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WAN_Technologies - 1 Copyright: see page 2
WAN Technologies(to interconnect IP routers)
Mario Baldiwww.baldi.info
WAN_Technologies - 2 Copyright: see page 2
Copyright NoticeThis set of transparencies, hereinafter referred to as slides, is protected bycopyright laws and provisions of International Treaties. The title andcopyright regarding the slides (including, but not limited to, each and everyimage, photography, animation, video, audio, music and text) are property ofthe authors specified on page 1.The slides may be reproduced and used freely by research institutes,schools and Universities for non-profit, institutional purposes. In suchcases, no authorization is requested.Any total or partial use or reproduction (including, but not limited to,reproduction on magnetic media, computer networks, and printedreproduction) is forbidden, unless explicitly authorized by the authors bymeans of written license.Information included in these slides is deemed as accurate at the date ofpublication. Such information is supplied for merely educational purposesand may not be used in designing systems, products, networks, etc. In anycase, these slides are subject to changes without any previous notice. Theauthors do not assume any responsibility for the contents of these slides(including, but not limited to, accuracy, completeness, enforceability,updated-ness of information hereinafter provided).In any case, accordance with information hereinafter included must not bedeclared.In any case, this copyright notice must never be removed and must bereported even in partial uses.
WAN_Technologies - 3 Copyright: see page 2
The Context
Wide Area
IP host
IP router
IP network
WAN_Technologies - 4 Copyright: see page 2
Why Not Just Cables? Expensive! Time consuming
To lay To modify
WAN_Technologies - 5 Copyright: see page 2
Use a Network Cables are laid once Interconnectivity can be configured Resources (and their costs) shared
Interconnecting a new site implies just laying a “short” cable
New “virtual” interconnectionscan be easily and quickly created
WAN_Technologies - 6 Copyright: see page 2
And before building new ones Reuse existing technologies Specifically, existing networksThey are “Dead”: there is no new development Old: designed tens of years ago with
various purposes in mind Not for interconnecting IP routers
With one exception (frame relay) … but huge investments
WAN_Technologies - 7 Copyright: see page 2
Commonly Deployed Technologies Circuit switching
ISDN PDH SONET/SDH
Frame Relay ATM
Dead and old, but still heavily used→ relevant!
[also optical networks, which are a (relatively)new technology]
WAN_Technologies - 8 Copyright: see page 2
Circuit Switching Technologies
WAN_Technologies - 9 Copyright: see page 2
TDM: Time Division Multiplexing
Switch Switch
BANDWIDTH
WAN_Technologies - 10 Copyright: see page 2
Interconnections based on TDM TDM (Time Division Multiplexer)
divide the total bandwidth in sub-bands Each network user (e.g., router) can “see”
only its assigned sub-band as asynchronous channel with fixed bit rate
Routers can use a channel as the equivalentof a physical link
In reality at any given time the link carriestraffic of only one user
WAN_Technologies - 11 Copyright: see page 2
TDM: Time Division MultiplexingTake turns
at predefined, recurring time instants → time rules
Switch Switch
BANDWIDTH
WAN_Technologies - 12 Copyright: see page 2
Good service without flexibility (by design) Deterministic performance
Delay Jitter Bandwidth
Fixed rate Bandwidth not actually used by a user (in a
certain interval of time) cannot be used byother services and it is wasted Higher costs Particularly for bursty traffic
E.g., data traffic
Designed for voice traffic
WAN_Technologies - 13 Copyright: see page 2
Standard Channel Hierarchies Standardized channel speeds Standardized transmission speeds
And corresponding equipment Transmitters Receivers Cables
Copper Fibers
How to combine multiple low speedchannels into a high speed signaltransmitted on a linkMultiplexing and demultiplexing
WAN_Technologies - 14 Copyright: see page 2
PDH: Plesiochronous Digital Hierarchy Looser synchronization requirements
Limited transmission speeds High overhead
USA
T1 - DS1 1.544 Mbps
T3 - DS3 44.736 Mbps
Europe
E1 2.048 Mbps
E3 34.368 Mbps
E4 139.26 Mbps
32 x 64 kb/s24 x 64 kb/s
2816
4
WAN_Technologies - 15 Copyright: see page 2
Why a hierarchy? Hierarchy: how to combine multiple lower
rate frames into higher rate frame Higher capacity links in the backbone, lower
capacity at the accessGrooming and degrooming
WAN_Technologies - 16 Copyright: see page 2
SDH: Synchronous Digital HierarchySONET: Syncronous Optical Network
USA: SONET Europe: SDH
OC-3c / STS-3c 155.52 Mbps
STM-1155.52 Mbps
STM-4622.08 Mbps
OC-12c / STS-12c 622.08 Mbps
STM-122.4 Gbps
OC-48c / STS-48c 2.4 Gbps
OC-1c / STS-1c 51.84 Mbps
Higher com
plexity → costs
Mor
e st
ringe
nt s
ynch
roni
zatio
n
Higher transmission speeds Lower overhead
WAN_Technologies - 17 Copyright: see page 2
InteroperabilityPDH
hierarchies
USA
T1 - DS1 1.544 Mbps
T3 - DS3 44.736 Mbps
SDH hierarchies
USA: SONET Europe: SDH
OC-3c / STS-3c 155.52 Mbps
STM-1155.52 Mbps
STM-4622.08 Mbps
OC-12c / STS-12c 622.08 Mbps
STM-122.4 Gbps
OC-48c / STS-48c 2.4 Gbps
OC-1c / STS-1c 51.84 Mbps
Europe
E1 2.048 Mbps
E3 34.368 Mbps
E4 139.26 Mbps
WAN_Technologies - 18 Copyright: see page 2
Physical architecture Section: fiber optic between repeaters Line: sequence of sections between devices
oeprating at line level Path: end-to-end connection
T
SON
ET/S
DH
M
UXT
TA
dd/D
rop
MU
X
SON
ET/S
DH
M
UX
T
T
T
Section Section Section SectionLine Line
Path
Repeater Repeater
WAN_Technologies - 19 Copyright: see page 2
Protocol architecture Multiple layers
Complex protocol architecture
Monitoring functionalites Fast fault recovery
50 ms Ring topology
Photonic Layer
Section Layer
Line Layer
Path Layer
Frame
Photonic Layer
Section Layer
Photonic Layer
Section Layer
Line Layer
Photonic Layer
Section Layer
Line Layer
Path Layer
Higher Layer Higher Layer
Light
STS-N / STM-N Block
Envelope
Terminal TerminalRepeater Multiplexer
WAN_Technologies - 20 Copyright: see page 2
Frame formatSTS-1: 810 bytes transmitted in 125 s 51.84 Mbps
A1 A2 C1 J1
B1
D1
H1
B2
D4
D7
D10
Z1
D2
H2
K1
D5
D8
D11
Z2
F1
D3
H3
K2
D6
D9
D12
E2
B3
C2
G1
E1
F2
H4
Z3
Z4
Z5
Payload Payload
90 octets
9 oc
tets
s
sSection Overhead Line Overhead Path Overhead
Synchronous Payload Environment (SPE) 87 octets3 octets
WAN_Technologies - 21 Copyright: see page 2
Frames In packet switching
Frame contains bytes of a single communication Destination (source) identified in the header Frames are transmitted asynchronously
Whenever there is data to transmit Whenever a link is free
Statistical multiplexing In circuit switching
Frame contains bytes of multiple communications Destination (source) identified by the position Frames are transmitted synchronously
Back-to-back Independently of whether there is data to transmit
WAN_Technologies - 22 Copyright: see page 2
What do we do with them? Same duration (125 µs) at any bit rate
1 byte carries one 64kb/s channel More bytes per frame at higher rates Hierarchy: how to combine multiple lower
rate frames into higher rate frame Higher capacity links in the backbone, lower
capacity at the accessGrooming and degrooming
WAN_Technologies - 23 Copyright: see page 2
How do we connect routers? One channel between two routers
All bytes in a frame A fraction of a channel
Multiple bytes in a frame
WAN_Technologies - 24 Copyright: see page 2
But this is not the way it was meant to be used
Voice
Integrated services
WAN_Technologies - 25 Copyright: see page 2
ISDN -Integrated Service Digital Network
TELEPHONE
COMPUTER
FACSIMILEGROUP 4
VIDEOTELEPHONE
MULTISERVICETERMINAL
TERMINAL/TELEX
ISDN
So what?Now it is normal, but back then it was a big step forward
WAN_Technologies - 26 Copyright: see page 2
ISDN Access Interface
ISDNExchange
(Multiplexer)NT1
ISDN phone
PC with ISDN
Customer Premises Operator
Bus S
Fax G.4
Videoconference
WAN_Technologies - 27 Copyright: see page 2
ISDN Access Interface Data + voice The user terminal becomes digital 2B + D or base access
2 data channels at 64 kbps 1 signaling channel at 16 kbps total 144 kbps up to user's premises
30B + D or primary access 30 data channels at 64 kbps 1 signaling channel at 64 kbps total 2 Mbps up to user's premises
WAN_Technologies - 28 Copyright: see page 2
Packet Switching Technologies
WAN_Technologies - 29 Copyright: see page 2
Packet-based multiplexing/switching If a source has no traffic, bandwidth is
not wastedStatistical multiplexing
The same network infrastructure canstatistically accommodate morecommunicationsCost of communicating is lowerService is not deterministic
WAN_Technologies - 30 Copyright: see page 2
Statistical Multiplexing
Switch Switch
BANDWIDTH
WAN_Technologies - 31 Copyright: see page 2
Statistical MultiplexingTake turns
opportunistically, i.e., as soon as link isavailable
Switch Switch
BANDWIDTH
WAN_Technologies - 32 Copyright: see page 2
Statistical MultiplexingIf one is using less, others can use more
Switch Switch
BANDWIDTH
WAN_Technologies - 33 Copyright: see page 2
Building packet switching on top of circuit switching
Use circuits through a circuit network to interconnect packet/frame
switches/routers
PDH SDH
Packet switching Cell switching
X.25 Frame Relay ATM
WAN_Technologies - 34 Copyright: see page 2
Frame Relay
WAN_Technologies - 35 Copyright: see page 2
Frame Relay Network Architecture
DTE
DTEDTE
DTE
DCE
DCE
DCE
DCE
Frame RelayNetwork
VirtualCircuits
Data Communication Equipment
Data Terminal Equipment
WAN_Technologies - 36 Copyright: see page 2
Frame Relay standard
Standard for DCE-DTE interfacesMultiple logical connections through a single
access link Similarly to X.25
Layer 2 only Switches do not need to process 2 headers (layer
2 and layer 3) like in the previous X.25 X.25 does have a layer 3
WAN_Technologies - 37 Copyright: see page 2
Core-Edge Approach Error correction: re-transmission only at the
network edge, not in the intermediate nodes(core) X.25 corrects errors at each hop
Requires reliable links Takes advantage of fast links Small latency:
2 ms per frame relay node from 5 to 20 ms per X.25 node
WAN_Technologies - 38 Copyright: see page 2
Frame Relay applications
Interconnection of Intermediate Systems(router, bridge, gateway) through WANs All commercial devices offer FR interfaces Physical layer is common (PDH) Data-link layer is implemented in software
It is possible to specify the bandwidthrequired by/provided to the customer
Variable transit times Problematic with voice/video transmission
WAN_Technologies - 39 Copyright: see page 2
CIR: Committed Information Rate Bc: committed burst size
Maximum burstiness Tc=Bc/CIR
Interval of time where CIR is applied It is possible to transmit up to Bc bit at wire speed
of the access link in each time interval Tc
Wire speed
CIR
Tc
Bc
Guaranteedservice
Non guaranteedservice
WAN_Technologies - 40 Copyright: see page 2
Asynchronous Transfer Mode (ATM)
WAN_Technologies - 41 Copyright: see page 2
Relationships among differenttechnologies
analog telephony leased analog
digital telephony leased digital
Switching
+
Frame Relay
+X.25
TDMISDN
B-ISDN ATM
SMDS
DQDB
Digital conversion
voice + data
wideband
frame
core-edge
cells
packet
core-edge
cells
cells
WAN_Technologies - 42 Copyright: see page 2
Distinguishing Factors
Protocol Architecture
Core & EdgeCells
System design choices
Asynchronous interconnectionservces
ATM
Enabling technlogies
Optical fibersVLSI (CMOS)
WAN_Technologies - 43 Copyright: see page 2
General features Switching of small, fixed length data units:
cells 53 bytes
Fast links (with low bit error rate) 150 Mb/s
Low latencyGood for data, voice and video
For deployment in both LAN and WAN Selected for implementing the B-ISDN
WAN_Technologies - 44 Copyright: see page 2
Sophisticated signaling:Multiparty or point-to-point connections
Sophisticated mechanisms for flow control Sliding window is not efficient on long, fat pipes
Dynamic bandwidth allocation Bandwidth management
Fine granularity in bandwidth allocation Support for “bursty” traffic Adaptability for applications that are
sensible to time or data loss
General features
Anything else?!?!
WAN_Technologies - 45 Copyright: see page 2
Virtual channels
4 Mbps (3 party conference)50 Mbps (Image transfer)
ATM net
ATM Switch
WAN_Technologies - 46 Copyright: see page 2
Cell switching
Cell = 53 bytes
485
ATMSwitch
WAN_Technologies - 47 Copyright: see page 2
Statistical multiplexing
A C B C A
A A
C C
B MultiplexATM
WAN_Technologies - 48 Copyright: see page 2
ATM technology
Switch Switch
BANDWIDTH
ATMSwitch
ATMSwitch
WAN_Technologies - 49 Copyright: see page 2
1
2
3
4
5
6
53
.
.
Hea
der
Payl
oad
GFC VPIVPI VCI
VCIVCI PT CLP
HEC
User Data
(48 octets)
7 6 5 4 3 2 1 0
UNI Cell
ATM Cell
WAN_Technologies - 50 Copyright: see page 2
Header Field Names GFC: General Flow Control VPI: Virtual Path Identifier VCI: Virtual Channel Identifier PT: Payload Type CLP: Congestion Loss Priority HEC: Header Error Control
WAN_Technologies - 51 Copyright: see page 2
A couple more details Cells are transmitted back-to-back,
poossibly inserting empty ones Each cell carries an indentifier of the circuit
VCI/VPI: Virtual Channel/Path Identifier Error correction:
Core-edge approach as in frame relay Flow control more sophisticated than
sliding windows, to take into account: Different types of traffic The“memory” of the channel
WAN_Technologies - 52 Copyright: see page 2
Cell Routing
VCI/VPI changes each time an ATM switch is traversed
C
D
B A 2
n
2
mi
1 1
Port Label
Look-upport #2
i D
1 C
WAN_Technologies - 53 Copyright: see page 2
Core-Edge Principle Nodes execute only basic functionalities
(switching and multiplexing) ATM Layer (L1-L2 OSI stack)
Additional functionalities for the differentservices are implemented at the edge
PHY PHY PHY
ATM ATM (core)AAL
PHYATM
AALError control (only for some services and upon request)
Userterminal
ATMswitch
Upper layer
protocols
Upper layer
protocols
Userterminal
WAN_Technologies - 54 Copyright: see page 2
B-ISDN/ATM Reference Model
Control Plane User Plane
Management Plane
Laye
r Man
agem
ent
PlM
t
Physical Layer
ATM Layer
ATM Adaption Layer (AAL)
Higher Layer ProtocolsHigher Layer Protocols
WAN_Technologies - 55 Copyright: see page 2
AAL 5 Segmentation and Reassembly
USER BITS
0 to 65,000 Bytes
L3-PDU
REASSEMBLYSEGMENTATION
PAD Ctrl/Length CRC
0-47 4 4Bytes
WAN_Technologies - 56 Copyright: see page 2
The Vision
PrivateNNI
Bridge /Router
PublicNNI
PublicUNI
Private ATM Network
Public ATM Network
PublicUNI
Bridge /Router
PrivateUNI
PrivateUNI
PublicUNI
PrivateUNI
PublicUNI
PublicUNI
PrivateUNI
WAN_Technologies - 57 Copyright: see page 2
Reality
ATM
IP host
IP router
IP network
WAN_Technologies - 58 Copyright: see page 2
A problematic solution How can R know that Q is
the next hop towards D? How can R know the ATM
address of Q?
ATM
D
R
Q
WAN_Technologies - 59 Copyright: see page 2
B
ATM SWITCH
Ethernet
Access device
workstation
PHYATMAAL
HigherLayerLLC
LAN em
PHY
MAC
HigherLayerLLC
PHY PHYATMAAL MAC
LAN emBridging
PHYATMAAL
Signalling
ATMWorkstation
Access devices operate as bridges
ATM LAN Emulation
WAN_Technologies - 60 Copyright: see page 2
LES
BUS
SWITCH ATM Access device
ATMWorkstation
Access device
Server
ATM LAN Emulation
WAN_Technologies - 61 Copyright: see page 2
IP over ATM: Classical model Direct communication within a subnet Use router across subnets Emulate ARP for address resolution within
the subnet Find ATM address of destination or router
It does not use ATM potential (performance)IP Subnet BIP Subnet A
ARP Server B
H3
ARP Server AH1
H2
R
WAN_Technologies - 62 Copyright: see page 2
Advanced Solutions:Next Hop Resolution Protocol Source finds the ATM address of the best
hop to a destination Destination itself if it is on the ATM network A router connected out of the ATM network if the
destination is not on the ATM network Complex
Logical Address Group BLogical Address Group ANHRP Server B
H3
NHRP Server AH1
H2
WAN_Technologies - 63 Copyright: see page 2
Only one good way outRouters and ATM switches “speak the same language”
It’s the MPLS solution! Same control plane
Routers and ATM/MPLSswitches exchange routinginformation
ATM
D
R
Q
Destinations are identified with IP addresses