Transportand Metro Networks

Transcription

1 Transportand Metro Networks To automatically and easily route high-speed traffic in metro and transport networks optical technologies are necessary. Use of optical circuits allows routing of traffic flows along desired paths, with a limited degree of circuits reconfiguration which is suited to the need of management with low dynamics (i.e. routes change very infrequently). Routing techniques in optical networks are well-suited with the most effective Internet technologies and with the great capacity needed to carry information over long distances. This allowed (in Italy in 1990) network simplification, once much more complex, into only 2 layers: optical layer based on the use of different wavelengths, in practice the level of transmission on which actual data flows. IP layer, consisting of data packets which can efficiently transport any type of information (full integration of services). 1 53

2 EvolutionofTransportNetwork 2 Modern transport networks assume a very simple structure, with an upper layer, which integrates all the services in the form of IP packets, and a lower layerthat provides the necessary transport resources (circuits); this second layer is also capable of providing circuit services directly to the large clients who request them (typically they are large companies and other operators that do not have their own infrastructure). New transport network oftelecom Italia (2011) 54

3 Access Network 3 Provides the connection between the customer s telephone and the local exchange Ordinary customers use two wires, a pair, as a subscriber loop Business customers need higher capacity optical fibers Subscriber cables contain many pairs that are shielded with common aluminum foil and plastic shield In urban areas cables dug into the ground, may be very large (hundreds of pairs) In suburban or country areas, overhead cables are often a more economical solution Example of a local-access network 55

4 Access Network Types 4 The access network realizes the connections between the Central Office (CO)*, which is the telephone node closest to the customer. It is possible, at least in principle, to make the connections according to different network topologies. Topologies also depend on the type of transmission medium which is employed. Transmission can be based on the use of cables (physical carriers) and on the use of radio waves (radio carriers). Wired media are then classified according to the type of support, metallic or dielectric: we have copper pairs (twisted-pair) and coaxial metal lines, both suitable to carry signals in electrical form, while the transmission medium (dielectric) suitable for conveying signals to a distance in the form of light, is the optical fiber. *Nellaterminologia impiegata da Telecom Italia per le proprie centrali locali si parla di Stadio di Linea (SL). 56

5 Distribution Frames 5 All subscriber lines are wired to the Main Distribution Frame (MDF) At the telephone exchange (Central Office) end the wires are terminated on a distribution frame, which provides a point where cross-connections can be made and replaced anytime it is needed. The distribution frame has two sets of termination points, one set for the permanent external cable termination, and another for the permanent connection to interface circuits. (incumbent local exchange carrier) Role of the Main Distribution Frame 57

6 Access Network in Italy 1 Primary network: connects a patch panel (permutatore) called Main Distribution Frame (MDF) located in the central office (CO) to a SubloopDistribution Frame (SDF) located in a street cabinet (armadio ripartilinea) 6 Secondary network: connects the SDF to the distribution box located at a building (chiostrina o distributore) Termination line (raccordoditerminazione): from the distribution box up to the customers dwellings (unità abitative). (MDF) armadio ripartilinea SDF Central Office Stadio di Linea RIF: P. Impiglia etal., La rete in rame di Telecom Italia: caratteristiche e potenzialità per lo sviluppo delle tecnologie xdsl, Notiziario Tecnico Telecom Italia, Anno 13 n. 1 giugno 2004, pp

7 Access Network in Italy 2 7 Telecom Italia fixed access network (year 2008): 104 million kilometers of wire pairs (doppini) 575,000 km of cables (half brought on by about 9 million poles air network infrastructure, half grounded) 3.9 million outdoor distributors, 1.5 million indoor distributors 140,000 outdoor cabinets 10,400 main distribution frames SGU: Stadio di Gruppo Urbano SL: Stadio di Linea DSLAM: Digital Subscriber Line Access Multiplexer 59

8 MainDistributionFrame 8 60

9 Street Cabinetsand Distributors 9 distributore armadietto distributore 61

10 Cablesin the accessnetwork ofti 10 Primary network (from MDF to SDF): laid cables containing 1200 or 2400 pairs; Street cabinet: in input cables with 400 pairs; Capacity of a street cabinet: up to 1200 pairs; input 600 pairs (from primary network); output 600 pairs (to secondary network); Telecom Italy generally in the street cabinet terminates 400 pairs incoming from the primary network and 600 pairs outgoing to the secondary; The primary network cables can be: 400, 800, 1200, 1600 and 2400 pairs. Examples: cables with 2400 pairs 62

11 Cablearea (areacavo) pairs per cable 400 pairs into the street cabinet 200 pairs out, going towards the distributors 63

12 Cumulative distributionoflocalloop 12 La distribuzione cumulativa della lunghezza del collegamento di utente in rame è diversa nei vari paesi. La rete italiana è mediamente più corta di quella degli altri paesi. 64

13 Network Management 13 Efficientnetwork management is key in helping a network operator improve services and make them more competitive. A system that take care of control and supervisory functions in a TLC network is called Operations Support System(OSS). The Network OSS is in charge of the O&M (Operations & Maintenance) function, needed to configure and provision network nodes, to monitor network health and performance. Some of the factors which impact the configuration are: number of subscribers, peakhour call rate, nature of services, etc. Operations functions include: subscriber management (e.g. manage subscriptions, collect charging data) traffic monitoring and network control (needed to minimize the risk of network overload by switching traffic away from overloaded connections) logging of various network nodes actions. Maintenance functions include: continuous measure of parameters, such as Bit Error Rate (BER), loss of synchronization, etc. network alarm monitoring (when a fault occurs, take corrective actions), network statistics collection. There are several Management Protocols, among them: SNMP developed by the TCP/IP (ARPANET) community CMIP developed by the ISO/OSI community TMN (Telecommunication Management Network) developed by the ITU. 65

14 SNMP 14 Simple Network Management Protocol (SNMP) is a network protocol belonging to the suite of protocols defined by the IETF (Internet Engineering Task Force). SNMP operates at layer 7 (application) of the OSI model and enables the configuration, management and monitoring of network devices (both switching nodes and user terminal nodes), regarding all aspects that require administration and management actions. SNMP management architecture Legend: SMI (structure of management information) NOC (network operations center) MIB (management information base) 66

15 TMN 1 ITU-T defined a common management concept, TMN (Telecommunications Management Network) to cover all aspects needed to centralize O&M in a multivendor environment. 15 TMN takes care of FCAPS functions, i.e., the following actions: Fault management: collect alarm information and take corrective action; detect system malfunction and carry out measurements to locate faults Configuration management: change configuration of network elements; disconnect subscriber who did not paid the bill Accounting: set accounting functions in network elements Performance: measure network performance to detect faults and bottlenecks in advance Security: detect security threats, i.e. collect data about users of a corporate network frequently providing wrong security codes (in order to detect hackers). TMN specifications: Physical architecture: what systems are needed in TMN and how they are interconnected Interface protocols: structure and types of messages to exchange information between network elements and management systems Management functions: what functions in the network elements the network management system should be able to access Information model: for each different system in the network, how each manageable function is described in management messages. 67

16 TMN 2 16 TMN is separate from the actual telecommunications network, though network systems must provide the management interfaces and functions that they are able to perform. The physical architecture of TMN contains these elements: Operations system(os) for centralized network management Data communications network (DCN) for management data transfer Mediation devices(md) to adapt proprietary management interfaces to Q3 interfaces under standardization Management functions integrated in the network elements (NEs) of the telecommunications network. 68

17 DCN 17 In TMN, a fault on a transmission link may disturb management messages that are necessary for fault localization. Therefore, the DCN should be designed to be as independent as possible from the network that transmits user data. According to the TMN concept, the transmission of management data between management workstations and network elements is separated from the transmission of user data. The transportation network of management data is the DCN (Data Communications Network). Data Communications Network (DCN) 69