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Author: admin    Add Date: 2010-6-3    Click: 608     Font Size:  Big  Medium  Small

As more and more operators announced to the LTE evolution and released commercially available schedule, focusing LTE demand has become the key to the development of network technology of bearing. In order to meet the demand of high quality business LTE bearing, bearing network needs to have three key attributes: the whole scene, telecom and easy maintenance.
The whole scene
PWE3 / MPLS multiple service bearing support 2G / 3G / LTE long-term coexistence
From 2G / 3G to LTE period, more than 90% of the radio station will reuse, and 2G / 3G will coexist with LTE, which determines the transmission network must adapt to the wireless technology development at different stages of differentiation needs.
But in the wireless network construction investment, site ( room, rent ) investment of nearly 50%, the radio base station is occupied about 40%, while the transmission network is less than 10%. Due to the great differences of investment, operators will rarely due to transmission network IP to transform existing 2G / 3G base station, in turn, request to send the net making multi service transmission capacity.
Currently supports TDM / ATM / Eth multiple service transmission technology only two: the traditional MSTP technology, and based on the PWE3 / MPLS packet transport technology. As the transport network IP transition, PWE3 / MPLS technology has become the key demand of mobile bearing field.
IEEE 1588v2 support low cost timing and depth of coverage
TD-SCDMA, CDMA, WiMAX and LTE ( including the LTE TDD and LTE FDD ) are present on the demand of time synchronization, the only GPS or IEEE 1588v2 can meet the requirements of. LTE due to frequency effects, the ability to cover less than 2G / 3G, means that the future requires more base stations to cover, if the network using the GPS means investment increases, and the IEEE 1588v2 GPS ground synchronization technology can reduce the investment, and can be used as in the GPS fail synchronous protection scheme, thereby telecommunication infrastructure security.
Moreover, wireless broadband is another major application scene is indoor, because GPS cannot penetrate the roof, indoor base station synchronization requirements also must rely on the transport network to meet, so GPON, Ethernet access technology also needs the support of IEEE 1588v2 capacity.
OTN / WDM bandwidth expansion, low OPEX supporting high speed mobile
LTE coverage for high-speed railway mobile scenario, the mainstream of the current scheme is to take over the RRU area distributed base station coverage, which can realize switching in an internal BBU completed, reducing cross BBU cell switching times, effectively reduce the high speed movement of the dropping rate, enhance the user experience of broadband business.
Because BBU and RRU standard intermediate frequency optical interface ( CPRI ) bandwidth greatly, reach 1G bit / s above, at the same time the railway station sites exist to maintain security and difficult and other objective factors, in bearing solutions tend to introduce small OTN / WDM device for CPRI bearing, to realize centralized management of BBU, RRU remote distributed deployment. This scheme can realize saving fiber, reducing base station acquisition difficulty, reduce maintenance cost of base station. Protection from investment point of view, now the deployment of the IP bearer network have upgraded to OTN / WDM ability is valuable.
LTE bearing demand is the essence of connection based IP Technology
LTE access bearer network face two main interface, a S1 interface, used for base and core network gateway is connected between the; another is the X2 interface, used logical connection between the base station and base station.
S1 interface similar to 2G Abis topology and 3G Iub interface. For disaster recovery, S1 interface with Flex demand, this demand is not unique, in the 2G / 3G IP process on Abis and Iub interface also has similar requirements, but in the end did not get applied. Because use what protection is not only a technical issue, but also consider the actual network topology, room number, to network construction cost and actual demand and other factors, because S-GW will be transferred to the RNC position of the computer room, therefore in the S-GW only under the dual ownership protection needs, while the MME is located in the core room, be in the core layer to consider realization of Flex protection.
For the X2 interface, considering LTE is public service of telecommunication network, need to follow the national policy regulations, including overseas also has a similar " lawful intercept" demand, all of a user's flow must be controlled through the gateway for content monitoring, mobile phone users can not appear between uncontrolled access intercommunication. Therefore, the carriers for the base station and the base station for interconnection between X2 interface location, only to improve user cross base station mobile switching time experience, completion of the handover, business or to go through S1 transmission.
Because the switching occurs only in between adjacent base stations, so the X2 interface design, mainstream operators to make clear a requirement to allow only between adjacent base stations exist logical connection, rather than the adjacent base stations do not allow interchange, from a base station fault spreads to all other base angle consideration, avoid all base station whole MESH interchange is reasonable.
Because of the complexity of the relationship between adjacent base station coverage, this connection was only possible by static allocation; due to X2 and S1 transmission has strict delay and protection requirements, may not be in the business demand appears again when the through route to create a link to the support, this means, LTE bearer network in business before, X2 and S1 interface includes connection, protection mode and characteristics of QoS has been configured, the connection is not automatically aging and change. So, LTE bearer network is essentially a connection technology based on network.
Low delay forwarding capability business experience
LTE design goal is to be able to reach the fixed broadband service ability. The traditional 3G / HSDPA architecture from the end user to operate between four protocol processing, great delay and high cost. While the LTE support flat structure, greatly reducing the protocol processing delay, improve the broadband business performance.
But because the wireless side port on the encoding of consuming a large amount of delay, in order to achieve the same with the fixed network end-to-end service performance index, LTE bearing network delay requirements than traditional fixed-line broadband bearer network more strict. Transmission delay is greater, the throughput of the system is lower, means that the wireless air interface spectrum efficiency is low, in order to meet the demand for wireless coverage capacity increase more carrier to cover, which will bring about the rising cost of wireless network. Therefore, reducing the transmission delay is to save money for wireless network.
In bearing technology choice, because the traditional access switches and routers transmission time delay discrete relatively large, single station delay and sometimes even more than 1ms, and general base station access network through the 10-20 station transmission, it is difficult to guarantee the LTE bearer end-to-end, stable low delay demand. Therefore in the LTE bearing, operators tend to take Cell based on fixed length packet forwarding packet transmission equipment, in order to reduce the end-to-end delay, the need to minimize L3 processing link, minimize the number of hops.
H-QoS capability base station not losing a line
LTE wireless layer through the signaling control, resource reservation, end to end business layer of QoS control, but with the IP bearer network, network congestion, packet delay, jitter, and other quality problems will affect the LTE business layer of QoS quality. Congestion free IP bearer network does not exist, the key is congestion occurs, how to guarantee the quality of service.
LTE base station bearing QoS has two key requirements: one is the guarantee for high grade business priority repeater, which is the traditional concept of Differ-Serv, another is the guarantee in congestion important base station service available ( such as a disaster or major event occurs, government agencies, hospitals, schools and other important regions of the base station ). This requires the bearer network can support a hierarchical QoS ( H-QoS ) processing capability, can according to the different base stations and different execution hierarchical scheduling capabilities, to ensure that the important base station never loses a line.
Easy maintenance
LTE bearing focuses on S1 instead of X2
The new LTE X2 logical interface is mainly used for switching, the interface appearance, base station there are logic part MESH interconnection bearing problem, the traditional point-to-point transmission network architecture presents a challenge. But further analysis can be found, the actual X2 interface bandwidth demand will not be great ( maximum does not exceed 3% S1 interface ), X2 business transmission delay end-to-end signaling plane 50100ms, transmission delay of about 1020ms, this requirement than S1 user plane delay 5ms loose a lot.
Because the X2 interface delay consideration is the mobility needs, while the S1 delay consideration is the business and throughput requirements, this results in a fact: if the bearer network can satisfy the S1 delay requirements, then the X2 delay is a very loose and easy to meet. So, X2 logic switching in bearer network or AGW convergence point to achieve acceptable. But the concern is if the bearer network support X2 logic interconnection, will bring the maintenance and equipment function demand, such as support for L3 VPN capacity. At the same time, in order to prevent the illegal interconnect adjacent base stations, also need to introduce the corresponding security control strategy, can cause bearing net to increase investment of more than 30%. For the 3% increase in flow rate 30% of the investment, and affects 97% of the S1 business QoS and maintenance quality, whether it is worth to further study.
Can learn from the fixed network operator in broadband network construction experience, for the enterprise business flow is not L3 VPN, currently the mainstream pattern is, in the metropolitan core room set VPN PE router. The configuration and management mode with the X2 load demand and fixed network enterprise L3 VPN needs there are many similarities: do not flow, configuration, often change. As long as the delay index can meet the requirement, the configuration of the VPN PE router may be X2 carrying a reasonable solution.
Maintenance and management to ensure the smooth evolution of unity
For LTE transmission, there are two kinds of typical thinking: a new technology -- 2G / 3G there are concerns by MSTP bearing, LTE is to build a packet transport network; another advocates the protection of future investment -- 3G and LTE are used for packet transport network bearer network, 2G business gradually from the MSTP moved to packet transmission network.
Either way, must take into account the fact that: a base station terminal room space is generally small, transfer apparatus built in base station, space only 2U3U. While the station itself is support for 3G to LTE smooth evolution, and 2G / 3G in quite a long time not to draw back the net. This means that, either in terminal access points are uniform, and it is through a box to realize the.
The traditional wireless only need to consider and MSTP maintenance team to an interface, taking into account the wireless network often need to adjust bandwidth, carrier frequency, increased migration sites and other objective conditions, the transport network packet of wireless transmission network, and keep only the maintenance interface is very necessary, otherwise it will lead to a lot of cross-functional communication costs rise, and can reduce troubleshooting efficiency. Therefore, packet transport network and the existing MSTP network maintenance and management is the smooth evolution of key requirements.
IP visualization management realization of OPEX reduction
The LTE scale deployment of the biggest challenge lies in OPEX. From OECD ( OECD ) for wireless broadband analysis can be found, wireless broadband development initial stage basically is the investment in network construction, but soon leveled off, and later OPEX will become carriers of the heavy burden. How to effectively reduce the OPEX broadband operators is currently one of the most concern.
Therefore, in bearer network construction must fully consider the ease of maintenance and upgrade the network availability, and this problem is the traditional SDH network. With the IP bearer network, how to maintain the IP bearer network like SDH is maintenance of performance and reliability of network is a carrier of the focus of attention.
The traditional SDH network provides a wealth of alarm, performance monitoring capability is based on hierarchical overhead and maintenance information, packet transport network equipment also needs the support of similar layered SDH OAM ability, provide rich maintenance information to the management system, to support the visualization of IP network end-to-end configuration and fast fault location. With traditional IP device based on single station command line configuration, based on the visualization of IP network management configuration efficiency can be increased by 95%, while in the fault detection and location, visual management also significantly improve maintenance efficiency, the future LTE scale deployment provides reduced OPEX may.
Odd micro IEEE1588v2 solutions
Odd Micro Communication focusing operator LTE bearing key demand, launched with the core intellectual property rights of the IEEE1588v2 master clock, the clock, clock monitor, and stack products, enabling the operator to use mature grouping technology and standard, promote packet transport network in multiple scenes, telecom and easy maintenance characteristics become possible, thus helping the operator from 2G / 3G to LTE full service bearing.
Note: This article is part of the contents and technical data from the" Huawei Technologies".