The Network Domain maintains standards and policies that enable a common, uniform network infrastructure that provides transparent, reliable, and ubiquitous communications for DHS' distributed information processing environment. This domain contains standards regarding every aspect of networking within DHS, Business Partner and interagency computer connections to DHS, and the use of wireless and video conferencing technologies throughout DHS.
The infrastructure of most large-scale business operations at DHS consists of a series of Local Area Networks (LAN) connected together on a Wide Area Network (WAN). This topology allows for the seamless integration between, and centralized administration of, all of the devices within the DHS. The principles that govern good network design include the ability to provide a wide range of applications and resources, affordability to the organization, high reliability, scalability, and support of new technologies.
This section consists of the following areas:
- Landlines - Modern telephone communication systems are generally classified by the number of telephones and telephone lines they support. The classification is either "Small" or "Large", depending on the number of stations (telephones) served by the system. Generally a Small system is one which has 60, or less, stations. A Large System has over 60 stations. This is a general rule, because some Small systems may be capable of being expanded, while others may have a smaller station capacity. These systems are further classified according to their internal architecture (construction) and as to whether the central controlling mechanism for the system is placed on the customer's premise or elsewhere, such as in a telephone company's central office. There are numerous advantages and disadvantages with each type of telephone system. Generally speaking, the cost per station and functionality of the telephone system improves with the size of the system. DHS primarily uses either Centrex or PBX/Small Key configurations according to site location and requirements.
CENTREX - A private telephone communication system provided on a lease basis by the telephone company (Currently, almost all leases are with Level 3). This service includes various features provided by equipment located on facilities operated and maintained by the telephone company. This facility is referred to as the "Central Office". The Central Office or "CO" is usually located in or near the community in which DHS and/or other agencies of the Commonwealth have offices. Features are extended to the DHS' premises by local telephone wires or fiber.
PBX/Small Key - A PBX (Private Branch Exchange) or Small Key System is a series of telephone equipment and features provided by small computer based equipment, commonly referred to as a "SWITCH". The Switch controls a given number of on-premise telephones and related equipment. In addition, it interconnects telephone calls off-premise, usually via telephone lines to the public telephone network. A PBX usually, but not always, requires an attendant, who intercepts incoming calls and distributes the call to the caller's desired destination. Since a PBX concentrates a relatively large number of on-premise telephone lines to a small number of outside public telephone lines, and because it potentially provides tighter controls and accountability for telephone utilization, it may be the most cost beneficial system when the number of telephones supported by the PBX exceeds 60. Small Key Systems are utilized to handle 80 lines or less. Environmental matters of air conditioning and heating must be considered when deploying a PBX or Small Key Systems.
- Wireless - A Wireless Communications Device transmits and receives data, text, and/or voice without being physically connected to a network. This definition includes but is not limited to such devices as cellular telephones and wireless data devices (e.g., Blackberry Devices). The portability, small size, coverage area and capabilities of these devices make them an attractive option for a variety of data communication needs. However, the documents below are meant to address issues related to the use of such devices as a telephone.
- Wide, Metropolitan, and Local Area Networks - Network administrators often classify networks according to geographical size. The smallest kind, Local Area Network (LAN), is a group of computers and other devices interconnected within a geographically limited area, such as a building or campus. Wide Area Networks (WAN) and Metropolitan Area Networks (MAN) interconnect several LANs. In addition, a WAN can connect several MANs. Computers within a WAN exist in an unlimited geographical area. WANs can utilize telephone lines or radio waves and typically transfer data at lower speeds than LANs. A MAN is more geographically confined than a WAN. MANs are usually high-speed connections using fiber optic cable or other digital media.
DHS - This subsection contains standards and policies regarding WAN, MAN, and LAN network connections at various DHS office locations.
Business Partners - This subsection contains information regarding business partner WAN, MAN, and LAN network connections to the DHS network.
- Templates and Forms
Protocols - A network protocol is an agreed-upon format for transmitting data between two devices and determines four primary rules for data transmission: the type of error checking to be used, data compression method (if any), how the sending device will indicate that it has finished sending a message, and how the receiving device will indicate that it has received a message.
- Templates and Forms
In addition, generic WAN, MAN, and LAN standards and policies, which pertain to the three subsections above, are listed below:
- Standards - TCP/IP is the DHS' standard network protocol
Policy Standards Guidelines
- Network Connectivity
- Video Conferencing - allows people to conduct a conference between two or more participants at different sites by using computer networks to transmit audio and video data. Multipoint video conferencing allows three or more participants to sit in a virtual conference room and interact as if sitting right next to one another.
- Physical Media and Mechanisms - the physical hardware and wiring that enable networks to function. The more popular cabling, or media, used in land-based networks include shielded and unshielded twisted pair, coaxial, and fiber-optic. Other types of physical mechanisms include switches, routers, hubs, and concentrators. Without such physical means, networks would merely be conceptual ideas. This section consists of the following areas:
- Cabling - Physical network cabling, or bounded media, enables the transmission of electronic signals from one network device to another. Such network transmission media include coaxial, shielded and unshielded twisted-pair, and fiber-optic. Each has specialized characteristics applicable to different network types. The following chart shows similarities and differences in the cabling types listed above.
Generic cabling standards and policies, which pertain to these two subsections, follow:
|Coaxial Thin net||Less than Shielded Twisted-Pair||10 Mbps||185 m|
|Coaxial Thick net||Greater than Shielded Twisted-Pair, Less than Fiber||10 Mbps||500 m|
|Shielded Twisted-Pair (STP)||Greater than Unshielded Twisted-Pair, less than Thick net||16 - 500 Mbps||100 m|
|Unshielded Twisted-Pair (UTP)||Lowest||100 Mbps||100 m|
|Fiber-optic||Highest||100 Mbps||10s of Km|
In addition, generic cabling standards and policies, which pertain to these subsections, follow:
- Fiber Optics - This section contains all formal DHS standards and policies regarding fiber-optic network cabling used at DHS locations.
Generic physical media standards and policies, which pertain to these two subsections, follow:
- Hardware - Communication signals are broadcast to other computers and devices through physical hardware in networks. Such hardware operates at the physical, data link, and network layers of the OSI model. The following table shows the seven OSI layers. The rows highlighted in yellow indicate the layers used by network hardware.
This section consists of the following areas:
|7||Application Layer||Program-to-program communication.|
|6||Presentation Layer||Manages data representation conversions. For example, the Presentation Layer would be responsible for converting from EBCDIC to ASCII.|
|5||Session Layer||Responsible for establishing and maintaining communications channels. In practice, this layer is often combined with the Transport Layer.|
|4||Transport Layer||Responsible for end-to-end integrity of data transmission.|
|3||Network Layer||Routes data from one node to another.|
|2||Data Link Layer||Responsible for physical passing data from one node to another.|
|1||Physical Layer||Manages putting data onto the network media and taking the data off.|
Generic hardware standards and policies, which pertain to these six subsections, follow:
- Switches - This section contains all formal DHS standards and policies regarding network switches in use at DHS locations.
- Routers - This section contains all formal DHS standards and policies regarding network routers in use at DHS locations.
- Network Design
- Administrative Procedures - comprised of the formal actions necessary for connecting an individual to the network. The network division approves a connection only through a formal application procedure. Such procedures ensure a safer and more manageable network.
- Network Management - General network administrative/management procedures
Templates and Forms
- Data Transfers - formal standards and policies regarding the networking aspect of Data Exchanges at DHS.