**1. Introduction**

Depending on how far the glass fiber extends into the access network, one speaks of "Fiber to the Curb" (FTTC), "Fiber to the Building" (FTTB), "Fiber to the Home" (FTTH), "Fiber to the Desk" (FTTD). As an alternative, DSL technology, outdoor DSLAMs and VDSL with vectoring, contribute data transmission rates of up to 200 Mbit/s for broadband distribution to the subscriber, whereby these copper-based connection technologies have reached now their capacity limits [1].

As shown in **Figure 1**, the international optical network is essentially divided into three levels. Based on the international level of the global area network with

**Figure 1.** *Worldwide optical network structure.*

very high data rates of 10–100 Gb/s, branches go to the level of regional networks with data rates of 1–10 Gb/s and from there to the third level of the customer network. There we speak of data rates of 100 Mb/s to 10 Gb/s. Based on this core network, the wireless networks (4G, 5G) to supply the mobile devices in the area with up to 1Gb/s are realized [2].

The mobile networks with LTE or 5G and the cable television networks also use this term for the part of their networks that includes the subscriber connections and offers access to higher network levels. However, radio technology can only be seen as an alternative to fiber optic infrastructure in rural areas, as little cabling needs to be installed. Unfortunately, the bandwidth of these radio networks decreases quadratic by the distance to the radio base station, so that the effectively transferable data rate will fall down strictly in rural areas. The cable television networks are currently based on DOCSYS 3.1 and already use fiber optic connections as FTTB variants and are therefore to be seen as fiber optic technology despite different software and hardware configurations. Currently, most of the optical fiber optic connections are made in the FTTB area [3, 4].

At a connection point in the basement of the building, the fiber optic cable coming from the outside is connected to a router or switch. Starting from there, the data is transferred to the different areas and floors of the office building or the apartment block either via fiber optics, polymer fibers or electrical Ethernet cables (e.g. CAT 7). This is referred as network levels 3 and 4, before branching from the different floors to the individual offices or apartments via switches. The other cabling in the apartments and offices is called network level 5. Here, in turn, there are appropriate routers for the apartments or switches for the offices in order to distribute the data in the individual rooms. Levels 3–5 are nowadays mainly connected via optical cables and will be analyzed in this chapter in a differentiated manner and discussed with examples. This also includes the use of additional technologies such as WiFi, Zigbee, Bluetooth or dLAN/powerline [5] in the home and office [6–8].

#### **2. Distributed network structures**

Computer networks in apartments, small buildings and office environments (Small Office/Home Office - SoHo) are typical fields of application for Ethernetbased communication networks [9]. Local services such as network printers or file shares are implemented on these network structures, or DSL and cable providers offer their customers IP-based services such as Internet access, IP-TV or VoIP (Voice over IP).

For the implementation of Ethernet/POF-based SoHo networks, different areas must be conceptually considered (e.g. laying cables, selection and structuring of electronic components), implemented and connected to the Internet using suitable devices and processes [10–13].

Based on the sub-areas to be implemented for the realization of a network in the desired SoHo target market, the protocols and standards to be considered are so diverse that the existing orientations as well as the derived test methods and devices appear unsuitable.

For the design of a general and expandable structure in the SoHo environment, an abstraction model was developed - which is suitable as a basis for orientation for the implementation of network structures, service models and test methods in the SoHo environment.

In the telecommunication networks a special scheme is applied to distribute the data from the source/headend to the customer. The distribution is divided into five levels (see **Table 1** and **Figure 2**):


**Table 1.**

*Network levels in the telecommunication network.*

#### **Figure 2.**

*Distribution of the telecommunications transmission path from the provider via the curb distribution to the building and in the building to the flats.*

Level 1: Content/data production.

These include program providers such as Premiere, the public and private broadcasting stations and also Cloud applications.

Level 2: Operation of head-end stations.

The internet data is received via these stations and then passed on. In the case of the TV cable network, one of these head-end stations is always required, as this is where the signals from the satellite are converted and processed for cable reception, among other things. The reception technology in the cable networks has been completely converted to the digital standard since DOCSYS 3.1 [14] and is therefore at the same level as the telecommunications networks. Typical data rates are between 10 Gb/s up to 100Gb/s.

Level 3: Street distributor/curb.

This refers to the network areas that were relocated from the head-end stations to the residential areas (FTTC-fiber to the curb). Typical data rates are between 1 Gb/s up to 10Gb/s.

Level 4: house distributor.

Customers can only be reached via the fourth network level into the houses (FTTB fiber to the building). Many small operators are exclusively active here, the number of which is estimated at several thousand. In order to offer new products and services, the operator must be able to feed them into the network. This requires an adaptation of several network levels, which, however, often turns out to be very difficult due to the large number of responsible companies at the various levels. Only in the rarest of

cases does an operator have several levels, which makes the actual structure difficult to understand for the end user. Typical data rates are between 100 Mb/s up to 10Gb/s.

Level 5: Flat distribution.

The network connection directly with the customer is now being rolled out worldwide via optical fibers, since only these technologies enable a correspondingly high bandwidth. This level is between router and telephone/Internet devices such as smartphones, tablets or IP TV realized. Typical data rates are between 10 Mb/s up to 1Gb/s (FTTH - fiber to the home).

### **3. Open building interconnection reference model - OBI**

Based on the different orientations of the four identified work areas (building blocks) (see **Figure 3**) as well as the multitude of standards and guidelines to be taken into account, which data center operators are familiar with - but not known to house and apartment owners in the targeted SoHo target market - the following situation arises:

A model is required that includes the four identified work areas - defines interfaces and thus offers orientation for further work [15, 16]. All areas relevant for the conception, construction and operation of SoHo networks and in-house communication can be structured, edited and tested in a reproducible manner [17, 18].

Based on the basic services defined within the OBI model, the conception of test scenarios was started. For this it is necessary to classify the network structure that is likely to be encountered. Starting from a transfer point (e.g. DSL [19], FTTH, DOCSIS [20] that connects to the public wide area data network (WAN) [18], SoHo routers are used that provide services for the internal network that are defined using an operating system (firmware) (LAN) (e.g. switch, WLAN, FXS (Foreign eXchange Station), FITH (Fiber In The Home)). The owner of the SoHo network has no influence on the implementation of the WAN area, apart from the choice of provider and product. The situation is different with the implementation of the LAN structure. Which implementation is used primarily defines the intended use of the LAN. The router already mentioned shows the following structure (**Figure 4**) taking into account its functions (**Figure 5**):

**Figure 3.** *O B I - open building reference model.*

#### **Figure 4.**

*Functional overview of a SoHo router.*


#### **Figure 5.**

*Network structure in the SoHo-environment.*

Due to the owner's preference, all technical options (e.g., WLAN, fiber optic, POF, Cat [5–7], etc.) as well as the associated active and passive components are available for a structure.

If the SoHo network is viewed from the point of view of the services operated on it, the guarantee of the correct functioning and the quality of service by the provider of the WAN connection ends in the SoHo router which is depicted in **Figure 6**. It is assumed here that the provider of the WAN connection terminates the VoIP traffic on a SIP registrar [21] integrated in the SoHo router. All local end devices contact this SIP registrar, which in turn forwards the VoIP traffic to the telephone server of the WAN provider for termination using a SIP trunk.

The configurations, implementations and functions in the LAN area for mapping the functional correctness and quality of service for the defined basic services (network access, VoIP, WLAN) are part of the current work. For the investigation of the bandwidth-prioritized VoIP, a test scenario specially adapted to SoHo environments was designed.

In order to obtain reproducible results, the dependency on external disturbances (on the WAN side) must be excluded, which is why a local VoIP registrar was configured (codecs: g.711u [22], h264 [23]) and used. The SIP video telephones use for the VoIP within the LAN - different transmission media, e.g., Cat (5/6/7), POF and WLAN and different combinations and configurations of the active and passive components. The ITU standards for PESQ [24] and the E-model [25] are used for objective assessment of the voice quality of VoIP calls.

Both test methods take into account all parameters involved in the transmission (e.g., noise, SNR, latencies, jitter, echoes, packet losses, etc.) as well as their mutual dependency. For the examination, a defined language file is transmitted (see **Figure 7**- red/

**Figure 6.**

*SoHo - network topology for VoIP test.*

**Figure 7.**

reduced) and compared with the original file (see **Figure 7**- blue/reference). The result is a numerical score value (PESQ-MOS factor for PESQ, R factor for E-model) for the comparison tables.

After calibration of the individual transmission links and selection of suitable test parameters and routines, the configurable parameters of the active components (e.g., QoS, VLAN, IPv6) can be examined in the context of "Influence on the quality of VoIP transmissions in SoHo environments". Statements can also be made about the influence of the codecs used (e.g., H264, G711, G722 [26]) or the number of maximum SIP connections in the context of the bandwidth limit of the existing network topology. By using the VoIP registrar function in commercially available SoHo routers that are already available on the market (today already with all major Internet providers), the test routines can be run through - without measurement setups and configurations - and thus provide comparable results. By using the OBI model, communication and network structures in SoHo environments, especially for technology-supported care assistance systems [27] with the personal data that arise there, can be referenced and verified.
