Internet Draft Network Working Group Luca Martini Internet Draft Nasser El-Aawar Expiration Date: March 2001 Level 3 Communications, LLC. Dimitri Stratton Vlachos Daniel Tappan Eric C. Rosen Cisco Systems, Inc. Steve Vogelsang John Shirron Laurel Networks, Inc. Andrew G. Malis Ken Hsu Vivace Networks, Inc. September 2000 Transport of Layer 2 Frames Over MPLS draft-martini-l2circuit-trans-mpls-03.txt Status of this Memo This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC2026. 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. Martini, et al. [Page 1] Internet Draft draft-martini-l2circuit-trans-mpls-03.txt September 2000 Abstract This document describes methods for transporting the Protocol Data Units (PDUs) of layer 2 protocols such as Frame Relay, ATM AAL5, Ethernet, and providing a SONET circuit emulation service across an MPLS network. Table of Contents 1 Specification of Requirements .......................... 2 2 Introduction ........................................... 3 3 Tunnel Labels and VC Labels ............................ 3 4 Optional Sequencing and/or Padding ..................... 4 5 Protocol-Specific Issues ............................... 5 5.1 Frame Relay ............................................ 5 5.2 ATM .................................................... 6 5.2.1 F5 OAM Cell Support .................................... 6 5.2.2 CLP Bit ................................................ 7 5.2.3 PTI Field in ATM Cell Mode ............................. 7 5.3 Ethernet VLAN .......................................... 7 5.4 Ethernet ............................................... 7 5.5 Circuit Emulation Service over MPLS (CEM) .............. 8 5.5.1 CEM Encapsulation Format ............................... 8 5.5.2 Clocking Mode .......................................... 9 5.5.3 Synchronous ............................................ 9 5.5.4 Asynchronous ........................................... 10 6 LDP .................................................... 10 7 Security Considerations ................................ 13 8 Open Issues ............................................ 13 9 Intellectual ........................................... 13 10 References ............................................. 13 11 Author Information ..................................... 14 12 Appendix A: SONET/SDH Rates and Formats ................ 15 1. Specification of Requirements 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 RFC 2119. Martini, et al. [Page 2] Internet Draft draft-martini-l2circuit-trans-mpls-03.txt September 2000 2. Introduction In an MPLS network, it is possible to carry the Protocol Data Units (PDUs) of layer 2 protocols by prepending an MPLS label stack to these PDUs. This document specifies the necessary label distribution and encapsulation procedures for accomplishing this. We restrict discussion to the case of point-to-point transport. QoS related issues are not discussed in this draft. This document also describes a method for transporting time division multiplexed (TDM) digital signals (TDM circuit emulation) over a packet-oriented MPLS network. The transmission system for circuit- oriented TDM signals is the Synchronous Optical Network (SONET)[5]/Synchronous Digital Hierarchy (SDH) [6]. To support TDM traffic, which includes voice, data, and private leased line service, the MPLS network must emulate the circuit characteristics of SONET/SDH payloads. MPLS labels and a new circuit emulation header are used to encapsulate TDM signals and provide the Circuit Emulation Service over MPLS (CEM). 3. Tunnel Labels and VC Labels Suppose it is desired to transport layer 2 PDUs from ingress LSR R1 to egress LSR R2, across an intervening MPLS network. We assume that there is an LSP from R1 to R2. That is, we assume that R1 can cause a packet to be delivered to R2 by pushing some label onto the packet and sending the result to one of its adjacencies. Call this label the "tunnel label", and the corresponding LSP the "tunnel LSP". The tunnel LSP merely gets packets from R1 to R2, the corresponding label doesn't tell R2 what to do with the payload, and in fact if penultimate hop popping is used, R2 may never even see the corresponding label. (If R1 itself is the penultimate hop, a tunnel label may not even get pushed on.) Thus if the payload is not an IP packet, there must be a label, which becomes visible to R2, that tells R2 how to treat the received packet. Call this label the "VC label". So when R1 sends a layer 2 PDU to R2, it first pushes a VC label on its label stack, and then (if R1 is not adjacent to R2) pushes on a tunnel label. The tunnel label gets the MPLS packet from R1 to R2; the VC label is not visible until the MPLS packet reaches R2. R2's disposition of the packet is based on the VC label. If the payload of the MPLS packet is, for example, an ATM AAL5 PDU, the VC label will generally correspond to a particular ATM VC at R2. That is, R2 needs to be able to infer from the VC label the outgoing Martini, et al. [Page 3] Internet Draft draft-martini-l2circuit-trans-mpls-03.txt September 2000 interface and the VPI/VCI value for the AAL5 PDU. If the payload is a Frame Relay PDU, then R2 needs to be able to infer from the VC label the outgoing interface and the DLCI value. If the payload is an ethernet frame, then R2 needs to be able to infer from the VC label the outgoing interface, and perhaps the VLAN identifier. This process is unidirectional, and will be repeated independently for bidirectional operation. It is desirable, but not required, to assign the same VC, and Group ID for a given circuit in both directions. Note that the VC label must always be at the bottom of the label stack, and the tunnel label, if present, must be immediately above the VC label. Of course, as the packet is transported across the MPLS network, additional labels may be pushed on (and then popped off) as needed. Even R1 itself may push on additional labels above the tunnel label. If R1 and R2 are directly adjacent LSRs, then it may not be necessary to use a tunnel label at all. This document does not specify a method for distributing the tunnel label or any other labels that may appear above it on the stack. Any acceptable method of MPLS label distribution will do. This document does specify a method for assigning and distributing the VC label. Static label assignment MAY be used, and implementations SHOULD provide support for this. If signaling is used, the VC label MUST be distributed from R2 to R1 using LDP in the downstream unsolicited mode; this requires that an LDP connection be created between R1 and R2. Note that this technique allows an unbounded number of layer 2 "VCs" to be carried together in a single "tunnel". Thus it scales quite well in the network backbone. The MPLS network should be configured with a MTU that is at least 12 bytes larger then the largest packet size that will be transported in the LSPs. If a packet, once it has been encapsulated, exceeds the LSP MTU, it MUST be dropped. 4. Optional Sequencing and/or Padding Sometimes it is important to guarantee that sequentiality is preserved on a layer 2 virtual circuit. To accommodate this requirement, we provide an optional control word which may appear immediately after the label stack and immediately before the layer 2 PDU. This control word contains a sequence number. R1 and R2 both need to be configured with the knowledge of whether a control word will be used for a specific virtual circuit. Sometimes it is necessary to transmit a small packet on a medium Martini, et al. [Page 4] Internet Draft draft-martini-l2circuit-trans-mpls-03.txt September 2000 where there is a minimum transport unit larger than the actual packet size. In this case, padding is appended to the packet. When the VC label is popped, it may be desirable to remove the padding before forwarding the packet. To facilitate this, the control word has a length field. If the packet's length (without any padding) is less than 256 bytes, the length field MUST be set to the packet's length (without padding). Otherwise the length field MUST be set to zero. The value of the length field, if non-zero, can be used to remove any padding. The generic control word is defined as follows: 0 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 2 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Reserved | Length | Sequence Number | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ The first 8 bits are reserved for future use. They MUST be set to 0 when transmitting, and MUST be ignored upon receipt. The length byte is set as specified above. The next 16 bits are the sequence number that is used to guarantee ordered packet delivery. For a given VC label, and a given pair of LSRs, R1 and R2, where R2 has distributed that VC label to R1, the sequence number is initialized to 0, and is incremented by one for each successive packet carrying that VC label which R1 transmits to R2. The sequence number space is a 16 bit unsigned circular space. PDUs carrying the control word MUST NOT be delivered out of order. They may be discarded or reordered. 5. Protocol-Specific Issues 5.1. Frame Relay A Frame Relay PDU is transported in its entirety, including the Frame Relay Header. The sequencing control word is OPTIONAL. The BECN and FECN signals are carried unchanged across the network in the frame relay header. These signals do not appear in the MPLS header, and are unseen by the MPLS network. If the MPLS edge LSR detects a service affecting condition as defined Martini, et al. [Page 5] Internet Draft draft-martini-l2circuit-trans-mpls-03.txt September 2000 in [2] Q.933 Annex A.5 sited in IA FRF1.1, it will withdraw the label that corresponds to the frame relay DLCI. The Egress side should generate the corresponding errors and alarms as defined in [2] on the Frame relay VC. The ingress LSR MAY consider the DE bit of the Frame Relay header when determining the value to be placed in the EXP fields of the MPLS label stack. In a similar way, the egress LSR MAY consider the EXP field of the VC label when queuing the packet for egress. 5.2. ATM Two modes are supported for ATM transport, ATM Adaptation Layer 5 (AAL5) and ATM cell. In ATM AAL5 mode the ingress LSR is required to reassemble AAL5 CPCS-PDUs from the incoming VC and transport each CPCS-PDU as a single packet. No AAL5 trailer is transported. The sequencing control word is OPTIONAL. In ATM cell mode the ingress LSR transports each ATM cell payload as a single packet. No ATM cell header is transported. The sequencing control word is OPTIONAL. 5.2.1. F5 OAM Cell Support F5 OAM cells are not transported on the VC LSP. If an F5 end-to-end OAM cell is received from a VC by a LSR with a loopback indication value of 1 and the LSR has a label mapping for the VC, the LSR must decrement the loopback indication value and loop back the cell on the VC. Otherwise the loopback cell must be silently discarded by the LSR. A LSR may optionally be configured to periodically generate F5 end- to-end loopback OAM cells on a VC. In this case, the LSR must only generate F5 end-to-end loopback cells while a label mapping exists for the VC. If the VC label mapping is withdrawn the LSR must cease generation of F5 end-to-end loopback OAM cells. If the LSR fails to receive a response to an F5 end-to-end loopback OAM cell for a pre- defined period of time it must withdraw the label mapping for the VC. If an ingress LSR receives an AIS F5 OAM cell, fails to receive a pre-defined number of the End-to-End loop OAM cells, or a physical interface goes down, it must withdraw the label mappings for all VCs associated with the failure. When a VC label mapping is withdrawn, Martini, et al. [Page 6] Internet Draft draft-martini-l2circuit-trans-mpls-03.txt September 2000 the egress LSR must generate AIS F5 OAM cells on the VC associated with the withdrawn label mapping. 5.2.2. CLP Bit The ingress LSR MAY consider the CLP bit when determining the value to be placed in the EXP fields of the MPLS label stack. The egress LSR MAY consider the value of the EXP field of the VC label when determining the value of the ATM CLP bit. 5.2.3. PTI Field in ATM Cell Mode ATM cell mode is intended for transporting non-AAL5 traffic only. The ingress LSR must transport cells with a PTI of 0. Cells with a PTI other than 0 are not transported on the LSP. The egress LSR must set the PTI to 0 for cells switched from a VC LSP to an outgoing VC. 5.3. Ethernet VLAN For and ethernet 802.1q VLAN the entire ethernet frame without the preamble or FCS is transported as a single packet. The sequencing control word is OPTIONAL. If a packet is received out of sequence it MUST be dropped. The VLAN 4 byte tag is transported as is, and MAY be overwritten by the egress LSR. The ingress LSR MAY consider the user priority field [4] of the VLAN tag header when determining the value to be placed in the EXP fields of the MPLS label stack. In a similar way, the egress LSR MAY consider the EXP field of the VC label when queuing the packet for egress. Ethernet packets containing hardware level CRC, Framing errors, or runt packets MUST be discarded on input. 5.4. Ethernet For simple ethernet port to port transport,the entire ethernet frame without the preamble or FCS is transported as a single packet. The sequencing control word is OPTIONAL. If a packet is received out of sequence it MUST be dropped. As in the Ethernet VLAN case, ethernet packets with hardware level CRC, framing, and runt errors are discarded. Martini, et al. [Page 7] Internet Draft draft-martini-l2circuit-trans-mpls-03.txt September 2000 5.5. Circuit Emulation Service over MPLS (CEM) This section describes how to provide CEM for the following digital signals: 1. SONET STS-1 synchronous payload envelope (SPE)/SDH VC-3 2. STS-Nc SPE (N = 3, 12, or 48)/SDH VC-4, VC-4-4c, VC-4-16c Other SONET/SDH signals, such as virtual tributary (VT) structured sub-rate mapping, are not explicitly discussed in this document; however, it can be extended in the future to support VT services. OC-192c SPE/VC-4-64c are also not included at this point, since most MPLS networks use OC-192c or slower trunks, and thus would not have sufficient capacity. As trunk capacities increase in the future, the scope of this document can be accordingly extended. 5.5.1. CEM Encapsulation Format A TDM data stream is segmented into packets and encapsulated in MPLS packets. Each packet has one or more MPLS labels, followed by a 32- bit TDM header to associate the packet with the TDM stream. Note that the CEM control word is used instead of the generic control word in section 4. The outside label is used to identify the MPLS LSP used to tunnel the TDM packets through the MPLS network (the tunnel LSP). The interior label is used to multiplex multiple TDM connections within the same tunnel. The 32-bit CEM control word has the following format: 0 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 2 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Reserved | Sequnce Num | Structure Pointer |N|P| BIP-4 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ The above fields are defined as follows: - Reserved These eight bits are reserved for future use, such as alarm signaling or OAM. Martini, et al. [Page 8] Internet Draft draft-martini-l2circuit-trans-mpls-03.txt September 2000 - Structure Pointer The pointer points to the J1 byte in the payload area. The value is from 0 to 1,022, where 0 means the first byte after the CEM control word. The pointer is set to 0x3FF (1,023) if a packet does not carry the J1 byte. See [5] and [6] for more information on the J1 byte and the structure pointer. - The N and P bits See Section 5.4.2 below for their definition. - Seq Num This is a packet sequence number, which continuously cycles from 0 to 255. It begins at 0 when a TDM LSP is created. - BIP-4 The bit interleaved even parity over the first 28 header bits. 5.5.2. Clocking Mode It is necessary to be able to regenerate the input service clock at the output interface. Two clocking modes are supported: synchronous and asynchronous. 5.5.3. Synchronous When synchronous SONET timing is available at both ends of the circuit, the N(JE) and P(JE) bits are set for negative or positive justification events. The event is carried in five consecutive packets at the transmitter. The receiver plays out the event when three out of five packets with NJE/PJE bit set are received. If both bits are set, then path AIS event has occurred. If there is a frequency offset between the frame rate of the transport overhead and that of the STS SPE, then the alignment of the SPE shall periodically slip back or advance in time through positive or negative stuffing. The N(JE) and P(JE) bits are used to replay the stuff indicators and eliminate transport jitter. Martini, et al. [Page 9] Internet Draft draft-martini-l2circuit-trans-mpls-03.txt September 2000 5.5.4. Asynchronous If synchronous timing is not available, the N and P bits are not used for frequency justification and adaptive methods are used to recover the timing. The N and P bits are only checked for the occurrence of a path AIS event. An example adaptive method can be found in Section 3.4.2 of [7]. 6. LDP The VC label bindings are distributed using the LDP downstream unsolicited mode described in [1]. The LSRs will establish an LDP session using the Extended Discovery mechanism described in [1, section 2.4-2.5], for this purpose a new type of FEC TLV element is defined. The FEC element type in 128. [note1] The Virtual Circuit FEC TLV element, is defined as follows: 0 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 2 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | VC tlv |C| VC Type | VC ID len | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Group ID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | | VC ID | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ - VC Type A 15 bit quantity containing a value which represents the type of VC. Assigned Values are: VC Type Description 0x0001 Frame Relay DLCI 0x0002 ATM AAL5 PVC 0x0003 ATM Cell 0x0004 Ethernet VLAN 0x0005 Ethernet 0x0006 HDLC ( Cisco ) 0x0007 PPP 0x8008 CEM Martini, et al. [Page 10] Internet Draft draft-martini-l2circuit-trans-mpls-03.txt September 2000 The highest order bit is used to flag the presence of a control word as follows: bit 15 = 1 control word present on this VC. bit 15 = 0 no control word present on this VC. - VC ID length Length of the VC ID field in octets. If this value is 0, then it references all VCs using the specified group ID - Group ID An arbitrary 32 bit value which represents a group of VCs that is used to augment the VC space. This value MUST be user configurable. The group ID is intended to be used as either a port index , or a virtual tunnel index. In the latter case a switching function at ingress will map a particular circuit from a port to a circuit in the virtual tunnel for transport to the egress router. - VC ID Identifies a particular VC. The interpretation of the identifier depends on the VC type: * Frame Relay A 32-bit value representing a 16-bit DLCI value as follows: 0 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 2 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Reserved | DLCI | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ * ATM AAL5 PVC A 32-bit value representing a 16-bit VPI, and a 16-bit VCI as follows: 0 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 2 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | VPI | VCI | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Martini, et al. [Page 11] Internet Draft draft-martini-l2circuit-trans-mpls-03.txt September 2000 * ATM Cell A 32-bit value representing a 16-bit VPI, and a 16-bit VCI as follows: 0 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 2 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | VPI | VCI | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ * Ethernet VLAN A 32 bit value representing 16bit vlan identifier as follows: 0 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 2 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Reserved | VLAN ID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ * Ethernet A 32 bit port identifier. * HDLC ( Cisco ) A 32-bit port identifier (details TBD). * PPP A 32-bit port identifier (details TBD). * CEM A 32-bit value used follows: 0 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 2 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Reserved | Circuit ID | Payload Bytes | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Circuit ID: An assigned number for the SONET circuit being transported. Martini, et al. [Page 12] Internet Draft draft-martini-l2circuit-trans-mpls-03.txt September 2000 Payload Bytes(N): the number of TDM payload bytes contained in all packets on the CES stream, from 48 to 1,023 bytes. All of the packets in a given CES stream have the same number of payload bytes. Note that there is a possibility that the packet size may exceed the SPE size in the case of an STS-1 SPE, which could cause two pointers to be needed in the CEM header, since the payload may contain two J1 bytes for consecutive SPEs. For this reason, the number of payload bytes must be less than 783 for STS-1 SPEs. The reserved fields in the above specifications MUST be set to 0 in the FEC TLV, and ignored when received. 7. Security Considerations This document does not affect the underlying security issues of MPLS. 8. Open Issues Future revisions of this draft will discuss QoS requirements for CEM, methods to provide (or simulate) bi-directional LSPs (perhaps using the Group ID from [5]), signaling for the number of payload bytes, and sending additional end-to-end alarm information in addition to AIS. 9. Intellectual This document is being submitted for use in IETF standards discussions. Vivace Networks, Inc. has filed one or more patent applications relating to the CEM technology outlined in this document. 10. References [1] "LDP Specification", draft-ietf-mpls-ldp-07.txt ( work in progress ) [2] ITU-T Recommendation Q.933, and Q.922 Specification for Frame Mode Basic call control, ITU Geneva 1995 [3] "MPLS Label Stack Encoding", draft-ietf-mpls-label-encaps-07.txt ( work in progress ) Martini, et al. [Page 13] Internet Draft draft-martini-l2circuit-trans-mpls-03.txt September 2000 [4] "IEEE 802.3ac-1998" IEEE standard specification. [5] American National Standards Institute, "Synchronous Optical Network (SONET) - Basic Description including Multiplex Structure, Rates and Formats," ANSI T1.105-1995. [6] ITU Recommendation G.707, "Network Node Interface For The Synchronous Digital Hierarchy", 1996. [note1] FEC element type 128 is pending IANA approval. 11. Author Information Luca Martini Level 3 Communications, LLC. 1025 Eldorado Blvd. Broomfield, CO, 80021 e-mail: luca@level3.net Nasser El-Aawar Level 3 Communications, LLC. 1025 Eldorado Blvd. Broomfield, CO, 80021 e-mail: nna@level3.net Dimitri Stratton Vlachos Cisco Systems, Inc. 250 Apollo Drive Chelmsford, MA, 01824 e-mail: dvlachos@cisco.com Dan Tappan Cisco Systems, Inc. 250 Apollo Drive Chelmsford, MA, 01824 e-mail: tappan@cisco.com Martini, et al. [Page 14] Internet Draft draft-martini-l2circuit-trans-mpls-03.txt September 2000 Eric Rosen Cisco Systems, Inc. 250 Apollo Drive Chelmsford, MA, 01824 e-mail: erosen@cisco.com Steve Vogelsang Laurel Networks, Inc. 2607 Nicholson Rd. Sewickley, PA 15143 e-mail: sjv@laurelnetworks.com John Shirron Laurel Networks, Inc. 2607 Nicholson Rd. Sewickley, PA 15143 e-mail: sjv@laurelnetworks.com Andrew G. Malis Vivace Networks, Inc. 2730 Orchard Parkway San Jose, CA 95134 Phone: +1 408 383 7223 Email: Andy.Malis@vivacenetworks.com Ken Hsu Vivace Networks, Inc. 2730 Orchard Parkway San Jose, CA 95134 CA Phone: +1 408 432 7772 Email: Ken.Hsu@vivacenetworks.com 12. Appendix A: SONET/SDH Rates and Formats For simplicity, the discussion in this section uses SONET terminology, but it applies equally to SDH as well. SDH-equivalent terminology is shown in the tables. The basic SONET modular signal is the synchronous transport signal- level 1 (STS-1). A number of STS-1s may be multiplexed into higher- level signals denoted as STS-N, with N synchronous payload envelopes Martini, et al. [Page 15] Internet Draft draft-martini-l2circuit-trans-mpls-03.txt September 2000 (SPEs). The optical counterpart of the STS-N is the Optical Carrier- level N, or OC-N. Table 1 lists standard SONET line rates discussed in this document. OC Level OC-1 OC-3 OC-12 OC-48 OC-192 SDH Term - STM-1 STM-4 STM-16 STM-64 Line Rate(Mb/s) 51.840 155.520 622.080 2,488.320 9,953.280 Table 1. Standard SONET Line Rates Each SONET frame is 125 us and consists of nine rows. An STS-N frame has nine rows and N*90 columns. Of the N*90 columns, the first N*3 columns are transport overhead and the other N*87 columns are SPEs. A number of STS-1s may also be linked together to form a super-rate signal with only one SPE. The optical super-rate signal is denoted as OC-Nc, which has a higher payload capacity than OC-N. The first 9-byte column of each SPE is the path overhead (POH) and the remaining columns form the payload capacity with fixed stuff (STS-Nc only). The fixed stuff, which is purely overhead, is N/3-1 columns for STS-Nc. Thus, STS-1 and STS-3c do not have any fixed stuff, STS-12c has three columns of fixed stuff, and so on. The POH of an STS-1 or STS-Nc is always nine bytes in nine rows. The payload capacity of an STS-1 is 86 columns (774 bytes) per frame. The payload capacity of an STS-Nc is (N*87)-(N/3) columns per frame. Thus, the payload capacity of an STS-3c is (3*87 - 1)*9 = 2,340 bytes per frame. As another example, the payload capacity of an STS-192c is 149,760 bytes, which is exactly 64 times larger than the STS-3c. There are 8,000 SONET frames per second. Therefore, the SPE size, (POH plus payload capacity) of an STS-1 is 783*8*8,000 = 50.112 Mb/s. The SPE size of a concatenated STS-3c is 2,349 bytes per frame or 150.336 Mb/s. The payload capacity of an STS-192c is 149,760 bytes per frame, which is equivalent to 9,584.640 Mb/s. Table 2 lists the SPE and payload rates supported. SONET STS Level STS-1 STS-3c STS-12c STS-48c STS-192c SDH VC Level - VC-4 VC-4-4c VC-4-16c VC-4-64c Payload Size(Bytes) 774 2,340 9,360 37,440 149,760 Payload Rate(Mb/s) 49.536 149.760 599.040 2,396.160 9,584.640 SPE Size(Bytes) 783 2,349 9,396 37,584 150,336 SPE Rate(Mb/s) 50.112 150.336 601.344 2,405.376 9,621.504 Table 2. Payload Size and Rate Martini, et al. [Page 16] Internet Draft draft-martini-l2circuit-trans-mpls-03.txt September 2000 To support circuit emulation, the entire SPE of a SONET STS or SDH VC level is encapsulated into packets, using the encapsulation defined in the next section, for carriage across MPLS networks. Martini, et al. [Page 17]