PWE3 Working Group Andrew G. Malis Internet Draft Vivace Networks, Inc. Expiration Date: July 2003 Prayson Pate Overture Networks, Inc. January 2003 SONET/SDH Circuit Emulation over Packet (CEP) draft-ietf-pwe3-sonet-01.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. Abstract The generic requirements and architecture for Pseudo Wire Emulation Edge-to-Edge (PWE3) have been described in [PWE3-REQ] and [PWE3- ARCH]. Additional requirements for emulation of SONET/SDH and lower-rate TDM circuits has been defined in [PWE3-TDM-REQ]. This draft provides encapsulation formats and semantics for emulating SONET/SDH circuits and services over a packet-switched network (PSN). pwe3-sonet Expires July 2003 [Page 1] Internet Draft draft-ietf-pwe3-sonet-01 January 2003 Co-Authors The following individuals are co-authors of this document Craig White Level3 Communications David Zelig Corrigent Systems Ed Hallman Litchfield Communications Jeremy Brayley Laurel Networks Jim Boyle Protocol Driven Networks John Shirron Laurel Networks Luca Martini Level3 Communications Marlene Drost Litchfield Communications Ron Cohen Lycium Networks Steve Vogelsang Laurel Networks Tom Johnson (Editor) Litchfield Communications Table of Contents 1 Conventions used in this document 2 2 Acronyms 3 3 Scope 4 4 CEP Encapsulation Format 5 4.1 SONET/SDH Fragment 6 4.2 CEP Header 7 4.3 RTP Header 9 4.4 PSN Encapsulation 10 4.5 L2TP Encapsulation 13 5 SONET/SDH Transport Timing 14 6 SONET/SDH Pointer Management 14 6.1 Explicit Pointer Adjustment Relay (EPAR) 14 6.2 Adaptive Pointer Management (APM) 15 7 CEP Performance Monitors 15 7.1 Near-End Performance Monitors 16 7.2 Far-End Performance Monitors 17 8 Payload Compression Options 17 8.1 Dynamic Bandwidth Allocation 18 8.2 Service-Specific Payload Formats 19 9 Open Issues 26 10 Security Considerations 27 11 Intellectual Property Disclaimer 27 12 References 27 13 Author's Addresses 29 1 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 [RFC 2119]. pwe3-sonet Expires July 2003 [Page 2] Internet Draft draft-ietf-pwe3-sonet-01 January 2003 2 Acronyms ADM Add Drop Multiplexer AIS Alarm Indication Signal AU-n Administrative Unit-n (SDH) AUG Administrative Unit Group (SDH) BIP Bit Interleaved Parity BITS Building Integrated Timing Supply CEP Circuit Emulation over Packet DBA Dynamic Bandwidth Allocation - see [CEP-SPE] EBM Equipped Bit Mask LOF Loss of Frame LOS Loss of Signal LTE Line Terminating Equipment PSN Packet Switched Network POH Path Overhead PTE Path Terminating Equipment PWE3 Pseudo-Wire Emulation Edge-to-Edge RDI Remote Defect Indication SDH Synchronous Digital Hierarchy SONET Synchronous Optical Network STM-n Synchronous Transport Module-n (SDH) STS-n Synchronous Transport Signal-n (SONET) TDM Time Division Multiplexing TOH Transport Overhead TU-n Tributary Unit-n (SDH) TUG-n Tributary Unit Group-n (SDH) pwe3-sonet Expires July 2003 [Page 3] Internet Draft draft-ietf-pwe3-sonet-01 January 2003 VC-n Virtual Container-n (SDH) VT Virtual Tributary (SONET) VTG Virtual Tributary Group (SONET) 3 Scope This document describes how to emulate the following digital signals over a packet switched network: 1. Synchronous Payload Envelope (SPE): STS-1/VC-3, STS-3c/VC-4, STS- 12c/VC-4-4c, STS-48c/VC-4-16c, STS-192c/VC-4-64c. 2. Virtual Tributary (VT): VT1.5/VC-11, VT2/VC-12, VT3, VT6/VC-2 For the remainder of this document, these constructs will be referred to as SONET/SDH channels. Although this document currently covers up to OC-192c/VC-4-64c, future revision MAY address higher rates. pwe3-sonet Expires July 2003 [Page 4] Internet Draft draft-ietf-pwe3-sonet-01 January 2003 4 CEP Encapsulation Format In order to transport SONET/SDH circuits through a packet-oriented network, the SPE (or VT) is broken into fragments, and a CEP Header is pre-pended to each fragment. The resulting packet is encapsulated in RTP for transmission over an arbitrary PSN. (Note: under certain circumstances the RTP header may be suppressed to conserve network bandwidth. See section 4.4.3 for details). The basic CEP packet appears in Figure 1. +-----------------------------------+ | PSN and Multiplexing Layer | | Headers | +-----------------------------------+ | RTP Header | | (RFC1889) | +-----------------------------------+ | CEP Header | +-----------------------------------+ | | | | | SONET/SDH | | Fragment | | | | | +-----------------------------------+ Figure 1 - Basic CEP Packet pwe3-sonet Expires July 2003 [Page 5] Internet Draft draft-ietf-pwe3-sonet-01 January 2003 4.1 SONET/SDH Fragment The SONET/SDH Fragments MUST be byte aligned with the SONET/SDH SPE (or VT). The first bit received from each byte of the SONET/SDH MUST be the Most Significant Bit of each byte in the SONET/SDH fragment. SONET/SDH bytes are placed into the SONET/SDH fragment in the same order in which they are received. SONET/SDH optical interfaces use binary coding and therefore are scrambled prior to transmission to insure an adequate number of transitions. For clarity, this scrambling will be referred to as physical layer scrambling/descrambling. In addition, many payload formats (such as for ATM and HDLC) include an additional layer of scrambling to provide protection against transition density violations within the SPEs. This function will be referred to as payload scrambling/descrambling. CEP assumes that physical layer scrambling/descrambling occurs as part of the SONET/SDH section/line termination Native Service Processing (NSP) functions. However, CEP makes no assumption about payload scrambling. The SONET/SDH fragments MUST be constructed without knowledge or processing of any incidental payload scrambling. CEP implementations MUST include the H3 (or V3) byte in the SONET/SDH fragment during negative pointer adjustment events, and MUST remove the stuff-byte from the SONET/SDH fragment during positive pointer adjustment events. All CEP Implementations MUST support a packet size of 783 Bytes and MAY support other packet sizes. VT emulation implementations MUST support payload size of 1/4 VT superframe fragment, and MAY support 1/2 and full VT superframe payload sizes. OPTIONAL SONET/SDH Fragment formats have been defined to reduce the bandwidth requirements of the emulated SONET/SDH circuits under certain conditions. These OPTIONAL Formats are included in Appendix B. pwe3-sonet Expires July 2003 [Page 6] Internet Draft draft-ietf-pwe3-sonet-01 January 2003 4.2 CEP Header The CEP Header supports a basic and extended mode. The Basic CEP Header provides the minimum functionality necessary to accurately emulate a TDM SONET over a PSN if a common reference is available at both ends of the PW. Enhanced functionality and commonality with other real-time Internet applications is provided by RTP encapsulation. Bit 0 of the first 32-bit CEP header indicates whether or not the extended header is present. When this bit is 0, then no extended header is present. When this bit is 1, then an extended header is present. Extended headers are utilized for the some of the OPTIONAL SONET/SDH fragment formats described in Appendix B. The Basic CEP header 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |0|R|D|N|P| Structure Pointer[0:12] | Sequence Number[0:13] | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 2 - Basic CEP Header Format The above fields are defined as follows: R bit: CEP-RDI. This bit is set to one to signal to the remote CEP function that a loss of packet synchronization has occurred. D bit: Signals DBA Mode. MUST be set to zero for Normal Operation. MUST be set to one if CEP is currently in DBA mode. DBA is an optional mode during which trivial payloads are not transmitted into the packet network. See Table 1 and section 8.1 for further details. The N and P bits: MAY be used to explicitly relay negative and positive pointer adjustment events across the PSN. They are also used to relay SONET/SDH maintenance signals such as AIS-P/V. See Table 1 and section 6.1 for more details. pwe3-sonet Expires July 2003 [Page 7] Internet Draft draft-ietf-pwe3-sonet-01 January 2003 +---+---+---+----------------------------------------------+ | D | N | P | Interpretation | +---+---+---+----------------------------------------------+ | 0 | 0 | 0 | Normal Mode - No Ptr Adjustment | | 0 | 0 | 1 | Normal Mode - Positive Ptr Adjustment | | 0 | 1 | 0 | Normal Mode - Negative Ptr Adjustment | | 0 | 1 | 1 | Normal Mode - AIS-P/V | | | | | | | 1 | 0 | 0 | DBA Mode - STS Unequipped | | 1 | 0 | 1 | DBA Mode - STS Unequipped Pos Ptr Adj | | 1 | 1 | 0 | DBA Mode - STS Unequipped Neg Ptr Adj | | 1 | 1 | 1 | DBA Mode - AIS-P/V | +---+---+---+----------------------------------------------+ Table 1 - Interpretation of D, N, and P bits Sequence Number[0:13]: This is a packet sequence number, which MUST continuously cycle from 0 to 0x3FFF. It is generated and processed in accordance with the rules established in [RFC1889]. When the RTP header is used, this sequence number MUST match the LSBs of the RTP sequence Number. Structure Pointer[0:12]: The Structure Pointer MUST contain the offset of the first byte of the payload structure. For SPE emulation, the structure pointer locates the J1 byte within the CEP SONET/SDH Fragment. (For VT emulation the structure pointer locates the V5 byte within the SONET/SDH fragment). The value is from 0 to 0x1FFE, where 0 means the first byte after the CEP header. The Structure Pointer MUST be set to 0x1FFF if a packet does not carry the J1 (or V5) byte. pwe3-sonet Expires July 2003 [Page 8] Internet Draft draft-ietf-pwe3-sonet-01 January 2003 4.3 RTP Header CEP uses the fixed RTP Header as shown below. 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |V=2|P|X| CC |M| PT | sequence number | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | timestamp | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | synchronization source (SSRC) identifier | +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+ Figure 3 - RTP Header V : (version) always set to 2 P : (padding) always set to 0 X : (header extension) always set to 0 CC: (CSRC count) always set to 0 M : (marker) set to 0 for CEP packets. PT: (payload type) used to identify packets carrying the packetized SONET/SDH data. One PT value should be allocated from the range of dynamic values (see [RTP-TYPES]) for every CEP PW. Allocation is done during the PW setup and MUST be the same for both PW directions. The PE at the PW ingress MUST set the PT value in the RTP header to the allocated value. Sequence Number : used primarily to provide the common PW sequencing function as well as detection of lost packets. It is generated and processed in accordance with the rules established in [RFC1889]. Timestamp : used primarily for carrying timing information over the network. Their values are used in accordance with the rules established in [RFC1889]. Frequency of the clock used for generating timestamps MUST be 19.44 MHz based on a local reference. SSRC : (synchronization source) MAY be used for detection of misconnections. pwe3-sonet Expires July 2003 [Page 9] Internet Draft draft-ietf-pwe3-sonet-01 January 2003 4.4 PSN Encapsulation In principle, CEP packets can be carried over any packet-oriented network. The following sections describe specifically how CEP packets MUST be encapsulated for carriage over MPLS or IP networks. 4.4.1 IP Encapsulation CEP uses the standard IP/UDP/RTP encapsulation scheme as shown below. The UDP destination port MUST be used to Demultiplex individual SONET channels. +-----------------------------------+ | | | IPv6/v4 Header | | | +-----------------------------------+ | UDP Header | +-----------------------------------+ | RTP Header | +-----------------------------------+ | CEP Header | +-----------------------------------+ | | | | | SONET/SDH Fragment | | | | | +-----------------------------------+ Figure 4 - IP Transport Encapsulation pwe3-sonet Expires July 2003 [Page 10] Internet Draft draft-ietf-pwe3-sonet-01 January 2003 4.4.2 MPLS Encapsulation RTP MAY be directly encapsulated in MPLS as shown below. To transport a CEP packet over an MPLS network, an MPLS label-stack MUST be pushed on top of the CEP packet. The bottom label in the MPLS label stack MUST be used to demultiplex individual SONET channels. In keeping with the conventions used in [PWE3-CONTROL], this demultiplexing label is referred to as the PW Label and the upper labels are referred to as Tunnel Labels. +-----------------------------------+ | One or more MPLS Tunnel Labels | +-----------------------------------+ | PW Label | +-----------------------------------+ | RTP Header | +-----------------------------------+ | CEP Header | +-----------------------------------+ | | | | | SONET/SDH Fragment | | | | | +-----------------------------------+ Figure 5 - Typical MPLS Transport Encapsulation pwe3-sonet Expires July 2003 [Page 11] Internet Draft draft-ietf-pwe3-sonet-01 January 2003 4.4.3 RTP Header Suppression In addition to normal RTP header compression mechanisms as described in [RFC2508] and [RFC3095], an additional option may be used in CEP which suppresses transmission of the RTP header altogether. This mode may be used when both SONET Emulation PEs have access to a common reference clock and both support RTP Header Suppression. Under these conditions the following encapsulation formats may be used. The choice to utilize RTP Header Suppression may be statically configured using [CEM-MIB], or signaled using a PW maintenance protocol such as [PWE3-CONTROL]. +-----------------------------------+ | | | IPv6/v4 Header | | | +-----------------------------------+ | UDP Header | +-----------------------------------+ | CEP Header | +-----------------------------------+ | | | | | SONET/SDH Fragment | | | | | +-----------------------------------+ Figure 6 - IP Transport Encapsulation w/ RTP Header Suppression pwe3-sonet Expires July 2003 [Page 12] Internet Draft draft-ietf-pwe3-sonet-01 January 2003 +-----------------------------------+ | One or more MPLS Tunnel Labels | +-----------------------------------+ | PW Label | +-----------------------------------+ | CEP Header | +-----------------------------------+ | | | | | SONET/SDH Fragment | | | | | +-----------------------------------+ Figure 7 - MPLS Transport Encapsulation w/ RTP Header Suppression 4.5 L2TP Encapsulation Encapsulation for L2TP PSNs is for future study. pwe3-sonet Expires July 2003 [Page 13] Internet Draft draft-ietf-pwe3-sonet-01 January 2003 5 SONET/SDH Transport Timing It is assumed that the distribution of SONET/SDH Transport timing information is addressed through external mechanisms such as Building Integrated Timing System (BITS), Stand Alone Synchronization Equipment (SASE), Global Positioning System (GPS) or other such methods , or is addressed through an adaptive timing recovery algorithm, and is therefore outside of the scope of this specification. 6 SONET/SDH Pointer Management A pointer management system is defined as part of the definition of SONET/SDH. Details on SONET/SDH pointer management can be found in [SONET], [GR253], and [G707]. If there is a frequency offset between the frame rate of the transport overhead and that of the SONET/SDH SPE, then the alignment of the SPE (or VT) will periodically slip back or advance in time through positive or negative stuffing. The emulation of this aspect of SONET networks may be accomplished using a variety of techniques including (but not limited to) explicit pointer adjustment relay (EPAR) and adaptive pointer management (APM). In any case, the handling of the SPE data by the CEP packetizer is the same. During a negative pointer adjustment event, the CEP packetizer MUST incorporate the H3 (or V3) byte from the SONET/SDH stream into the CEP packet payload in order with the rest of the SPE. During a positive pointer adjustment event, the CEP packetizer MUST strip the stuff byte from the CEP packet payload. When playing out a negative pointer adjustment event, the appropriate byte of the CEP payload MUST be placed into the H3 (or V3) byte of the SONET/SDH stream. When playing out a positive pointer adjustment, the CEP de-packetizer MUST insert a stuff-byte into the appropriate position within the SONET/SDH stream. The details regarding the use of the H3 (and V3) byte and stuff byte during positive and negative pointer adjustments can be found in [SONET], [GR253], and [G707]. 6.1 Explicit Pointer Adjustment Relay (EPAR) pwe3-sonet Expires July 2003 [Page 14] Internet Draft draft-ietf-pwe3-sonet-01 January 2003 CEP provides an OPTIONAL mechanism to explicitly relay pointer adjustment events from one side of the PSN to the other. This technique will be referred to as Explicit Pointer Adjustment Relay (EPAR). The mechanics of EPAR are described below. The following text only applies to implementations that choose to implement EPAR. Any CEP implementation that does not support EPAR MUST either set the N and P bits to zero or utilize them to relay AIS-P/V and STS/VT Unequipped as shown in table 1. For SPE Emulation, the pointer adjustment event MUST be transmitted in three consecutive packets by the packetizer. The de-packetizer MUST play out the pointer adjustment event when any one packet with N/P bit set is received. The CEP de-packetizer MUST utilize the CEP sequence numbers to insure that SONET/SDH pointer adjustment events are not played any more frequently than once per every three CEP packets transmitted by the remote CEP packetizer. For VT emulation, a pointer adjustment event MUST be transmitted in all packets carrying a single VT superframe, starting from the packet carrying the V5 byte and not including the packet carrying the V5 byte of the next VT superframe. Pointer adjustment events at the VT and STS-1 levels are mapped to N and P indications. Pointer adjustments at the VT level are mapped 1:1 to CEP indications, while STS-1 indications are mapped according to the ratio of VT/SPE byte rates. If both bits are set, then an AIS-P/V event has been detected at the PW ingress, making the pointer invalid. When DBA is invoked (i.e. the D-bit = 1), N and P have additional meanings. See Table 1 and section Appendix C for more details. 6.2 Adaptive Pointer Management (APM) Another OPTIONAL method that may be used to emulate SONET pointer management is Adaptive Pointer Management (APM). In basic terms, APM uses information about the depth of the CEP jitter buffers to introduce pointer adjustments in the reassembled SONET SPE. Details about specific APM algorithms is not considered to be within scope for this document. 7 CEP Performance Monitors SONET/SDH as defined in [SONET], [GR253], and [G707] includes the definition of several counters that may be used to monitor the pwe3-sonet Expires July 2003 [Page 15] Internet Draft draft-ietf-pwe3-sonet-01 January 2003 performance of SONET/SDH services. These counters are referred to as Performance Monitors. In order for CEP to be utilized by traditional SONET/SDH network operators, CEP SHOULD provide similar functionality. To this end, the following sections describe a number of counters that will collectively be referred to as CEP Performance Monitors. 7.1 Near-End Performance Monitors These performance monitors are maintained by the CEP De-Packetizer during reassembly of the SONET stream. The performance monitors are based on two types of defects. Type 1 defect is defined as: missing or dropped packet. Type 2 defect is defined as: buffer under run, buffer over-run, LOPS. The specific performance monitors that are defined for CEP are as follows: ES-CEP - CEP Errored Seconds SES-CEP - CEP Severely Errored Seconds UAS-CEP - CEP Unavailable Seconds Each second that contain at least one type 1 defect SHALL be declared as ES-CEP. Each second that contain type 2 defect, or missing packets above pre-defined, configurable threshold of missing/dropped packets SHALL be declared both SES-CEP and ES-CEP. Default value for missing packet to SES is 3. UAS-CEP SHALL be declared after X consecutives SES-CEP, cleared after X consecutive seconds without SES-CEP. Default value of X is 10 seconds. Once unavailability is declared, ES and SES counts SHALL be inhibited up to the point where the unavailability was started. Once unavailability is removed, ES that occurred along the X seconds clearing period SHALL be added to the ES counts. An update is required even for closed intervals if necessary. FC-CEP is the number of time type 1 or type 2 defect states were declared. The NE SHALL have thresholding on ES-CEP, SES-CEP and UAS-CEP (thresholding mean activate a notification if more than pre- defined # of seconds are declared as ES, etc. in 15 minutes interval). pwe3-sonet Expires July 2003 [Page 16] Internet Draft draft-ietf-pwe3-sonet-01 January 2003 7.2 Far-End Performance Monitors These performance monitors provide insight into the CEM De- packetizer at the far-end of the PSN. Far end statistics are based on the RDI-CEP bit. Limited functionality is supported compared to [GR-253] for simplicity and because it is assumed that all relevant statistics are available from the end point of the PW. CEP-FE defect is declared when CEP-RDI is set in the incoming CEP packets. CEP-FE failure declared after 2.5 +/- 0.5 seconds of CEP-FE defect, and cleared after 10 seconds free of CES-FE defect state. Sending notification to the OS for CEP-FE failure is local policy. This draft does not attempt to define SES-CEPFE, UAS-CEPFE and FC- CEPFE, but they can be added if to fully emulate GR-253 far end PM (thresholding is required too here except for FC-CEPFE). (Note that ES-CEPFE is not relevant since CEP does not report back missing packets - only LOPS which is SES). The definition of additional performance monitors is for future study. 8 Payload Compression Options In addition to pure emulation, CEP also offers a number of options for reducing the total bandwidth utilized by the emulated circuit. These options fall into two categories: Dynamic Bandwidth Allocation and Service-Specific Payload Formats. Dynamic Bandwidth Allocation suppresses transmission of the CEP payload altogether under certain circumstances such as AIS-P/V and STS/VT Unequipped. Service-Specific Payload formats reduce bandwidth by suppressing transmission of portions of the SPE based on specific knowledge of the SPE payload. Details on these payload compression options are described in the following subsections. pwe3-sonet Expires July 2003 [Page 17] Internet Draft draft-ietf-pwe3-sonet-01 January 2003 8.1 Dynamic Bandwidth Allocation Dynamic Bandwidth Allocation (DBA) is an OPTIONAL mechanism for suppressing the transmission of the SPE (or VT) fragment when one of two trigger conditions are met, AIS-P/V or STS/VT Unequipped. Implementations that support DBA MUST include a mechanism for disabling DBA on a channel-by-channel basis to allow for interoperability with implementations that do not support DBA. When a DBA trigger is recognized at a PW ingress, the CEP packets will be constructed as shown in figure C.1. Optional padding bytes may be included if the intervening packet network has a minimum packet size which is less than the DBA packet. +-----------------------------------+ | PSN and Multiplexing Layer | | Headers | +-----------------------------------+ | RTP Header | | (RFC1889) | +-----------------------------------+ | CEP Header | +-----------------------------------+ | (Optional) Padding | +-----------------------------------+ Figure 8 - Basic CEP-DBA Packet If RTP Header suppression is utilized, the CEP packets will be constructed as shown in figure A2.2 +-----------------------------------+ | PSN and Multiplexing Layer | | Headers | +-----------------------------------+ | CEP Header | +-----------------------------------+ | (Optional) Padding | +-----------------------------------+ Figure 9 - CEP-DBA Packet with RTP Header Suppression Other than the suppression of the CEP payload, the CEP behavior during DBA should be equivalent to normal CEP behavior. In particular, the packet transmission rate during DBA should be equivalent to the normal packet transmission rate. pwe3-sonet Expires July 2003 [Page 18] Internet Draft draft-ietf-pwe3-sonet-01 January 2003 8.2 Service-Specific Payload Formats In addition to the standard payload encapsulations for SPE and VT transport, several OPTIONAL payload formats have been defined to provide varying amounts of payload compression depending on the type and amount of user traffic present within the SPE. These are described below: 8.2.1 Fractional STS-1 (VC-3) Encapsulation Fractional STS-1 (VC-3) encapsulation carries only selected set of VTs within an STS-1 container. This mode is applicable for STS-1 with POH signal label byte C2=2 (VT-structured SPE) and for C2=3 (Locked VT mode). The mapping of VTs into an STS-1 container is described in section 3.2.4 of [GR253] and the mapping into VC-3 is defined in section 7.2.4 in [G.707]. The CEP packetizer removes all fixed column bytes (columns 30 and 59) and all bytes that belong to the removed VTs. Only STS-1 POH bytes and bytes that belong to the selected VTs are carried within the payload. The CEP de-packetizer adds the fixed stuff bytes and generates unequipped VT data replacing the removed VT bytes. Figure 21 below describes VT mapping into an STS-1 SPE. 1 2 3 * * * 29 30 31 32 * * * 58 59 60 61 * * * 87 +--+------------------+-+------------------+-+------------------+ 1 |J1| Byte 1 (V1-V4) |R| | | | |R| | | | | +--+---+---+------+---+-+------------------+-+------------------+ 2 |B3|VT | | | |R| | | | |R| | | | | +--+1.5| | | +-+---+---+------+---+-+------------------+ 3 |C2| | | | |R| | | | |R| | | | | +--+ | | | +-+---+---+------+---+-+------------------+ 4 |G1| | | | |R| | | | |R| | | | | +--+ | | | +-+---+---+------+---+-+------------------+ 5 |F2| | | | |R| | | | |R| | | | | +--|1-1|2-1| * * *|7-4|-|1-1|2-1| * * *|7-4|-|1-1|2-1| * * *|7-4| 6 |H4| | | | |R| | | | |R| | | | | +--+ | | | +-+---+---+------+---+-+------------------+ 7 |Z3| | | | |R| | | | |R| | | | | +--+ | | | +-+---+---+------+---+-+------------------+ 8 |Z4| | | | |R| | | | |R| | | | | +--+ | | | +-+---+---+------+---+-+------------------+ 9 |Z5| | | | |R| | | | |R| | | | | +--+---+---+------+---+-+---+---+------+---+-+------------------+ | | | +-- Path Overhead +--------------------+-- Fixed Stuffs pwe3-sonet Expires July 2003 [Page 19] Internet Draft draft-ietf-pwe3-sonet-01 January 2003 Figure 10 - SONET SPE Mapping of VT1.5 The SPE always contains seven interleaved VT groups (VTGs). Each VTG contains a single type of VT, and each VTG occupies 12 columns (108 bytes) within each SPE. A VTG can contain 4 VT1.5s (T1s), 3 VT2s (E1s), 2 VT3s or a single VT6. Altogether, the SPE can carry 28 T1s or carry 21 E1s. The fractional STS-1 encapsulation can optionally carry a bit mask that specifies which VTs are carried within the STS-1 payload and which VTs have been removed. This optional bit mask attribute allows the ingress circuit emulation node to remove an unequipped VT on the fly, providing the egress circuit emulation node enough information for reconstructing the VTs in the right order. The use of bit mask enables "on the fly" compression, whereby only equipped VTs (carrying actual data) are sent. 8.2.1.1 Fractional STS-1 CEP header The fractional STS-1 CEP header uses the STS-1 CEP header encapsulation as defined in this draft. Optionally, an additional 4 byte header extension word is added. The extended header is described in Figure 23. 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |1|R|D|N|P| Structure Pointer[0:12] | Sequence Number[0:13] | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |E|0|0|0| Equipped Bit Mask (EBM) [0:27] | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 11 - Extended Fractional STS-1 Header The following fields are used within the extended header: - R, D, N, P, Structured Pointer and Sequence Number: All fields are used as defined in this draft for STS-1 encapsulation. - E: Extension bit. E=0: indicates that extended header is not used. E=1: indicates that extended header is carried within the packet. The E bit in the first word is set to 1 to indicate use of the Equipped Bit Mask (EBM). The E bit in the second word indicates whether the extended header (to be defined pwe3-sonet Expires July 2003 [Page 20] Internet Draft draft-ietf-pwe3-sonet-01 January 2003 in future revision of this draft) is used. - EBM: Each bit within the bit mask refers to a different VT within the STS-1 container. A bit set to 1 indicates that the corresponding VT is equipped, hence carried within the fractional STS-1 payload. The format of the EBM is defined in Figure 24. 0 1 2 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | VTG7 | VTG6 | VTG5 | VTG4 | VTG3 | VTG2 | VTG1 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 12 - Equipped Bit Mask (EBM) for fractional STS-1 The 28 bits of the EBM are divided into groups of 4 bits, each corresponding to a different VTG within the STS container. All 4 bits are used to indicate whether VT1.5 (T1) tributaries are carried within a VTG. The first 3 bits read from right to left are used to indicate whether VT2 (E1) tributaries are carried within a VTG. For example, the EBM of a fully occupied STS-1 with VT1.5 is all ones, while that of an STS-1 fully occupied with VT2 (E1) tributaries has the binary value 0111011101110111011101110111. 8.2.1.2 B3 Compensation Fractional STS-1 encapsulation can be implemented in Line Terminating Equipment (LTE) or in Path Terminating Equipment (PTE). PTE implementations terminate the path layer at the ingress PE and generate a new path layer at the egress PE. LTE implementations do not terminate the path layer, and therefore need to keep the content and integrity of the POH bytes across the PSN. In LTE implementations, special care must be taken to maintain the B3 bit-wise parity POH byte. The B3 compensation algorithm is defined below. Since the BIP-8 value in a given frame reflects the parity check over the previous frame, the changes made to BIP-8 bits in the previous frame shall also be considered in the compensation of BIP-8 in the current frame. Therefore the following equation shall be used for compensation of the individual bits of the BIP-8: B3[i]'(t) = B3[i](t-1) || B3[i]'(t-1) || B3[i](t) || B*3[i](t-1) Where: B3[i] = the existing B3[i] value in the incoming signal pwe3-sonet Expires July 2003 [Page 21] Internet Draft draft-ietf-pwe3-sonet-01 January 2003 B3[i]' = the new (compensated) B3[i] value. B3*[i] = the B3[i] value of the unequipped VT(VC)s in the incoming signal || = exclusive OR operator. t = the time of the current frame. t-1 = the time of the previous frame. The egress PE MUST reconstruct the unequipped VTs and modify the B3 parity value in the same manner to accommodate for the additional VTs added. In this way the end-to-end BIP is preserved. 8.2.2 Asynchronous T3/E3 STS-1 (VC-3) Encapsulation Asynchronous T3/E3 STS-1 (VC-3) encapsulation is applicable for STS- 1 with POH signal label byte C2=4, carrying asynchronous mapping of T3 or E3 signals. A T3 is encapsulated asynchronously into an STS-1 SPE using the format defined in section 3.4.2.1 of [GR253]. The STS-1 SPE is then encapsulated as defined in this draft. Optionally, the STS-1 SPE can be compressed by removing the fixed columns leaving only data columns. STS-1 columns are numbered 1 to 87, starting from the POH column numbered 1. The following columns have fixed values and are removed: 2, 3, 30, 31, 59, 60 Figure 13 - Fixed columns removed within T3 mapping to STS-1 Bandwidth saving is approximately 7% (6 columns out of 87). The B3 parity byte need not be modified as the parity of the fixed columns amounts to zero. A T3 is encapsulated asynchronously into a VC-3 container as described in section 10.1.2.1 of [G.707]. VC-3 container has only 85 data columns, which is identical to the STS-1 container with the two fixed stuff columns 30 and 59 removed. Other than that, the mapping is identical. An E3 is encapsulated asynchronously into a VC-3 SPE using the format defined in section 10.1.2.2 of [G.707]. The VC-3 SPE is then encapsulated as defined in this draft. Optionally, the VC3 SPE can be compressed by removing the fixed columns leaving only data columns. VC-3 columns are numbered 1 to 85 (and not 87), starting from the POH column numbered 1. The following columns have fixed values and are removed: 2, 6, 10, 14, 18, 19, 23, 27, 31, 35, 39, 44, 48, 52, 56, 60, 61, 65, 69, 73, 77, 81 pwe3-sonet Expires July 2003 [Page 22] Internet Draft draft-ietf-pwe3-sonet-01 January 2003 Figure 14 - Fixed columns removed within E3 mapping to VC-3 Bandwidth saving is approximately 28% (24 columns out of 85). The B3 parity byte need not be modified as the parity of the fixed columns amounts to zero. Implementations of asynchronous T3/E3 STS-1 (VC-3) encapsulation MUST support payload length of one SPE and MAY support payload length of 1/3 SPE. The actual payload size are smaller and are described in appendix B. 8.2.3 Fractional VC-4 Encapsulation SDH defines a mapping of VC-11, VC-12, VC-2 and VC-3 directly into VC-4. This mapping does not have an equivalent within the SONET hierarchy. The VC-4 mapping is common in SDH implementations. VC-4 <--x3-- TUG-3 <----x1-------- TU-3 <---- VC-3 >---- E3/T3 | +--x7-- TUG-2 <--x1- TU-2 <-- VC-2 <---- DS-2 | +----x3---- TU-12 <-- VC-12<---- E1 | +----x4---- TU-11 <-- VC-11<---- T1 Figure 15 - Mapping of VCs into VC-4 Figure 27 describes the mapping options of VCs into VC-4. A VC-4 contains three TUG-3s. Each TUG-3 is composed of either a single TU- 3, or 7 TUG-2s. A TU-3 contains a single VC-3. A TUG-2 contains either 4 VC-11s (T1s), 3 VC-12s (E1s) or one VC-2. Therefore a VC-4 may contain 3 VC-3s, 1 VC-3 and 42 VC-12s, 63 VC-12s, etc. Fractional VC-4 encapsulation carries only selected set of VCs within a VC-4 container. This mode is applicable for VC-4 with POH signal label byte C2=2 (TUG structure) and for C2=3 (Locked TU-n). The mapping of VCs into a VC-4 container is described in section 7.2 of [G.707]. The CEP packetizer removes all fixed column bytes and all bytes that belong to the removed VCs. Only VC-4 POH bytes and bytes that belong to the selected VCs are carried within the payload. The CEP de-packetizer adds the fixed stuff bytes and generates unequipped VC data replacing the removed VC bytes. The fractional VC-4 encapsulation can optionally carry a bit mask that specifies which VCs are carried within the VC-4 payload and which VCs have been removed. This optional bit mask attribute allows the ingress circuit emulation node to remove an unequipped VCs on the fly, providing the egress circuit emulation node enough information for reconstructing the VCs in the right order. The use of bit mask pwe3-sonet Expires July 2003 [Page 23] Internet Draft draft-ietf-pwe3-sonet-01 January 2003 enables "on the fly" compression, whereby only equipped VCs (carrying actual data) are sent. VC-3 carrying asynchronous T3/E3 signals within the VC-4 container can optionally be compressed by removing the fixed column bytes as described in section 7.2.2, providing additional bandwidth saving. Implementations of fractional VC-4 encapsulation MUST support payload length of 1/3 SPE and MAY support payload lengths of 4/9, 5/9, 6/9, 7/9, 8/9 and full SPE. The actual payload size of fractional VC-4 encapsulation depends on the number of VCs carried within the payload. The possible actual payload sizes are described in appendix B. 8.2.3.1 Fractional VC-4 Mapping [G.707] defines the mapping of TUG-3 to a VC-4 in section 7.2.1. Each TUG-3 includes 86 columns. TUG-3#1, TUG-3#2 and TUG-3#3 are byte multiplexed, starting from column 4. Column 1 is the VC-4 POH, while columns 2 and 3 are fixed, and therefore removed within the fractional VC-4 encapsulation. The mapping of TU-3 into TUG-3 is defined in section 7.2.2 of [G.707]. The TU-3 consists of the VC-3 with a 9-byte VC-3 POH and the TU-3 pointer. The first column of the 9-row by 86-column TUG-3 is allocated to the TU-3 pointer (bytes H1, H2, H3) and fixed stuff. The phase of the VC-3 with respect to the TUG-3 is indicated by the TU-3 pointer. The mapping of TUG-2 into TUG-3 is defined in section 7.2.3 of [G707]. The first two columns of the TUG-3 are fixed and therefore removed in the fractional VC-4 encapsulation. The 7 TUG-2, each 12 columns wide, are byte multiplexed starting from column 3 of the TUG- 3. This is the equivalent of multiplexing 7 VTGs within STS-1 container in SONET terminology, except for the location of the fixed columns. The static fractional VC-4 mapping assumes that both the ingress and egress nodes are preconfigured with the set of equipped VCs carried within the fractional VC-4 encapsulation. The ingress emulation edge removes the fixed columns as well as columns of the VCs agreed upon by the two edges, and updates the B3 VC-4 byte. The egress side adds the fixed columns and the unequipped VCs and updates B3. 8.2.3.2 Fractional VC-4 CEP Header The fractional VC-4 CEP header uses the VC-4 CEP header encapsulation defined Section 3.3 in this draft. Optionally, an additional 12 byte header extension word is added. The extended header is described in Figure 28. pwe3-sonet Expires July 2003 [Page 24] Internet Draft draft-ietf-pwe3-sonet-01 January 2003 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |1|R|D|N|P| Structure Pointer[0:12] | Sequence Number[0:13] | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |1|0| Equipped Bit Mask #1 (EBM) [0:29] TUG-3#1 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |1|0| Equipped Bit Mask #2 (EBM) [0:29] TUG-3#2 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |E|0| Equipped Bit Mask #3 (EBM) [0:29] TUG-3#3 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 16 - Extended Fractional VC-4 Header The following fields are used within the extended header: - R, D, N, P, Structured Pointer and Sequence Number: All fields are used as defined in this draft for VC-4 encapsulation. - E: Extension bit. E=0: indicates that extended header is not used. E=1: indicates that extended header is carried within the packet. The E bit in the first word is set to 1 to indicate use of the Equipped Bit Mask (EBM). The E bit in the forth word indicates whether the extended header (to be defined in future revision of this draft) is used. The MSB bit of word two and three is always set to 1 to indicate that header is extended. - EBM: The Equipped Bit Mask indicate which tributaries are carried within the fractional VC-4 payload. Three EBM fields are used. Each EBM field corresponds to a different TUG-3 within the VC-4. The EBM includes 7 groups of 4 bits per TUG-2. A bit set to 1 indicates that the corresponding VC is equipped, hence carried within the fractional VC-4 payload. Additional 2 bit within the EBM indicates whether VC-3 carried within the TUG-3 is equipped and whether it is in AIS mode. The format of the EBM for fractional VC-4 is defined corresponding to one of the TUG-3 is defined in Figure 29. 0 1 2 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |A|T|TUG2#7 |TUG2#6 |TUG2#5 |TUG2#4 |TUG2#3 |TUG2#2 |TUG2#1 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ pwe3-sonet Expires July 2003 [Page 25] Internet Draft draft-ietf-pwe3-sonet-01 January 2003 Figure 17 - Equipped Bit Mask (EBM) for fractional VC-4 The 30 bits of the EBM are divided into two bits that control the VC- 3 within the TUG-3 and 7 groups of 4 bits, each corresponding to a different TUG-2 within the TUG-3 container. For a TUG-3 containing TUG-2, the first two A and T bits MUST be set to zero. The TUG-2 bits indicate whether the VCs within the TUG-2 are equipped. All 4 bits are used to indicate whether VC11 (T1) tributaries are carried within a TUG-2. The first 3 bits read right to left are used to indicate whether VC12 (E1) tributaries are carried within a TUG-2. The first bit is used to indicate a VC-2 is carried within a TUG-2. For example, 28 bits of the EBM of a fully occupied TUG-3 with VC11 is all ones, while that of a TUG-3 fully occupied with VC12 (E1) tributaries has the binary value 0111011101110111011101110111. For a TUG-3 containing VC-3, all TUG-2 bits MUST be set to zero. The A and T bits are defined as follows: T : TUG-3 carried bit. If set to 1, the VC-3 payload is carried within the TUG-3 container. If set to 0, all the TUG-3 columns are not carried within the fractional VC-4 encapsulation. The TUG-3 columns are removed either because the VC-3 is unequipped or in AIS mode. A: VC-3 AIS bit. The A bit MUST be set to 0 when the T bit is 1 (i.e. when the TUG-3 columns are carried within the fractional VC-4 encapsulation). The A bit indicate the reason for removal of the entire TUG-3 columns. If set to 0, the TUG-3 columns were removed because the VC-3 is unequipped. If set to 1, the TUG-3 columns were removed because the VC-3 is in AIS mode. 8.2.3.3 B3 Fractional VC-4 encapsulation can be implemented in Line Terminating Equipment (LTE) or in Path Terminating Equipment (PTE). PTE implementations terminate the path layer at the ingress PE and generate a new path layer at the egress PE. LTE implementations do not terminate the path layer, and therefore need to keep the content and integrity of the POH bytes across the PSN. In LTE implementations, special care must be taken to maintain the B3 bit- wise parity POH byte. The same procedures for B3 compensation as described in section 7.2.1.2 for fractional STS-1 encapsulation are used. 9 Open Issues pwe3-sonet Expires July 2003 [Page 26] Internet Draft draft-ietf-pwe3-sonet-01 January 2003 This version of the draft does not tie into PWE3 maintenance mechanisms for the setup and tear down of services. That short- coming will be addressed in future revisions of this document. Underlying MPLS QoS requirements are not covered by this revision of the draft. Future revisions may discuss underlying QoS requirements. An alternate version of DBA has been suggested that would suppress transmission of the entire CEP packet stream under certain circumstances. Future versions of this draft may define such a mechanism. It is possible to define SONET Emulation specific redundancy mechanisms, such as 1+1 or N:1. Future versions of this draft may define such mechanisms. 10 Security Considerations This document does not address or modify security issues within the relevant PSNs. 11 Intellectual Property Disclaimer This document is being submitted for use in IETF standards discussions. Vivace Networks, Inc. has filed one or more patent applications relating to the CEP technology outlined in this document. Vivace Networks, Inc. will grant free unlimited licenses for use of this technology. Also, Lycium Networks has filed one or more patent applications that may be related to the CEP technology outlined in this document. Lycium Networks grants free unlimited licenses for use of this technology. 12 References [RFC2026] Bradner, S., "The Internet Standards Process -- Revision 3", BCP 9, RFC2026, October 1996. [PWE3-REQ] XiPeng Xiao et al, Requirements for Pseudo Wire Emulation Edge-to-Edge (PWE3), Work in Progress, July-2001, draft-ietf-pwe3- requirements-01.txt [PWE3-TDM-REQ] Max Riegel, Requirements for Edge-to-Edge Emulation of TDM Circuits over Packet Switching Networks (PSN), Work in Progress, December 2002, draft-riegel-pwe3-tdm-requirements-01.txt. [PWE3-ARCH] Stewart Bryant and Prayson Pate, PWE3 Architecture, Work in progress, November 2002, draft-ietf-pwe3-arch-01.txt pwe3-sonet Expires July 2003 [Page 27] Internet Draft draft-ietf-pwe3-sonet-01 January 2003 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [SONET] American National Standards Institute, "Synchronous Optical Network (SONET) - Basic Description including Multiplex Structure, Rates and Formats," ANSI T1.105-1995. [GR253] Telcordia Technologies, "Synchronous Optical Network (SONET) Transport Systems: Common Generic Criteria", GR-253-CORE, Issue 3, September 2000. [G707] ITU Recommendation G.707, "Network Node Interface For The Synchronous Digital Hierarchy", 1996. [RFC1889] H. Schulzrinne et al, RTP: A Transport Protocol for Real- Time Applications, RFC 1889, IETF, 1996 [ROHC-LLA] Lars-Eric Jonsson et al, A Link-Layer Assisted ROHC Profile for IP/UDP/RTP draft-ietf-rohc-rtp-lla-03.txt. [CEP-MIB] Danenberg et al, "SONET/SDH Circuit Emulation Service Over PSN (CEP) Management Information Base Using SMIv2", draft-danenberg- pw-cem-mib-02.txt, work in progress, Feb 2002. [PWE3-CONTROL] Martini et al, " Transport of Layer 2 Frames Over MPLS", draft-ietf-pwe3-control-protocol-01.txt, work in progress, November 2002. [RFC2508] S.Casner, V.Jacobson, Compressing IP/UDP/RTP Headers for Low-Speed Serial Links, RFC 2508, IETF, 1999 [RFC3095] C.Bormann (Ed.), RObust Header Compression (ROHC): Framework and four profiles: RTP, UDP, ESP, and uncompressed, RFC 3095, IETF, 2001 [AAL1] ITU-T, "Recommendation I.363.1, B-ISDN Adaptation Layer Specification: Type AAL1", Appendix III, August 1996. [T1.403] ANSI, "Network and Customer Installation Interfaces - DS1 Electrical Interfaces", T1.403-1999, May 24, 1999. pwe3-sonet Expires July 2003 [Page 28] Internet Draft draft-ietf-pwe3-sonet-01 January 2003 13 Author's Addresses Andrew G. Malis Vivace Networks, Inc. 2730 Orchard Parkway San Jose, CA 95134 Email: Andy.Malis@vivacenetworks.com Ken Hsu Vivace Networks, Inc. 2730 Orchard Parkway San Jose, CA 95134 Email: Ken.Hsu@vivacenetworks.com Jeremy Brayley Laurel Networks, Inc. 2706 Nicholson Rd. Sewickley, PA 15143 Email: jbrayley@laurelnetworks.com Steve Vogelsang Laurel Networks, Inc. 2706 Nicholson Rd. Sewickley, PA 15143 Email: sjv@laurelnetworks.com John Shirron Laurel Networks, Inc. 2607 Nicholson Rd. Sewickley, PA 15143 Email: jshirron@laurelnetworks.com Luca Martini Level 3 Communications, LLC. 1025 Eldorado Blvd. Broomfield, CO 80021 Email: luca@level3.net Tom Johnson (Editor) Litchfield Communications, Inc. 76 Westbury Park Rd. Watertown, CT 06795 Email: tom_johnson@litchfieldcomm.com Ed Hallman Litchfield Communications, Inc. 76 Westbury Park Rd. Watertown, CT 06795 Email: ed_hallman@litchfieldcomm.com pwe3-sonet Expires July 2003 [Page 29] Internet Draft draft-ietf-pwe3-sonet-01 January 2003 Marlene Drost Litchfield Communications, Inc. 76 Westbury Park Rd. Watertown, CT 06795 Email: marlene_drost@litchfieldcomm.com Jim Boyle Protocol Driven Networks, Inc. 1381 Kildaire Farm #288 Cary, NC 27511 Email: jboyle@pdnets.com David Zelig Corrigent Systems LTD. 126, Yigal Alon st. Tel Aviv, ISRAEL Email: davidz@corrigent.com Ron Cohen Lycium Networks 14 Hatidhar St., P.O.Box 2088 Ra'anana 43000, Israel Email: ronc@lyciumnetworks.com Prayson Pate Overture Networks P. O. Box 14864 RTP, NC, USA 27709 Email: prayson.pate@overturenetworks.com Craig White Level3 Communications, LLC. 1025 Eldorado Blvd, Broomfield CO 80021 Email: Craig.White@Level3.com pwe3-sonet Expires July 2003 [Page 30] Internet Draft draft-ietf-pwe3-sonet-01 January 2003 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 (SPEs). The optical counterpart of the STS-N is the Optical Carrier- level N, or OC-N. Table 2 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 2 - 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 64 times the capacity of an 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. pwe3-sonet Expires July 2003 [Page 31] Internet Draft draft-ietf-pwe3-sonet-01 January 2003 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 3 - Payload Size and Rate To support circuit emulation, the entire SPE of a SONET STS or SDH VC level is encapsulated into packets, using the encapsulation defined in section 4, for carriage across packet-switched networks. VTs are organized in SONET superframes, where a SONET superframe is a sequence of four SONET SPEs. The SPE path overhead byte H4 indicates the SPE number within the superframe. The VT data can float relative to the SPE position. The overhead bytes V1, V2 and V3 are used as pointer and stuffing byte similar to the use of the H1, H2 and H3 TOH bytes. Table 3 below indicates the number of bytes occupied by a VT within a superframe. Mapping VT size Reference ------------------------------------------------------------- VT1.5/VC-11 104 bytes [GR253] Section 3.4.1.1 VT2/VC-12 140 bytes [G.707] Section 10.1.4.1 VT3 212 bytes [GR253] Section 3.4.1.3 VT6/VC-2 428 bytes [GR253] Section 3.4.1.4 Table 4 - Number of Bytes in a VT Superframe To support circuit emulation, the entire SONET SPE or VT or SDH VC level is encapsulated into packets, using the encapsulation defined in section 3, for carriage across packet-switched networks. pwe3-sonet Expires July 2003 [Page 32] Internet Draft draft-ietf-pwe3-sonet-01 January 2003 Appendix B. Payload sizes CEP packets are normally fixed in length for all packets of a particular emulated SONET/SDH stream. The exceptions are DBA CEP packets and on the fly compression within the fractional STS-1/VC- 3/VC-4 mode. When the fractional encapsulation does not carry the equipped flag indications, the EBM to be transmitted MUST be statically provisioned at both ends. The length of each CEP packet does not need to be carried in the CEP header because it can be uniquely determined for each CEP packet as a function of the provisioned payload size, the type of VTs carried within the STS-1 signal, the DBA indication and the equipped flags (either dynamically or statically provisioned). The following payload lengths can be statically provisioned for fractional STS-1 encapsulations: 1. Full SPE length (783 bytes) 2. Third of SPE length (261 bytes) The actual payload sizes would be smaller, depending on the number of virtual tributaries carried within the fractional SPE. Figure 21 provides the actual payload length as a function of N, the number of tributaries carried within the fractional STS-1. In particular, when all VTs are equipped, the fractional STS-1 full SPE payload size is 765 bytes. VT Type Full SPE SPE/3 ---------------------------------------------- VT1.5 (T1) 27*N+9 9*N+3 N=0..28 VT2 (E1) 36*N+9 12*N+3 N=0..21 Figure 18 - Fractional STS-1 Actual Payload Size The following payload lengths can be statically provisioned for fractional VC-4 encapsulation: 1. Full SPE length (2349 bytes) 2. 8/9 SPE length (2088 bytes) 3. 7/9 SPE length (1827 bytes) 4. 6/9 SPE length (1566 bytes) 5. 5/9 SPE length (1305 bytes) 6. 4/9 SPE length (1044 bytes) 7. 1/3 SPE length (783 bytes) The actual payload sizes would be smaller, depending on the number of virtual tributaries carried within the fractional SPE. Each equipped VC contributes the following number of bytes per SPE: Each VC-11 contributes 27 bytes Each VC-12 contributes 36 bytes Each VC-2 contributes 108 bytes pwe3-sonet Expires July 2003 [Page 33] Internet Draft draft-ietf-pwe3-sonet-01 January 2003 Each VC-3(DS-3) contributes 738 bytes (including pointers) Each VC-3(E-3) contributes 576 bytes (including pointers) Each VC-3(not compressed) contributes 774 bytes (including pointers) Figure 19 - Fractional VC-4 Actual Payload Size For example, the payload size of a fractional VC-4 configured to third SPE encapsulation that carries a single T3 VC-3 and 6 VC-12s would be: 9 (VC-4 POH) + 6 * 36 + 738 / 3 = 221 bytes payload per each packet. The following payload lengths can be statically provisioned for asynchronous T3/E3 STS-1/VC-3 encapsulations: 1. Full SPE length (783 bytes) 2. Third of SPE length (261 bytes) The actual payload sizes would be smaller as described in figure 23. Signal Full SPE SPE/3 ---------------------------------------------- T3 729 243 E3 567 189 Figure 20 - Asynchronous T3/E3 STS-1/VC-3 Actual Payload Size pwe3-sonet Expires July 2003 [Page 34] Internet Draft draft-ietf-pwe3-sonet-01 January 2003 Appendix C: Example Network Diagram Figure 7 below shows an example of SONET interconnect. Site A and Site B are connected back to a Hub Site, Site C by means of a SONET infrastructure. The OC3 from Site A and the OC12 from Site B are partially equipped. Each of them is transported through a SONET network back to a hubbing site (C). Equipped SPEs (or VTs) are then groomed onto the OC-12 towards site C. SONET Network ____ ___ ____ _/ \___/ \ _/ \__ +------+ Physical / \__/ \ |Site A| OC-12 / +---+ OC-12 \ Hub Site | |=================|\S/|-------------+-----+ \ +------+ | | \ |/ \|=============|\ /| \ | | +------+ /\ +---+-------------| \ / | / OC12 | | / | S |=========|Site C| +------+ Physical/ +---+-------------| / \ | \ | | |Site B| OC-12 \ |\S/|=============|/ \| \ | | | |=================|/ \|-------------+-----+ / +------+ | | \ +---+ OC12 __ / +------+ \ __/ \ / \ ___ ___ / \_/ \_/ \____/ \___/ Figure 21 - SONET Interconnect Example Diagram pwe3-sonet Expires July 2003 [Page 35] Internet Draft draft-ietf-pwe3-sonet-01 January 2003 Figure 8 below shows the same pair of OC12s being emulated over a PSN. This configuration frees up bandwidth in the grooming network, since only equipped SPEs (or VTs) are sent through the PSN. Additional bandwidth savings can be realized by taking advantage of the various payload compression options described in section 8. SONET/TDM/Packet Network ____ ___ ____ _/ \___/ \ _/ \__ +------+ Physical /+-+ \__/ \_ |Site A| OC12 / | | +---+ \ Hub Site | |=============|P|=| R | +---+ +-+ +-----+ \ +------+ | | \ |E| | |===| | | |=|\ /| \ | | +------+ /\+-+ +---+ | | | | | \ / | / OC12| | / | R |=|P| | S |========|Site C| +------+ Physical/ +-+ +---+ | | |E| | / \ | \ | | |Site B| OC12 \ |P| | R |===| | | |=|/ \| \ | | | |=============|E|=| | +---+ +-+ +-----+ / +------+ | | \ | | +---+ __ / +------+ \ +-+ __/ \ / \ ___ ___ / \_/ \_/ \____/ \___/ Figure 22 - SONET Interconnect Emulation Example Diagram pwe3-sonet Expires July 2003 [Page 36] Internet Draft draft-ietf-pwe3-sonet-01 January 2003 Full Copyright Statement Copyright (C) The Internet Society (2001). All Rights Reserved. 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