IP over ATM Integrated Network Services Almerindo Graziano Introduction • • • • • • • • Characteristics of IP and ATM IP over ATM - Overlay Model Data encapsulation CLIP NHRP LANE MPOA Conclusions ATM • • • • • ATM is connection oriented IP is connectionless ATM has built-in QoS support IP uses best-effort Two approaches – Connections established on demand – IP traffic is carried over pre-configured circuits • Both approaches have pros and cons IP over ATM • Overlay Model • ATM is treated as a Data Link layer on which IP runs – – – – Classical IP over ATM (CLIP) Next Hop Resolution Protocol (NHRP) LAN Emulation (LANE) Multiprotocol Over ATM (MPOA) CLIP • All members of a LIS (host or router) are under the same administrative control • A LIS is given ONE IP subnet address • CLIP Classical IP over ATM • The ATM network is divided into a number of Logical IP Subnet (LIS) • Systems within a LIS communicate through direct ATM connections – Each LIS has an ARP server called ATMARP – ARP queries are sent to the ATMARP server • Systems in different LIS communicate through a router – A router is a member of multiple LIS ATMARP server • There is one for each LIS – It holds a table of <IP address,ATM address> • A wants to communicate with B and it knows B’s IP address – A send an ARP_REQUEST to the ATMARP server – If the IP address is found an ARP_REPLY is sent – Otherwise an ARP_NACK packet is sent Classical IP Over ATM ATM Network LIS 3 R2 ATM ARP server R3 H1 H2 H3 LIS 1 H6 ATM ARP server R1 ATM ARP server H4 H5 LIS 2 R4 R5 Data Encapsulation • How do we carry different protocols • How do we identify different protocols – VC multiplexing – LLC/SNAP – TULIP – TUNIC VC multiplexing • VC multiplexing or null encapsulation • A different VC is required to carry each layer 3 protocol – One VC carries the IP protocol – One VC carries the IPX protocol etc.. • Not very suitable in a multiprotocol environment LLC/SNAP encapsulation • Similar to the IEEE 802 • Multiple protocols can be carried in the same VC • Less expensive • Can we do better than this? – Once established a VC, we don’t actually need the IP header TULIP/TUNIC • TULIP (TCP an UDP over Lightweight IP) – Only the layer 4 protocol identifier is kept • TUNIC (TCP and UDP over Nonexistent IP) Connection – The IP header is eliminated – A different VC is created for each layer 4 protocol CLIP Limitations • Inter-LIS communication has to go through a router – Both parties are attached to same ATM network • Can be a problem in an ATM WAN – NHRP – MPOA NHRP • NHRP (Next Hop Resolution Protocol) • NHRP servers and NHRP client • Each LIS has at least 1 NHRP server – A server can serve more than 1 LIS – A server has a table of <IP address,ATM address> • Every ES is a NHRP client NHRP • For intra-LIS communication, an NHRP server works as an ATMARP server – It resolves IP addresses into ATM addresses • For inter-LIS communication, NHSs are interconnected to exchange NHRP queries – When an NHS cannot solve an IP address, it forwards the query to another NHS – If the destination host is not part of the same ATM network, the NHS provides the address of the egress router – Intermediate NHSs store NHRP replies into their cache NHRP ATM Network NHS R2 NHS ATM ARP server R3 H1 H2 H3 LIS 1 LIS 3 H6 ATM ARP server R1 ATM ARP server H4 H5 LIS 2 R4 R5 LANE • LAN technologies such as Ethernet are widely used • However, new applications require higher bandwidth and QoS support • LANE (LAN Emulation) – Allows ATM to coexist with legacy LANs – Allows ATM to be gradually introduced into existing legacy LANs – Emulates IEEE 802 LANs without any change to upper layer protocols Legacy LANs • Connectionless MAC – ATM is connection oriented • Broadcast transmission – Difficult to achieve in ATM • No guaranteed QoS – In-built support in ATM LANE entities • LEC (LAN Emulation Client) • LES (LAN Emulation Server) • LECS (LAN Emulation Configuration Server) • BUS (Broadcast and Unknown Server) LEC • Runs on an ATM station and simulates an Ethernet or Token Ring network • Encapsulates upper layer protocols into ELAN frames • Decapsulate incoming ELAN frames into upper layer protocol data unit (e.g. IP packets) LES and BUS • Every ELAN has a LES – It acts as a coordinator and resolves MAC addresses into ATM addresses – LECs register with the LES giving <MAC address,ATM address> • BUS – Used to emulate broadcast feature of a legacy LAN – Packet sent to the BUS are sent to all LECs in the ELAN – It is used before a direct connection is established between two LECs LECS • More than one ELAN can run on an ATM network • A LECS assigns LECs to their ELAN – When a station starts up it queries the LECS to find out its LES – The station then registers with the LES – The BUS address is determined through an LE_ARP with a MAC address of all 1s Advantages and Disadvantages • Advantages – Higher speed (not completely true) – Allows the creation of multiple VLANs • Disadvantages – It hides QoS features of ATM – With LANEv2 a LEC can provide 8 levels of QoS to higher layers, each with a different VC MPOA • Communication over multiple sub-networks requires routers – Bottleneck – A connection is set up with router and then from the router to the destination • Combination of LANE and NHRP – Aims at optimal, direct communication between end systems without crossing any router MPOA • MPOA (Multi-Protocol Over ATM) – ATM hosts – Edge devices such as switches, routers etc.. • MPOA is built on top of LANE – Intra-LANE traffic follows LANE specification – Inter-LANE traffic is optimized by integrating NHRP functionalities MPOA • MPOA Client (MPC) • MPOA Server (MPS) MPOA R ATM Network H5 H1 H2 ELAN 1 ELAN 2 H2 H3 H4 H6 Conclusions • Problems with IP over ATM • Overlay Model • Integration with legacy systems – LANE • CLIP, NHRP, MPOA