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Data/Link Layer Issues. Protocol & Services Topology Error Detection & Recovery. Topology vs Geography. Physical Layout How the signal actually travels. Logical Layout "How devices talk to each other" -or- "How devices hear each other". Topologies. BUS.

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Data link layer issues l.jpg
Data/Link Layer Issues

  • Protocol & Services

  • Topology

  • Error Detection & Recovery


Topology vs geography l.jpg
Topology vs Geography

Physical Layout

How the signal

actually travels

Logical Layout

"How devices talk to

each other" -or-

"How devices hear

each other"



Slide4 l.jpg
BUS

• Every node hears every other node's transmission

directly.


Slide5 l.jpg
Ring

• Series of unidirectional point-to-point links

without "store & forward", usually with a bypass

ability.


Slide6 l.jpg
Star

• Switching functions all in central node


Slide7 l.jpg
Mesh

• Each node independently routes over

(bi-directional) point-to-point links.


Ieee osi l.jpg
IEEE & OSI

LLC

2

MAC

1

PHY

LLC = Logical Link Control

MAC = Media Access Control

PHY = Physical


Link physical layer standards l.jpg
Link/Physical Layer Standards

  • Ethernet

    • 10BASET, Fast Ethernet, Gigabit Ethernet

  • Token Ring

    • 4/16MB

  • FDDI

  • ATM


Ethernet ieee 802 3 l.jpg
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.


Ethernet l.jpg
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.


Csma cd l.jpg
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"


Normal ethernet operation l.jpg

B

C

Address mismatch

packet discarded

Address mismatch

packet discarded

Send data

to node D

Address match

packet processed

Transmitted packet seen

by all stations on the LAN

(broadcast medium)

A

D

Data

Normal Ethernet Operation


Ethernet collisions l.jpg
Ethernet Collisions

B

C

Collision

Data transmission

for C

Data transmission for A

A

D


Csma cd a simple definition l.jpg
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.


Frame packet format l.jpg
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.


Ethernet addressing l.jpg
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.


Ethernet cable names l.jpg
Ethernet Cable Names

Name

Thick coaxial

Thin coaxial

Unshielded Twisted Pair

Fiber

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


Thick coax makeup l.jpg

Thick braid for EMI

Foil

Thin braid for EMI

Thin foil bonded to insulation

Jacket of PVC or Teflon

Thick Coax Makeup

Center conductor of tin plated

solid copper conductor

Teflon is used for

fire code regulations


Thick coaxial connection l.jpg

500 meter maximum cable run

Black marks

every 2.5 meters

to show transceiver

placement

Transceiver

cable

Transceiver

Thick Coaxial Connection

Pierce clamp


Transceivers l.jpg
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.)


Thin coaxial cable makeup l.jpg
Thin Coaxial Cable Makeup

Polyethylene foam

Tinned copper wire

Jacket made of PVC or Teflon

EMI braided shielding


Thin coaxial connection l.jpg
Thin Coaxial Connection

Concatenation of network attachments

Direct

connection

to card

T connector

BNC connector at each cable end


Thin coaxial connection cont l.jpg

On-board

transceiver logic

ASIC

02608C

Thin Coaxial Connection (cont.)

AUI connector

T connector for connection

to cable plant

BNC

connector

Interface to computer

bus


Utp makeup l.jpg
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.


Unshielded twisted pair l.jpg
Unshielded Twisted Pair

Unshielded twisted

pair cable

Repeater unit

required

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


Concentrator hub management l.jpg
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 workstation’s 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.


Ethernet repeaters l.jpg
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).


Ieee802 3 efficiency l.jpg
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


Token ring ieee 802 5 l.jpg
Token Ring - IEEE 802.5

What the IEEE standard covers

History

Differences 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"


Token ring history l.jpg
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.


Token ring technology summary l.jpg
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.


  • Trn features l.jpg
    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..."


    Controller attachment to a mau l.jpg
    Controller Attachment to a MAU

    The IBM 8228 MAU

    Shielded or UTP cable

    Lobe cables


    Cable connectors l.jpg

    Token Ring controller

    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


    Multiple mau connection l.jpg

    Ring out

    Ring in

    MAU

    Ring out

    Ring in

    MAU

    Type 6 patch cables

    Ring out

    MAU

    Ring in

    Multiple MAU Connection


    Mau operation l.jpg

    Closed

    Closed

    Closed

    MAU Operation

    Lobe cables

    Relays

    MAU top view

    Ring out

    Ring in

    MAU bus

    All stations are active


    Mau operation inactive station l.jpg
    MAU Operation (Inactive Station)

    Lobe cables

    Relays

    Closed

    Closed

    Closed

    MAU top view

    Ring out

    Ring in

    MAU bus

    Inactive station


    Token ring cable types l.jpg
    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.


    Type 3 media filter l.jpg
    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.


    802 5 framing l.jpg
    802.5 Framing

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

    Manchester

    “1” bit

    “0” bit

    Violations!


    Token ring frames l.jpg

    Physical header

    no preset size

    Physical trailer

    Routing

    Information

    Fields

    IEEE

    802.2

    FC

    DA

    SA

    Data

    FCS

    ED

    FS

    SD

    AC

    MAC or LLC Frame

    Token frame

    SD

    AC

    ED

    1 byte 1 byte 1 byte

    Abort frame

    SD

    ED

    Token Ring Frames

    1 byte 1 byte


    Token ring frame field definitions l.jpg
    Token Ring Frame Field Definitions

    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

    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

    <= 18 bytes

    DSAP

    SSAP

    Control

    Legend

    1 or 2 bytes

    1 byte

    1 byte


    The sd and the ac fields l.jpg

    Field

    Bit 0

    Bit 7

    SD

    J K 0 J K 0 0 0

    PPP - priority bits

    P P P T M R R R

    T - Token bit

    AC

    M - Monitor bit

    RRR - Reservation bits

    The SD and the AC Fields


    The fc ed and fs fields l.jpg
    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


    Bit order transmission for token ring l.jpg
    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


    Token passing policies defn l.jpg
    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


    Token passing policies usage l.jpg
    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)


    Token passing policies perf l.jpg
    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 << 1, RAR is OK.


    Controller operation phases 0 and 1 l.jpg
    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.


    Controller initialization phases 2 3 and 4 l.jpg
    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


    Claim token process l.jpg
    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.


    Details of the claim token process l.jpg
    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 else’s 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.


    Claim token process example l.jpg

    Detected condition

    1

    4

    C

    Token Claim

    frames

    B transmits its own

    Token Claim frames

    D

    Not

    participating

    B has higher

    priority than A

    B

    3

    2

    A transmits its own

    Token Claim frames

    Repeat frame

    A

    Higher priority

    than C. Does

    not repeat C’s

    5

    6

    Continues

    transmitting

    its own

    Stops transmitting

    its own Claim frames

    and repeats B’s

    C

    D

    B

    7

    Repeats

    B's Token

    Claim frame

    8

    A

    Stops transmitting its own

    and repeats B’s claim frames

    Claim Token Process Example


    Token ring transmit mode l.jpg
    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 station’s 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.


    Token ring copy mode l.jpg
    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.


    Normal repeat mode l.jpg
    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.


    The active monitor am l.jpg
    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 .


    Token recovery l.jpg
    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)


    Options for token ring l.jpg
    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.


    Data link layer l.jpg
    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.


    Data link services l.jpg
    Data Link Services

    • Unacknowledged Connectionless Service

      • Most LANs

      • Upper layers handle error recovery

    • Acknowledged Connectionless Service

      • Odd duck. Example?

    • Connection-oriented Service

      • Reliable Delivery ...


    Link protocols l.jpg
    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.


    Performance l.jpg
    Performance

    • Overhead vs Frame Length

    • Error rate (bit error vs block error)

    • Physical Layer

      • distance

      • propagation delay


    Error control l.jpg
    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


    Connection oriented services l.jpg
    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.


    Ieee osi again l.jpg
    IEEE & OSI {again}

    LLC

    2

    MAC

    1

    PHY

    LLC = Logical Link Control

    MAC = Media Access Control

    PHY = Physical


    Ieee 802 2 fields l.jpg
    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 or 2 bytes

    1 byte

    Source

    address

    Length

    field

    Destination

    address

    IEEE 802.2 field

    CRC


    Sap types l.jpg
    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


    Subnetwork access protocol snap l.jpg
    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 802.2’s 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.


    Protocol discriminator l.jpg
    Protocol Discriminator

    SNAP

    header

    Destination

    address

    Source

    address

    Length

    field

    SSAP

    Control

    Data

    Pad

    CRC-32

    DSAP

    03

    AA

    AA

    Type

    field

    OUI

    Protocol discriminator

    00-00-00

    08-00

    3 bytes

    2 bytes


    Verification l.jpg
    Verification

    • Finite State Machines

    • Estelle & Other Languages

    • Petri Nets

    • Blind Faith (or, code it in C...)


    Naming conventions l.jpg
    Naming Conventions

    {and Confusion}



    Intro to atm l.jpg
    Intro to ATM

    • Asynchronous Transfer Mode

    • Text References

      • Sect 2.6

      • Sect 3.6.3

      • Sect 5.6

      • Sect 6.5


    Atm background l.jpg
    ATM Background

    • Outgrowth of TELCO transition to integrated services

    • Only “real” >100Mbit standard

    • Offers multiservice (voice video data) potential

    • Switched architecture familiar to TELCOs, not to high speed data networks


    What is atm l.jpg
    What is ATM?

    Note: Tanenbaum considers

    this more a network layer

    technology.


    Atm a layered standard l.jpg
    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)


    Atm a switched architecture l.jpg
    ATM - A Switched Architecture

    • Cells (small, fixed length packets) are switched in a connection-oriented manner but not using circuits like today’s voice.

    • Switch

    • Switch

    Edge

    Device

    Edge

    Device


    What is atm switching l.jpg
    What is ATM Switching?

    • Why small cells?

      • (32+64)/2=48 + 5 header bytes

      • Mixed Traffic

    • Packet (random)vs Circuit (TDM) Switching

    • Q.2931

      • SVC, PVC


    Physical layer options l.jpg
    Physical Layer Options

    • • SONET (US)/ SDH (Europe)

    • • SMDS

    • • DQDB

    • • Speeds from DS3 on up! (45Mbs to Gbps)

    • OC-3c => 155.52Mbps => 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]


    Atm adaptation layer aal l.jpg
    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


    Atm cell l.jpg
    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


    Vci vpi operation l.jpg
    VCI/VPI Operation

    • A Virtual Channel exists between two switching points

    • A Virtual Path contains 'bundles' of VCs


    Atm switch architecture l.jpg
    ATM Switch Architecture

    • Crossbar

    • Banyan

    • TDM busses

    • Buffering

      • Input

      • Output

      • Both?


    Atm protocols l.jpg
    ATM Protocols

    • UNI, NNI

    • Services

    • “LAN” Stuff


    Atm services l.jpg
    ATM Services

    • CBR

    • VBR (RT, NRT)

    • UBR

    • ABR


    Atm quality of service l.jpg
    ATM Quality of Service

    • QoS: A contract

    • Traffic Descriptors

    • Cell Rate Options (pg 462)

    • Traffic Shaping

    • Traffic Policing


    Atm congestion control l.jpg
    ATM Congestion Control

    • Admission Policy

    • Reservation System

    • Rate Based Control

    • Other


    Atm flow control l.jpg
    ATM Flow Control

    • The leaky bucket algorithm

    • CLP in ATM header

    • Frame Relay comparisons


    Routing l.jpg
    Routing

    • IISP (Interim Inter-switch Signaling Protocol)

    • PNNI (Private Network-Network Interface)

      • Phase 1

      • Phase 2


    Slide92 l.jpg
    IISP

    • Interim

      • Allowed multi-vendor interoperability before completion of NNI

    • Signaling

    • Routing via manually configured NSAP prefixes


    Slide93 l.jpg
    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


    Pnni routing l.jpg

    A12

    A22

    B3

    A23

    A21

    B1

    B2

    A11

    A13

    A2

    B

    A1

    B25

    A117

    PNNI Routing

    NSAP Domain

    A12

    A2

    B

    A11

    A13

    View from A117 at A11


    Sequence of events l.jpg
    Sequence of Events

    • A117 -> 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)

      • [A12][A2][B]

      • [A22][A23][B]

      • [B2]


    Atm lan stuff l.jpg
    ATM “LAN” Stuff

    • LAN == Link Layer Domain

    • ELANs & VLANs

    • LANE & MPOA

      • LECS, LES, BUS


    Lane v1 l.jpg
    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


    Lec lan emulation client l.jpg
    LEC - LAN Emulation Client

    • Software process on any ATM-connected LAN switch, router, PC, or workstation

    • Layer 2 process

    • Prior knowledge of certain parameters

      • LEC’s 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


    Lecs lan emulation configuration server l.jpg
    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


    Les lan emulation server l.jpg
    LES- LAN Emulation Server

    • Adds LEC’s 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


    Bus broadcast and unknown server l.jpg
    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



    Connections l.jpg
    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


    Slide104 l.jpg

    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)


    Slide105 l.jpg
    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


    Slide106 l.jpg
    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


    Slide107 l.jpg
    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



    Competing technologies l.jpg
    Competing Technologies

    • “Fast Ethernet”

      • 100BASE-TX, 100BASE-FX,100BASE-T4, 100BASE-VG

    • FDDI, FDDI- II

    • HPPI

    • Gigabit Ethernet (IEEE 802.3z)


    Atm issues l.jpg
    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


    Internetworking l.jpg
    “Internetworking”

    • Bridges

      • Transparent bridges

      • Source Routing - Transparent Bridges

    • Routers (Network Layer)

    • Brouters

    3

    2

    2

    2

    1

    1

    1

    1


    Why bridges l.jpg
    Why Bridges

    • Isolation of Physical Layer Effects

    • Bandwidth Multiplication

    • Security or Traffic Isolation


    Segmenting traffic l.jpg

    File server

    Workstations

    LAN traffic

    Bridge

    LAN traffic

    Terminal server

    Host

    Terminals

    Segmenting Traffic


    Transparent bridges l.jpg
    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.


    T l f bridges l.jpg
    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.


    Learning filtering and forwarding l.jpg

    Node D

    Node F

    Terminals

    Node C

    Cable segment 1

    Node C, D and F are on this

    cable segment through port 2.

    Port 2

    Forwarding table

    Bridge

    Nodes A, B, and E are on this

    cable segment though port 1.

    Port 1

    Cable segment 2

    Node E

    Node A

    Node B

    Learning, Filtering, and Forwarding


    Filtering an example l.jpg

    Node B

    Node A

    Cable segment 2

    Port ID 1

    C 2

    D 2

    A 1

    B 1

    Fowarding Table

    Port ID 2

    Filtered

    Cable segment 1

    Packet transmitted

    Node C

    Node D

    Filtering - An Example


    Forwarding an example l.jpg

    Node B

    Node A

    Cable segment 2

    Forwarded

    Port ID 1

    C 2

    D 2

    A 1

    B 1

    Forwarding table

    Port ID 2

    Cable segment 1

    Node C

    Node D

    Forwarding - An Example


    Forwarding beyond one bridge l.jpg

    Node B

    Node A

    Cable segment Z

    A B

    Bridge 1

    C D

    Cable segment Y

    A B

    Bridge 2

    Bridge table

    C D

    Cable segment X

    A B

    Bridge 3

    C D

    Cable segment V

    Node C

    Node D

    Forwarding Beyond One Bridge


    Loops l.jpg
    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.


    Duplicate packets l.jpg

    Node B

    Node A

    Two packets received

    Cable segment 2

    Bridge 1

    Bridge 2

    Cable segment 1

    Single packet transmitted

    Node D

    Node C

    Duplicate Packets


    Broadcasts l.jpg

    Packet received and

    transmitted back by

    second bridge

    Node B

    Node A

    Cable segment 2

    Loop

    Bridge 2

    Bridge 1

    Cable segment 1

    Broadcast packet transmitted

    Node D

    Node C

    Broadcasts


    Unknown destination address l.jpg

    Node A

    Node B

    Packet received and

    transmitted back by

    second bridge

    Cable segment 2

    Loop

    Bridge 1

    Bridge 2

    Cable segment 1

    Destination Z packet transmitted

    Node D

    Node C

    Unknown Destination Address


    Spanning tree algorithm l.jpg
    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. Don’t 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.


    Source routing bridges l.jpg
    Source Routing Bridges

    • Developed as a bridge protocol for Token Ring LANs.

    • Source routing gained popularity due to IBM’s 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.


    Source routing features l.jpg
    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.


    Source routing features cont l.jpg
    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.


    Source routing overview l.jpg
    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.


    Source routing example l.jpg
    Source Routing Example

    MAU

    MAU

    2

    Find a

    station off

    ring

    Bridge 5

    Node 2

    Node 1

    Bridge 6

    1

    Find a

    station on

    the local ring

    Bridge 7

    Ring 4

    Ring 3


    Routing information field l.jpg

    Routing Information Indicator (RII)

    Optional

    Routing

    Information

    Field

    Source Service

    Access Protocol

    (SSAP)

    Destination Service

    Access Protocol

    (DSAP)

    Source

    Address

    Starting

    Delimiter

    Access

    Control

    Frame

    Control

    Destination

    Address

    Rest of Token

    Ring frame

    Up to 8 RD fields

    2 bytes

    Routing

    Control

    Route

    Designator

    Route

    Designator

    . . . . . .

    Bridge

    number

    Ring number

    B B B L L L L L

    D F F F r r r r

    12 bits

    4 bits

    1 - F

    bridge IDs

    1 - 4095

    rings

    Routing Information Field


    The route designator l.jpg
    The Route Designator

    Bridge 1

    Discovery

    frame

    Ring B

    Ring A

    RC

    RC

    RD1 RD2

    Token

    Frame

    Header

    Token

    Frame

    Trailer

    Token

    Frame

    Header

    Token

    Frame

    Trailer

    Routing

    Control

    Routing

    Control

    00B1 00A0

    Routing

    Information

    Field

    Routing

    Information

    Field


    Source route frame types l.jpg
    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.


    Token ring to ethernet conversion l.jpg

    Copy and

    bit reverse

    Token Ring frame

    SNAP header

    AC

    OUI

    SD

    FC

    DA

    SA

    RIF

    DSAP

    SSAP

    CTRL

    Type

    Info

    FCS

    ED

    FS

    Discard

    Copy

    Ethernet frame

    Preamble

    DA

    SA

    Type

    Info

    FCS

    Token Ring to Ethernet Conversion


    Ethernet to token ring conversion l.jpg
    Ethernet to Token Ring Conversion

    Copy and

    bit reverse

    Ethernet frame

    FCS

    Type

    Preamble

    DA

    SA

    Info

    Copy

    SD

    AC

    FC

    DA

    SA

    RIF

    DSAP

    SSAP

    CTRL

    Type

    Info

    FCS

    ED

    FS

    OUI

    Insert

    SNAP header

    Token Ring frame


    Token ring to ieee 802 3 conversion l.jpg

    Copy and

    bit reverse

    Token Ring frame

    SD

    AC

    FC

    DA

    SA

    RIF

    DSAP

    SSAP

    CTRL

    ED

    FS

    Info

    FCS

    Cut

    Insert

    Copy

    Length

    Info

    PAD

    FCS

    Preamble

    SFD

    DA

    SA

    DSAP

    CTRL

    SSAP

    IEEE 802.3 frame

    Token Ring to IEEE 802.3 Conversion


    Ieee 802 3 to token ring conversion l.jpg
    IEEE 802.3 to Token Ring Conversion

    Copy and

    bit reverse

    IEEE 802.3 frame

    FCS

    Length

    PAD

    Preamble

    SFD

    DA

    SA

    SSAP

    DSAP

    Info

    CTRL

    Cut

    Insert

    Copy

    SD

    AC

    FC

    DA

    SA

    RIF

    DSAP

    SSAP

    CTRL

    FS

    ED

    Info

    FCS

    Token Ring frame


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