PCE Working Group D. Dhody Internet-Draft U. Palle Intended status: Standards Track Huawei Technologies India Pvt Ltd Expires: March 4, 2012 Sept 2011 OSPF Protocol Extensions for Boundary Node Discovery (BND) draft-dhody-pce-bn-discovery-ospf-03 Abstract There are various circumstances where it is highly desirable to be able to dynamically and automatically discover a set of Boundary Nodes (BN) along with their domain information. For that purpose, this document defines extensions to the Open Shortest Path First (OSPF) routing protocol for the advertisement of Boundary Node (BN) Discovery information within an OSPF area or within the entire OSPF routing domain. Status of This Memo This Internet-Draft is submitted to IETF in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. 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." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on March 4, 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 Dhody & Palle Expires March 4, 2012 [Page 1] Internet-Draft OSPF BND Sept 2011 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 BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 3. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 3.1. Boundary Node (BN) Discovery Information . . . . . . . . . 4 3.2. Flooding Scope . . . . . . . . . . . . . . . . . . . . . . 4 4. Applications . . . . . . . . . . . . . . . . . . . . . . . . . 5 5. Existing Mechanisms . . . . . . . . . . . . . . . . . . . . . 7 5.1. OSPF LSA . . . . . . . . . . . . . . . . . . . . . . . . . 7 5.2. Inter-AS TE Link . . . . . . . . . . . . . . . . . . . . . 7 5.3. OSPF Area Topology . . . . . . . . . . . . . . . . . . . . 9 5.4. HPCE . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 6. Static Configurations . . . . . . . . . . . . . . . . . . . . 9 7. Importance of Domain Information along with BNs . . . . . . . 9 8. Relationship to Domain-Sequence . . . . . . . . . . . . . . . 10 9. The OSPF BND TLV . . . . . . . . . . . . . . . . . . . . . . . 10 9.1. BN-ADDRESS Sub-TLV . . . . . . . . . . . . . . . . . . . . 11 9.2. BN-DOMAIN Sub-TLV . . . . . . . . . . . . . . . . . . . . 12 10. Elements of Procedure . . . . . . . . . . . . . . . . . . . . 12 11. Backward Compatibility . . . . . . . . . . . . . . . . . . . . 13 12. Impact on Network . . . . . . . . . . . . . . . . . . . . . . 14 13. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14 13.1. OSPF TLV . . . . . . . . . . . . . . . . . . . . . . . . . 14 14. Security Considerations . . . . . . . . . . . . . . . . . . . 14 15. Manageability Considerations . . . . . . . . . . . . . . . . . 14 16. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 14 17. References . . . . . . . . . . . . . . . . . . . . . . . . . . 15 17.1. Normative References . . . . . . . . . . . . . . . . . . . 15 17.2. Informative References . . . . . . . . . . . . . . . . . . 15 Dhody & Palle Expires March 4, 2012 [Page 2] Internet-Draft OSPF BND Sept 2011 1. Introduction This document defines extensions to OSPFv2 [RFC2328] and OSPFv3 [RFC5340] to allow a boundary node in an OSPF routing domain to advertise its location, along with domain information. Generic capability advertisement mechanisms for OSPF are defined in [RFC4970]. These allow a router to advertise its capabilities within an OSPF area or an entire OSPF routing domain. This document leverages this generic capability advertisement mechanism to fully satisfy the dynamic BN discovery. This document defines a new TLV (named the Boundary Node Discovery TLV (BND TLV)) to be carried within the OSPF Router Information LSA ([RFC4970]). The Boundary Node information advertised is detailed in Section 3. Protocol extensions and procedures are defined in Sections 6 and 7. The OSPF extensions defined in this document allow for Boundary Node discovery within an OSPF routing domain. Boundary Node can be an ABR or ASBR. 1.1. Requirements Language 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. 2. Terminology The following terminology is used in this document. ABR: OSPF Area Border Router. Routers used to connect two IGP areas. AS: Autonomous System. ASBR: Autonomous System Border Router. Router used to connect together ASes of the same or different service providers via one or more inter-AS links BN: A boundary node is either an ABR in the context of inter-area Traffic Engineering or an ASBR in the context of inter-AS Traffic Engineering. Dhody & Palle Expires March 4, 2012 [Page 3] Internet-Draft OSPF BND Sept 2011 BND: Boundary Node Discovery BRPC: Backward Recursive Path Computation Domain: Any collection of network elements within a common sphere of address management or path computational responsibility. Examples of domains include Interior Gateway Protocol (IGP) areas and Autonomous Systems (ASs). IGP: Interior Gateway Protocol. Either of the two routing protocols, Open Shortest Path First (OSPF) or Intermediate System to Intermediate System (IS-IS). LSA: Link State Advertisement. OSPF: Open Shortest Path First. PCE: Path Computation Element. An entity (component, application, or network node) that is capable of computing a network path or route based on a network graph and applying computational constraints. TLV: Type-Length-Variable data encoding. 3. Overview 3.1. Boundary Node (BN) Discovery Information The BN discovery information is composed of: o The BN location: an IPv4 and/or IPv6 address that is used to reach the BN. It is RECOMMENDED to use an address that is always reachable from all connected domains; o The set of two or more Domain(s) into which the BN has connectivity; Changes in BN discovery information may occur as a result of BN configuration update or domain status change. 3.2. Flooding Scope The flooding scope for BN information advertised through OSPF can be limited to OSPF area(s) the BN belongs to, or can be extended across the entire OSPF routing domain. Dhody & Palle Expires March 4, 2012 [Page 4] Internet-Draft OSPF BND Sept 2011 4. Applications BRPC procedure as defined in [RFC5441], requires Path Computation Element (PCE)[RFC4655] to be aware of the BNs for the inter-domain path computation. As shown in the figure 1, Incase of OSPF Area0, configuration of BNs at PCE5 is extensive. BRPC procedure guarantees a best path only if BNs are selected correctly, any change in BNs at run time may lead to sub-optimal path. Also Administrator need to configure ABR / ASBR ID in such a way that it is reachable from all the domains, BND Tlv can take care of this automatically. Dhody & Palle Expires March 4, 2012 [Page 5] Internet-Draft OSPF BND Sept 2011 +--------------------+ | +-----+| | Area 2 | PCE2|| | +-----+| | | | | | BN4+----+ | +--------+----+------+ +----------+----+---------+ | +----+ | | | | | | | +---------------+ | |+----------------+ | BN1 | | || BN5 | | +-+-++ +++--+ | | | | || ||| | | | +-+-++ +++--+ | | | | || | | BN2 | | || BN6 | | +-+-++ Area 0 +++--+ | | Area 1 | | || ||| | Area 3 | | +-+-++ +++--+ | | | | || | | BN3 | | +-----+ || BN7 | |+-----+ +-+-++ | PCE5| +++--+ +-----+ | || PCE1| | | || +-----+ ||| | | PCE3| | |+-----+ +-+-++ +++--+ +-----+ | | | | || | +---------------+ | |+----------------+ | | | | | +----+ | +----------+----+---------+ +--------+----+------+ | BN8 +----+ | | | | | | Area 4 +-----+| | | PCE4|| | +-----+| +--------------------+ Figure 1: OSPF Area Topology Dhody & Palle Expires March 4, 2012 [Page 6] Internet-Draft OSPF BND Sept 2011 5. Existing Mechanisms 5.1. OSPF LSA o E bit and B bit of Router LSA defined in [RFC2328] can help in finding a router acting as ABR/ASBR but there is no way to find out the domain information of this ABR/ASBR. As stated in section 7, Selection of correct BN is based on domain and thus it is ineffective. o Selection of ABR based on summary LSA or ASBR based on AS-external LSA is not a good idea, first it requires PCE to look into LSDB thus adding to coupling, second it MAY require BGP routes to be redistributed into OSPF which is also not a good network design principle. 5.2. Inter-AS TE Link o [RFC5392] specifies how to advertise TE properties of inter-AS links; through which ASBR and remote AS can be discovered, but ABR and their domain information cannot be discovered via above RFC. o AS is made up of multiple Area, there maybe a need to clearly identify a BN by combination of both AS number and Area-id. Refer Section 3.3.3 of [DOMAIN-SEQ]. o AS shown in below figure, just the knowledge of AS 100 and AS 200 is not sufficient, the BN should have both AS and Area information. Dhody & Palle Expires March 4, 2012 [Page 7] Internet-Draft OSPF BND Sept 2011 | | +-------------+ +----------------+ | |Area 2 | |Area 4 | | | +--+| | +--+ | | | | || | | | | | | +--+ +--+| | +--+ +--+ | | | | | | | | | | | | *--+ | | +--+ | | | / +--+ | | +--+ | | |/ | | | | | | | | / +--+ | | +--+ +--+ | | /| +--+ |+--------------+| | | | |/ | | | ++-+ +-++ +--+ | +-------------+/ | +--+ || | | || | | /| | ++-+ +-++ | | +--*|| +-------------+| |+----------------+ | | ||| | +--+ | | +--+|| | | | | | +--+ || | +--+ | | | | || | | | +--+ || | | | || | +--+ | |+--+ || | | | | || | || | +--+ | |+--+ || | | | || | +--+ | | +--+ || +------------+ | | | |+----------------+ | | | || |Area 3 +-++ +--+ +-++ Area 5 | | +--+ || | | || | || | | || | +-++ +-++ | | +--+|| | +--+ | | Area 0 || +--+ | | | ||| | | | | +--------------+| | | | | +--*|| | +--+ | | +--+ | | \| | | | +--+ | |Area 1 |\ | +--+ | | +--+ | | | +-------------+|\ | | | | | | | +--+ | | \| +--+ +--+ | +--+ | | \ | | | | | |\ +--+ | +--+ | | | \ +--+ | | | | | | | \| | | | +--+ | | | *--+ | | | | | | | | | +------------+ +----------------+ | | As 100 | AS 200 | Dhody & Palle Expires March 4, 2012 [Page 8] Internet-Draft OSPF BND Sept 2011 5.3. OSPF Area Topology o Consider OSPF topology as shown in figure 1, One can make a generalization that all ABR connects to Area 0, and one doesnt need the area information. o But as per [RFC3509], there are alternative interpretaion of ABR, which needs to be considered. If there is a connectivity between Area 1 and Area 2 directly that needs to be considered. . . . Area 0 . +--+ +--+ ..|R1|.. ..|R2|.. . +--+ .. +--+ . . .. . . +--+ . . Area1 |R3| Area2 . . +--+ +--+ . . .. |R4| . . . . +--+ . ....... ....... 5.4. HPCE o Section 4 of [H-PCE] specifies each child PCE should know the identity of the domains that neighbor its own domain and advertises the same to the parent PCE. No method exist to find the neighbor domain which need to be carried in NEIG-PCE-DOMAIN Sub-TLV and BN discovery along with neighbor domain information can help in generating NEIG-PCE-DOMAIN Sub-TLV. 6. Static Configurations A simple solution would be to configure BNs [ABR and ASBR] at PCE(s) along with their domain information. As this information is fairly static this could work in simple situations. But as PCE are being used in bigger and multiple domains, any sort of static configurations would put extra effort on the system administrator. Selection of correct BNs is the core of the BRPC procedure, we feel this information should be dynamically learned and maintained. 7. Importance of Domain Information along with BNs There are methods to learn BNs dynamically from IGP, but the knowledge of neighboring-domains is not possible to obtain. Without this the correct BN based on the domain-path can't be selected. [RFC5441] mentions: Dhody & Palle Expires March 4, 2012 [Page 9] Internet-Draft OSPF BND Sept 2011 " Note that PCE(i) only considers the entry BNs of domain(i), i.e., only the BNs that provide connectivity from domain(i-1). In other words, the set BN-en(k,i) is only made of those BNs that provide connectivity from domain (i-1) to domain(i). " This selection of correct BNs providing connectivity between correct domains cannot be made by the information obtained from IGP. Without the correct selection we would not be following [RFC5441]. 8. Relationship to Domain-Sequence [DOMAIN-SEQ] provides a standard representation of Domain Sequence in all deployment scenarios. The Domain Information carried in the BN- DOMAIN sub-tlv is same as the sub-objects inside the domain sequence. 9. The OSPF BND TLV The OSPF BN Discovery TLV (BND TLV) contains a non-ordered set of sub-TLVs. The format of the OSPF BND TLV and its sub-TLVs is identical to the TLV format used by the Traffic Engineering Extensions to OSPF[RFC3630]. That is, the TLV is composed of 2 octets for the type, 2 octets specifying the TLV length, and a value field. The Length field defines the length of the value portion in octets. The OSPF BND TLV has the following format: 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | // sub-TLVs // | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Type: To be assigned by IANA (suggested value 8) Length: Variable Value: This comprises of following sub-TLVs Two sub-TLVs are defined: Sub-TLV type Length Name 1 variable BN-ADDRESS sub-TLV 2 4 BN-DOMAIN sub-TLV The BN-ADDRESS and BN-DOMAIN sub-TLVs MUST always be present within Dhody & Palle Expires March 4, 2012 [Page 10] Internet-Draft OSPF BND Sept 2011 the BND TLV. Malformed BND TLVs or sub-TLVs not explicitly described in this document MUST cause the LSA to be treated as malformed according to the normal procedures of OSPF. Any unrecognized sub-TLV MUST be silently ignored. The BND TLV is carried within an OSPF Router Information LSA defined in [RFC4970]. The following sub-sections describe the sub-TLVs which are carried within the BND TLV. 9.1. BN-ADDRESS Sub-TLV The BN-ADDRESS sub-TLV specifies an IP address that can be used to reach the BN. It is RECOMMENDED to make use of an address that is always reachable, provided that the BN is alive and reachable. The BN-ADDRESS sub-TLV is mandatory; it MUST be present within the BND TLV. It MAY appear twice, when the BN has both an IPv4 and IPv6 address. It MUST NOT appear more than once for the same address type. If it appears more than once for the same address type, only the first occurrence is processed and any others MUST be ignored. The format of the BN-ADDRESS sub-TLV is as follows: 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type = 1 | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | address-type | Reserved | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | // BN IP Address // | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ BN-ADDRESS sub-TLV format Type: 1 Length: 8 (IPv4) or 20 (IPv6) Address-type: 1 IPv4 2 IPv6 Dhody & Palle Expires March 4, 2012 [Page 11] Internet-Draft OSPF BND Sept 2011 Reserved: SHOULD be set to zero on transmission and MUST be ignored on receipt. BN IP Address: The IP address to be used to reach the BN. 9.2. BN-DOMAIN Sub-TLV The BN-DOMAIN sub-TLV specifies a BN-Domain (area or AS) where the BN has topology connectivity. The BN-DOMAIN sub-TLV is mandatory; it MUST be present within the BND TLV. A BND TLV MUST include two or more BN-DOMAIN sub-TLVs as the BN has connectivity into multiple BN-Domains. The BN-DOMAIN sub-TLV has the following format: 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type = 2 | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Domain-type | Reserved | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Domain ID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ BN-DOMAIN sub-TLV format Type: 2 Length: 8 Two domain-type values are defined: 1 OSPF Area ID 2 AS Number Domain ID: With the domain-type set to 1, this indicates the 32-bit Area ID of an area where the BN (ABR) has connectivity. With domain- type set to 2, this indicates an AS number of an AS where the BN (ASBR) has connectivity. When the AS number is coded in two octets, the AS Number field MUST have its first two octets set to 0. 10. Elements of Procedure The BND TLV is advertised within OSPFv2 Router Information LSAs (Opaque type of 4 and Opaque ID of 0) or OSPFv3 Router Information LSAs (function code of 12), which are defined in [RFC4970]. As such, Dhody & Palle Expires March 4, 2012 [Page 12] Internet-Draft OSPF BND Sept 2011 elements of procedure are inherited from those defined in [RFC4970]. In OSPFv2, the flooding scope is controlled by the opaque LSA type(as defined in [RFC5250]) and in OSPFv3, by the S1/S2 bits (as defined in [RFC5340]). If the flooding scope is area local, then the BND TLV MUST be carried within an OSPFv2 type 10 router information LSA or an OSPFV3 Router Information LSA with the S1 bit set and the S2 bit clear. If the flooding scope is the entire IGP domain, then the BND TLV MUST be carried within an OSPFv2 type 11 Router Information LSA or OSPFv3 Router Information LSA with the S1 bit clear and the S2 bit set. When the BN function is deactivated, the OSPF speaker MUST originate a new Router Information LSA that no longer includes the corresponding BND TLV, provided there are other TLVs in the LSA. If there are no other TLVs in the LSA, it MUST either send an empty Router Information LSA or purge it by prematurely aging it. The BN address (i.e., the address indicated within the BN-ADDRESS sub-TLV) SHOULD be reachable via some prefixes advertised by OSPF. The BND TLV information regarding a specific BN is only considered current and useable when the router advertising this information is itself reachable via OSPF calculated paths in the same area of the LSA in which the BND TLV appears. A change in the state of a BN (activate, deactivate, domain change) MUST result in a corresponding change in the BND TLV information advertised by an OSPF router (inserted, removed, updated)in its LSA. The way BNs determine the information they advertise, and how that information is made available to OSPF, is out of the scope of this document. Some information may be configured and other information may be automatically determined by the OSPF. A change in information in the BND TLV MUST NOT trigger any SPF computation at a receiving router. 11. Backward Compatibility The BND TLV defined in this document does not introduce any interoperability issues. A router not supporting the BND TLV will just silently ignore the TLV as specified in [RFC4970]. Dhody & Palle Expires March 4, 2012 [Page 13] Internet-Draft OSPF BND Sept 2011 12. Impact on Network The routers acting as BNs will originate Opaque LSA with BND Tlv; As there are only few BNs exist in the network, the performance impact in flooding is very less. 13. IANA Considerations 13.1. OSPF TLV IANA has defined a registry for TLVs carried in the Router Information LSA defined in [RFC4970].A number of IANA considerations have been highlighted in previous sections of this document. IANA is requested to make the following allocations. Value TLV Name Reference ----- -------- ---------- To be BND (this document) assigned by IANA 14. Security Considerations This document defines OSPF extensions for BN discovery within an administrative domain. Hence the security of the BN discovery relies on the security of OSPF. Mechanisms defined to ensure authenticity and integrity of OSPF LSAs [RFC2154], and their TLVs, can be used to secure the BN Discovery information as well. OSPF provides no encryption mechanism for protecting the privacy of LSAs and, in particular, the privacy of the BN discovery information. 15. Manageability Considerations TBD 16. Acknowledgments We would like to thank Quintin Zhao, Daniel King, Adrian Ferral, Suresh babu, Pradeep Shastry, Saravana Kumar and srinivasan for their useful comments and suggestions. 17. References Dhody & Palle Expires March 4, 2012 [Page 14] Internet-Draft OSPF BND Sept 2011 17.1. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", March 1997. [RFC2154] Murphy, S., Badger, M., and B. Wellington, "OSPF with Digital Signatures", June 1997. [RFC2328] Moy, J., "OSPF Version 2", April 1998. [RFC3630] Katz, D., Kompella, K., and D. Yeung, "Traffic Engineering (TE) Extensions to OSPF Version 2", September 2003. [RFC4970] Lindem, A., Shen, N., Vasseur, JP., Aggarwal, R., and S. Shaffer, "Extensions to OSPF for Advertising Optional Router Capabilities", July 2007. [RFC5250] Berger, L., Bryskin, I., Zinin, A., and R. Coltun, "The OSPF Opaque LSA Option", July 2008. [RFC5340] Coltun, R., Ferguson, D., Moy, J., and A. Lindem, Ed, "OSPF for IPv6", July 2008. 17.2. Informative References [DOMAIN-SEQ] Dhody, D. and U. Palle, "Standard Representation Of Domain Sequence", March 2011. [H-PCE] King, D. and A. Farrel , "The Application of the Path Computation Element Architecture to the Determination of a Sequence of Domains in MPLS & GMPLS", December 2009. [RFC3509] Zinin, A., Lindem, A., and D. Yeung, "Alternative Implementations of OSPF Area Border Routers", April 2003. [RFC4655] Farrel, A., Vasseur, J., and J. Ash, "A Path Computation Element (PCE)-Based Architecture", August 2006. [RFC5392] Chen, M., Zhang, R., and X. Duan, "OSPF Extensions in Support of Inter-Autonomous System (AS)MPLS and GMPLS Traffic Engineering", January 2009. [RFC5441] Vasseur, JP., Zhang, R., Bitar, N., and JL. Le Roux, "A Backward-Recursive PCE-Based Computation (BRPC) Dhody & Palle Expires March 4, 2012 [Page 15] Internet-Draft OSPF BND Sept 2011 Procedure to Compute Shortest Constrained Inter-Domain Traffic Engineering Label Switched Paths", April 2009. Authors' Addresses Dhruv Dhody Huawei Technologies India Pvt Ltd Leela Palace Bangalore, Karnataka 560008 INDIA EMail: dhruv.dhody@huawei.com Udayasree Palle Huawei Technologies India Pvt Ltd Leela Palace Bangalore, Karnataka 560008 INDIA EMail: udayasreepalle@huawei.com Dhody & Palle Expires March 4, 2012 [Page 16]