Network Working Group Luca Martini
Internet Draft Nasser El-Aawar
Expiration Date: August 2001 Giles Heron
Level 3 Communications, LLC.
Daniel Tappan
Eric C. Rosen
Alex Hamilton
Jayakumar Jayakumar
Cisco Systems, Inc.
Steve Vogelsang
John Shirron
Toby Smith
Laurel Networks, Inc.
Andrew G. Malis
Vinai Sirkay
Vivace Networks, Inc.
Dimitri Stratton Vlachos
Mazu Networks, Inc.
February 2001
Transport of Layer 2 Frames Over MPLS
draft-martini-l2circuit-trans-mpls-05.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-05.txt February 2001
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.
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 Protocol-Specific Details .............................. 4
4.1 Frame Relay ............................................ 5
4.2 ATM .................................................... 5
4.2.1 ATM AAL5 VCC Transport ................................. 5
4.2.2 ATM Transparent Cell Transport ......................... 5
4.2.3 ATM VCC and VPC Cell Transport ......................... 5
4.2.4 OAM Cell Support ....................................... 6
4.2.5 ILMI Support ........................................... 6
4.3 Ethernet VLAN .......................................... 7
4.4 Ethernet ............................................... 7
4.5 HDLC ( Cisco ) ......................................... 7
4.6 PPP .................................................... 7
4.7 Static MPLS ............................................ 7
5 LDP .................................................... 8
5.1 Interface Parameters Field ............................. 9
6 IANA Considerations .................................... 11
7 Security Considerations ................................ 11
8 References ............................................. 11
9 Author Information ..................................... 12
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-05.txt February 2001
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
procedures for accomplishing this using the encapsulation methods in
[7]. We restrict discussion to the case of point-to-point transport.
QoS related issues are not discussed in this draft.
An accompanying document [8] 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). This encapsulation method
is described in [8].
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.
Note that the tunnel could be a GRE encapsulated MPLS tunnel between
R1 and R2. In this case R1 would be adjacent to R2 , and only the VC
label would be used, and the intervening network need only carry IP
Martini, et al. [Page 3]
Internet Draft draft-martini-l2circuit-trans-mpls-05.txt February 2001
packets.
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
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 REQUIRED to assign the same VC ID for
a given circuit in both directions. The transported frame MAY be
modified when it reaches the egress router. If the header of the
transported layer 2 frame is modified, this MUST be done at the
egress LSR only. 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 the VC label 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. [1]
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.
4. Protocol-Specific Details
Martini, et al. [Page 4]
Internet Draft draft-martini-l2circuit-trans-mpls-05.txt February 2001
4.1. Frame Relay
The Frame Relay PDUs are encapsulated according to the procedures
defined in [7]. The MPLS edge LSR MUST provide Frame Relay PVC status
signaling to the Frame Relay network. If the MPLS edge LSR detects a
service affecting condition as defined in [2] Q.933 Annex A.5 sited
in IA FRF1.1, it MUST withdraw the label that corresponds to the
frame relay DLCI. The Egress LSR SHOULD generate the corresponding
errors and alarms as defined in [2] on the Frame relay VC.
4.2. ATM
4.2.1. ATM AAL5 VCC Transport
ATM AAL5 CSPS-PDUs are encapsulated according to [7] ATM AAL5 CPCS-
PDU mode. At the edge LSRs, R1 and R2, if ATM ILMI signaling is
supported it SHOULD be connected to VC signaling. This mode allows
the transport of ATM AAL5 CSPS-PDUs traveling on a particular ATM PVC
across the mpls network to another ATM PVC.
4.2.2. ATM Transparent Cell Transport
This mode is similar to the Ethernet port mode. Every cell that is
received at the ingress ATM port on the ingress LSR, R1, is
encapsulated according to [7], ATM cell mode, and sent across the LSP
to the egress LSR, R2. This mode allows an ATM port to be connected
to only one other ATM port. [7] allows for grouping of multiple cells
into a single MPLS frame. Grouping of ATM cells is OPTIONAL for
transmission at the ingress LSR, R1. If the Egress LSR R2 supports
cell concatenation the ingress LSR, R1, should only concatenate cells
up to the "Maximum Number of concatenated ATM cells" parameter
received as part of the FEC element.
4.2.3. ATM VCC and VPC Cell Transport
This mode is similar to the ATM AAL5 VCC transport except that only
cells are transported. Every cell that is received on a pre-defined
ATM PVC, or ATM PVP, at the ingress ATM port on the ingress LSR, R1,
is encapsulated according to [7], ATM cell mode, and sent across the
LSP to the egress LSR R2. Grouping of ATM cells is OPTIONAL for
transmission at the ingress LSR, R1. If the Egress LSR R2 supports
cell concatenation the ingress LSR, R1, MUST only concatenate cells
up to the "Maximum Number of concatenated ATM cells in a frame"
parameter received as part of the FEC element.
Martini, et al. [Page 5]
Internet Draft draft-martini-l2circuit-trans-mpls-05.txt February 2001
4.2.4. OAM Cell Support
OAM cells MAY be transported on the VC LSP. When the LSR is operating
in AAL5 PDU transport mode if it does not support transport of ATM
cells, the LSR MUST discard incoming MPLS frames on an ATM VC LSP
that contain a VC label with the T bit set [7]. When operating in
AAL5 PDU transport mode an LSR that supports transport of OAM cells
using the T bit defined in [7], or an LSR operating in any of the
three cell transport modes MUST follow the procedures outlined in [9]
section 8 for mode 0 only, in addition to the applicable procedures
specified in [6].
4.2.4.1. OAM Cell Emulation Mode
AN LSR that does not support transport of OAM cells across an LSP MAY
provide OAM support on ATM PVCs using the following procedures:
If an F5 end-to-end OAM cell is received from a ATM VC by an ingress
LSR or egress LSR, with a loopback indication value of 1 and the LSR
has a label mapping for the ATM VC, the LSR MUST decrement the
loopback indication value and loop back the cell on the ATM VC.
Otherwise the loopback cell MUST be discarded by the LSR.
The ingress LSR, R1, may also optionally be configured to
periodically generate F5 end-to-end loopback OAM cells on a VC. 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, R1, 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,
the egress LSR, R2, MUST generate AIS F5 OAM cells on the VC
associated with the withdrawn label mapping. In this mode it is very
useful to apply a unique group ID to each interface. In the case
where a physical interface goes down, a wild card label withdraw can
be sent to all LDP neighbors, greatly reducing the signaling response
time.
4.2.5. ILMI Support
An MPLS edge LSR MAY provide an ATM ILMI to the ATM edge switch. If
an ingress LSR receives an ILMI message indicating that the ATM edge
switch has deleted a VC, or if the physical interface goes down, it
MUST withdraw the label mappings for all VCs associated with the
failure. When a VC label mapping is withdrawn, the egress LSR SHOULD
Martini, et al. [Page 6]
Internet Draft draft-martini-l2circuit-trans-mpls-05.txt February 2001
notify its client of this failure by deleting the VC using ILMI.
4.3. Ethernet VLAN
The Ethernet frame will be encapsulated according to the procedures
in [7]. It should be noted that if the VLAN identifier is modified
by the egress LSR, according to the procedures outlined above, the
Ethernet spanning tree protocol might fail to work properly.
4.4. Ethernet
The Ethernet frame will be encapsulated according to the procedures
in [7]. If the LSR detects a failure on the Ethernet physical port,
or the port is administratively disabled, the corresponding VC label
mapping MAY be withdrawn. If the egress LSR, R2, does not have a VC
label mapping for the corresponding Ethernet port, the Ethernet port
physical layer MAY be disabled.
4.5. HDLC ( Cisco )
If the MPLS edge LSR detects that the physical link has failed it
MUST withdraw the label that corresponds to the HDLC link. The Egress
LSR SHOULD notify the CE device of this failure by using a physical
layer mechanism to take the link out of service.
4.6. PPP
If the MPLS edge LSR detects that the physical link has failed it
MUST withdraw the label that corresponds to the PPP link. The Egress
LSR SHOULD notify the CE device of this failure by using a physical
layer mechanism to take the link out of service.
4.7. Static MPLS
The MPLS frames encapsulated according to [3] using any layer 2
technology that is commonly used to transport MPLS can be transported
across the service provider MPLS network using the methods described
in this document. The VC label in this case is the statically
configured label that is accepted at the ingress LSR R1, and
advertised with an associated VC ID in LDP. The VC ID has to match in
both directions on a particular VC. At the egress LSR, R2 a common
MPLS label swap operation will swap the VC label with the label that
is statically configured for this particular VC. This transport mode
can be used to offer packet transport using different kinds of layer
2 access infrastructures.
Martini, et al. [Page 7]
Internet Draft draft-martini-l2circuit-trans-mpls-05.txt February 2001
5. 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 element is
defined. The FEC element type is 128. [note1]
The Virtual Circuit FEC 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| VC tlv |C| VC Type |VC info Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Group ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| VC ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Interface parameters |
| " |
| " |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- 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 VCC transport
0x0003 ATM transparent cell transport
0x0004 Ethernet VLAN
0x0005 Ethernet
0x0006 HDLC ( Cisco )
0x0007 PPP
0x8008 CEM [8]
0x0009 ATM VCC cell transport
0x000A ATM VPC cell transport
0x000B MPLS
- Control word bit (C)
The highest order bit (C) of the Vc type is used to flag the
presence of a control word ( defined in [7] ) as follows:
Martini, et al. [Page 8]
Internet Draft draft-martini-l2circuit-trans-mpls-05.txt February 2001
bit 15 = 1 control word present on this VC.
bit 15 = 0 no control word present on this VC.
- VC information length
Length of the VC ID field and the interface parameters field in
octets. If this value is 0, then it references all VCs using the
specified group ID and there is no VC ID present, nor any
interface parameters.
- 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 a port
index, or a virtual tunnel index. To simplify configuration a
particular VC ID at ingress could be part of the virtual tunnel
for transport to the egress router. The Group ID is very useful
to send a wild card label withdrawals to remote LSRs upon
physical port failure.
- VC ID
A non zero 32-bit connection ID that together with the VC type,
identifies a particular VC.
- Interface parameters
This variable length field is used to provide interface specific
parameters, such as interface MTU.
5.1. Interface Parameters Field
This field specifies edge facing interface specific parameters and
SHOULD be used to validate that the LSRs, and the ingress and egress
ports at the edges of the circuit have the necessary capabilities to
interoperate with each other. The field structure is defines 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Parameter ID | Length | Variable Length Value |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Variable Length Value |
| " |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Martini, et al. [Page 9]
Internet Draft draft-martini-l2circuit-trans-mpls-05.txt February 2001
The parameter ID is defined as follows:
Parameter ID Length Description
0x01 4 Interface MTU in octets.
0x02 4 Maximum Number of concatenated ATM cells.
0x03 up to 82 Optional Interface Description string.
0x04 4 CEM [8] Payload Bytes.
0x05 4 CEM options.
The Length field is defined as the length of the interface parameter
including the parameter id and length field itself.
- Interface MTU
A 2 octet value indicating the MTU in bytes. This is the Maximum
Transmit Unit of the egress packet interface that will be
transmitting the decapsulated PDU that is received from the MPLS
network. This parameter is REQUIRED, and SHOULD match in both
direction of a specific circuit. The MTU is specified in bytes,
and if it does not match on a specific circuit, that circuit
should not be enabled. This parameter is applicable only to VC
types 1, 2, 4, 5, 6, 7, and 0x0b.
- Maximum Number of concatenated ATM cells
This 2 octet parameter specifies the maximum number of
concatenated ATM cells that can be processed as a single PDU by
the egress LSR. This parameter does not need to match in both
directions of a specific LSR. This parameter is REQUIRED for the
following VC types: 3, 9, and 0x0a. An LSR transmitting
concatenated cells on this VC can concatenate a number of cells
up to the value of this parameter, but MUST NOT exceed it.
- Optional Interface Description string
This arbitrary, OPTIONAL, interface description string can be
used to send an administrative description text string to the
remote LSR. This parameter is OPTIONAL, and is applicable to all
VC types. The interface description parameter length is variable,
and can be up to 80 octets.
- Payload Bytes
A 2 octet value indicating the the number of TDM payload octets
contained in all packets on the CEM stream, from 48 to 1,023
octets. All of the packets in a given CEM 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
Martini, et al. [Page 10]
Internet Draft draft-martini-l2circuit-trans-mpls-05.txt February 2001
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 or equal to 783 for STS-1 SPEs.
- CEM Options. An optional 16 Bit value of CEM Flags. Bit 0 is
defined being set to indicate CEM-DBA in operation.
6. IANA Considerations
As specified in this document, a Virtual Circuit FEC element contains
the VC Type field. VC Type value 0 is reserved. VC Type values 1
through 11 are defined in this document. VC Type values 12 through 63
are to be assigned by IANA using the "IETF Consensus" policy defined
in RFC2434. VC Type values 64 through 127 are to be assigned by IANA,
using the "First Come First Served" policy defined in RFC2434. VC
Type values 128 through 32767 are vendor-specific, and values in this
range are not to be assigned by IANA.
As specified in this document, a Virtual Circuit FEC element contains
the Interface Parameters field, which is a list of one or more
parameters, and each parameter is identified by the Parameter ID
field. Parameter ID value 0 is reserved. Parameter ID values 1
through 5 are defined in this document. Parameter ID values 6
through 63 are to be assigned by IANA using the "IETF Consensus"
policy defined in RFC2434. Parameter ID values 64 through 127 are to
be assigned by IANA, using the "First Come First Served" policy
defined in RFC2434. Parameter ID values 128 through 255 are vendor-
specific, and values in this range are not to be assigned by IANA.
7. Security Considerations
This document does not affect the underlying security issues of MPLS.
8. References
[1] "LDP Specification." L. Andersson, P. Doolan, N. Feldman, A.
Fredette, B. Thomas. January 2001. RFC3036
[2] ITU-T Recommendation Q.933, and Q.922 Specification for Frame
Mode Basic call control, ITU Geneva 1995
[3] "MPLS Label Stack Encoding", E. Rosen, Y. Rekhter, D. Tappan, G.
Fedorkow, D. Farinacci, T. Li, A. Conta. RFC3032
[4] "IEEE 802.3ac-1998" IEEE standard specification.
Martini, et al. [Page 11]
Internet Draft draft-martini-l2circuit-trans-mpls-05.txt February 2001
[5] American National Standards Institute, "Synchronous Optical
Network Formats," ANSI T1.105-1995.
[6] ITU Recommendation G.707, "Network Node Interface For The
Synchronous Digital Hierarchy", 1996.
[7] "Encapsulation Methods for Transport of Layer 2 Frames Over
MPLS", draft-martini-l2circuit-encap-mpls-01.txt ( Work in progress )
[8] "SONET/SDH Circuit Emulation Service Over MPLS (CEM)
Encapsulation", draft-malis-sonet-ces-mpls-01.txt ( Work in progress
)
[9] "Frame Based ATM over SONET/SDH Transport (FAST)," 2000.
[note1] FEC element type 128 is pending IANA approval.
9. 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
Giles Heron
Level 3 Communications
66 Prescot Street
London
E1 8HG
United Kingdom
e-mail: giles@level3.net
Dimitri Stratton Vlachos
Mazu Networks, Inc.
125 Cambridgepark Drive
Cambridge, MA 02140
e-mail: d@mazunetworks.com
Martini, et al. [Page 12]
Internet Draft draft-martini-l2circuit-trans-mpls-05.txt February 2001
Dan Tappan
Cisco Systems, Inc.
250 Apollo Drive
Chelmsford, MA, 01824
e-mail: tappan@cisco.com
Jayakumar Jayakumar,
Cisco Systems Inc.
225, E.Tasman, MS-SJ3/3,
San Jose, CA, 95134
e-mail: jjayakum@cisco.com
Alex Hamilton,
Cisco Systems Inc.
285 W. Tasman, MS-SJCI/3/4,
San Jose, CA, 95134
e-mail: tahamilt@cisco.com
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: jshirron@laurelnetworks.com
Martini, et al. [Page 13]
Internet Draft draft-martini-l2circuit-trans-mpls-05.txt February 2001
Andrew G. Malis
Vivace Networks, Inc.
2730 Orchard Parkway
San Jose, CA 95134
Phone: +1 408 383 7223
Email: Andy.Malis@vivacenetworks.com
Vinai Sirkay
Vivace Networks, Inc.
2730 Orchard Parkway
San Jose, CA 95134
e-mail: vinai.sirkay@vivacenetworks.com
Martini, et al. [Page 14]
