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New trends like network structure flattening_ increasingly intelligent

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					                                                                                                   Huawei Communicate




Optical access
network trends
New trends like network structure flattening, increasingly intelligent management and maintenance,
integrated bearing of convergence services, even higher network security and reliability, make it critical for
the optical access network to adapt both on the network and equipment layers.
By Ao Li




                                                                                                     MAY 2009 . ISSUE 49   14
   Expert’s Forum
               Expert’s Forum
                                  will deliver our promise
             “Batelco’s NGNDeputy Director of Institute of Communications Policy Research, China Academy of Telecom Research (CATR),
                         Ao Li,
                         Ministry of Industry and Information Technology all Vice
             to bring affordable broadband access to(MIIT);of Chairman of Transport and Access Network Technical
                         Committee, and Head of Access Network Workgroup, China Communications Standards Association.
             Bahrain’s households, making them among the
             best connected in the world.




   A
                   s a result of telecom                       structure of the wired access network.                    challenges and must consider the following
                   restr ucturing, the time is                    T h e l a r g e c a p a c i t y, h i g h a c c e s s   issues comprehensively.
                   near for China’s three major                bandwidth, high reliability, and multi-
                   telecom operators to launch
   full-service operations. As a basic bearer
                                                               service QoS support capability features
                                                               of the optical access network enable the
                                                                                                                         Construction, operation
   network, the access network has to bear                     access network to evolve towards a unified,               and maintenance
   multiple services such as voice, data, video,               converged and efficient bearer platform.
   enterprise access and backhaul services of                     The optical fiber broadband access                        By substituting fiber for copper cable,
   the radio base station.                                     network was deployed on a considerable                    operators can reinforce the effectiveness
      Tr a d i t i o n a l c o p p e r w i r e d a c c e s s   scale in China during 2007. The future                    of overall planning for access optical fiber,
   networks are constrained by attenuation                     development strategy of China’s FTTx                      OLT, ODN and system devices during
   in signal transmission, so the coverage of                  has set a clear objective for operators                   FTTx network construction.
   an end office is usually within 3km and a                   to “vigorously advance the substitution                      It is necessary to strengthen the linkage
   large number of end offices are deployed                    of fiber for copper cable, deploy access                  between front-end and back-end devices,
   in the network. This poses a challenge                      networks of optical fiber, realize FTTB                   power supply assurance, IT support,
   for operators to build equipment rooms                      (fiber to the building) and FTTV (fiber                   project construction, operation and
   and auxiliary facilities and to control                     to the village) in newly built areas and                  maintenance and to quickly transform the
   OPEX. The dispersed distribution of end                     strengthen renovation of existing metro                   access capability into service capabilities.
   offices requires adding a metropolitan                      areas.”                                                      The actual situation indicates that
   convergence layer. Consequently, there are                     Current statistics show that more than                 FTTx deployment now faces numerous
   more network layers in metropolitan areas,                  4.5 million Chinese homes are passed                      problems that arise due to the lack of
   the structure is complicated and network                    by FTTx. The network has been built                       adequate capability and experience on the
   OPEX gets higher.                                           by taking FTTB/C as the predominant                       part of the operator in the construction,
      The introduction of the optical access                   mode and FTTH as the supplementary                        operation and maintenance of the
   network with a coverage of 20km ensures                     mode. In actual network construction, the                 optical fiber access network, especially in
   that optical line terminals (OLTs) can be                   optical access network also faces multiple                operation and maintenance.
   advanced to the traditional metropolitan
   convergence nodes at the initial stage of
   optical access network construction. It
   simplifies the network structure of the
   convergence layer for the access network
   and reduces the number of end offices.
   This is important not only for the network
   upgrades of traditional fixed operators, but
   also for the new networks from emerging
   broadband operators who lack equipment
   room resources.
      While accelerating optical fiber
   access applications, operators should
   pay attention to setting up OLTs in a
   centralized manner under unified planning
   to realize “large capacity and fewer nodes
   deployment” and to optimize the network


15 MAY 2009 . ISSUE 49
                                                                                                                   Huawei Communicate


   First, the deployment, configuration,      board bus bandwidth, uplink port capacity          In the FTTB/C mode, as the remote
and upgrade of devices is a complicated       of OLTs, and the system’s switching             device of the PON, the optical network
and cumbersome affair. The types of           capacity all need to be increased. This         unit (ONU) should meet network
devices and the quantity of network           trend is reflected in the emergence of large-   and service needs in functionality and
elements are increasing and their             capacity OLTs (with 800GB switching             performance. PON ONU devices
management and maintenance are                capacity, eight PON ports per board and         support the switching between VLAN
complicated and laborious. Multi-service      10GB uplink ports).                             1:1 and n:1 and cross-VLAN multicast
configuration and service provision involve       When network layers are simplified, it      replication, meet the requirements for
multiple devices and multiple back-end        is preferential that OLTs should be directly    QoS deployment and support the queue
support systems and operation is very         connected to the upper-link BRAS/SR             dispatching based on 802.1P and priority.
complicated.                                  equipment. In addition, the growing OLT         The ONU will provide the built-in voice
   Second, the number of remote nodes         capacity and the increasing number of           function based on service development
requiring maintenance and management          users covered in the future will impose an      needs.
has doubled along with the gradual            increasingly higher requirement on FTTx            Different building and application
devolution of optical fiber. As remote        network reliability.                            environments have different requirements
devices are removed from the equipment            One primary requirement for PON             for the ONU port density. Generally,
room, the operating environment of the        devices is to fully consider protecting         the configurations of 8, 16, 24 and 32
device is poor and the fault rate is on the   the key components of OLTs (such as             ports can cover requirements in various
rise. The devices are widely dispersed,       redundancy protection for the power             scenarios.
leading to a significant amount of            panel, main control board, and uplink              The narrowband to broadband (NB-BB)
troubleshooting workloads.                    board). For networking protection,              ratio of the ONU is specified based on
   These issues have imposed very             the OLT needs to provide dual uplink            the service penetration rate. To guarantee
high requirements for FT Tx device            protection to key customers or critical         long-term operating performance, the
management, device deployment, service        services, avoiding any single-point fault       ONU should be able to work in the -10°C
issuance, fault monitoring, and control       and providing reliable access.                  to +55°C environment and have a solid
capability on network security.                   At the initial stage of FTTx                design for heat dissipation. The plug-in
                                              construction, uplink redundancy                 ONU can dissipate heat by using a fan
                                              protection can be realized for OLTs             with a minimum service life of 50,000
Capacity configurations                       directly connected to the BRAS/SR by way        hours. The integrated ONU can use a
for PON OLT                                   of link bundling or VRRP. The carrier-
                                              class Ethernet protection technology can
                                                                                              natural heat dissipation design in lieu of a
                                                                                              fan in consideration of the special stairway
                                              then be introduced to realize millisecond       installation environment and the impact
   The large capacity, fewer offices and      protection between active and standby           on households. ONUs should also have
network flattening trend implies an           links of OLTs as well as the dual-homed         superior lightning protection performance.
increase in the number of users covered by    configuration of BRAS/SR of the OLT.            Power supply ports and DSL/POTS
the OLT, which creates new requirements                                                       ports when equipped with 4kV lightning
for OLT capacity. The number of passive                                                       protection capability can provide remote
optical network (PON) ports per board,        Requirements for PON ONU                        surveillance over temperature, municipal




While accelerating optical fiber access applications, operators should
pay attention to setting up OLTs in a centralized manner under unified
planning to realize “large capacity and few nodes deployment” and
to optimize the network structure of the wired access network.


                                                                                                                    MAY 2009 . ISSUE 49      16
   Expert’s Forum
    Optical access network trends



   power, battery and access control. The
   ONUs mainly use the local power supply
                                                     directly open the SNMP MIB database to
                                                     support the NMS of the IP MAN network
                                                                                                     Multi-service bearing
   of AC 220V or DC -48V and may use a               and softswitch network and to configure         impact on service
   backup battery or UPS as required. The            and manage services such as VLAN, QoS
   height of ONUs needs to be low in order           and voice access remotely.                      control
   to meet the installation requirements of             Access devices with built-in voice under
   the narrow staircase environment.                 the FTTH mode can be managed by using               The service access control layer consists
      The ONU is a terminal access device            the ACS management system specified             of two structures: single-edge and multi-
   that can also be connected to the BTS and         in the TR-069, or by temporarily using          edge. If all the services and traffic of a user
   support the private line access for small-        the PON NMS. In principle, standalone           are terminated in the same service access
   and medium-sized business users. In the           NMSs will no longer be established for          control device, it is a single-edge structure.
   substitution of fiber for copper cable            FTTH voice access devices. As for the           If different services of a user are terminated
   scenario, the ONU platform architecture           built-in voice access devices under the         in different service access control devices,
   supports smooth upgrades from the                 FTTB mode, NEs of different vendors             it is a multi-edge structure.
   existing ADSL2+ to VDSL2 or LAN so                can be managed by their respective                  The support capability of the FTTx
   as to support smooth upgrading of service         NMS. A small number of new external             network on integrated service bearing
   bandwidth.                                        integrated access devices (IADs) can also       will have relative impact on the service
                                                     be incorporated into the vendor’s PON           control layer of MANs. For important
                                                     NMS. Access gateways (AGs) should be            government and enterprise customers, SR
   FTTx device management                            managed by the softswitch NMS in a              access shall be adopted. For public users,
                                                     unified manner.                                 small and medium-sized government/
      New issues facing network management                                                           enterprise customers, single-edge structure
   and maintenance that come with the                                                                networking is used if BRASs of superior
   introduction of the PON system are: an            Integrated service                              functionality and high performance are
   increase in the number of access points, the
   shift from single service to multiple services,
                                                     bearer capability                               deployed in IP MANs. If the service
                                                                                                     volume is large and the BRAS cannot
   the greater granularity or refinement in                                                          support multi-service access control well,
   service management and an increase in the            When constructing an FTTx network,           multi-edge structure networking can be
   amount of maintenance workloads for the           operators need to consider their ability to     used. The same MAN can simultaneously
   optical cable network. As the number of           meet the future requirements of bearing         use the mixed networking of both single-
   ONUs increases significantly after mass           integrated multi-services. The FTTx             edge and multi-edge structures.
   deployment of the optical access network          network can be equipped with customer               To fulfill the requirements of multiple
   using the PON, the operation, management          and service-differentiated bearing capability   services such as IPTV, WLAN and VoIP,
   and maintenance of ONUs become quite              for high quality access of voice and            operators should consider introducing
   important.                                        video services. The FTTx access network         the dynamic host configuration protocol
      Under the FTTB mode, the                       should deploy the 802.1P-based QoS              (DHCP) into the IP MAN and gradually
   management and maintenance of PON                 strategies and implement corresponding          building the DHCP platform. The
   ONUs uses the combined management                 priority queues for OLTs and ONUs. In           management system of the DHCP
   mode of OAM + SNMP (EPON) or                      addition, the FTTx must have service            platform can be deployed in a centralized
   OMCI + SNMP. The OAM or OMCI                      traffic classification, priority marking, and   way.
   is responsible for managing functions             priority queue dispatching capability to            The DHCP server function can be
   related to the PON protocols. The SNMP            realize service packet forwarding based on      enabled directly on BRAS/SR if the
   interface is responsible for functions            service priority and assure the quality of      requirements of the DHCP system for
   related with ports, protocols, and services.      different services.                             security, reliability, and scalability are not
   Under the FTTH mode, the management                  In respect to WLAN functions, to             high. Based on the actual needs of services,
   and maintenance of PON ONUs uses the              adapt to the development trends of future       the IPoE access authentication method
   joint management mode of OAM/OMCI                 networks, PON devices should support the        capable of centralized management can
   + TR-069.                                         VLAN stacking function. In particular, the      be introduced in conjunction with the
      The PON OLT and ONU devices                    outer VLAN tag is used to identify services     renovation of Radius and the related
   under the FTTB mode are managed and               and represent OLTs. The inner VLAN tag          support system, smoothly adapting to
   configured according to the network               can be used to represent different users        services that are always online and those
   management system (NMS) of PON                    or different services of the same user and      with multicast requirements.
   devices by providing northbound                   to support the VLAN mapping function
   interfaces, or by allowing PON devices to         between 1:1 and n:1.                                Editor: Xue Hua xuehua@huawei.com



17 MAY 2009 . ISSUE 49

				
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Description: Means of optical access fiber-to-floor; in addition to fiber to the home (FTTP / FTTH) cable has been extended to the home or business; FTTO, FTTC ... fiber-optic broadband network in a variety of transmission media in an ideal it is characterized by a large transmission capacity, transmission quality, low loss, long distance relay.