week 3 1 week 3 virtual lans, wireless lans, ppp, atm
TRANSCRIPT
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)
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
Virtual Channels (VC)
Virtual Channels (VC)
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
Traffic Control Techniques
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
EnteringCross Traffic
EnteringCross Traffic
DepartingCross Traffic
DepartingCross 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
Traffic Control Techniques
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
Traffic Control Techniques
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
Traffic Control Techniques
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
Traffic Control Techniques
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
Traffic Control Techniques
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