U.S. patent application number 09/952284 was filed with the patent office on 2003-03-13 for metropolitan area local access service system.
Invention is credited to Guess, Michael, Niezgoda, Paul, Street, Fraser.
Application Number | 20030048501 09/952284 |
Document ID | / |
Family ID | 25492743 |
Filed Date | 2003-03-13 |
United States Patent
Application |
20030048501 |
Kind Code |
A1 |
Guess, Michael ; et
al. |
March 13, 2003 |
Metropolitan area local access service system
Abstract
A local access fiber optical distribution network is disclosed
in which a dedicated pair of diversely routed optical fibers is
routed in the distribution network for each customer. In a
preferred embodiment, a dual physical overlay ring core topology is
used in the core. The distribution network includes working and
protection logical path connectivity. No 802.1D Spanning Tree is
required for recovery, providing resilience to any single network
failure in any device or link, quick recovery times from failure,
and a failure detection/recovery protocol that is not active on any
devices other than the devices directly attached to the
subscriber.
Inventors: |
Guess, Michael; ( Austin,
TX) ; Niezgoda, Paul; (Austin, TX) ; Street,
Fraser; (San Jose, CA) |
Correspondence
Address: |
VINSON & ELKINS, L.L.P.
1001 FANNIN STREET
2300 FIRST CITY TOWER
HOUSTON
TX
77002-6760
US
|
Family ID: |
25492743 |
Appl. No.: |
09/952284 |
Filed: |
September 12, 2001 |
Current U.S.
Class: |
398/58 ;
385/24 |
Current CPC
Class: |
H04L 69/40 20130101;
H04L 49/602 20130101; H04L 49/354 20130101; H04L 49/351 20130101;
H04Q 2011/0073 20130101; H04L 12/4637 20130101; H04L 49/357
20130101; H04Q 11/0071 20130101; H04Q 2011/0081 20130101; H04L
12/2852 20130101; H04Q 11/0067 20130101 |
Class at
Publication: |
359/118 ;
385/24 |
International
Class: |
H04B 010/20; H04J
014/00; G02B 006/28 |
Claims
What is claimed is:
1. A fiber optic distribution network comprising: a network feeder
loop, said network feeder loop connected to a hub communicating
with a metropolitan area network; and a plurality of collector
loops extending from said network feeder loop, each comprising a
plurality of optical fibers, such that each of said collector loops
forms a plurality of intersections with said feeder loop.
2. The distribution network of claim 1, wherein at least some of
said plurality of intersections are disposed at different physical
locations on said feeder loop.
3. The distribution network of claim 1, wherein said intersections
of said collector loops with said network feeder loop are formed by
splices.
4. The distribution network of claim 3, wherein said splices are
fusion splices.
5. The distribution network of claim 4, wherein said network feeder
loop comprises 288 optical fibers.
6. The distribution network of claim 4, wherein said network feeder
loop comprises 432 optical fibers.
7. The distribution network of claim 4, wherein said network feeder
loop comprises an amount of optical fibers equal to one half the
sum of the count of the optical fibers comprising all of said
collector loops.
8. The distribution network of claim 1, wherein a plurality of
subscriber laterals are disposed on said collector loops and form
connections therewith, and wherein said subscriber laterals extend
to a plurality of subscriber facilities.
9. The distribution network of claim 8, wherein said laterals each
comprise a plurality of optical fibers.
10. The distribution network of claim 8, wherein at least some of
said connections between said subscriber laterals and said
collector loops are formed with mechanical splices.
11. The distribution network of claim 8, wherein said at least one
of said laterals comprises 48 optical fibers.
12. The distribution network of claim 8, wherein all of said
laterals on one of said collector loops comprise a number of
optical fibers substantially equal to the count of the optical
fibers comprising that collector loop.
13. A fiber optic distribution network comprising: an exterior
feeder loop, said exterior feeder loop connected to a hub, wherein
said hub communicates with a wide area distribution network; a
plurality of exterior collector loops connected to said exterior
feeder loop, wherein said exterior collector loops form a plurality
of intersections with said exterior feeder loop; an interior feeder
loop, said interior feeder loop connected to said hub, and wherein
said interior feeder loop is disposed at least in substantial part
within said exterior feeder loop; and an interior collector loop
connected to said interior feeder loop, wherein said interior
collector loop forms a plurality of intersections with said
interior feeder loop.
14. The distribution network of claim 13, wherein said
intersections between said exterior collector loops with said
exterior feeder loops are formed by splices.
15. The distribution network of claim 14, wherein at least some of
said splices are fusion splices.
16. The distribution network of claim 13, further comprising a
plurality of subscriber laterals forming connections with said
exterior collector loops and extending from said exterior collector
loops to a plurality of subscriber facilities.
17. The distribution network of claim 16, wherein at least one of
said laterals comprises a plurality of optical fibers.
18. The distribution network of claim 16, wherein at least some of
said connections are formed with mechanical splices.
19. The distribution network of claim 13, wherein said interior
collector loop is closer to said hub facility than said exterior
feeder loops.
20. The distribution network of claim 13, wherein said interior
feeder loop is disposed to reduce a longest subscriber path of the
distribution network.
21. A core service network comprising: a dual overlay ring
comprising a plurality of complete physical paths from a carrier
party to a subscriber party, wherein one of said plurality of
complete physical paths is allocated as a primary virtual line; and
wherein one of said complete physical paths is allocated as a
secondary virtual line.
22. The core service network of claim 21, wherein said primary
virtual line is configured to serve as a data channel.
23. The core service network of claim 22, wherein said secondary
virtual line is configured to serve as a back-up channel to said
primary virtual line.
Description
FIELD OF THE INVENTION
[0001] The invention generally relates to the field of fiber optic
communications networks, and more particularly to a new system and
method for deploying and operating a metropolitan area local access
distribution network.
RELATED ART
[0002] The growth of the Internet has created unprecedented demand
for high-speed broadband connectivity in telecommunications
networks. However, access connections between corporate Local Area
Networks ("LANs") and existing service provider networks, such as
those operated by long-haul carriers and Internet Service Providers
("ISPs"), generally have been limited to relatively slow, hard to
provision Ti (1.5 Mbps) or DS-3 (45 Mbps) data speeds due to
infrastructure limitations in most metropolitan areas.
[0003] The lack of bandwidth throughout metropolitan areas is a
function, principally, of two independent factors. First, there is
a deficiency in high speed fiber optic access rings and/or fiber
optic "tails" into major buildings in metro areas. Second, the
existing metropolitan area carriers continue to use older,
installed SONET (Synchronous Optical NETwork) architecture which,
although it allows data streams of different formats to be combined
onto a single high speed fiber optic synchronous data stream,
cannot be scaled to meet future bandwidth requirements. Although
customer demand for increased bandwidth has been growing at
exponential rates, there is a mismatch between carrier long-haul
backbones and metro area backbones on the one hand and local loop
access on the other hand. Despite the aggressive deployment of
fiber-optic networks nationwide, relatively little fiber has been
deployed in the local access market or "last mile." Fiber
deployment in Metro Area Networks ("MANs") has been primarily to
carrier and service provider locations, or to a relatively small
number of very large commercial office building sites. At the
current time, it is estimated that as few as 10% of all commercial
buildings in the United States are served with fiber-optic
networks.
[0004] Currently, most local connectivity service providers are
primarily providing SONET-based services and are investing little
in the services required for expanded local connectivity--e.g.,
Ethernet and Wavelength services. In general, existing local
service providers have not moved forward to upgrade local fiber
infrastructure to support these latter services.
[0005] In order to provide compatibility and easy upgrading from
existing services to new services, it is desirable to provide
SONET, Ethernet and Wavelength services in the metropolitan and
access segments of the communications infrastructure, making use of
a common interface system and fiber optic cables. In this way, it
is possible for customers to migrate smoothly and at an opportune
time from the traditional SONET-based circuits to Ethernet circuits
and, possibly, to transparent wavelengths. Such an evolutionary
connectivity path enables customers to access the right amount of
bandwidth at the right time.
SUMMARY OF THE INVENTION
[0006] In accordance with the present invention, a service network
provides customers with a highly-available transparent Layer 2
network connection between their edge IP equipment and their
subscribers' edge IP equipment.
[0007] Layer 2, known as the bridging or switching layer, allows
edge IP equipment addressing and attachment. It forwards packets
based on the unique Media Access Control ("MAC") address of each
end station. Data packets consist of both infrastructure content,
such as MAC addresses and other information, and end-user content.
At Layer 2, generally no modification is required to packet
infrastructure content when going between like Layer 1 interfaces,
like Ethernet to Fast Ethernet. However, minor changes to
infrastructure content--not end-user data content--may occur when
bridging between unlike types such as FDDI and Ethernet.
Additionally, the Ethernet service can inter-connect customers to
create an "extended" LAN service.
[0008] Layer 3, known as the routing layer, provides logical
partitioning of subnetworks, scalability, security, and Quality of
Service ("QoS"). Therefore, it is desirable that the network remain
transparent to Layer 3 protocols such as IP. This is accomplished
by the combination of a particular network topology combined with
failure detection/recovery mechanisms, as more fully described
herein.
[0009] Embodiments of the present invention may include the
following advantages: (1) in the BDN, a dedicated pair of diversely
routed optical fibers for each customer; (2) in the core, a dual
physical overlay ring core topology; (3) working and protection
logical path connectivity; (4) no 802.1D Spanning Tree for
recovery; (5) resilience to any single network failure in any
device or link; (6) quick recovery times from failure relative to
mechanisms based on Spanning Tree; and (7) a failure
detection/recovery protocol that is not "active" on any devices
other than the devices directly attached to the subscriber.
[0010] Further features and advantages of the invention will appear
more clearly from a reading of the detailed description of the
preferred embodiments of the invention, which are given below by
way of example only, and with reference to the accompanying
drawings, in which like references indicate similar elements, and
in which:
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] FIG. 1 is a schematic diagram of a local distribution
portion of an overall fiber optic network, illustrating the
relationship between multiple subscribers disposed on collection
loops connected to a hub facility via a feeder loop;
[0012] FIG. 2 is a schematic diagram illustrating a typical longest
path around an access distribution network;
[0013] FIG. 3 is a schematic diagram illustrating an alternative
design with nested feeders;
[0014] FIG. 4 is a schematic diagram of a dual overlay ring
topology within the core;
[0015] FIG. 5 is a schematic diagram of a working path and a
protection path across the core connecting a subscriber's Layer 3
switch to its carrier/ISP; and
[0016] FIG. 6 is a simplified logical diagram of the end-to-end
Ethernet service indicating where ESRP is utilized.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0017] A fiber optic transport network can generally be described
in terms of three primary components: (i) a leased transport
network (LTN), (ii) a leased distribution network (LDN); and (iii)
a built distribution network (BDN), which may be a distribution
network in accordance to the present invention (see FIGS. 1-6).
[0018] The LTN is the main transport layer of each metropolitan
system. It typically consists of a high-bandwidth, flexible DWDM
transport pipe used to connect customer locations (such as data
centers, co-location hotels, and large customer POPs) to
distribution networks.
[0019] The distribution networks may comprise both LDN and BDN
designs, though either may be excluded. Although similar in general
purpose, an LDN and a BDN may use differing architectural
approaches to bring traffic to the LTN. While the LDN typically
relies on TDM (and sometimes WDM) electronics to multiplex traffic
onto limited quantities of fiber, the distribution network
according to the present invention uses larger quantities of fiber,
enabling a reduced reliance upon multiplexing electronics. The
following description will focus specifically on the architectural
design and operation of a distribution network especially suitable
for a BDN, though it may have other applications, particularly to
an LDN. Detailed discussions of LTN and LDN designs may be found in
other publicly available documents. The distribution network
architecture maximizes the saturation of the potential subscriber
base at minimal expense and is designed with the following criteria
in mind.
[0020] Each subscriber should have access to a route-diverse
connection to the LTN hub. In a preferred embodiment, these
connections are capable of supporting:
[0021] (1) SONET services that require Line Overhead termination
and Automatic Protection Switching (APS) controlled by the
distribution network (DS-3, OC-3/OC-3c, OC-12/OC-12c, and
OC-48/OC-48c).
[0022] (2) Data devices with SONET interfaces that require Line
Overhead termination, but may lack APS functionality (DS-3, OC-3c,
OC-12c, and OC-48c).
[0023] (3) Ethernet services (10, 100, and 1000 base).
[0024] (4) Wavelength services (1000-LX/LH/ZX, OC-48/OC-48c).
[0025] In a preferred embodiment, the distribution design is
scalable and flexible enough to adapt to the eventual traffic needs
of the network. Circuits from multiple subscribers should be
reasonably segregated. Where feasible, the distribution
architecture should ensure that work requested by one subscriber
seldom impacts other subscribers.
[0026] Referring now to FIG. 1, the distribution network comprises
a major feeder ring 10 with a series of smaller, subtending
collector rings 11-13. In a common metropolitan-wide network
design, collector rings are installed to follow city streets.
Feeder ring 10 accesses at least one LTN Hub 20, where the
distribution network fiber may be terminated to high-density fiber
distribution panels (FDPs).
[0027] One particular feature of any local distribution
architecture is the quantity of fiber run on the distribution
network. Although fiber counts will vary based on the logistics of
the distribution area, a typical feeder ring 10 will contain 432
fibers, and typical collectors 11-13 each will contain 144 fibers.
Laterals (e.g., 15) extend from the collector rings 11-13 to
subscriber buildings (e.g., 17), and will typically contain 48
fibers. As shown, each collector (11-13) is preferably deployed
with two splice points to the feeder 10. A person of ordinary skill
in the art will readily appreciate that fiber counts may be varied
upwardly or downwardly without deviation from the present
invention. The overall goal of the preferred embodiment is to
provide, for each subscriber, optical service with at least one
diversely-routed, dedicated fiber pair.
[0028] Select embodiments of the presently proposed distribution
network architecture have the following advantages over
conventional TDM and WDM distribution networks.
[0029] (i) Lower cost--At the present time, the major cost
associated with any new fiber run is the cost of opening and
closing the trench. Since this cost is substantially independent of
the number of fibers being run, the comparison between a bulk-fiber
distribution network and a TDM-based distribution network (similar
to the LDN design), for example, becomes mainly a comparison
between costs of fiber versus electronics. On relatively short
fiber runs (like a distribution network), additional fiber is
generally less expensive than TDM electronics. When the costs
associated with space, power, operation, maintenance, and
management of the TDM electronics is added, the cost advantages of
a bulk-fiber approach increase dramatically.
[0030] (ii) Manageability--Connecting subscribers to a distribution
network becomes a relatively simple task of splicing fibers between
the subscriber building and the collector. This design eliminates
an extra layer of TDM circuit provisioning and management.
Requirements of TDM software upgrades and equipment failures are
likewise reduced.
[0031] (iii) Scalability--Since each subscriber's optical service
may be on a dedicated fiber pair, significant capacity exists at
the outset and there is no concern regarding TDM circuit fill
ratios or provisioning anomalies. This design also minimizes the
need for TDM reconfigurations to support capacity expansions.
[0032] (iv) Circuit protection--Isolating each subscriber's optical
service on a dedicated fiber pair reduces the possibility that work
requested by one subscriber affects other subscribers. This
represents a significant advantage in network accessibility when
compared to designs that rely on multiple subscribers sharing a TDM
resource.
[0033] Although a primary goal of the preferred embodiment of the
BDN design is to reduce the use of electronics at each subscriber
site, electronic components will still be required for subscribers
who elect to use electrical circuits (e.g., DS-3, 10-base, and
100-base). Electrical circuits must still be converted into optical
circuits for transport around the BDN. Due to the distances within
the BDN, single-mode fiber connectivity is the preferred embodiment
to support the connection between the subscriber site and the hub
location. Therefore, additional electronics may be required for
subscribers who desire optical circuits when these subscribers
occupy locations or operate equipment with an embedded base of
Multi-Mode Fiber ("MMF").
[0034] FIG. 2 illustrates the longest optical path 25 around the
distribution network. This calculation is the sum of the length of
the longest collector (shown as 11) and the length of the feeder
20. The longest optical path 25 is a significant limitation to be
considered in the design of the distribution network, as discussed
in greater detail below.
[0035] The physical connections of circuits and facilities on the
distribution network are described in greater detail below.
Exemplary subscriber connections can be found by reference to FIGS.
3-7, discussed below.
[0036] LTN Hubs
[0037] At LTN Hub 20 locations, distribution network fiber can be
terminated to high-density Fiber Distribution Panels (FDPs). From
these locations, subscriber circuits may be cross-connected to ADM
equipment, Ethernet switches, or directly to an LTN DWDM system.
The ADMs and Ethernet switches aggregate circuits with common
destinations (e.g., customer locations) and transfer them to the
LTN for transport around the metropolitan network.
[0038] Single-Tenant Subscriber Facilities
[0039] In a single-tenant subscriber facility, a lateral fiber
offshoot can be deployed to connect the appropriate feeder 10
fibers to a low-density FDP on the subscriber's premises. For
optical services, this FDP will serve as a demarcation point
between the distribution network and the subscriber equipment. For
electrical services, an additional component can be placed at the
subscriber's site. This component typically will be a media
converter capable of converting an electrical signal into a
higher-rate optical signal for transport over the distribution
network. This converter equipment can usually be powered by the
subscriber's AC power facilities, although a small UPS
(Uninterruptible Power Supply) device may be required in cases
where brownout protection is lacking from the subscriber's AC
feed.
[0040] Multiple-Tenant Subscriber Facilities
[0041] Access to multiple-tenant facilities may be similarly
designed. A primary difference will often be the equipment
location. Any necessary auxiliary electrical equipment (FDP, DSX,
patch panel, SONET TDM, Ethernet switch, media converter) may be
located either within a Minimum Point of Entry (MPOE) facility
inside the building or within the subscriber's location. When it is
located within the MPOE, such equipment preferably should be within
a protected enclosure (e.g., a cage or locked cabinet). DC power
(e.g., -48V regulated with battery reserve) may be provided as an
option in larger MPOE facilities. However, AC power with a UPS
reserve is also feasible.
[0042] Fiber Plant
[0043] At present, the majority of optical circuits transported
over the distribution network preferably will utilize 1310 nm
lasers and therefore, Non-Dispersion Shifted Fiber (NDSF) is the
preferred fiber for such distribution network deployment. Non-Zero
Dispersion Shifted Fibers (NZ-DSF) and Multi-Mode Fiber (MMF),
though not presently preferred, may be used in alternative
embodiments.
[0044] Subscriber Laterals
[0045] Normally, a 48-count fiber bundle can be run in a single
1.5" conduit between the collectors 11-13 and subscriber
facilities. As a result, most laterals will be single-threaded. A
person of ordinary skill in the art will readily appreciate that
dual-threaded laterals, and laterals of different fiber counts, may
also be run. Depending on system requirements, fusion or mechanical
splices may be utilized. Mechanical splices are preferably used
between the lateral and the Collector fibers. High quality
mechanical splices can be obtained that provide typical insertion
loss below 0.10 dB. Fusion splices are preferably utilized between
the lateral and the FDP within the subscriber site. Fusion splices
can routinely introduce insertion losses of less than 0.05 dB.
[0046] Collector Loops
[0047] In a preferred embodiment, a collector loop will consist of
a 144-count fiber bundle run in a single 4" conduit. The 4"
collector can compartmentalized, such as with individual 1.0"
conduits or "MaxCell".RTM. fabric inner ducts. In cases where a
single Collector runs in the same trench as a Feeder loop, it is
expected that the Collector fibers will utilize one of the Feeder's
expansion conduits instead of the 4" conduit discussed above. Both
ends of a Collector loop will not necessarily intersect the Feeder
at the same physical location. Fusion splices are preferably
utilized between the Collector and Feeder loops.
[0048] In order to minimize the frequency of adding new splices
between Collector and Feeder loops, a reasonable quantity of
splices will be generated at the outset to cover the near-term
growth of traffic on the distribution network.
[0049] Feeder Loops
[0050] In most cases, feeder loop 10 will consist of a 288 or
432-count fiber bundle run in a single 1.5" conduit. A person of
ordinary skill in the art will readily appreciate that fiber
bundles of greater or lesser count may be used as appropriate.
Additional conduits preferably will be included along the Feeder
path to accommodate future growth. In cases where a Collector loop
runs parallel to a Feeder loop, it is expected that the Collector
will utilize one of the Feeder's surplus 1.5" conduits instead of
the Collector's usual 4" conduit. Fusion splices should be utilized
for all connections to and from Feeder loops. All fusion splices
should introduce an insertion loss of no greater than 0.05 dB.
[0051] Feeder 10 fibers can be spliced to pigtails and terminated
in the Hub 20 location on initial installation. This reduces the
frequency of adding new splices on the feeder loop 10 and reduces
the interval required for service activation.
[0052] An Alternative Embodiment--Additional Equipment
[0053] In this embodiment, in addition to the conventional
feeder/collector architecture, additional electronic equipment can
be deployed at either the subscriber facility or the hub 20 to
provide intermediate-reach optics on both sides of the transmission
link.
[0054] For example, with respect to SONET equipment, a series of
ADMs will already exist at the hub locations to aggregate
subscriber traffic, and IR-1 optics can be supported on each
optical interface of the ADMs. Wavelength services pose a more
complex problem. Since these services enter the DWDM directly at
the Hub, they are limited by the current SR client-side interface
on the DWDM equipment. Since it is unlikely that any wavelength
service below an OC-48 or Gigabit Ethernet data rate will be used
in this context (as this would require dedicating a DWDM wavelength
to an OC-3 or OC-12 rate circuit), this would only pose a problem
for OC-48 or Gigabit Ethernet wavelength services.
[0055] In the case of Gigabit Ethernet services, upgrading a
subscriber to a GBIC equivalent to the Finisar 1319-5A-30 would
improve the optical reach to roughly 16.3 miles. This is less than
one mile shorter than the range of a bi-directional IR-1 link. The
OC-48/OC-48c case is more difficult. To support this service, a
subscriber positioned near a Hub either should use LR-1 optics
(assuming they are available on the subscriber equipment), or place
an OC-48 regenerator at the Hub location.
[0056] Second Alternative Embodiment--Nested Feeders
[0057] In this scenario, the distribution network provider deploys
a pair of nested Feeder rings 30 in each distribution network. The
collectors 31, 32 and 33 closest to the hub 20 are placed on the
nested feeder 30, while the collectors 40, 41 and 42 located
farther out are placed on the longer feeder 40. FIG. 3 displays a
generic example of this configuration. With the FIG. 3 type of
configuration, the longer feeder 40 can remain longer (e.g., more
than 7 miles in circumference) without stranding capacity because
the collectors closest to the LTN hub 20 have a shorter path
available to them.
[0058] Although the additional cross-section of fiber that
completes the interior Feeder may increase the cost of the
distribution network, it may also provide the opportunity to place
one or more additional Collectors that would have otherwise been
difficult to attach to the single Feeder design.
[0059] Decision Rule for Distribution Network Variants
[0060] In significant part, the distribution network design can be
directed based on the guidelines below. In each case, the longest
subscriber path is calculated as follows. Each Collector has a
corresponding longest circuit path. The longest circuit path can be
defined as the sum of the circumference of the Collector and the
longest route around the Feeder between the Collector and the Hub.
This value represents the maximum distance that a subscriber
circuit on that Collector can possibly travel en route to the Hub.
This value is unique to each Collector on the distribution network.
After calculating this value for each collector on the distribution
network, the largest of these values would represent the longest
subscriber path on that distribution network.
[0061] Longest Subscriber Path is Less than 9 Miles
[0062] Any distribution network that meets this requirement can be
designed using the conventional single Feeder, multiple Collector
architecture.
[0063] Longest Subscriber Path is Between 9 and 16 Miles
[0064] Any distribution network that falls in this category will
encounter complications based on the optical link budget. With this
in mind, the distribution network should be examined in detail to
determine whether a nested feeder approach is appropriate. In most
cases, the nested feeder architecture is desirable when a
significant portion of potential subscribers must traverse more
than nine miles of fiber (longest route around the Feeder) to
access the Hub or the additional cross section of fiber added to
create an Interior Feeder allows the addition of a new, desirable
Collector that would have otherwise been inaccessible.
[0065] Longest Subscriber Path is Greater than 16 Miles
[0066] Any distribution network in this classification gives rise
to design problems as one begins to exceed the limits of both
Gigabit Ethernet and SONET IR-1 optics. In this case, either the
distribution network may be configured to utilize the nested feeder
architecture, or it can be redesigned to shorten the longest
subscriber path.
[0067] Synchronization Subscribers purchasing SONET services can
synchronize their equipment with the Network by line-timing from
the optics of the ADM at the Hub. Similarly, subscribers purchasing
Ethernet services can line-time from the optics of the system
Ethernet Switch at the Hub facility. However, this option is not
available for wavelength services, as these circuits bypass any
equipment that can connect to a BITS clock. Subscribers who desire
wavelength services must therefore either provide their own clock
source or line-time from the customer equipment that they logically
attach to on the far end of the distribution network. Should either
of these options be unavailable for a given subscriber circuit,
there is still a likely option available to provide error-free
service. Depending on the age of the equipment, Telcordia compliant
devices should contain an internal SONET Minimum Clock (SMC) source
or Stratum 3 clock source. Either should provide adequate
synchronization for SONET signals. Any equipment free-running on a
Stratum 3 or SMC source should operate error-free under normal
conditions. The major perceptible difference will be an increase in
the frequency of pointer justification events between
interconnected devices.
[0068] Depending on the situation, SONET equipment installed at a
subscriber site may be owned and maintained either by the
distribution network operator or by the individual subscriber.
Ethernet equipment installed at a subscriber site will generally be
owned and maintained by the subscriber.
[0069] All distribution network electronics installed at subscriber
locations that are owned and maintained by the distribution network
operator should be remotely manageable, and should be capable of
forwarding alarm messages to the system NOC. SONET equipment will
commonly utilize the SONET Section Data Communications Channel
(SDCC) to communicate with the ADM equipment installed at the
Hub.
[0070] The Ethernet Services Network
[0071] Resiliency
[0072] It is desirable that a network of the type described herein
be substantially always available. In addition, a desirable network
architecture will provide fast recovery from failure to meet uptime
objectives. Taking as an example Ethernet as the local loop
technology, it is an objective that Ethernet services be highly
available. This objective makes the elimination of any Spanning
Tree Protocol ("STP") from the architecture desirable. In a
preferred embodiment, STP is not used because otherwise, network
recovery times may be of the order of minutes per failure.
[0073] The network elements which provide redundancy need not be
co-located with the primary network elements. This design technique
reduces the probability that problems with the physical environment
will interrupt service. Problems with software bugs or upgrades or
configuration errors or changes can often be dealt with separately
in the primary and secondary forwarding paths without completely
interrupting service. Therefore, network-level redundancy can also
reduce the impact of non-hardware failure mechanisms. With the
redundancy provided by the network, each network device no longer
needs to be configured for the ultimate in standalone fault
tolerance. Redundant networks can be configured to fail-over
automatically from primary to secondary facilities without operator
intervention. The duration of service interruption is equal to the
time it takes for fail-over to occur. Fail-over times as low as a
few seconds are possible in this manner.
[0074] Dual Physical Overlay Ring Core Topology
[0075] The local services network (e.g., Ethernet) according to the
preferred embodiment of the present invention comprises a dual
overlay ring topology within the core. This topology is shown in
FIG. 4. As can be seen, the dual overlay ring topology is a
physical topology in which two complete physical paths are disposed
to ensure that two data channels are available during normal
periods of use so that at least one is available to communicate
information in the event the other becomes unavailable.
[0076] This physical topology allows the creation of a working path
50 and a protection path 52 across the network connecting each
subscriber (L3 Switch 54) to their carrier/ISP (L3 Switches 56,
58). The working path 50 can be provisioned on one ring while the
protection path 52 can be provisioned on the other ring shown,
creating the logical connectivity topology shown in FIG. 5.
[0077] Logical connectivity may be accomplished in many ways, such
as by using Ethernet Virtual LAN (VLAN) tagging, as defined in the
IEEE 802.1Q standard. A VLAN can be roughly equated to a broadcast
domain. More specifically, VLANs can be seen as analogous to a
group of end-stations, perhaps on multiple physical LAN segments,
which are not constrained by their physical location and can
communicate as if they were on a common LAN. The 802.1Q header adds
two octets to the standard Ethernet frame. By configuring ports on
the Ethernet switches (e.g., 54) to be part of the specific
customer's VLAN, the logical connectivity paths are created through
the network. This process is somewhat analogous to creating a
Permanent Virtual Circuit ("PVC") in the Frame Relay or ATM
environment.
[0078] Extreme Network's Standby Router Protocol ("ESRP") may be
used to detect and recover from failures that occur within the
Ethernet Network. Additional protocols may be implemented to
support detection and recovery of failures that occur at the
Carrier/ISP connection. Some of these protocols are Hot Standby
Router Protocol ("HSRP") and Virtual Router Redundancy Protocol
("VRRP"). Note that standard Layer 2 protection protocols such as
802.1D Spanning Tree are not required in some embodiments of the
present invention.
[0079] Overview of ESRP
[0080] ESRP is a feature of the Extreme OS (operating system) that
allows multiple switches to provide redundant services to users. In
addition to providing Layer 3 routing redundancy for IP, ESRP also
provides Layer 2 redundancy. The Layer 2 redundancy features of
ESRP offer fast failure recovery and provide for a dual-homed
system design generally independent of end-user attached
equipment.
[0081] ESRP is configured on a per-VLAN basis on each switch. This
system utilizes ESRP in a two switch configuration, one master and
one standby. The switches exchange keep-alive packets for each VLAN
independently. Only one switch can actively provide Layer 2
switching for each VLAN. The switch performing the forwarding for a
particular VLAN is considered the "master" for that VLAN. The other
participating switch for the VLAN is in `standby` mode.
[0082] For a VLAN with ESRP enabled, each participating switch uses
the same MAC address and must be configured with the same IP
address. It is possible for one switch to be master for one or more
VLANs while being in standby for others, thus allowing the load to
be split across participating switches.
[0083] To have two or more switches participate in ESRP, the
following must be true. For each VLAN to be made redundant, the
switches must have the ability to exchange packets on the same
Layer 2 broadcast domain for that VLAN. Multiple paths of exchange
can be used, and typically exist in most network system designs
that take advantage of ESRP. In order for a VLAN to be recognized
as participating in ESRP, the assigned IP address for the separate
switches must be identical. ESRP must be enabled on the desired
VLANs for each switch. Extreme Discovery Protocol (EDP) must be
enabled on the ports that are members of the ESRP VLANs.
[0084] Master Switch Behavior
[0085] If a switch is master, it actively provides Layer 2
switching between all the ports of that VLAN. Additionally, the
switch exchanges ESRP packets with other switches that are in
standby mode.
[0086] Standby Switch Behavior
[0087] If a switch is in standby mode, it exchanges ESRP packets
with other switches on that same VLAN. When a switch is in standby,
it does not perform Layer 2 switching services for the VLAN. From a
Layer 2 switching perspective, no forwarding occurs between the
member ports of the VLAN. This prevents loops and maintains
redundancy.
[0088] ESRP Tracking
[0089] ESRP can be configured to track connectivity to one or more
specified VLANs as criteria for fail-over. The switch that has the
greatest number of active ports for a particular VLAN takes highest
precedence and will become master. If at any time the number of
active ports for a particular VLAN on the master switch becomes
less than the standby switch, the master switch automatically
relinquishes master status and remains in standby mode.
[0090] Additionally, ESRP can be configured to track connectivity
using a simple ping to any outside responder (ping tracking). The
responder may represent the default route of the switch, or any
device meaningful to network connectivity of the master ESRP
switch. It should be noted that the responder must reside on a
different VLAN than ESRP. The switch automatically relinquishes
master status and remains in standby mode if a ping keep-alive
fails three consecutive times.
[0091] A simplified drawing of the logical topology is shown in
FIG. 6, indicating where ESRP is utilized in the present
distribution network design. FIG. 6 depicts ESRP enabled in the
switches (62, 63) directly attached to the subscriber 60. Port
track is used to detect local failure of a link directly connected
to these switches while ping track is used to detect core network
failures. If a failure is detected anywhere along the active path
64, ESRP will failover to allow traffic to flow on the standby path
65. As shown, ESRP port count can be used to protect dual customer
connections to the network. ESRP ping tracking is used to protect
the core VLAN. In the exemplary embodiment shown, VRRP or HSRP
protects the Carrier/ISP L3 switch.
[0092] ESRP Enhancements
[0093] A preferred embodiment of the network includes network
enhancements, including Extreme Network's ESRP, to support rapid
failover of subscriber equipment when a network or core failure
occurs. In the context of ESRP, this is referred to as "ESRP
Failover Link Transition Enhancement." This enhancement refers to
the ability of a "Master" ESRP switch, when transitioning to
standby state to "bounce" or restart auto-negotiation on a set of
physical ports. This enhancement will cause an end device to flush
its Layer 2 forwarding database and cause it to re-broadcast
immediately for a new path through the network. This provides the
end station the ability to switch from the primary to the secondary
path in a very short time.
[0094] This enhancement relates to the ability of a "Master" ESRP
switch, when transitioning to a standby state to "bounce" or
restart auto-negotiation on a set of physical ports. This is useful
in this architecture to inform an end-user Layer 2 device of a
failure farther within the network that does not directly impact
the end-user Layer 2 device. As background: Typical Layer 3
switches use the Address Resolution Protocol (ARP) to populate
their forwarding databases. This forwarding database determines
which port packets are sent out on based on destination MAC
address. Once this information is learned through the ARP process,
typical Layer 2 devices will not modify this forwarding information
unless one of two events occur. First, a Loss of Signal (LOS)
occurs on the port or 2) the ARP max age timer expires. Typically,
the ARP max age value is set to 5 minutes. When this timer expires,
the Layer 2 device will re-ARP to update its forwarding database
information. Therefore, if a failure occurs within the core of the
network that does not cause a LOS on the end-user device, that
device will continue to forward packets into the network even
though they cannot reach their ultimate destination until the ARP
max age timer expires. This is known as a black hole situation. The
enhancement proposed here prevents a black hole situation, by
notifying the end device of the core failure by "bouncing" the port
to force the equipment to re-ARP to update its forwarding database
information immediately.
[0095] Although certain preferred embodiments of the present
invention have been described above by way of example, it will be
understood that modifications may be made to the disclosed
embodiments without departing from the scope of the invention,
which is defined by the appended claims. The benefits, advantages,
solutions to problems, and any element(s) that may cause any
benefit, advantage, or solution to occur or become more pronounced
are not to be construed as a critical, required, or essential
feature or element of any or all the claims. As used herein, the
terms "comprises," "comprising," or any other variation thereof,
are intended to cover a non-exclusive inclusion, such that a
process, method, article, or apparatus that comprises a list of
elements does not include only those elements but may include other
elements not expressly listed or inherent to such process, method,
article, or apparatus.
Glossary of Terms
[0096] ADM--Add/Drop Multiplexer. A SONET component capable of
inserting and removing traffic to/from the SONET line payload. ADMs
also commonly perform other functions, such as
generating/processing APS commands and synchronizing the transport
optics to an external clock source.
[0097] APS--Automatic Protection Switching. A SONET fault recovery
protocol standardized by Telcordia. APS will generally provide
fault recovery in less than 50 ms.
[0098] BDN--Built Distribution Network. A portion of a network
dedicated to the aggregation of multiple subscribers. A BDN
typically utilizes fiber to provide dedicated fiber links between
individual subscribers and a Hub facility.
[0099] BITS--Building Integrated Timing Source. A highly accurate
and precise clock source used to synchronize multiple nodes on a
SONET transport system.
[0100] Chromatic Dispersion--A linear effect that causes pulse
broadening or compression within an optical transmission system.
Chromatic Dispersion is occurs because different wavelengths of
light travel at different velocities through the transmission
media.
[0101] Collector Loop--A fiber loop (typically 144 ct) used to
connect multiple subscribers to the larger Feeder loop on a
BDN.
[0102] Customer--A business entity (such as an ISP or LEC) that
provides telecommunications service within a Metropolitan area. The
BDN operator typically will serve as an intermediate transport
mechanism to connect subscribers to various customers.
[0103] DMD--Differential Mode Delay. A linear effect that degrades
the quality of laser transmissions across MMF. A single laser
transmission can inadvertently become subdivided upon ingress to
MMF. These identical signals traverse unique transmission paths
within the large core of MMF and leave the fiber offset in
time.
[0104] DS3--Digital Signal 3. A digital signal rate of
approximately 44.736 Mb/s corresponding to the North American T3
designator. A plesiochronous transport protocol equivalent to 672
voice lines at 64 kb/s each.
[0105] DWDM--Dense Wavelength Division Multiplexing. A method of
allowing multiple transmission signals to be transmitted
simultaneously over a single fiber by giving each a unique
frequency range (or wavelength) within the transmission spectrum.
DWDM wavelengths within the C-Band are standardized by the
ITU-T.
[0106] Ethernet--A standardized (IEEE 802.3) packet-based data
transport protocol developed by Xerox Corporation.
[0107] Ethernet Switch--A device used to route data packets to
their proper destination in an Ethernet-based transport
network.
[0108] FDP--Fiber Distribution Panel. An enclosure built to
organize, manage, and protect physical cross-connections between
multiple fiber-optic cables.
[0109] Feeder Loop--A fiber loop (typically 432 ct) used to connect
multiple collector loops to a Hub facility on a BDN.
[0110] Fusion Splice--The process of joining of two discrete
fiber-optic cables via localized heating of the fiber ends. Fusion
splices are typically characterized as permanent in nature and
exhibit relatively minor loss (<0.05 dB) at the fusion
point.
[0111] Hub Facility--A facility used to connect a distribution
network (BDN or LDN) to a transport network (LTN) within a
Metropolitan area.
[0112] IR-1--A specification for transmission lasers and receiver
photodiodes standardized by Telcordia. IR-1 optics typically
provide a 13.0 dB link budget and are optimized for NDSF.
[0113] ITU-T--International Telecommunications
Union--Telecommunications Standardizations Sector.
[0114] Lateral--A fiber spur containing multiple fibers (e.g., 48
ct) used to connect a Collector loop to a subscriber site.
[0115] LDN--Leased Distribution Network. A portion of a network
dedicated to the aggregation of multiple subscribers. An LDN
typically utilizes fiber to provide fiber links between individual
subscribers and a Hub facility.
[0116] LR-1--A specification for transmission lasers and receiver
photodiodes standardized by Telcordia. LR-1 optics typically
provide a 25 dB link budget and are optimized for NDSF.
[0117] LTN--Leased Transport Network. A portion of a network
dedicated to connecting various Customer sites to Hub facilities.
An LTN will typically utilize TDM and DWDM equipment over a small
quantity of leased fiber.
[0118] MCP--Modal Conditioning Patch cord. A hybrid fiber-optic
cable used to overcome DMD problems by allowing a laser to mimic
the overfilled launch characteristics of an LED.
[0119] Mechanical Splice--The process of joining of two discrete
fiber-optic cables by aligning them within a mechanical enclosure
or adhesive media. Mechanical splices typically utilize an
index-matching gel to reduce reflection at the splice point. Expect
a moderate power loss (0.10 to 0.20 dB) at the splice point.
[0120] Media Converter--A generic classification of devices used to
alter protocols and/or media of a transmitted signal.
[0121] MMF--Multi-Mode Fiber. A fiber-optic cable with a relatively
large (50 to 62 .mu.m) transmission core that allows signals to
traverse multiple, discrete transmission paths (modes) within the
cable. MMF is typically utilized with LED-based optical
transmission systems.
[0122] Modal Distortion--A linear effect that causes pulse
broadening of transmission signals over MMF. Rays taking more
direct paths (fewer reflections in the core) through the MMF core
traverse the fiber more quickly than rays taking less direct paths.
Modal distortion limits the bandwidth and distance of transmission
links over MMF.
[0123] MPOE--Minimum Point of Entry. A common space within a
multi-tenant building used to interconnect multiple tenants with
common external telecommunications facilities.
[0124] NDSF--Non Dispersion-Shifted Fiber. Single-mode optical
fiber with a nominal zero-dispersion wavelength within the
conventional 1310 nm transmission window.
[0125] NZ-DSF--Non-Zero Dispersion-Shifted Fiber. Single-mode
optical fiber with a nominal zero-dispersion wavelength shifted to
reduce chromatic dispersion within the 1530 nm to 1560 nm
transmission window.
[0126] OC-3--Optical Carrier 3. The optical equivalent to an STS-3,
with a digital signal rate of approximately 155.52 Mb/s. A
synchronous transport protocol equivalent to 2016 voice lines at 64
kb/s each. Protocol is specified by Telcordia standards.
[0127] OC-3c--Optical Carrier 3, Concatenated. A non-channelized
variant of the OC-3, primarily utilized for data transmissions over
SONET. Protocol is specified by Telcordia standards.
[0128] OC-12--Optical Carrier 12. The optical equivalent to an
STS-12, with a digital signal rate of approximately 622.08 Mb/s. A
synchronous transport protocol equivalent to 8064 voice lines at 64
kb/s each. Protocol is specified by Telcordia standards.
[0129] OC-12c--Optical Carrier 12, Concatenated. A non-channelized
variant of the OC-12, primarily utilized for data transmissions
over SONET. Protocol is specified by Telcordia standards.
[0130] OC-48--Optical Carrier 48. The optical equivalent to an
STS-48, with a digital signal rate of approximately 2.488 Gb/s. A
synchronous transport protocol equivalent to 32256 voice lines at
64 kb/s each. Protocol is specified by Telcordia standards.
[0131] OC-48c--Optical Carrier 48, Concatenated. A non-channelized
variant of the OC-48, primarily utilized for data transmissions
over SONET. Protocol is specified by Telcordia standards.
[0132] Plesiochronous--The relationship between two transmission
devices, where each is timed from similar, yet diverse clock
sources. A slight difference in either frequency or phase must
exist between the diverse clocks.
[0133] POP--Point of Presence. The physical facility in which
interexchange carriers and local exchange carriers provide access
services.
[0134] SMF--Single Mode Fiber. A type of optical fiber in which
only a single transport path (mode) is available through the core
at a given wavelength.
[0135] SONET--Synchronous Optical NETwork. A circuit-based
transmission/restoration protocol defined by Telcordia standards.
Use of the SONET TDM protocol is primarily limited to North
America.
[0136] Splice Box--An enclosure built to organize, manage, and
protect physical splices between multiple fiber-optic cables.
[0137] SR--A specification for transmission lasers and receiver
photodiodes standardized by Telcordia. SR optics typically provide
an 8 dB link budget and are optimized for NDSF.
[0138] Subscriber--An end-user (or desired end-user) of a
Customer's telecommunications service. A BDN operator typically
will serve as an intermediate transport mechanism between
subscribers and customers.
[0139] Synchronous--The relationship between two transmission
devices, where both are timed from identical clock sources. The
clocks must be identical in frequency and phase.
[0140] TDM--Time-Division Multiplexing. Combining multiple
transmission signals into a common, higher-frequency
bit-stream.
[0141] WDM--Wavelength-Division Multiplexing. A method of allowing
multiple transmission signals to be transmitted simultaneously over
a single fiber by giving each a unique frequency range (or
wavelength) within the transmission spectrum.
* * * * *