Week 3 1 Week 3 Virtual LANs, Wireless LANs, PPP, ATM

Week 31

Week 3Virtual LANs, Wireless LANs,

PPP, ATM

Week 32

Virtual LANs

It is the territory over which a broadcast or multicast packet is delievered (also known as a broadcast domain)

The difference in a VLAN and a LAN, if there is any, is in packaging

Virtual LANs allow you to have separate LANs among ports on the same switch

For example, a switch might be told that ports 1-32 are in VLAN A and ports 33-64 are in VLAN B

Week 33

Virtual and Physical LANsVLAN A

VLAN B

AQ V J

MB D K

MB D K

A Q V J

R

Week 34

Why VLANs IP requires that all nodes on a LAN share the

same IP address prefix; therefore a node that moves to a different LAN must change its address

Changing IP addresses manually is annoying IP broadcasts traffic within a LAN, something

that can cause congestion in a large LAN Routing IP (rather than bridging) was slow It might be tempting to bridge everything

making your whole topology one giant LAN from the perspective of IP and use layer 2 switches

Week 35

Disadvantages of one single LAN Broadcast traffic (such as ARP) grows in

proportion to the number of stations Users can snoop on the traffic of other users

on the same LAN, so it might be safer to isolate groups of users onto different LANs

Some protocols are overly chatty or they get into modes such as broadcast storms.

So it seems desirable for users that need to talk to each other a lot to be in the same LAN but keep other groups of users in separate LANs

A VLAN makes us broadcast domain as large as we want it

Week 36

Mapping ports to VLANs

The switch has ports 1 to k in one VLAN and has ports k+1 to 2k in another LAN

The switch can be configured with a port/VLAN mapping The switch can be configured with a table of VLAN/MAC

address mappings. It then dynamically determines the VLAN/port mapping based on the learned MAC address of the station attached to the port.

The switch can be configured with a table of VLAN/IP prefix mappings. It then dynamically determines the VLAN/port mapping based on the source IP address from the station attached to the port.

The switch can be configured with a table of VLAN/protocol mappings. It then dynamically determines the VLAN/port mappings based on the protocol type of the stations attached to the port.

Week 37

VLAN forwarding with separate router

Router R

a.b.c.H

a.b.c.Df.g.k.X

f.g.k.Q

q

x

h

d

f j

a.b.c.R1 f.g.k.R2

2

3

7

9

1311

Router connects VLANs

Week 38

VLAN forwarding with switch as router

Router does not use up ports The switch must know that R’s mac

address on VLAN A is f and on VLAN B is j.

a..b.c.H

a..b.c.D

VLAN A2

3

f.g.k.Q

f.g.k.X

VLAN BSwitch/

Router R

9

12

Week 39

Dynamic binding of links to VLANs

Q.FQ.DQ.E

X.BZ.C

X.AZ.Dab

c Q.F

The switch now learns that there are two VLANs on port aIf enough stations move around, advantage disappears

Week 310

VLAN Tagging

VLAN 1

VLAN 2

VLAN 1

VLAN 1

VLAN 1

VLAN 2

VLAN 2

VLAN 2

Interswitch port;Packets can belong in either

VLAN1 or VLAN2

IEEE standardized a scheme for VLAN tagging

VLAN1

Week 311

IEEE 802.11 Wireless LAN

802.11b 2.4-5 GHz unlicensed

radio spectrum up to 11 Mbps direct sequence

spread spectrum (DSSS) in physical layer

• all hosts use same chipping code

widely deployed, using base stations

802.11a 5-6 GHz range up to 54 Mbps

802.11g 2.4-5 GHz range up to 54 Mbps

All use CSMA/CA for multiple access

All have base-station and ad-hoc network versions

Week 312

802.11 LAN architecture

wireless host communicates with base station base station = access

point (AP) Basic Service Set (BSS)

(aka “cell”) in infrastructure mode contains: wireless hosts access point (AP): base

station ad hoc mode: hosts

only

BSS 1

BSS 2

Internet

hub, switchor routerAP

AP

Week 313

802.11: Channels, association 802.11b: 2.4GHz-2.485GHz spectrum divided

into 11 channels at different frequencies AP admin chooses frequency for AP interference possible: channel can be same as

that chosen by neighboring AP! host: must associate with an AP

scans channels, listening for beacon frames containing AP’s name (SSID) and MAC address

selects AP to associate with may perform authentication will typically run DHCP to get IP address in

AP’s subnet

Week 314

IEEE 802.11: multiple access avoid collisions: 2+ nodes transmitting at same

time 802.11: CSMA - sense before transmitting

don’t collide with ongoing transmission by other node

802.11: no collision detection! difficult to receive (sense collisions) when transmitting

due to weak received signals (fading) can’t sense all collisions in any case: hidden terminal,

fading goal: avoid collisions: CSMA/C(ollision)A(voidance)

AB

CA B C

A’s signalstrength

space

C’s signalstrength

Week 315

IEEE 802.11 MAC Protocol: CSMA/CA

802.11 sender1 if INITIALLY sense channel idle for DIFS

then transmit entire frame (no CD)

2 if sense channel busy then start random backoff timetimer counts down while channel idletransmit when timer expiresif no ACK, increase random backoff

interval, repeat 2

802.11 receiver- if frame received OK return ACK after SIFS (ACK needed due

to hidden terminal problem)

sender receiver

DIFS

data

SIFS

ACK

Week 316

Avoiding collisions (more)

idea: allow sender to “reserve” channel rather than random access of data frames: avoid collisions of long data frames

sender first transmits small request-to-send (RTS) packets to BS using CSMA RTSs may still collide with each other (but they’re

short) BS broadcasts clear-to-send CTS in response to RTS RTS heard by all nodes

sender transmits data frame other stations defer transmissions

Avoid data frame collisions completely using small reservation packets!

Week 317

Collision Avoidance: RTS-CTS exchange

APA B

time

RTS(A)RTS(B)

RTS(A)

CTS(A) CTS(A)

DATA (A)

ACK(A) ACK(A)

reservation collision

defer

Week 318

framecontrol

durationaddress

1address

2address

4address

3payload CRC

2 2 6 6 6 2 6 0 - 2312 4

seqcontrol

802.11 frame: addressing

Address 2: MAC addressof wireless host or AP transmitting this frame

Address 1: MAC addressof wireless host or AP to receive this frame

Address 3: MAC addressof router interface to which AP is attached

Address 4: used only in ad hoc mode

Week 319

Internetrouter

AP

H1 R1

AP MAC addr H1 MAC addr R1 MAC addr

address 1 address 2 address 3

802.11 frame

R1 MAC addr AP MAC addr

dest. address source address

802.3 frame

802.11 frame: addressing

Week 320

framecontrol

durationaddress

1address

2address

4address

3payload CRC

2 2 6 6 6 2 6 0 - 2312 4

seqcontrol

TypeFromAP

SubtypeToAP

More frag

WEPMoredata

Powermgt

Retry RsvdProtocolversion

2 2 4 1 1 1 1 1 11 1

802.11 frame: moreduration of reserved transmission time (RTS/CTS)

frame seq #(for reliable ARQ)

frame type(RTS, CTS, ACK, data)

Week 321

hub or switch

AP 2

AP 1

H1 BBS 2

BBS 1

802.11: mobility within same subnet

router H1 remains in same

IP subnet: IP address can remain same

switch: which AP is associated with H1? self-learning (Ch. 5):

switch will see frame from H1 and “remember” which switch port can be used to reach H1

Week 322

Point to Point Data Link Control one sender, one receiver, one link: easier than

broadcast link: no Media Access Control no need for explicit MAC addressing e.g., dialup link, ISDN line

popular point-to-point DLC protocols: PPP (point-to-point protocol) HDLC: High level data link control (Data link

used to be considered “high layer” in protocol stack!

Week 323

PPP Design Requirements [RFC 1557]

packet framing: encapsulation of network-layer datagram in data link frame carry network layer data of any network layer

protocol (not just IP) at same time ability to demultiplex upwards

bit transparency: must carry any bit pattern in the data field

error detection (no correction) connection liveness: detect, signal link failure to

network layer network layer address negotiation: endpoint can

learn/configure each other’s network address

Week 324

PPP non-requirements

no error correction/recovery no flow control out of order delivery OK no need to support multipoint links (e.g.,

polling)

Error recovery, flow control, data re-ordering all relegated to higher layers!

Week 325

PPP Data Frame

Flag: delimiter (framing) Address: does nothing (only one option) Control: does nothing; in the future possible

multiple control fields Protocol: upper layer protocol to which frame

delivered (eg, PPP-LCP, IP, IPCP, etc)

Week 326

PPP Data Frame

info: upper layer data being carried check: cyclic redundancy check for error

detection

Week 327

Byte Stuffing “data transparency” requirement: data field

must be allowed to include flag pattern <01111110> Q: is received <01111110> data or flag?

Sender: adds (“stuffs”) extra < 01111101> byte before each < 01111110> data byte

Receiver: 01111101 and 01111110 bytes in a row:

discard first byte, continue data reception single 01111110: flag byte

Week 328

Byte Stuffing

flag bytepatternin datato send

flag byte pattern plusstuffed byte in transmitted data

Week 329

PPP Data Control ProtocolBefore exchanging network-

layer data, data link peers must

configure PPP link (max. frame length, authentication)

learn/configure network layer information

for IP: carry IP Control Protocol (IPCP) msgs (protocol field: 8021) to configure/learn IP address

Week 330

Link Layer

5.1 Introduction and services

5.2 Error detection and correction

5.3Multiple access protocols

5.4 Link-Layer Addressing

5.5 Ethernet

5.6 Hubs and switches 5.7 PPP 5.8 Link Virtualization:

ATM and MPLS

Week 331

Virtualization of networks

Virtualization of resources: a powerful abstraction in systems engineering:

computing examples: virtual memory, virtual devices Virtual machines: e.g., java IBM VM os from 1960’s/70’s

layering of abstractions: don’t sweat the details of the lower layer, only deal with lower layers abstractly

Week 332

The Internet: virtualizing networks

1974: multiple unconnected nets ARPAnet data-over-cable networks packet satellite network (Aloha) packet radio network

… differing in: addressing conventions packet formats error recovery routing

ARPAnet satellite net"A Protocol for Packet Network Intercommunication", V. Cerf, R. Kahn, IEEE Transactions on Communications, May, 1974, pp. 637-648.

Week 333

The Internet: virtualizing networks

ARPAnet satellite net

gateway

Internetwork layer (IP): addressing: internetwork

appears as a single, uniform entity, despite underlying local network heterogeneity

network of networks

Gateway: “embed internetwork packets

in local packet format or extract them”

route (at internetwork level) to next gateway

Week 334

Cerf & Kahn’s Internetwork ArchitectureWhat is virtualized? two layers of addressing: internetwork and local

network new layer (IP) makes everything homogeneous at

internetwork layer underlying local network technology

cable satellite 56K telephone modem today: ATM, MPLS

… “invisible” at internetwork layer. Looks like a link layer technology to IP!

Week 335

Generic connection – oriented network For A to talk to B, there must be a special call setup

packet that travels from A to B, specifying B as the destination.

Each router along the path must make a routing decision based on B’s address

This is the identical problem in IP In addition to simply forwarding the call setup packet,

the goal is to assign the call a small identifier, which we now call the CI (connection identifier)

CIs can be small because they are handed out dynamically and are significant only on a link

They only need to be large enough to distinguish between the total number of calls that might simultaneously be routed on the same link

Week 336

A wants to talk to B and use CI 57

Why does the CI have to change hop by hop? The answer is that it would be very difficult to choose

a CI that was unused on all the links along the path

A

X

B

R1 R2

R4R3

R5a

b

57 c,33

c33 a,57 33d,79 79a,33

a c

b

a

c79c,22 22b,79

Week 337

ATM and MPLS

ATM, MPLS separate networks in their own right different service models, addressing, routing

from Internet viewed by Internet as logical link

connecting IP routers just like dialup link is really part of separate

network (telephone network) ATM, MPLS: of technical interest in their

own right

Week 338

Asynchronous Transfer Mode: ATM 1990’s/00 standard for high-speed

(155Mbps to 622 Mbps and higher) Broadband Integrated Service Digital Network architecture

Goal: integrated, end-end transport of carry voice, video, data meeting timing/QoS requirements of voice,

video (versus Internet best-effort model) “next generation” telephony: technical roots

in telephone world packet-switching (fixed length packets, called

“cells”) using virtual circuits

Week 339

ATM architecture

adaptation layer: only at edge of ATM network data segmentation/reassembly roughly analagous to Internet transport layer

ATM layer: “network” layer cell switching, routing

physical layer

Week 340

ATM: network or link layer?Vision: end-to-end

transport: “ATM from desktop to desktop” ATM is a network

technologyReality: used to connect

IP backbone routers “IP over ATM” ATM as switched

link layer, connecting IP routers

ATMnetwork

IPnetwork

Week 341

ATM Adaptation Layer (AAL)

ATM Adaptation Layer (AAL): “adapts” upper layers (IP or native ATM applications) to ATM layer below

AAL present only in end systems, not in switches

AAL layer segment (header/trailer fields, data) fragmented across multiple ATM cells analogy: TCP segment in many IP packets

Week 342

ATM Adaptation Layer (AAL) [more]Different versions of AAL layers, depending on ATM

service class: AAL1: for CBR (Constant Bit Rate) services, e.g. circuit

emulation AAL2: for VBR (Variable Bit Rate) services, e.g., MPEG video AAL5: for data (eg, IP datagrams)

AAL PDU

ATM cell

User data

Week 343

ATM LayerService: transport cells across ATM network analogous to IP network layer very different services than IP network layer

NetworkArchitecture

Internet

ATM

ATM

ATM

ATM

ServiceModel

best effort

CBR

VBR

ABR

UBR

Bandwidth

none

constantrateguaranteedrateguaranteed minimumnone

Loss

no

yes

yes

no

no

Order

no

yes

yes

yes

yes

Timing

no

yes

yes

no

no

Congestionfeedback

no (inferredvia loss)nocongestionnocongestionyes

no

Guarantees ?

Week 344

ATM Layer: Virtual Circuits VC transport: cells carried on VC from source to dest

call setup, teardown for each call before data can flow each packet carries VC identifier (not destination ID) every switch on source-dest path maintain “state” for each

passing connection link,switch resources (bandwidth, buffers) may be allocated

to VC: to get circuit-like perf.

Permanent VCs (PVCs) long lasting connections typically: “permanent” route between to IP routers

Switched VCs (SVC): dynamically set up on per-call basis

Week 345

ATM VCs

Advantages of ATM VC approach: QoS performance guarantee for connection

mapped to VC (bandwidth, delay, delay jitter)

Drawbacks of ATM VC approach: Inefficient support of datagram traffic one PVC between each source/dest pair)

does not scale (N*2 connections needed) SVC introduces call setup latency,

processing overhead for short lived connections

Week 346

ATM Layer: ATM cell 5-byte ATM cell header 48-byte payload

Why?: small payload -> short cell-creation delay for digitized voice

halfway between 32 and 64 (compromise!)

Cell header

Cell format

Week 347

ATM cell header

VCI: virtual channel ID will change from link to link thru net

PT: Payload type (e.g. RM cell versus data cell)

CLP: Cell Loss Priority bit CLP = 1 implies low priority cell, can be

discarded if congestion HEC: Header Error Checksum

cyclic redundancy check

Week 348

ATM VCs

Advantages of ATM VC approach:QoS performance guarantee for

connection mapped to VC (bandwidth, delay, delay jitter)

Drawbacks of ATM VC approach: Inefficient support of datagram trafficOne PVC between each source/dest pair)

does not scale (N*2 connections needed) SVC introduces call setup latency,

processing overhead for short lived connections

Week 349

Virtual Path Concept The connection identifier in the ATM cell header

has two complexities: It’s hierarchical and divided into two subfields VPI

(Virtual Path Identifier) and VCI (Virtual Circuit Identifier)

VCI is 16 bits VPI is 12 bits

What’s a VPI? There might be very high speed backbone carrying many millions of calls

The split between VPI and VCI saves the switches in the backbone from requiring that their call mapping database keep track of millions of calls

Week 350

Virtual Path Concept

The backbone routers only use the VPIU field then if needed

Outside the backbone, the switches treat the entire VPI:VCI field as one nonhierarchical unit

VP switch looks at only the VPI portion VC switch looks at both

Week 351

Example

S1

S2S3

S4S5

D

a

b

c

S1 is to receive a call setup on port b with CI 17 for destination D• Normal VP switching inside the core with the CI being the 12 bit VPI• Switches outside the core do normal VC switching with the CI being 28 bits• Switches at the border also do VC swiching but the outgoing CI must be chosen so that the VPI portion of the outgoing CI is to the outgoing VPI

e

Week 352

Example

S1

S6S4

S5

S8

S9S2

S3

a

d

c d

e89c,187.42

187. d,13

13. e,57 57.42 d,83

64000 VCs can be carried within a single VP dramatically reducing the switch table sizes

Week 353

Virtual Path and Virtual Channels

ATM Physical LinkVirtual Channel Connection (VCC)

Virtual Path(VP)

Contains Multiple VCs

Virtual Channel Connection(VCC)

Contains Multiple VPs

Virtual Channel(VC)

Logical PathBetween ATM End Points

Virtual Channels (VC)


E3OC–12 Virtual Path (VP)

Virtual Path (VP)

Connection Identifier = VPI/VCIVPI/VCI

Week 354

ATM Switches

ATM switches translate VPI/VCI values VPI/VCI value unique only per interface—

eg: locally significant and may be re-used elsewhere in network

45

2929

33

22

11

64642929

45

6464

2929

1

2

11

33

45

29

2929

6464

2

1

33

11

VPI/VCIPort VPI/VCIPort

Input Output

Week 355

VP and VC Switching

VCI 1 VCI 2 VCI 3 VCI 4

VPI 2VPI 2VPI 3VPI 3VPI 1VPI 1

VPI 2VPI 2

VPI 3VPI 3

VPI 5

VPI 1VPI 1

VPI 4

Port 1Port 1

Port 2Port 2

Port 3Port 3

VCI 1

VCI 2

VCI 1

VCI 2

VP Switch

VC Switch

Week 356

Virtual Channels

and Virtual Paths

This hop-by-hop forwarding is known as cell relay

Virtual Channel Connection (VCC)

Virtual PathConnection (VPC)

VPSwitch

VCSwitch

VCSwitch

NNI NNI

VPI = 2VCI = 44

VPI = 1VCI = 1

VPI = 26VCI = 44

VPI = 20VCI = 30

UNIUNI

Week 357

Virtual Path and Virtual Channels

ATM Physical LinkVirtual Channel Connection (VCC)

Virtual Path(VP)

Contains Multiple VCs

Virtual Channel Connection(VCC)

Contains Multiple VPs

Virtual Channel(VC)

Logical PathBetween ATM End Points



E3OC–12 Virtual Path (VP)

Virtual Path (VP)

Connection Identifier = VPI/VCIVPI/VCI

Week 358

ATM Switches

ATM switches translate VPI/VCI values VPI/VCI value unique only per interface—

eg: locally significant and may be re-used elsewhere in network

45

2929

33

22

11

64642929

45

6464

2929

1

2

11

33

45

29

2929

6464

2

1

33

11

VPI/VCIPort VPI/VCIPort

Input Output

Week 359

VP and VC Switching

VCI 1 VCI 2 VCI 3 VCI 4

VPI 2VPI 2VPI 3VPI 3VPI 1VPI 1

VPI 2VPI 2

VPI 3VPI 3

VPI 5

VPI 1VPI 1

VPI 4

Port 1Port 1

Port 2Port 2

Port 3Port 3

VCI 1

VCI 2

VCI 1

VCI 2

VP Switch

VC Switch

Week 360

Virtual Channels

and Virtual Paths

This hop-by-hop forwarding is known as cell relay

Virtual Channel Connection (VCC)

Virtual PathConnection (VPC)

VPSwitch

VCSwitch

VCSwitch

NNI NNI

VPI = 2VCI = 44

VPI = 1VCI = 1

VPI = 26VCI = 44

VPI = 20VCI = 30

UNIUNI

Week 361

Example

Week 362

ATM Physical Layer (more)

Two pieces (sublayers) of physical layer: Transmission Convergence Sublayer (TCS): adapts

ATM layer above to PMD sublayer below Physical Medium Dependent: depends on physical

medium being used

TCS Functions: Header checksum generation: 8 bits CRC Cell delineation With “unstructured” PMD sublayer, transmission

of idle cells when no data cells to send

Week 363

ATM Physical Layer

Physical Medium Dependent (PMD) sublayer

SONET/SDH: transmission frame structure (like a container carrying bits); bit synchronization; bandwidth partitions (TDM); several speeds: OC3 = 155.52 Mbps; OC12 =

622.08 Mbps; OC48 = 2.45 Gbps, OC192 = 9.6 Gbps

TI/T3: transmission frame structure (old telephone hierarchy): 1.5 Mbps/ 45 Mbps

unstructured: just cells (busy/idle)

Week 364

IP-Over-ATMClassic IP only 3 “networks” (e.g., LAN segments) MAC (802.3) and IP addresses

IP over ATM replace “network”

(e.g., LAN segment) with ATM network

ATM addresses, IP addresses

ATMnetwork

EthernetLANs

EthernetLANs

Week 365

IP-Over-ATM

AALATMphyphy

Eth

IP

ATMphy

ATMphy

apptransport

IPAALATMphy

apptransport

IPEthphy

Week 366

Datagram Journey in IP-over-ATM Network at Source Host:

IP layer maps between IP, ATM dest address (using ARP) passes datagram to AAL5 AAL5 encapsulates data, segments cells, passes to ATM

layer

ATM network: moves cell along VC to destination at Destination Host:

AAL5 reassembles cells into original datagram if CRC OK, datagram is passed to IP

Week 367

IP-Over-ATM

Issues: IP datagrams into

ATM AAL5 PDUs from IP addresses

to ATM addresses just like IP

addresses to 802.3 MAC addresses!

ATMnetwork

EthernetLANs

Week 368

ATM LayerService: transport cells across ATM

network analogous to IP network layer very different services than IP network

layerNetwork

Architecture

Internet

ATM

ATM

ATM

ATM

ServiceModel

best effort

CBR

VBR

ABR

UBR

Bandwidth

none

constantrateguaranteedrateguaranteed minimumnone

Loss

no

yes

yes

no

no

Order

no

yes

yes

yes

yes

Timing

no

yes

yes

no

no

Congestionfeedback

no (inferredvia loss)nocongestionnocongestionyes

no

Guarantees ?

Week 369

Traffic Management

Why traffic management? Traffic control techniques AAL5/ABR congestion feedback Buffers are your friend

Week 370

Why Traffic Management?

Proactively combat congestion Provision for priority control Maintain well-behaved traffic

Week 371

Ethernet (1500 Bytes) = 32 Cells

FDDI (4470 Bytes) = 96 Cells

IP over ATM–1577 (9180 Bytes) = 192 Cells

Why Traffic Management?

Lose one cell and the rest are useless Need to re-transmit 32+ cells for one cell lost Congestion collapseCongestion collapse is the result PPD (Partial Packet Discard) EPD (Early Packet Discard)

TCP/IP Packet

X

Cell LossCell Loss—Data’s Critical Enemy

Week 372

Traffic Control Techniques

Connection management—Acceptance Traffic management—Policing Traffic smoothing—Shaping

Week 373

Contract


Contract

ContractContract� Traffic Parameters

Peak cell rate

Sustainable cell rate

Burst tolerance

Etc.

� Quality of ServiceDelay

Cell loss

Connection Management

ATM Network

Week 374

Traffic Descriptors Peak Cell Rate(PCR) = 1/T in units of

cells/second, where T is the minimum intercell spacing in seconds(i.e., the time interval from the first bit of one cell to the first bit of the next cell)

Sustainable Cell Rate(SCR) is the maximum average rate that a bursty, on-off traffic source can be sent at the peak rate

Maximum Burst Size(MBS) is the maximum number of cells that can be sent at the peak rate

Week 375

QoS Expectations Applications have service requirements on:

Throughput Maximum Delay Variance of Delays(Delay Jitter) Loss Probability

Network has to guarantee the required Quality of Service(Traffic Contract)

Major Problem: Bursty Traffic, i.e., Peak Traffic Rate >> Average Traffic Rate

Week 376

Traffic Control TechniquesConnection Management

Connection Admission Control (CAC)

ATM Network

I want a VC:X MbpsY DelayZ Cell Loss

CACCACCan I Support this Reliably without

Jeopardizing Other Contracts

Noor

Yes, Agree to aTraffic Contract

Guaranteed QoS Request

ContractContract

Week 377

Connection Admission Control The primary function of the CAC is to accept a new

connection request only if its stated QoS can be maintained without influencing the QoS of the already accepted connections.

It is very likely that certain calls will require more than one connection (e.g., teleconferencing) CAC procedure must be performed for each requested VCC or VPC.

CAC must Decide whether connections can be accepted or

not. Provide parameters required by the UPC. Perform routing and resource allocation.

Week 378

Bandwidth Allocation Peak Allocation

– Suppose a source has an average BW of 20 Mbps and a peak BW of 45 Mbps. Peak BW allocation requires that 45 Mbps be reserved at the output port for the specific source independent of whether or not the source transmits continuously at 45 Mbps.

– Peak BW allocation is used for CBR services. The advantage of peak BW allocation is that it is easy to decide whether to accept a new connection or not.

– The new connection is accepted, if the sum of the peak rates of all the existing connections plus the peak rate of the new connection is less than the capacity of the output link.

– The disadvantage of the Peak BW allocation is that the output port link will be underutilized if the sources do not transmit at their peak rates.

Week 379

Bandwidth Allocation

Statistical Allocation The allocated BW is less than the peak rate

of the source. The sum of all peak rates may be greater

than the capacity of the output link. An equivalent capacity is allocated between

the peak rate and the mean rate Call admission: if the sum of the equivalent

capacities is less than the capacity, reject the incoming call

Week 380

Source BehaviorCBR

VBR

time

time

Burst DurationCellInterarrivalTime

Burst to BurstInterval

CellInterarrivalTime

Call Duration

Call Set-up Call Tear-Down

ON OFFVBR Source Description:

orBurst Length DistributionInterarrival Distribution During BurstIdle (silent) Length Distribution

Peak Arrival RateAverage Arrival RateMean Burst Length

< Bp, Bm, T >

Week 381

End-to-end ModelCAC is based on an abstractperformance model of the network.

Multiplexing Demultiplexing

DepartingCross Traffic

EnteringCross Traffic





- FINITE BUFFERS- DETERMINISTIC SERVICE TIMES

Modeling Problems

Challenges - Arrival streams are non-Poisson - Finite buffers at the multiplexers and switches- Correlated cell arrivals- Large state-space of the resulting system- Simulations of such systems take very long to converge

Week 382

ATM Network


You areNot in Conformance

with the Contract.What Should the

Penalty Be??

• PASSPASS• MARK CLP BITMARK CLP BIT• DROPDROP

?DECISION??DECISION?

Contract

Traffic ManagementUsage Parameter Control (UPC) aka PolicingPolicing

REBELREBELAPPLICATIONAPPLICATION

Week 383


00 00 00 00 1 00MarkedMarked

UPC

• PASSPASS• MARK CLP BITMARK CLP BIT• DROPDROP

?DECISION??DECISION?

Traffic Management

CLP Control—When congested dropdrop markedmarked cells Public UNI—Generic Cell Rate Algorithm (GCRA)

DDrroopp

Week 384

Policing The operation of the CAC and the correct allocation of resources

depend heavily on the guarantee that the traffic source will behave as expected, i.e., as described by the traffic descriptor.

Thus a monitoring/policing function is needed to force the traffic to comply to the traffic descriptor.

This monitoring/policing function is performed by the UPC (policer).

The UPC is in the form of preventive congestion control. It enforces a certain cell arrival rate or “shape”, such that it does

not exceed certain values that would cause network elements to overload and lead to congestion.

A UPC usually consists of a counter-based mechanism that drops or marks data units when they are found in violation of a certain agreement between end-user and the communication system.

It does not use information from remote network elements.

Week 385

Generic Cell Rate Algorithm (I, L)The GCRA is reference algorithm for a cell rate which determines if a cell is conforming.

Arrival of a cell k at time ta (k)

VIRTUAL SCHEULING ALGORITHM

TAT Theoretical Arrival Timeta(k) Time of arrival of a cell

TAT ta(k) YES

YES

TAT = ta(k)

TAT < ta(k) + LNon

ConformingCel

NO

TAT = TAT + IConforming Cell

X’=X-(ta(k)-LCT)

X’< 0

X’>= L

X=X’+ILCT = ta(k)

Conforming Cell

YES

X’=0YESNonConforming

Cell

CONTINUOUS-STATELEAKY BUCKET ALGORITHMX : Value of the Leaky Bucket counterX’ : auxiliary variableLCT Last Compliance Time

I : IncrementL : Limit

Virtual Scheduling AlgorithmTAT:= ta(1) initially

Leaky Bucket AlgorithmX := 0LCT := ta(1) initially

Week 386

Traffic Contact and Performance Definitions

CBR GCRA(T0+1 , CDVT) in relation to the PCR0+1

T0+1 is the inverse of PCR0+1

Nonconformant cells are dropped

VBR (one of the standardized definitions) GCRA(T0+1 , CDVT) in relation to the PCR0+1

GCRA(Ts0 , BT0 + CDVT) in relation to the SCR of the CLP = 0 cell stream

• BT = (MBS – 1) (1/SCR - 1/PCR) If CLP = 0 cell conforms to (1) and (2), that cell is

conformant If CLP = 0 cell is not conforming to (2) but is conforming to

(1) then it will be remarked as CLP = 1

Week 387

Example• Consider a Video-on-Demand service where the negotiated PCR = 50kcells/s and theand the CDV Tolerance ( ) =50sec. • The cells arrive at times as indicated by t(k).

Note: GCRA(I,L) where I = T = 1/PCR = 20sec/cell and L = t = 50 sec.

GCRA(T,)

1

2

3

4

56

7

8

9

10

0

k

Figure: Example of the GCRA

LCT(k) X(k) X'(k) ConformingT(k)

0s 0s 0s 0s Yes

20s 0s 20s 0s Yes

25s 20s 20s 15s Yes

30s 25s 35s 30s Yes

35s 30s 50s 45s Yes

40s 35s 65s 60s No

45s 35s 65s 50s No

50s 35s 65s 50s No

55s 50s 70s 65s No

80s 50s 70s 40s Yes

100s 80s 60s 40s Yes

22

Week 388


Intelligent Packet Discard—IPDIPD Discard cells from same ‘bad’ packet Tail packet discard Maximize “GoodputGoodput”

3 2

00 00 00 00 1 00MarkedMarked

UPC

Traffic Management

DDrroopp

Week 389

Private ATM Network Public ATM Network


Shaped DataActual Data

I Want to Comply With My

Contract. So, I Will Smooth/Shape

My Traffic

Go Ahead,

Make My Day

Traffic shaper at customer site Changes traffic characteristics Leaky bucket algorithm

Sh

ap

er

Traffic Smoothing

Week 390


Absorb traffic bursts from simultaneous connections

Switches schedule traffic based on priority of traffic according to QoS

Switch must reallocate buffers as the traffic mix changes

Effective bufferingEffective buffering maximizes throughput of usable cells as opposed to raw cells (aka goodputaka goodput)

Buffers Are Your Friend

Documents

Week 3 1 Week 3 Virtual LANs, Wireless LANs, PPP, ATM