SS7 Networks
Features
- Consolidate Equipment at STP Switching Offices
- Reduce Capital and Operating Costs
- Simplify Remote Equipment Test and Management
- Minimize Space Requirements
Introduction
Common Channel Signaling System No. 7 (SS7) is a global ITU standard that defines the procedures and protocols by which network elements exchange call information in the Public Switched Telephone Network (PSTN). The SS7 network is an out-of-band digital overlay network using 56/64 Kbps DS0 channels for message units.
Recently, the replacement of traditional Class 5 switches with decentralized soft switches and the installation of new switching offices by wireless service providers and competitive carriers have dramatically increased the number of ports deployed in the SS7 network. These dynamics stress traditional deployment topologies from a cost, size, and management perspective.
Regardless of the service provider type, each and every switch connected to the PSTN must have an SS7 connection. The SS7 circuits are used to direct calls via outbound trunks and carry information pertaining to call set up and routing. For redundancy purposes, SS7 connections (links) are always engineered in pairs. There are six different link types, each defined by the type of connection it supports. As illustrated below, a service provider leasing SS7 service from another provider would use "A" links as a gateway into the SS7 backbone. An SS7 provider would use various link types to interconnect the Signal Transfer Points (STPs) and to connect an STP with a Service Control Point (SCP) within its network. STPs act as message routers, and SCPs contain the central database for the entire region served.
SS7 Backbone
Besides the large, well-established providers, SS7 access is also obtained by leasing the service from another carrier. All IXCs and ILECs maintain SS7 networks for their own consumption and, in some cases, for resale. There are also independent switchless SS7 providers who solely provide SS7 access.
Application Overview
SS7 providers interconnect STPs and SCPs with T1/E1 circuits carrying 56 Kbps message links, as depicted below. Because of network resilience requirements, each T1/E1 circuit is configured partially filled. On average, the DS0 count is eight to ten per T1/E1 circuit. Based on this low utilization number, SS7 providers use Digital Cross-connect Systems (DCS) to groom the bandwidth as it enters the switching office prior to being sent to channel banks. Otherwise, they would need a channel bank for every eight DS0 ports. Channel banks convert groomed T1/E1 circuits into the appropriate DS0 interface for connection to the STP.
STP Switching Office Before DNX
SS7 providers use one of three DS0 interface types: V.35 synchronous, OCU-DP, or a DS0-DP. Independent switchless providers typically use a V.35 or OCU-DP interface. ILECs/traditional providers use the DS0-DP interface because of its simplicity, cost, and ease-of-cabling.
DNX Consolidation Solution
Sycamore DNX Multiservice Cross-Connects support OCU-DP, DS0-DP, and V.35 interfaces, for flexible deployment in every type of SS7 provider network. The DNX solution consolidates channel bank, digital cross-connect, and T1/E1 CSU functionality into a single, cost-effective and compact device. Common practice requires the use of a DSX field between each device. DNX functional consolidation minimizes this need, along with total space requirements and the cost and complexity of additional cabling.
STP Switching Office After DNX
The DNX-11 can support up to 80 synchronous data interfaces and 8 T1/E1 interfaces in 6 rack units of space. System expansion can be achieved using the DNX-88, and all components within the DNX-11 can be reused. The DNX-88 can provide over 600 ports of synchronous data capacity for terminating T1, E1, T3, E3, STS-1 and OC-3/STM-1, and can be remotely managed as a single device.
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