segments on a transport path to which OAM operations apply. This enables a more fine-grained scoping of OAM operations such as fault localization and performance monitoring Farrel, et al. Expires January 12, 2012 [Page 8] Internet-Draft Internal MIP Handling July 2011 which gives operators better information to deal with adverse networking conditions. Customer Operator's administrative Customer Domain Domain Domain ------->|<--------------------------------------->|<------ CE1 | PE1 P1 PE2 | CE2 | <--------> <--------> <--------> | +---+ | +-+ +-+ +-+ +-+ +-+ +-+ +-+ +-+ +-+ | +---+ | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | +---+ | +-+ +-+ +-+ +-+ +-+ +-+ +-+ +-+ +-+ | +---+ | In FW Out In FW Out In FW Out | | | FWD LSP | o-----------------------------------> | | V-------*------*------*-----*-------V | | MEP1 MIP1 MIP2 MIP3 MIP4 MEP2| | | BWD LSP | <-----------------------------------o | | MEP1' MIP1' MIP2' MIP3' MIP4' MEP2'| (S'1)<======> (S'2)<=============> (S'3)<====================> (S'4)<==========================> (S'5)<==================================> Figure 3: Example of OAM relying on per-interface MIPs and MEPs Farrel, et al. Expires January 12, 2012 [Page 9] Internet-Draft Internal MIP Handling July 2011 5. Overview In-band OAM messages are sent using the G-ACh [RFC5586] for MPLS-TP LSPs and MPLS-TP PWs, respectively. OAM messages for the transit points of PWs or LSPs are delivered using the expiration of the time- to-live (TTL) field in the top LSE of the MPLS packet header. OAM messages for the end points of PWs and LSPs are simply delivered as normal. OAM messages delivered to end points or transit points are distinguished from other (data) packets so that they can be processed as OAM. In LSPs, the mechanism used is the presence of the Generic Associated Channel Label (GAL) in the LSE under the top LSE [RFC5586]. In PWs, the mechanism used is the presence of the PW Associated Channel Header [RFC4385]. Any solution for sending OAM to the in and out-MIPs must fit within these existing models of handling OAM. Additionally, many MPLS-TP nodes contain an optimization such that all queuing and the forwarding function is performed at the incoming interface. The abstract functional representation of such a node is shown in Figure 4. As shown in the figure, the outgoing interfaces are minimal and for this reason it may not be possible to include MIP functions on those interfaces. This is in particular the case for existing deployed implementations. Any solution that attempts to send OAM to the outgoing interface of an MPLS-TP node must not cause any problems when such implementations are present. ------------------ |------------ | | MIP | | | ---- | | ----->-| In | XC | |-->--|->--- | i/f ---- | | |------------ | ------------------ Figure 4: Abstract Functional Representation of an Optimized MPLS-TP Node Lastly, OAM must operate on MPLS-TP nodes that are branch points on point-to-multipoint (P2MP) trees. That means that it must be possible to target individual outgoing MIPs as well as all outgoing MIPs in the abstract functional representation shown in Figure 5, as Farrel, et al. Expires January 12, 2012 [Page 10] Internet-Draft Internal MIP Handling July 2011 well as to handle the optimized P2MP node as shown in Figure 6. -------------------------- | -----| | | MIP | | ->-| |->---- | | | Out | | | | i/f | | | -----| |----- | -----| | MIP | ---- | | MIP | | | | |- | | ----->-| In |->-| XC |--->-| Out |->---- | i/f | | |- | i/f | |----- ---- | -----| | | -----| | | | MIP | | | | | | ->-| Out |->---- | | i/f | | -----| -------------------------- Figure 5: Abstract Functional Representation of an MPLS-TP Node Supporting P2MP ------------------ | ->-|->---- | | | |------------ | | | | | | | MIP ---- | | | | | | |- | ----->-| In | XC | |--->-|->---- | i/f | | |- | | ---- | | | | | | | |------------ | | | | | | ->-|->---- ------------------ Figure 6: Abstract Functional Representation of an Optimized MPLS-TP Node Supporting P2MP In summary, the solution for OAM message delivery must support the Farrel, et al. Expires January 12, 2012 [Page 11] Internet-Draft Internal MIP Handling July 2011 following features: o Forwarding of OAM packets exactly as data packets. o Delivery of OAM messages to the correct MPLS-TP node. o Direction of OAM instructions to the correct MIP within an MPLS-TP node. o Packet inspection at the incoming and outgoing interfaces must be minimized. Note that although this issue appears superficially to be an implementation matter local to an individual node, the format of the message needs to be standardised so that: o An upstream MEP can correctly target the outgoing MIP of a specific MPLS-TP node. o A downstream node can correctly filter out any OAM messages that were intended for its upstream neighbor's outgoing MIP, but which were not handled there because the upstream neighbor is an optimized implementation. Note that the last bullet point describes a safety net and an implementation should avoid that this situation ever arises. 5.1. Rejected Partial Solution A reject solution is depicted in Figure 7. All data and non-local OAM is handled as normal. Local OAM is intercepted at the incoming interface and delivered to the MIP at the incoming interface. If the OAM is intended for the incoming MIP it is handled there with no issue. If the OAM is intended for the outgoing MIP it is forwarded to that MIP using some internal messaging system that is implementation-specific. ------------------------ |----- -----| local OAM ----->-| MIP |----->------| MIP | | | ---- | | data =====>=| In |=>=| XC |=>=| Out |=>==== data non-local OAM ~~~~~>~| i/f |~>~| |~>~| i/f |~>~~~~ non-local OAM |----- ---- -----| ------------------------ Figure 7: OAM Control Message Delivery Bypassing the Switching Fabric Farrel, et al. Expires January 12, 2012 [Page 12] Internet-Draft Internal MIP Handling July 2011 This solution is fully functional for the incoming MIP. It also supports control of data loopback for the outgoing MIP, and can adequately perform some OAM features such as interface identity reporting at the outgoing MIP. However, because the OAM message is not forwarded through the switch fabric, this solution cannot correctly perform OAM loopback, connectivity verification, LSP tracing, or performance measurement. Farrel, et al. Expires January 12, 2012 [Page 13] Internet-Draft Internal MIP Handling July 2011 6. Possible Solutions We briefly present here a number of possible solutions to the problem outlined so far with the hope that the WG will quickly converge towards adopting one of them. The appendix of this document already contains a few solutions that the authors have discarded which have been left in the document for informational purposes. 6.1. ID-based Solution An ID-based solution leverages existing identification information in OAM messages. OAM solutions therefore need to individually make sure that enough of that information is present to support the per- interface model. In particular, the MIP identifiers as described in [I-D.ietf-mpls-tp-identifiers] need to be present in OAM messages. [I-D.ietf-mpls-tp-identifiers] defines a format that supports the per-interface model which is sufficient for this purpose. In addition, some constraints must be agreed on. From a requirements-perspective this means: o Forwarding of OAM packets exactly as data packets - This way of internal-MIP addressing has no implications on the way data packets and non-local OAM packets are handled. The TTL processing remains untouched. This also means that the TTL will expire on the ingress. o Delivery of OAM messages to the correct MPLS-TP node - The TTL addresses the node. o Direction of OAM instructions to the correct MIP within an MPLS-TP node - The ID information containted in the OAM packet is used to tell whether the packet is for the in or out-MIP. o Packet inspection at the incoming and outgoing interfaces must be minimized - packet inspection becomes a bit more complicated since the required information can be in different places for different types of OAM. o An upstream MEP can correctly target the outgoing MIP of a specific MPLS-TP node - this is simple as the TTL addresses the node and the ID information in the packet addresses the respective MIP. o A downstream node can correctly filter out any OAM messages that were intended for its upstream neighbor's outgoing MIP, but which were not handled there because the upstream neighbor is an optimized (legacy) implementation - OAM messages expire on the Farrel, et al. Expires January 12, 2012 [Page 14] Internet-Draft Internal MIP Handling July 2011 ingress so the legacy upstream neighbor will process the packet. Since the ID information is not correct, the node will discard the packet. Leakage should therefore not occur. 6.2. Using an ACH reserved bit The ACH contains eight reserved bits which currently all need to be set to zero and ignored on reception. One bit could be reserved as an out-MIP address flag. In other words, in case the bit is set, the out-MIP is addressed. An advantage of this approach is that there is no semantic overlap with anything that exists today, as the bits are not in use. Existing implementations need to ignore it. That means that existing implementations will process the OAM packets at the in- MIP/per-node MIP. From a requirements-perspective this means: o Forwarding of OAM packets exactly as data packets - This way of internal-MIP addressing has no implications on the way data packets and non-local OAM packets are handled. The TTL processing remains untouched. o Delivery of OAM messages to the correct MPLS-TP node - The TTL addresses the node. o Direction of OAM instructions to the correct MIP within an MPLS-TP node - The newly defined bit addresses the correct place within the node (0 = in-MIP and 1 = out-MIP). o Packet inspection at the incoming and outgoing interfaces must be minimized - packet inspection requires to check an additional bit, which however is at a fixed location. o An upstream MEP can correctly target the outgoing MIP of a specific MPLS-TP node - this is simple as the TTL addresses the node and the new flag indicates the place within the node. o A downstream node can correctly filter out any OAM messages that were intended for its upstream neighbor's outgoing MIP, but which were not handled there because the upstream neighbor is an optimized (legacy) implementation - Since the TTL will expire on the node the message will be processed by it. Since it is not targeted at that MIP, it will discard it. Farrel, et al. Expires January 12, 2012 [Page 15] Internet-Draft Internal MIP Handling July 2011 ------------------------ |----- -----| | MIP | ---- | MIP | ----->-| In |->-| XC |->-| Out |->---- | i/f | ---- | i/f | |----- -----| ------------------------ ----------------- in-MIP | Label=x | TTL=0 |--- OAM |-----------------| | | GAL | TTL=m | | |-----------------| | | ACH res bit x=0 | | ----------------- | <------ ----------------- ----------------- out-MIP | Label=x | TTL=0 |--------------->| Label=y | TTL=0 |--- OAM |-----------------| |-----------------| | | GAL | TTL=m | | GAL | TTL=m | | |-----------------| |-----------------| | | ACH res bit x=1 | | ACH res bit x=1 | | ----------------- ----------------- | <------- Figure 8: Packet Formats for in and out-MIP OAM (for LSPs) Farrel, et al. Expires January 12, 2012 [Page 16] Internet-Draft Internal MIP Handling July 2011 7. Security Considerations OAM security is discussed in [I-D.ietf-mpls-tp-oam-framework] and [I-D.manral-mpls-tp-oam-security-tlv]. OAM can provide useful information for detecting and tracing security attacks. OAM can also be used to illicitly gather information or for denial of service attacks and other types of attack. Implementations therefore are required to offer security mechanisms for OAM. Deployments are strongly advised to use such mechanisms. Mixing of per-node and per-interface OAM on a single node is not advised as OAM message leakage could be the result. Farrel, et al. Expires January 12, 2012 [Page 17] Internet-Draft Internal MIP Handling July 2011 8. IANA Considerations This revision of this document does not make any requests of IANA. Farrel, et al. Expires January 12, 2012 [Page 18] Internet-Draft Internal MIP Handling July 2011 9. Acknowledgments The authors gratefully acknowledge the substantial contributions of Zhenlong Cui. We would also like to thank Eric Gray and Sami Boutros for interesting input to this document through discussions. Farrel, et al. Expires January 12, 2012 [Page 19] Internet-Draft Internal MIP Handling July 2011 10. References 10.1. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC4385] Bryant, S., Swallow, G., Martini, L., and D. McPherson, "Pseudowire Emulation Edge-to-Edge (PWE3) Control Word for Use over an MPLS PSN", RFC 4385, February 2006. [RFC5586] Bocci, M., Vigoureux, M., and S. Bryant, "MPLS Generic Associated Channel", RFC 5586, June 2009. 10.2. Informative References [I-D.ietf-mpls-tp-identifiers] Bocci, M., Swallow, G., and E. Gray, "MPLS-TP Identifiers", draft-ietf-mpls-tp-identifiers-06 (work in progress), June 2011. [I-D.ietf-mpls-tp-oam-framework] Allan, D., Busi, I., Niven-Jenkins, B., Fulignoli, A., Hernandez-Valencia, E., Levrau, L., Sestito, V., Sprecher, N., Helvoort, H., Vigoureux, M., Weingarten, Y., and R. Winter, "Operations, Administration and Maintenance Framework for MPLS-based Transport Networks", draft-ietf-mpls-tp-oam-framework-11 (work in progress), February 2011. [I-D.manral-mpls-tp-oam-security-tlv] Manral, V., "MPLS-TP General Authentication TLV for G-ACH", draft-manral-mpls-tp-oam-security-tlv-00 (work in progress), June 2009. [RFC6291] Andersson, L., van Helvoort, H., Bonica, R., Romascanu, D., and S. Mansfield, "Guidelines for the Use of the "OAM" Acronym in the IETF", BCP 161, RFC 6291, June 2011. Farrel, et al. Expires January 12, 2012 [Page 20] Internet-Draft Internal MIP Handling July 2011 Appendix A. Previously considered solutions A.1. GAL TTL The use of the GAL TTL has been considered before. This transforms the GAL TTL into some kind of node-internal TTL, i.e. a GAL TTL of 0 would address the in-MIP and a GAL TTL of 1 the out-MIP. The main drawback of this approach is that it (as of now at least) would only be applicable to LSPs and not to PWs. A.2. A separate channel type for the out-MIP This approach would require two channel types for the exact same OAM type, one to address the in-MIP and another one to address the out- MIP. This seems like a waste of channel types, however it appears that there is no expected shortage of them. Legacy nodes will discard the packets as the new channel types are unkonwn. Having two channel types for the same OAM however feels a bit hacky. A.3. Decrement TTL once per MIP Decrementing the TTL more than once per node seems a "natural" way of per-interface MIP addressing since TTL expiry is all that is needed for the per-node MIP case. In other words, by decrementing the TTL once per MIP (twice per node) no extra mechanism is needed to solve the internal MIP addressing problem. The solution has been discarded since it does not represent the typical mode of network operation today (since also for normal data packets the TTL needs to be decremented more than once). Farrel, et al. Expires January 12, 2012 [Page 21] Internet-Draft Internal MIP Handling July 2011 Authors' Addresses Adrian Farrel Huawei Technologies Email: adrian.farrel@huawei.com Hideki Endo Hitachi, Ltd. Email: hideki.endo.es@hitachi.com Rolf Winter NEC Email: rolf.winter@neclab.eu Yoshinori Koike NTT Email: koike.yoshinori@lab.ntt.co.jp Manuel Paul Deutsch Telekom Email: Manuel.Paul@telekom.de Farrel, et al. Expires January 12, 2012 [Page 22]