Home > Articles > Networking > Routing & Switching

Interexchange Carrier MPLS Network Design Study

USCom is a fictitious nationwide data and long-distance voice service provider in the U.S. This chapter discusses the current USCom MPLS network design, its evolution, and how USCom characteristics and objectives influenced the corresponding design decisions that were made in order to illustrate how design decisions should stem from the characteristics of your company.
This chapter is from the book

This chapter is from the book

USCom is a fictitious nationwide data and long-distance voice service provider in the U.S. that provides connectivity between local exchanges in different geographic regions. It also facilitates inter-Local Access and Transport Area (LATA) services (as described in the Federal Communications Commission [FCC] Telecommunications Act of 1996), as well as a complete portfolio of data services. USCom may be classified as an Interexchange Carrier (IXC) that owns its fiber and transmission facilities as well as a Layer 2 switching infrastructure (ATM and Frame Relay) spanning its service footprint.

This chapter discusses the current USCom MPLS network design, its evolution, and how USCom characteristics and objectives influenced the corresponding design decisions that were made.

USCom's Network Environment

USCom has been offering Internet access for many years to other service providers (wholesale), Enterprises, and small/medium business customers. It currently has an installed base of more than 35,000 Internet ports. These Internet ports are supported on 350 Internet edge routers (called Internet access provider edge [PE] routers) located in their 100 Points of Presence (POPs) that are situated across the country. Internet connectivity is obtained via transit providers, private peering sessions, and connections in major cities to various Network Access Points (NAPs).

USCom has also had great success with its Layer 3 Multiprotocol Label Switching (MPLS) VPN service (which is based on the architecture described in [2547bis]) since its inception in 2002. Acceptance of the service has grown throughout USCom's customer base. Currently some 12,500 VPN ports are installed across the country, and this number is growing considerably on a monthly basis. The customer-managed customer edge (CE) routers are connected via 255 Layer 3 MPLS VPN PE routers hosted in USCom's various POPs. Note that PE routers are dedicated to either the Internet or Layer 3 MPLS VPN access. Given the success of this offering, USCom plans to add 6000 customer access links per annum, although based on the current trend this figure is considered conservative. Total traffic volume, which includes both Internet and VPN, is expected to grow at approximately 30 percent per annum.

USCom owns fiber across the country and is running a long-distance optical core based on dense wavelength division multiplexing (DWDM) technology. This translates to availability of raw high-speed links (OC-48 (2.488 Gbps) and OC-192 (10 Gbps)) for provider router (P router) and PE router interconnection, at relatively low cost and provisioning time. USCom can activate additional capacity by enabling additional wavelengths (lambdas) in a relatively short time frame. USCom takes advantage of this to enforce an overengineering policy for core router links.

The high-speed core links are provided to routers as native lambdas straight from the DWDM equipment without any intermediate SONET Add/Drop Multiplexer (ADM). (Note that SONET framing is in use between the routers and the DWDM equipment.) These links do not benefit from any protection at the optical level. Some links interconnecting P routers and PE routers are provided through a SONET infrastructure overlaid over the optical infrastructure. The SONET links are protected by means of SONET protection provided by Bidirectional Line Switch Rings (BLSRs) with four fibers, also called BLSR/4. (See [NET-RECOV] for more details on SONET-SDH recovery mechanisms.)

Intra-POP connectivity is achieved via Packet over SONET (PoS) or switched Gigabit Ethernet. Because of the relatively low cost of switched Gigabit Ethernet technology and the negligible cost of fibers within a premises, USCom also maintains an overengineered intra-POP capacity.

Access from CE router to PE router for both Internet and Layer 3 MPLS VPN connectivity is provided via Frame Relay, ATM, leased line, or SONET. Each of these physical (or logical) links is dedicated to a single CE router. These links involve a significant cost that typically precludes simple overengineering and mandates tight dimensioning. Access speeds range from 64 kbps to OC-48.

The USCom nationwide backbone POP topology, interconnected through OC-48 and OC-192 links, is illustrated in Figure 3-1.

Figure 1

Figure 3-1 USCom Nationwide Topology

The USCom network is structured into three levels of POPs. Each POP is classified as either a backbone (Level 1), medium (Level 2), or small (Level 3) facility. The level depends on the density of the customer access and combined traffic throughput requirements. All routers are operated as a single autonomous system, with American Registry for Internet Numbers (ARIN) assigned AS number 32765. USCom has been assigned the 23/8 IP address space. The company uses this for its internal infrastructure as well as customer allocation.

Level 1 POPs are the backbone POPs (as shown in Figure 3-1) comprising the high-capacity backbone P routers dedicated to long-distance transit and interconnection of lower-level POPs to this long-distance transit backbone. PE routers providing Internet and Layer 3 MPLS VPN services from these major locations are also deployed, as well as some additional P routers acting as an aggregation layer inside the POP for these PE routers. Aggregation P routers reduce the number of IGP adjacencies that have to be maintained by the backbone P routers to two, because each core P router has to peer with only two aggregation P routers (in addition to the other core P routers in the backbone) instead of with all the PE routers in the POP (whose number can be fairly high, and growing, in a Level 1 POP).

Each Level 1 POP has two backbone P routers that interconnect via OC-48, dual OC-48, or OC-192 links to the rest of the backbone network. They also interconnect with lower-level POPs using either OC-3 (155.52 Mbps) or OC-48 links. Each backbone P router is connected to both local aggregation P routers via a point-to-point OC-48 link. Each PE router (and there may be several) is connected to both aggregation P routers via OC-3 PoS links. There are currently 15 Level 1 POPs, the structure of which is illustrated in Figure 3-2.

Figure 2

Figure 3-2 USCom Level 1 POP Design

The Level 2 POPs are composed of P routers that connect to the Level 1 POPs, or another Level 2 POP, via OC-3 or OC-48 links, and the PE routers in medium access locations. Each PE router is connected to both backbone P routers via redundant switched Gigabit Ethernet (using two separate Gigabit Ethernet switches). There are currently 25 Level 2 POPs, the structure of which is illustrated in Figure 3-3.

Figure 3

Figure 3-3 USCom Level 2 POP Design

The Level 3 POPs are composed of PE routers in remote locations and P routers that connect to Level 2 POPs via OC-3 links. There are currently 60 Level 3 POPs, the structure of which is illustrated in Figure 3-4.

Figure 4

Figure 3-4 USCom Level 3 POP Design

Several years ago, USCom deployed a SONET network providing OC-3 links. These links are protected at the SONET layer by the protection mechanisms provided by four-fiber BLSRs. These allow recovery from any link failure, with some special conditions specified by the SONET standard, within 60 ms. USCom satisfies all the conditions, including ring distance limited to 1200 km, less than 16 SONET stations, and ring in idle state before protection. Figure 3-5 shows the protected OC-3 links provided by the four-fiber BLSRs and used between Level 1 and Level 2/3 POPs. Because these links are protected and stable, USCom decided to use them in the core network without any changes.

Figure 5

Figure 3-5 Protected OC-3 Links Provided by Four-Fiber BLSRs

Figure 3-5 also shows that the USCom optical network uses DWDM technology, allowing the multiplexing of tens of light paths over a single fiber. Note that USCom has deployed Coarse Wave Division Multiplexing (CWDM) equipment in some metro areas, offering a lower degree (4) of multiplexing. The DWDM equipment lets the company provide 1+1 optical protection. Such a protection scheme relies on specialized optical equipment performing traffic bridging along the primary and secondary light paths, each of which follows diverse paths. Upon a link failure, such as a fiber cut or optical equipment failure, the receiving side quickly detects the failure and switches the traffic received from the primary light path to the secondary. This type of mechanism, usually qualified as "single-ended," is undoubtedly efficient because it does not require any extra signaling mechanisms or coordination between the sender and receiver (just the receiving side performs the switching function). Hence, the rerouting time is very fast (a few milliseconds). Moreover, a strictly equivalent quality of service (QoS) is guaranteed upon a network element failure because the secondary path is identical to the primary path (although it might be longer to be diverse from the primary path). On the other hand, this requires dedicating half of the fiber capacity for backup recovery. Furthermore, such a protection scheme implies that additional optical equipment needs to be purchased.

Hence, USCom decided to use all the network bandwidth to route the primary traffic and rely on some upper-layer protection mechanisms (see the section "Network Recovery Design") to offer equivalent rerouting time at significantly lower costs. All the light paths provided to the IP/MPLS layer for inter-Level 1 links and Level 1-to-Level 2 links therefore are unprotected. This is perfectly in line with the previously described core network overengineering strategy adopted by USCom.

Although DWDM offers the ability to provide high bandwidth in a very cost-effective fashion, it has a downside. Multiple links share some common resources and equipment whose failure may impact several links. This is called Shared Risk Link Group (SRLG), and the production design should take it into account.

Putting all this information together, you can see from Figure 3-6 how connectivity is typically achieved from a Level 3 to a Level 2 to a Level 1 POP.

Figure 6

Figure 3-6 Inter-POP Connectivity Within the USCom Network

Table 3-1 summarizes the various types of links used in the USCom network, along with their main characteristics and localization.

Table 3-1 Link Types and Characteristics in the USCom Backbone

Link Type

Speed

Protection

Localization

OC-192 DWDM

10 Gbps

None

Level 1 POP-Level 1 POP

OC-48 DWDM

2.5 Gbps

None

Level 1 POP-Level 1 POP

Level 1 POP-Level 2 POP

OC-48 SONET

2.5 Gbps

SONET protection

Level 1 POP-Level 2 POP

Level 2 POP-Level 2 POP

OC-3 SONET

155 Mbps

SONET protection

Level 2 POP-Level 3 POP

Gigabit Ethernet

1 Gbps

None

Intra-Level 2 POP

Intra-Level 3 POP

During the past several years, USCom has gathered various network failure statistics; they are summarized in Table 3-2. These statistics have been used to assess USCom's design requirements for its backbone network.

Table 3-2 Link Failure Statistics Within the USCom Network

Failure Type

Link/Router Type

Occurrence

Duration

Link failure

OC-3 SONET links

On average once a day in the network

From a few seconds to several days (fiber cut)

Link failure

OC-48 and OC-192 links

Unknown

Unknown

Router interface failure

Edge+core

Negligible

A few hours

Router failure (such as power supply, router software failure with traffic impact)

Edge+core

Once every two months

Variable

Router reboot (planned failure)

Edge (IA and VPN PE routers)

Once every six months

10 minutes

Router reboot (planned failure)

Core

Once a year

10 minutes

InformIT Promotional Mailings & Special Offers

I would like to receive exclusive offers and hear about products from InformIT and its family of brands. I can unsubscribe at any time.

Overview


Pearson Education, Inc., 221 River Street, Hoboken, New Jersey 07030, (Pearson) presents this site to provide information about products and services that can be purchased through this site.

This privacy notice provides an overview of our commitment to privacy and describes how we collect, protect, use and share personal information collected through this site. Please note that other Pearson websites and online products and services have their own separate privacy policies.

Collection and Use of Information


To conduct business and deliver products and services, Pearson collects and uses personal information in several ways in connection with this site, including:

Questions and Inquiries

For inquiries and questions, we collect the inquiry or question, together with name, contact details (email address, phone number and mailing address) and any other additional information voluntarily submitted to us through a Contact Us form or an email. We use this information to address the inquiry and respond to the question.

Online Store

For orders and purchases placed through our online store on this site, we collect order details, name, institution name and address (if applicable), email address, phone number, shipping and billing addresses, credit/debit card information, shipping options and any instructions. We use this information to complete transactions, fulfill orders, communicate with individuals placing orders or visiting the online store, and for related purposes.

Surveys

Pearson may offer opportunities to provide feedback or participate in surveys, including surveys evaluating Pearson products, services or sites. Participation is voluntary. Pearson collects information requested in the survey questions and uses the information to evaluate, support, maintain and improve products, services or sites, develop new products and services, conduct educational research and for other purposes specified in the survey.

Contests and Drawings

Occasionally, we may sponsor a contest or drawing. Participation is optional. Pearson collects name, contact information and other information specified on the entry form for the contest or drawing to conduct the contest or drawing. Pearson may collect additional personal information from the winners of a contest or drawing in order to award the prize and for tax reporting purposes, as required by law.

Newsletters

If you have elected to receive email newsletters or promotional mailings and special offers but want to unsubscribe, simply email information@informit.com.

Service Announcements

On rare occasions it is necessary to send out a strictly service related announcement. For instance, if our service is temporarily suspended for maintenance we might send users an email. Generally, users may not opt-out of these communications, though they can deactivate their account information. However, these communications are not promotional in nature.

Customer Service

We communicate with users on a regular basis to provide requested services and in regard to issues relating to their account we reply via email or phone in accordance with the users' wishes when a user submits their information through our Contact Us form.

Other Collection and Use of Information


Application and System Logs

Pearson automatically collects log data to help ensure the delivery, availability and security of this site. Log data may include technical information about how a user or visitor connected to this site, such as browser type, type of computer/device, operating system, internet service provider and IP address. We use this information for support purposes and to monitor the health of the site, identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents and appropriately scale computing resources.

Web Analytics

Pearson may use third party web trend analytical services, including Google Analytics, to collect visitor information, such as IP addresses, browser types, referring pages, pages visited and time spent on a particular site. While these analytical services collect and report information on an anonymous basis, they may use cookies to gather web trend information. The information gathered may enable Pearson (but not the third party web trend services) to link information with application and system log data. Pearson uses this information for system administration and to identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents, appropriately scale computing resources and otherwise support and deliver this site and its services.

Cookies and Related Technologies

This site uses cookies and similar technologies to personalize content, measure traffic patterns, control security, track use and access of information on this site, and provide interest-based messages and advertising. Users can manage and block the use of cookies through their browser. Disabling or blocking certain cookies may limit the functionality of this site.

Do Not Track

This site currently does not respond to Do Not Track signals.

Security


Pearson uses appropriate physical, administrative and technical security measures to protect personal information from unauthorized access, use and disclosure.

Children


This site is not directed to children under the age of 13.

Marketing


Pearson may send or direct marketing communications to users, provided that

  • Pearson will not use personal information collected or processed as a K-12 school service provider for the purpose of directed or targeted advertising.
  • Such marketing is consistent with applicable law and Pearson's legal obligations.
  • Pearson will not knowingly direct or send marketing communications to an individual who has expressed a preference not to receive marketing.
  • Where required by applicable law, express or implied consent to marketing exists and has not been withdrawn.

Pearson may provide personal information to a third party service provider on a restricted basis to provide marketing solely on behalf of Pearson or an affiliate or customer for whom Pearson is a service provider. Marketing preferences may be changed at any time.

Correcting/Updating Personal Information


If a user's personally identifiable information changes (such as your postal address or email address), we provide a way to correct or update that user's personal data provided to us. This can be done on the Account page. If a user no longer desires our service and desires to delete his or her account, please contact us at customer-service@informit.com and we will process the deletion of a user's account.

Choice/Opt-out


Users can always make an informed choice as to whether they should proceed with certain services offered by InformIT. If you choose to remove yourself from our mailing list(s) simply visit the following page and uncheck any communication you no longer want to receive: www.informit.com/u.aspx.

Sale of Personal Information


Pearson does not rent or sell personal information in exchange for any payment of money.

While Pearson does not sell personal information, as defined in Nevada law, Nevada residents may email a request for no sale of their personal information to NevadaDesignatedRequest@pearson.com.

Supplemental Privacy Statement for California Residents


California residents should read our Supplemental privacy statement for California residents in conjunction with this Privacy Notice. The Supplemental privacy statement for California residents explains Pearson's commitment to comply with California law and applies to personal information of California residents collected in connection with this site and the Services.

Sharing and Disclosure


Pearson may disclose personal information, as follows:

  • As required by law.
  • With the consent of the individual (or their parent, if the individual is a minor)
  • In response to a subpoena, court order or legal process, to the extent permitted or required by law
  • To protect the security and safety of individuals, data, assets and systems, consistent with applicable law
  • In connection the sale, joint venture or other transfer of some or all of its company or assets, subject to the provisions of this Privacy Notice
  • To investigate or address actual or suspected fraud or other illegal activities
  • To exercise its legal rights, including enforcement of the Terms of Use for this site or another contract
  • To affiliated Pearson companies and other companies and organizations who perform work for Pearson and are obligated to protect the privacy of personal information consistent with this Privacy Notice
  • To a school, organization, company or government agency, where Pearson collects or processes the personal information in a school setting or on behalf of such organization, company or government agency.

Links


This web site contains links to other sites. Please be aware that we are not responsible for the privacy practices of such other sites. We encourage our users to be aware when they leave our site and to read the privacy statements of each and every web site that collects Personal Information. This privacy statement applies solely to information collected by this web site.

Requests and Contact


Please contact us about this Privacy Notice or if you have any requests or questions relating to the privacy of your personal information.

Changes to this Privacy Notice


We may revise this Privacy Notice through an updated posting. We will identify the effective date of the revision in the posting. Often, updates are made to provide greater clarity or to comply with changes in regulatory requirements. If the updates involve material changes to the collection, protection, use or disclosure of Personal Information, Pearson will provide notice of the change through a conspicuous notice on this site or other appropriate way. Continued use of the site after the effective date of a posted revision evidences acceptance. Please contact us if you have questions or concerns about the Privacy Notice or any objection to any revisions.

Last Update: November 17, 2020