1. Overview of Metro Area Network (MAN)

1.1  Basic Concepts and Features of Metro Area Network (MAN)

The advent of the Internet has brought dramatic changes to human social and economic life. In recent years, the rapid development of IP and VPN facilitated data services, such as Internet access, IP-based virtual private networks, IP phone, and multi-media applications. This development requires a data network that offers wide coverage, high-speed bandwidth and fast services. The global telecom industry is evolving from the voice-based network services into multi-services.

Generally, MAN is a broadband network with unified protocols, which connects government agencies, enterprises, educational institutes, companies, and family users. The network concentrates on offering data services and integrated services of multi-media applications such as packet voice, images and video that cover metropolitan areas and local public networks in the range of suburbs.

Individual telecom operators may arrange MANs differently, and MANs also have to transmit multiple services by providing a series of features that are different from other networks, such as: 

• MAN is a public network in a multi-user oriented environment, requiring a certain level of QoS assurance.
• MAN supports various signals from all client layers, and rapidly provides the bandwidth required by these signals.
• MAN is a multi-service network covering data, voice and image.
• The coverage of the MAN is in the range of 50km~150km around metropolitan areas.

1.2 The Basic Architecture of Metro Area Network (MAN)

Horizontally, MAN is divided into the access layer, aggregation layer and core layer.

• The access layer implements access to various types of users.
• The aggregation layer controls the aggregation of distributed access points, implements data multiplexing, switches data, and provides flow control and user management. 
• The core layer completes the interaction of high-speed information over the whole networks, and interconnects with the backbone networks.

Vertically, MAN can be divided into the service layer and the transmission layer.

• The service layer consists of ATM and IP equipment, which can implement services such as narrow-band voice, Internet services, remote calculating and transaction processing, E-commerce, videoconference, video-telephone, multi-media integrated information service, remote computer communication and control, and line lease.
• The transmission layer refers to the metro optical network that carries these services, and provides a unified transmission platform with high efficiency, high capacity and low cost for all services. It consists of DWDM and SDH equipment.

2. ZTE Metro Optical Network MSTP Solution

ZTE MSTP solution involves multi-wavelength and single wavelength schemes.

2.1 Multi-Wavelength Solution

This solution is based on OADM and DWDM technologies, applying to both the backbone layer and the aggregation layer of the metro optical network.

Transmission capacity

In the case of no protection, the maximum capacity is 32Ч2.5G or 32Ч10G. In the case of protection, it is 16Ч2.5G or 16Ч10G.
( Transmission distance )

• 12Ч8dB: 12Ч20km, perimeter 240km, line loss 0.4dB/km
• 8Ч14dB: 8Ч40km, perimeter 320km, line loss 0.35dB/km
• 5Ч24dB: 5Ч80km, perimeter 400km, line loss 0.3dB/km

Access capability

•  SDH services (including STM-1/4/16/64)
• SONET services (including OC-3/12/48/192)
• ATM services or POS (including STM-4c/16c)
• Ethernet services (including 10M/100M/GE)
• Enterprise interconnection service (ESCON)
• Fiber Channel (FC)

Aggregation capability

• Add/drop multiplexing two GE signals into one STM-16 signal
• Add/drop multiplexing four STM-4 signals into one STM-16 signal
• Aggregation function for low-rate services of 10 FE (100M), and 16 STM-1(155M)

Wavelength add/drop capability

Add/drop capability for multi-wavelength and typical configurations are:

• Add/drop 32 wavelengths
• Add/drop 24/16/12/8/4/2/1 wavelengths and directly connect remaining wavelength or part of wavelengths.
• Nodes can be upgraded and configured as add/drop nodes. When upgrading, boards can be added without interruption of services.

Networking capability

Ring, ring with chain, tangent ring, intersection ring, chain and cross-connect

Protection capability

• Chain-type based: 1+1 path protection, and 1+1 multiplex section protection
• Ring-type based: channel-shared protection, and two-fiber bi-directional multiplexing section protection

Network management

Supports end-to-end configuration for wavelength and automatically extracts the network connection
 
2.2 Single-Wavelength Solution

This solution is based on the Multi-Service Transmission Platform (MSTP) technology, which is applied to both the aggregation layer and the access layer of the metro optical network. MSTP also supports data service transmission and processing in addition to traditional SDH functions, which covers:

The Ethernet processing

• Provides rich and highly integrated Ethernet interface boards, such as 10M, FE and GE.
• Supports multiple Ethernet over SDH protocols, including Multi-link PPP, HDLC, PPP/HDLC, LAPS and GFP.
• Supports the Transparent LAN Service (TLS).
• Supports L2 switching at linear speed.
• Supports classification of VLAN (ID-tagged and port).
• Supports multiple virtual bridges, and offers Spanning Tree Protocol (STP) and MAC address study ability.

ATM processing

• Supports ATM VP/VC switching and AAL layer protocol. 
• Supports VP-Ring protection.
• All the 155M (ATM-UNI interface) bandwidth can be flexibly configured, and a certain amount of STM-1/STM-4 bandwidth can be shared. The maximum aggregation ratio of board service can be 8:1.
• It supports flow control function, and provides multiple billing modes (time, flow rate and throughput rate.)

Service aggregation and transparent transmission

• T-MUX technology allows low-rate services to converge and transparently transmit, and the aggregation capability is 16(155M, 4(622M, 4(2.5G, and 8(GE.
• The overhead byte is transparently transmitted to ensure the integrality of other networks.

Flexible PoS interface

• PoS interface is of the cascading function for VC4-4c, VC4-16c, VC4-64c and VC4-Nc. Either the fixed VC4 cascading length like 4,16,64 can be selected, or the cascading length can be chosen in the light of the actual traffic capacity.

3. ZTE´s Concept About The MSTP Development

ZTE believes that MSTP will undergo 4 stages during its development.

• The first stage is Original MSTP

In this stage, MSTP provides transparent transport of Ethernet and interconnection of remote LANs for carriers.

• The second stage is Flexible MSTP

In this stage, MSTP supports Ethernet L2 switching, ATM service access and aggregation. Metro WDM has such functions as self-adaptive multi-service access, sub-rate aggregation, and optical layer protection.

• The third stage is Dynamic MSTP.

In this stage, RPR is incorporated into MSTP to offer fair bandwidth allocation, strict COS/QOS and safer customer isolation; Metro OADM/OXC can integrate optical/electric cross connect quickly and dynamically.

• The final stage is Intelligent MSTP.

In this stage, MSTP adds intelligent management layer to respond quickly to the bandwidth applications at the service layer, without restoring or reestablishing circuits or channels in response to requirements from carriers, and offering intelligent strategies for bandwidth lease and O-VPN.