PDF of this tutorialNetwork Topology
The flexibility of SDH can be used to best advantage by introducing a new network topology. Traditional networks make use of mesh and hub (i.e., star) arrangements, but SDH, with the help of DXCs and hub multiplexers, allows these to be used in a much more comprehensive way. SDH also enables these arrangements to be combined with rings and chains of ADMs to improve flexibility and reliability across the core and access areas of a network. Figure 4 shows the basic fragments of network topology that can be combined.
Figure 4. Basic Fragments of Network Topology
Rings could supply improved services to a high-density business area, a major science park, or a conference/exhibition center. In addition, they may displace multiple local exchanges by multiplexers and fiber connections to a single major exchange for lower costs.
Introduction Strategy for SDH
Depending on the regulatory position and the relative age and demands of different parts of an operator's network, SDH may be introduced first for the following reasons:
- for trunk transmission where line capacity is inadequate or unreliable, such as by introducing 2.5 Gbps optical-line systems
- to provide improved capacity for digital services in an area, such as by introducing rings of ADM
- to give broadband and flexible access to customers over optical fibers where provision of copper pairs is inadequate for the demand, such as by introducing IDLC–type systems (integrated digital loop carrier using remote multiplexers connected to a service switch via optical fibers)
- to provide bandwidth flexibility in the trunk network for provisioning and restoration, by introducing DXC 4n/4 high-order cross-connect switches
- to give time-switched leased lines, other services, and improved utilization of the network or to maximize the availability of specific services; these applications would use ADMs, hubs, or low-order DXC–types such as 4/1 or 1/1
