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IP over ATM
Integrated Network Services
Almerindo Graziano
Introduction
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Characteristics of IP and ATM
IP over ATM - Overlay Model
Data encapsulation
CLIP
NHRP
LANE
MPOA
Conclusions
ATM
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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
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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