LANs, High Speed LANs & LAN Interconnections, 2002, Dr. Z. Sun 1
Components of DATA and INTERNET NETWORKING MODULE
(MSc EEM.din & Linked UG EE4.din)
LANs, High Speed LANs and LAN Interconnections
Dr Zhili SUNUniversity of Surrey
GuildfordSurrey
GU2 7XHTel: 01483 68 9493Fax: 01483 68 6011
Email: [email protected]
LANs, High Speed LANs & LAN Interconnections, 2002, Dr. Z. Sun 2
Sections
� 1. Local Area Networks (LANs): IEEE 802 standard LANs: Ethernet (803.3), Token Ring (802.5), Token Bus (802.4), MAC sublayer, LLC sublayer.
� 2. High Speed LANs (HSLANs): Fast Ethernet (IEEE802.3u), Hub, Switched Ethernet, gigabit Ethernet (IEEE802.3z), FDDI,
� 3. Wireless NetworksWireless LAN (IEEE803.11a, 11b & 11g), Broadband Wireless (IEEE802.16), Bluetooth (IEEE802.15)
� 4. LAN interconnection: Repeaters; Bridges - Transparent and Source Routing; Spanning Tree Algorithm, internetworking different LAN types, VLAN (IEEE802.1Q)
� Recommended text books
LANs, High Speed LANs & LAN Interconnections, 2002, Dr. Z. Sun 4
Introduction
� LAN classification� IEEE 802 standard LANs:
• Ethernet (802.3) • Token Ring (802.5) • Token Bus (802.4)
� Medium Access Control (MAC) sublayer� Logical Link Control (LLC) sublayer
LANs, High Speed LANs & LAN Interconnections, 2002, Dr. Z. Sun 5
LAN Classification
Classifications are based on:� Physical Transmission Medium: Shielded/Unshield
Twisted Pair (STP/UTP) 10baseT, Co-axial Cable (10base2 thin 0.25 and 10base5 thick 0.5 inch diameter), optical Fibre 10baseF, wireless,
� Topology: Bus, Ring, Tree/Hub, Star
� Media Access Control: CSMA/CD, control token, fixed slots
� Standards bodies: IEEE, ISO
LANs, High Speed LANs & LAN Interconnections, 2002, Dr. Z. Sun 6
Standards - IEEE 802.x (ISO 8802.x)
� At start of LAN development many incompatible networks were developed
� In the early 1980’s an IEEE committee examined the various types, classified them and proposed standards to remove much of the incompatibility.
� LAN types thus became known by the IEEE 802 classification e.g. 802.3, 802.4, 802.5 ...
� ISO adopted IEEE 802 as ISO 8802
LANs, High Speed LANs & LAN Interconnections, 2002, Dr. Z. Sun 7
The framework of IEEE 802 Standards
802.1 Architecture, Management & Internetwork
802.2 Link Services
802.3 802.4 802.5 802.6 802.9
CSM
A/C
D
Tok
en B
us
Tok
en R
ing
MA
Ns
Inte
grat
ed
voic
e/da
ta
802.7 Broadband
LANs
802.8 FDDI
802.10 Secure LANs
LANs, High Speed LANs & LAN Interconnections, 2002, Dr. Z. Sun 8
IEEE 802 relevant to LANs� 802.1 — High layer LAN Protocol: Overview & architecture, bridging, VLAN� 802.2 — Logical Link Control services Working Group (WG) (inactive)� 802.3 — Ethernet (CSMA/CD) WG: access method & physical signalling� 802.4 — Token Bus WG: access method & physical signalling (inactive)� 802.5 — Token Ring WG: access method & physical signalling � 802.6 — Metropolitan Area Network - MAN (DQDB): WG (inactive)� 802.7 — Broadband Technical Advisory Group (TAG) (inactive)� 802.8 — Fiber-Optic Technical Advisory Group (FDDI-II): � 802.9 — Isochronous LAN WG: Integrated Service LAN� 802.10 — LAN Security Architecture WG: for all IEEE 802 at various level� 802.11 — Wireless LAN (HiperLAN in ETSI): access method & physical signalling � 802.12 — Demand priority WG. 802.13: not used. � 802.14 — Cable modem WG. 802.15 — Wireless personal area network WG. � 802.16 — Broadband wireless access Study Group (SG)� QoS / Flow control study group
LANs, High Speed LANs & LAN Interconnections, 2002, Dr. Z. Sun 9
LAN Protocol and OSI reference model
Application
Presentation
Session
TransportNetwork
Data Link
Physical
Logical Link Control
Medium Access Control
Physical
Service Access Points
LANs, High Speed LANs & LAN Interconnections, 2002, Dr. Z. Sun 10
Functions of LLC, MAC and PHY layers
� Logic Link Control (LLC) - Provide one or more Service Access Points (logical interfaces between adjacent layers)
� Media Access Control (MAC) - On transmission assemble data into frames with address and CRC; On reception disassemble frame and perform address recognition and CRC validation; and Manage communication over link
� Physical layer - Encoding/decoding of signals; Preamble generation/removal (for synchronization); and bit transmission/reception.
LANs, High Speed LANs & LAN Interconnections, 2002, Dr. Z. Sun 11
Topologies
Bus
Tree
Ring
Hub/Switch
LANs, High Speed LANs & LAN Interconnections, 2002, Dr. Z. Sun 12
Medium access control (MAC) techniques
� Round robin: With round robin, each station in turn is given the opportunity to transmit. During that opportunity, the station may decline to transmit or may transmit subject to a specified upper bound (maximum amount of data or time)
� Reservation: For stream traffic, reservation techniques are well suited.
� Contention: For bursty traffic, contention techniques are usually appropriate
LANs, High Speed LANs & LAN Interconnections, 2002, Dr. Z. Sun 13
Standardised MAC techniques
CSMA/CD (802.3)CSMA/CD (802.3)CSMA (802.11)
Contention
DQDB (802.6)Reservation
Request/priority (802.12)
Token ring (802.5, FDDI)
Token bus (402.4)Polling (802.11)
Round robin
Switched technology
Ring technology
Bus technology
LANs, High Speed LANs & LAN Interconnections, 2002, Dr. Z. Sun 14
Aloha and Slotted Aloha
Contention system:�Transmit whenever have data �Listen to the channel to see if the frame is OK�If not, back-off and re-transmit
� For slotted Aloha, transmit only at beginning of the slot to improve performance
LANs, High Speed LANs & LAN Interconnections, 2002, Dr. Z. Sun 15
The channel efficiency
� Throughput S = GP0
� Poisson distribution:P[k] = Gk e-G / k!
In 2 frame interval, the number of frames generated is 2G, thus P0 = e -2G
=> S = G e -2G
� Max. throughputS = 1/(2e), when G=1/2
� For slotted Alohathe vulnerable period is 1 frame period
(halved), thus P0 = e -G
=> S = G e -G
LANs, High Speed LANs & LAN Interconnections, 2002, Dr. Z. Sun 16
Carrier Sense Multiple Access (CSMA)
� 1-persistent: the station listens before sending. If the channel is busy, it waits until it idle. Transmit when the channel is idle. if collision, the station waits a random amount of time and start all over again
� non-persistent: If busy, the station does not continually sense. Instead, waiting for a random period, then repeating the algorithm
� p-persistent: It applies to slotted channel. If it is idle, it transmits with probability of p.
LANs, High Speed LANs & LAN Interconnections, 2002, Dr. Z. Sun 17
CSMA Persistence and Back-off
Channel Busy
Constant or Variable Delay
Ready p-persistent: transmit as soon as channel goes idlewith a probability p, otherwisedelay one slot and repeat process
1-persistent: transmitas soon as channel goes idle.If collision, back-off and try again.
non-persistent:transmit if idle, otherwise, delay and try again
Slot time
LANs, High Speed LANs & LAN Interconnections, 2002, Dr. Z. Sun 18
CSMA with Collision Detection (CD)
� Further improvement than persistent and non-persistence over Aloha, by aborting transmission as soon as stations detect a collision
� Contention period is 2τ where τ is propagation delay� Example: for a 1 km cable, the τ is about 5 µs (micro-
second)� Ethernet is one of this version� No MAC-sublayer protocol guarantees reliable delivery
LANs, High Speed LANs & LAN Interconnections, 2002, Dr. Z. Sun 19
Ethernet System
� The CSMA/CD system (as defined by IEEE 802.3) is based upon the original Ethernet specification defined by Xerox. The two are not identical.
CarrierSenseMultipleAccess CSMA/CDwithCollisionDetection
Attachment Unit Interface (AUI)
PC PC
Channel
PCTransceiver Medium Access Unit (MAU)
with network interface card (LANCE)
LANs, High Speed LANs & LAN Interconnections, 2002, Dr. Z. Sun 20
Ethernet Cabling
The most common kinds of Ethernet cabling.
LANs, High Speed LANs & LAN Interconnections, 2002, Dr. Z. Sun 21
Physical layer signal encoding
(a) Binary encoding, (b) Manchester encoding, (c) Differential Manchester encoding.
LANs, High Speed LANs & LAN Interconnections, 2002, Dr. Z. Sun 22
Ethernet Frame Format
Preamble Destination address
Source address Data Pad Checksum
7 1 2 or 6 2 or 6 2 46–1500 0–46 4Bytes
Start of frame
delimiter
Length of LLC data fieldor Ethernet type field
Preamble: Receiver synchronization (10101011)Destination address: Identifies intended receiver Source address: Hardware address of sender Length/Type: Type of data carried in frameData: Frame payload CRC: 32-bit CRC code
LANs, High Speed LANs & LAN Interconnections, 2002, Dr. Z. Sun 23
� Retransmission scheduling uses the Truncated Binary Exponential Back-off algorithm
� On the Nth retransmission attempt the station chooses to retransmit after waiting a random integer number of ‘slot’ times, R, where:
0 <= R <= 2k
K = min(N, Back-off limit)
� Bit rate 10 Mbps� Slot time 512 bit times� Interframe gap 9.6 µs� Attempt limit 16� Backoff limit 10� Jam size 32 bits� Max frame size 1518 octets� Min frame size 64 octets
Back-off algorithm & Operational Parameters
LANs, High Speed LANs & LAN Interconnections, 2002, Dr. Z. Sun 24
ReceiveTransmit
Wait for a frame to transmit. Format frame for transmission.
Carrier sense signal on?
Wait interframe gap time. Start transmission.
Collision detected?
Complete transmission and set status as done.
Set status as attempt limit exceeded. Attempt limit reached?
Compute and wait backoff time
Transmit jam sequence. Increment attempts count.
yn
n
y
y
n
Incoming signal detected?
Set carrier sense signal on. Get bit sync and wait for SFD.
Receive frame.
FCS and frame size OK?
Destination address matches own or group address?
Pass frame to higher layer for processing.
Discard frame.
n
n
y
y
y
n
CSMA/CD Operational Parameters
LANs, High Speed LANs & LAN Interconnections, 2002, Dr. Z. Sun 25
Token Ring
� The Token Ring is described by the IEEE 802.5 specification. This is based upon the original work by IBM and now defines both 4Mbps and 16 Mbps rings.
� Suitable for real time� Delimiter, access control,
frame control � Sources, destination address,
and checksum are the same as the IEEE 802.3 PC
PCPC
SD EDAC
Token
LANs, High Speed LANs & LAN Interconnections, 2002, Dr. Z. Sun 27
Token Ring Frame Formats
DASD AC FC SA DATA FCS ED FS
SD AC ED
JK 0J K 00 0
JK1JK1 I E
PPP RRRT M
FF ZZZZZZ
ACxx ACxx
1 1 1
1 1 1 2 or 6 2 or 6 < 5000 4 1 1
Bytes
Start delimiter (SD)
End delimiter (ED)
Access Control
Frame Control (FC)
Frame Status (FS)
Token Format
Frame format
32-bit CRC: Frame Check Sequence (FCS)
LANs, High Speed LANs & LAN Interconnections, 2002, Dr. Z. Sun 28
Token Ring Operation
Transmit Receive
Waiting for token to be received
Frame waiting to be transmitted?
Token priority <= frame priority?
Token holding timer expired?Forward token
with correct priority
Transmit waiting frame. Remove frame after
circulating ring. Pass A and C bits from tail
of frame to higher layer
R bits < frame priority?
Forward token with correct priority
Set R bits to frame priority
n
y
n
yn
y
y
n
Token?
Set A and C bits at tail of frame. Pass stored frame to higher layer.
Store frame contents and repeat at ring interface
Frame addressed to me?
Wait for a frame to be received
Enter transmit routine.
Discard frame.
n
y
y
n
LANs, High Speed LANs & LAN Interconnections, 2002, Dr. Z. Sun 29
Ring Management
� In addition to tokens and data frames the Token Ring protocol employs a number of special frame types to facilitate ring management.
� Ring management is required for:• Initialization• Active monitoring• Standby monitoring• Fault diagnosis
� The different ring management frames include:• Duplicate Address Test
(DAT)• Active Monitor Present
(AMP)• Standby Monitor Present
(SMP)• Claim Token (CT)• Purge (PRG)• Beacon (BCN)
LANs, High Speed LANs & LAN Interconnections, 2002, Dr. Z. Sun 31
Ring Fault Detection and Recovery
A B C D
EFGH
Standby ring
A B C D
EFGH
TCUFailure
LANs, High Speed LANs & LAN Interconnections, 2002, Dr. Z. Sun 35
IEEE 802.2 Logical link control
� Hide difference between the various 802 networks by providing a single format and interface to the network layer
� Based on HDLC, provide 3 service options as the link layer
� Error control using acknowledgement
� Flow control using a slide window
� All 802 LANs and MAN offer best-efforts service
LANs, High Speed LANs & LAN Interconnections, 2002, Dr. Z. Sun 36
Logical Link Control (LLC)� The various IEEE 802 MAC
sublayers are all designed to work with the 802.2 Logical Link Control (LLC) sublayer
� The LLC is based upon HDLC and is thus similar to the LAPB protocol used in X.25
� The LLC sublayer can optionally support three types of service:• Type 1: Unacknowledged
connectionless• Type 2: Connection-oriented• Type 3: Acknowledged
connectionless� LLC frames are carried in the data
field of the MAC sublayer’s frame.
DSAP address
SSAP address Control Information
1 1 1 or 2 >=0Bytes:
LLC Frame format (LLC-PDU)
LANs, High Speed LANs & LAN Interconnections, 2002, Dr. Z. Sun 37
LLC Control Field
0
11
1
N(S) N(R)
N(R)
P/F0
S P/F
P/FM M
Information frame
Supervisory frame
Unnumbered frame
N(S),N(R) = send / receive sequence numbers (7 bits)S = supervisory function bitM = modifier function bitp/f = poll/final bit
LANs, High Speed LANs & LAN Interconnections, 2002, Dr. Z. Sun 38
Summary
� LANs � IEEE 802 standard LANs:� Ethernet (802.3) � Token Ring (802.5) � Token Bus (802.4)� MAC sublayer protocols� LLC sublayer
LANs, High Speed LANs & LAN Interconnections, 2002, Dr. Z. Sun 40
Introduction
� Fast Ethernet (IEEE802.3u)• Ethernet shared medium Hub• Switched Ethernet
� Gigabit Ethernet (IEEE802.3z)� FDDI
LANs, High Speed LANs & LAN Interconnections, 2002, Dr. Z. Sun 41
Ethernet Shared Medium Hub
Hub
DTE DTE DTE
LANs, High Speed LANs & LAN Interconnections, 2002, Dr. Z. Sun 42
Switched Ethernet
A simple example of switched Ethernet.
LANs, High Speed LANs & LAN Interconnections, 2002, Dr. Z. Sun 43
Switched Ethernet
� Add electronics to Hub so hub can recognise (remember) the addresses of DTE connected to each port thus only need to transmit frames intended for that DTE (need FIFO to buffer until DA appears)
� Arrange backplane with one line/port - steer frames to specific line - several frames can be transit at same time
� Can have higher speed port to link to server DTE -recipient of all unrecognised frames
� Collision Detection only required when frame received for a port already receiving a frame
LANs, High Speed LANs & LAN Interconnections, 2002, Dr. Z. Sun 44
Fast Ethernet Specifications
IEEE 802.3 (100 Mbit/s)
100BASE-X
100BASE-TX
• 2 STP
• 2 Category 5 UTP
100BASE-FX
100BASE-T4
• 2 Optical fibre• 4 Category 3
• 4 Category 5
15
IEEE 802.3 concise notation:<rate in Mbit/s> <signalling method> <Max Length in 100m>
LANs, High Speed LANs & LAN Interconnections, 2002, Dr. Z. Sun 45
Fast Ethernet: IEEE802.3u
� They must use hubs or switches
LANs, High Speed LANs & LAN Interconnections, 2002, Dr. Z. Sun 46
Fast Ethernet 100base4T
� Main problem is to transmit 100Mb/s over Twisted pair!� The 100base4T scheme uses all 4 pairs in parallel � Uses 8B6T (8bits translated to 6 ternary symbols) to
reduce baud/pair to below 30Mbaud(100 x (6/8))/3 = 25 MHz
DTE Hub
LANs, High Speed LANs & LAN Interconnections, 2002, Dr. Z. Sun 47
Fast Ethernet 100baseX
� 100baseX uses single, higher specified twisted pair (or optical fibre - hence X)
� For FX - optical fibre cable,4B5B is used as used in FDDI.� For TX - Shielded twisted pair (STP), MTL-3 signalling
scheme is used.
LANs, High Speed LANs & LAN Interconnections, 2002, Dr. Z. Sun 48
Gigabit Ethernet – IEEE802.3z
The strategy for Gigabit Ethernet is the same as that for fast Ethernet:� New media and transmission specification
• Point to point• Carrier extension• Frame bursting
� The same CSMA/CD protocols and Ethernet format and backward compatible
(a) A two-station Ethernet. (b) A multistation Ethernet.
LANs, High Speed LANs & LAN Interconnections, 2002, Dr. Z. Sun 49
Gigabit Ethernet cabling
� 1000BASE-SX: uses short-wavelength� 1000BASE-LX: uses long-wavelength, � 1000BASE-CX: use two pairs specialise shielded
twisted-pair (STP) cable � 1000BASE-T: use four pair of Category 5 UTP� New encoding rules are used on fibres (10B/10B)� IEEE802.3ae is under studies for 100 gigabit Ethernet
LANs, High Speed LANs & LAN Interconnections, 2002, Dr. Z. Sun 50
Fibre distributed data interface (FDDI)
n Modelled on IEEE 802.5n High speed LAN 100 Mbit/sn synchronised frame every 125 µs, support 96
PCM channels (4xT1 or 3xE1)n Bit error rate 2.5x10E-10n 4B/5B encoding
LANs, High Speed LANs & LAN Interconnections, 2002, Dr. Z. Sun 51
Fibre Distributed Data Interface (FDDI)
� ISO 9314, 100 Mbps, � 200Km, 1000 nodes� Token passing� Dual ring structure� Intended primarily as a
means of interconnecting LANs (via relays) but individual nodes can be attached.
� Two station types:• Single Attach Station (SAS)• Dual Attach Station (DAS)
A
B A
B
A B
M
S S
M
wiring concentrator
DASDAS
SASSAS
inserted bypassed
slave key
master keyprimary ring
primary ring
secondary ring
inserted bypassed
optical coupling unit
LANs, High Speed LANs & LAN Interconnections, 2002, Dr. Z. Sun 52
FDDI frame formats
Pre SD FC DA SA data FCS ED FS
Pre SD FC ED
Frame check sequence coverage
2>16 2 4 / 12 8 1/2 34 / 12
symbols
token
<=9000
LANs, High Speed LANs & LAN Interconnections, 2002, Dr. Z. Sun 53
FDDI – Physical Layer Signalling
� To enable clock synchronisation FDDI uses a 4 of 5 group code at the physical layer.
� Symbols have at most 2 consecutive 0’s thus when using NRZI (signal transition on each ‘1’) at most two bits between transitions.
� J and K symbols break 2 ‘0’s rule and are used as end-markers
� IDLE has all ‘1’s and thus max clock transitions - used in preamble
0000 0001 0010 0011 0100 0101 0110 0111 1000 1001 1010 1011 1100 1101 1110 1111
11110 01001 10100 10101 01010 01011 01110 01111 10010 10011 10110 10111 11010 11011 11100 11101
IDLE J K T R S
QUIET HALT
11111 11000 10001 01101 00111 11001 00000 00100
Control Symbols
Data Symbols
4-bit data 5-bit symbol
LANs, High Speed LANs & LAN Interconnections, 2002, Dr. Z. Sun 54
Latency
n SD field of 2 symbols (5bits) requires a buffer at receiver before SA known thus introduces latency of 0.08µs
n Generally rounded as 1µs / ring interfacen Thus latency = propagation delay (5µs/km) +
N x Station latency (1µs)n 20km ring with 200 stations = 300µs
or 30,000bits
LANs, High Speed LANs & LAN Interconnections, 2002, Dr. Z. Sun 55
Timed Token Rotation Protocol
n FDDI uses same approach as used in Token Ringn Preset parameter - Target Token Rotation Timen For each rotation of token station computes time since
last received token - TRT (Token Rotation Time)n TRT is a measure of loading on ringn The station computes THT = (TTRT-TRT)
this THT is Token Hold Time and determines how long the station may hold the token and thus continue to transmit frames
LANs, High Speed LANs & LAN Interconnections, 2002, Dr. Z. Sun 56
Max Throughput or Untilisation
N stations Τ = ring latencyi.e. time taken to pass token around loopTTRT = Timed token rotation timeτ = time required to transmit token
A
B
C
Assume heavily loaded ring - all stations have frames to transmitConsider B - when token first passed will not be able to transmit astimed out - thus need complete token rotation (Τ)On completion B transmits with holding time TTRT-ΤIt then has to transmit token time τ which takes Τ/n to reach C
LANs, High Speed LANs & LAN Interconnections, 2002, Dr. Z. Sun 57
Max Utilization
TTRT-Τ
(TTRT-Τ) + Τ + τ + Τ/n Umax =
TTRT >> τ thus
n(TTRT-Τ)
nTTRT+ΤUmax = thus -> 1 as TTRT increases
LANs, High Speed LANs & LAN Interconnections, 2002, Dr. Z. Sun 58
Maximum Access Delay
Have to wait for all other stations to transmit + token rotation times
Amax = (n-1) (TTRT-Τ) + nΤ + Τ
= (n-1)TTRT + 2Τ
LANs, High Speed LANs & LAN Interconnections, 2002, Dr. Z. Sun 59
Summary
� High speed LANs and technologies� Ethernet Hubs and Switches� Fast Ethernet� Gigabit Ethernet� FDDI
LANs, High Speed LANs & LAN Interconnections, 2002, Dr. Z. Sun 61
Outline
� Wireless LAN (IEEE802.11a, 11b & 11g)• The 802.11 Protocol Stack• The 802.11 Physical Layer, MAC Sublayer Protocol,
Frame Structure, and Services� Broadband Wireless (IEEE802.16)
• The 802.16 Protocol Stack• The 802.16 Physical Layer, MAC Sublayer Protocol,
and Frame Structure� Bluetooth (IEEE802.15)
• Bluetooth Architecture• Bluetooth Applications, Protocol Stack, Radio Layer,
Baseband Layer, L2CAP Layer and Frame Structure
LANs, High Speed LANs & LAN Interconnections, 2002, Dr. Z. Sun 62
The 802.11 Protocol Stack
Part of the 802.11 protocol stack.
LANs, High Speed LANs & LAN Interconnections, 2002, Dr. Z. Sun 63
The 802.11 MAC Sublayer Protocol
(a) The hidden station problem.(b) The exposed station problem.
LANs, High Speed LANs & LAN Interconnections, 2002, Dr. Z. Sun 64
The 802.11 MAC Sublayer Protocol (2)
The use of virtual channel sensing using CSMA/CA.
LANs, High Speed LANs & LAN Interconnections, 2002, Dr. Z. Sun 65
The 802.11 MAC Sublayer Protocol (3)
A fragment burst.
LANs, High Speed LANs & LAN Interconnections, 2002, Dr. Z. Sun 66
The 802.11 MAC Sublayer Protocol (4)
Interframe spacing in 802.11.
LANs, High Speed LANs & LAN Interconnections, 2002, Dr. Z. Sun 67
The 802.11 Frame Structure
The 802.11 data frame.
Data,Control,management
RTSCTSACK
More fragments
PowerManage
More frames
•WEP used &•Order for processing
LANs, High Speed LANs & LAN Interconnections, 2002, Dr. Z. Sun 68
802.11 Services
� Distribution services• Association: connect mobile station to base stations• Disassociation: release connection• Reassociation: move rom one cell to another• Distribution: route frame from the base station• Integration: frame needs to be sent through non-802.11
� Intracell services• Authentication: authenticate the mobile station• Deauthentication: the station leaves the network• Privacy: Encryption using RC4• Data delivery: data transmission
LANs, High Speed LANs & LAN Interconnections, 2002, Dr. Z. Sun 69
Broadband wireless (IEEE802.16)
The 802.16 transmission environment.
LANs, High Speed LANs & LAN Interconnections, 2002, Dr. Z. Sun 70
The 802.16 Protocol Stack
The 802.16 Protocol Stack.
LANs, High Speed LANs & LAN Interconnections, 2002, Dr. Z. Sun 71
The Physical Layer and service classes
Frames and time slots for time division duplexing.
• Service Classes• Constant bit rate service• Real-time variable bit rate service• Non-real-time variable bit rate service• Best efforts service
LANs, High Speed LANs & LAN Interconnections, 2002, Dr. Z. Sun 72
The 802.16 Frame Structure
(a) A generic frame. (b) A bandwidth request frame.
EC: Encryption, type: packet or fragment, CI: present or not of checksum, EK: encryption key used, length: frame length, connection id: the packet belong to,
LANs, High Speed LANs & LAN Interconnections, 2002, Dr. Z. Sun 73
Bluetooth Architecture (IEEE802.15)
Two piconets can be connected to form a scatternet.
LANs, High Speed LANs & LAN Interconnections, 2002, Dr. Z. Sun 74
Bluetooth Applications
The Bluetooth profiles.
LANs, High Speed LANs & LAN Interconnections, 2002, Dr. Z. Sun 75
The Bluetooth Protocol Stack
The 802.15 version of the Bluetooth protocol architecture.
LANs, High Speed LANs & LAN Interconnections, 2002, Dr. Z. Sun 76
The Bluetooth Frame Structure
A typical Bluetooth data frame.
Identify the master
Identifydevices
Frametypes
F: flow control by slaveA: ack is used by piggybackS: sequence to detect re-transmission
LANs, High Speed LANs & LAN Interconnections, 2002, Dr. Z. Sun 77
Summary
� Wireless LAN (IEEE802.11a, 11b & 11g)� Broadband Wireless (IEEE802.16)� Bluetooth (IEEE802.15)
LANs, High Speed LANs & LAN Interconnections, 2002, Dr. Z. Sun 79
Introduction
� Repeaters� Bridges � Transparent Routing; � Spanning Tree Algorithm� Source Routing; � Internetworking different LAN types� VLAN
LANs, High Speed LANs & LAN Interconnections, 2002, Dr. Z. Sun 80
Repeaters, Bridges & Routers and Gateways
(a) Which device is in which layer.(b) Frames, packets, and headers.
LANs, High Speed LANs & LAN Interconnections, 2002, Dr. Z. Sun 81
Hubs, Bridges and Switches
(a) A hub. (b) A bridge. (c) a switch.
LANs, High Speed LANs & LAN Interconnections, 2002, Dr. Z. Sun 82
Repeater and Bridge functions
Transport
Network
LLC
MAC
Physical
LAN Segment 1
Transport
Network
LLC
MAC
Physical
End Station End Stati
LAN Segment 2
MACPhysical
MACPhysical
Relay
BridgeTransport
Network
LLC
MAC
Physical Repeater
LAN Segment 1
Transpor
Network
LLC
MAC
Physical
End Station End Stat
LAN Segment 2
Repeater Bridge
LANs, High Speed LANs & LAN Interconnections, 2002, Dr. Z. Sun 83
Why Bridges ?
� Removal of physical constraints such as length, number of stations, segments, etc (geographical separated and physical distance limit)
� Buffering allows mix of LAN types (Different department have different LANs initially)
� Transparent to protocols above MAC� Easier management and security� Partitioning improves overall reliability� Accommodate the load
LANs, High Speed LANs & LAN Interconnections, 2002, Dr. Z. Sun 84
Bridge Types
� Transparent (or Spanning Tree)• bridges make all routing decisions• IEEE 802.1(D) standard
� Source Routing• end-stations make major routing decisions• part of IEEE 802.5 - token ring - standard
LANs, High Speed LANs & LAN Interconnections, 2002, Dr. Z. Sun 85
Transparent Bridges
LLC Entities
MAC Entity
LLC Entities
MAC Entity
LAN 1 LAN 2
MAC Relay Entity
Higher Layer Entities (Bridge Protocol Entity, Bridge Management, etc.)•Bridge uses a
database so that frames can be forwarded to correct port
•Need someway for this database to be dynamically created and maintained
LANs, High Speed LANs & LAN Interconnections, 2002, Dr. Z. Sun 86
Bridge Architecture
ForwardDataBase
Stationaddress
PortNo.
Port management
BridgeProtocol
MAC Memory MAC
LAN seg A LAN seg B
LANs, High Speed LANs & LAN Interconnections, 2002, Dr. Z. Sun 87
Bridge Learning
� If LAN segments + bridges arranged in a tree structure (i.e. only 1 possible route from any station to any other station) then possible for Bridge to learn station addresses by monitoring traffic on each port. During this learning phase frames are forwarded on all ports (‘flooding’)
� By including an inactivity timer to limit remembrance of address then DTE allowed to move around
LANs, High Speed LANs & LAN Interconnections, 2002, Dr. Z. Sun 88
Multiple Paths
� If however there are two paths between any segments then the entry in the Forward DataBase will be continually updated
1
2
1
2
receive
flood
flood
LANs, High Speed LANs & LAN Interconnections, 2002, Dr. Z. Sun 89
Need to agree single path
� Need to arrange single ‘logical’ path between any two segments
� Bridges regularly exchange special framesBridge Protocol Data Units
� Each Bridge allocated priority value + unique identifier� Special Root Bridge dynamically chosen
(with highest priority and smallest id
LANs, High Speed LANs & LAN Interconnections, 2002, Dr. Z. Sun 90
Spanning Tree Algorithm
� A single bridge is dynamically chosen to be the Root Bridge.
� Each bridge decides which of its ports has the least Path Cost to the Root (RPC). This port is treated as the Root Port (RP).
� For each LAN segment a single bridge port is selected for forwarding frames. This is known as the Designated Port (DP).
� RPs cannot also be DPs.� Bridge ports which are neither RPs
nor DPs are ‘switched off’, i.e. a port can either be in a forwarding state or a blocking state.
� The Spanning Tree Algorithm works dynamically and in a distributed fashion.
� Bridges exchanging Bridge Protocol Data Units (BPDUs) between themselves.
� All the bridges have a unique MAC group address for exchanging BPDUs.
� Each BPDU contains a number of fields including:• Bridge ID of the Root• RPC to the root from the bridge• ID of the bridge sending the BPDU• ID of the port sending the BPDU
LANs, High Speed LANs & LAN Interconnections, 2002, Dr. Z. Sun 92
Source Routing Bridges
� Can be used with any LAN type though primarily used with Token Ring LANs
� The end station perform the routing function. The routeing information is inserted into the frame and is used by each bridge.
� Routeing information comprises of segment-bridge, segment-bridge, ...., identifiers.
� Each end station need to know the routeing information.� If a destination unknown, discovery frame is broadcasted to
find the routeing information� Spanning tree is used to avoid frame explosion.
LANs, High Speed LANs & LAN Interconnections, 2002, Dr. Z. Sun 93
Token Ring Frame Format (Routing)
SD AC FC Destinationaddress
IG
Sourceaddress
Routinginformation
Data FCS ED FS
1= Routing information field present0= No routing available
1 1 1 2 or 6 2 or 6 variable variable 4 1 1
Frametype
Maximumframe size
Routingfield length
Segmentidentifier
Bridgeidentifier
Routingcontrol
Routedesignator 1
Routedesignator 2
Routedesignator N
Routinginformation
2 2 2 2
LANs, High Speed LANs & LAN Interconnections, 2002, Dr. Z. Sun 94
Source Routing Frame Explosion
A B• • • •
Bridge
Ring
1 2 N1 Frame 3 Frames 3 N-1 Frames
LANs, High Speed LANs & LAN Interconnections, 2002, Dr. Z. Sun 95
Source Routing vs Transparent
� Routing PhilosophyUser chooses vs Bridge cooperation
� Quality of RoutesSpanning tree avoid loops but doesn’t guarantee best;
with source routing can find all paths and choose best for specific destination
� Use of available bandwidthsource routing could load balance
� Route forwarding overheadsTransparent bridge has to keep large route table -
slow search especially with high speed LANs
LANs, High Speed LANs & LAN Interconnections, 2002, Dr. Z. Sun 96
Source Routing vs Transparent (cont.)
� Route finding efficiencyConcerning with cost of determining route -
Transparent scheme needs 1 frame/branch of tree from a bridge node; source routing although initial route frames also follow tree subsequent all-routes broadcast frames do not
� ReliabilityTransparent regularly check for bridge/link failures - in
source routing this task moved to stations which may not have information
LANs, High Speed LANs & LAN Interconnections, 2002, Dr. Z. Sun 97
Remote bridges
� It connect two or more distant LANs
� Put a bridge in each LAN and connect the bridge pair-wise with point to point lines (such as leased telephone line)
� Various protocols can be used on the point to point lines (such as data link protocol) putting complete MAC frame in the payload
� Or strip off the MAC header and tailor at the sources and put it back at the destination
LANs, High Speed LANs & LAN Interconnections, 2002, Dr. Z. Sun 98
Mixed LAN Bridging
Unfortunately this is not as straight forward is it may at firstappear. Problems are caused by:
� Different frame formats: frames need reformatting - not too much of problem
� Different data rates: bottlenecks fast->slow involves queuing
� Different maximum frame sizes: potential problem as different MACs have different sizes - segmentation not part of 802.1(D) - get into Bridge-Routers
� Priorities• Token Ring’s A and C bits• Token Bus’s temporary token handoff feature
LANs, High Speed LANs & LAN Interconnections, 2002, Dr. Z. Sun 99
IEEE 802 MAC Frame Formats (1/2)
PreambleStart
delimiterAccess control
Frame control DA, SA Length Data Pad FCS
End delimiter
Frame status
802.3
802.4
802.5
LANs, High Speed LANs & LAN Interconnections, 2002, Dr. Z. Sun 100
IEEE 802 MAC Frame Formats (2/2)
The IEEE 802 frame formats. The drawing is not to scale.
LANs, High Speed LANs & LAN Interconnections, 2002, Dr. Z. Sun 101
Virtual LANs (802.1Q)
(a) Four physical LANs organized into two VLANs, gray & white, by two bridges. (b) The same 15 machines organized into two VLANs by switches.
LANs, High Speed LANs & LAN Interconnections, 2002, Dr. Z. Sun 102
The IEEE 802.1Q Standard
Transition from legacy Ethernet to VLAN-aware Ethernet. The shaded symbols are VLAN aware. The empty ones are not.
LANs, High Speed LANs & LAN Interconnections, 2002, Dr. Z. Sun 103
The IEEE 802.1Q frame
The 802.3 (legacy) and 802.1Q Ethernet frame formats.
LANs, High Speed LANs & LAN Interconnections, 2002, Dr. Z. Sun 104
Summary
� Repeaters;� Bridges � Transparent Routing; � Spanning Tree Algorithm� Source Routing; � Internetworking different LAN types� VLAN