- Email: [email protected]
Future access network architectures
Computer Communications 22 (1999) 1638–1640 www.elsevier.com/locate/comcom
Future access network architectures H. Stewart* Italtel Central Research Labs, 20019 Settimo Milanese, Milan, Italy
The ACTS (Advanced Communications Technologies and Services) programme is the focus of the European Union’s research effort in advanced communications. Its aim is to support the early deployment and effective use of advanced communication services. Experts from all over Europe are working together on around 200 projects covering a wide range of novel technologies, applications and services. A group of projects has considered the architectures for future access networks and, in a recent guideline, have been reviewed the future architectures for three contrasting access environments: • mobile access networks; • fixed access networks; • wireless business networks.
1. Mobile access networks One of the ACTS programme’s technical themes is the development of the next generation of mobile communications systems—the so-called Universal Mobile Communications System (UMTS). This will not only offer high speed mobile connections but also an approach to integrating fixed and mobile services. The generic UMTS architecture is shown below.
The individual network elements are • MT: The Mobile Terminal, i.e. the customer’s handset. • BTS: The Base Transceiver Station providing radio coverage of a particular area. • CSS: The Cell Site Switch providing control and switching at the access network level. • LE: The Local Exchange providing switching at the core network level. • MSCP: The Mobility Server Control Point handling the users’ mobility (Location Update and Paging). It can be located in the access and/or core network. • MSDP: The Mobility Server Data Point providing a Distributed Database (DDB) for mobility management. The MSDP can also be located in the access and/or core network. This generic UMTS architecture allows a variety of network arrangements with functionality located where it is most appropriate. To allow this, the call set-up and mobility management procedures have been defined in terms of messages exchanged between functions rather than network nodes. This gives mobile operators the flexibility to deploy network structures tailored to the expected traffic and signalling characteristics of a particular environment. In densely populated areas, where heavy traffic and high handover rates are expected, the MSCP node would be deployed in both the access and the core network. This provides efficient mobility management since most of the signalling overhead is handled at the access level and reduces the load on the Local Exchange. In a suburban or rural area where relatively light traffic is expected, the Local Exchange can handle the signalling load. The CSS and access network MSCP elements are not required and the BTSs can be connected directly to the LE.
2. Fixed access networks
* Corresponding author. Tel. 1 39-2-4388-8030. E-mail address: [email protected] (H. Stewart)
In the future, future-fixed access networks will have to distribute a range of narrowband, broadband and interactive services. The ability of Passive Optical Networks (PONs) to handle these tasks has been investigated in detail within the
0140-3664/99/$ - see front matter q 1999 Elsevier Science B.V. All rights reserved. PII: S0140-366 4(99)00144-9
H. Stewart / Computer Communications 22 (1999) 1638–1640
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ACTS programme. The generic PON architecture allows for a range of splitting factors and transport techniques and appropriate combinations can be selected to meet the specific requirements of an access network (e.g. coverage area, bandwidth, traffic capacity). Three variants are of particular interest: • TPONs (Telephony over PONs) meet the requirements of narrow band services using a time division multiplexing technique to carry the signals for a large number of customers on a single PONs with a high splitting factor. • APONs (ATM-based PONs), with splitting factors up to 32 and a reach of 10–20 km, can deliver a mix of narrow and broadband services using FTTC (Fibre To The Curb) or FTTB (Fibre To The Building) configurations. • SUPER PONs offer wider ranges (,100 km) and higher splitting factors (,2000) by integrating optical amplifiers in the PON. They allow operators to cut cost by bypassing conventional local exchanges and reducing the number of switching nodes in their networks. Although, still optically transparent SUPER PONs are not really passive, since optical amplifiers are integrated in the network.
The diagram shows a SUPER PON with up to 2048 Optical Network Units (ONU) connected to one-line termination (SPOLT) in the access node. The ONU contains a SPONT that terminates the optical network and one or more LIMs (Line Interface Module) that provide the interface to the required services. In the case of FTTB/C, the LIM terminates the twisted pair in the last drop. Time Division Multiplexing (TDM) is used to deliver a bit rate of 2.5 Gbit/s downstream to the SPONT and a Time Division Multiple Access (TDMA) protocol is used to share the 311 Mbit/s upstream bit rate. An ATM cross-connect concentrates the traffic from various PONs and grooms the narrowband and the broadband services. 3. Connecting wireless business networks Wireless customer premises networks, providing broadband business services, will become increasingly popular in the future.
The figure shows a typical scenario based on wireless ATM access with pico/micro cells within the buildings and the base stations served by a generic workgroup switch.
These workgroup switches are interconnected via a Customer Premises Backbone Network. Four principal interfaces can be identified: • the radio interface between the mobile terminals and the base stations; • the base-station to workgroup switch interface; • the workgroup switch to Customer Premises Network interface; • the interface between Customer Premises Network and Corporate Network. A Wide Area Network (public or private) is needed to link the business’ individual sites. In the medium term ( . 5 years) the principal technology solutions for this network are SMDS, ATM and SDH: • SMDS is protocol-translation limited to data throughputs up to about 155 Mbit/s, but offers a true connectionless service. • ATM is a software intensive network platform, but can
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H. Stewart / Computer Communications 22 (1999) 1638–1640
carry real-time and data services in an integrated manner. There are still circuit control and traffic policing problems to be fully sorted out, and protocol conversions are needed to support legacy network platforms. • SDH is effectively a managed large bandwidth pipe offering the same capabilities as a leased line. It is of value when data has already been multiplexed by the customer premises network and does not need demultiplexing/switching/multiplexing within the WAN. In the longer term photonic multi-channel and switching techniques offer great potential. They will
allow the same fibre route to be used for different applications and will add re-routing and protection strategies for these applications. 4. Conclusions The three architectures presented illustrate the wide range of advanced communications technology being developed within the ACTS programme and demonstrate how that technology can be used to meet the needs of strongly contrasting access network environments.
Future access network architectures H. Stewart* Italtel Central Research Labs, 20019 Settimo Milanese, Milan, Italy
The ACTS (Advanced Communications Technologies and Services) programme is the focus of the European Union’s research effort in advanced communications. Its aim is to support the early deployment and effective use of advanced communication services. Experts from all over Europe are working together on around 200 projects covering a wide range of novel technologies, applications and services. A group of projects has considered the architectures for future access networks and, in a recent guideline, have been reviewed the future architectures for three contrasting access environments: • mobile access networks; • fixed access networks; • wireless business networks.
1. Mobile access networks One of the ACTS programme’s technical themes is the development of the next generation of mobile communications systems—the so-called Universal Mobile Communications System (UMTS). This will not only offer high speed mobile connections but also an approach to integrating fixed and mobile services. The generic UMTS architecture is shown below.
The individual network elements are • MT: The Mobile Terminal, i.e. the customer’s handset. • BTS: The Base Transceiver Station providing radio coverage of a particular area. • CSS: The Cell Site Switch providing control and switching at the access network level. • LE: The Local Exchange providing switching at the core network level. • MSCP: The Mobility Server Control Point handling the users’ mobility (Location Update and Paging). It can be located in the access and/or core network. • MSDP: The Mobility Server Data Point providing a Distributed Database (DDB) for mobility management. The MSDP can also be located in the access and/or core network. This generic UMTS architecture allows a variety of network arrangements with functionality located where it is most appropriate. To allow this, the call set-up and mobility management procedures have been defined in terms of messages exchanged between functions rather than network nodes. This gives mobile operators the flexibility to deploy network structures tailored to the expected traffic and signalling characteristics of a particular environment. In densely populated areas, where heavy traffic and high handover rates are expected, the MSCP node would be deployed in both the access and the core network. This provides efficient mobility management since most of the signalling overhead is handled at the access level and reduces the load on the Local Exchange. In a suburban or rural area where relatively light traffic is expected, the Local Exchange can handle the signalling load. The CSS and access network MSCP elements are not required and the BTSs can be connected directly to the LE.
2. Fixed access networks
* Corresponding author. Tel. 1 39-2-4388-8030. E-mail address: [email protected] (H. Stewart)
In the future, future-fixed access networks will have to distribute a range of narrowband, broadband and interactive services. The ability of Passive Optical Networks (PONs) to handle these tasks has been investigated in detail within the
0140-3664/99/$ - see front matter q 1999 Elsevier Science B.V. All rights reserved. PII: S0140-366 4(99)00144-9
H. Stewart / Computer Communications 22 (1999) 1638–1640
1639
ACTS programme. The generic PON architecture allows for a range of splitting factors and transport techniques and appropriate combinations can be selected to meet the specific requirements of an access network (e.g. coverage area, bandwidth, traffic capacity). Three variants are of particular interest: • TPONs (Telephony over PONs) meet the requirements of narrow band services using a time division multiplexing technique to carry the signals for a large number of customers on a single PONs with a high splitting factor. • APONs (ATM-based PONs), with splitting factors up to 32 and a reach of 10–20 km, can deliver a mix of narrow and broadband services using FTTC (Fibre To The Curb) or FTTB (Fibre To The Building) configurations. • SUPER PONs offer wider ranges (,100 km) and higher splitting factors (,2000) by integrating optical amplifiers in the PON. They allow operators to cut cost by bypassing conventional local exchanges and reducing the number of switching nodes in their networks. Although, still optically transparent SUPER PONs are not really passive, since optical amplifiers are integrated in the network.
The diagram shows a SUPER PON with up to 2048 Optical Network Units (ONU) connected to one-line termination (SPOLT) in the access node. The ONU contains a SPONT that terminates the optical network and one or more LIMs (Line Interface Module) that provide the interface to the required services. In the case of FTTB/C, the LIM terminates the twisted pair in the last drop. Time Division Multiplexing (TDM) is used to deliver a bit rate of 2.5 Gbit/s downstream to the SPONT and a Time Division Multiple Access (TDMA) protocol is used to share the 311 Mbit/s upstream bit rate. An ATM cross-connect concentrates the traffic from various PONs and grooms the narrowband and the broadband services. 3. Connecting wireless business networks Wireless customer premises networks, providing broadband business services, will become increasingly popular in the future.
The figure shows a typical scenario based on wireless ATM access with pico/micro cells within the buildings and the base stations served by a generic workgroup switch.
These workgroup switches are interconnected via a Customer Premises Backbone Network. Four principal interfaces can be identified: • the radio interface between the mobile terminals and the base stations; • the base-station to workgroup switch interface; • the workgroup switch to Customer Premises Network interface; • the interface between Customer Premises Network and Corporate Network. A Wide Area Network (public or private) is needed to link the business’ individual sites. In the medium term ( . 5 years) the principal technology solutions for this network are SMDS, ATM and SDH: • SMDS is protocol-translation limited to data throughputs up to about 155 Mbit/s, but offers a true connectionless service. • ATM is a software intensive network platform, but can
1640
H. Stewart / Computer Communications 22 (1999) 1638–1640
carry real-time and data services in an integrated manner. There are still circuit control and traffic policing problems to be fully sorted out, and protocol conversions are needed to support legacy network platforms. • SDH is effectively a managed large bandwidth pipe offering the same capabilities as a leased line. It is of value when data has already been multiplexed by the customer premises network and does not need demultiplexing/switching/multiplexing within the WAN. In the longer term photonic multi-channel and switching techniques offer great potential. They will
allow the same fibre route to be used for different applications and will add re-routing and protection strategies for these applications. 4. Conclusions The three architectures presented illustrate the wide range of advanced communications technology being developed within the ACTS programme and demonstrate how that technology can be used to meet the needs of strongly contrasting access network environments.