unit i complete
TRANSCRIPT
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UNIT I - HIGH SPEED NETWORKS
Sl.No WEEK/ DATE TOPICS TO BE COVERED PAGE IN TEXTBOOK/REFERENCE
REMARKS
1. Introduction to HSN
2. Frame relay networks R1(82-88) ASSIGNMENT NO:1
3. Asynchronous transfer mode R1(91-92)
4. ATM protocol architecture andATM logical connection
R1(92-98)
5. ATM cell,ATM service categories ,
AAL
R1(98-117)
6. High speed LANs - Fast ethernet,gigabit Ethernet, Fiber channel
R1(121-144)
7. Wireless LANs– Applications&
Requirements
R1(144-147)
8. Architecture of 802.11 R1(147-151) SEMINAR NO:1
TEXT BOOK
1. Jean warland and Pravin Wadaja, “HIGH PERFORMANCE COMMUNICATION NETWORKS”, 2nd
Edition, Jean Harcourt Asia Pvt. Ltd., 2001.
REFERENCES
1. William Stallings, “High Speed Networks and Internet”, 2nd Edition, Pearson Education,2002.
2. Irvan Pepelnjk, Jim Guichard and Jeff Apcar, “Mpls and Vpn Architecture”,
Volume 1 and 2, Cisco Press, 2003
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1.INTRODUCTION TO HIGH
SPEED NETWORKS
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Introduction - Taxonomy
Circuit -Switched Packet -Switched
Virtual CircuitDatagram
Communication
Networks
TDMFDM
Frame Relay
ATM
The Internet
(TCP/IP)
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Circuit-Switching
• Historically – long-haul telecom networksdesigned for voice and/or constant bit rateapplications
• Network resources dedicated to one “call”after circuit setup
• Shortcomings when used for data:
– Inefficient (high idle time) for “bursty” sources – Constant data rate not appropriate for varied
endpoint capabilities
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Packet-Switching
• Historically – network technology designed for generaldata communications
• Basic technology is the same as in the 1970s
• One of the few effective technologies for long distancedata communications in use today
• Frame relay and ATM are variants of packet-switching(using virtual circuits)
•Advantages: – flexible, resource sharing, robust, responsive
• Disadvantages: – Time delays in distributed network, overhead penalties – Need for routing and congestion control
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Packet-Switching
• Data transmitted in short blocks, or packets
• Packet length typically < 1000 octets
• Each packet contains user data plus control
info (routing)
• Store and forward
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Use of Packets
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A Simple Switching Network
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Advantages over Circuit-Switching
• Greater line efficiency (many packets can
go over shared link)
• Data rate conversions
• Non-blocking (e.g. no “busy signals”) under
heavy traffic (but increased delays)
• Each packet can be handled based on a
priority scheme
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Disadvantages relative to Circuit-
Switching• Packets incur delay with every node they pass through
Q * (d prop + dtrans + dqueue + d proc)
• Jitter: variation in end-to-end packet delay• Data overhead in every packet for routing
information, etc
• More processing overhead for every packetat every node traversed… circuit switchinghas little/no processing at each node
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Switching Technique• Large are messages broken up into smaller
“chunks,” generically called packets
• Store and forward packet handling in core
•Two approaches to switching data: – Datagram
• Each packet sent independently of the others
• No call setup
• More reliable (can route around failed nodes or congestion)
– Virtual circuit
• Fixed route established before any packets sent
• No need for routing decision for each packet at each node
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Packet Switching: Datagram
Approach
Advantages:
• No call setup•Flexible routes•Reliability
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Packet Switching: Virtual-Circuit
Approach
Advantages:
• Network services•sequencing•error control
•Performance
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Routing
• Key function of any packet-switchednetwork: forwarding packets to adestination
• Adaptive routing, routes are adjusted basedon: – Node/trunk failure
– Congestion• Nodes (routers/switches) must exchange
information about the state of the network
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The Use of Virtual Circuits
Virtual end-to-end
circuits
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X.25• First commercial packet switched network interfacestandard
• Motivates discussion of frame relay and ATMdesign
• X.25 defines 3 levels of functionalityL1 - Physical level (X.21, EIA-232, etc.): physical
connection of a station to the link
L2 - Link/frame level (LAPB, a subset of HDLC): logical,reliable transfer of data over the physical link
L3 - Packet level: network layer, provides virtual circuitservice to support logical connections between twosubscriber stations (multiplexing)
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User Data and X.25 Protocol Control
Information
•Virtual circuit id#• Sequence #s
3 bytes ≤ 128 bytes
• Flags, address, control, FCS• Link layer framing• Reliable physical transfer
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X.25 Features• Call control packets
– set up and tear down virtual circuits
– use same channel and VC as data
packets• Multiplexing of VCs at layer 3
• Layers 3 (packet) and 2 (frame) both
include extensive flow control anderror control mechanisms
ProcessingProcessing
OverheadOverhead(t(t
proc proc))
at eachat each
node!node!
RESULT:RESULT:64kbps64kbps
Max. dataMax. data
raterate
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2.FRAME RELAY NETWORKS
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Frame Relay Networks
• Most widely deployed WAN link-layer protocol inuse today
• Designed to eliminate much of the processing
overhead in X.25
• Designed to support “bandwidth on demand” for
modern, bursty applications
• Throughput is an order of magnitude higher than
X.25• ITU-T Recommendation I.233 indicates effective
rates of frame relay of up to 2 Mbps, but current
practice is much higher (up to T-3 equivalent, or
44.376 Mbps)
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Frame Relay Networks
Important Improvement over X.25:• Call control signaling is on a separate logical
connection from user data
• Multiplexing/switching of logical connections is at
layer 2 (not layer 3)
• No hop-by-hop flow control and error control;
responsibility of higher layers
• Frames sizes can vary (up to 9000 bytes),supporting all current LAN frame sizes
• Direct support for TCP/IP packets, since no
network layer redundancy
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Comparison of X.25 and Frame Relay
Protocol Stacks
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Virtual Circuits and Frame Relay
Virtual Connections
X.25 Packet-Switching
network
(a) X.25 Packet Switching
(b) Frame Relay
Frame Relay network
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Frame Relay Architecture
• X.25 has 3 layers: physical, link, network
• Frame Relay has 2 layers: physical and data
link (or LAPF)
• LAPF core: minimal data link control
– Preservation of order for frames
– Small probability of frame loss
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LAPF Core
• Frame delimiting, alignment and
transparency
• Frame multiplexing/demultiplexing
• Inspection of frame for length constraints
• Detection of transmission errors
• Congestion control
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LAPF-core Formats
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User Data Transfer Frame
• No connection control fields, which arenormally used for: – Identifying frame type (data or control)
– Sequence numbers, used for error/flow control
• Implication: – Connection setup/teardown carried on separate
channel
– No flow and error control, must be handled byhigher layer in protocol stack
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Frame Relay Call Control
• Frame Relay Call Control – Details of call control depend on the context of
its use – Assumes FR over ISDN
– Generally simpler for point-to-point use
• Data transfer involves:
– Establish logical connection and assign a uniqueDLCI
– Exchange data frames
– Release logical connection
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Frame Relay Call Control
4 message types needed
• SETUP…request link establishment
• CONNECT…reply to SETUP withconnection accepted
• RELEASE…request to clear (tear down) a
connection• RELEASE COMPLETE… reply to SETUP
with connection denied, or response to
RELEASE
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3.ASYNCHRONOUS TRANSFER
MODE(ATM)
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Introduction
• ATM Protocol Architecture
• Logical connections
• ATM cell structure
• Service levels/categories
•ATM Adaptation Layer (AAL)
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Introduction•
ATM evolved from B-ISDN development efforts – Frame Relay: high-speed WAN (1.5+ Mbps)
– ATM: very high speed WAN (155 Mbps and 622Mbps)
• ATM, like Frame Relay, was built on the assumptionthat the underlying physical media was reliable andflexible – minimal error and flow control capabilities
– even more streamlined, therefore faster, than Frame Relay
• Specifications developed by ITU-T and ATM Forum
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ATM Protocol Architecture
• Fixed-size packets called cells – “cell switching” like packet switching
• 2 primary protocol layers relate to ATMfunctions: – Common layer providing packet transfers,
logical connections (ATM)
– Service dependent ATM adaptation layer (AAL)• AAL maps other protocols to ATM
– like IP (AAL5)
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Protocol Model has 3 planes
• User – provides for user information
transfer and associated controls (flow
control, congestion control)• Control – performs call control and
connection control functions (signaling)
• Management – provides plane managementand layer management and coordination
functions
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ATM Protocol Reference Model
Various data rates (155.52 Mbps,622.08 Mbps) over variousphysical media types (Fiber Optic,SONET, UTP, etc.)
Framing, cell structure
& Logical Connections
Map data tothe ATM cellstructure
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User Plane Layers
AALAAL
ATMATM
Userinformation
Userinformation
AALAAL
ATMATM
PHYPHYPHYPHY
ATMATM
PHYPHY
ATMATM
PHYPHY
……
End systemEnd system End systemEnd system Network Network
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User Plane LayersUser
informationUser
information
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Logical Connections
• VCC (Virtual Channel Connection): a
logical connection analogous to a virtualcircuit in X.25, or Frame Relay data link connection – full-duplex flow between end users
– user-network control signaling
– network-network management/routing
• VPC (Virtual Path Connection): a bundle of
VCCs with the same end points (notnecessarily same end-users)
– and switched along the same path
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ATM Connection Relationships
Virtual ChannelVirtual Channel: basic logical communications channel: basic logical communications channelVirtual PathVirtual Path: groups of “common” virtual channels: groups of “common” virtual channelsPhysical Transmission PathPhysical Transmission Path: physical communications link: physical communications link
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VCC (logical connection) Uses• Exchange between end users
– user data
– control signaling (more later )
• Exchange between an end user and a network entity
– control signaling (more later )
• Exchange between 2 network entities – traffic management
– routing functions
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Advantages of Virtual Paths
• Simplified network architecture – allows separation of functionality into into individual logical connections and related
groups of logical connections
• Increased network performance and reliability – network consists of fewer aggregated entities
• Reduced processing and short connection setup
time – complex setup tasks are in virtual paths, simplifies setup
of new virtual channels over existing virtual path• Enhanced network services – supports user-specified
closed groups/networks of VC bundles
Vi t l P th/Vi t l Ch l
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Virtual Path/Virtual Channel
Terminology
Virtual ChannelVirtual Channel (VC) A generic term used to(VC) A generic term used todescribe unidirectional transportdescribe unidirectional transportof cells associated by a commonof cells associated by a commonunique identifierunique identifier
Virtual Channel IdentifierVirtual Channel Identifier (VCI) A unique numerical tag for a(VCI) A unique numerical tag for aparticular VC linkparticular VC link
Virtual Channel LinkVirtual Channel Link A means of unidirectional transportA means of unidirectional transportof cells between the point where aof cells between the point where aVCI is assigned and where it isVCI is assigned and where it is
translated or terminatedtranslated or terminatedVirtual Channel ConnectionVirtual Channel Connection (VCC) A concatenation of VC links(VCC) A concatenation of VC links
that extends between twothat extends between twoconnected ATM end-pointsconnected ATM end-points
Vi t l P th/Vi t l Ch l
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Virtual Path/Virtual Channel
TerminologyVirtual PathVirtual Path (VP) A generic term which describes(VP) A generic term which describes
unidirectional transfer of cells thatunidirectional transfer of cells thatare associated with a common uniqueare associated with a common uniqueidentifieridentifier
Virtual Path IdentifierVirtual Path Identifier (VPI) Identifies a particular VP(VPI) Identifies a particular VP
Virtual Path LinkVirtual Path Link A group of VC links identified by aA group of VC links identified by acommon identifier between the pointcommon identifier between the pointwhere the identifier (VPI) is assignedwhere the identifier (VPI) is assignedand where it is translated orand where it is translated orterminatedterminated
Virtual Path ConnectionVirtual Path Connection (VPC) A concatenation of VP links that(VPC) A concatenation of VP links thatextends between ATM end-pointsextends between ATM end-pointswhere the VCIs are assigned andwhere the VCIs are assigned andwhere they are translated orwhere they are translated or
terminatedterminated
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ATM Connection Relationships
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VPC/VCC Characteristics
• Quality of Service (QoS)• Switched and semi-permanent virtual
channel connections
• Cell sequence integrity• Traffic parameter negotiation and usage
monitoring
– average rate, peak rate, burstiness, peak duration, etc.
• (VPC only) virtual channel identifier
restriction within a VPC
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Call Establishment with Virtual Paths
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ATM Signaling
X
X
X
X
X
X
X
X
X
Private
UNI
Public
UNI
NNI
Private
NNI
Private ATM
network
Public
UNIB-ICI
P u b l i
c U N I
Public ATM
network A
Public ATM
network B
Q-2931Q-2931
Q-2931Q-2931
PNNIPNNI
PNNIPNNI
PNNIPNNI
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Control Signaling
• A mechanism to establish and release VPCsand VCCs (per ITU-T Rec. I.150)
• 4 methods for VCCs: – Semi-permanent VCC: no control signaling required –
Meta-signaling channel: permanent, low data ratechannel for setting up signaling channels – User-to-network signaling virtual channel: set up
between user and network – User-to-user signaling virtual channel: set up
between users within a VPC, allowing users to setup and tear down VCCs, without network intervention
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Control Signaling• 3 methods for VPCs
– Semi-permanent: no control signaling required
– Customer controlled: customer uses a signaling
VCC to request VPC from the network
– Network controlled: Network establishes VPC for
its own control and signaling use
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ATM Cells
• Fixed size
– 5-octet header
– 48-octet information field
• Small cells may reduce queuing delay for
high-priority cells (essential for low delay)
• Fixed size facilitates more efficientswitching in hardware (essential for very
high data rates)
ATM C ll F t
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ATM Cell Format
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Header Format
• Generic flow control (more ->)
• Virtual path identifier (VPI)
• Virtual channel identifier (VCI)
• Payload type (3 bits: identifies cell as user
data or network management cell, presence
of congestion, SDU type)
• Cell loss priority (0: high; 1: low)
• Header error control (more ->)
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Generic Flow Control (GFC)• Control traffic flow at user to network interface (UNI)
to alleviate short term overload
• Two sets of procedures
– Uncontrolled transmission
– Controlled transmission
• Every connection either subject to flow control or not
• Subject to flow control
– May be one group (A) default – May be two groups (A and B)
• Flow control is from subscriber to network
– Controlled by network side
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Single Group of Connections (1)
• Terminal equipment (TE) initializes twovariables
– TRANSMIT flag to 1
– GO_CNTR (credit counter) to 0• If TRANSMIT=1 cells on uncontrolled
connection may be sent any time
• If TRANSMIT=0 no cells may be sent (oncontrolled or uncontrolled connections)
• If HALT received, TRANSMIT set to 0 and
remains until NO HALT
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Single Group of Connections (2)• If TRANSMIT=1 and no cell to transmit on
any uncontrolled connection: – If GO_CNTR>0, TE may send cell on controlled
connection
• Cell marked as being on controlled connection• GO_CNTR decremented
– If GO_CNTR=0, TE may not send on controlled
connection
• TE sets GO_CNTR to GO_VALUE upon
receiving SET signal
– Null signal has no effect
i l l ( ) i ld
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Generic Flow Control (GFC) Field
Coding
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Header Error Control
• 8-bit field - calculated based on the other 32 bits in the header – CRC based on x8 + x2 + x + 1 ->
generator is 100000111• error detection
• in some cases, error correction of single-biterrors in header
• 2 modes: – Error detection
– Error correction
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HEC Operation at Receiver
Based on recognition of fact thatBased on recognition of fact that
bit errors occur in bursts. bit errors occur in bursts.
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Effect of
Error in
Cell Header
I t f R d Bit E
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Impact of Random Bit Errors on
HEC Performance
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Use of HALT
• To limit effective data rate on ATM
• Should be cyclic
• To reduce data rate by half, HALT issued to
be in effect 50% of time
• Done on regular pattern over lifetime of
connection
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ATM Service Categories• Real-time service
– Constant bit rate (CBR )
– Real-time variable bit rate (rt-VBR )
• Non-real-time service
– Non-real-time variable bit rate (nrt-VBR )
– Available bit rate (ABR )
– Unspecified bit rate (UBR )
– Guaranteed frame rate (GFR )
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ATM SERVICE CATEGORIES
Class Description Example
CBR Constant Bit Rate T1 circuit
RT-VBR Real Time Variable Bit Rate Real-timevideoconferencing
NRT-VBR Non-real-time Variable BitRate
Multimedia email
ABR Available Bit Rate Browsing the Web
UBR Unspecified Bit Rate Background filetransfer
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Real Time Services
• Amount of delay
• Variation of delay (jitter)
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CBR
• Fixed data rate continuously available
• Tight upper bound on delay
• Uncompressed audio and video
– Video conferencing
– Interactive audio
– A/V distribution and retrieval
rt VBR
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rt-VBR • Time sensitive application
– Tightly constrained delay and delay variation
• rt-VBR applications transmit at a rate that
varies with time
• e.g. compressed video
– Produces varying sized image frames
– Original (uncompressed) frame rate constant
– So compressed data rate varies
• Can statistically multiplex connections
nrt VBR
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nrt-VBR • May be able to characterize expected traffic
flow
• Improve QoS in loss and delay
• End system specifies:
– Peak cell rate
– Sustainable or average rate
– Measure of how bursty traffic is
• e.g. Airline reservations, banking
transactions
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UBR • May be additional capacity over and above
that used by CBR and VBR traffic
– Not all resources dedicated
– Bursty nature of VBR
• For application that can tolerate some cell
loss or variable delays
– e.g. TCP based traffic
• Cells forwarded on FIFO basis
• Best efforts service
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ABR
• Application specifies peak cell rate (PCR)
and minimum cell rate (MCR)
• Resources allocated to give at least MCR • Spare capacity shared among all ARB
sources
• e.g. LAN interconnection
Guaranteed Frame Rate (GFR)
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• Designed to support IP backbone sub networks
• Better service than UBR for frame based traffic
– Including IP and Ethernet• Optimize handling of frame based traffic passing
from LAN through router to ATM backbone – Used by enterprise, carrier and ISP networks
– Consolidation and extension of IP over WAN• ABR difficult to implement between routers over
ATM network
• GFR better alternative for traffic originating on
Ethernet – Network aware of frame/packet boundaries
– When congested, all cells from frame discarded
– Guaranteed minimum capacity
– Additional frames carried of not congested
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ATM Bit Rate Service Levels
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AAL
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ATM Adaptation Layer (AAL)
• Support higher-level protocols and/or native
applications
– e.g., PCM voice, LAPF, IP• AAL Services
– Handle transmission errors
– Segmentation/reassembly (SAR ) – Handle lost and misinserted cell conditions
– Flow control and timing control
Voice ATM Adaptation Layers
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A/D
s1 , s2 …
Digital voice samples
A/D
Video
… Compression
compressed
frames picture frames
Data
Bursty variable-length
packets
cells
cells
cells
Figure 9.3Leon-Garcia & Widjaja: Communication NetworksCopyright ©2000 The McGraw Hill Companies
AAL
AAL
AAL
p y
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ATM ADAPTATION LAYER ATM ADAPTATION LAYER
(AAL)(AAL)
• Specifically, the AAL receives packets from upper-Specifically, the AAL receives packets from upper-
level protocols and breaks them into the 48-bytelevel protocols and breaks them into the 48-byte
segments that form the payload field of an ATMsegments that form the payload field of an ATM
cell.cell.
• AALprotocol model consists of a Segmentation andAALprotocol model consists of a Segmentation and
Reassembly (SAR) sublayer and ConvergenceReassembly (SAR) sublayer and Convergence
Sublayers (CPCS and SSCS).Sublayers (CPCS and SSCS).
• Convergence Sublayers further subdivided asConvergence Sublayers further subdivided as
Common part & Service SpecificCommon part & Service Specific
•The ATM Adaptation Layer (AAL) provides support for higher-layer
services such as signaling, circuit emulation, voice, and video.
AALs also support packet-based services, such as IP, LANs, and
Frame Relay
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AAL Protocols• AAL layer has 2 sublayers:
– Convergence Sublayer (CS)• Supports specific applications/protocols using AAL
• Users attach via the Service Access Point (like a port
number)• Common part (CPCS) and application service-
specific part (SSCS)
– Segmentation and Reassembly Sublayer (SAR)
• Packages data from CS into ATM cells and unpacksat other end
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AAL AAL
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ATM Adaptation Layer (AAL)
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AAL Types AAL Types
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Applications of AAL and ATM
• Circuit emulation (e.g., T-1 synchronous
TDM circuits)
• VBR voice and video• General data services
• IP over ATM
• Multiprotocol encapsulation over ATM
(MPOA)
• LAN emulation (LANE)
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AAL Protocol and Services
Basis for classification:Basis for classification:
• requirement for a timing relationship betweenrequirement for a timing relationship betweensource and destinationsource and destination
• requirement for a constant bit rate data flowrequirement for a constant bit rate data flow• connection or connectionless transferconnection or connectionless transfer
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AAL Protocols and PDUs
AAL Protocol Descriptions
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AAL Protocol Descriptions
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Service Classes
and AAL typesClass A Class B Class C Class D
Timing
Relation
between
source &
destination
Required Not Required
Bit Rate Constant Variable
Connection
Mode
Connection Oriented Connectio
nless
AAL Types AAL1 AAL2 AAL 3/
4, 5
AAL 3/ 4
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AAL Type 1
• Constant-bit-rate source
• SAR simply packs bits into cells and
unpacks them at destination• One-octet header contains 3-bit SC field to
provide an 8-cell frame structure
• No CS PDU structure is defined since CSsublayer primarily for clocking and
synchronization
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AAL 1 AAL 1
• AAL1, a connection-oriented service, is suitable for handling constant bitAAL1, a connection-oriented service, is suitable for handling constant bitrate sources (CBR), such as voice and videoconferencing.rate sources (CBR), such as voice and videoconferencing.
• The sequence number field (SN) and sequence number protection (SNP)The sequence number field (SN) and sequence number protection (SNP)fields provide the information that the receiving AAL1 needs to verify thatfields provide the information that the receiving AAL1 needs to verify that
it has received the cells in the correct order. The rest of the payload field isit has received the cells in the correct order. The rest of the payload field isfilled with enough single bytes to equal 48 bytes.filled with enough single bytes to equal 48 bytes.
• AAL1 requires timing synchronization between the source and destinationAAL1 requires timing synchronization between the source and destinationand, for that reason, depends on a media that supports clocking, such asand, for that reason, depends on a media that supports clocking, such asSONET. The standards for supporting clock recovery are currently beingSONET. The standards for supporting clock recovery are currently beingdefined.defined.
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AAL 1 AAL 1
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Structured mode AAL1 SAR and CSStructured mode AAL1 SAR and CS
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AAL Type 1
AAL 1
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…Higher layer User data stream
Convergence
sublayer
SAR sublayer
ATM layer
CS PDUs
SAR PDUs
ATM Cells
47 47 47
1 47 1 47 1 47
H H H
5 48
H
5 48
H
5 48
H
b1 b2 b3
Figure 9.10
AAL 1
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AAL Type 2
• Intended for variable bit rate applications thatgenerate bursty data and demand low loss
• Originally, connectionless (AAL4) or connection
(AAL3) oriented, now combined into single format(AAL 3/4)• Provides comprehensive sequencing and error
control mechanisms
AAL Type 3/4 AAL Type 3/4
Intended for use with applications withIntended for use with applications withvariable bit-rate service on multiplevariable bit-rate service on multiplechannels (multiplexing), or low bit rate,channels (multiplexing), or low bit rate,short-frame trafficshort-frame traffic
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AAL 2 AAL 2• Designed to support Variable Bit Rate (“Bandwidth on Demand”)Designed to support Variable Bit Rate (“Bandwidth on Demand”)• Provides for partial payloads to support low rate dataProvides for partial payloads to support low rate data
• Error protection over full PDUError protection over full PDU
• Simple flag to indicate position in messageSimple flag to indicate position in message
• Also AAL 2 was designed to multiplex a number of such low variableAlso AAL 2 was designed to multiplex a number of such low variable bit rate data streams on to a single ATM connection. bit rate data streams on to a single ATM connection.
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AAL2 Operation AAL2 OperationCPS packet
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CPS packetCPS packet• Channel identifier (CID)Channel identifier (CID): CPS can multiplex several streams onto a single: CPS can multiplex several streams onto a single
ATM connection. The CID identifies each channel. CID values areATM connection. The CID identifies each channel. CID values areallocated as follows: the 0 value is used as padding, and the 8 to 255 valuesallocated as follows: the 0 value is used as padding, and the 8 to 255 valuesare valid CID values used to identify channels.are valid CID values used to identify channels.
• Length indicator (LI) Length indicator (LI): Its value is one less than the number of bytes in the: Its value is one less than the number of bytes in the
CPSpacket payload. The default maximum length of the CPS-packetCPSpacket payload. The default maximum length of the CPS-packet payload is 45 bytes. payload is 45 bytes.
• Header error control (HEC) Header error control (HEC): It use the pattern: It use the pattern x x5 +5 + x x2 + 1. The receiver 2 + 1. The receiver uses the contents of the HEC to detect errors in the header.uses the contents of the HEC to detect errors in the header.
• User-to-user-indication (UUI)User-to-user-indication (UUI): used for transferring information between: used for transferring information betweenthe peer CPS users. The CPS transports this information transparently.the peer CPS users. The CPS transports this information transparently.
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AAL2 Operation AAL2 Operation
• (CPS) PDU format(CPS) PDU format
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CPS-PDUCPS-PDU
• Parity (P) Parity (P): A 1-bit field used to detect errors in the STF.: A 1-bit field used to detect errors in the STF.
• Sequence numbers (SN)Sequence numbers (SN): A 1-bit field used to number modulo 2 the: A 1-bit field used to number modulo 2 the
successive CPSPDUs.successive CPSPDUs.
• Offset field (OSF)Offset field (OSF): The CPS-PDU payload can carry CPS packets in a: The CPS-PDU payload can carry CPS packets in avariety of different arrangements. To extract the CPS-packets from thevariety of different arrangements. To extract the CPS-packets from theCPS-PDU payload, a 6-bitCPS-PDU payload, a 6-bit offset field (OSF)offset field (OSF) is used to indicate theis used to indicate thestart of a new CPS-packet in the CPS-PDU payload. Specifically, OSFstart of a new CPS-packet in the CPS-PDU payload. Specifically, OSF
gives the number of bytes between the end of the STF and the start of gives the number of bytes between the end of the STF and the start of the first CPS-packet in the CPS-PDU payload.the first CPS-packet in the CPS-PDU payload.
AAL2 Operation AAL2 Operation
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AAL2 Operationp
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AAL 3/4 AAL 3/4
• AAL3/4 supports both connection-oriented and connectionless data. ItAAL3/4 supports both connection-oriented and connectionless data. It
was designed for network service providers and is closely aligned withwas designed for network service providers and is closely aligned with
Switched Multimegabit Data Service (SMDS). AAL3/4 is used toSwitched Multimegabit Data Service (SMDS). AAL3/4 is used to
transmit SMDS packets over an ATM network.transmit SMDS packets over an ATM network.
• Originally 2 separate AALs:Originally 2 separate AALs:
– – AAL3: Connection-oriented packet svcs (X.25)AAL3: Connection-oriented packet svcs (X.25)
– – AAL4: Connectionless svcs (IP)AAL4: Connectionless svcs (IP)
•• Eventually combined into a single type for all data serviceEventually combined into a single type for all data service
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AAL3/4 CS PDU AAL3/4 CS PDU
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AAL3/4 SAR PDU AAL3/4 SAR PDU
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AAL3/4 Operation AAL3/4 Operation
AAL 3/4
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AAL 3/4
AAL 3/4
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Higher layer
Common part
convergencesublayer
SAR sublayer
ATM layer
Service specific
convergence
sublayer
Information
Assume null
TPAD
User message
Pad message to multiple
of 4 bytes. Add header and trailer.
Each SAR-PDU consists
of 2-byte header, 2-byte
trailer, and 44-byte payload.
H
4 4
2 44 2 2 44 2 2 44 2
…
…
Information
Figure 9.15
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AAL Type 5
• Streamlined transport for connection
oriented protocols
– Reduce protocol processing overhead – Reduce transmission overhead
– Ensure adaptability to existing transport
protocols
– primary function is segmentation and
reassembly of higher-level PDUs
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AAL5AAL5• AAL 5 is used for the transfer of data. Due to its simplicity, it is the mostAAL 5 is used for the transfer of data. Due to its simplicity, it is the most
popular adaptation layer. popular adaptation layer.
• AAL5 is a Simple Efficient Adaptation Layer (SEAL). The Common PartAAL5 is a Simple Efficient Adaptation Layer (SEAL). The Common Part(CP) AAL5 supports Variable Bit Rate (VBR) traffic, both connection-(CP) AAL5 supports Variable Bit Rate (VBR) traffic, both connection-oriented and connectionless.oriented and connectionless.
• It is used to transfer most non-SMDS data, such as classical IP over ATMIt is used to transfer most non-SMDS data, such as classical IP over ATMand LAN Emulation (LANE).and LAN Emulation (LANE).
• Efficiency: Efficiency:
AAL3/4: 4 bytes per message + 4 bytes per cell => 44 User Data BytesAAL3/4: 4 bytes per message + 4 bytes per cell => 44 User Data Bytes/ Cell/ Cell
AAL5: 8 bytes per message => 48 User Data Bytes / Cell, 8%AAL5: 8 bytes per message => 48 User Data Bytes / Cell, 8%improvementimprovement
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AAL5 CS PDU AAL5 CS PDU
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AAL5 CS PDU AAL5 CS PDU • Padding (Pad) Padding (Pad): It can be between 0 and 47 bytes long, and is added so that: It can be between 0 and 47 bytes long, and is added so thatthe entire CPS-PDU including the padding and the remaining fields in thethe entire CPS-PDU including the padding and the remaining fields in the
trailer becomes an integer multiple of 48 bytes.trailer becomes an integer multiple of 48 bytes.
• CPS user-to-user indication (CPS-UU)CPS user-to-user indication (CPS-UU): A 1-byte field used to transfer : A 1-byte field used to transfer transparently CPS user-to-user information.transparently CPS user-to-user information.
• Common part indicator (CPI)Common part indicator (CPI): A 1-byte field to support future AAL 5: A 1-byte field to support future AAL 5functions.functions.
• Length Length: A 2-byte field used to indicate the length in bytes of the CPS-: A 2-byte field used to indicate the length in bytes of the CPS-
PDU payload .PDU payload .
• CRC-32CRC-32: This 4-byte field contains the FCS calculated by the transmitting: This 4-byte field contains the FCS calculated by the transmittingCPS over the entire contents of the CPS-PDU The pattern used is:CPS over the entire contents of the CPS-PDU The pattern used is: x x32 +32 + x x26 +26 + x x23 +23 + x x22 +22 + x x16 +16 + x x12 +12 + x x11 +11 + x x10 +10 + x x8 +8 + x x7 +7 + x x5 +5 + x x4 +4 + x x2 +2 + x x + 1.+ 1.
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AAL5 SAR AAL5 SAR
• Simply breaks CS PDU into 48-byte chunks and passes them to ATMSimply breaks CS PDU into 48-byte chunks and passes them to ATM
Layer.Layer.
• No overhead bytes added. No overhead bytes added.
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AAL5 Operation AAL5 Operation
AAL5
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AAL5
AAL 5
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Higher layer
Common part
convergence
sublayer
SAR sublayer
ATM layer
PTI = 0
Service specific
convergence
sublayer Assume null
48
(1)
Information
TPAD
…
…
Information
48
(0)
48
(0)
PTI = 0PTI = 1
Figure 9.18
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Copyright ©2000 The McGraw Hill Companies
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S
A
R
C
S
AAL
ATM Adaptation Layer—AALPBX
ATMATM
Adaptation Layer Adaptation Layer
(AAL)(AAL)
ATM Layer ATM Layer
Physical Layer Physical Layer
AAL = CS + SAR • CS—cell tax
• SAR—cell <-> packet
AAL Cell Tax
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1 Byte1 Byte
5 Byte5 ByteHeader Header
47 Byte47 Byte
PayloadPayload
1–481–48
BytesBytes
5 Byte5 ByteHeader Header
1–47 Byte1–47 Byte
PayloadPayload
5 Byte5 Byte
Header Header
44 Byte44 BytePayloadPayload
4 Bytes4 Bytes
5 Byte5 Byte
Header Header
48 Byte48 BytePayloadPayload
nono
taxtax
AAL-1 Cell Tax AAL-2 Cell Tax
AAL-3/4 Cell Tax AAL-5 Cell Tax
AAL Cell Tax
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HIGH SPEED LAN
• Range of technologies
– Fast and Gigabit Ethernet
– Fibre Channel – High Speed Wireless LANs
Why High Speed LANs?
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• Office LANs used to provide basic connectivity – Connecting PCs and terminals to mainframes and
midrange systems that ran corporate applications
– Providing workgroup connectivity at departmental level
– Traffic patterns light• Emphasis on file transfer and electronic mail
• Speed and power of PCs has risen – Graphics-intensive applications and GUIs
• MIS organizations recognize LANs as essential –
Began with client/server computing• Now dominant architecture in business environment
• Intranetworks
• Frequent transfer of large volumes of data
Applications Requiring High
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Speed LANs• Centralized server farms
– User needs to draw huge amounts of data from multiple centralizedservers
– E.g. Color publishing
• Servers contain tens of gigabytes of image data
• Downloaded to imaging workstations
• Power workgroups
• Small number of cooperating users
– Draw massive data files across network
– E.g. Software development group testing new software version or computer-aided design (CAD) running simulations
• High-speed local backbone
– Processing demand grows
– LANs proliferate at site
– High-speed interconnection is necessary
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Classical Ethernet
• Bus topology LAN
• 10 Mbps
• 2 problems: – A transmission from any station can be received
by all stations
– How to regulate transmission
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Solution to First Problem
• Data transmitted in blocks called frames:
– User data
– Frame header containing unique address of destination station
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Figure 6.1
/
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CSMA/CD
Carrier Sense Multiple Access/ Carrier Detection
1. If the medium is idle, transmit.
2. If the medium is busy, continue to listen until thechannel is idle, then transmit immediately.
3. If a collision is detected during transmission,immediately cease transmitting.
4. After a collision, wait a random amount of time,then attempt to transmit again (repeat from step1).
i
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Figure 6.2
Fi 6 3
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Figure 6.3
M di O i 10Mb
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Medium Options at 10Mbps
• <data rate> <signaling method> <max length>
• 10Base5
– 10 Mbps
– 50-ohm coaxial cable bus
– Maximum segment length 500 meters
• 10Base-T
– Twisted pair, maximum length 100 meters – Star topology (hub or multipoint repeater at central point)
10Mb S ifi i (E h )
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10Mbps Specification (Ethernet)
10BASE5 10BASE2 10BASE-T 10BASE-FP
Transmission
medium
Coaxial cable (50
ohm)
Coaxial cable (50
ohm)
Unshielded twisted
pair
850-nm optical fiber
pair
Signaling
technique
Baseband
(Manchester)
Baseband
(Manchester)
Baseband
(Manchester)
Manchester/on-off
Topology Bus Bus Star Star
Maximum segment
length (m)
500 185 100 500
Nodes per segment 100 30 — 33
Cable diameter
(mm)
10 5 0.4 to 0.6 62.5/125 µm
100Mbps Fast Ethernet
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• Use IEEE 802.3 MAC protocol and frame format
• 100BASE-X use physical medium specificationsfrom FDDI – Two physical links between nodes
• Transmission and reception
– 100BASE-TX uses STP or Cat. 5 UTP• May require new cable
– 100BASE-FX uses optical fiber
– 100BASE-T4 can use Cat. 3, voice-grade UTP• Uses four twisted-pair lines between nodes
• Data transmission uses three pairs in one direction at a time
• Star-wire topology – Similar to 10BASE-T
100Mb F E h
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100Mbps Fast Ethernet
100BASE-TX 100BASE-FX 100BASE-T4
Transmission
medium
2 pair, STP 2 pair, Category
5 UTP
2 optical fibers 4 pair, Category
3, 4, or 5 UTP
Signalingtechnique
MLT-3 MLT-3 4B5B, NRZI 8B6T, NRZ
Data rate 100 Mbps 100 Mbps 100 Mbps 100 Mbps
Maximum
segment length
100 m 100 m 100 m 100 m
Network span 200 m 200 m 400 m 200 m
100BASE X
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100BASE-X
• uses a unidirectional data rate 100 Mbps over singletwisted pair or optical fiber link
• encoding scheme same as FDDI
– 4B/5B-NRZI
• two physical medium specifications
– 100BASE-TX
• uses two pairs of twisted-pair cable for tx & rx
• STP and Category 5 UTP allowed
• MTL-3 signaling scheme is used
– 100BASE-FX
• uses two optical fiber cables for tx & rx
• convert 4B/5B-NRZI code group into optical signals
100BASE T4
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100BASE-T4
• 100-Mbps over lower-quality Cat 3 UTP – takes advantage of large installed base
– does not transmit continuous signal between packets
– useful in battery-powered applications
• can not get 100 Mbps on single twisted pair
– so data stream split into three separate streams
– four twisted pairs used
– data transmitted and received using three pairs
– two pairs configured for bidirectional transmission
• use ternary signaling scheme (8B6T)
100BASE-X Data Rate and
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Encoding
• Unidirectional data rate 100 Mbps over
single link
– Single twisted pair, single optical fiber • Encoding scheme same as FDDI
– 4B/5B-NRZI
– Modified for each option
100BASE-X Media• Two physical medium specifications
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Two physical medium specifications
• 100BASE-TX
– Two pairs of twisted-pair cable
– One pair for transmission and one for reception
– STP and Category 5 UTP allowed
– The MTL-3 signaling scheme is used
• 100BASE-FX – Two optical fiber cables
– One for transmission and one for reception
– Intensity modulation used to convert 4B/5B-NRZI codegroup stream into optical signals
– 1 represented by pulse of light
– 0 by either absence of pulse or very low intensity pulse
100BASE-T4• 100-Mbps over lower-quality Cat 3 UTP– Taking advantage of large installed base
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Taking advantage of large installed base
– Cat 5 optional
– Does not transmit continuous signal between packets – Useful in battery-powered applications
• Can not get 100 Mbps on single twisted pair – Data stream split into three separate streams
• Each with an effective data rate of 33.33 Mbps
– Four twisted pairs used
– Data transmitted and received using three pairs
– Two pairs configured for bidirectional transmission
• NRZ encoding not used – Would require signaling rate of 33 Mbps on each pair
– Does not provide synchronization
– Ternary signaling scheme (8B6T)
100BASE T O ti
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100BASE-T Options
Full Duplex Operation• Traditional Ethernet half duplex
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p – Either transmit or receive but not both simultaneously
• With full-duplex, station can transmit and receivesimultaneously
• 100-Mbps Ethernet in full-duplex mode, theoreticaltransfer rate 200 Mbps
• Attached stations must have full-duplex adapter cards
• Must use switching hub – Each station constitutes separate collision domain
– In fact, no collisions
– CSMA/CD algorithm no longer needed
– 802.3 MAC frame format used
– Attached stations can continue CSMA/CD
Mixed Configurations• Fast Ethernet supports mixture of existing 10-Mbps
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Fast Ethernet supports mixture of existing 10 Mbps
LANs and newer 100-Mbps LANs
• E.g. 100-Mbps backbone LAN to support 10-Mbps
hubs
– Stations attach to 10-Mbps hubs using 10BASE-T
– Hubs connected to switching hubs using 100BASE-T• Support 10-Mbps and 100-Mbps
– High-capacity workstations and servers attach directly to
10/100 switches
– Switches connected to 100-Mbps hubs using 100-Mbpslinks
– 100-Mbps hubs provide building backbone
• Connected to router providing connection to WAN
Gigabit Ethernet Configuration
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g g
Gigabit Ethernet – Physical
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• 1000Base-SX – Short wavelength, multimode fiber
• 1000Base-LX – Long wavelength, Multi or single mode fiber
• 1000Base-CX – Copper jumpers <25m, shielded twisted pair
• 1000Base-T
– 4 pairs, cat 5 UTP
• Signaling - 8B/10B
Gbit Ethernet Medium Options
(l l )
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(log scale)
10Gbps Ethernet - Uses• High-speed, local backbone interconnection between large-
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capacity switches
• Server farm• Campus wide connectivity
• Enables Internet service providers (ISPs) and network
service providers (NSPs) to create very high-speed links at
very low cost• Allows construction of (MANs) and WANs
– Connect geographically dispersed LANs between campuses or
points of presence (PoPs)
• Ethernet competes with ATM and other WAN technologies
• 10-Gbps Ethernet provides substantial value over ATM
10Gbps Ethernet - AdvantagesN i b d idth i i
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• No expensive, bandwidth-consuming conversion
between Ethernet packets and ATM cells• Network is Ethernet, end to end
• IP and Ethernet together offers QoS and traffic
policing approach ATM
• Advanced traffic engineering technologies
available to users and providers
• Variety of standard optical interfaces (wavelengths
and link distances) specified for 10 Gb Ethernet• Optimizing operation and cost for LAN, MAN, or
WAN
10Gbps Ethernet - Advantages• Maximum link distances cover 300 m to 40 km
• F ll d ple mode onl
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• Full-duplex mode only
• 10GBASE-S (short): – 850 nm on multimode fiber
– Up to 300 m
• 10GBASE-L (long) – 1310 nm on single-mode fiber
– Up to 10 km• 10GBASE-E (extended)
– 1550 nm on single-mode fiber
– Up to 40 km
• 10GBASE-LX4: – 1310 nm on single-mode or multimode fiber
– Up to 10 km
– Wavelength-division multiplexing (WDM) bit stream across four light waves
Figure 6 11
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Figure 6.11
Fibre Channel - Background
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• I/O channel
– Direct point to point or multipoint comms link
– Hardware based
– High Speed
– Very short distance – User data moved from source buffer to destination buffer
• Network connection
– Interconnected access points
– Software based protocol
– Flow control, error detection &recovery
– End systems connections
Fibre Channel
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Fibre Channel
• 2 methods of communication with processor: – I/O channel
– Network communications• Fibre channel combines both
– Simplicity and speed of channel
communications – Flexibility and interconnectivity of network communications
Fibre Channel I/O channel Oriented
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Facilities• Data type qualifiers for routing payload
• Link-level constructs for individual I/Ooperations
• Protocol specific specifications to supporte.g. SCSI
Fibre Channel Network-Oriented
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Facilities
• Full multiplexing between multiple
destinations
• Peer-to-peer connectivity between any pair of ports
• Internetworking with other connection
technologies
Fibre Channel Requirements
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Fibre Channel Requirements
• Full duplex links with 2 fibres/link • 100 Mbps – 800 Mbps• Distances up to 10 km• Small connectors• high-capacity• Greater connectivity than existing multidrop
channels• Broad availability
• Support for multiple cost/performance levels• Support for multiple existing interface command
sets
Fibre Channel Elements
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Fibre Channel Elements
• End systems - Nodes
• Switched elements - the network or fabric
• Communication across point to point links
Fibre Channel Network
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Fibre Channel Network
Fibre Channel Protocol Architecture
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Fibre Channel Protocol Architecture
• FC-0 Physical Media
• FC-1 Transmission Protocol
• FC-2 Framing Protocol• FC-3 Common Services
• FC-4 Mapping
Fibre Channel ProtocolArchitecture (1)
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Architecture (1)• FC-0 Physical Media
– Optical fiber for long distance
– coaxial cable for high speed short distance
– STP for lower speed short distance
• FC-1 Transmission Protocol – 8B/10B signal encoding
• FC-2 Framing Protocol
– Topologies
– Framing formats
– Flow and error control
– Sequences and exchanges (logical grouping of frames)
Fibre Channel Protocol
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• FC-3 Common Services
– Including multicasting
• FC-4 Mapping – Mapping of channel and network services onto
fibre channel
• e.g. IEEE 802, ATM, IP, SCSI
Architecture (2)
Fibre Channel Physical Media
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Fibre Channel Physical Media
• Provides range of options for physical
medium, the data rate on medium, and
topology of network
• Shielded twisted pair, video coaxial cable,
and optical fiber
• Data rates 100 Mbps to 3.2 Gbps• Point-to-point from 33 m to 10 km
Topologies
• Point to point topology
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• Point-to-point topology
– Only two ports – Directly connected, with no intervening switches
– No routing
• Arbitrated loop topology – Simple, low-cost topology
– Up to 126 nodes in loop
– Operates roughly equivalent to token ring• Topologies, transmission media, and data
rates may be combined
Fibre Channel Fabric• General topology called fabric or switched topology
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p gy p gy
• Arbitrary topology includes at least one switch to interconnect number
of end systems• May also consist of switched network
– Some of these switches supporting end nodes
• Routing transparent to nodes
– Each port has unique address
– When data transmitted into fabric, edge switch to which node
attached uses destination port address to determine location
– Either deliver frame to node attached to same switch or transfers
frame to adjacent switch to begin routing to remote destination
Fabric Advantages
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• Scalability of capacity
– As additional ports added, aggregate capacity of network increases
– Minimizes congestion and contention
– Increases throughput
• Protocol independent• Distance insensitive
• Switch and transmission link technologies maychange without affecting overall configuration
• Burden on nodes minimized – Fibre Channel node responsible for managing point-to-
point connection between itself and fabric
– Fabric responsible for routing and error detection
Five Applications of Fibre
Channel
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Channel
WLANs – Wireless LANs
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WLANs Wireless LANs
• Rely upon wireless transmission media
• Infrared, spread spectrum, narrowband
microwave• Follow IEEE 802.11 standard
– Services include managing associations,
delivering data, and security
WLAN Advantages
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WLAN Advantages
• Mobility – enable users to access data while
they are on the move
• Ease and speed of deployment – older building difficult to wire, cable installation
costs, etc.
• Flexibility – no need to re-cable or reconfigure network when someone
changes offices
• Cost
WLAN applications
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WLAN applications
• LAN extension - extension of an existing
wired LAN
– for large open areas; historical buildings; small
offices, etc.
• Cross-Building Interconnect
– Connect two buildings without wires
• Nomadic access
• Ad hoc networking
Multi-Cell Wireless LAN
C fi i
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Configuration
Infrastructure Wireless LAN
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Infrastructure Wireless LAN
Applications –
Ad H N ki
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Ad Hoc Networking
• Peer-to-peer network
• Set up temporarily to meet some immediate
need• E.g. group of employees, each with laptop
or palmtop, in business or classroom
meeting• Network for duration of meeting
Wireless LAN Requirements• Same as any LAN
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– High capacity, short distances, full connectivity, broadcastcapability
• Throughput: efficient use wireless medium
• Number of nodes:up to hundreds of nodes across multiplecells
• Connection to backbone LAN: Use control modules to
connect to both types of LANs
• Service area: 100 to 300 m
• Low power consumption:Need long battery life on mobilestations
– Mustn't require nodes to monitor access points or frequenthandshakes
• Transmission robustness and security:Interference proneand easily eavesdropped
• Collocated network operation:Two or more wireless LANs
WLAN Technology• Infrared (IR) LANs: Individual cell of IR LAN
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limited to single room – high speed
– IR light does not penetrate opaque walls – High security for a small area, and no interference from
other IR LANs in other rooms
– Can’t use outdoors – need to
•Spread spectrum LANs: Mostly operate in ISM(industrial, scientific, and medical) bands – No Federal Communications Commission (FCC)
licensing is required in USA
• Narrowband microwave: Microwave frequencies
but do not use spread spectrum – just wide enoughto transmit – Some require FCC licensing, which guarantees no
channel interference
IEEE 802.11 Architecture
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80 . c ec u e
802.11 Nomenclature and Design
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g
• Access Points – perform the wireless to
wired bridging function between networks
• Wireless medium – means of movingframes from station to station
• Station – computing devices with wireless
network interfaces• Distribution System – backbone network
used to relay frames between access points
Access and Privacy Services -
Authentication• On wireless LAN, any station within radio range of other devices can
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transmit
• Any station within radio range can receive• “Wireless Ethernet”
• Authentication: Used to establish identity of stations to each other
– Wired LANs assume access to physical connection conveysauthority to connect to LAN
– Not valid assumption for wireless LANs• Connectivity achieved by having properly tuned antenna
– Authentication service used to establish station identity
– 802.11 supports several authentication schemes
– Does not mandate any particular scheme
– Range from relatively insecure handshaking to public-keyencryption schemes
– 802.11 requires mutually acceptable, successful authentication before association
Medium Access Control
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• MAC layer covers three functional areas
– Reliable data delivery
– Access control
– Security
• Beyond our scope
Reliable Data Delivery• 802.11 physical and MAC layers subject to unreliability
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• Noise, interference, and other propagation effects result in
loss of frames• Even with error-correction codes, frames may not
successfully be received
• Can be dealt with at a higher layer, such as TCP
– However, retransmission timers at higher layerstypically order of seconds
– More efficient to deal with errors at the MAC level
• 802.11 includes frame exchange protocol
– Station receiving frame returns acknowledgment (ACK)frame
– Exchange treated as atomic unit
• Not interrupted by any other station
– If noACK within short period of time, retransmit
Distributed Coordination Function
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• DCF sublayer uses CSMA
• If station has frame to transmit, it listens to medium
• If medium idle, station may transmit
• Otherwise must wait until current transmission complete
• No collision detection – Not practical on wireless network
– Dynamic range of signals very large
– Transmitting station cannot distinguish incoming weak
signals from noise and effects of own transmission• DCF includes delays
– Amounts to priority scheme
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IEEE 802.11Medium
Access
ControlLogic
802.11 Physical Layer • Issued in four stages
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• First part in 1997 – IEEE 802.11
– Includes MAC layer and three physical layer specifications
– Two in 2.4-GHz band and one infrared
– All operating at 1 and 2 Mbps
• Two additional parts in 1999 – IEEE 802.11a
• 5-GHz band up to 54 Mbps
– IEEE 802.11b• 2.4-GHz band at 5.5 and 11 Mbps
• Most recent in 2002 – IEEE 802.g extends IEEE 802.11b to higher data rates
Original 802.11 Physical Layer -
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DSSS• Three physical media
• Direct-sequence spread spectrum
– 2.4 GHz ISM band at 1 Mbps and 2 Mbps – OR
• FHSS
– 2.4 GHz ISM band at 1 Mbps and 2 Mbps – OR
• Infrared
At 1 and 2 Mb s
802.11a• 5-GHz band
U th l f di i i
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• Uses orthogonal frequency division
multiplexing (OFDM) – Not spread spectrum
• Also called multi-carrier modulation
• Multiple carrier signals at differentfrequencies
• Some bits on each channel
– Similar to FDM but all subchannels dedicated tosingle source
• Data rates 6, 9, 12, 18, 24, 36, 48, and 54Mbps
802.11b
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• Extension of 802.11 DS-SS scheme
• 5.5 and 11 Mbps
802.11g
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g
• Higher-speed extension to 802.11b
• Combines physical layer encoding
techniques used in 802.11a and 802.11b to provide service at a variety of data rates
Chapter 17 – Review Questions
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• Discuss the advantages of wireless LANS
• Discuss how a WLAN can be employed to connectLANs from separate buildings
• Describe the purpose of peer-to-peer (ad hoc)networking. Provide examples.
• Describe the WLAN requirements
• Describe an infrared LAN. What are its strengths
and weaknesses?