ACCESS NETWORKS

ACCESS NETWORK

ACCESS NETWORKS

• The ‘last leg’ of a network that runs frm the service provider’s facility to the home or business is called the access network.

• Types of services: – plain old telephony service (POTS)

– broadcast analog video over the cable network• List of services- Internet access, distance learning,

video on demand and high definition TV.

CLASSIFICATION OF ACCESS NETWORKS

ACCESS NETWORK CLASSIFICATION

• based on service– Broadcast– Switched

• bandwidth requirementDedicated - feeder network can allot different

bandwidth to different NIUShared - total bandwidth is shared by all the NIU

NETWORK ARCHITECTURE OVERVIEW

• Access network consists of a hub, Remote Nodes (RNs), Network Interface Units (NIUs)

• Hub is the central office- serves several homes through NIU and sometimes thro RN

• Feeder network - network between hub and RN-

• Distribution network - network between RN and NIU-

Architecture of an access network

NETWORK ARCHITECTURE OVERVIEW (contd..)

• In a broadcast network, an RN sends all the data it receives from the feeder network to all its NIUs.

• In a switched network, RN processes the data coming in and sends different data to different NIUs.

• Broadcast network “intelligence” is in NIU whereas it is in the network in the switched network case.

TODAY’S ACCESS NETWORKTelecom Network

TODAY’S ACCESS NETWORKCATV network

TODAY’S ACCESS NETWORK

• Telephone Network-– point-to-point copper wires (twisted pair cables) from the

central office to individual subscribers• Cable network

– head end broadcasts signals over fiber to the remote node which then distributes to subscribers thro coaxial cable drops.

– Head end to RN– sub carrier multiplexing on a linear laser.

– From RN coaxial cables are used.

TODAY’S ACCESS NETWORK

• A RN serves- 500 to 2000 homes. Such a network is called HFC (hybrid fiber coax)

• Cable bandwidth-50 to 500 MHz• Cable carries AM-VSB signals placed 6MHz

apart in the American NTSC• Cable network- provides large bandwidth but

uni-directional, no switching and simple management.

ACCESS NETWORK

• Integrated Services Digital Network (ISDN)--128 kbps bandwidth over twisted pair

• Asymmetric Digital Subscriber Loop (ADSL)– twisted pair with more bandwidth of the order of few Mbps

ACCESS NETWORK (contd..)• New approach is to use satellites. Offer more bandwidth , but

spatial reuse of bandwidth is limited.• Wireless access– limited bandwidth and range but provide

mobility• Multichannel Multipoint distribution service (MMDS)– a

terrestrial line-of-sight system with 336 MHz channels in the 2-3 GHz band.

• Local Multipoint Distribution Service (LMDS)– a non LOS system with 28 GHz of 1.3 GHz b/w

• Two main architectures– HFC and FTTC

Enhanced HFC (Hybrid Fiber Coax)

OPTICAL ACCESS NETWORK ARCHITECTURE

• PONs (passive optical network)– uses passive components such as star coupler, static wavelength router

• Reliability, ease of maintenance, network need not be powered

• Transparent to bit rates and modulation formats and can be upgraded without any change in the network

Broadcast and select TPON

Broadcast and select WDM PON

•CO equipement have WDM array of transmitter•Each ONU have electronics that runs at the rate it receives•No. of ONUs limited by splitting ratio of coupler

WRPON(wavelength routing PON)

•Allows pt. to pt. dedicated service•Solves splitting loss problem•Not economical (requires expensive laser at CO and at ONU)

RITENET WRPON ARCHITECTURE

•Uses tunable laser at CO•A frame sent to ONU consists of data part and return traffic part where no data is sent•Modulator is used at the ONU to modulate the return traffic part

LARNET WRPON ARCHITECTURE

Spectral slicing