Spirent SmartBits System, Reference Manual

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Glossary of Terms
Features and Terminology
256 SmartBits System Reference
Configuration Server. They resolve MAC addresses to ATM addresses through the
services of a LAN Emulation Server; send broadcast and multicast frames, and also
send unicast frames that have no direct VC to a Broadcast and Unicast Server. LANE
uses the VC multiplexing encapsulation formats for Bridged Etherent/802.3 (without
LAN FCS) or Bridged 802.5 (without LAN FCS) for the Data Direct, LE Multicast
Send and Multicast Forward VCCS. However, the initial PAD field described in this
memo is used as an LE header, and might not be set to all '0'.
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Classical IP
Characteristics of the classical model are:
– The same maximum transmission unit (MTU) size is the default for all VCs in a
LIS. However, on a VC-by-VC point-to-point basis, the MTU size may be negoti-
ated during connection setup using Path MTU Discovery to better suit the needs
of the cooperating pair of IP members or the attributes of the communications
path. (Refer to Section 7.3).
– Default LLC/SNAP encapsulation of IP packets.
– End-to-end IP routing architecture stays the same.
– IP addresses are resolved to ATM addresses by use of an ATMARP service within
the LIS - ATMARPs stay within the LIS. From a client's perspective, the
ATMARP architecture stays faithful to the basic ARP model presented in [3].
– One IP subnet is used for many hosts and routers. Each VC directly connects two
IP members within the same LIS. (RFC2225).
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LLC PPP
LLC encapsulated PPP over AAL5 is the alternative technique to VC multiplexed PPP
over AAL5.
The AAL5 CPCS-PDU payload field is encoded:
– LLC header: 2 bytes encoded to specify a source SAP and destination SAP of the
routed OSI PDU (values 0xFE 0xFE), followed by an Un-numbered Information
(UI) frame type (value 0x03).
– Network Layer Protocol IDentifier (NLPID) representing PPP, (value 0xCF).
– The PPP protocol identifier field, can be either 1 or 2 octets long. (RFC2364).
Available only when SmartWindow is connected to a chassis with cards supporting
PPP over ATM (AT-9155C and AT-9622, firmware version 3.00 and higher).
•
VC Mux PPP
The Common Part Convergence Sub-layer (CPCS)-PDU Payload field contains user
information up to 2^16 - 1 octets. The PAD field pads the CPCS-PDU to fit exactly
into the ATM cells such that the last 48 octet cell payload created by the SAR sublayer
will have the CPCS-PDU Trailer right justified in the cell. The CPCS-UU (User-to-
User indication) field is used to transparently transfer CPCS user to user information.
(RFC2364).
Available only when SmartWindow is connected to a chassis with cards supporting
PPP over ATM (AT-9155C and AT-9622, firmware version 3.00 and higher).