Transcript AAL5

Chapter Objectives
After completing this chapter you will be able to:
Define RFC 1483
Describe logical link control (LLC) encapsulation
Describe VC multiplexing
State when both methods are used
RFC 1483
IP & IPX
VPI/VCI
IP
IPX
AAL5 Frame Format
Higher-layer PDU
Network Layer Protocol Data Unit
pad (0 - 47 octets)
to fill cell payload
pad
ctrl
len
CRC
Length of pad Field (16 bits)
AAL5 CRC (32 bits)
Payload
Payload 48 bytes
LLC/SNAP Encapsulation for a Routed
Non-ISO PDU
SubNetwork Attachment Point (SNAP) header
LLC
3 octet LLC header
OUI
PID
2 octet Protocol Identifier
3 octet Organisationally Unique Identifier
NON ISO PDU
IP Packet
2^16 - 9 octets
VC based Multiplexing - Characteristics
 Each protocol is carried over a separate
virtual channel
 No need for LLC/SNAP header
 Less overhead and processing required
Choice of Encapsulation Method
RFC 1483
In reality
VC-based multiplexing
 Private ATM networks where there
is dynamic creation of large
numbers of VCs
 Where a fast and economical
method is required
VC-based multiplexing
 LANEv1
LLC Encapsulation
 Where the ATM network only
supports PVCs
 Where charging depends on the
number of simultaneous VCs
LLC/SNAP Encapsulation
 IP over ATM
 MPOA