Transcript A6_Oct_07_08 - Raadio- ja sidetehnika instituut

IEX8175 RF Electronics
Avo Ots
telekommunikatsiooni õppetool,
TTÜ raadio- ja sidetehnika inst.
[email protected]
1
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
2
Shared & Dedicated B W
Dedicated Bandwidth Circuits
Actual Data Rate
Usage vs. Time
Sum of Aggregate Bandwidth
Much Less Wasted Bandwidth
Mbps
Mbps
Dedicated Transport &
Transfer Rate In Network
Shared Bandwidth Circuits
Time
Time
Wasted Bandwidth
Multiple Data Customers in
Shared Trunk Bandwidth
3
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
4
IP address
128.140.5.40
128.135.40.1
Interface
Address is
128.135.10.2
H
Network
Interface
Address is
128.140.5.35
R
128.135.0.0
H
128.135.10.20
H
Network
128.140.0.0
H
128.135.10.21
Address with host ID=all 0s refers to the network
Address with host ID=all 1s refers to a broadcast packet
H
128.140.5.36
R = router
H = host
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Routing in Packet Networks
1
3
6
4
2
5
Node
(switch or router)
• 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?
6
1
1
2
2



N
•••
•••
•••
Packet Switch: Meet



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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Generic Packet Switch
“Unfolded” View of Switch
• Ingress Line Cards
– Header processing
– Demultiplexing
– Routing in large switches
Controller
•
N
Line card
1
Line card
2
Line card
3
Line card
Input ports
Data path
Control path
…
Line card
Line card
…
…
3
Line card
Interconnection
fabric
2
Line card
…
1
N
Controller
– Routing in small switches
– Signalling & resource
allocation
• Interconnection Fabric
– Transfer packets between line
cards
• Egress Line Cards
– Scheduling & priority
– Multiplexing
Output ports
(a)
8
Shared Memory Packet Switch
Ingress
Processing
Connection
Control
Output
Buffering
1
1
Queue
Control
2
2
3
N
Shared
Memory
…
…
3
N
Small switches can be built by reading/writing into shared memory
9
Crossbar Switches
(b) Output buffering
(a) Input buffering
Inputs
Inputs
1
3
1
2
83
2
3
…
…
3
N
N
…
1



2 3
Outputs
…
N
1
2 3
Outputs
N
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
1
2
A
...
n
1
2
...
n
1
2
...
UDP
UDP
UDP
IP
IP
IP
B
n
C
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Congestion Control
• Buffers at intermediate routers between source and
destination may overflow
Router
Packet
flows from
many
sources
R bps
• Congestion occurs when total arrival rate from all packet flows
exceeds R over a sustained period of time
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Throughput (bps)
Phases of Congestion Behavior
R
1. Light traffic
–
–
–
Arrival Rate << R
Low delay
Can accommodate more
2. Knee (congestion onset)
Delay (sec)
Arrival
Rate
–
–
–
Arrival rate approaches R
Delay increases rapidly
Throughput begins to saturate
3. Congestion collapse
R
Arrival
Rate
–
–
–
Arrival rate > R
Large delays, packet loss
Useful application throughput
drops
13
Compute
Communications and computing
14
Compute
Act
Sense
Environment
15
Computation
Devices
Devices
Control
Dynamical Systems
16
From
• Software to/from human
• Human in the loop
Compute
To
• Software to Software
• Full automation
• Integrated control,
comms, computing
• Closer to physical
substrate
Computation
• New capabilities & robustness
• New vulnerabilities
Devices
Devices
Control
Dynamical Systems
17
IPv4 >to>> IPv6
• Expanded addressing capabilities
• Header format simplification
• Improved support for extensions and
options
• Flow labelling capability
• Authentication and privacy capabilities
18
Basic Headers
• IPv6 Header
• IPv4 Header
19
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
21
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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Lõpulingid
http://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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Links
http://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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