Radio Planning Procedures and Guidelines for TCI Roll Out Project v1.0
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The OSS as any other network management system requires a packet data network to exchange data with the managed network elements (MSCs and BSCs) as well other systems required for efficient operation support. These systems may be work stations, printers, or X-terminals but also other types of management systems, e.g. to create a complete network alarm picture including also other parts than the purely OSS related. This packet data network is called the Data Communication Network (DCN) for the management solution.
The DCN is a network. Its task is to carry the O&M data for the management solution. Thus, to create a DCN for a GSM OSS solution is a task which must be considered seriously in order to provide a good total solution. It may be trivial in some cases; in many other it will require a thorough and structured preparation.
A structured preparation comprises the collection of the requirements and precautions, set by the managed GSM network and the OSS solution, as well as the specific circumstances that will occur in every customer case. This information shall be presented in a comprehensible way to facilitate the discussion and decision on an appropriate DCN solution.
Figure1The DCN cloud view
Creating the DCN is basically a matter of resolving the connectivity requirements, i.e. the logical connections required by the OSS solution, in an optimal way.
This requires knowledge of DCN related characteristics of the systems that shall be interconnected, i.e. OSS, MSC, BSC, work station, X terminal, X terminal server, printers, other nodes (e.g. HLR and IN-nodes), and other traffic nodes (e.g. GPRS) or management systems. Further, knowledge is required for all systems and transmission means used to build the DCN itself, i.e. X.25 switch, router, LAN hub and switch, modem/CSU/DSU, MSC/BSC, DXX, etc. These characteristics comprise network protocols as well as link interfaces.
The network protocols for OSS solutions today are X.25 for the OSS to nodes parts and TCP/IP for the part between OSS and workstations, X-terminals, other traffic nodes and management systems.
There are two basic network layer technologies involved in the DCN for GSM OSS, X.25 and TCP/IP. Both are packet routed/switched protocols and have their specific characteristics concerning addressing, routing, etc. The preferred routing protocol for TCP/IP (or, more precisely, IP) is OSPF. The X.25 switching procedure is depending on equipment vendor.
These switches or routers may be interconnected in different ways to achieve desired characteristics. Three basic structures (topologies) can be identified. The star is the simplest way to interconnect systems. One single router or switch is the central of the whole network. It is sufficient when the number of links and the total traffic is limited. See Figure 2.
A natural extension of the star is the tree, where a number of routers act as traffic concentrators. The tree can be extended to several layers. See Figure 3.
Figure 4Simple ring
The third basic structure is the ring. It has the advantage, that an alternate route is available if the primary route is broken. See Figure 4.
A high availability network may comprise one or two switches/routers on each site and at least two links connecting each switch/router to the other switches/routers, forming a ring or meshed topology. Combinations of tree and ring structures may be appropriate to meet the requirements for a specific OSS solution. Please see Appendix 1 for exiting topology and new NMC topology.
Link Capacity Requirements
The following table serves as a rule-of-thumb for usual bandwidths between the OSS and each managed MSC/BSC, as well as to other systems.
OSS - MSC64 kbpsValid also for remote MSC
OSS - BSC64 kbpsValid also for remote BSC
OSS - WS64 kbpsSee also X-terminal references.
OSS - XTS256 kbps 1 MbpsDepending on number of concurrent users;
XTS - XT256 kbpsMax using for X-terminal
OSS - printer64 kbpsMax using for printer
Required link capacities calculations can be based on the minimum end-to-end capacities. The primitive algorithm is to sum the capacities in each switch/router, starting from the peripheral systems or MSCs/BSCs and adding the capacities towards the OSS. Interfaces should be select out of the preferred set if no strong reasons for other alternatives exist.
One effort to enable efficient handling of transmission operation and support is to limit the number of different link interfaces and capacities to a small-preferred set. Figure 5.
The preferred set of interfaces comprises.
V.36 300 bps - 2 Mbps
G.703 E064 kbps (co- or contradirectional)
G.703 E12 Mbps (75 ohm unbalanced or 120 ohm balanced)
G.703 T11,5 Mbps (100 ohm)
10Base-T10 Mbps (nominal), RJ45 UTP, Ethernet
100Base-T100 Mbps (nominal) Rj45 UTP, Ethernet
This interface set enables the connection of OSS solution and all network elements to the most common transmission possibilities in the GSM markets. If possible, the O&M connection for the OSS and the MSCs/BSCs should be ordered with fitting interfaces out of this set for the O&M connection (HIS, MSC/BSC and ETC respectively). See Figure 6 B and C.
To connect a MSC/BSC (if configured for V.36) or the OSS to a G.703 E0 interface, a DSU (Data Service Unit - modem) is required.
IP routers and X.25 switches can be configured to fit all the preferred interfaces, the corresponding interface units must of course be ordered.
64 kbps links between sites with BSC, remote BSC or MSC can be achieved by:
ETC to ETC (if time slot 16 is free) connections, the interface is V.36 with a special cabling, see Figure 66 B.
PCD-D to PCD-D (semi permanent path as used for SS7 between signalling terminals - ST), the interface is G.703 E0, see Figure 66 C.
External means, i.e. fixed or dial-up links outside the MSC/BSC network, see Figure 66 D.
Transmission for BSC and MSC payload (GSM traffic) is typically (n*2 Mbps), provided over G.703 E1 interfaces. For DCN purposes, an additional 2 Mbps should be assigned between those sites where the higher capacity is appropriate, see Figure 66 E.
It is desirable to cooperate with the transmission planning for the radio network in order to achieve a simple and clean transmission solution.
Between sites with O&M equipment (remote WS, X-terminals, printers) but without an MSC or BSC, and the OSS site, transmission must be provided by external means.
Within a site, a LAN is often better to connect the systems than serial links. See Figure 6 F. A 100Base-T LAN hub is the default choice for most sites, a 100Base-T LAN switch may be appropriate to control traffic paths better in central network management sites. If the LAN connects equipment with different power circuits, galvanic isolation over 100Base-FL (fibre link) is a possible solution.
For completeness, Figure 66 A indicates cables as connection possibility over limited distances.
Figure 6Basic link alternatives
Below follows a couple of examples to illustrate the practical usage of the different link alternatives. The figures depict only a small sample of how the link alternatives may be used. In real cases many other combinations will often be appropriate.
Figure 7 shows a very simple configuration, using alternatives A and F.
Figure 7Basic link usage example 1
In Figure 8, the most common usage of the alternative B, the connection of a remote BSC, is illustrated.
Figure 8Basic link usage example 2
Figure 9 illustrates a basic usage of routers for X.25 over IP. As links, alternatives D/E and B are used. Note that the router on the OSS site in this example is not connected to the LAN. This is because the LAN connects all TCP/IP based equipment. The routers are solely used to transport X.25 traffic (over IP).
Figure 9Basic link usage example 3
Figure 10 adds the aspect of using the routers also for TCP/IP based systems.
Figure 10Basic link usage example 4
In Figure 11, finally, an example with link alternative C is illustrated. Please note that the PCDD paths also may be used in a router solution if the routers are equipped with the corresponding interfaces.
Figure 11Basic link usage example 5
Modem in this text is the function of adapting communicating systems to link interfaces (external as well as internal) when they do not fit. Thus, if the responsible link provider installs a G.703 interface (or something else), a modem is necessary to connect the link to the system. The device is often called a CSU or DSU. This adaptation function is required for all systems that lack the necessary interface.
A rule of thumb for MSC/BSCs and OSS may be:
V.36 - no modem required (it is installed by the link provider), see Figure 12 A.
G.703 - modem (CSU or DSU) required for equipment with V.36 interfaces, see Figure 12 B.
other - modem typically required to adapt to V.36 or G.703
Figure 12Modems and Link provider responsibilities
Modems may also be used to provide galvanic separation of equipment, when the power is supplied over separate circuits, e.g. in different parts of a large