Provider Backbone Bridge Traffic Engineering

In the industry of the Telecommunications, " Provider Backbone Bridging Engineering" Traffic; (PBB-TE) , also known under the name of Provider Backbone (PBT) Transport, is a whole of technical improvements made to Ethernet, protocol of level 2 usually used in the lans of low dimensions, in order to make it extensible and deterministic more reliable, and that it can be used as protocol of transport within the wide-area networks such as those of the landline operators and mobiles, like certain large companies.

Context and motivations

Many operators use today MPLS in the central part of their network to ensure the engineering of traffic and quality of service. On the other hand, the extension of MPLS to the access and in the metropolitan part of the network is less advanced. This solution, if it technically viable, is introduced into many cases a whole of difficulties related on the management and the evolutionarity of the network, which in the final analysis increase the cost and the complexity of exploitation. Several alternative solutions were proposed among which Transport MPLS (T-MPLS), " Provider VLAN Transport" (PVT) and PBT. The interest of the market for this last solution went increasing partly since BT announced in January 2007 to want to deploy it in its underground railway network, renonçant to deploy there solutions based on MPLS. Since this date, several industrialists integrated PBT into their catalog and the IEEE created an work group in order to standardize formally technology (802.1Qay). Estimating that the activity of standardization in progress would not modify in a fundamental way the preliminary specifications, several operators started to evaluate or deploy these solutions.

PBT is a technology based on Ethernet which aims at obtaining performances comparable or better with those of solutions based on MPLS (VPWS and VPLS):

Engineering of traffic
Administration and maintenance (OAM)
Guaranteed in terms of quality of service and band-width
Re-establishment of connections according to 50ms
Scalabilité equivalent

with the advantages of Ethernet in terms of economies and simplicity:

Facililité of training
Facililité of management

Applications

PBT was conceived so as to be able to implement demanding applications in terms of band-width and quality of service (QOS). In particular PBT is had a presentiment of:

As a technology of transport in the part of the network of the operators in load of the collection (" backhauling") of traffic high speed portable (3G/4G) and fixes (ADSL, ADSL2+, VDSL, FTTH/Fiberoptic). The flows reached make expensive the use of traditional technologies SDH/SONET, also the operators often examine the possibility of using Ethernet like more economic alternative solution.
As a technology to provide the services VPN and Ethernet to the customers undertaken, a market currently in full growth. Certain alternative operators start to offer this service type with a cost price lower than that of the historical operators who use traditional solutions SDH/SONET.

PBT is compatible with the implementation of services to the users like the communications voice on IP, the diffusion of numerical video contents (IPTV), the services high banc with the companies and the new interactive applications multi-media.

In many cases, PBT is positioned as a solution complementary with MPLS, deployed to the access and in the metropolitan part of the network of the operators, and not only like one replacement solution with MPLS.

Beyond the market of the operators, the large companies in particular in the sector of finance, also start to show interest for technology PBT

Ethernet in the networks: interfaces, services and transport

PBT is based on the technology Ethernet which has interested for several years the operators for the deployment of underground railway networks because they must support a large volume of traffic in package mode related to the new services like the video, the mobile services 3G, and the services of connector industry VPN and Ethernet with the companies.

The interfaces Ethernet are largely widespread in the lans, of company in particular, because of the ease of use and the low costs of the equipment.

Various operators in various countries offer already various types of services of connectivity Ethernet through their network. For as much, that does not mean that they use nativement Ethernet as a subjacent technology of transport in their network.

Technologies of transport employed up to now

The operators used up to now various technologies of transport, in particular the traditional numerical systems SDH, SONNET or RPR. With the continuous increase of the data transmissions (Internet, Voices on IP, videos, mobile 3G and connectivity in company etc), these technologies are however in process of obsolescence.

In the networks of new generation, the operators more and more frequently use a plan of transport in package mode, in particular IP and MPLS with protocols of tunnellisation like L2TPv3, Layer 2 MPLS VPN (L2VPN) or VPLS.

The use of Ethernet as a technology of transport was not easily possible up to now in the networks of operators because of certain functionalities missing, available with PBT.

Gaps of Ethernet and how PBT cures it

With the difference of ATM, Ethernet is based on an operating process without connection, in mode datagram, unreliable. Such as, Ethernet does not make it possible to the operators to correctly satisfy their contractual obligations (SLA with QOS), in particular for the applications in real-time like the video voice or it.

In addition, Ethernet is not scalable: it is not appropriate for networks of very great scale (complexity of the aspects of management, resources network mobilized by the constant communications between a great number of Ethernet nodes).

PBT is a technology of " tunnellisation point-with point" who adds to Ethernet the determinism: this makes it possible to the operators to specify the way which on the network the screens Ethernet will have to borrow.

PBT also ensures QoS by holding a bandwidth for the services in real-time. It provides a time of recovery of 50 milliseconds in the event of rupture of connection - what is equivalent to the time imposed by the standards of the networks optical SONNET and SDH of today.

PBT can solve certain problems arising from the extensibility of Ethernet while releasing from the resources network which would be mobilized by the constant communications between a great number of Ethernet nodes on the network.

PBT uses the concepts of marking of VLAN according to the specification IEEE 802.1Q, " Q-in-Q" according to the specification IEEE 802.1ad (Provider Bridging) and " Mac-in-MAC" according to the specification IEEE 802.1ah (Provider Backbone Bridge or " PBB"). But PBT decontaminates the concept of " flooding/broadcasting" and the protocol " spanning tree ".

PBT simplifies the operational aspects of maintenance and administration by using extensions based on the specification IEEE 802.1ag (Connectivity Fault Management). It provides extensions to ensure the protection of conduit of manner similar to one-way protection " Unidirectional Path Switched Ring" (UPSR) in the networks SDH and SONNET.

The packages are transferred on the basis from the identifier from VLAN (VID) and from the MAC address from destination. The function of MAC training is decontaminated and the transfer is based on a table of mixing of connections updated by orders of management. Packages of " broadcast" are ignored. The packages emitted at the time of failure of research of the destination (Destination Failure Lookup - DLF) are not diffused. They are simply ignored.

The protection of conduit is provided by using an active VID and a VID of protection. When the active conduit failing (is indicated by the loss of message test of continuity 802.1ag " CC"), the source rocks the value of the VID to redirect the traffic towards the conduit of protection within a 50 ms maximum delay.

Standardization

Technology is in the course of standardization with the IEEE, the authority which is at the origin of the specifications of Ethernet, which can let suppose that in the long term the standard will be supported by a very great number of equipment Ethernet of the market, and that thus important economies of scale could be realized.

A request for authorization of project (BY) was subjected in March 2007 and approved by the IEEE in May 2007 in order to initiate work of standardization. On the basis of this request, the IEEE proposed the name " PBB-TE" (" Provider Backbone Bridging with Engineering" Traffic; - 802.1Qay), although the name " Provider Backbone Transport" (PBT) was often used in the past to indicate same technology.

The concept was accepted by ITU-T in the group of study SG15/Q12 under the title " Provider Backbone Transport" (g.pbt).

Additional contributions are subjected to IETF CCAMP (" Common Control and Measurement Plane").

Several industrialists started with developed products, estimating that the activity of standardization in progress would not modify in a fundamental way the preliminary specifications presented during the tender of BY bus the concept is based on a combination of existing specifications Ethernet of the IEEE:

802.1Q VLANs
802.1ad double marking Q-in-Q
Subset of 802.1ah Mac-in-MAC

Interworking

Parallel to work of standardization in the IEEE, several industrialists formed in June 2007 an association with an aim of facilitating interworking in heterogeneous environment of network, with manufacturers different or based on hybrid architectures PBT/MPLS. Founding members of the " éco-système" are ANDA Networks, Axerra Networks, Extreme Networks, Hammerhead Systems, Lightstorm Networks, Meriton Networks, Nortel, RAD Dated Communications and Soapstone Networks. Other specialized companies (testing equipments, solutions microwaves, engineering of traffic, activation of service etc) joined this first in September 2007 group like dragonwave, Gridpoint Systems, Ixia, Spirent Communications, TPACK Systems, and TranSwitch.

Public tests of interworking implying several technologies whose MPLS and several manufacturers were carried out successfully on various occasions, for example in the laboratories of center EANTC (European Advanced Networking Test Center) in Berlin in August 2007 and lasting congress CEWC (Carrier Ethernet World Congress) in Geneva in September 2007.

Alternative or complementary technologies

"PWE3 on MPLS": Require to implement a plan of control MPLS for the equipment " Edge" and " Core" in order to create a tunnel. The equipment " Edge" must be adapted for services VPN of level 2 " Virtual Private Wire Service" (VPWS, also called " psuedowire" , " martini circuit" , " PWE3") or " Virtual Private Lan Service" (VPLS).
" Transport MPLS (T-MPLS) ": activities of standardization in progress to ITU-T. The principle is to define a subset of MPLS by masking some of its complexities, and thus its problems of costs and scalability.
Mixing of VLAN also called " Provider VLAN Transport" (PVT).

The review Light Reading of September 2007 includes an interesting table which indicates the strategy produced currently retained by the principal industrialists (Alcatel-Lucent, Cisco Systems, Nokia Siemens Networks, Nortel, etc), to see.

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