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]
