IP over ATM

volleyballbeginnerΔίκτυα και Επικοινωνίες

27 Οκτ 2013 (πριν από 4 χρόνια και 14 μέρες)

77 εμφανίσεις

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

H3

H2

H5

H4

H6

ATM
ARP
server

ATM
ARP
server

ATM
ARP
server

H1

R4

R3

R1

R5

R2

LIS 1

LIS 3

LIS 2

ATM Network

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

H3

H2

H5

H4

H6

ATM
ARP
server

ATM
ARP
server

ATM
ARP
server

H1

R4

R3

R1

R5

R2

LIS 1

LIS 3

LIS 2

ATM Network

NHS

NHS

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)

ATM Network

H1

H2

H6

H5

H4

H3

H
2

ELAN 1

ELAN 2

R

MPOA

Conclusions


Problems with IP over ATM


Overlay Model


Integration with legacy systems


LANE


CLIP, NHRP, MPOA