netinsightdtm_200

8/8/2019 NetInsightDTM_200

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2001

DRAFT VERSION

DTM technology and its merits

ABSTRACT

After almost a century of plain old telephony as the main service, the world ofcommunications changed dramatically in 1994 with the arrival and followingunprecedented growth of the Internet and the World Wide Web. The communicationindustry was revolutionized and information technology was made available to the

public.Still, so far we have only seen the initial wave of Internet growth, the one involvinggetting users connected and getting attractive web applications up and running. The next

wave will be even more dramatic, as the applications take the leap from static browsingand email services, to fully-fledged media applications. Whether being business-to-consumer or consumer-to-consumer environments, whether being services broadcastedto large audiences or services customized by or for the individual user, applications willbe rich on media content, with quality sound and video as the expected experience inaddition to regular data information.

This change in traffic character is driven from both ends - both by the professionalmedia industry and by the consumers themselves. Within the media industry,

digitalization of content as well as digitization and customization of the production havealso made new workflows possible. These new editing and distribution workflows rely

Author:

Dr. Christer Bohm - CTO

Net Insight AB

[email protected]

2001-08-10


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on, interact with, and put requirements on the quality and capacity capabilities ofdistributed networking and Internet. Content that previously was exclusive for TV andradio broadcasters are now made available via Internet services. Simultaneously, the endconsumers are generating high-bandwidth media-rich traffic themselves, exchangingmusic, photos, video clips, and participating in net gaming.

As media oriented services starts to dominate, a new technological shift follows - thedeployment of infrastructure that can handle large quantities of streaming services withmaintained high quality. The Internet as it works today is staggering to support anythingother than best-effort send-and-pray applications without resorting to huge amountsof over-provisioning. And even though impressive amounts of investments have beenmade in deploying huge optical fiber backbones, the high cost associated with lighting up

wavelengths and adding active routing and switching equipment burdens the economics.It significantly limits the real-world applicability of simply relying on overprovisioning totake care of problems with traffic quality.Dynamic synchronous Transfer Mode (DTM) is a network technology that serves thetransport needs of media-rich applications, and at the same time offers a converged

platform for handling conventional types of voice and Internet traffic over fiberinfrastructures. DTM is a Time Division Multiplexing technology that extends andimproves the services offered by SDH/SONET to fit with the new demands fromdatacom and media applications. This white paper gives an overview of DTM and itsbenefits when building Internet and media centric communication networks.


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Background

As the battle of market shares is growing ever tougher, operators are faced with ever

decreasing revenues from traditional telephony services accompanied by a flat rate pricemodel for Internet services. To maintain and grow profitability, there are three ways forthe operators to go: Increase the customer base, reduce the costs of operations, and findnew attractive services that brings in new revenue streams.

t

$

Telephony

New services

Data

Figure 1 Operators situation

Against that background, a revolutionary migration is taking place. The digitized mediaand entertainment industry, including both content creation and distribution, is graduallymoving from their own exclusive lines of production and distribution towards Internetbased platforms and applications, and are met there by the end consumers desire to be

informed, entertained and offered richer services. This creates opportunities for networkoperators that grow business within the new segments that are born from the merger ofpreviously separated worlds telecommunication and media&entertainment.

teledata

media

Figure 2 Media The next level of convergence

The new services span from media-capable Intranet/Extranet services for professionalbusiness customers and media distribution services targeting the end customer, to video-centric personal or corporate communication, including examples such as:


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- Transport of digital material for TV production, sport events, editing, anddistribution over fiber-based converged video and data backbones to Internet

enabled cable TV HFC networks.

- Different types of premium enterprise solutions, including video conferencingapplications, from high-resolution seminars to videophone-like applications, andinherently reliable VPN connections with guaranteed performance and flexiblecapacity.

- Entertainment services such as digital TV, Video-on-demand (VOD), DVD capablecable TV and Near-VOD

These applications will all have different demands when it comes to quality and capacity,spanning from handling narrow capacity MPEG coded traffic to uncompressed highquality video requiring hundreds of megabits for its transport. And for those operatorsdeploying networks that can stand to the test in the light of such requirements, the newsegments are there to be won.

Empowering a Media & Entertainment Capable Internet

From a technology perspective, vendors and operators have for a long time pursued thegoal of providing an integrated services network with the capability to transport bothdatacom and telecom traffic over the same infrastructure. This development started withthe work with ATM (Asynchronous Transfer Mode), continued with IP and is now beingpursued with MPLS (Multi Protocol Label Switching). Development of communicationtechnologies has thus over the last decade been focused on packet switching. However,circuit switching is often used at the lowest layers for providing reliable transport. Forexample, both DWDM and SDH/SONET are circuit-based.Packet switching technology offers a dynamic and efficient application interface, and isalso optimized for dynamic aggregation of best effort traffic. In packet switching, the

packets are transported using resources (such as communication links and buffer space inswitches/routers) that are statistically shared with traffic from other sources through thenetwork, giving a flexible utilization of the network resources. Since the resources areshared, it is very difficult to give guarantees on the transport. This does not form aproblem for best effort traffic, since timely arrival of traffic is not important and data canalways be retransmitted if data is lost as a result of congestion in the network. However,for audio and video traffic, or other services for which service quality and reliability mustbe ensured, trying to make traffic prioritization when traffic loads are increasing is ahighly complex task.

The strive for an integrated service network has thus not been an easy task, chieflybecause of the underestimated complexity of introducing full QoS support in packet

switched networks. Stateless priority schemes are however fairly easy to introduce, andhave also to some extent been taken into operation. Even though this may seem to workfine for prioritizing e.g. a small number of IP-telephony calls over a large amount ofbest-effort traffic, a fundamental problem with the method becomes obvious whenmedia oriented traffic starts dominating the bandwidth spectrum. The priority schemescurrently proposed to solve the QoS problem (for example DiffServ and IEEE 802.3q)fails, as they only work when the relative amount of quality demanding traffic is smallcompared to the other traffic in the network. The requirements from a media &entertainment rich Internet has more or less been neglected.It has also been argued that the quality problem in packet switched networks could besolved by overprovisioning. Real-world data however shows that overprovisioning is a

very costly way of addressing the issue, since a substantial cost of a network is the fiberinfrastructure and the utilization of the fiber will be very low. Furthermore, also the


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complexity of overprovisioning grows with the size and complexity of the network, up toa point where it will be virtually impossible to calculate how much extra capacity isneeded and where when the network is expanded.

A Service Centric Approach to TDM

Circuit switching, as compared to packet switching, does on the other hand inherentlyguarantee the transport of data at the expense of limiting the freedom of bursty besteffort traffic. For streaming applications, where the flows are relatively long lived, bothutilization and quality are very good. The major reason for this is that the traffic thatbelongs to one stream is completely separated from other traffic throughout the network,and therefore there will be no congestion or delay variation in the network. Theutilization of the circuits will therefore be high since the circuits will be filled with data toa large extent. This is of course under the assumption that the size of the circuits fits thesize of the transported streams.

FiberTDM

Packet

Figure 3 TDM in the transmission/switching hierarchy

The Time Division Multiplexing (TDM) layer operates between packet services and thewavelengths and adds the following functionality to the model:- Channelization of bandwidth Wavelengths are a too coarse unit to use for many

applications (such as private lines, router interconnects, Internet exchange points),and for an operator, connectivity is more important than having a few very bigchannels (i.e., a whole wavelengths). Connectivity is important since channels arenormally not the size of a wavelength and its is not economically feasible to have onesignal per wavelength.

- QoS Packet networks can only prioritize and never give strict guarantees for aservice. For traffic types in need of strict guarantees, such as leased lines, professional

video transport, PDH transport and CATV distribution, the TDM layer provides a100% quality service.

- Monitoring and network maintenance The TDM layer handles functions suchas performance monitoring, protection switching, framing, etc.

- Simple and high performance TDM technology is very simple in its structure.The simplicity makes TDM the most cost-efficient and stable technology baseavailable for high performance network equipment.

However, despite the advantages, traditional TDM technology also have a number ofdrawbacks in terms of static nature of connections, lack of dynamics for resourcedistribution, and expensive manual management. This has limited the applicability of

TDM in datacom networks.


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To enable an Internet that efficiently supports all types of traffic needs, including therapidly increasing amount of media & entertainment oriented services, the technologymust make use of the best of both packet and circuit switching.

DTM A New Generation Circuit SwitchingDTM is a technology that has developed circuit switching to support media oriented services

AND to be an efficient transport network for packet switched data, such as IP and Ethernet

traffic, as well as traditional PBX traffic.

The great advantage of circuit switching is its characteristic of providing predictable delayand guaranteed reliable transport. On the other hand does traditional circuit switchingtechnologies, such as SDH/SONET and PDH, show drawbacks in multi-serviceenvironments, while originally developed for narrowband telephony. The DTMtechnology removes such shortcomings, and enables convergence of data and voiceservices with supreme, future-proof support for media-rich applications of all sorts.

The most important improvements of DTM as compared to SDH/SONET are:- Arbitrary channel size Channels can have arbitrary size and they can be

symmetric or asymmetric according to desire, thereby dramatically increasingbandwidth utilization.

- Flexible topologies The data link topologies can be configured to build ring, bus,and/or point-to-point/mesh structures as desired.

- Non hierarchical switching Channels can be switched arbitrarily betweennetwork links, without considering network hierarchies. Links can be setup as desiredto build large network structures, without affecting the characteristics of thetransport. There are no limitations of the size of the channels being switched.

- Signaled end-to-end provisioning Channels automatically find their paths

through the network during provisioning, only requiring identification of end points.In-band signaling protocol handles the setup through the network.

- Multicast - DTM channels can be point-to-multipoint, essential to theaccommodation of media services of high quality to a large number of receivers. Anexample of such a service is IP based cable TV.

The DTM technology is standardized by the European TelecommunicationStandardization Institute (ETSI). The standardization does not only involve theproperties of DTM, but a large effort is put into the specifications of interoperabilitytowards other technologies, such as DWDM, SDH/SONET, PDH and Ethernet. Thefocus on interoperability aspects is driven by the urge that not only new networks shouldbe able to utilize the technology, but also existing telecom and datacom infrastructure

investments should be upgradeable to support media networking.Furthermore, other parts of the industry are working to create a common control planefor all layers (from packets to fiber). GMPLS (Generalized Multi Protocol LabelSwitching) and DTM fit very well into that model. A future introduction of DTM in theGMPLS model will thus ensure a truly homogenous management of multi-servicenetworks built on the best components from several technologies.


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Arbitrary channel size through non hierarchical multiplexing

In DTM, a channel can be set to have an arbitrary size in steps of 512 kbps up to full linkspeed. Channels can be provisioned to fit the service instead of fitting the service tostatic network conditions. For example, a 10 Mbps IP service can be transported in a 10

Mbps channel. Unlike the case in a SDH/SONET network, it is not necessary to let theservice consume an entire 45 Mbps circuit.

Traditional telecom signals typically require set amounts of capacity as a telephone circuitconsume 64 kbps in each direction. The infrastructure is developed to optimize thetransport by providing bandwidth in fixed rates suited for this purpose. SDH/SONETnetworks are therefore optimized to multiplex signals in increments of 1.522 Mbps, 45Mbps, 155 Mbps, etc. (or 2.048 Mbps, 34 Mbps and 155 Mbps in Europe). This causesproblems with utilization when trying to fit new services into existing networks sincemedia signals do not conform to the telecom rates. For example, MPEG coded video

with VHS quality requires 4-6 Mbps capacity, HDTV typically requires 19-50 Mbpsdepending on compression, and most production video uses 270 Mbps. This, in

combination with the flexible bandwidth requirements from pure datacom services,makes arbitrary sizes of channels essential for efficient bandwidth utilization.

Additionally, a significant part of the media related traffic is unidirectional, or at leastasymmetric. Again, support for asymmetric channels are often key for bandwidthefficiency. In practice, this often translates into 100 percent increase in networkutilization. Or, in economical terms, to a doubling of the theoretical revenues that can begenerated from a given infrastructure.

To accomplish this, DTM at the lowest level uses a dynamic multiplexing scheme wherethe capacity is divided into frames of 125 microseconds. Each frame is further dividedinto 64-bit slots. The number of slots per frame is dependent on the bit rate. With the bitrate of 2,5 Gbps, the number of available slots per frame is approximately 4800. A single

slot as such, while occupying 64 bits per 125 microsecond frame, represents a bandwidthcapacity of 512 kbps.

Figure 4 DTM multiplexing format

A DTM channel is provisioned to consist of a selected, arbitrary number of timeslots perframe, which are allocated from ingress to egress(es) of the channel. The number of slotsallocated determines the capacity of the channel. For example, a channel requiring 1.5

Mbps will be allocated three slots (3 512 kbps = 1.5 Mbps). Of course, the equipmentis self-sustaining in tracking which slots are allocated for a specific channel.

The channels are arbitrarily provisioned to transport traffic such as IP, Ethernet, video

streams, and PDH circuits, as selected at provisioning, thus providing a true multi-serviceinfrastructure


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Flexible topologies building blocks for efficient network engineering

When engineering a network, the operator is faced with the reality of how alreadyinstalled fiber is laid out, and also which topologies that are feasible when installing newfiber. The cabling is normally done in such a way that a single topology will not besufficient to engineer the entire network. For example, if the installed fiber has as a staror a mesh topology, it is impractical if the chosen networking technology for the newinstallation only supports a ring topology.

There is also a scaling issue with different topologies. In for example a ring topology, thebandwidth is shared between the nodes on the ring, and the available bandwidth to eachnode will decrease when more nodes are connected to the ring. On the other hand, ringsoffer benefits such as building networks more efficiently, with less need for fiber andports. DTM supports all relevant data link topologies, including point-to-point, dual bus,ring and dual ring links, which can be seen as building blocks to engineer the network.

These data link topologies can be connected using switches to form an arbitrary network.Importantly, the topologies supports crucial reliability functions such as self-healing dualring structures and automatic alternative path re-routing of channels at link or equipment

failure. Furthermore, such service restoration can be provisioned to use either full 1+1protection for critical services, with a down-time of less than 50 milliseconds, or thesimpler alternative of so-called service re-routing, with a typical less than one seconddown-time.

Non hierarchical switching

To scale the network in terms of number of nodes, and maintain the characteristics ofthe transport, it is essential that the technology also natively support switching.

A DTM network is expanded by interconnecting several links with switch nodes. Theswitching of channels between links is non-hierarchical, meaning that no hierarchical

demultiplexing or multiplexing of larger channels into smaller channels, and vice versa, isneeded to switch a single service from one link to another. Not only does this allow forgreater freedom in service provisioning, it also dramatically reduces the amount ofequipment needed, as add/drop multiplexing and switching is integrated into a singleplatform.Furthermore, the switching is synchronous, which means that the switching delay isconstant for a channel. Multi-hop channels therefore display the same properties as achannel on a single link. The only difference is that a multi-hop channel has slightlylonger delay. Due to the strict resource allocation, and as no dynamic buffers are used forswitching data, there cannot be any overflow or congestion inside the network.

Figure 5 DTM switching

The way in which a channel should be switched is determined at the establishment of thechannel. Thereafter, during the lifetime of the channel, the switching as such is a simple


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process of remapping slots on incoming links to slots on outgoing links. There is noneed for complex processing in the transport of data, making it possible to build veryhigh performance switches at low cost.

Signaled end-to-end provisioning

To achieve high utilization and low-cost operation, it is crucial that the provisioning ofservices over the networks is a simple task to perform. The provisioning system mustalso recognize and accommodate that whereas some services allow for manualparticipation in the provisioning process, as is typically the case when ordering PDHtransport and VPNs, others require automatic provisioning, such as Video On Demandservices.

To simplify provisioning, avoid node-by-node management and allow for automaticprovisioning, DTM equipment uses in-band signaling for automatic service set-up. Morespecifically, a separate channel is at all times used for DTM specific control informationsuch as signaling, path selection information, resource management and bootstrapping.

With automatic in-band provisioning scheme, channels can be established by specifying

cannel end points only, using network unique addresses. The signaling protocol alsoallows for changing the capacity of a provisioned channel during its existence. Inpractice, this means that services are provisioned in no-time using simple point-and-clickmanagement, not resorting to hours or days waiting for clarification, identification, and

verification of suitable circuit paths.

QoS capable multicasting

A substantial part of next generation media-based Internet services will be of multicast or

broadcast nature. One big problem with todays IP infrastructure is that it does not support the

high level of QoS needed for such multicast sessions. Most efforts on multicast try to offer a

very generic multicast service supporting many receivers, but at the same time potentially

many senders, without considering QoS. This although most media services will only haveone sender and be very dependent on the quality offered. For example, cable TV and NVOD

(Near Video on Demand) have one sender and multiple receivers and demand a high quality

transport.

To provide a perfect match for this, DTM channels, while preserving its guaranteed QoS, can

have one sender and any number of receivers. Mapping for example IP/MPEG services on top

of the quality preserving DTM channels, with one sender and many receivers, solves QoS

problem for multicast very elegantly. Other types of non-critical IP multicast applications is

most efficiently handled on the best-effort IP structure, since many mechanisms, such as

multicast routing, application signaling protocols and session protocols, are already there.

DTM Interoperability

In networks operational today, there is a lot of equipment based on differenttechnologies and standards. Operators have invested a lot of money in these networksand interoperability with existing and new equipment is essential.

To be interoperable with the existing transport network, DTM is run both over darkfibers, DWDM and SDH/SONET. When running over dark fiber, Gigabit speed opticsis used. This benefits from the price pressure on this type of components and allows theequipment cost of DTM to be at the same price level as Gigabit Ethernet. For higherspeeds, DTM runs over SDH/SONET. The frame structure of DTM is simply mapped

into the Virtual Containers. This allows for interoperability with both existing


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SDH/SONET network and all types of DWDM (Dense Wavelength DivisionMultiplexing) equipment.On the application/service side, DTM equipment present standards based interfaces,such as Fast and Gigabit Ethernet, T1/E1, DVB-ASI, etc. As far as the services areconcerned, DTM offers a completely transparent transport layer, as will be discussed in

the following chapter.The vision of having a common control plane for controlling the network from fiber toservices will become a reality with GMPLS. GMPLS is being developed within theInternet community to have an IP centric control plane and benefit from thedevelopment of MPLS. The control plane in DTM is currently IP like, but proprietaryand the functionality are very similar to the one of GMPLS. Since GMPLS is still in anearly phase and lots of functions are not ready yet, a migration towards a GMPLS controlplane is a couple of years ahead.

Network services

A DTM network provides a general infrastructure that can transport all types of traffic.Between the applications and the actual transport, the equipment provide differentnetwork services to map traffic of different characteristics efficiently. Each networkservice is optimized for the characteristics and demands of the traffic the applicationsgenerate. For example, a PDH transport differs very much from transport of best effortIP packets. PDH is a fixed rate bi-directional service with tight requirements on jitter anddata loss while best-effort IP traffic is very bursty and has limited demands on jitter andtolerates some loss of data.

Physical fibernetwork

Best effortoverlay network

Streaming services

overlay network

Figure 6 Service overlay networks

In DTM networks, there are different network services for different types of traffic. Allnetwork services uses the same underlying DTM transport. The network services areused to create overlay networks over the physical infrastructure thereby allowing for bothseparation of different types of traffic and/or users. There are basically two types ofservices, streaming services that transparently transport traffic through the network anddatacom services where aggregation of traffic is done using packet switching.


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Streaming synchronous services

For streaming synchronous services, like PDH (E1/T1), SDH/SONET and professionalSDI BT601 video, the transport service offers a completely transparent bridge ortunnel from ingress interface to egress interface.For bi-directional, symmetric traffic like PDH, the DTM service offers bi-directional,symmetric tunnels, and for unidirectional traffic like SDI video, the DTM service offers aunidirectional tunnel. The size of the tunnels is predefined to match the respective traffictype.

Also, the operator can decide whether or not to use 1+1 protection for the individualservice.

Streaming data services

For streaming data traffic with identified reliability and quality of service requirements,such as streaming ASI, IP/MPEG video or guaranteed VPNs, end-to-end uni- or bi-directional tunnels are offered (IP tunnels, Ethernet tunnels, or ASI tunnels). These

tunnels maintain characteristics similar to the ones used for streaming synchronousservices.In contrary to streaming synchronous services (having predefined bandwidths),streaming data service are offered with configurable bandwidth. Mapping or routing atthe edges of the tunnels make sure that the tunnels are used exclusively for the desiredquality traffic, as identified using interface, port, IP/Ethernet/VLAN address, servicetype, or similar sorts of information.For quality broadcast and multicast services, point-to-multipoint tunnels are available. Inthe case of multicast IP traffic, mapping of IP multicast signaling to attach to IP overDTM multicast tunnel trees, is accomplished by using standard protocols like forexample IGMP (Internet Group Management Protocol).

Datacom services

For scalable management and aggregation of best effort traffic, DTM offers a dedicateddatacom service, IPOD (IP over DTM). IPOD is a tight integration of a logical IPconnectivity structure on top of DTM with the following main features:- Automatic address resolution between IP and DTM channels.- Automatic channel provisioning, change of bandwidth and channel removal.- Shortcut establishment for QoS demanding and/or large file transfers.- Use of traditional IP routing protocols such as OSPF (Open Shortest Path First) for

path finding.The chapter Network Solutions will illustrate how these types of services are combined

in some exemplified scenarios to deliver a full multi-service environment.

Network management

A lead star when developing DTM was to simplify network management. Thetechnology should fit in different network environments. From long haul backbonenetwork all the way down to access networks.In backbone networks control is important to efficiently handle large amount of traffic.Occasional manual operation is not a big problem in such environments, since it isdesirable to engineer the network for optimal operation.

The requirements in an access network are very different where automatic configuration,provisioning and maintenance is essential to make it economically viable.


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Media networks

Within the media industry, a lot of rich media content is produced. Content is deliveredbetween different production sites in a very inefficient way, either by:- Satellite There are several drawback of satellite. One drawback is that it is very

costly. Another drawback is that the capacity of satellite is limited and the videostream needs to be compressed. The quality of the video signals is degraded and forsome applications, such as, in the production of film or TV programs, full quality isrequired when editing the material.

- Tapes When higher quality is required and the editing shall be done several times,the delivery of video content needs to be delivered uncompressed, in full studioquality. Since there currently are no economically sound transport technologiesavailable that can do this, the material has to be put on tape and delivered manually

with for example car or airplane. This is a very time consuming and inefficient way ofdelivering content.

ONE

ONE

ONE

ONE

Wide Media Network

STADIUM

CITY HALL

FILM BANKS

STUDIO

Editing unit

BT.601

Saturday:

Footballmatch

Sunday:ShootingSoap Opera

Recieve filmvia BT.601

Request filmvia IP

Figure 7 Media network

The fiber capacity has increased dramatically the last years and has made it possible totransport the video material over fiber optical networks. Although the raw capacity of thefiber has increased, there are still problems with the transport since the transporttechnologies are designed for telecom and datacom applications. Another big problem isthe fact that existing transport technologies are not designed to handle the formats andquality requirements of the media industry. This result in complex solutions, lowutilization of the infrastructure, extensive equipment needs for format conversion, and aproblem with scaling to a generally available media network.In the media industry most filmmakers, broadcasters and programmers already use digital

equipment (such as cameras, monitors, editing machines, video servers and storage units)with SDI (Serial Digital Interface) interface. The SDI physical interface is used for


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transporting both MPEG coded (as ASI) and uncompressed video signals, and is set fora capacity of 270 Mbps. SDI can be said to be the Ethernet interface of media. Thereis also a trend to put less quality demanding material over IP. Both types of transport willcoexist.In a DTM based network, both SDI and the IP traffic can coexist and be transported

with maintained quality, since the DTM technology provides transparent transport withmaintained characteristics. In the same infrastructure, it is still possible to combine the

video transport with other services, such as traditional IP services. This for exampleopens the possibility of remote controlling of editing machines and cameras.Furthermore, DTM is a network technology designed for building large networks withmany network nodes. The service transparency and the scaling characteristics of DTM,make it possible to migrate all services into the same infrastructure.

The applications of the media network can be:- Media Intranet A media company can handle its internal communication over a

long distance fiber infrastructure, thereby connecting their local production studiosto virtually one.

- Media Extranet It is also possible to connect different media companies, helpingthem with means for exchange of material between each other.- Content trading network In the content trading network, storage is connected to

the network, and media companies can up- and download their material on storagemachines to trade it with other media companies.

- Event networking Connect facilities, such as sport stadiums, parliament buildingsand theaters, and send the video signals to the broadcasters facilities over the fiberoptical network.

Normally, media companies are not network operators. Therefore operators and fiberowners will offer these services. They can add media networking services to their serviceoffering and leverage on their knowledge of running networks.

Service rich IP network

Broadband access networks today are normally based on xDSL, Ethernet (or GigabitEthernet) or some wireless solution. Common to the solutions is that they are designedfor offering best effort services, potentially with some support for narrow-band qualitytraffic (i.e. telephony). There is a difference in the bandwidth that they can offer. The one

with highest bandwidth is Ethernet solutions where typically 10 or 100 Mbps is offeredto the end customer. xDSL and wireless solutions normally offer a modest number ofmegabits (< 4 Mbps). The problem with this type of network is that their service offeringis rather limited, basically consisting of telephony and best effort Internet access.

To increase the revenues for the operators (and also for content owners), it is desired to

complement the offering with media services. Initially, those services will be traditionalservices such as CATV like services (with normal and DVD quality), VOD, NVOD, andprogrammed TV. Later on we will see other services such as games, services whereInternet and video is combined, such as shopping systems with video show, and personalinteractive multimedia services.Example of interactive services can for example be Watch the shape of your favoriterace horse at the stable. The new applications will spread the Information technologyeven further out to the public since more people watch TV than spending timer surfingon their computer.


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Internet surfing routed viashared best-effort channels

VoIP routed via sharedquality channel

Dedicated short-cut unicastchannel established on-the-fly for on-demand unicastvideo stream.

PSTN

Internet

MPEG2videoserver

VoIPGateway

Gameserver

210

210

210

QoS multicastchannel forMPEG-basedTV-distribution

Figure 8 Service rich Broadband network

DTM enables this type of development by providing the quality means for efficientdelivery of guaranteed quality video, voice and Internet service over the sameinfrastructure. In such a broadband network all traffic is delivered over IP to the enduser, but the transport of different services is done through the DTM network inseparated logical overlay networks:- Multicast overlays This overlay network uses DTM multicast capabilities to

implement CATV like services. The IP packets carrying the MPEG coded video aresent on a DTM channel and received at many locations.

- Shortcut overlay This overlay is used to send establish point-to-point channels tooffer VOD services, enabling video conferencing, game sessions, etc.

- Best effort overlay To efficiently transport best effort traffic, and to utilize theresources (fibers and router) in the network, the best effort overlay uses DTM as adynamic transport network where middle level routers aggregate traffic from manyusers.

Since the DTM network is the basis for all overlay networks, it is easy to build out thenetwork with the resources that is needed. For example, initially most traffic might bebest effort and most of the DTM capacity can then be used for the best effort overlay.

As more media oriented services are introduced, capacity can be added or reallocated tomulticast or short cut overlays.


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