lecture7-cell switching and atm networks.pdf
TRANSCRIPT
-
Bi 7
ATM Networks
Why ATM?
BISDN Reference Model
ATM Layer
ATM Adaptation Layer
-
Chapter 9
ATM Networks
Why ATM?
-
The Integrated Services Vision
Mang in thoai ban u ton tng t
Truyn dn & Chuyn mach
Chuyn dn sang phn loi ton s
1960s: truyn dn mang loi chuyn sang s
1970s: chuyn mach chuyn thnh s
Vong thu bao t khach hng n mang vn con l tng t
Tm nhin cho Dich vu tich hp:
Mang cn phai s t u cui n u cui
Mang cn h tr tt ca cac dich vu: telephone, data, video
Ba giai phap cho Integrated Services Network
ISDN in 1980s
ATM/BISDN in 1990s
Internet in 2000s
-
Basic rate interface (BRI): 2B+D
BRI
PRI
BRI
PRI
Circuit-
switched
network
Private channel-
switched network
Signaling
network
Packet-
switched
networks
Integrated Services Digital
Network (ISDN)
Primary rate interface (PRI): 23B+D
ISDN:
Integrated access
to end-to-end digital communication services
through a standard set of user-to-network interfaces
Network consisted of separate networks for voice, data, signaling
B=64 kbps
D=16 kbps
-
Broadband ISDN
BISDN: Mt single universal network mm deo co th cung cp tt ca cac dich vu ngi dung
ISDN khng ap ng c: nhu cu cn 10s to 100s Mbps cho kt ni LAN v digital TV
Synchronous Transfer Mode (kt ni nx64 kbps) ban u c ky vong BISDN, nhng
Asynchronous Transfer Mode (ATM) c chon
Multiplexing & switching framework
connection-oriented virtual circuits
fixed-length packets, cells, with short headers
-
u im cua ATM
C s ha tng mang v quan ly c n gian hoa do s dung mt ch duy nht cho mang
Ky vong s dung LAN, MAN, v WAN
Kha nng quan ly bng thng rng rai
SONET-like grooming capabilities, but at arbitrary bandwidth granularities
ATM khng bi gii han bi tc v c ly
50-600 Mbps for ATM
Cac thuc tinh QoS cua ATM cho phep vn chuyn voice, data, va video, vi vy lm cho ATM phu hp cho mang a dich vu
-
Pham vi ky vong cua ATM
Tt ca thng tin truyn bi mang x ly cac cell 53bytes
Co th m rng v tc
Giai phap chuyn mach lm vic LAN, MAN, hoc WAN
ATM fibre backbone
Wide Area Network (WAN)
supercomputer
wireless
interface
wireless
interface
multimedia
terminal
local area
network
(LAN)
User information Network header
5 bytes 48 bytes
video
server
data
base
-
ATM
Adaptation
Layer
ATM
Adaptation
Layer
ATM Network
Video Packet Voice Video Packet Voice
ATM Networking
-
AAL chuyn Thng tin thanh Cells
A/D AAL
Voice
s1 , s2 Digital voice samples
cells
AAL Data
Bursty variable-length
packets
cells
A/D AAL
Video
Compression
compressed
frames picture
frames
cells
-
Thit lp kt ni thit lp knh ao bng cach t pointers trong cac bang trn ng qua mang
Tt ca cac cells cho mt kt ni i theo mt ng Header xac inh kt ni Cells xp hng ch c truyn tai cac ATM switches & multiplexers Co th truyn dich vu CBR v VBR thng qua thoa thun trong qua
trinh thit lp kt ni Phm cht tr v mt mat co th thoa thun trc khi thit lp kt ni
Cell-Switching Virtual Circuit
Switches
Cells
Destination
Source
Cells
Cells
Cells
-
Switch thc hin oc bang v inh tuyn
ATM switches co th thc hin nh s dung b nh chia se, Bang kt ni chia se, hoc c cu a tng t inh tuyn
ATM Switching
2
3
N
1
Switch
N
1
5
6
video
video
voice
data
25
32
32
61
75
67
39
67
N
1
3
2
video 75
voice
data
video
32
25 32
61
39
67
67
-
1
2
N
1
2
N
Lu lng packet ghep cac ng u vo
Tach ra tai cac input port
Chuyn tip ti output port
Multiplexing in ATM Switches
-
Call Admission Control da trn Traffic Descriptors & QoS Reqts
Cell streams c giam sat tai User Network Interface
Cell Enqueueing Policy, Cell Transmission Scheduling, Flow Control
Generalized Processor Sharing, Weighted Fair Queueing, etc.
Multiplexing Gain
Cell Multiplexing implies Delay, Jitter, Loss
VCs
with
different TDs
&
different
QoS reqts
ATM Support for Multiple QoS Levels
-
Chapter 9
ATM Networks
BISDN Reference Model
-
M hinh tham chiu BISDN
User Plane: truyn tai user information; flow control;
error recovery
Control Plane: thit lp, quan ly, v ngt kt ni
Layer Management Plane: quan ly cac thc th lp & OAM
Plane Management: quan ly tt ca cac planes
Physical Layer
ATM Layer
ATM Adaptation Layer
Higher Layers
User Plane Control Plane
Management Planes
Layer M
an
ag
em
en
t P
lan
e M
an
ag
em
en
t
-
Y nghia cua Plane
Ba loai mang logic tham gia vo vic phn phi cac dich vu truyn thng
User Network: truyn tai thng tin ngi dung
Control (Signaling) Network: mang ban tin bao hiu thit lp, duy tri v ngt kt ni
Management Network: mang thng tin quan ly: thng tin giam sat, bao canh v s liu thng k s dung
Mt tp giao thc ring, goi l plane, c inh nghia cho mt trong ba mang ny
-
ATM Adaptation Layer
(AAL)
ATM Network Layer
Physical Layer
Higher Layers
ATM Adaptation Layer
(AAL)
ATM Network Layer
Physical Layer
Higher Layers
ATM Network Layer
Physical Layer
USER NETWORK USER
ATM Layered Architecture
-
ATM Layered Architecture
ATM Adaptation Layer
Giao din chun ti cac lp cao hn
Thc hin cac chc nng phi hp
Lm vic E2E gia cac h thng u cui
Phn oan thnh cells v tai rap
ATM Layer Truyn tai Cells
Tao/Tach Cell-Header
Dich (translation) VPI/VCI
Cell multiplexing/demultiplexing
iu khin lung v tc nghen
Physical Layer
Chuyn i Cell stream / bit stream
Truyn dn s
ATM Adaptation Layer
(AAL)
ATM Network Layer
Physical Layer
Higher Layers
-
Cac giao din ATM
X
X
X
X
X
X
X
X
X
Private
UNI
Public
UNI
NNI
Private
NNI
Private
ATM
network
Public
UNI B-ICI
Public ATM
network A
Public ATM
network B
UNI: User-Network Interface
NNI: Network-Network Interface
B-ICI: Broadband Inter-carrier i/f
-
ATM Physical Layer
TC Sublayer:
Cell Delineation
Kim tra li Header
Cell Rate Decoupling
(Insertion of Idle Cells)
Ring cho PMD
PMD Sublayer:
Line code
Connectors
Tai s dung cac chun cua lp vt ly hin tai
Transmission
convergence
(TC)
sublayer
Physical medium
dependent
(PMD) sublayer
-
Private UNI Physical Layers
UTP = Unshielded twisted pair STP = Shielded twisted pair
MMF = Multimode fiber SMF = Single-mode pair
STS = Synchronous Transport Signal
Frame format Bit rate Media
Cell stream 25.6 Mbps UTP-3
STS-1 51.84 Mbps UTP-3
FDDI 100 Mbps MMF
STS-3c, STM-1 155.52 Mbps UTP-3, UTP-5, STP,
SMF, MMF coaxial
pair
Cell stream 155.52 Mbps MMF, STP
STS-12, STM-4 622.08 Mbps SMF, MMF
-
Public UNI Physical Layers
Frame format Bit rate Media
DS-1 1.655 Mbps Twisted pair
DS-3 44.736 Mbps Coaxial
STS-3c, STM-1 155.52 Mbps SMF
E-1 2.048 Mbps Twisted pair
Coaxial
E3 34.368 Mbps Coaxial
J2 6.312 Mbps Coaxial
-
Chapter 9
ATM Networks
ATM Layer
-
ATM Layer
Lin quan n truyn theo th t cac cells qua kt ni mang
Kt ni ATM im-Ni-im: mt chiu hoc hai chiu
Point-to-Multipoint: mt chiu
Permanent Virtual Connections (PVC): cac kt ni di han cung cp bng thng gia cac im u cui trong mt mang ATM
Switched Virtual Connections (SVC): kt ni ngn han thit lp nhm ap ng cho cac yu cu cua khach hng
-
Virtual Channel Connections: virtual circuit
Virtual Path Connections: tp hp cua mt s kt ni ao (VPC) ATM Header cha thng tin v kt ni ao: 8-bit Virtual Path Identifier 16-bit Virtual Channel Identifier
ATM Virtual Connections
Virtual paths
Virtual channels
-
Tai sao cell co 53 Bytes?
Anh hng cua tr vo cac packet thoai co tac ng ti vic la chon kich thc cell
Tr tao goi ln ln theo kich c cell
@64kbps: packetization delay = cell size * 125 sec
Nu tr qua lu, cn s dung thit bi trit ting vong
Europe co cac ng truyn ngn v khng cn s dung b trit ting vong, vi vy xut s dung 32 byte payload
U.S. s dung cac ng truyn di v cn s dung cac b trit, vi vy, xut s dung 64 byte payload
Thoa hip: 48 byte payload
-
The ATM Cell
GFC-undefined
UNI cells has GFC field
NNI cells allocate these 4 bits to VPI; 4096 VPs
GFC (4 bits) VPI (4 bits)
VPI (4 bits) VCI (4 bits)
VCI (8 bits)
VCI (4 bits) PT (3 bits) CLP
(1 bit)
HEC (8 bits) AT
M c
ell
he
ad
er
Payload
(48 bytes)
Virtual Path Identifier
8-bits: 256 VC bundles
Virtual Channel Identifier
16 bits: 65,536 VCs/VP
Payload Type Indicator
Bit 3: data vs. OAM cell
Bit 2: Congestion indication in
data cells
Bit 1: Carried transparently
end-to-end; Used in AAL5
Cell Loss Priority
if 1, cell can be discarded by
network
-
Header Error Check
The HEC only covers the 5 bytes of the header to protect
against cell misdelivery
Since VPI/VCI changes at every switch, HEC must be
recomputed
HEC used for cell delineation
Two modes: Header Error Detection / Correction
Generating Polynomial: g(x)=x8+ x2+ x+ 1
The pattern 01010101 is XORed to r(x); keeps idle cells
from having HEC=0 and preventing cell delineation
The pattern 01010101 is XORed to r(x) in received
header prior to error checking
-
ATM Permanent Virtual
Connections
Quan tri mang thit lp bng nhn cng cac bang VPI/VCI tai cac switches v terminals
Thi gian thit lp kt ni lu, cac kt ni keo di
ATM
Switch
ATM
Switch
Operator at
Network Control Center
-
ATM Switched Virtual
Connections
Terminals v switches s dung VPI/VCI xac inh trc thit lp kt ni ng, theo yu cu
Giao thc bao hiu c s dung trao i vi h thng x ly cuc goi
ATM
Switch
ATM
Switch
-
Traffic Contract
Trong qua trinh thit lp kt ni, ngi dung v mang thoa thun hai tp tham s cho mi kt ni
Traffic descriptor: ngi dung xac inh lu lng mong mun mang chuyn giup
QoS requirements: ngi dung xac inh loai phm cht mang yu cu bi cac cell
Traffic Contract
Ngi dung cn tun theo traffic descriptor
Mang cn chuyn cell theo cam kt QoS
-
Cac tham s QoS
Sau tham s QoS
Ba tham s khng c thoa thun trong qua trinh thit lp kt ni:
Cell error ratio: ti l cell c chuyn bi li
Cell mis-insertion ratio: s cells trung binh/second bi chuyn nhm
Severely errored cell block ratio: M hay nhiu hn trong s N cells bi mt, li, hay chuyn nhm
-
Negotiable QoS Parameters
D0 Peak-to-Peak CDV
Dmax
pro
babili
ty d
ensity o
f cell
dela
y
Cell Loss Ratio (CLR): ti l cells bi mt
Xac inh bi u tin buffer
Cell Transfer Delay (CTD): thoa thun maximum delay Dmax: 1- of cells co tr it hn Dmax
Xac inh bi cell scheduling
Cell Delay Variation (CDV): Peak-to-Peak variation: Dmax-D0
-
Traffic Descriptors
Peak Cell Rate: tc cells/second mt ngun khng c phep vt
Sustainable Cell Rate: tc cell trung binh do ngun tao ra trong mt khoang thi gian di
Maximum Burst Size: s cell lin tip cc ai mt ngun co th phat tai tc peak cell rate (PCR)
Minimum Cell Rate: tc cell trung binh cells/second, ngun lun c phep truyn
Cell Delay Variation Tolerance: bin ng cell delay cho phep (tolerated) cho mt kt ni cho trc.
-
CBR VBR
real-time
VBR non-real-time
ABR UBR
Cell Loss
Rate
Cell Transfer
Delay
Cell Delay
Variation
Traffic
Descriptors
Flow Control
specified
specified
specified
unspecified
unspecified
unspecified
PCR/CDVT PCR/CDVT
SCR/BT
PCR/CDVT
& others PCR/CDVT
no yes no
CBR = Constant Bit Rate
VBR = Variable Bit Rate
ABR = Available Bit Rate
UBR = Unspecified Bit Rate
PCR = Peak Cell Rate
CDVT = Cell Delay Variation Tolerance
SCR = Sustainable Cell Rate
BT = Burst Tolerance
Cell transfer services provided by ATM Network
ATM Service Categories
-
Multiplexing & QoS Guarantees
ATM provides per-connection QoS guarantees
Many cell flows are multiplexed onto a common stream, so how are guarantees delivered?
CBR: scheduler must ensure transmission opportunities are regularly available for each connection
Real-time VBR: expect some multiplexing gain from combining VBR flows; however need to meet delay and loss requirements
Non-real-time VBR: can attempt higher multiplexing gains, subject only to loss requirement
UBR: no guarantees, but excellent performance at light traffic
ABR: some degree of guarantee: low CLR if source responds to network feedback; MCR can be negotiated
-
Traffic Contract & Call Admission
Control
Traffic contract: bao gm loai dich vu ATM, traffic descriptors, yu cu QoS
Connection admission control (CAC) xac inh xem mt yu cu kt ni co th c chp nhn hay khng
Mi switch trn ng cn xac inh xem no co th chp nhn thm lung mi trong khi vn am bao cam kt vi cac lung hin tai; nu co th, phn b ti nguyn cho lung mi
CAC khng c tiu chun hoa, tuy thuc vo nh cung cp dich vu
Cho phep mc overbooking thu c multiplexing gain khac nhau
Tinh cc khac nhau cho cac dich vu cung cp
-
Policing, Traffic Shaping, and
Congestion Control
am bao v QoS chi co y nghia khi ngi dung tun theo connection contract
Usage parameter control (UPC) l qua trinh cng ch thoa thun lu lng tai UNI Generic Cell Rate Algorithm co th s dung cho UPC; lin quan
n thut toan leaky-bucket Non-conforming cells co th bi anh du (CLP=1) hoc loai bo
Traffic shaping: ngun co th s dung TS am bao lu lng cua no tun theo connection contract Co th s dung Token bucket
Congestion control Cac cell co CLP=1 bi loai bo trc khi xay ra tc nghen Cac kt ni ABR phai ap ng vi thng tin phan hi tc nghen
nhn c t mang
-
Chapter 9
ATM Networks
ATM Adaptation Layer
-
ATM Adaptation Layer AAL: giao thc E2E dung phi hp dich vu truyn tai cell do
mang ATM cung cp theo yu cu cua application classes xac inh
Bao gm chuyn i cells v ngc lai, v cac chc nng phi hp b sung nh khi phuc inh thi, truyn tai tin cy
ITU inh nghia cac loai dich vu sau
Class
End-to-End
Timing
Bit Rate
Connection
Mode
A B C D
required not required
constant variable
connection-oriented connectionless
Class A = circuit emulation
Class B = variable bit-rate video
Class C & D = packet transmission
-
Cu trc giao thc AAL
AAL co hai lp con:
Segmentation & Reassembly Phn oan PDUs thnh cell
payloads; Tai rap PDUs t cell payloads nhn c
Convergence Common Part: packet
framing v error detection yu cu bi tt ca AAL users
Specific Part: cac chc nng phu thuc vo yu cu ring cua AAL user classes
ATM
Higher Layers
Segmentation
and
Reassembly
Sublayer
AAL
Layer
Convergence
Sublayer
Common Part
Service Specific
Convergence
Sublayer
-
AAL1
Higher layer User data stream
Convergence
sublayer
SAR sublayer
ATM layer
CS PDUs
SAR PDUs
ATM Cells
47 47 47
1 47 1 47 1 47
H H H
5 48
H
5 48
H
5 48
H
b1 b2 b3
Cung cp truyn dn CBR
-
AAL2
Truyn dn co hiu qua bng thng cac dich vu tc thp, lu lng packet ngn vi yu cu tr thp
B sung thm lp multiplexing th 3 cho cu truc VP/VC cua ATM, vi vy cac low-bit-rate users co th chia se mt kt ni ATM.
AAL
2
ATM cells
Low bit rate
Short voice packets
Mobile
switching
office
-
AAL2
Higher layer This example
assumes 24 byte
packets
Common part
convergence
sublayer
SAR sublayer
ATM layer
1 47
5 48
H
P3
Service specific
convergence
sublayer
P2 P1
Assume null
1 47
3 24 3 24 3 24
PAD
5 48
H
Add 3-byte
header to each
user packet
Segment into SAR
PDUs
H H H
-
AAL3/4
Why 3 / 4 ?
AAL3: Truyn dn d liu connection-oriented
AAL4: Truyn dn d liu connectionless Tt ca packet connectionless s dung cung mt VPI/VCI tai UNI
Multiplexing ID (MID) dung phn bit connectionless packets
AAL3 v AAL4 kt hp thnh AAL co th dung cho truyn dn connection-oriented hay connectionless
AAL3/4 cho phep nhiu ngi dung c ghep knh va ghep xen (interleaved) trong cung ATM VC
Message mode: ban tin cua mt ngi s dung phn oan thnh ATM payloads
Stream mode: mt hoc nhiu ban tin phn oan thnh ATM payloads v phn phi khng cn chi ra phn inh
Assured mode: phn phi ban tin khng li
Non-Assured mode: ban tin co th c phn phi co li hoc khng co li
-
Higher layer
Common part
convergence
sublayer
SAR sublayer
ATM layer
Service specific
convergence
sublayer
Information
Assume null
T PAD
User message
Pad message to
multiple of 4 bytes.
Add header and trailer.
Each SAR-PDU
consists of 2-byte
header, 2-byte trailer,
and 44-byte payload.
H
4 4
2 44 2 2 44 2 2 44 2
Information
AAL 3/4
-
Higher layer
Common part
convergence
sublayer
SAR sublayer
ATM layer
PTI = 0
Service specific
convergence
sublayer
48
(1)
Information
T PAD
Information
48
(0)
48
(0)
PTI = 0 PTI = 1
AAL5
n gian hn than AAL3/4
48 bytes payload
Truyn tng packet cho VCI
PTI in ATM
header indicates
last cell for a
given packet
-
Examples: Voice and Video
Voice
AAL1 for individual PCM
voice calls
AAL1 with structured
transfer for nx64 kbps
AAL2 for low-bit-rate
cellular voice
AAL5 for inexpensive
voice
CBR MPEG2 Video
Timing recovery at AAL
or at MPEG systems
layer?
Error detection &
correction at which
layer?
Timing recovery at
MPEG2 systems level
and AAL5 over CBR
ATM was selected
-
Example: ATM & ADSL
IP over PPPoE frames segmented by AAL5 into ATM cells at
ADSL modem
ATM cells flow through DSLAM and ATM network to Internet
Service Provider
ISP
AD
SL
AT
M
DSL Access Mux
User Premise Central Office
Telephone
Switch Telephone
Network
ATM
Network
IP
PPPoE
AAL5
ATM
ADSL
splitter
splitter Subscriber
loop