1. 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

2. RFC 1483 IP & IPX VPI/VCI IP IPX VPI/VCI

3. AAL5 Frame Format Network Layer Protocol Data UnitpadctrllenCRC Higher-layer PDU pad (0 - 47 octets) to fill cell payload Length of pad Field (16 bits) AAL5 CRC (32 bits) Payload Payload 48 bytes

4. LLC/SNAP Encapsulation for a Routed Non-ISO PDU LLCPIDOUINON ISO PDU SubNetwork Attachment Point (SNAP) header 3 octet Organisationally Unique Identifier 2 octet Protocol Identifier IP Packet 2^16 - 9 octets 3 octet LLC header

5. VC based Multiplexing - Characteristics Each protocol is carried over a separate virtual channel No need for LLC/SNAP header Less overhead and processing required

6. Choice of Encapsulation Method VC-based multiplexing Private ATM networks where there is dynamic creation of large numbers of VCs Where a fast and economical method is required LLC Encapsulation Where the ATM network only supports PVCs Where charging depends on the number of simultaneous VCs VC-based multiplexing LANEv1 LLC/SNAP Encapsulation IP over ATM MPOA RFC 1483In reality