Transcript ATM: a view from the trenches

ATM: A view from the
trenches
.
Introduction
• Laura Grill: [email protected]
• *my* experience with ATM
• cisco environment at Northwestern
University
Agenda
• Why ATM?
• Review of basic ATM theory and LANE
• A look at NU’s network topology
Why ATM?
• 1996 ATM was the next big thing
– connection oriented benefits of circuit switched using
virtual circuits
– efficient use of bandwidth as in packet switched
• Decision was made at executive level for:
– combine voice and data worlds
– ATM to the desktop
• 1997 built ATM backbone and bought OC-12 to Ameritech NAP
– to handle voice data and video to and from the university
New technologies:New
strategy
• The enabling technologies that make it feasible to integrate
services w/o ATM
– voice over IP
– QOS for connectionless networks
– gigabit ethernet
• Today, ATM as a backbone and wan technology w/ no plans to
grow it
• Moving gigabit into the backbone (keeping existing ATM)
• Frame versus cell: I'd rather have frames
Basic ATM theory
• Connection oriented vs. connectionless
• 53 byte cells
• Uses virtual circuits, identified with
VPI/VCI
Broadcast based "legacy"
protocols
• IP, IPX, AppleTalk (use broadcast discovery)
• Why is this a problem?
• Catch 22 - can’t talk on the network until a circuit is
established and can’t establish a circuit without an
address
• Can’t broadcast on the phone network (no
mechanism for this)
Ways to solve the broadcast
problem
• RFC 1483 [native IP over ATM]
• RFC 1577 [classical IP]
• LANE (LAN Emulation)
• MPOA
LANE system
• 3 servers: LECS, LES, BUS
• 1 client: LEC
Servers
• LECS - LAN Emulation Configuration Server
– hold information about the LES for each
emulated LAN and gives that info to the LEC
when it comes on-line
• LES - client register their MAC and ATM address
with the LES
• BUS- maintains a VC that connects all the clients
together emulated a broadcast
Client
• LEC - LAN Emulation Client (can be a
host or router or switch)
Procedure for a LEC to
become part of the emulated
LAN
• LEC comes up and creates VC to LECS (using well
known address or ILMI or statically configured)
• LECS tells it what to emulate and who the LES is
and what it's ATM address is
• The client then registers it's MAC and ATM address
with the LES
• LES assigns a BUS
• At this point many VC’s have been built to mesh all
the LEC’s together
ATM Topology at NU
• See diagrams
• ATM as a backbone technology to
connect buildings to the core
• use ATM for our WAN - OC-3c to NAP and
OC-3c to Chicago campus
• Some FDDI still remains
• Will add gigabit this year
The end
• Questions?