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cell relay

Cell relay and frame relay are transmission techniques from the field of fast packetswitching. The International Telecommunication Union( ITU) defines a fixed-length transmission block for cell relay on the bit transmission layer of the OSI reference model.

The individual blocks can be identified by delimiters. Specifying very fast transmission paths in the megabit range(>33 Mbit/s), cell relay aims to provide fixed data packet sizes at defined intervals, as in TDM systems and in the LAN area( token bus or token ring). With frame relay data packets, too, an ATM data packet is assumed to have a routable destination address in each case.

Thus, the time slots of time division multiplexing (TDM) are replaced by cells, the destination address is added, and thus the advantages of a TDM system are combined with those of data packet switches. The data packet size is 53 bytes, consisting of 48 bytes of data and 5 bytes of additional information.

Cell relay frame

Cell relay frame

The implemented TDM technology makes Cell-Relay suitable for very fast LAN-LAN connections (e.g. FDDI) and host-host couplings as well as for real-time transmission ofvoice and video. The routing capability through inserted addresses makes terminal equipment multip oint capable or substitute path capable. A disadvantage for "real-time" operation is the time delays caused by the packet assembly/disassembly( PAD) process, so that speeds below 2.048 Mbit/s do not appear suitable for cell relay due to the resulting transmission delay.

It is important to note that the ITU-defined services for broadband ISDN do not consider ATM-based services until speeds exceed 33 Mbps, such as H.21 at 33 Mbps, H.22 at 45 Mbps, and H4x at 140 Mbps.

Cell relay is an asynchronous transmission. Standards based on cell relay technology are IEEE 802.6 Distributed Queue Dual Bus( DQDB) for metropolitan area networks( MAN) and ATM for B-ISDN.

Englisch: cell relay
Updated at: 22.04.2013
#Words: 297
Links: frame relay (FR), transmission, field, international telecommunication union (ITU), block
Translations: DE

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