Frf.12 End-To-End Fragmentation - Alcatel-Lucent 7750 Configuration Manual

Port Features

FRF.12 End-to-End Fragmentation

The user enables FRF.12 e2e fragmentation on a per FR SAP basis. A fragmentation header is
added between the standard Q.922 header and the payload. This header consists of a 2-byte
Network Layer Protocol ID (NLPID) of value 0xB1 to indicate e2e fragmentation payload and a 2-
byte containing the Beginning bit (B-bit), the End-bit (E-bit), the Control bit (C-bit), and the
Sequence Number field.
The following is the mode of operation for the fragmentation in the transmit direction of the FR
SAP. Frames of all the FR SAP forwarding class queues are subject to fragmentation. The
fragmentation header is, however, not included when the frame size is smaller than the user
configured fragmentation size. The SAP transmits all fragments of a frame before sending the next
full or fragmented frame. The fragmentation threshold is configurable in the range 128 — 512
bytes. In the receive direction, the SAP accepts a full frame interleaved with fragments of another
frame to interoperate with other vendor implementations.
A FR SAP with FRF.12 e2e fragmentation enabled can be part of a VPLS service, an IES service,
a VPRN service, an Ethernet VLL service, or an IP VLL service. This SAP cannot be part of a FR
VLL service or an FRF.5 VLL service. However, fragmented frames received on such VLLs will
be passed transparently as in current implementation.
SAP Fragment Interleaving Option
This option provides a different mode of operation for the fragmentation in the transmit direction
of the FR SAP than in the default behavior of a FRF.12 end-to-end fragmentation. It allows for the
interleaving of high-priority frames and fragments of low-priority frames.
When the interleave option is enabled, only frames of the FR SAP non expedited forwarding class
queues are subject to fragmentation. The frames of the FR SAP expedited queues are interleaved,
with no fragmentation header, among the fragmented frames. In effect, this provides a behavior
like in MLPPP Link Fragment Interleaving (LFI). The receive direction of the FR SAP supports
both modes of operation concurrently, for example, with and without fragment interleaving.
Page 54 7750 SR Interface Configuration Guide