ATM in Local Area Networks - Departamento de Ingeniería Telemática

Switching: ATM
ATM in Local Area
Networks
José Félix Kukielka
David Larrabeiti
Piotr Pacyna
(c) Departamento de Ingeneria Telemática, Universidad Carlos III de Madrid
Programme authors and contributors
Teaching material:
‹ David
‹
‹
‹
Larrabeiti López
José Félix Kukielka
Huw Oliver
Piotr Pacyna
(c) Departamento de Ingeneria Telemática, Universidad Carlos III de Madrid
2
Index: ATM
‹
1. ATM in Local Area
Networks
™
™
‹
™
™
‹
LAN Emulation (LANE)
Multiprotocol
Encapsulation over AAL5
2. ATM and Internetworking
™
Classical IP over ATM
Next Hop Resolution
Protocol (NHRP)
Introduction to
Multiprotocol over ATM
(MPOA)
3. ATM Traffic Management
and Congestion Control
™
™
The traffic contract
™
™
™
‹
Reference models
Quality of Service (QoS)
Traffic parameters
ATM service categories
4. ATM Traffic Control
™
™
™
™
™
Connection Admission
Control
Usage and network
parameter control
Traffic shaping
Delay and loss priority
control
Other traffic control
methods
9
Congestion recovery
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ATM in
Local Area Networks
LAN Emulation
(c) Departamento de Ingeneria Telemática, Universidad Carlos III de Madrid
Motivation (1)
‹
‹
¾
Currently: Majority of data traffic in private
networks sent using Local Area Networks (LANs)
™
ISO Ethernet / IEEE 802.3
™
Token Ring (IEEE 802.5)
Services available in LANs different from those
available in ATM networks, for example:
™
Connection-less in LAN vs. connection-oriented in ATM
™
Broadcast and Multicast easily to implement on a shared
medium as used for LANs
™
LAN MAC addresses based on fabrication number,
independent of the network topology
Need interoperability between ATM and LAN!
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Motivation (2): LAN Emulation
LANE
LAN
LAN A
A
ATM network
Corporate Network
SME network
LANE
LANE
Residential network
‹
LAN
LAN C
C
Objective:
™
™
™
‹
LAN
LAN B
B
Reuse existing applications designed for LANs in an ATM network
Define a new ATM service: LAN Emulation (LANE)
Applications on end systems (work stations, routers, bridges) can connect to
ATM networks
Allows for interoperability of applications with both, ATM devices and
LAN devices
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LAN Emulation: Need for
Interconnection
‹
‹
Different scenarios interconnecting LANs and ATM
networks:
™
LAN/ATM (direct connection)
™
LAN/ATM/LAN (connect two LANs with ATM links)
General solution: Routers
™
‹
Further solutions:
™
‹
Effective, but introduction of extra processing Æ delay
Transform all end systems to ATM stations Æ cost
Advantage of LAN Emulation:
™
Interoperability between shared medium LANs and ATM
networks
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Characteristics of LAN Emulation
‹
‹
Connection-less services
Multicast / broadcast services
™
Limits overall size of emulated LAN
9
Example: STM-1 line, 5% broadcast Æ 8 Mbit/s
¾Emulate 10-Mbit/s Ethernet: Capacity almost used...
9
‹
‹
‹
In reality: Emulate LANs of < 500 – 2000 stations
MAC-layer interface (operating system layer) on
ATM stations
Emulation of LANs
Interconnection of existing LANs
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Emulated LANs: Service Description
Two
Two types
types of
of emulated
emulated LANs
LANs
Token Ring/IEEE 802.5
ATM network
Ethernet/IEEE 802.3
‹
em. LAN
A
B
One or more emulated LANs can
coexist in the same ATM network
™
‹
em. LAN
Being independent from each
other
em. LAN
Z
Communicate with each other
using routers or bridges
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Hardware and Software in LANE
Computer/Workstation
Applications
Oper. System
LAN Driver
L
ATM NIC A
N
Driver
E
ATM
Bridge/Router
Computer/Workstation
LANE
AAL
Computer
ATM
CPU and
Memory
PHY
MAC
Applications
Oper. System
LAN Driver
PHY
Computer
CPU and
Memory
LAN NIC
Driver
Computer bus
ATM NIC
AAL
Software
ATM
Computer bus
ATM
network
MAC
LAN NIC
PHY
Software
PHY
ATM physical medium
Legacy LAN
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NIC: Network
Interface Card
10
Architecture of LANE Protocols
(Data Path)
ATM Client
ATM
ATM
Switch
LAN Client
Bridge
LAN
network
Applications
Applications
TCP/IP
TCP/IP
LLC
LLC
LANE
LANE
AAL5
ATM
Phy. layer
MAC
Layer
MAC
Phy. layer
Phy. layer
AAL5
ATM
Phy. layer
Phy. layer
ATM
Phy. layer
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LANE: Problems to Handle
‹ For
™
™
™
devices connected to the ATM network:
How translate ATM addresses to MAC
addresses?
How adapt a connection-less protocol to a
connection-oriented protocol?
How to manage multicast and broadcast?
‹ Solution:
™
Client/Server model
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LANE Components
‹
Two different classes: Clients and Servers
™
™
LANE client (LEC): on a bridge, a terminal, an ATM
server,…
LANE server:
9
Can be implemented on separate components or on an
ATM switch
‹
Each emulated LAN consists of:
™
™
One or several clients
A single LAN emulation service with three type of
servers:
9
LAN Emulation Configuration Server (LECS)
9
LAN Emulation Server (LES)
9
Broadcast and Unknown Server (BUS)
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LANE Components: Example
MAC
LANE Server
(LES)
Hub
ATM
MAC
LANE Client
(LEC)
LAN
Switch
LANE Client
(LEC)
ATM
ATM network
BUS
LANE Configuration Server
(LECS)
MAC
MAC MAC
Router
ATM
MAC
WWW
ATM
MAC
LANE Client
(LEC)
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LANE Client
(LEC)
14
LANE Client (LEC)
ATM LAN
‹ Performs
data
forwarding and
address resolution
‹ Provides
MAC
level emulated
Ethernet service
to
higher level
software
determine
determine ATM
ATM
addresses
addresses of
of
LES
LES and
and BUS
BUS
‹ Interfaces
‹ Implements
LEC
LECS
LES
LUNI
in order to
communicate with
other components
ATM
Workstation
Used
Used by
by all
all
stations
stations to
to
Control
Control distribute
distribute
Control
Control direct
direct
VCC’s
VCC’s
Multicast
Multicast forward
forward
Multicast
Multicast send
send
BUS
LAN
LAN
Emulation
Emulation
Data
Data direct
direct
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LAN Emulation Configuration Server
(LECS)
LEC
LEC obtain
obtain info
info using
using
configuration
configuration protocol
protocol
Physical location
(ATM address)
A
em. LAN 1
LEC
LECS
Assign LEC to em. LAN
(by giving the client the
the LES ATM address
LECS
Depending on:
or
B
LEC
LEC
LEC obtain
obtain info
info using
using
configuration
configuration protocol
protocol
em. LAN 2
The identity of a
LAN destination
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LAN Emulation Server (LES)
ATM
Workstation
s
ATM Bridge
ATM
Host
ATM End Systems
Emulated LAN
LES
‹
‹
‹
‹
LEC
Implements control coordination function for emulated LANs
Registers and resolves unicast and multicast MAC addresses
Registers and resolves unicast/multicast route descriptors to ATM
addresses
Only one LANE Server for each LEC
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Broadcast and Unknown Server (BUS)
em. LAN
ATM
Workstation
LEC
LEC sees
sees
aa single
single BUS
BUS
Directly
Multicast traffic
LEC
LEC
Unicast data
BUS
LEC
Relaying Frames
‹
LEC
Multicasting/bcsting
In-directly
Main tasks of the BUS:
™
™
™
™
Distribute (broadcast) multi/unicast data from LEC to
MAC addresses
Deliver initial unicast data when MAC not yet resolved
Support multicasting/broadcasting
Relaying frames to stations with unknown MAC address
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LANE Connection Types
LEC
ATM LAN
LES
LECS
6
LEC
5
6
1
1
ATM Bridge
3
LEC
LEC
2
2
4
ATM
Workstation
1 Control direct VCC
2 Multicast send VCC
‹
‹
‹
‹
BUS
LEC - LAN Emulation Client
LEC
LES - LAN Emulation Server
LECS - LAN Emulation Configuration Server
BUS - Broadcast and Unknown Server
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3 Data direct VCC
4 Multicast forward VCC
5 Control Distribute VCC
6 Configuration direct VCC
19
Basic Steps of LANE (LUNI Protocol)
‹ Initialization
‹ Configuration
‹ Joining
‹ Data
and Registration
Transfer Phase
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Initialization
1.
LEC: Getting its appropriate ATM address
™
Registration of the address using ILMI
9
™
2.
3.
Interim Local Management Interface
Alternative: Manual pre-configuration
LEC: Getting the LECS address:
™
Using the ILMI procedure
™
Using a well-known SVC (VPI=0, VCI=17) to the LECS
™
Using a well-known LECS address
™
Manual configuration (in a configuration file on the LEC)
LEC: Establishment of a direct connection VCC to
the LECS
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Example: Initialization
Connection with LECS to obtain the LES address
1. ILMI procedure with a local switch
2. Connecting to a well-known address
3. Connecting to a well-known VPI/VCI
LANE Server
(LES)
ATM network
LANE Client
(LEC)
BUS
ILMI
LAN
Switch
MAC
LANE Configuration Server
(LECS)
MAC
MAC
ATM
MAC
LANE Client
(LEC)
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Configuration
4. If LEC and LECS connected:
™ Utilize a configuration protocol between both
™ LECS: sends the following information:
9 ATM address of the LES
9 ID (textual description) of the LANE in which the LES is
a member
9 Maximum frame size
9 Type of the emulated LAN
5. LEC: sends its ATM address & MAC address
6. Release of the configuration-direct VCC to the
LECS
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Configuration: Example (Client
Configuration)
LANE Server
(LES)
ATM network
LANE Client
(LEC)
LAN
Switch
MAC
MAC
BUS
LANE Configuration Server
(LECS)
MAC
ATM
MAC
LANE Client
(LEC)
‹
LECS assigns a concrete em. LAN to an LEC
™
‹
ATM address of LES
LECS informs about MAC protocol, MTU,...
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Joining and Registration: LES
7. LEC: Sets up a direct control VCC to the LES
8. LEC: Send a Join_request message to register its
MAC address and ATM address at LES
7. Optionally: Could register further MAC addresses for
which is acts as proxy
9. LES: Assigns a unique identifier to the LEC
(LECID)
10. LES: Adds LEC to the point-to-multipoint controldistribute VCC
11. LES: Adds available information about the LEC to
its table for the address resolution protocol of
LANE (LE_ARP). Uses a control direct VCC /
control distribute VCC for LE_ARP
7. LE_ARP message: contains the ATM address
corresponding to a particular MAC address
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Example: Joining with the LES
Establishing a control connection to the LES
Request for inclusion into the emulated LAN
• LEC parameters:
ATM address, MAC address, MTU, client id, representation id
Response (accept or deny)
JOIN
REQUEST
ATM network
LANE Client
(LEC)
BUS
LAN
Switch
LANE Configuration Server
(LECS)
JOIN
RESPONSE
MAC
MAC
LANE Server
(LES)
MAC
ATM
MAC
LANE Client
(LEC)
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Joining and Registration: BUS
12. LEC: Uses the LE_ARP mechanism to get the
ATM address of the BUS
™ Sending an LE_ARP message for the broadcast MAC
address (all ones) to the LES
™ LES responds with the ATM address of the BUS
13. LEC: Uses this address to prepare a point-topoint multicast send VCC to the BUS
14. BUS: Adds the LEC to its point-to-multipoint
multicast forward VCC
Î
ÎInitialization,
Initialization,configuration,
configuration,and
andregistration
registration
completed.
completed.
LEC
LECready
readyto
tosend
senddata.
data.
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Example: Registration and Retrieving
the BUS ATM Address
Register: List of MAC addresses of the traditional LAN
Request of the ATM address of the BUS
REGISTER
LANE Server
(LES)
LANE Client
(LEC)
LAN
Switch
MAC
MAC
REQUEST FOR
BUS
ATM network
BUS
LANE Configuration Server
(LECS)
MAC
ATM
MAC
LANE Client
(LEC)
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Data Transfer
‹ After
configuration, initialization, and
registration:
™
Client can already send and receive frames
‹ Basic
™
™
Transform MAC frames into ATM cells for
transmission
Inverse procedure for receiving
‹ Three
™
™
™
scheme always the same:
cases:
Unicast MAC frame, known ATM address
Unicast MAC frame, unknown ATM address
Multicast / broadcast MAC frame
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LANE Encapsulation (V 1.0)
Bridge PDU
(TR or Ethernet)
LANE
PDU
AAL 5 PDU
LECID
Bridge
header
Application data
Bridge
Trailer
Token
Bridge
Ring
/ Router
or Ethernet
PDU Frame
LANE PDU
AAL 5
CS
ATM cells
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Data Transfer Example (Case 1)
Unicast MAC frame, known ATM address
Source LEC: verify that destination VC existing
‹ No: create one
‹ Yes: send the frame
LANE Server
(LES)
ATM network
LANE Client
(LEC)
MAC
BUS
LANE Configuration Server
(LECS)
MAC
MAC
ATM
MAC
LANE Client
(LEC)
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Data Transfer Example (Case 2)
Unicast MAC frame, unknown ATM address
Setup of data connection to BUS
Send the frame to BUS
BUS: forwards to the destination
ARP request to LES not to use BUS again later
ARP response from LES
LE_ARP_RESPONSE
LE_ARP_REQUEST
LANE Server
(LES)
ATM network
BUS
LANE Client
(LEC)
LANE Configuration Server
(LECS)
MAC
MAC
MAC
ATM
MAC
LANE Client
(LEC)
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Data Transfer: Unicast
‹
Basic scheme:
™
™
™
Send first packets via broadcast
Send LE_ARP to get to know ATM address
If response to LE_ARP:
9
Store LE_ARP response in a cache (LE_ARP cache)
9
Send flush packet via broadcast
¾Avoid out-of-order delivery!
9
™
If no answer to LE_ARP (timeout):
9
‹
Send further packets using unicast
Continue broadcast & resend LE_ARP
Alternative scheme:
™
™
Send LE_ARP first and buffer packets until answer
arrives
Problem: Long delay possible before packets are sent
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Data Transfer Example (Case 3)
Multicast or broadcast MAC frame
LANE Server
(LES)
MAC
Hub
ATM
MAC
LANE Client
(LEC)
BUS
ATM
LANE Client
(LEC)
MAC
ATM network
LANE Configuration Server
(LECS)
MAC
MAC
Router
ATM
MAC
WWW
ATM
MAC
LANE Client
(LEC)
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LANE Client
(LEC)
34
LANE and Spanning Trees
LANE Protocol supports IEEE spanning tree protocol
‹ LECs within switches or LAN bridges exchange bridge
packets (BPDU) for the spanning tree protocol using BUS
‹
™
For each emulated LAN:
9
™
BUS: Forwards BPDU to all LECs in the emulated LAN
9
™
Bridge sends BPDUs over the “multicast send” VC to the BUS.
Each BPDU is seen by all other bridges (as in an Ethernet LAN)
If a bridge detects a loop (using the spanning tree protocol):
9
Disable one of the external ports involved in the loop
9
First: Turn off LAN ports, then ATM ports (with higher
bandwidth)
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Implementation (1)
‹
Client functions (LEC):
™
™
‹
Resides on each LANE station connected to the ATM
network
Part of the ATM end station
9 Represents a set of users identified by their MAC
addresses
Server functions (LECS, LES, BUS):
™
™
™
Implemented separately or jointly
On any device with ATM connectivity
9 LANE Protocol: No specification where the components
should be located
However: Vendor prefer to implement server functions in
network devices (ATM switches, routers) instead of in
terminal equipments or end hosts
¾ Ensure a high reliability and performance
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Implementation: Example
Intermediate
Intermediate system
system
Hosts
Work station
Bridges
Routers
Terminal
Terminal stations
stations
ATM Switch
Bridges
Routers
LANE
LANE service
service
implemented
implemented
in
in Router/bridge/
Router/bridge/
switch
switch or
or dedicated
dedicated
station
station
PCs
Intermediate
Intermediate systems
systems
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Implementation (2)
‹
‹
‹
Communication LEC-LEC and LEC-LES:
™
Using an ATM virtual channel connection (VCC)
™
LEC-LES: Control VCC and Data VCC
Emulated LANs can operate on:
™
Switched virtual circuits (SVCs)
™
Permanent virtual circuits (PVCs)
™
A mixture of SVCs and PVCs
Due to the “flat” (non-hierarchical) architecture of
MAC addresses:
™
Bridges flood the emulated LAN with connectivity
information
9
Reducing the scalability of the approach
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Implementation (3)
‹ Interconnection
™
Using routers
‹ Vendors
™
™
™
™
of emulated LANs:
implement LANE protocols on:
ATM network interface cards
ATM switches
LAN switches
Routers
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Optional LANE Capabilities
‹
LE_NARP messages:
™
Send to indicate availability of one particular new MAC address
9
™
™
‹
Distributed to other LECs which update their address caches
Improves convergence for dynamically changing LANs
Intelligent BUS
™
™
¾
‹
For example, after startup of a portable computer
Shares knowledge of MAC address reachability with LES
Then: Direct forwarding of packets to other LECs possible
Minimizes the complexity of the LEC implementation
Virtual LANs
™
Enable multiple emulated LANs (virtual LANs) over a common
ATM network
9
By controlling the assignments of LES and BUS to the LEC,
terminal equipment, bridges and LAN switches
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LANE: Advantages and
Disadvantages
‹ Advantages:
™
™
Enables connectivity between Ethernet / Token
Ring and ATM
Physical flexibility
‹ Disadvantages:
™
™
Limited to bridging (does not scale well)
Bridge or router between emulated LANs
necessary
9 Potential
™
™
performance bottleneck
Problem of managing a bridge / router
QoS of ATM hidden to the routing protocols
(e.g., IP RSVP & OSPF) (LANE v1.0)
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LANE: Updates
‹
LANE 1.0
™
™
Only multiplexing of VCs
No support for multiple LES or BUS within one emulated
LAN
9
‹
Possible problems: Reliability and bottleneck
LANE 2.0
™
™
™
LLC multiplexing to share VCC between different
protocols
ABR support and other QoS categories of ATM
Improved multicast capabilities:
9
Define filters determining which members of the
emulated LAN receive a particular multicast message (no
pure broadcast anymore)
™
Support for MPOA (Multiprotocol over ATM)
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With Buffering of Frames
IP/ARP
LECA
BUS
LES
LECB
IP/ARP
IPA, MACA
Packet IP 1
IPA -> IPB
MACB, IPB
ARP(IPA, MACA, IPB, MACB?)
MACA -> broadcast
LE_DATA[A
RP(IPA, MAC
A
, IPB , MAC ?)
]
B
ARP(IPA, MACA, IPB, MACB?) CACHE B
MACA -> broadcast
<IPA, MACA>
, ATM A?]
AC , ATMB, MAC A
LE_ARP_REQ[M B
LE_ARP_RESP[M
CACHE A
ACB, ATM , MAC ,
B
A ATMA]
ARP_REPLY(IPA, MACA, IPB, MACB)
MACB -> MACA
CACHE B
<MACA, ATMA>
<MACB, ATMB>
UNI signaling – establishment of SVC ATMB-ATMA
CACHE A
<IPB, MACB>
ARP_REPLY(IPA, MACA, IPB, MACB)
)]
IP , MACB
P A, MAC A, B
(I
Y
L
P
E
[ARP_R
LE_DATA
AC
MACB -> M A
MACB -> MACA
ETHER[Packet IP 1]
MACA ->MACB
LE_DATA[E
THER[Packe
t IP 1]]
MACA ->MAC
B
ETHER[Packet IP 1]
Packet IP 1
MACA ->MACB
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Without Buffering
(BUS used to send unknown traffic)
IP/ARP
LECA
BUS
LES
LECB
IP/ARP
IPA, MACA
Packet IP 1
IPA -> IPB
MACB, IPB
ARP(IPA, MACA, IPB, MACB?)
LE_DATA[ARP(IPA, MACA, IPB, MACB?)]
MACA -> broadcast
ARP(IPA, MACA, IPB, MACB?) CACHE B
MACA -> broadcast
<IPA, MACA>
, ATM A?]
AC , ATMB, MAC A
LE_ARP_REQ[M B
CACHE A
<IPB, MACB>
ARP_REPLY(IPA, MACA, IPB, MACB)
, MAC A, IP B,
RP_REPLY(IP A
LE_DATA[A
C
MAC -> MA A
ARP_REPLY(IPA, MACA, IPB, MACB)
MACB -> MACA
MACB)]
B
MACB -> MACA
ETHER[Packet IP 1]
MACA ->MACB
CACHE A
<MACB, ATMB>
LE_ARP_REQ[MACA, ATMA, MACB, ATMB?]
LE_ARP_RES
LE_DATA[E
P[MAC , ATM
THER[Packe
A
A MACB , ATM
t IP 1]]
B]
MACA ->MA
CB
CACHE B
<MACA, ATMA>
ETHER[Packet IP 1]
Packet IP 1
MACA ->MACB
Packet IP 2
IPA -> IPB
ETHER[Packet IP 2]
MACA ->MACB
UNI signaling – establishment of SVC ATMB-ATMA
LE_DATA[E
THER[Packe
t IP 2]]
MACA ->MAC
ETHER[Packet IP 2]
B
Packet IP 2
MACA ->MACB
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ATM in
Local Area Networks
Multiprotocol Encapsulation
over AAL5
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Basic Modes of Operation
Different
LAN
ATM
device
Different
LAN
ATM network
protocols
ATM
device
ATM network
protocols
ATM
device
LLC/SNAP encapsulation
(Protocol multiplexing)
‹
ATM
device
VC multiplexing
RFC 2684: defines specific formats for multiprotocol
encapsulation over ATM using AAL5. Two transport
mechanisms specified:
™
Protocol encapsulation (or LLC/SNAP encapsulation)
9
™
Provides capability to multiplex several protocols over one VCC
VC multiplexing:
9
Each protocol is carried over a separate VCC
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46
LLC/SNAP Encapsulation
‹
‹
Adds an IEEE 802.2 Logical Link Control (LLC)
SubNetwork Attachment Point (SNAP) header to
the Protocol Data Unit (PDU)Î therefore:
LLC/SNAP encapsulation
LLC/SNAP header: Identifies the PDU type
™
‹
Advantages:
™
‹
Enables multiplexing of distinct protocols over a single
VC
Lower costs (if costs determined per VC)
Disadvantages:
™
™
Same QoS and bandwidth for all multiplexed protocols in
one VC
Lower efficiency
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LLC Encapsulation PDUs
(Used in LANE 2.0)
Application Payload
Bridge / Router
PDU
LANE PDU
RFC
2684
PDU
AAL 5
PDU
LLC / SNAP
Header
Bridge/Router
Header
LECID (2
Bytes)
Application Payload
Bridge
Tail
Bridge / Router PDU
LANE PDU
RFC 2684 PDU
AAL 5
Tail
ATM Cells
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LLC/SNAP Encapsulation: Header
Fields
(Non-ISO
Protocols)
LLC
SNAP
DSAP SSAP
FE
FE
Ctrl
03
OUI
FE-FE = ISO Frame
AA-AA = SNAP Header
(bridge / router frame)
Unnumbered
Unnumbered
Information
Information
Frame
Frame
00-80-C2
00-80-C2 == Bridge
Bridge PDU
PDU
00-00-00
00-00-00 == Routed
Routed PDU
PDU
PID Type
Bridge / Router PDU
00-01
00-01 == 802.3
802.3 Bridge
Bridge PDU
PDU (CRC
(CRC included)
included)
00-02
00-02 == 802.4
802.4 Bridge
Bridge PDU
PDU (CRC
(CRC included)
included)
00-03
00-03 == 802.5
802.5 Bridge
Bridge PDU
PDU (CRC
(CRC included)
included)
00-04
=
FDDI
Bridge
PDU
(CRC
included)
00-04 = FDDI Bridge PDU (CRC included)
00-07
00-07 == 802.3
802.3 Bridge
Bridge PDU
PDU (without
(without CRC)
CRC)
00-08
00-08 == 802.4
802.4 Bridge
Bridge PDU
PDU (without
(without CRC)
CRC)
00-09
00-09 == 802.5
802.5 Bridge
Bridge PDU
PDU (without
(without CRC)
CRC)
00-0A
00-0A == FDDI
FDDI Bridge
Bridge PDU
PDU (without
(without CRC)
CRC)
00-0B
00-0B == 802.6
802.6 Bridge
Bridge PDU
PDU
00-0E
00-0E == 802.1(d)
802.1(d) or
or 802.1(g)
802.1(g) STAP
STAP Bridge
Bridge PDU
PDU
06-00
06-00 == XNS
XNS Routed
Routed PDU
PDU
08-00
08-00 == IP
IP Routed
Routed PDU
PDU
60-03
60-03 == DECnet
DECnet Routed
Routed PDU
PDU
81-37
81-37 == IPX
IPX Routed
Routed PDU
PDU
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LLC/SNAP Encapsulation: Header
Fields (Routed ISO Protocols)
ISO PDU
≤ 65.532 octets
LLC
DSAP
FE
LLC
LLC
DSAP
DSAP
SSAP
SSAP
SAP
SAP
SSAP
FE
Ctrl
03
Example:
Routed ISO PDU
Logical
Logical Link
Link Control
Control
Destination
Destination SAP
SAP
Source
Source SAP
SAP
Service
Service Access
Access Point
Point
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LLC/SNAP Encapsulation: Header
Fields (Routed Non-ISO Protocols)
DSAP
AA
SSAP
AA
LLC
LLC
DSAP
DSAP
SSAP
SSAP
SAP
SAP
Non-ISO PDU
≤ 65.527 octets
SNAP
LLC
Ctrl
03
OUI
00 00 00
Logical
Logical Link
Link Control
Control
Destination
Destination SAP
SAP
Source
Source SAP
SAP
Service
Service Access
Access Point
Point
PID Type
08 00
SNAP
SNAP
OUI
OUI
PID
PID
Non-ISO routed
PDU (e.g., IP)
SubNetwork
SubNetwork Attachment
Attachment Point
Point
Organizationally
Organizationally Unique
Unique Identifier
Identifier
Protocol
Protocol ID
ID
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LLC/SNAP Encapsulation with Bridges
LLC
DSAP SSAP
AA
AA
SNAP
Ctrl
03
OUI
00 80 C2
LLC
DSAP SSAP
AA
AA
PID Type
PAD MAC destina- Rest of MAC If PID =
0001/
00 00 tion address
frame
00 01
0007
SNAP
Ctrl
03
OUI
00 80 C2
FCS LAN
802.3
PID Type Common.MAC destina- Rest of MAC Common
PDU
00 0B
frame PDU trailer
header tion address
802.6 (MAN)
LLC
LLC
DSAP
DSAP
SSAP
SSAP
SAP
SAP
Logical
Logical Link
Link Control
Control
Destination
Destination SAP
SAP
Source
Source SAP
SAP
Service
Service Access
Access Point
Point
SNAP
SNAP
OUI
OUI
PID
PID
FCS
FCS
SubNetwork
SubNetwork Attachment
Attachment Point
Point
Organizationally
Organizationally Unique
Unique Identifier
Identifier
Protocol
Protocol ID
ID
Frame
Frame Check
Check Sequence
Sequence (CRC)
(CRC)
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VC Multiplexing
‹
Only one protocol per virtual channel (VC)
™
In this case: VCs are multiplexed, not the protocols
Used in scenarios where a user can dynamically create and
release many ATM VCs economically (e.g., in private ATM
networks or ATM SVC networks)
‹ Advantages:
‹
™
™
‹
Disadvantages:
™
‹
Greater number of ATM VCs necessary
Routed protocols:
™
‹
Different protocols can get different QoS levels / bandwidth
More efficient (smaller protocol headers)
Can make use of all 65.535 octets of an AAL5 PDU
Bridged protocols:
™
™
Header fields LLC, OUI, PID not necessary.
Using the LAN FCS is implicitly defined by the VCC association
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Selection of Multiplexing Method
‹ PVCs:
™
Configuration option to be chosen manually
‹ SVCs:
™
™
Information elements in the signaling protocol
between two routers about what multiplexing
method to use
Also: signaling whether FCS is included in the
PDU or not
‹ Decision
™
which method to use:
Also depends on the efficiency of each method
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Efficiency of Multiplexing Methods
‹
Efficiency: Example
™
Encapsulation of an TCP/IP ACK packet (40 bytes: 20 bytes
TCP and 20 bytes IP)
Cell
header
TCP/IP
ACK
Trailer
AAL5
VC Multiplexing
5
40
8
11ATM
ATMcell
cell
Payload
Payloadefficiency:
efficiency:
40+8/48
40+8/48==100%
100%
Cell
header
LLC/
SNAP
5
8
Cell
TCP/IP
ACK
header
40
5
PAD
AAL5
Trailer
AAL5
40
8
LLC/SNAP
Encapsulation
22ATM
ATMcells
cells
Payload
Payloadefficiency:
efficiency:
48
48++88//96
96==58%
58%
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