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Data/Link Layer Issues

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What the IEEE standard covers- Physical layer and. interface to ... CSMA/CD 'Carrier Sense/Multiple Access. with Collision Detection' ... CSMA/CD - A ... – PowerPoint PPT presentation

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Title: Data/Link Layer Issues


1
Data/Link Layer Issues
  • Protocol Services
  • Topology
  • Error Detection Recovery

2
Topology vs Geography
Physical Layout How the signal actually travels
Logical Layout "How devices talk to each other"
-or- "How devices hear each other"
3
Topologies
4
BUS
Every node hears every other node's
transmission directly.
5
Ring
Series of unidirectional point-to-point
links without "store forward", usually with a
bypass ability.
6
Star
Switching functions all in central node
7
Mesh
Each node independently routes over
(bi-directional) point-to-point links.
8
IEEE OSI
LLC
2
MAC
1
PHY
LLC Logical Link Control MAC Media Access
Control PHY Physical
9
Link/Physical Layer Standards
  • Ethernet
  • 10BASET, Fast Ethernet, Gigabit Ethernet
  • Token Ring
  • 4/16MB
  • FDDI
  • ATM

10
Ethernet IEEE 802.3
What the IEEE standard covers- Physical layer
and interface to the link layer. IEEE 802.2 is
the Link layer standard. History-
DEC/Intel/Xerox came up with it, then submitted
to IEEE for standardization. Some changes were
made so Ethernet is not identical to IEEE
802.3 Differences between Ethernet and 802.3
There are some electrical and connector
differences most equipment uses IEEE
802.3. There is difference in the header. DIX
uses TYPE, 802.3 uses LENGTH. SInce the frame is
limited in size, the two coexist. Most people use
the DIX format.
11
Ethernet
  • Work started back in 1973 by Bob Metcalfe and
    David Boggs from Xerox Palo Alto Research Center
    (PARC).
  • He studied the Aloha network and "fixed" the
    mathematics.
  • Experimental Ethernet implemented in 1975.
  • Cooperative effort between Digital, Intel, and
    Xerox produced Ethernet Version 1.0 in 1980.
  • This also became known as the Blue Book
    specification or DIX standard. Ethernet V2.0
    adopted in 1982.
  • Ethernet was adopted with modifications by the
    standards committees IEEE 802.3 and ANSI 8802/3.
  • Ethernet allows for only connectionless
    communication.

12
CSMA/CD
"Carrier Sense/Multiple Access with
Collision Detection"
"Driving in Boston"
BUS!
51.2 microseconds
"Many stations Listen before talking listen
while talking if a collision, backoff and try
again"
13
Normal Ethernet Operation
14
Ethernet Collisions
B
C
Collision
Data transmission for C
Data transmission for A
A
D
15
CSMA/CD - A Simple Definition
  • A network station wishing to transmit will first
    check the cable plant to ensure that no other
    station is currently transmitting (CARRIER
    SENSE).
  • The communications medium is one cable,
    therefore, it does allow multiple stations access
    to it with all being able to transmit and receive
    on the same cable (MULTIPLE ACCESS).
  • Error detection is implemented throughout the use
    of a station "listening" while it is transmitting
    its data.
  • Two or more stations transmitting causes a
    collision (COLLISION DETECTION)
  • A jam signal is transmitted to network by the
    transmitting stations that detected the
    collision, to ensure that all stations know of
    the collision. All stations will "backoff" for a
    random time.
  • Detection and retransmission is accomplished in
    microseconds.

16
Frame/Packet Format
Preamble
SFD
Dst
Src
Type
Data/Pad
FCS
Size 7 1 6
6 2 46-1500
4 (octets) In IEEE 802.3, the Type field is
used as a Length field. Addresses are
generally (3) octets vendor code, (3) octets
device number.
17
Ethernet Addressing
Each station recognizes three classes of
addresses. Own address Broadcast address (all
1's) Optionally, one or more multicast
addresses Major reason for broadcast is address
discovery. Multicast addresses are used for
specialized link layer functions.
18
Ethernet Cable Names
Name
Fiber
Unshielded Twisted Pair
Thin coaxial
Thick coaxial
RG-8
Wire Type
22 - 26 AWG
62.5/125 micron
RG-58
10BASE5
10BASE2
10BASEF
10BASET
IEEE Name
N/A
Standard Number
IEEE 802.3
IEEE 802.3a
IEEE 802.3i
Other names
Thick net
Thin net
UTP
19
Thick Coax Makeup
Center conductor of tin plated solid copper
conductor
Teflon is used for fire code regulations
20
Thick Coaxial Connection
Pierce clamp
21
Transceivers
  • Transmitter/Receiver AUI on one side, media on
    the other
  • Used on all Ethernet networks and is the device
    that allows data to flow between the controller
    card and the network.
  • Detects errors on the bus cable plant and reports
    them to the station's controller card.
  • For thick coaxial cable, the transceiver is
    external to the controller card and attaches
    directly to the thick coaxial cable via a special
    cable known as the transceiver cable.
  • External transceivers have a SQE function that
    enables the controller to determine the status of
    the transceiver.
  • Usually has status indicators (LEDs) physically
    located on it to indicate the state of the
    transceiver (transmitting, receiving, collision,
    and power.)

22
Thin Coaxial Cable Makeup
Polyethylene foam
Tinned copper wire
Jacket made of PVC or Teflon
EMI braided shielding
23
Thin Coaxial Connection
Concatenation of network attachments
Direct connection to card
T connector
BNC connector at each cable end
24
Thin Coaxial Connection (cont.)
AUI connector
T connector for connection to cable plant
BNC connector
Interface to computer bus
25
UTP Makeup
  • UTP was standardized by the IEEE 802.3 committee
    in October of 1990.
  • Standardized by the EIA under TIA 568A.
  • UTP for LANs is now classified as
  • Category 3 - used for LANs up to 10 Mbps.
  • Category 4 - used for LANs up to 16 Mbps.
  • Category 5 - used for LANs up to 100 Mbps.
  • Cable is made up of 8 strands of 24 AWG wire.
  • Only 2 pair are used for single 10BASET
    connection.

26
Unshielded Twisted Pair
Repeater unit required
  • Unshielded twisted
  • pair cable

100m max cable run
Straight through pins 1, 2, 3 and 6
Unshielded twisted pair atleast two (2)
twists per foot
RJ-45 connector
RJ-45 Connector
8 pin
8 pin
27
Concentrator (Hub) Management
  • With the concentration of the wiring into a
    common point, network managers can manage the hub
    with specialized software.
  • Network management software resides not only in
    the concentrator but on an external workstations
    device (a PC, for example).
  • The workstation can query the concentrator for
    information.
  • Concentrators also allow the control of
    individual ports.
  • This software allows managers to extract
    information from each card that is inserted in
    the repeater. You could query the hub for
    statistics such as
  • number of packets (bytes),
  • number of collisions (single and multiple),
  • number of framing errors,
  • number of time the particular card de-inserted
    itself from the network,
  • ability to turn on/off any repeater card in the
    hub, and
  • all information is time and date stamped.
  • With 10BASET, all information is provided on an
    individual-connection basis, giving a manager
    information right from the desktop.

28
Ethernet Repeaters
  • Extend the network by interconnecting multiple
    segments
  • Extend the physical domain of the network
  • Governed by the IEEE 802.3c working group
    standard.
  • This governs the electrical specifications of a
    repeater.
  • The physical configurations of a repeater varied
    from vendor to vendor.
  • Some repeaters contain the intelligence to
  • detect collisions per cable plant (will not
    repeat collision fragments to other cable
    plants).
  • de-insert themselves from a wiring concentrator
    (when there are excessive errors on the cable
    plant).
  • submit network management information to a
    central controller.
  • Repeaters have been transformed into wiring
    concentrators or hubs
  • Repeaters can be used to interconnect different
    wiring types but not different access methods
    (i.e., not Token Ring to Ethernet).

29
IEEE802.3 Efficiency
"WARNING Opinion" Utilization
Status 0 - 10 Great! 10 -
40 OK 40 - 60
Performance Problems -- look at it 60

"Utilization"
Signal On
Time
30
Token Ring - IEEE 802.5
What the IEEE standard covers History Differen
ces between 802.5 and 802.3
"Physical layer standard (gives link layer
format)"
Essentially an IBM standard 'given' to the
industry"
"Guaranteed response Priorities Controlled
delays"
31
Token Ring History
  • Presented by IBM in 1982 to IEEE 802 committee.
  • First prototype developed in 1983 in Geneva,
    Switzerland.
  • Cabling System was announced in 1984.
  • Officially announced in 1985.
  • Standardized by IEEE in 1985.
  • Only one adopted by the IEEE 802.5 committee.

32
Token Ring Technology Summary
  • Access method by which network attachments gain
    access to the cable plant by acquiring a special
    frame called the token. Token is a special
    24-bit pattern that continuously circulates the
    ring.
  • Token Ring is a broadcast medium. To receive
    data, a destination station performs an address
    match.
  • The destination station merely copies the frame
    as it repeats it back to the ring.
  • When the frame arrives back to the source
    station, it strips the frame from the ring and
    then releases the token (4 megabit operation
    only).
  • The token is allowed to be released prior to
    frame reception on 16-megabit rings.
  • Token Ring originally ran at 4 Mbps. Upgraded in
    1989 to 16 Mbps
  • Maximum frame size for 4 Mbps is 4472.
  • This is based only on the fact a station cannot
    hold the token longer than 10 milliseconds.
  • Maximum frame size for 16 Mbps is 17,800.

33
TRN Features
"data rate of 4 or 16Mbps"
Traffic usually (always in 802.5)
unidirectional RAR (802.5) vs RAT (FDDI) for
Token Passing Recovery from lost
token Priorities Frame Structure
"one frame on the net at a time..."
34
Controller Attachment to a MAU
The IBM 8228 MAU
Shielded or UTP cable Lobe cables
35
Cable Connectors
Hermaphroditic or RJ-45 connectors on MAU
DB-9 connector
MAU
Media filter for UTP only
RJ-11 or RJ-45 connector
Media filter can be on-board
36
Multiple MAU Connection
37
MAU Operation
Lobe cables
Relays
MAU top view
Ring out
Ring in
MAU bus
All stations are active
38
MAU Operation (Inactive Station)
Lobe cables
Relays
Closed
Closed
Closed
MAU top view
Ring out
Ring in
MAU bus
Inactive station
39
Token Ring Cable Types
  • Type 1
  • A shielded data grade cable with two solid wire
    twisted pairs.
  • Available in indoor and outdoor versions.
  • Type 2
  • A Type 1 indoor cable with four solid twisted
    pairs of 24 AWG wire.
  • Contains four voice grade wires along with four
    data grade wires.
  • Type 3
  • Unused existing telephone wire or EIA category 3
    wire (4 Mbps operation).
  • Category 4 is needed for 16 Mbps (speed of the
    Token Ring) operation.
  • Must use a special media filter.
  • Type 5
  • 100/140 micron fiber cable used for fiber optic
    repeater links.
  • Type 6
  • Often used for patch cables.
  • Patch cables can be used for MAU-to-MAU
    connection or from a wall outlet to a network
    attachment.

40
Type 3 Media Filter
  • Type 3 cable requires a device known as a media
    filter.
  • Its purpose is to filter out any unwanted
    signals.
  • It is a small rectangular device that is usually
    part of the UTP cable itself.
  • It can be a separate device that attaches to the
    UTP cable at the end of the cable that attaches
    to the controller card.
  • It can be used on 16- or 4-mb Token Rings.
  • It is only used with Type 3 (UTP) cable.

41
802.5 Framing
  • IEEE 802.5 uses special characters, but does not
    use bit stuffing!

Manchester
1 bit
0 bit
Violations!
42
Token Ring Frames
1 byte 1 byte
43
Token Ring Frame Field Definitions
no preset size
Routing Information Fields
IEEE 802.2
SD
AC
DA
Data
FCS
ED
FS
FC
SA
4 bytes
1 byte
1 byte
1 byte
1 byte
1 byte
6 bytes
6 bytes
lt 18 bytes
DSAP
SSAP
Control
Legend
1 or 2 bytes
1 byte
1 byte
  • SD - Starting Delimiter
  • AC - Access Control
  • FC - Frame Control
  • DA - Destination Address
  • SA - Source Address
  • FCS - Frame Control Sequence
  • ED - Ending Delimiter
  • FS - Frame Status

44
The SD and the AC Fields
45
The FC, ED, and FS Fields
Field
Bit 0
Bit 7
FF - indicates a MAC or LLC frame. ZZZZ -
indicates the type of MAC frame.
FC
F F r r Z Z Z Z
I - Intermediate bit
ED
J K 1 J K 1 I E
E - Error bit
A - Address recognized bits
FS
A C r r A C r r
C - Frame copied bits
46
Bit Order Transmissionfor Token Ring
  • Bit 0 is the first bit transmitted.
  • Bit 0 is the left most bit of the byte.
  • Unlike Ethernet, the bits in the bytes are not
    reversed as they are transmitted.
  • Example
  • 40-00-12 are the first three bytes of a MAC
    address.
  • Translated to binary
  • 01000000-00000000-00010010
  • As transmitted on a Token Ring
  • 01000000-00000000-00010010
  • Compared to Ethernet transmission
  • 00000010-00000000-01001000

47
Token Passing Policies (Defn)
  • Multiple Token
  • RAT (FDDI) free token is appended to tail of
    last packet
  • Single Token
  • ? Token is released upon receipt of leading edge
    of own packet
  • Single Packet
  • RAR (802.5)Token is released upon receipt of
    trailing edge of own packet

48
Token Passing Policies (Usage)
  • Multiple Token
  • Allows multiple packets on the segment at one
    time. Good when packet length is less than ring
    latency
  • Single Token
  • More efficient than RAR when packet length is
    about the same as ring latency
  • Single Packet
  • Least efficient, but allows controlling station
    knowledge of (un)successful transfer before the
    token is released (see pg. 224, 1st paragraph)

49
Token Passing Policies (Perf.)
  • Multiple Token
  • Always the best performer, but more complex
  • Single Token
  • Closer to RAR than RAT
  • Single Packet
  • Worst performance
  • KEY POINT Ratio of ring latency to packet
    length, a, is real determiner of performance.
    For a ltlt 1, RAR is OK.

50
Controller Operation - Phases 0 and 1
  • Five-phase initialization
  • Phase 0 - Lobe test
  • The controller transmits frames between the
    controller card and the cable attached between
    the controller card and the MAU.
  • The controller tests to ensure that the lobe
    cable can successfully transmit and receive
    frames.
  • Phase 1 - Monitor Check
  • Station inserts into the ring (flips the relay in
    the MAU) and looks for special frames that are
    transmitted by the monitors.
  • Sets a timer to wait for these frames.
  • If the station does not receive any of the
    frames, the controller assumes
  • it is the first ring station on the network,
  • there is not an Active Monitor present, or
  • inserting into the ring disrupted the ring.
  • The controller may initiate the token claim
    process.

51
Controller Initialization - Phases 2, 3, and 4
  • Phase 2 - Duplicate address check.
  • Checks to ensure that it can successfully
    transmit and receive a frame and to detect other
    stations that might have the same MAC address.
  • The controller transmits a frame to itself.
  • If the frame returns with the address recognized
    bit set, it notifies one of the monitors and
    removes itself from the ring.
  • Phase 3 - Participation in neighbor notification.
  • The station transmits a special frame that will
    identify itself to its downstream neighbor.
  • The station should receive a similar frame for
    its upstream neighbor.
  • Phase 4 - Lan Network Manager Notification
  • Notifies LAN Network Manager about its presence
    on the ring

52
Claim Token Process
  • A ring cannot operate without a token circulating
    on the ring.
  • There is only one token per ring.
  • The token-claiming process allows one station to
    insert the token onto the ring.
  • This station will be elected as the AM.
  • It will purge the ring (ability to transmit a
    frame to itself).
  • After purging the ring, it will insert a new
    token on the ring.
  • The Token-Claim process can be started when the
    AM
  • detects a loss of signal,
  • a timer expires and it has not yet received its
    AM frame back, or the AM
  • cannot receive enough of its own Purge Ring MAC
    frames.
  • It can be started when the SM
  • detects loss of signal or
  • detects expiration of its timer for receiving SM
    frames.

53
Details of the Claim Token Process
  • If there is no token on the ring, all activity
    will cease on the ring.
  • The Active Monitor should be able to recover by
    purging the ring and issuing a new Token.
  • If the Active Monitor cannot recover, the
    token-claim process will begin.
  • Any station will insert its master clock, a
    24-bit delay, and start to transmit Token-Claim
    frames.
  • These frames are received by all stations on the
    ring.
  • The station will follow these frames with idle
    (clock) signals.
  • After transmitting the Token Claim frames, the
    station starts a timer.
  • If it does not receive its frames or someone
    elses claim frames, it will beacon the ring.
  • Once the process is started other stations may
    participate.
  • Stations bid for the right to become the AM.
  • The station with the highest priority (MAC
    address) wins.
  • That station becomes the AM.
  • It will purge the ring and insert a new token.

54
Claim Token Process Example
55
Token Ring Transmit Mode
  • A station that needs to transmit receives the SD
    of approaching frame. This station quits
    transmitting idles (clock signals).
  • Checks for priority.
  • If the priority in the frame is greater than the
    station's priority, then
  • the station sets reservation bits and awaits new
    token.
  • If the priority in the frame is less than or
    equal to the stations priority then
  • the station changes the T bit in the AC field
    from a 0 to a 1,
  • appends its information to the rest of the frame
    and transmits the frame.
  • If the end of its transmission is reached and it
    has not received its current transmission back,
    the station
  • transmits idle characters and awaits current
    transmission.
  • When the station receives its frame back it will
    strip the frame and release the token.
  • The station enters normal repeat mode.

56
Token Ring Copy Mode
  • The destination Token Ring controller recognizes
    its address in the destination field of a
    received frame and copies the frame into its
    buffer.
  • If at any time an error is detected, the copy
    phase ends and the controller sets the A and E
    bits and repeats the frame back to the ring.
  • If no errors are found, the destination sets the
    A and C bits and repeats the frame back to the
    ring.
  • The destination station enters Normal Repeat
    mode.
  • The frame travels on the ring until it reaches
    the originator and that station strips the frame
    off of the ring and submits the token to the ring.

57
Normal Repeat Mode
  • A station in normal repeat mode checks current
    frames and token for signalling errors.
  • If any errors are found the station sets the E
    bit and repeats the frame back to the ring.
  • A station in this mode also checks every frame
    for its address.
  • A duplicate address could be found.
  • If a duplicate address is found, the station will
    transmit a soft error MAC frame to one of the
    monitors.

58
The Active Monitor (AM)
  • Functional address is C00000000001.
  • It must be present in order for the ring to
    function properly.
  • The AM is the kingpin of the ring.
  • The AM
  • tracks lost tokens and ensures that only one
    token exists on a single ring.
  • monitors frames and priority tokens that
    circulate the ring more than once.
  • initiates neighbor notification,
  • provides a latency buffer to recover the clock
    signal and so that at least 24 bits (the size of
    the token) can be transmitted on the ring, and
  • supplies the master clocking .

59
Token Recovery
  • Monitor Station
  • 1 station becomes responsible for monitoring the
    token for token loss or token busy
  • Time Outs
  • Token time out (Beaconing)
  • No monitor (Claim frames (highest addr wins)

60
Options for Token Ring
  • For 16 megabit rings, early token release allows
    a ring station to release the token before
    receiving its original frame back.
  • It is based on the ring length
  • A station will not release the token when it is
    still transmitting its frame and it has started
    to receive its frame back.
  • Allows greater use of Token Ring bandwidth.
  • Token Ring operates at 4 and 16 Mbps.
  • 4 and 16 Mbps controllers are not allowed on the
    same ring.
  • Ring will beacon when this condition occurs.
  • To have 4 and 16 Mbps ring interoperate, you must
    use a data forwarding device such as a bridge or
    a router.
  • IBM is currently experimental with a new Token
    Ring controller which allow it to operate between
    52 - 100 Mbps.

61
Data Link Layer
Uses 'bit pipe' Physical Layer to send
packets Packet Formats - Generic Framing
(Layer 1), Addresses and control information
(layer 2), and data (info from layer 3 and
up) Point-to-Point vs Broadcast - Key idea is
that not all packet formats are alike. One needs
to look at particluar technologies to see what is
needed.
62
Data Link Services
  • Unacknowledged Connectionless Service
  • Most LANs
  • Upper layers handle error recovery
  • Acknowledged Connectionless Service
  • Odd duck. Example?
  • Connection-oriented Service
  • Reliable Delivery ...

63
Link Protocols
Used to provide reliability. Basic idea can be
used at any layer ABP SRP GoBack
N Windowing Flow Control
Don't need to know details at this time, but know
general operation and that they provide assured
delivery.
64
Performance
  • Overhead vs Frame Length
  • Error rate (bit error vs block error)
  • Physical Layer
  • distance
  • propagation delay

65
Error Control
Error Detection - Methods Parity, Checksum, CRC
-- generically Frame Check Sequences Error
Correction - The basic idea is to add redundant
information so that the receiver can deocde the
message even if some (specified) number of bits
are damaged (e.g., Hamming codes) Error
Recovery includes error correction but also
includes actions taken to get a message
retransmitted
66
Connection Oriented Services
  • Two modes of operation
  • Operational
  • Non-operational
  • Operational mode incorporates three functions
  • Link establishment.
  • A source station sends a frame to a destination
    station requesting a connection.
  • The destination station may accept or reject the
    connection request.
  • Information transfer.
  • Allows information to be transferred after a
    connection is set up and the required handshaking
    has taken place.
  • Reliable information is transferred between the
    two stations.
  • Link termination.
  • Either side of the connection may terminate the
    connection at any time.

67
IEEE OSI again
LLC
2
MAC
1
PHY
LLC Logical Link Control MAC Media Access
Control PHY Physical
68
IEEE 802.2 Fields
Bit 0
I/G D D D D D D D D
C/R S S S S S S S
Length of the Information field is access method
dependent
SSAP address
DSAP address
Control
Information
1 byte
1 byte
1 or 2 bytes
Source address
Length field
Destination address
IEEE 802.2 field
CRC
69
SAP Types
  • E0 - Novell NetWare
  • F0 - NetBIOS
  • 06 - TCP/IP
  • 42 - Spanning Tree BPDU
  • FF - Global SAP
  • F4 - IBM Network Management
  • 7F - ISO 802.2
  • 00 - NULL LSAP
  • F8, FC - Remote Program Load
  • 04, 05, 08, 0C - SNA
  • AA - SNAP
  • 80 - XNS
  • FE - OSI

70
SubNetwork Access Protocol (SNAP)
  • Most common implementation of LLC1 is from a
    subsection of the IEEE 802.2 standard known as
    SNAP.
  • At the time of IEEE 802.2s introduction, most
    network protocols were designed to use the
    Ethernet packet format.
  • SNAP allows for the migration of the standard
    network protocols to the IEEE 802.2 format.
  • Supported by TCP/IP, NetWare, OSI, AppleTalk, and
    many other protocols.
  • The second purpose for the SNAP protocol is to
    allow those protocols that do not support the
    IEEE 802 standard to be able to traverse IEEE 802
    LANs.
  • SNAP uses a reserved SAP AA (for both the DSAP
    and SSAP).
  • It uses the unnumbered frame format control
    field equal to 03.
  • Actual SNAP header consumes 5 bytes
  • Three bytes for the Organizationally Unique
    Identifier (OUI) field, and
  • Two bytes for an Ethernet Type field.

71
Protocol Discriminator
SNAP header
Length field
Source address
Destination address
SSAP
Control
Data
Pad
CRC-32
DSAP
AA
AA
03
Type field
OUI
Protocol discriminator
00-00-00
08-00
3 bytes
2 bytes
72
Verification
  • Finite State Machines
  • Estelle Other Languages
  • Petri Nets
  • Blind Faith (or, code it in C...)

73
Naming Conventions
and Confusion
74
Naming Conventions cont
75
Intro to ATM
  • Asynchronous Transfer Mode
  • Text References
  • Sect 2.6
  • Sect 3.6.3
  • Sect 5.6
  • Sect 6.5

76
ATM Background
  • Outgrowth of TELCO transition to integrated
    services
  • Only real gt100Mbit standard
  • Offers multiservice (voice video data) potential
  • Switched architecture familiar to TELCOs, not to
    high speed data networks

77
What is ATM?
Note Tanenbaum considers this more a network
layer technology.
78
ATM - A layered standard
AAL - ATM Adaptation Layer Assembles
and disassembles broadband servicesinto
a stream of cells Each cell has a
header that contains routing information ATM -
Asynchronous Transfer Mode Switches the
cells around the network based on the routing
information in the header Physical Layer
Provides the physical transportation of
cells across the network (Note CCITT
reference model, p. 63)
79
ATM - A Switched Architecture
  • Cells (small, fixed length packets) are switched
    in a connection-oriented manner but not using
    circuits like todays voice.

Switch
Switch
Edge Device
Edge Device
80
What is ATM Switching?
  • Why small cells?
  • (3264)/248 5 header bytes
  • Mixed Traffic
  • Packet (random)vs Circuit (TDM) Switching
  • Q.2931
  • SVC, PVC

81
Physical Layer Options
  • SONET (US)/ SDH (Europe)
  • SMDS
  • DQDB
  • Speeds from DS3 on up! (45Mbs to Gbps)
  • OC-3c gt 155.52Mbps gt 149.76Mbps
  • optical carrier
  • 3rd level in heirarchy
  • full duplex (two strands of fiber)
  • Also OC-12c (622Mbps), OC-48c (2048Mbps)
  • Look at the interesting way to frame cells

82
ATM Adaptation Layer(AAL)
Classes of Service 1, 2, 3/4, 5 1 circuit
emulation 2 variable bit rate service 3/4
connection oriented data service 5
connectionless data service SAR - Segmentation
and Reassembly Convergence Sublayer the
miscellaneous category
83
ATM Cell
ATM cells are constant size packets of 53 bytes
size. -- 48 bytes payload, 5 bytes
header/overhead.
VPI - Virtual Path ID VCI - Virtual Channel
ID Type - Payload type (internal) Res -
reserved CLP- Cell loss priority HEC- Header
Error Control
84
VCI/VPI Operation
A Virtual Channel exists between two
switching points
A Virtual Path contains 'bundles' of VCs
85
ATM Switch Architecture
  • Crossbar
  • Banyan
  • TDM busses
  • Buffering
  • Input
  • Output
  • Both?

86
ATM Protocols
  • UNI, NNI
  • Services
  • LAN Stuff

87
ATM Services
  • CBR
  • VBR (RT, NRT)
  • UBR
  • ABR

88
ATM Quality of Service
  • QoS A contract
  • Traffic Descriptors
  • Cell Rate Options (pg 462)
  • Traffic Shaping
  • Traffic Policing

89
ATM Congestion Control
  • Admission Policy
  • Reservation System
  • Rate Based Control
  • Other

90
ATM Flow Control
The leaky bucket algorithm CLP in ATM
header Frame Relay comparisons
91
Routing
  • IISP (Interim Inter-switch Signaling Protocol)
  • PNNI (Private Network-Network Interface)
  • Phase 1
  • Phase 2

92
IISP
  • Interim
  • Allowed multi-vendor interoperability before
    completion of NNI
  • Signaling
  • Routing via manually configured NSAP prefixes

93
PNNI
  • Topology abstraction
  • Peer group(group of nodes)
  • One switch elected Peer Group Leader
  • All nodes in group have identical view of group
  • Hierarchy of logical groups
  • Up to 105 levels of hierarchy

94
PNNI Routing
NSAP Domain
A12
A2
B
A11
A13
View from A117 at A11
95
Sequence of Events
  • A117 -gt B25
  • Forward to switch (A11)
  • Switch knows topology of A1 group
  • B reachable by A2 - A2 reachable by either A12 or
    A13
  • DTL (Designated Transit List)
  • A12A2B
  • A22A23B
  • B2

96
ATM LAN Stuff
  • LAN Link Layer Domain
  • ELANs VLANs
  • LANE MPOA
  • LECS, LES, BUS

97
LANE v1
  • LAN Emulation
  • No QoS (Quality of Service) Support
  • Uses AAL5 signaling
  • optimized for data transport
  • entire cell payload available for user data
  • LEC - LAN Emulation Client
  • LAN Emulation Service
  • LECS - LAN Emulation Configuration Server
  • LES - LAN Emulation Server
  • BUS - Broadcast and Unknown Server
  • STP (Spanning Tree Protocol) supported

98
LEC - LAN Emulation Client
  • Software process on any ATM-connected LAN switch,
    router, PC, or workstation
  • Layer 2 process
  • Prior knowledge of certain parameters
  • LECs ATM address
  • LAN type to be emulated
  • maximum data frame size
  • any route descriptors (for SR bridging)
  • whether it is willing to proxy (respond to
    LE-ARP)
  • LAN name - SNMPv2 display string

99
LECS - LAN Emulation Configuration Server
  • One per administrative domain
  • Gives identity of ELAN (Emulated LAN)
  • Returns ATM address of LES, type of LAN emulated,
    and maximum PDU size of ELAN
  • Controls which physical LANs are combined to form
    VLANs (Virtual LAN)
  • LECS address known via ILMI or its well-known
    NSAP address

100
LES- LAN Emulation Server
  • Adds LECs to ELAN
  • Assigns LECID to joining LEC
  • Table of address information of LEC
  • MAC address
  • proxy for MAC address
  • Token Ring route descriptors
  • LECs can communicate directly with each other
    only when they are connected to the same LES
  • Multiple LESs on the same physical ATM LAN
  • Answers LE-ARP requests from LECs

101
BUS- Broadcast and Unknown Server
  • During address resolution LEC forwards all frames
    to the BUS
  • floods frames to all LECs
  • after address resolved flush protocol used to
    guarantee order of cells
  • All multicast and broadcast traffic sent through
    BUS
  • Traffic limited to 10 frames/second
  • Intelligent BUS
  • resolve destinations
  • CLS- connectionless server

102
LANE Setup
103
Connections
  • All SVC (switched virtual circuits)
  • SVCs required
  • LECs and LECS
  • LES and LECS
  • Control Direct - LECs and LES
  • pt-mpt Control Distribute - LES to LECs
  • Multicast Send - LECs and BUS
  • pt-mpt Multicast Forward - BUS to LECs
  • Data Direct - LEC and LEC
  • PVC (permanent virtual circuit) possible to
    connect LEC and LECS

104
Virtual Channel Connections
LANE Server (LES)
Broadcast and Unknown Server (BUS)
Control Direct VCC
Control Direct VCC
Multicast Send VCC
Multicast Send VCC
LANE Client (LEC)
LANE Client (LEC)
LANE Client (LEC)
LANE Client (LEC)
Control Distribute VCC
Multicast Forward VCC
LAN Switch
Data Direct VCC
LAN Switch
ATM Host
ATM Host
Configuration Direct VCC
Configuration Direct VCC
LANE Configuration Server (LECS)
105
NHRP
  • Next Hop Resolution Protocol
  • Grew out of ATMARP
  • Only IP
  • Allows shortcut routes (pt-pt)
  • direct VCCs across ATM network
  • Address resolution across multiple IP networks
  • If network unknown, request forwarded to other
    NHSs (Next-hop Server)
  • NHS with knowledge will forward response to
    source router
  • Router must have ability to bypass default route

106
RSVP
  • Resource Reservation Protocol
  • Provides QoS (Quality of Service) guarantees
  • Operates in simplex
  • each direction has separate reservation
  • maps well to ATM (two individual VCCs)
  • Built on IP, but no data transport built-in
  • Only if resources available and does not conflict
    with policy
  • Flowspec (bandwidth and delay) and filterspec
    (type of packets) transmitted downstream
  • hop by hop

107
MPOA
  • Multiprotocol over ATM
  • EDFG (Edge Device Functional Groups)
  • existing LAN segments via LAN switches
  • AHFG (ATM-attached Host Functional Groups)
  • ATM-connected host
  • Layer 3
  • Only supports IP for now
  • Uses LANE for Layer 2 forwarding within a single
    Layer 3 subnet
  • Adaptation of NHRP to provide connectivity
    between hosts in different subnets

108
MPOA Operation
109
Competing Technologies
  • Fast Ethernet
  • 100BASE-TX, 100BASE-FX,100BASE-T4, 100BASE-VG
  • FDDI, FDDI- II
  • HPPI
  • Gigabit Ethernet (IEEE 802.3z)

110
ATM Issues
  • SONET/SDH duplication of services
  • ATM overhead
  • ATM granularity and bandwidth management
  • ATM connectionless service
  • End point synchronization
  • Flow Control !!! (bandwidth allocation,
    correlated traffic)
  • ATM Forum

111
Internetworking
  • Bridges
  • Transparent bridges
  • Source Routing - Transparent Bridges
  • Routers (Network Layer)
  • Brouters

3
2
2
2
1
1
1
1
112
Why Bridges
  • Isolation of Physical Layer Effects
  • Bandwidth Multiplication
  • Security or Traffic Isolation

113
Segmenting Traffic
114
Transparent Bridges
  • Interconnect multiple cable segments to allow for
    extension of a network.
  • Can be used to interconnect different access
    methods (Ethernet to Token Ring) and different
    physical layers.
  • Operate at the data link layer.
  • They are protocol transparent.
  • They are designed to operate regardless of the
    upper-layer protocol.
  • They operate on the source and destination
    address in the MAC header.

115
T-L-F Bridges
  • Bridges only forward traffic destined for other
    cable segments.
  • They operate transparently to any stations that
    are active on the network.
  • Packet formats and software drivers on the
    workstations remain the same.
  • Bridges do not have to be programmed with the
    addresses of all the devices on the network.

116
Learning, Filtering, and Forwarding
117
Filtering - An Example
118
Forwarding - An Example
119
Forwarding Beyond One Bridge
120
Loops
  • Complexity of bridging arises when two or more
    bridges interconnect the same two cable segments.
  • This is called providing redundancy or providing
    a loop.
  • There are problems with this type of design
    including
  • duplicate packets,
  • broadcast packets, and
  • unknown destination packets.

121
Duplicate Packets
122
Broadcasts
123
Unknown Destination Address
124
Spanning Tree Algorithm
  • Bridged networks must allow for redundancy. Only
    one path should be enabled to any destination on
    the network.
  • STA is a protocol unto itself. Dont confuse it
    with the transparent bridge protocol. IEEE
    802.1d
  • In an active STA topology certain bridges are
    allowed to forward packets.
  • Other bridges will participate in the STA but do
    not forward packets.
  • These are backup bridges that dynamically become
    available.
  • Bridges that do not forward packets are placed in
    blocking mode.
  • These bridges still participate in the spanning
    tree protocol.

125
Source Routing Bridges
  • Developed as a bridge protocol for Token Ring
    LANs.
  • Source routing gained popularity due to IBMs
    support of it.
  • It is easy to install a source route network.
  • It is not easy to grow a source route network
    into a large network.
  • Invented due to technical limitations of the
    source route chip set.. Early source route chip
    sets could not be set for promiscuous mode.
  • Source routing was also invented to allow two
    non-routing protocols to be placed on a LAN
    NetBIOS and SNA.
  • Source Routing does not build forwarding tables
    based on MAC addresses.
  • Most of the intelligence for this algorithm is
    found in the network stations.
  • Each frame carries complete route information
    with it.

126
Source Routing Features
  • Source routing requires split intelligence to be
    carried in the node and the bridge.
  • All frames contain routing information, which
    does produce more overhead.
  • Uses STA to configure which bridges will forward
    single route broadcast frames.
  • All paths are active which legally allows loops
    to be designed.
  • Provided a routing solution for those protocols
    that could not be routed (NetBIOS).
  • Easy to follow ring/MAC address for
    troubleshooting.

127
Source Routing Features (cont.)
  • Source Routing originated as an alternative to
    transparent bridging
  • Originally, Token Ring could not be placed in
    promiscuous mode ( requirement for transparent
    bridging) and therefore an alternative model was
    created
  • Allowed for SNA and NetBIOS traffic an attempt to
    enjoy the benefits of routing
  • As a data link layer implementation.

128
Source Routing Overview
  • Each separate ring is assigned a unique ring
    number, assigned on the source route bridge port
    and not on the ring station.
  • Each bridge is assigned a bridge number. There is
    a single number for the whole bridge, no matter
    how many ports it has.
  • End stations try to find destination ring
    stations by broadcasting special discovery
    frames.
  • A frame will contain source route information
    based on one bit in the source address.
  • A source route frame may not cross more than
    seven bridges.
  • At the eighth bridge, the frame is discarded.

129
Source Routing Example
MAU
MAU
2
Find a station off ring
Bridge 5
Node 1
Node 2
Bridge 6
1
Find a station on the local ring
Bridge 7
Ring 4
Ring 3
130
Routing Information Field
131
The Route Designator
Bridge 1
Discovery frame
Ring B
Ring A
RC
RD1 RD2
RC
Token Frame Header
Token Frame Trailer
Token Frame Header
Token Frame Trailer
Routing Control
Routing Control
00B1 00A0
Routing Information Field
Routing Information Field
132
Source Route Frame Types
  • Four types of Source Route frames
  • Single Route Explorer (SRE)
  • Also known as Spanning Tree Explorers (STE)
  • So named by the IEEE 802.5 working group
  • All Routes Explorer (ARE)
  • Specifically Routed Frame (SRF)
  • Single Route Explorer with a specific route
    return.

133
Token Ring to Ethernet Conversion
134
Ethernet to Token Ring Conversion
Copy and bit reverse
Ethernet frame
Type
FCS
DA
SA
Info
Preamble
Copy
SD
AC
FC
DA
SA
RIF
DSAP
SSAP
CTRL
Type
Info
FCS
ED
FS
OUI
Insert
SNAP header
Token Ring frame
135
Token Ring to IEEE 802.3 Conversion
136
IEEE 802.3 to Token Ring Conversion
Copy and bit reverse
IEEE 802.3 frame
FCS
DA
SA
Info
Preamble
SFD
Length
DSAP
SSAP
PAD
CTRL
Cut Insert
Copy
SD
AC
FC
DA
SA
RIF
DSAP
SSAP
CTRL
Info
FCS
ED
FS
Token Ring frame
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