Agilent Technologies J3972A - Manual (Page 156)

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ATM Adaptation Layer 0 (AAL-0)
ATM Adaptation Layer 0 (AAL-0) supports raw cell transport. It has an SAR-
PDU header or trailer.
ATM Adaptation Layer 1 (AAL-1)
ATM Adaptation Layer 1 (AAL-1) supports constant bit rate data such as voice,
video, or other continuous user data. AAL-1 transfers data at a fixed speed. AAL-
1 contains a 47-byte payload and a 1-byte header.
ATM Adaptation Layer 3/4 (AAL-3/4)
ATM Adaptation Layer 3/4 (AAL-3/4) supports variable bit rate data with
connection oriented (type 3) or connectionless (type 4) data services. AAL-3/4
supports two modes of operation - Message Mode which is used for framed data,
and Stream Mode which is used for low-speed continuous data. AAL-3/4 contains
a 44-byte payload with a 2-byte header and a 2-byte trailer.
ATM Adaptation Layer 5 (AAL-5)
ATM Adaptation Layer 5 (AAL-5) supports variable bit rate data with connection
oriented or connectionless data services. AAL-5 was designed as a simple
protocol that assumes some of the functions such as error detection, timing and
other overhead information is accomplished by the next level protocol. AAL-5
contains a 48-byte payload with control information in the normal ATM 5-byte
header.
ATM Cell
An ATM Cell is a 53-byte protocol data unit made up of a 5-byte cell header and a
48-byte payload (information field).
ATM Layer
The layer in ATM that switches cells to their correct destinations within the
network.
ATMProbe
See probe.
Auto-Negotiation
The process by which a probe determines the network speed and automatically
sets its own configuration to match that speed.