Lect-12-1: IP over ATMComputer Networks : An Introduction to Computer Networks Handout #16: IP over ATM Homepage

Lect-12-1: IP over ATMComputer Networks2 Motivation for IP over ATM  By now ATM has a large installed base  Although intended to be ubiquitous, the ATM-only dream was not realized  ATM co-exists with many legacy networks  legacy networks: Ethernet, Token Ring etc.  IP remains a popular internetworking solution  Therefore, we need to know how to run IP over ATM networks

Lect-12-1: IP over ATMComputer Networks3 IP over ATM Architectures  IP machines (desktop or router) connected to ATM networks need mechanisms to run connectionless IP over connection-oriented ATM  Two standard mechanisms  LAN Emulation (ATM Forum Solution)  Classical IP over ATM (IETF, RFC2255)

Lect-12-1: IP over ATMComputer Networks4 LANE : Motivations  Quick deployment of ATM  Makes ATM look like either Ethernet or Token Ring  No changes required for existing network software  Existing network protocols and software, e.g. IP, IPX, AppleTalk, running on Ethernet will also run on ATM

Lect-12-1: IP over ATMComputer Networks5 LANE Address Structure  Each host connected to a LANE network has three addresses  IP address : needed for internetworking  MAC address: an Ethernet or Token Ring address to emulate an Ethernet or a Token Ring  ATM address : physical ATM address to locate devices in ATM network IP Address Ethernet Address ATM Address

Lect-12-1: IP over ATMComputer Networks6 LAN Emulation (LANE)  Each host runs a LAN Emulation Client (LEC); it  does the address resolution (MAC-ATM) for the host  sets up data connections to other hosts  sets up control connections to LANE servers  Each host communicates with 3 servers  Broadcast and Unknown Server (BUS)  LAN Emulation Server (LES)  LAN Emulation Configuration Server (LECS)

Lect-12-1: IP over ATMComputer Networks7 LANE Servers LECS LES BUS LEC

Lect-12-1: IP over ATMComputer Networks8 What LANE Servers Do IP-MAC address resolution is done by ARP servers as usual. On top of that, MAC-ATM resolution is needed.

Lect-12-1: IP over ATMComputer Networks9 LANE Sequence of Events (LECS) Initialization Configuration Registration with LES (BUS) Initialization Data Transfer Discover LECS’s ATM address and establish communication with the LECS Based upon some policy, the LECS assigns the client to a particular LES (gives the LES’s ATM address to client) The client joins the ELAN by registering its ATM and MAC address with the LES The client obtains the BUS’s ATM address from LES. This address is used for broadcasting. The client now can send MAC frames. Address resolution with LES may be necessary. ATM VC setup may be req’d.

Lect-12-1: IP over ATMComputer Networks10 Interoperability Legacy LAN and LANE Ethernet LAN ATM LANE ATM-LAN Converter Physical Scenario Extended Ethernet Logical Scenario

Lect-12-1: IP over ATMComputer Networks11 Classical IP over ATM (CLIP) Motivation  LANE hides ATM technology and mimics Ethernet  Since LANE mimics Ethernet, it inherits Ethernet’s undesirable features  broadcast-like competition for resources  No ATM QoS available to network layer

Lect-12-1: IP over ATMComputer Networks12 CLIP Basics  CLIP treats ATM as a new link layer network technology  Advantages : With CLIP, the host software is aware of ATM and makes use of ATM QoS  Disadvantages  Ethernet-based software will not work  CLIP is IP-only solution, (does not cover IPX etc.)

Lect-12-1: IP over ATMComputer Networks13 LANE vs CLIP Existing IP Existing IPXExisting Netbeui LANE CLIP New IP Supports all existing software Cannot support any existing software, supports only new IP software

Lect-12-1: IP over ATMComputer Networks14 CLIP Components  There is only one server, called ATM ARP Server  Instead of using broadcasting, the IP host communicates with this server directly whenever it needs to resolve IP-ATM addresses

Lect-12-1: IP over ATMComputer Networks15 Classical IP Over ATM Connecting Hosts with ARP Server Client ATM ARP Server ATM Network ATM ARP Request Reply to ARP Request

Lect-12-1: IP over ATMComputer Networks16 CLIP Sequence of Events Registration with ARP Server Obtain ATM addr of dest Data Transfer When an IP host joins a LAN, it registers its ATM and IP addresses with the ATM ARP server When an IP host wants to communicate with another, it obtains the ATM address of the dest from ARP server if it is not in the local cache The client sets up an ATM VC (if such a VC is not there) with the destination and sends ATM cells over the VC.