PDN043 Carrier Ethernet Services Explained Pre Course Reading v4 1

8/12/2019 PDN043 Carrier Ethernet Services Explained Pre Course Reading v4 1

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Carrier Ethernet Services Explained

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On completion of the 5-day Carrier Ethernet Services Explained course,participants will have the opportunity to sit the MEF Carrier Ethernet CertifiedProfessional (CECP) examination.

The exam is a 1 hour 45 minute multiple choice paper containing 80 questions.The exam is a closed book exam with no access to other materials beingpermitted.

This pre-course reading material forms part of the course material and theparticipant is required to read this material before attending the course. Inaddition to this pre-course reading material, the participant should also have anawareness of at least some of the following transport technologies :

SONET/SDH

MPLS

GMPLS

MPLS VPWS

MPLS VPLS

MPLS-TP

OTN

WDM

DSL

HFC

PON

WDM PON

It is suggested that if you feel your knowledge of the above is lacking, that you

should research these transport technologies to gain at least, a basicunderstanding of each.

It is also suggested that you complete some research of the MEF specificationsand presentations that can be found on the MEF website:

www.metroethernetforum.org


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http://www.metroethernetforum.org/http://www.metroethernetforum.org/


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The Metro Ethernet Forum (MEF) is the defining body for Carrier Ethernet. It is aglobal industry alliance responsible for the acceleration of the worldwide adoption

of Carrier Ethernet services and networks.

The MEF develops Carrier Ethernet Technical Specifications and ImplementationAgreements to promote interoperability and to promote the worldwide deploymentof Carrier Ethernet.


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The Metro Ethernet Forum (MEF) was formed in 2001 with the purpose ofdeveloping ubiquitous business services for Enterprise users. At that time the

services were mainly those of Enterprise LAN interconnect over metropolitannetworks using optical fibre cable.

Since that time the scope of the MEF has expanded and there are now a numberof committees that have responsibility for standards, education, and compliance.

The Technical Committee is responsible for the development of technicalspecifications, implementation agreements, test specifications and position

statements.

The Marketing Committee is responsible for the development of presentations,white papers and videos to promote the adoption of Carrier Ethernet services andequipment. It participates in major events and marketing programmes, and in thedevelopment of toolkits for service providers.

The Certification Committee is responsible for defining and facilitating bothvendor and service provider certification programmes to ensure compliance of

equipment and services to MEF specifications. It is not directly involved in testingcompliance but has an approved Certification Lab for this purpose. The latestcertification addition is that of the MEF Carrier Ethernet Certified Professional.


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Metro Ethernet services have grown in popularity and hence the MEF-definedservices have expanded to include worldwide services carried over national and

global networks, and access networks. This provides greater availability ofservices to the end users over a wider range of access technologies.

Economy of scale is supported due to the convergence of business, residentialand wireless networks sharing the same infrastructure and services. This permitsrapid deployment of scalable business applications.

The adoption of the certification programme has been an important driver for the

expansion of the services to Carrier Ethernet.

The expansion to Carrier Ethernet is achieved whilst retaining the cost model andsimplicity of Ethernet.


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The purpose of the MEF Certification Programs is to accelerate the deploymentof Carrier Ethernet in the access, metropolitan, and wide area network.

The two main areas of certification are manufacturer certification and serviceprovider certification.

The manufacturer certification aims to assure compliance of MEF CarrierEthernet specifications for equipment supplied to service providers. Serviceprovider certification assures compliance of Carrier Ethernet services to MEFspecifications and to assure service level agreements and service level

specifications.


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The latest addition to the Certification Committees programmes is the MEF

Carrier Ethernet Certified Professional (CECP) examination and is designed to

enable Carrier Ethernet personnel to demonstrate and validate their knowledgeand Carrier Ethernet expertise.

The programme is targeted towards product managers/planners, salesmanagers/engineers, and technical marketing representatives and serves toenable them to demonstrate their ability to promote, define, market and sellCarrier Ethernet products and services.


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Carrier Ethernet is defined by the MEF from the user perspective, as aubiquitous, standardized, carrier-class service and network defined by five

attributes that distinguish it from familiar LAN-based Ethernet. The service a userpurchases will be defined in a Service Level Agreement.

Carrier Ethernet from the service providers perspective is a set of MEF-certifiednetwork elements that connect to transport Carrier Ethernet services for all userslocally and globally. The network elements may be wholly within the serviceproviders network or may span multiple operators networks. The services may

be carried over physical Ethernet networks or over other legacy transporttechnologies.


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Carrier Ethernet to the vendor is the provision of external interface equipmentfunctionality that provides UNI and ENNI functionality that can be deployed in the

implementation of Carrier Ethernet services. This equipment will comply with therequirements and features specified in the MEF technical specifications and testsuites and will therefore be able to be evaluated for compliance to the MEFspecifications and thus aid interoperability.


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The MEF has defined five attributes to distinguish Carrier Ethernet services fromfamiliar LAN-based Ethernet.

These attributes are:

Standardized Services

Scalability

Reliability

Quality of Service

Service Management

These attributes will be defined and described in a later chapter.


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Traditional carrier networks were voice oriented and carrier data an afterthought.Voice network design evolved within government controlled PTTs where

maintaining stable reliable infrastructure was key and there was little motivationto develop technology quickly. Price of services was controlled and PTTs hadmarket monopoly so there was little motivation to improve business efficiency.This started to change in the 1980s with the breakup of AT&T in the USA and theprivatization of telecommunications out of PTTs.

In some countries governments were very protective of the status quo and simplynominally changed the ownership to make the PTT a privately owned institution.They often included a golden share ensuring political control remained withingovernment hands. However over time these institutions have become more

independent and commercially aware.

With the creation of competitive markets by allowing competition from newcommercially independent carriers and between countries the market hassubstantially changed. The growth of the Internet has cemented these changes.

Today data is the main business. Within the customer site Ethernet is the networkof choice. Deploying Ethernet within the carrier network also simplifies thenetwork and makes it cheaper. Even the old voice networks are evolving toreplace carrier technologies with new generation designs based upon Ethernetand IP.


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Price and speed are the two key drivers of growth. The price of interfaces usedwithin carrier services have always been high because the demands for high

reliability implied designs with internal management and redundancy.

However the growth of speed in the field of communications driven by Moore'sLaw has changed the dynamic. This increasing density of micro-integration in thetechnology has allowed computer system based interfaces to grow in speedmuch faster than Telecom Interface standards, and adding greater redundancy byduplication of some functions has even enabled carrier class levels of reliabilitytoo.

Moore's law describes a long-term trend in the history of computing hardware.The number of transistors that can be placed inexpensively on an integratedcircuit doubles approximately every two years. This trend has continued for morethan half a century and is expected to continue until 2015 or 2020 or later.Moore's law describes a driving force of technological and social change in thelate 20th and early 21st centuries. His prediction has proved to be uncannilyaccurate.


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The per port cost of Ethernet ports has made a big impact. A reduction in the perinterface cost of connect devices with Ethernet over traditional SONET/SDH

today now means this migration can result in 90% reduction in some casesolarge that the whole design approach can change and make cost reductions.

Indeed the price of placing gigabit Ethernet ports on board PC motherboards isnow so low, few new desktop computers are produced without them.

Looking back to the 1990s, SONET and ATM interfaces ran at thousands ofdollars per port and have changed little in all this time. It is no surprise therefore

that Ethernet now leads the way to the future.


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Ethernet started its life as a 10 Mbit/s LAN technology using 0.4 inch thick yellowcoaxial cable in 1979.

It has evolved over time to include multiple cable types, extended speeds andcomplexity until now it is possible to build short, medium and long distanceservices with a range of features and reliabilities with the technology.

Today, Ethernet can be used to provide:

Full duplex 10G point-to-point optical links

Ethernet in the first mile DSL access

Passive optical GEPON networksMetro Ethernet networks

Wireless Ethernet hot spots


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The early LAN interfaces were rather clunky by modern standards and requiredcareful installation planning in offices. Early 10BASE-5 systems, often called

Thicknet, took experience to install well. However even from the start, the perinterface cost was low when compared with Telecom interfaces.

In 1979 State-of-the-art 9.6 kbps modem links were being installed tointerconnect systems in the UK. Each link then cost 4500 per end to connectthe 4-wire modems. In 1980 the first Ethernet was installed in Europe and theprice for the first 24 interfaces worked out at 500 each interface. Even from thestart this was a big price reduction and a major (1000 times) increase in speed.


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IEEE 802 standards generally provide the standardization of protocols andservices at the physical and data link layers.

The physical layer defines the transmission of bits and the hardware elements ofconnection.

The data link layer is responsible for the transmission of frames of data, errordetection within those frames and the sharing of access to the physicaltransmission medium.


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While the IEEE are the original owners of Ethernet as a technology, other

standards bodies have now taken an interest.

The IEEE views Ethernet as a set of LAN/MAN standards

The ITU-T views Ethernet as several packet-based OSI layers

The MEF views Ethernet as a service provided to a customer

The IETF views Ethernet as an IP-helper


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The IEEE 802 committee forms working groups to work on extensions and newtechnological ideas. Extensions and options are identified using single or double

letter codes after the number for the working group. The slide illustrates some ofthese extensions.


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Ethernet and 802.3 are subtly different. It is the 802.3 standard that has beenextended to multiple versionsnot Ethernet!


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The recent fast growth in diversity of physical technology options has delivered arange of physical interfaces and higher speeds. Some options deliver increased

range too.

So we started with 10 Mbps with range limited to 2.5 km on thick copper coaxand can now get speeds up to 10 Gbps on single mode fibre with rangesexceeding 70 km without a repeater.


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Notation for different types of Ethernet specification has evolved over time. Thistells us in shorthand form the speed, kind of signalling used and the kind of

interface cabling used. If the last element is numeric then it is coaxial cable.


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The most widely used form of Ethernet today in LANs uses unshielded twistedpair (UTP) which evolved from telephone wire.


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All communications has evolved over time. However the drivers of this evolutioncan be classified into three groups.

Firstly our need for compatibility with existing services has meant that sometechnology characteristics are controlled by history. Where we can recogniselimitations that exist because of historic evolution, it is possible to discard theselimitations and build systems in new ways.

Limitations based upon physics, such as the speed of light, or those based uponthe laws of nature such as Shannons Limit cannot be changed. Recognising

where the limitations come from is important to engineers because they can thenconcentrate their efforts upon working in areas where innovation is possiblerather than in areas where changes cannot be readily realised ever.

Sometimes limitations come from commercial interestpatents and marketdominance. These can be changed with time but these changes are much lesseasy to predict. The dominance of Microsoft Windows in the desktop operatingsystem market is an example of this. However how easy was it to predict thesudden change in the dominance of Nokia in the mobile handset market in the

1990s with the sudden rise in popularity of the Apple iPhone?


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In 1948 Claude Shannon wrote two key papers in information theory and withwork that followed then from Ralph Hartley, the ShannonHartley theorem was

born. It is an application of the noisy channel coding theorem to the archetypalcase of a continuous-time analogue communications channel subject toGaussian noise.

The theorem establishes Shannon's channel capacity, a bound on the maximumamount of error-free digital data (that is, information) that can be transmitted oversuch a communication link with a specified bandwidth in the presence of thenoise interference, under the assumption that the signal power is bounded andthe Gaussian noise process is characterized by a known power or power spectral

density.

Considering all possible multi-level and multi-phase encoding techniques, theShannonHartley theorem states that the channel capacity C, meaning thetheoretical maximum rate of clean (or arbitrarily low bit error rate) data that canbe sent with a given average signal power S through an analogue communicationchannel subject to additive white Gaussian noise of power N, is :

C=B log2 (1+S/N)

In approximate terms this is one third of the bandwidth times the SNR in dB.


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It is this massive bandwidth that makes fibre optic communications the favouritefor future bulk communications. The question is not whether Fibre systems will

dominate carrier Ethernet it is just how soon. Also will the massive bandwidth andlow price compared with copper mean that even domestic and LANcommunications will eventually move the same way?


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Communications Theory and Shannons Limit have shown us that Noise is one ofthe two keys to communication speed. Optical physical systems deliver the

lowest noise options and so inevitably must dominate the future of cabledsystems.


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At 100 Mbps existing copper is a convenient means of connecting LAN services.Optical versions allow us to build carrier connections over longer distance.


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There are advantages in delivering Ethernet over fibre. The fibre is immune toradio frequency interference and electromagnetic interference, it has greater

bandwidth therefore giving greater capacity and it gives better signal to noiseratio. Different laser wavelengths can be used to give short range, long range andextended reach fibre cable coverage.


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The protocol model for the gigabit Ethernet standard is highlighted in the slide.Much of the existing Ethernet functionality is retained but a few additional

elements are introduced and of course a variety of different PHY are defined.

Between the reconciliation entity and the PHY, the Gigabit Media IndependentInterface has been defined.


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Extending the speed particularly over optical interfaces is easy so gigabit opticalservices offer very competitive options to carriers. However as speed increases

above this level the cost of the end equipment starts to rise at an increasing rate.The difficulty of squeezing increases in power of signals into the small sizesrequired in single mode fibre makes precision manufacture and good cooling vitalparts of these designs. This adds cost at least for now.


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The reference model for the 10 Gigabit Ethernet standard is highlighted in theslide.

This model caters for LAN and WAN PHY interfaces. The interface between thereconciliation entity and the PHY is called the XGMII interface.

The LAN PHY uses 8B/10B coding but the WAN PHY makes use of the 64B/66Bcoding scheme. The WAN PHY has an additional entity known as the WANInterface Sublayer (WIS), the purpose of which is to support features for OAMthat may be required on the WAN link.


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Further extension from 1Gbps to 10 Gbps may increase the interface cost by asmuch as 5 times or more. While still showing an improvement in price per bit per

second, this may be less easy to justify in all circumstances. We may be payingfor speed we do not yet need.

Selection of the right speed to match the service and sizing services accuratelyare becoming key to carrier designs.


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The table highlights more of the current 10Gbps standards.


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Lets look at some examples of differences in the price of Ethernet endequipment.

Here three 10 Gbps interfaces differ in price per end between 737 (about $1100)for a short range multimode device at 850 nm up to 9531 (about $14,000) anend for a range of 80km over single mode fibre.


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Example using Force 10.


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Notice that these 1Gbps devices are dramatically cheaper than the 10 Gbpsdevices on the previous slide.

Short range systems are one eighth of the price, and long range systemsperhaps one fifth.


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40 Gigabit Ethernet (40GbE) and 100 Gigabit Ethernet (100GbE) are standardsdeveloped by IEEE P802.3ba Ethernet Task Force which started in November

2007, and ratified in June 2010. These standards support sending Ethernetframes at 40 and 100 gigabits per second. Previously, the fastest publishedstandard was 10GbE.

40 Gigabit Ethernet is not compatible with current 40 Gigabit solutions whichcarry four 10 Gigabit signals into one optical medium using DWDM. Opticaldomain 100 Gigabit and 40 Gigabit Ethernet use a CWDM approach with four 25Gigabit or 10 Gigabit channels.

The slide highlights the objectives of the standard.


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The table highlights the PHYs that are being standardised.

The 100 m OM3 objective is being met by parallel ribbon cable with 850 nm10GBASE-SR like optics (40GBASE-SR4 and 100GBASE-SR10).

The 10 m backplane objective is being met with 4 lanes of 10GBASE-KR typePHYs (40GBASE-KR4).

The 10 m copper cable objective is met with 4 or 10 differential lanes using SFF-8642 and SFF-8436 connectors.

The 10 and 40 km 100G objectives are being met with four wavelengths (around1310 nm) of 25G optics (100GBASE-LR4 and 100GBASE-ER4).

The 10 km 40G objective is being met with four wavelengths (around 1310 nm) of10G optics (40GBASE-LR4).


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EFM is the most recent addition to the Ethernet family of interfaces. This allowsthe attachment of Ethernet native connections over single UTP telephone lines at

speeds dependent upon length. It also covers passive optical network interfaces.


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The four tracks of the 802.3ah task force are highlighted in the slide. This was todevelop EFM for transport over existing copper, over fibre optics, to support

point-to-multipoint connectivity using EPON, and to define Operations,Administration and Maintenance procedures for Ethernet.


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As the Next Generation of networks starts to be delivered, new services becomepossible. Through the single common interface we see on everything, Ethernet,

we want to access every service. Not just voice and Internet access but TV,information services and storage.

Why load software onto your computer and store data locally requiring softwareexpertise to protect the loss of data? Why not store applications and data on thenetwork too? With networked storage and applications, true mobility around thenetwork becomes much simpler.


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Multi-Service access Architecture depends upon the selection of protocols andtechnologies to deliver the required services to the user. Services are often

located in a centralized head-end serving users distributed over a wide areathrough a high speed core network.

Some services may need to be distributed over several head-end sites in order tominimize the traffic across the core.


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All flavours of Ethernet use the same basic MAC frame format. The original 802.3standards developed for 10BASE5 predated the existence of VLANs limiting the

total frame size to 1500 bytes plus the 18 byte header. There is also a further 8bytes of preamble used for clock recovery making a total of 1526 bytes.

When VLANs are used a further 4 byte tag header is added and recent practicemay require the deployment of multiple Tag headers. To accommodate this thestandard has now expanded the maximum frame size to 2000 bytes including allheaders although not all implementations support this.


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In the example, the uppermost frame indicates that IPv4 (0800) is being carriedin the Ethernet frame. The lower frame illustrates the case where the uppermost

frame has been tagged with its VLAN Identity. The VT field with a value of 8100indicates VLAN tagging and the 2-byte VLAN field will indicate the VLAN Identity.


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However powerful a network becomes there will be limits on its capacity.

By dividing this into two parts where most of the traffic stays local to each halfand only communication between devices on the two halves needs to passbetween, greater overall capacity is created.

The interconnecting device is called a bridge and a group of many bridges in asingle box is called a switch.


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When multiple segments are connected by bridges each device listens to thesource addresses of packets on each side and if it identifies in a packet that both

source and destination are on the same side it does not forward the data.However if the destination address in a packet is unknown or is a broadcastaddress (FF:FF:FF:FF:FF:FF) it is forwarded.

A problem will arise however if bridges are used to connect traffic in a loop. IEEE802.1D 1998 Transparent Spanning Tree overcomes this by building a treestructure and turning off interfaces that would form loops.

In 2004 this was upgraded to speed up the process and retitled Rapid SpanningTree.


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IEEE 802.1 is a large standard. Likewise, 802.1d which addresses MAC bridgesis also very large and has evolved over time. Some of the elements listed on this

slide will be examined later.


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IEEE 802.1d/w/s, etc. all use the same Baggy Pants model of service.

All these standards define forms of relay agent for bridging services betweenLAN segments. Bridges must work intelligently with little or no configurationstrue plug-and-play operation.

Each port interfaces potentially to a different LAN segment and must carry bothdata traffic and control protocol frames. The data traffic may, or may not beforwarded to other ports. The control frames are always passed up to the higherlayer entities which control the operation of the relay.


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The filtering database will be constructed based upon the source addressesobserved in frames passing over the interface and upon the port state.

The ports have two control variables which may be observed using NetworkManagement techniques in some cases over SNMP:

The Operational status indicates whether the port is operating correctly andcan function correctly. It can be observed by the manager but not changed.

The Administrative status is a variable that the manager can control and canforce a port to the down state even if operationally working.


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Data will be forwarded by the relay entity subject to MAC address filtering basedupon tables built dynamically from observed source addresses.


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The Bridge protocol entity is responsible for updating the port states based uponthe IEEE 802.1d/w/s PDUs which turn ports into a non-forwarding state based

upon the need to remove loops.

The protocol used is known as the Spanning Tree Protocol (STP).


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Although the concept of a bridge has just two ports, this can be expanded to Nports in effect formed from N bridge entities interfacing to the same internal LAN,

which in reality is the backbone bus of the switch.


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To work each bridge must be assigned a unique identification. This is formedeither by configuration or using the address of one of it ports, typically the lowest.

The slide illustrates the functional entities of a bridge.


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Each interface to a switch is normally full duplex and by ensuring that thebackbone path is greater than the sum of the interface speeds it is possible to

build full duplex non-blocking switches.


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The original IEEE 802 MAC address comes from the original Xerox Ethernetaddressing scheme. This 48-bit address space contains potentially 248 or

281,474,976,710,656 possible MAC addresses. All three numbering systems usethe same format and differ only in the length of the identifier. Addresses caneither be "universally administered addresses" or "locally administeredaddresses".

A universally administered address is uniquely assigned to a device by itsmanufacturer; these are sometimes called "burned-in addresses" (BIA). The firstthree octets (in transmission order) identify the organization that issued theidentifier and are known as the Organizationally Unique Identifier (OUI). Thefollowing three (MAC-48 and EUI-48) or five (EUI-64) octets are assigned by thatorganization in nearly any manner they please, subject to the constraint ofuniqueness. The IEEE expects the MAC-48 space to be exhausted no soonerthan the year 2100; EUI-64s are not expected to run out in the foreseeablefuture.

64-bit Extended Unique Identifier (EUI-64)

The EUI-64 is an identifier that is formed by concatenating the 24-bit OUI with a40-bit extension identifier that is assigned by the organization that purchased theOUIthe resulting identifier is generally represented as a set of octets separatedby dashes or colons.

According to the IEEE guidelines, the first four digits of the organizationallyassigned identifier (i.e., the first four digits of the extension identifier) portion of anEUI-64 shall not be FFFE or FFFF (i.e., EUI-64 identifiers of the formccccccFFFEeeeeee and ccccccFFFFeeeeee are not allowed)this is to supportthe encapsulation of MAC-48 and EUI-48 values into EUI-64 values.


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In IP multicast, several hosts need to be able to receive a single data stream witha common destination MAC address. Some means had to be devised so that

multiple hosts could receive the same packet and still be able to differentiatebetween several multicast groups. One method to accomplish this is to map IPmulticast Class D addresses directly to a MAC address. The IEEE LANspecifications made provisions for the transmission of broadcast and multicastpackets. In the 802.3 standard, bit 0 of the first octet is used to indicate abroadcast or multicast frame.

IANA owns a block of Ethernet MAC addresses that start with 01:00:5E inhexadecimal format. Half of this block is allocated for multicast addresses. Therange from 0100.5e00.0000 through 0100.5e7f.ffff is the available range of

Ethernet MAC addresses for IP multicast. This allocation allows for 23 bits in theEthernet address to correspond to the IP multicast group address. The mappingplaces the lower 23 bits of the IP multicast group address into these available 23bits in the Ethernet address. Because the upper five bits of the IP multicastaddress are dropped in this mapping, the resulting address is not unique. In fact,32 different multicast group IDs map to the same Ethernet address . Networkadministrators should consider this fact when assigning IP multicast addresses.

For example, 224.1.1.1 and 225.1.1.1 map to the same multicast MAC addresson a Layer 2 switch. If one user subscribed to Group A (as designated by

224.1.1.1) and the other users subscribed to Group B (as designated by225.1.1.1), they would both receive both A and B streams. This situation limits theeffectiveness of this multicast deployment.


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The complexities of networking are not of primary concern to most businesses.They need technology which is simple to use, cheap to deploy, widely compatible

and reliable to use. Ethernet has proved in practice that it can deliver this and sohas become the interface of choice for most businesses.


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The switches or concentrators at the edge of the network typically offer manyports, one per user, and combine traffic destined for ports on other switches into

an aggregated trunk. Typically today the access ports on a LAN are 100 Mbpsand the aggregated trunks are 1 Gbps.

As the number of ports in the whole network grows problems of scale start toresult. Firstly broadcasts must be flooded to every port on the network.Broadcasts are relatively rare in normal operation but are used about once aminute to run the ARP protocol. With a network containing 3600 devices eachsending one broadcast per minute every device receives 60 broadcasts asecond. This is enough to slow down normal operation.

One solution is to divide the network into VLANs. Ports are grouped together

and only see traffic from ports on their own VLAN. The bridge function inswitches must maintain tables for each VLAN but the tables are much smallerand so operation becomes faster.


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VLAN operation enables a manager to group ports together reflecting the mannerin which they normally interact. Separation into groups improves security.

Communication with devices in different groups should be rare but if requiredfrom time to time can be provided by a router, either separately connected or asfunctionality within one of the switches.


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Three basic mechanisms can be used for defining VLANS. Static VLANconfiguration is undertaken by network management operation or by attaching a

terminal device to the switch and configuring it through a console interface.Dynamic configuration can be achieved by an application that is VLAN aware anduses 802.1Q to register and use VLANS.


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Multicast and VLAN memberships are treated as attributes of an interface. Thesecan be registered with other bridges in the tree using multicast exchanges

containing attribute values.

The 802.1Q standard documents GVRP.


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Each VLAN is allocated a 12 bit code and an interface is placed into a VLAN byassigning an attribute to the interface that is set to the VLAN ID.


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As each VLAN is registered over an interface, the bridge function constructs afilter table for that VLAN over the interface.


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802.1P provides priority within the switch at layer 2. Frames sent without tagheaders are taken as priority zero. Priority 1 is considered lower than zero and

might for example be used for disk back-up. Priorities 3 and above areconsidered higher than priority zero and deliver precedence within queues insidethe switch. Switches may offer weighted fair queuing for frames identified ascoming from different streams with the same priority value but differentsource/destination address pairs.


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We would like to provide multiple services to customers to match the interfacesthat they demand. Also to provide services using protocols that are most efficient

or which are already imbedded within the network in order to minimise cost. Thismeans we need a mechanism to deliver multiple services through the same corenetwork.

MPLS enables us to do this.


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Often the technologies are operated by different departments of a carrier or bydifferent carrier organizations.


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Provisioning a service for a customer can be an expensive, error prone and timeconsuming activity.


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To establish the connection, agreements have to be established betweencustomer and service provider, and sometimes between service provider and

other network operators. If this agreement and connection establishment ismanual, it could take some time to complete the circuit turn up.


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A better solution would be to signal the service from end-to-end and automateprovisioning. This is now possible with Next Generation networks deployed using

MPLS/PWE3.


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Protection delivers the ability to continue to provide service in the event of afailure of a system service component. It might take the form of alternate fibers,

alternate switch paths or alternate network providers.

The MEF has set out requirements for both protection and quality of service. Wewill be looking at these requirements later.


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The goal of protection is to deliver the re-establishment of the full service within aknown time. The shorter this restoration time the more complex and more difficult

(and thus the more expensive) the protection becomes. Most layer 3 routingprotocols will allow for re-routing within 2 seconds, although it may take up to 3seconds to notice the actual failure if this depends upon hello messages sentevery second. SDH Automatic protection switching depends upon flag bitsexchanged 8000 times a second and can thus deliver switching must faster,perhaps within as little as 50 msec. Newer Rapid Packet Ring technologies canpotentially do even betterat a price!


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An important aspect of carrier Ethernet design is maintaining reliability andservice protection levels high enough to meet Service Level Agreements (SLAs).

High value business Ethernet services can only maintain their value by matchingor exceeding the SLA agreed between Carrier and Customer.


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Initially the MEF was responsible for the definition of Ethernet services at theMetro Network. This scope has been expanded and now the MEF Specifications

cover the definition of Carrier Ethernet Services across the Access Network andthe Core Network as well as across the Metro Network.

The Ethernet Services ETH Layer indicates Carrier Ethernet services end-to-end across the Access Network, Metro Network, Core Network and over theInternational network.


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Carrier Ethernet Architecture adds to the LAN implementations of Ethernet,providing additional protocol features to support different transport technologies,

reliability improvements and OAM.


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The concept of an Ethernet Virtual Connection allows carriers to deliver a site tosite service connection that can look to the customer like a cable connection

between routers or switches. However instead of the distance limitation of anormal LAN connection, the EVC could be delivered between locations indifferent cities or even different continents.

The actual physical technology used to deliver the service might vary from carrierto carrier and be very different from that deployed by the customer LAN. Howeverat the point of interface its presentation would look identical to normal EthernetLAN interfaces thus providing a transparent service to the customer.


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The MEF has defined five attributes to distinguish Carrier Ethernet services fromfamiliar LAN-based Ethernet.

These attributes are:

Standardized Services

Scalability

Reliability

Quality of Service

Service Management


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The Standardised Services attribute enables a Carrier Ethernet Service Providerto deliver a range of packet and TDM-based services in an efficient manner.

Carrier Ethernet enables ubiquitous Ethernet services to be provided viastandardised equipment independent of the underlying transport and media used.

The Carrier Ethernet services are based upon the three standardised servicetypes: E-Line; ELAN; and E-Tree.

Additionally Circuit Emulation Services allows traditional TDM services to becarried over the Carrier Ethernet infrastructure.

The services must meet the requirements of the customer and so must begranular in terms of bandwidth provision and quality of service.

All these standardised services should be delivered over a single Ethernet pipefrom the network to the customer.


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The scale of a LAN and the network of a Service Provider is fundamentallydifferent in terms of the geographical reach, the numbers of users (or End

Points), and bandwidth.

The dimensions scale collectively, thus making a formidable problem to deliverand manage large numbers of services.


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Provision of Quality of Service is necessary if Carrier Ethernet is to be viewed asbeing comparable or better than technologies such as ATM and Frame Relay,

etc.

Carrier Ethernet supports delivery of critical enterprise applications that areexpected to meet certain performance levels. The performance parameters ofCarrier Ethernet must therefore be quantifiable and measureable if they are to beincluded in Service Level Agreements.


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A Carrier Ethernet Service Provider is expected to manage large numbers ofcustomers and their multiple services, stretched over wide geographical areas.

The Service provider must have sophisticated capabilities for provisioning,maintaining and upgrading Ethernet services.


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For any given service provider delivering multiple services, the currentinfrastructure usually consists of parallel or "overlay" networks. Each of these

networks implements a specific service, such as Frame Relay, Internet access,etc. This is expensive, both in terms of capital expense and operational costs.Furthermore, the presence of multiple networks complicates planning. Serviceproviders wind up asking themselves these questions: - Which of my networks doI build out? - How many fibers do I need for each network? - How do I efficientlymanage multiple networks? A converged network helps service providers answerthese questions in a consistent and economical fashion. It delivers multipledifferent services by emulation.Pseudo Wire Emulation Edge-to-Edge (PWE3) is a mechanism that emulates the

essential attributes of a service such as ATM, Frame Relay or Ethernet over aPacket Switched Network (PSN). The required functions of PWs includeencapsulating service-specific PDUs arriving at an ingress port, and carryingthem across a path or tunnel, managing their timing and order, and any otheroperations required to emulate the behaviour and characteristics of the service asfaithfully as possible. From the customer perspective, the PW is perceived as anunshared link or circuit of the chosen service. However, there may bedeficiencies that impede some applications from being carried on a PW.


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There are three distinct functions of Layer 2 switching:

Address learning: Layer 2 switches and bridges remember the source hardwareaddress (MAC address) of each frame received on its ports. They store thisinformation in a MAC Address Table to enable them to decide how to forwardframes in the future.

Forward/Filter Decisions: When a frame is received at a port, the switch looks atthe destination MAC address and uses this to search the MAC Address Table fora corresponding mapping for this address to a port. If one exists, the frame isforwarded out over just this one port. If no entry exists, the frame will be floodedout on all ports except the port on which the frame was initially received.

Loop Avoidance: If multiple connections between switches are created forredundancy purposes, network loops can occur. The Spanning Tree Protocol(STP) is used to prevent network loops whilst still permitting redundancy.


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When a switch is first powered up, the MAC Address Table is empty, as shown inthe slide.

When a device transmits and the frame is received at a port of the switch, theswitch enters the source MAC address and the port ID on which the frame wasreceived in the MAC Address Table. The switch, not having any mappinginformation for the destination address, will flood the frame out on all ports exceptthe port over which the frame was received.


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The slide illustrates the process of address learning and updating of the MACAddress Table.

1. Host A sends a frame to Host B. Host As MAC address is 0800.460F.38F6and Host Bs MAC address is 0800.460E.29B1

2. The switch receives the frame on port E0/0 and enters the source MACaddress in the MAC Address Table

3. Since the destination address is not in the MAC Address Table, the switchforwards the frame out on all ports except port E0/0.

4. Host B receives the frame and responds to Host A. The switch receives this

response frame on port E0/1 and enters the source MAC address for Host Bin the MAC Address Table.

5. A point to point connection is made in the switch between Host A and Host B.Hosts C and D will not see any frames, nor will their MAC addresses be foundin the MAC Address Table

6. If Hosts A and B do not communicate with each other again within a certainperiod of time, the switch will purge their MAC addresses from its table .


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When a frame arrives at a switch port, the destination address is compared to theMAC Address Table entries. If the destination address is known and listed in the

table, the frame is sent only to the correct output port. This is known as framefiltering and preserves bandwidth on the other ports.

If the destination address is not listed in the MAC Address Table, then the frameis flooded out on all active ports except the port the frame was received on. If adevice answers the flooded frame, the MAC Address Table is updated with theMAC address of the responding device.

If a broadcast frame is received at the switch, it will flood the frame out on allactive ports except the port the frame was received on.


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The switch uses the destination MAC address field of the frame to determinewhich port to forward the received frame to. As the destination address field is

close to the beginning of the frame, the switch can decide quickly whether toforward the frame.

Switches usually support one or more frame processing methods:

Cut-through

Store and Forward

Fragment-free

These are methods are described over the next few pages.


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In this mode, the switch starts to forward the received frame once it has read thedestination MAC address and mapped it to the output port defined in the MAC

Address Table.

It is potentially the fastest switching method, but as the switch begins to forwardthe frame before collision detection occurs, the processing mode can incuroverheads.

Collision detection should occur during the first 64 bytes of the frame.


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In this mode, the switch does not forward the received frame until the completeframe has been received and it has been checked for errors. The frame is stored

in a buffer in the switch.

If the frame has been received in error, it will be discarded. If the frame isreceived without error, the switch maps the MAC address to the output portassociated with the address, or floods it out on all ports if the destination addressis not in the MAC Address Table.

The disadvantage of this mode is that all frames are delayed before a decision is

made when or how to forward the frame. The advantage is that unnecessaryprocessing is avoided as collision detection will have occurred for all frames.


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In this mode, the switch waits until the first 64 bytes of the frame have beenreceived before forwarding the frame to the output port.

This is a compromise between the other two methods, which serves to ensurethat collisions are detected before forwarding the frames onward.

This mode does not provide any check on the frames for errors, so some framesmay be unnecessarily forwarded.


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A broadcast domain is a collection of devices which can receive broadcastframes from any other device in the same domain.

The slide illustrates the concept of the broadcast domain. If Host A sends abroadcast frame into the switch, the switch will forward the frame out on all portsexcept port E0/0.


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A collision domain is a collection of devices which can transmit unicast framescapable of colliding with unicast frames transmitted by other devices in the same

domain.

Hubs provide a single collision domain, as any frame received by the hub isextended out on all ports.

A switch, however, is able to identify which device the frame is destined for and isable to forward the frame to just the one recipient port. That frame will not collidewith any other frame.

The switch potentially supports as many collision domains as it has ports. Theslide illustrates this concept, where the switch supports one broadcast domainand four collision domains.


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The slide illustrates a simple example of a LAN with a physical loop topology. Inthe absence of any loop avoidance mechanism such as STP, frames would be

forwarded in a loop from one switch to the other.

If PC 1 sends a broadcast frame to the LAN X hub, Switch A will flood the frameout on all ports except port E0/0. The frame will be forwarded via LAN Y and willbe received at Switch Bs E0/2 port. Switch B will flood the frame out on all ports

except E0/2. This may cause a collision on LAN X.

Similarly, the frame broadcast from PC 1 will reach Switch Bs port E0/0. Switch

B will flood it out on all ports except port E0/0. The frame will be extended toSwitch As port E0/2 where it will be flooded out on all ports except port E0/2.

This process would repeat, leading to a Broadcast Storm which would consumeunnecessary CPU time and use up bandwidth on the links. Devices on each LANwould receive multiple copies of the same frame.


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When PC 1 sends a unicast frame to PC 2 for the first time, neither Switch willhave an entry for PC 2 in its MAC Address Table. Switch A will receive it on port

E0/0 and will flood it out on all ports except port E0/0. The frame will reach PC 2from port E0/2 of Switch A.

Likewise, the frame received on port E0/0 of Switch B will be flooded out on allports of Switch B, including port E0/2. The frame will also reach PC 2 from portE0/2 of Switch B.

PC 2 will therefore receive duplicates of the same frame.


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In addition to frame duplication, switches may suffer database instability as aresult of the following:

On receipt of the unicast frame from PC 1, both Switches will map PC 1 MACaddress to their port E0/0.

The frame forwarded to LAN Y from Switch B will be extended to Switch A. Theframe will appear to have come from PC 1, so Switch A will also map PC 1 MACaddress to port E0/2.

This process repeats on Switch B.

Now in each Switch, PC 1 is mapped to 2 ports, leading to database instability.


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The purpose of STP is to automatically prevent loops in the infrastructure whilstpermitting resilience through redundancy of switches. The protocol is defined in

IEEE 802.1d.

When switches are introduced into the infrastructure, they exchange data witheach other to elect a root bridge (switch) using a special Bridge Protocol DataUnit (BPDU) which is multicast using the multicast address 0180.C200.000.

This information will cause other switches to stop forwarding frames on some oftheir ports so as to create a tree structured topology. This topology will have no

loops that span the whole LAN.


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There are a number of terms that are used within STP that we need to be awareof in order to understand the procedures of the STP protocol.

Root Bridge (Switch): one switch is elected as the root switch (remember STPforms an inverted tree structure). It will be the switch which has the lowest MACaddress associated with one of its ports.

Active Port: Any port which is in working order and which has not been shutdown administratively, is said to be an active port.

Active ports can be in one of two states:

Forwarding State: in this state, the switch ports can send and receive dataframes as well as send and receive BPDU multicast frames.

Blocking State: in this state, the switch ports can only receive BPDU frames. NoBPDU frames can be sent, nor can data frames be sent or received.


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Root Port (RP): Each switch will have one RP. It will be the port closest to theroot switch, and is used for forwarding data frames and BPDUs upstream to the

root switch.

Designated Port (DP): each LAN segment will have a designated switch with oneDP. It will be used for forwarding data frames and BPDUs downstream.

Non-designated Port (NP): any active port that is not a root port or a designatedport takes the role of NP. The port will be in the blocking state and will only beable to receive BPDUs.


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The slide illustrates the actual LAN implementation on the left. The equivalenttree structure created by STP for normal traffic handling is shown in the top right

of the slide.

The tree structure shown in the bottom right of the slide, illustrates the resilienceprovided by the other switches. If Switch C were to fail, Switch D would detect thefailure and start forwarding on port E0/4.


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When a switch is connected to a network and is powered up, it will transitionthrough a number of states before entering the forwarding state.

The slide summarises the transition states, describes the behaviour at each stateand the amount of time taken to transit to the next state.

A number of timers are used within STP to control the transitions. These areidentified in the table.

When first powered on all ports of the switch are in the blocking state and so canonly receive BPDUs. After 20 seconds the ports transition to the listening state. Atthis time ports can send and receive BPDUs. After 15 seconds, the ports enterthe learning state. In this state, the ports learn MAC addresses but cannotforward frames (due to database instability). After 15 seconds the ports enter theforwarding state. The database is now stable and ports are now able to forwardframes to destinations.

A total latency of 50 seconds exists from the switch being powered up to it beingin a stable state and being able to forward frames


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The Rapid Spanning Tree Protocol (RSTP) included in 802.1D in 2004 improvedthe earlier Transparent Spanning Tree by adding VLAN support and improving

the speed of convergence.


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In this example the devices have been assigned identifications based upon theirlowest port address. When a topology change is identified they output on every

port a multicast packet giving details of their identity and listen for similar packetsfrom their neighbors. Identifications are compared and when a device receives abetter (lower) identification it stops sending its own and forwards that receivedupdating the Root Path Cost.

The Root Path Cost is the cost of the path from the root bridge, in reality if allinterfaces are the same speed it is a hop count.

BPDU Content:

The Protocol Identifier is 0000 0000 0000 0000.The Protocol Version Identifier is 0000 0010.The BPDU Type is 0000 0010. This denotes a Rapid Spanning TreeFlags:

The Topology Change flag is encoded in Bit 1 of Octet 5The Proposal flag is encoded in Bit 2 of Octet 5The Port Role is encoded in Bits 3 and 4 of Octet 5The Learning flag is encoded in Bit 5 of Octet 5The Forwarding flag is encoded in Bit 6 of Octet 5The Agreement flag is encoded in Bit 7 of Octet 5The Topology Change Acknowledgment flag is encoded in Bit 8 of Octet 5as zero


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The Root Identifier is encoded in Octets 6 through 13The Root Path Cost is encoded in Octets 14 through 17The Bridge Identifier is encoded in Octets 18 through 25The Port Identifier is encoded in Octets 26 and 27

The Message Age timer value is encoded in Octets 28 and 29The Max Age timer value is encoded in Octets 30 and 31The Hello Time timer value is encoded in Octets 32 and 33The Forward Delay timer value is encoded in Octets 34 and 35The Version 1 Length value encoded in Octet 36 is 0000 0000, which indicatesthat there is no Version 1 protocol information present.


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By first broadcasting their own identity and then migrating to use the root bridgeidentity when lower MAC addresses are found, a single tree structure will

naturally result with optimal speed interconnections. Then only a single paththrough the network will result for traffic overcoming the possibility of loopingbroadcast and multicast transmissions.


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Rapid spanning tree protocol enhanced the earlier Transparent Spanning Tree(TST) by supporting different speeds of operation and the ability to vary timers

and counters. The original might have taken 45 seconds to migrate to a newtopology of operation after a link failure. RSTP can achieve this in 3 to 5 secondswith appropriate timer settings.


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Here bridge 111 has become the root.

Bridges that receive more than one copy of the information from the rootcompare the root path cost values and select the one with the lowest value as theinterface to use to reach the root. Other interfaces over which copies of the rootidentity were received with higher costs are turned off by discarding packets

received. Packets are then forwarded to/from the root port from/to all other ports.


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In effect the network becomes a tree.


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The original IEEE 802 MAC address comes from the original Xerox Ethernetaddressing scheme. This 48-bit address space contains potentially 248 or

281,474,976,710,656 possible MAC addresses. All three numbering systems usethe same format and differ only in the length of the identifier. Addresses caneither be "universally administered addresses" or "locally administeredaddresses".

A universally administered address is uniquely assigned to a device by itsmanufacturer; these are sometimes called "burned-in addresses" (BIA). The firstthree octets (in transmission order) identify the organization that issued theidentifier and are known as the Organizationally Unique Identifier (OUI). Thefollowing three (MAC-48 and EUI-48) or five (EUI-64) octets are assigned by thatorganization in nearly any manner they please, subject to the constraint ofuniqueness. The IEEE expects the MAC-48 space to be exhausted no soonerthan the year 2100; EUI-64s are not expected to run out in the foreseeablefuture.

64-bit Extended Unique Identifier (EUI-64)

The EUI-64 is an identifier that is formed by concatenating the 24-bit OUI with a40-bit extension identifier that is assigned by the organization that purchased theOUIthe resulting identifier is generally represented as a set of octets separatedby dashes or colons.

According to the IEEE guidelines, the first four digits of the organizationally

assigned identifier (i.e., the first four digits of the extension identifier) portion of anEUI-64 shall not be FFFE or FFFF (i.e., EUI-64 identifiers of the formccccccFFFEeeeeee and ccccccFFFFeeeeee are not allowed)this is to supportthe encapsulation of MAC-48 and EUI-48 values into EUI-64 values.

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When a device wishes to communicate with another device for which it knows thedestinations IP address, it must resolve the IP address to the MAC address that

is associated with that address. This is illustrated in the slide, and is achieved viathe Address Resolution Protocol (ARP). The source device sends an ARPRequest as a broadcast frame asking who has the destination IP address. Theidentified destination device should respond with an ARP Reply in which itprovides its MAC address for the IP address.

Once the source device has the IP address/MAC address resolution it can nowsend its data frame addressing it for the attention of just the device with the MACaddress shown in the Destination Address field, and indicating the source

devices MAC address in the Source Address field.

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Often it is necessary for a device to send a broadcast frame to all connecteddevices. In the illustration, this is achieved with the IP address of 82.116.255.255

(Obviously the first two or three address values represent the network addressidentity or sub-network identity. The equivalent MAC address is all FFs asillustrated.

For some distributive data transfers, it is necessary to transmit to each of a groupof destination devices. This is known as Multicast. A specific range of IPaddresses has been defined for Multicast use. The MAC address structure forMulticast is illustrated on the next page.

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In IP multicast, several hosts need to be able to receive a single data stream witha common destination MAC address. Some means had to be devised so that

multiple hosts could receive the same packet and still be able to differentiatebetween several multicast groups. One method to accomplish this is to map IPmulticast Class D addresses directly to a MAC address. The IEEE LANspecifications made provisions for the transmission of broadcast and multicastpackets. In the 802.3 standard, bit 0 of the first octet is used to indicate abroadcast or multicast frame.

IANA owns a block of Ethernet MAC addresses that start with 01:00:5E inhexadecimal format. Half of this block is allocated for multicast addresses. Therange from 0100.5e00.0000 through 0100.5e7f.ffff is the available range of

Ethernet MAC addresses for IP multicast. This allocation allows for 23 bits in theEthernet address to correspond to the IP multicast group address. The mappingplaces the lower 23 bits of the IP multicast group address into these available 23bits in the Ethernet address. Because the upper five bits of the IP multicastaddress are dropped in this mapping, the resulting address is not unique. In fact,32 different multicast group IDs map to the same Ethernet address . Networkadministrators should consider this fact when assigning IP multicast addresses.

For example, 224.1.1.1 and 225.1.1.1 map to the same multicast MAC addresson a Layer 2 switch. If one user subscribed to Group A (as designated by

224.1.1.1) and the other users subscribed to Group B (as designated by225.1.1.1), they would both receive both A and B streams. This situation limits theeffectiveness of this multicast deployment.

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All flavours of Ethernet use the same basic MAC frame format. The original 802.3standards developed for 10BASE5 predated the existence of VLANs limiting the

total frame size to 1500 bytes plus the 18 byte header. There is also a further 8bytes of preamble used for clock recovery making a total of 1526 bytes.

When VLANs are used a further 4 byte tag header is added and recent practicemay require the deployment of multiple Tag headers. To accommodate this thestandard has now expanded the maximum frame size to 2000 bytes including allheaders although not all implementations support this.

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There are scaling issues associated with Ethernet MAC addresses and VLANIdentifiers. Firstly the address space for VLAN Identifiers is 12 bits long giving a

4096 maximum number of unique VLAN Identifiers. For VLAN tagged serviceframes, the customer provides the destination and source MAC address foridentifying the source and destination hosts in the customers sites. This means

that the Providers provider edge equipment may still have to be aware of the

customers MAC addresses (Learning). It wasnever intended in the initial designof Ethernet for it to cater for anything other than LAN implementations. If it werepossible to increase the quantity of MAC addresses, how big would theforwarding tables of bridges and Ethernet switches have to be?

A solution to the problem is to be found in MAC-in-MAC. This uses the simpleconcept of encapsulating the original MAC frame including its source anddestination MAC addresses inside another MAC frame which provides its ownsource and destination addressing capability. Here the physical MAC addresscan be extended to cater for larger numbers of MAC addresses, enabling thecarrier to provide Ethernet service to larger numbers of customers.

The operation of MAC-in-MAC will be described in more detail later in thischapter.


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Usual practice in standard LAN environments is for each LAN to have its owninfrastructure comprising one broadcast domain and all stations seeing all traffic.

It may be desirable to have a single infrastructure to support many separate LANinstances. There are numerous reasons for this, as highlighted in the slide. Thisis the concept of Virtual LANs (VLANs), where each LAN instance is a separatebroadcast domain. Separation between VLANs may be based on switch ports,MAC address, or by assigning a VLAN Identifier (VLAN ID) in the form of a tag.

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The slide illustrates the format of the VLAN tag defined by IEEE in 802.1Q and802.1p, which is in the form of a 4-Byte header placed between the source

address field and the Type field of the Ethernet frame.

The first two bytes of the tag provide the Tag Protocol Identifier (TPID), oftenreferred to simply as the Type field. The remaining two bytes provide the TagControl Information (TCI) which comprises a 3-bit priority field, a 1-bit canonicalformat identifier (normally 0 for Ethernet), and a 12-bit VLAN Identifier (VLAN-ID )field. This is the field used primarily by the 802.1Q standard.

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VLAN-aware switches perform processing of frames using a 5-stage process.

The five stages are:

1. Ingress rule checking: admit all, or admit only tagged frames. Classify everyincoming frame to a VLAN ID. Discard the frame if it is not compliant with therules.

2. Active topology enforcement: Checking whether the frame should beforwarded or not taking into consideration MTU size, whether port is in theblocked state, etc.

3. Frame filtering: according to MAC address, VLAN ID and filtering database

entry.4. Egress rule checking: checking whether VLAN ID is in member set, taking

appropriate action on the tag.

5. Queuing for transmission

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We have seen the introduction of the 802.1Q tag comprising a EtherType field setto 8100 to indicate 802.1Q tagging and a VLAN ID placed between the source

address field and the Type field which indicates which protocol is carried in thepayload of the frame. But what if we introduce a second 802.1Q tag? This isknown as VLAN Stacking where the initial 802.1Q tag will have a different 802.1Qtag placed in front of it thus making it invisible to switching equipment until the


Documents

PDN043 Carrier Ethernet Services Explained Pre Course Reading v4 1