Network Working Group N. So Internet-Draft A. Malis Intended status: Standards Track D. McDysan Expires: April 24, 2009 Verizon L. Yong Huawei USA October 21, 2008 Framework and Requirements for Composite Transport Group (CTG) draft-so-yong-mpls-ctg-framework-requirement-00 Status of this Memo By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she becomes aware will be disclosed, in accordance with Section 6 of 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 April 24, 2009. So, et al. Expires April 24, 2009 [Page 1] Internet-Draft CTG framework and requirements October 2008 Abstract This document states a traffic distribution problem in today's IP/ MPLS network when multiple links are configured between two routers. The document presents a Composite Transport Group framework as the solution for the problems and specifies a set of requirements for Composite Transport Group(CTG). Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Conventions used in this document . . . . . . . . . . . . . . 4 2.1. Acronyms . . . . . . . . . . . . . . . . . . . . . . . . . 4 3. Problem Statements . . . . . . . . . . . . . . . . . . . . . . 5 3.1. Incomplete/Inefficient Utilization . . . . . . . . . . . . 5 3.2. Inefficiency/Inflexibility of Logical Interface Bandwidth Allocation . . . . . . . . . . . . . . . . . . . 6 4. Composite Transport Group Framework . . . . . . . . . . . . . 8 4.1. CTG Framework . . . . . . . . . . . . . . . . . . . . . . 8 4.2. Difference between CTG and A Bundled Link . . . . . . . . 10 4.2.1. Virtual Routable Link vs. TE Link . . . . . . . . . . 10 4.2.2. Component Link Parameter Independence . . . . . . . . 11 5. Composite Transport Group Requirements . . . . . . . . . . . . 12 5.1. CTG Appearance as a Routable Virtual Interface . . . . . . 12 5.2. CTG mapping of traffic to Component Links . . . . . . . . 12 5.2.1. Mapping Using Router TE information . . . . . . . . . 12 5.2.2. Mapping When No Router TE Information is Available . . 12 5.3. Bandwidth Control for Connections with and without TE information . . . . . . . . . . . . . . . . . . . . . . . 13 5.4. CTG Transport Resilience . . . . . . . . . . . . . . . . . 14 6. Security Considerations . . . . . . . . . . . . . . . . . . . 15 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 16 8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 17 9. Normative References . . . . . . . . . . . . . . . . . . . . . 18 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 19 Intellectual Property and Copyright Statements . . . . . . . . . . 20 So, et al. Expires April 24, 2009 [Page 2] Internet-Draft CTG framework and requirements October 2008 1. Introduction IP/MPLS network traffic growth forces carriers to deploy multiple parallel physical links between two routers. The network is also expected to carry some flows of a rate that can approach that of any single link or be very small comparing to a single link rate. There is not an existing technology today that allows carriers to efficiently utilize all parallel transport resources in a complex IP/ MPLS network environment. Composite Transport Group (CTG) provides the local traffic engineering management over multiple parallel links that solves this problem in MPLS networks. The primary function of Composite Transport Group is to efficiently transport aggregated traffic flows over multiple parallel links. CTG can take the flow TE information into account when distributing the flows over individual links to gain local traffic engineering management and link failure protection. Because all links have the same ingress and egress point, CTG does not need to perform route computation and forwarding based on the traffic unit end point information, which brings a unique local transport traffic engineering scheme. CTG also manages the flows that do not have TE information and associates them with CTG connections that have assigned TE information based on auto bandwidth measurement, and use the TE information in component link selection. This document contains the problem statements and the framework and a set of requirements for a Composite Transport Group (CTG). The necessity for protcol extensions to provide solutions is for future study. So, et al. Expires April 24, 2009 [Page 3] Internet-Draft CTG framework and requirements October 2008 2. Conventions used in this document 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]. 2.1. Acronyms BW: BandWidth CTG: Composite Transport Group ECMP: Equal Cost Multi-Path FRR: Fast Re-Route LAG: Link Aggregation Group LDP: Label Distributed Protocol LR: Logical Router LSP: Label Switched Path MPLS: Multi-Protocol Label Switch OAM: Operation, Administration, and Maintenance PDU: Packet Data Units PE: Provider Edge device RSVP: ReSource reserVation Protocol RTD: Real Time Delay TE: Traffic engineering VRF: Virtual Routing & Forwarding So, et al. Expires April 24, 2009 [Page 4] Internet-Draft CTG framework and requirements October 2008 3. Problem Statements Two applications are described here that encounter the problems when multiple parallel links are deployed between two routers in today's IP/MPLS networks. 3.1. Incomplete/Inefficient Utilization An MPLS-TE network is deployed to carry traffic on RSVP-TE LSPs, i.e. traffic engineered flows. When traffic volume exceeds the capacity of a single physical link, multiple physical links are deployed between two routers as a single backbone trunk. How to assign LSP traffic over multiple links and maintain this backbone trunk as a higher capacity and higher availability trunk than a single physical link becomes an extremely difficult task for carriers today. Three methods that are available today are described here. 1. A hashing method is a common practice for traffic distribution over multiple paths. This is used by Equal Cost Multi-Path (ECMP) for IP services, and IEEE-defined Link Aggregation Group (LAG) for Ethernet traffic. However, the traffic granularity in a MPLS-TE network is individual LSPs, and they typically contain a high rate of traffic flow(s) and have large differences in the rates; furthermore, the links may be of different speeds. In these cases hashing can cause some links to be congested while others are partially filled because hashing can only distinguish the flows, not the flow rates. 2. Assigning individual LSPs to each link through constrained routing. A planning tool can track the utilization of each link and assignment of LSPs to the links. To gain high availability, FRR [RFC4090] is used to create a bypass tunnel on a link to protect traffic on another link or to create a detour LSP to protect another LSP. If reserving BW for the bypass tunnels or the detour LSPs, the network will reserve a large amount of capacity for failure recovery, which reduces the capacity to carry other traffic. If not reserving BW for the bypass tunnels and the detour LSPs, the planning tool can not assign LSPs properly to avoid the congestion during link failure when there are more than two parallel links. This is because during the link failure, the impacted traffic is simply put on a bypass tunnel or detour LSPs which does not have enough reserved bandwidth to carry the extra traffic during the failure recovery phase. 3. Facility protection, also called 1:1 protection. Dedicate one link to protect another link. Only assign traffic to one link in the normal condition. When the working link fails, switch So, et al. Expires April 24, 2009 [Page 5] Internet-Draft CTG framework and requirements October 2008 traffic to the protected link. This requires 50% capacity for failure recovery. This works when there are only two links. Under the multiple parallel link condition, this causes inefficient use of network capacity because there is no protection capacity sharing. In addition, due to traffic burstiness, having one link fully loaded and another link idle increases transport latency and packet loss, which lowers the link performance quality for transport. None of these methods satisfies carrier requirement either because of poor link utilization or poor performance. This forces carriers to go with the solution of deploying single higher capacity link solution. However, a higher capacity link can be expensive as compared with parallel low capacity links of equivalent aggregate capacity; a high capacity link can not be deployed in some circumstances due to physical impairments; or the highest capacity link may not large enough for some carriers. An LDP network can encounter the same issue as an MPLS-TE enabled network when multiple parallel links are deployed as a backbone trunk. An LDP network can have large variance in flow rates where, for example, the small flows may be carrying stock tickers at a few kbps per flow while the large flows can be near 10 Gbps per flow carrying machine to machine and server to server traffic from individual customers. Those large traffic flows often cannot be broken into micro flows. Therefore, hashing would not work well for the networks carrying such flows. Without per-flow TE information, this type of network has even more difficulty to use multiple parallel links and keep high link utilization. 3.2. Inefficiency/Inflexibility of Logical Interface Bandwidth Allocation Logically-separate routing instances in some implementations further complicates the situation. Dedicating separate physical backbone links to each routing instance is not efficient. An alternative is to assign a logical interface and bandwidth on each of the parallel physical links to each routing instance, which improves efficiency as compared with dedicating physical links to each routing instance. Inefficiency can result if bandwidth on a logical interface is dedicated to each routing instance. For example, if there are 2 routing instances and 3 parallel links and half of each link bandwidth is assigned to a routing instance, then neither routing instance can support an LSP with bandwidth greater than half the link bandwidth. Note that the traffic flows and LSPs from these different routing instances effectively operate in a Ships-in-the-Night mode, where So, et al. Expires April 24, 2009 [Page 6] Internet-Draft CTG framework and requirements October 2008 they are unaware of each other. Inflexibility results if there are multiple sets of LSPs (e.g., from different routing instances) sharing a set of parallel links, and at least one set of LSPs can preempt another, then more efficient sharing of the link set between the routing instances is highly desirable. So, et al. Expires April 24, 2009 [Page 7] Internet-Draft CTG framework and requirements October 2008 4. Composite Transport Group Framework 4.1. CTG Framework Composite Transport Group (CTG) is the method to transport aggregated traffic over a composite link. A composite link defined in ITU-T [ITU-T G.800] is a single link that bundles multiple parallel links between the two same subnetworks. Each of component links of a composite link is independent in the sense that each component link is supported by a separate server layer trail. The composite link conveys communication information using different server layer trails thus the sequence of symbols across this link may not be preserved. Composite Transport Group (CTG) is primarily a local traffic engineering and transport technology over multiple parallel links or multiple paths. The objective is for a composite link to appear as a virtual interface to the connected routers. The router provisions incoming traffic over the CTG connection. CTG connections are transported over parallel links called Component Links. CTG Component Links can be either physical links or logical links such as LSP tunnels. The CTG distribution function can locally determine which component link CTG connections should traverse. The major components of CTG and their relationships are illustrated in Figure 1 below. +---------+ +-----------+ | +---+ +---+ | | | |============================| | | LSP,LDP,IP| | C |~~~~~~5 CTG Connections ~~~~| C | | ~~~|~~>~~| |============================| |~~~>~~~|~~~ ~~~|~~>~~| T |============================| T |~~~>~~~|~~~ ~~~|~~>~~| |~~~~~~3 CTG Connections ~~~~| |~~~>~~~|~~~ | | G |============================| G | | | | |============================| | | | | |~~~~~~9 CTG connections~~~~~| | | | | |============================| | | | R1 +---+ +---+ R2 | +---------+ +-----------+ ! ! ! ! ! !<----Component Links ------>! ! !<------ Composite Link ----------->! Figure 1: Composite Transport Group Architecture Model So, et al. Expires April 24, 2009 [Page 8] Internet-Draft CTG framework and requirements October 2008 In Figure 1, a composite link is configured between router R1 and R2. The composite link has three component links. CTG creates a CTG connection and select a component link for the CTG connection. LSP, LDP, and IP traffic are mapped to CTG connections. A CTG connection only exists in the scope of a composite link. The traffic in a CTG connection is transported over a single component link. A CTG connection is a point-to-point logical connection over a composite link. The connection rides on component link in a one-to- one or many-to-one relationship. LSPs map to CTG connections in a one-to-one or many-to-one relationship. The connection can have the following traffic engineering parameters: o bandwidth over-subscription o factor placement o priority o holding priority CTG connection TE parameters can be mapped directly from the LSP parameters signaled in RSVP-TE or can be set at the CTG management interface (CTG Logical Port). The connection bandwidth MUST be set. If a LSP has no bandwidth information, the bandwidth will be calculated at CTG ingress using automatic bandwidth measurement function. LDP LSPs can be mapped onto the connections per LDP label. Both outer label (PE-PE label) and Inner label (VRF Label) can be used for the connection mapping. CTG connection bandwidth MUST be set through auto-bandwidth measurement function at the CTG ingress. When the connection bandwidth tends to exceed the component link capacity, CTG is able to reassign the flows in one connection into several connections and assign other component links for the connections without traffic disruption. A CTG component link can be a physical link or logical link (LSP Tunnel) between two routers. When component links are physical links, there is no restriction to component link type, bandwidth, and performance objectives (e.g., RTD and Jitter). Each component link MUST maintain its own OAM. CTG is able to get component link status from each link and take an action upon component link status changes. Each component link can have its own Component Link Cost and Component Link Bandwidth as its associated engineered parameters. CTG uses component link parameters in the assignment of CTG connections to component links. So, et al. Expires April 24, 2009 [Page 9] Internet-Draft CTG framework and requirements October 2008 CTG provides local traffic engineering management over parallel links based on CTG connection TE information and component link parameters. Component link selection for CTG connections is determined locally and may change without reconfiguring the traffic flows. Changing the selection may be triggered by a component link condition change, a new traffic flow configured or existing one modified, or operator required optimization process. CTG component link selection for CTG connections enables TE based traffic distribution and link failure recovery with much less link capacity than current methods mentioned in the section of the problem statements. CTG connections are created for traffic management purpose on a composite link. They do not change the forwarding schema. The forwarding engine still forwards based on the LSP label created per traffic LSP. Therefore, there is no change to the forwarding. Since MPLS is built on the top of IP network, some IP PDUs are carried over the MPLS network. CTG may designate one CTG connection for such traffic or use hashing to distribute IP PDUs over component links. The assumption is that such traffic volume is very small compared to LSP or LDP traffic. CTG techniques applies to the situation that the rate of the distinct traffic flows are not higher than component link capacity in CTG. 4.2. Difference between CTG and A Bundled Link 4.2.1. Virtual Routable Link vs. TE Link CTG is a data plan transport function over a composite link. A composite link contains multiple component links that can carry traffic independently. CTG is the method to transport aggregated traffic over a composite link. The composite link appears as a single routable virtual interface between the connected routers. The network only maps LSP or LDP to a composite link, i.e. not to individual component links. CTG will select component link for individual LSP and LDP and merge them at composite link egress. A bundled link [RFC4201] is a collection of TE links. It is a logical construct that represents a way to group/map the information about certain physical resources that interconnect routers. The purpose of bundled link is to improve routing scalability by reducing the amount of information that has to be handled by OSPF/IS-IS. Each physical links in the bundled link are an IGP link in OSPF/IS-IS. A bundled link only has the significance to router control plane. The router has to map individual LSP to each component link in the bundled link, which is different from CTG. A bundled link only applies to RSVP-TE signaled traffic. So, et al. Expires April 24, 2009 [Page 10] Internet-Draft CTG framework and requirements October 2008 4.2.2. Component Link Parameter Independence CTG allows component links to have different costs, traffic engineering metric and resource classes. CTG can derive the virtual interface cost from component link costs based on operator policy. CTG can derive the traffic engineering parameter for a virtual interface from its component link traffic engineering parameters. However, a bundled link [RFC4201] requires that all component links in a bundle to have the same traffic engineering metric, and the same set of resource classes. So, et al. Expires April 24, 2009 [Page 11] Internet-Draft CTG framework and requirements October 2008 5. Composite Transport Group Requirements Composite Transport Group (CTG) is about the method to transport aggregated traffic over multiple parallel links. CTG can address the problems existing in today IP/MPLS network. Here are some CTG requirements: 5.1. CTG Appearance as a Routable Virtual Interface The carrier needs a solution where multiple routing instances see a separate "virtual interface" to a shared composite transport group composed of parallel physical links between a pair of routers. The CTG would communicate parameters (e.g., admin cost, available bandwidth, maximum bandwidth, allowable bandwidth) for the "virtual interface" associated with each routing instance. The "virtual interface" shall appear as a fully-featured IP adjacency to each routing instance, not just an FA [RFC3477] . In particular, it needs to work with at least the following IP/MPLS control protocols: IGP, LDP, IGP-TE, and RSVP-TE. 5.2. CTG mapping of traffic to Component Links The objective of CTG is to solve the traffic sharing problem at a virtual interface level by mapping traffic to component links (not using hashing): 1. using TE information from the control planes of the routing instances attached to the virtual interface when available, or 2. using traffic measurements when it is not. 5.2.1. Mapping Using Router TE information CTG SHALL use RSVP-TE for bandwidth signaled by a routing instance to explicitly assign a TE LSPs to CTG connection that is assigned to a specific link in the CTG. The CTG SHALL be able to receive, interpret and act upon at least the following router signaled parameters: minimum bandwidth, maximum bandwidth, preemption priority, and holding priority and apply them to CTG connections where the LSP is mapped. 5.2.2. Mapping When No Router TE Information is Available CTG SHALL map LDP-assigned labeled packets based upon local configuration (e.g., label stack depth) to define a CTG connection So, et al. Expires April 24, 2009 [Page 12] Internet-Draft CTG framework and requirements October 2008 that is mapped to one of the parallel links in the CTG between routers. CTG SHALL map LDP-assigned labeled packets that identify the source- destination LER as a CTG connection to a specific link in the CTG. CTG SHALL also handle IP traffic without MPLS labels. This could use locally defined methods to assign sets of IP traffic to a CTG connection. In all of the above mapping cases, CTG SHALL place an entire connection onto a single physical link. In a mapping case, the CTG SHALL measure the bandwidth actually used by a particular connection to determine which component link (physical link) on the CTG that CTG connection should be transmitted. The CTG SHALL support parameters that control the time period between moving a CTG connection from one link to another since this could cause reordering. The CTG SHALL support parameters that define at least a minimum bandwidth, maximum bandwidth, preemption priority, and holding priority for connections without TE information. 5.3. Bandwidth Control for Connections with and without TE information The following requirements apply to a virtual interface (i.e., composite link in section 4) that supports connections with TE information in conjunction with connections that do not have TE information. A "bandwidth shortage" issue can arise in CTG if the total bandwidth of the connections with TE information and those without TE information exceeds the bandwidth of the composite link. The CTG SHALL support a policy based preemption capability such that in the event of such a "bandwidth shortage" that the signaled or configured preemption and holding parameters can be applied to the following treatments to the connections: o For a connection that has RSVP-TE LSP(s), signal the router that the TE-LSP has been preempted. o For a connection that has LDP(s), where the CTG is aware of the LDP signaling involved to the preempted label stack depth, signal release of the label to the router So, et al. Expires April 24, 2009 [Page 13] Internet-Draft CTG framework and requirements October 2008 o For a connection that has IP traffic without MPLS labels, indicate congestion to the router (e.g., using ECN, PCN, or some local method) or block IP traffic. 5.4. CTG Transport Resilience Component link in CTG can fail independently. The failure of component link can impact some CTG connections. The impacted CTG connection SHALL be placed to other active component links by using the same rules as of component link section for CTG connections. So, et al. Expires April 24, 2009 [Page 14] Internet-Draft CTG framework and requirements October 2008 6. Security Considerations CTG is a local function on the router to support traffic engineering management over multiple parallel links. It does not introduce a security risk for control plane and dada plane. So, et al. Expires April 24, 2009 [Page 15] Internet-Draft CTG framework and requirements October 2008 7. IANA Considerations There is no IANA actions requested in this specification. So, et al. Expires April 24, 2009 [Page 16] Internet-Draft CTG framework and requirements October 2008 8. Acknowledgements Authors would like to thank Frederic Jounay from France Telecom, Adrian Farrel from Olddog, and Ron Bonica from Juniper for the review and great suggestions. So, et al. Expires April 24, 2009 [Page 17] Internet-Draft CTG framework and requirements October 2008 9. Normative References [ITU-T G.800] ITU-T Q12, "Unified Functional Architecture of Transport Network", ITU-T G.800, February 2008. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", RFC 2119, March 1997. [RFC3477] Kompella, K., "Signalling Unnumbered Links in Resource ReSerVation Protocol - Traffic Engineering (RSVP-TE)", RFC 3477, January 2003. [RFC4090] Pan, P., "Fast Reroute Extensions to RSVP-TE for LSP Tunnels", RFC 4090, May 2005. [RFC4201] Kompella, K., "Link Bundle in MPLS Traffic Engineering", RFC 4201, March 2005. So, et al. Expires April 24, 2009 [Page 18] Internet-Draft CTG framework and requirements October 2008 Authors' Addresses So Ning Verizon 2400 N. Glem Ave., Richerson, TX 75082 Phone: +1 972-729-7905 Email: ning.so@verizonbusness.com Andrew Malis Verizon 117 West St. Waltham, MA 02451 Phone: +1 781-466-2362 Email: andrew.g.malis@verizon.com Dave McDysan Verizon 22001 Loudoun County PKWY Ashburn, VA 20147 Phone: +1 707-886-1891 Email: dave.mcdysan@verizon.com Lucy Yong Huawei USA 1700 Alma Dr. Suite 500 Plano, TX 75075 Phone: +1 469-229-5387 Email: lucyyong@huawei.com So, et al. Expires April 24, 2009 [Page 19] Internet-Draft CTG framework and requirements October 2008 Full Copyright Statement Copyright (C) The IETF Trust (2008). This document is subject to the rights, licenses and restrictions contained in BCP 78, and except as set forth therein, the authors retain all their rights. 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