Computer network topologies have evolved from a bunch of hosts and servers that share resources in a clear defined space of a office building called Local Area Network – LAN, to the largest topology of networks called WAN’s – Wide Area Networks connecting dispersed geographically networks. The middle size networks are called MAN’s – Metropolitan Area Networks. The term is applied to the interconnection of networks in a city into a single larger network (which may then also offer efficient connection to a wide area network). It is also used to mean the interconnection of several local area networks by bridging them with backbone lines.
The diameter of such a network can range from 5 to 50 kilometers. As a rule, MAN does not belong to any particular organization, in most cases, a group of users or a provider who takes charge for the service own its connecting elements and other equipment. The transmission support for the MAN is represented by the links of fibre optic cable laid in a ring formation in a metropolitan area.
ATM (Asynchronous Transfer Mode) combines the characteristics of circuit switching and packet switching, which allows it to transfer even the real time data.
The MAN can be used to provide services including telecoms, Internet access, television and CCTV to businesses and citizens in these metropolitan areas.
Nowadays, MAN networks are connecting a number of Campus LAN networks which are designed in hierarchical structure such as: access , distribution and core.
Next Generation MAN : The Metro Ethernet Solutions
Service providers use Metro Ethernet to provide Layer 2 Ethernet connections between customer sites in metro area networks. Driven by its relative simplicity, high bandwidth, and low-cost switches, Ethernet has become the transport technology of choice in metro area networks. There are numerous applications that require pure Layer 2 connectivity in the metro area network (MAN) for providing simple point-to-point, point-to-multipoint, or multipoint-to-multipoint services with a relatively low number of customer sites. However, Ethernet limitations become apparent in large MANs with thousands of access nodes. In this
case, service providers are more likely to offer Layer 3 Virtual Private Network (L3 – VPN) services based on multiprotocol label switch (MPLS) transport. When interconnecting hundreds or thousands of customer sites, this approach gives more flexibility, better scale, and ease of OAM.
MPLS is best and most widely used to interconnect data centers with branch offices and branches to other branches. Ethernet is best for interconnecting data centers. MPLS can handle any-to-any connectivity, including voice and video. Ethernet offers low-latency and high-throughput, which is ideal for disaster recovery. Using MPLS for WAN connectivity requires that all network devices and management tools be compatible with both MPLS and Ethernet. Because LANs use Ethernet, using Ethernet for the WAN gives organizations an all-Ethernet infrastructure, which simplifies network management.
For the above-mentioned reasons, operators are thirst for carrying all services over one network. Several networks coexist within the existing MAN, of which the IP MAN is the best choice. Nevertheless, the IP MAN also has some problems in handling these services, which can be explained in detail as follows:
The existing IP MAN is out of order, in which the Layer 2 switching and Layer 3 routing are mixed. So it cannot meet the requirements of providing QoS guaranteed services.
The IP MAN mainly implements L3 switching architecture. With a single access mode, poor access capability and without overall planning of service access points, this kind of access mode is hardly possible to support
“full-coverage full-service network”.
Highly positioned Provider Edge Router (PE) is a networking that cannot take the advantages of MPLS VPN technology. Layer 2 network too large, which is confined by the Virtual LAN (VLAN) ID resources and makes network troubleshooting difficult.
It causes serious waste of optical fibers and transmission resources. In order to attract more group users, IP MAN mainly employs the direct optical-fiber connection mode. Users are directly connected to PE. In some cases nearly half of the fibers in MAN are used only to connect group users, really being a great burden of carriers.
The IP MAN equipment has differentiated capabilities. Most IP MAN is unable to deploy either the QoS guaranteed services or the multicast services over the entire network.