MT92220 Zarlink Semiconductor, MT92220 Datasheet - Page 211

• Manufacturer Part Number: MT92220
• Description: 1023 Channel Voice Over IP/AAL2 Processor
• Manufacturer: Zarlink Semiconductor

Data Sheet
MT92220
UTOPIA (U niversal T est and OP erations I nterface for A TM ): The electrical interface on which ATM cells are
passed.
UUI (U ser-to- U ser I ndication ): The UUI is a 5-bit field contained within the AAL2 header that is used to indicate the
type of an AAL2 mini-packet. When indicating voice data, the UUI is often used as a 4-bit sequence number.
VC (V irtual C ircuit ): VC define a point-to-point connection between two nodes in a network. A single ATM cell
carries data that belongs to a single VC.
VCI (V irtual C hannel I dentifier ): This is the label given to an ATM VC to identify it and determine its destination. The
VCI is a 16-bit number that is included in the header of an ATM cell.
VPI (V irtual P ath I dentifier ): A virtual path determines the way an ATM cell should be routed. The VPI is an 8-bit (in
UNI) or 12-bit (in NNI) number that is included in the header of an ATM cell.
WATOMIC: An uninterruptable Write operation.
Terms Specific to This Specification
AAL2 Mini-Packet: A mini-packet contained within one or many AAL2 cells. AAL2 mini-packets contain 3 bytes of
overhead (including CID, LI, UUI and HEC) and from 1 to 64 bytes of payload. Because of this 64-byte maximum,
they can straddle many cells.
Bearer : A unidirectional xxPCM stream. In PCM A-law or u-law, a single bearer will have a bandwidth of 64 kbps;
this bandwidth will be reduced in ADPCM. In this device, a single PCM channel may interleave many bearers.
Channel : A data stream of a given nature mapped over a connection is considered a channel. For example, a PCM
data stream mapped over an RTP connection would be a single channel, even if that data stream interleaved more
than 1 bearer in each packet. In like manner, any set of payload types that are all destined to the same HDLC endpoint
would also be considered a channel.
Connection : A link between two end-points that is unique through some look-up method, either through source &
destination IP addresses and UDP ports, through those plus RTP SSRC, or through ATM VC number and possibly
RTP SSRC on Null-application data VC. In AAL2, a VC and CID combination uniquely defines a connection.
HDLC Stream: A group of HDLC channels that are carried over the same time slots. HDLC mini-packets in streams
have an address byte that indicates to which HDLC channel they belong. Usually, HDLC streams carry a series of
channels communicating to and from the same agent (e.g. a DSP). HDLC Streams may be carried over one or
multiple consecutive time-slots on the H.100 bus. This device supports streams of length 1 to 2046 time slots.
PDV: P acket D elay V ariation. RTP packets and AAL2 mini-packets arrive with a certain delay with respect to when
they were sent. PDV is a measure of how much that delay varies on an xxPCM channel. PDV measures the
peak-to-peak packet delay throughout the network. PDV is only relevant on CBR connections.
Time Slot: In this document, the term time slot is often used to define a combination of a time slot and a stream on
the H.100 bus. Thus a time slot would represent a single 8-bit slot every 125 us on the TDM bus. Time slot/Stream
numbers are numbered 0 to 4095 according to the following equation: time slot * 32 + stream. On
reduced-frequency TDM streams, certain time slots become unusable. For streams running on a 4 MHz clock, time
slots are numbered 0 to 63, and the equations to determine TSSTs are the following: in the TX TDM, TSST = (time
slot * 2 + 1) * 32 + stream, and in the RX TDM, TSST = (time slot * 2) * 32 + stream. In like manner, for streams
running on a 2 MHz clock, time slots are numbered 0 to 31, and the equations are: in the TX TDM, TSST = (time
slot * 4 + 3) * 32 + stream, and in the RX TDM, TSST = (time slot * 4) * 32 + stream.
"Null" VC : A Null VC contains data in which some or all of the headers have been encoded into the VC number
itself. For example, a Null-application data VC's payload would begin with the application data itself (either RTP or
the payload) with no IP or UDP header, and no SNAP/LLC, LANE or other headers. Null encapsulation is referred to in
IETF RFC2684 as VC Multiplexing.
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