Frank - I would like your opinion on this article on MPLS from Internet Week. It appears that Juniper and Avici are taking different approaches to MPLS. Is that correct? What is the essential difference. Thanks.
Ken
internetwk.com
Tuesday, March 16, 1999, 11:00 a.m. ET.
One Way To Play In Heavy Traffic
By JOHN FONTANA
In life, the path less traveled often leads to the richest experiences. In networking, it's the path most efficiently traveled that yields the greatest value for end users.
A prominent signpost on that path is a maturing IETF standard called
Multiprotocol Label Switching (MPLS), which gives service providers and IT managers a way to build connection-oriented paths across an IP
network.
MPLS can be used to integrate IP and ATM, allow for traffic engineering and result in virtual private networks that are
more than just best-effort Internet tunnels.
MPLS networks also are expected to be used for e-commerce, voice over IP, true end-to-end quality of service (QoS) and Web conferencing. IT managers will be able to buy guaranteed levels of bandwidth and service level agreements. Coupled with other standards, most notably DiffServ, those features could be extended into the LAN.
Carriers such as AT&T, MCI WorldCom and Uunet already are testing MPLS.
Mega-enterprises such as General Motors are eyeing the technology for
traffic engineering. And vendors such as Argon Networks Inc., Avici Systems Inc., Cisco, Fore Systems, IBM, Lucent/Ascend and Newbridge
Networks Corp. are implementing MPLS in their hardware.
But MPLS suffers from one major issue:
It is not completed. The most notable omission is a protocol for
constraint-based routing (CBR), similar to Private Network-to-Network Interface(PNNI) in ATM.
The key to MPLS is that it separates the routing plane from the forwarding plane, creating a software-based, label-switching plane, similar to ATM. Changing the software that distributes the labels can change the way the network behaves.
Simply stated, MPLS-enabled routers assign a 32-bit label that specifies a packet's path through a network. The label contains information that routers in conventional networks would have to
calculate at each hop. Instead, each device switches the packet based on the label and a table of paths. When the packet exits the network, the label is removed.
MLPS eliminates the need for dedicated connections, but retains their
reliability," said John Morency, an analyst at Renaissance WorldWide Inc. "High performance is a given, but you also have more effective QoS across a service provider network than in a conventional routed backbone."
Momentum is building, and the IETF's
MPLS working group issued "last call"
Feb. 24 on the Label Distribution
Protocol (LDP), the signaling
mechanism MPLS devices use to
exchange label semantics such as
destination address, destination
networks or bandwidth to destination
networks. Drafts for MPLS over ATM, as
well as frame relay and MPLS
encapsulation, are complete.
MPLS also is expected to let large
enterprises engineer traffic and make IP
their protocol of choice while retaining
the reliability and scalability they had
with SNA and other legacy protocols.
General Motors is doing just that. Once it
can control IP routes, the company can
eliminate much of its legacy traffic and
tunnel the rest through IP.
"In that sense, IP switching becomes
important, and MPLS is the enabler of
that project," said Ajit Kapoor, director of
network architecture and standards at
GM.
GM, which spends $1 billion annually on
network support, hopes MPLS and IP
switching can cut that figure by 30
percent annually in the next three years.
Traffic engineering also has carriers
salivating by lowering costs and
reducing network complexity, said Joe
Skorupa, director of switching and
routing at RHK Inc., a consultancy. "It
could help lower overall network costs by
half," he said.
Last month, MCI launched an OC-48 link
between Los Angeles and San
Francisco as part of the National
Science Federation's vBNS research
network. The link features MPLS as its
traffic engineering mechanism. What
MCI learns from this project could wind
up in its commercial network.
AT&T is in beta with IP-enabled frame
relay that uses MPLS and is a model for
future VPN services to the enterprise.
"The architecture can create tactical
VPNs--ones that appear for a short time
and then go away," said Tom Nolle,
president of consultancy CIMI Corp. "We
could see VPNs that last a couple of
hours for NetMeeting sessions."
AT&T is using MPLS to leverage frame
relay permanent virtual circuits (PVCs)
for IP applications. Currently, its
enterprise customers require hundreds
of PVCs and complex routing tables to
create a meshed network for their IP
applications over frame relay. But with
MPLS, AT&T is moving that complexity
into its own network and allowing the
enterprise to use just a single PVC to
provide secure, fully meshed connectivity
to its network locations.
That lets customers establish a VPN for
applications, such as enterprise
resource planning or e-mail. They also
can retain their current IP addressing
and frame relay security.
Despite its promise, however, MPLS still
needs refinement.
"The signaling is not nailed down yet,
and there are issues around quick
response to failure and rerouting," said
MCI's Rick Wilder, director of advanced
Internet technology.
The signaling protocol for both CBR and
explicit path routing is missing. Both
routing methods can be used to optimize
bandwidth and support differentiated
services. Two protocols are vying to be
the standard: extensions to LDP and the
Resource Reservation Protocol (RSVP).
The signaling protocol is key because it
enables connection-oriented paths
within IP. Also missing are hooks in the
IP routing protocols to specify needed
bandwidth and check for its availability.
MCI sees a need for both RSVP and
LDP but uses RSVP, which is backed
by vendors such as Cisco, Juniper
Networks Inc. and Torrent Systems Inc.
"RSVP looks to be farther ahead in
setting up a label-switched path by
specifying all the intermediate nodes
and essentially doing source routing of
the signaling for the path," Wilder said.
Others, such as Nortel Networks,
Ericsson and General DataComm Inc.,
recently completed the first
constraint-based routing interoperability
test using LDP extensions.
Both LDP extensions and RSVP are
likely to be approved as signaling
protocols. Last call on both are expected
by early April. Until then, MPLS provides
no more than high-performance,
best-effort routing without QoS
mechanisms. But most observers say
that by early 2000, MPLS networks will
spring up. AT&T, GM and MCI all are
shooting for that time frame.
"Everybody wants everything to look and
smell like IP, and that means making
connectivity more and more the same,"
said Gene Cox, program director for
IBM's Network Hardware Division and
business development.
|
