Post on 17-Jan-2018
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transcript
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IEX8175 RF Electronics
Avo Otstelekommunikatsiooni õppetool,
TTÜ raadio- ja sidetehnika inst.avo.ots@ttu.ee
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Network Engineering• The process concerned with optimally selecting topology and
bandwidth in a layer network, based on – (pro-active) traffic demands expected between any two locations in the network
and – (re-active) the actual traffic demand
• It is an inter layer network process• NwE process in each layer network
– advertises the nodes and their ports within the layer network– monitors the layer network and determines if/when a new (topological) link
should be added or an existing link should be modified or released, based on the network provider's policy
– determines best set of connections between ports in the layer network– requests those connections to be set up by its server layer networks; i.e.
generates outgoing calls for client connections• It is implemented by the (distributed) Network Engineering
Controllers (NEC) within the layer network
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Shared & Dedicated B W
Dedicated Bandwidth Circuits Shared Bandwidth Circuits
Mbp
s
Time
Dedicated Transport & Transfer Rate In Network
Actual Data Rate Usage vs. Time
Wasted Bandwidth
Mbp
s
Time
Multiple Data Customers in Shared Trunk Bandwidth
Sum of Aggregate BandwidthMuch Less Wasted Bandwidth
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Internet protocol• Provides best effort, connectionless packet delivery
– motivated by need to keep routers simple and by adaptibility to failure of network elements
– packets may be lost, out of order, or even duplicated– higher layer protocols must deal with these, if necessary
• RFCs 791, 950, 919, 922, and 2474.• Internet STD also includes:
– Internet Control Message Protocol (ICMP), RFC 792– Internet Group Management Protocol (IGMP), RFC 1112
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IP address
RNetwork
128.135.0.0
Network
128.140.0.0
H H
HH H
R = routerH = host
Interface Address is
128.135.10.2
Interface Address is
128.140.5.35
128.135.10.20 128.135.10.21
128.135.40.1
128.140.5.36
128.140.5.40
Address with host ID=all 0s refers to the network
Address with host ID=all 1s refers to a broadcast packet
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1
2
3
4
5
6
Node (switch or router)
Routing in Packet Networks
• Three possible (loopfree) routes from 1 to 6:– 1-3-6, 1-4-5-6, 1-2-5-6
• Which is “best”?– Min delay? Min hop? Max bandwidth? Min cost?
Max reliability?
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Packet Switch: Meet
1
2
N
1
2
N
• • •
• • •
• Inputs contain multiplexed flows from access muxs & other packet switches
• Flows demultiplexed at input, routed and/or forwarded to output ports
• Packets buffered, prioritized, and multiplexed on output lines
• • •
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Controller
1
2
3
N
Line card
Line card
Line card
Line card
Inte
rcon
nect
ion
fabr
ic
Line card
Line card
Line card
Line card
1
2
3
N
Input ports Output ports
Data path Control path (a)
…………Generic Packet Switch
“Unfolded” View of Switch• Ingress Line Cards
– Header processing– Demultiplexing– Routing in large switches
• Controller– Routing in small switches– Signalling & resource
allocation• Interconnection Fabric
– Transfer packets between line cards
• Egress Line Cards– Scheduling & priority– Multiplexing
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1
2
3
N
1
2
3
N
…
SharedMemory
QueueControl
Ingress Processing
ConnectionControl
…
Shared Memory Packet Switch
Output Buffering
Small switches can be built by reading/writing into shared memory
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1
2
3
N
1 2 3 N
Inputs
Outputs
(a) Input buffering
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3…
…
1
2
3
N
1 2 3 N
Inputs
Outputs
(b) Output buffering
…
…
Crossbar Switches
Large switches built from crossbar & multistage space switches Requires centralized controller/scheduler (who sends to whom
when) Can buffer at input, output, or both (performance vs complexity)
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UDP Multiplexing
• All UDP datagrams arriving to IP address B and destination port number n are delivered to the same process
...
UDP
IP
1 2 n ...
UDP
IP
1 2 n ...
UDP
IP
1 2 n
A B C
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Congestion Control• Buffers at intermediate routers between source and
destination may overflow
Router
R bpsPacket flows from
many sources
• Congestion occurs when total arrival rate from all packet flows exceeds R over a sustained period of time
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Phases of Congestion Behavior
1. Light traffic – Arrival Rate << R– Low delay– Can accommodate more
2. Knee (congestion onset)– Arrival rate approaches R – Delay increases rapidly– Throughput begins to saturate
3. Congestion collapse– Arrival rate > R– Large delays, packet loss– Useful application throughput
drops
Thro
ughp
ut (b
ps)
Del
ay (s
ec)
R
R
Arrival Rate
Arrival Rate
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Compute
Communicate Communicate
StoreCommunicate
Communications and computing
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Compute
Sense
Environment
ActCommunicate Communicate
StoreCommunicate
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Computation
Devices
Dynamical Systems
DevicesCommunication Communication
Control
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From• Software to/from human• Human in the loop
To• Software to Software• Full automation• Integrated control,
comms, computing• Closer to physical
substrateCompute
Communicate Communicate
StoreCommunicate
Computation
Devices
Dynamical Systems
Devices
Communication Communication
Control
• New capabilities & robustness• New vulnerabilities
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IPv4 >to>> IPv6• Expanded addressing capabilities• Header format simplification• Improved support for extensions and
options• Flow labelling capability• Authentication and privacy capabilities
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Basic Headers• IPv6 Header
• IPv4 Header
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Basic Headers• Fields
– Version (4 bits) – only field to keep same position and name
– Class (8 bits) – new field– Flow Label (20 bits) – new field– Payload Length (16 bits) – length of data, slightly
different from total length– Next Header (8 bits) – type of the next header, new idea– Hop Limit (8 bits) – was time-to-live, renamed– Source address (128 bits)– Destination address (128 bits)
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Basic Headers
• Simplifications– Fixed length of all fields, not like old options field –
IHL, or header length irrelevant– Remove Header Checksum – rely on checksums at
other layers– No hop-by-hop fragmentation – fragment offset
irrelevant – MTU discovery– Add extension headers – next header type (sort of
a protocol type, or replacement for options)– Basic Principle: Routers along the way should do
minimal processing
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Extension Headers
• Extension Header Types– Routing Header– Fragmentation Header– Hop-by-Hop Options Header– Destinations Options Header– Authentication Header– Encrypted Security Payload Header
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Lõpulingidhttp://www.ietf.org/rfc/rfc0791.txt?number=791
http://www.ietf.org/rfc/rfc2474.txt?number=2474
http://www.apple.com/airportextreme/specs.html
http://tools.ietf.org/html/rfc1924
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Linkshttp://www.ietf.org/rfc/rfc0791.txt?number=791
http://www.ietf.org/rfc/rfc2474.txt?number=2474
http://www.apple.com/airportextreme/specs.html
http://tools.ietf.org/html/rfc1924