Networks - ICSY

Wahlpflichtfach
Multimediasysteme
Kapitel 5: Netzwerke
Simon Schwantzer
schwantzer@icsy.de
University of Kaiserslautern
Integrated Communication Systems
http://www.icsy.de
Wahlpflichfach
Multimediasysteme
TU Kaiserslautern
Oktober 2009
9. Oktober 2009
Simon Schwantzer
ICSY Lab, University of Kaiserslautern, Germany – http://www.icsy.de
1

• Switching
Overview
• ISO/OSI Reference Model
• QoS Mechanisms
• Networks
– Ethernet
– ISDN
– TCP/IP
– RTP
October 9, 2009
Simon Schwantzer
ICSY Lab, University of Kaiserslautern, Germany – http://www.icsy.de
2

Switching
ISO / OSI Reference
Model
Network QoS Mechanisms
ISO / OSI Reference
Model
SWITCHING
October 9, 2009 Simon Schwantzer ICSY Lab, University of Kaiserslautern, Germany – http://www.icsy.de 3

Switching
ISO / OSI Reference
Model
• Provide a "physical" link:
connection A, B established
connection C, B blocked
Circuit Switching
• Advantages:
– guaranteed bandwidth and delay
– worldwide available
• Disadvantages:
– bandwidth not scalable
– bad efficiency (bandwidth usage)
October 9, 2009
Simon Schwantzer
ICSY Lab, University of Kaiserslautern, Germany – http://www.icsy.de
4

Switching
Packet Switching
• Handle independent packages:
A+C sending packages of different size to B
Packet may get lost because of congestion
ISO / OSI Reference
Model
• Advantages:
– high efficiency (bandwidth usage)
– bandwidth is scalable
• Disadvantages:
– no guaranteed delay (bandwidth)
October 9, 2009
Simon Schwantzer
ICSY Lab, University of Kaiserslautern, Germany – http://www.icsy.de
5

Switching
Cell Switching
ISO / OSI Reference
Model
• Promises to combine the best of circuit switching and packet switching.
All data is segmented into small cells of fixed size.
Cells are multiplexed as needed.
• Advantages:
– high efficiency (bandwidth usage)
– bandwidth is scalable
– guaranteed bandwidth and delay
• Disadvantages:
– rare availability
October 9, 2009
Simon Schwantzer
ICSY Lab, University of Kaiserslautern, Germany – http://www.icsy.de
6

Switching
ISO / OSI Reference
Model
QoS Mechanisms
Networks
Switching
QoS Mechanisms
ISO / OSI REFERENCE
MODEL
October 9, 2009 Simon Schwantzer ICSY Lab, University of Kaiserslautern, Germany – http://www.icsy.de 7

Switching
ISO / OSI Reference
Model
QoS Mechanisms
ISO / OSI Reference Model
October 9, 2009
Simon Schwantzer
ICSY Lab, University of Kaiserslautern, Germany – http://www.icsy.de
8

Switching
ISO / OSI Reference
Model
ISO / OSI (Layer 1-3)
QoS Mechanisms
1
2
3
The physical layer defines electric signaling on the transmission channel;
how bits are converted into electric current, light pulses or any other
physical form. A serial line is an example of the physical layer. A network
device for this layer is called a repeater.
The data link layer defines how the network layer frames are
transmitted as bits. An example of a data link layer protocol is Ethernet.
A network device for this layer is called a bridge.
The network layer defines how information from the transport layer is
sent over networks and how different hosts are addressed. An example
of a network layer protocol is the Internet Protocol. A network device
for this layer is called a router.
Technology
(usually hardware)
Protocols
(usually software)
October 9, 2009
Simon Schwantzer
ICSY Lab, University of Kaiserslautern, Germany – http://www.icsy.de
9

Switching
ISO / OSI Reference
Model
ISO / OSI (Layer 4-7)
QoS Mechanisms
4
5
The transport layer takes care of data transfer, ensuring the integrity of data if
desired by the upper layers. TCP and UDP are operating at this layer.
The session layer establishes and terminates connections and arranges sessions
to logical parts. TCP and RPC provide some functions at this layer.
6
The presentation layer takes care of data type conversion. Protocols residing at
this layer are used to provide interoperability between heterogeneous computer
systems.
7
The application layer defines the protocols to be used between the application
programs. Examples of protocols at this layer are protocols for WWW (http)
electronic mail (e.g. SMTP) and file transfer (e.g. FTP).
October 9, 2009
Simon Schwantzer
ICSY Lab, University of Kaiserslautern, Germany – http://www.icsy.de
10

ISO / OSI Reference
Model
QoS Mechanisms
Networks
Switching
ISO / OSI Reference
Model
Networks
QOS MECHANISMS
October 9, 2009 Simon Schwantzer ICSY Lab, University of Kaiserslautern, Germany – http://www.icsy.de 11

ISO / OSI Reference
Model
QoS Mechanisms
Networks
Network QoS Mechanisms
• Network Device QoS Mechanisms
– Classification: type of incoming data
– Shaping & Policy: keep / monitor traffic characteristic
– Queueing: determine output schedule
• Network Mechanisms related to QoS
– Congestion control / avoidance
– Routing
– SLA / QoS Signaling
– Media transport & usage
October 9, 2009
Simon Schwantzer
ICSY Lab, University of Kaiserslautern, Germany – http://www.icsy.de
12

ISO / OSI Reference
Model
QoS Mechanisms
Networks
Traffic Classification
• In order to provide QoS in a packet switched network, a network
device has to classify each incoming packet
– distinguish flows and aggregations (terms: flow-based vs. class-based)
– Classification criteria
• physical port of incoming data
• frame/packet addresses (MAC, IP-Address, TCP/UDP Port-Number)
• protocol interpretation
– Obtaining classification info
• static: by (manual) configuration
• dynamic: by signaling
October 9, 2009
Simon Schwantzer
ICSY Lab, University of Kaiserslautern, Germany – http://www.icsy.de
13

ISO / OSI Reference
Model
QoS Mechanisms
Networks
Shaping vs. Policing
• policing: monitor the traffic characteristic, increases loss rate!
• shaping: keep a traffic characteristic, increases delay!
October 9, 2009
Simon Schwantzer
ICSY Lab, University of Kaiserslautern, Germany – http://www.icsy.de
14

ISO / OSI Reference
Model
QoS Mechanisms
Networks
• FIFO
Packet Scheduling / Queueing
– best effort service only
– prior admission control
and policing may
improve fairness
October 9, 2009 Simon Schwantzer ICSY Lab, University of Kaiserslautern, Germany – http://www.icsy.de 15

ISO / OSI Reference
Model
QoS Mechanisms
Networks
Packet Scheduling / Queueing
• (Strict) Priority
Queueing
– different services
according to bandwidth
and delay
– unfair, because
starvation of low priority
flows possible
October 9, 2009 Simon Schwantzer ICSY Lab, University of Kaiserslautern, Germany – http://www.icsy.de 16

ISO / OSI Reference
Model
QoS Mechanisms
Networks
Packet Scheduling / Queueing
• Weighted Fair Queueing
(WFQ)
– each queue receives a
portion of the available
bandwidth resources
– round robin according to
weight of queues,
guarantees fairness
October 9, 2009 Simon Schwantzer ICSY Lab, University of Kaiserslautern, Germany – http://www.icsy.de 17

ISO / OSI Reference
Model
QoS Mechanisms
Networks
Isochronism
An end-to-end network connection is called isochronous if
the bit rate and the jitter over the connection life time is
guaranteed and the jitter is small.
• Isochronism therefore simply defines the requirements of
continuous media streams.
• Remark:
– The property of media like audio and video, that must be
sampled and played in regular intervals is also called isochrony.
– Isochronism does not define quantitative values for jitter or
probabilities refereed to by guaranteed.
– If a jitter may be considered small depends on the application.
October 9, 2009
Simon Schwantzer
ICSY Lab, University of Kaiserslautern, Germany – http://www.icsy.de
18

ISO / OSI Reference
Model
QoS Mechanisms
Networks
Multicasting
• Multicasting is the capability to replicate data at certain internal
points. Replicated data is forwarded to endsystems which are part
of a multicast group.
– multicast avoids or minimizes the multiple transport of the same data
over the same network segments
– broadcast is a special case of multicast
– data duplication must be supported by forwarding engines in
switches
– multicast types
• one-to-many unidirectional
• one-to-many bi-directional
• many-to-many
Note: The multicast or broadcast capability on OSI layer 2 is usually a
prerequisite for the realization of multicast on layer 3.
October 9, 2009
Simon Schwantzer
ICSY Lab, University of Kaiserslautern, Germany – http://www.icsy.de
19

QoS Mechanisms
Networks
ISO / OSI Reference Model
QoS Mechanisms
NETWORKS
October 9, 2009
Simon Schwantzer
ICSY Lab, University of Kaiserslautern, Germany – http://www.icsy.de
20

QoS Mechanisms
Networks
Networks
• Different network characteristics lead to different usability for the
transport of multimedia data:
– QoS guarantees:
• bandwidth
• delay
• delay variation
– Isochronism
– Multicast capability
– Flexibility:
• bandwidth
• traffic types
• distance (LAN, WAN)
• physical media
– Efficiency/Utilization of physical media
– Costs
October 9, 2009
Simon Schwantzer
ICSY Lab, University of Kaiserslautern, Germany – http://www.icsy.de
21

QoS Mechanisms
Networks
Ethernet
• History:
– Xerox Corp.: R. Metcalfe (PHD at the M.I.T.) and D.
Boggs
– Standardized by IEEE 802.3
• there are vendor specific Ethernet variants, e.g. Ethernet V2
October 9, 2009
Simon Schwantzer
ICSY Lab, University of Kaiserslautern, Germany – http://www.icsy.de
22

QoS Mechanisms
Networks
Simon Schwantzer
Ethernet
• Characteristics:
– Original: Bus topology
– Bandwidth: 10 Mbit/s half-duplex
– Several physical media: coax cable, twisted-pair, fiber
– Access protocol CSMA/CD (Carrier Sense Multiple Access with
Collision Detection)
• Carrier sense: check if there is traffic on the net before sending
• Multiple access: each station "listens" simultaneously to the net and tries to
send
• Collision detection: if multiple stations are sending, data will be corrupted,
wait and try again
⇒ demands a minimum frame size!
– Evolution
• Using switches, leads to star topology ⇒ CSMA/CD no longer necessary ⇒
enables full-duplex
• Bandwidth: 100 Mbit/s, 1 Gbit/s, 10 Gbit/s
• Several extensions: auto negotiation, flow-control, burst modes, VLANtagging
(IEEE 802.3Q), priorities (IEEE 802.3p), link aggregation (IEEE 802.3ad)
October 9, 2009
ICSY Lab, University of Kaiserslautern, Germany – http://www.icsy.de
23

QoS Mechanisms
Networks
Ethernet: Frame
MAC = Medium Access Control LLC = Logical Link control
SNAP = Sub-network Access Protocol DSAP = Destination Service Access Point
SSAP = Source Service Access Point cntl = control
org code= organization code CRC = Cyclic Redundancy Check
October 9, 2009
Simon Schwantzer
ICSY Lab, University of Kaiserslautern, Germany – http://www.icsy.de
24

QoS Mechanisms
Networks
Ethernet: Usability for Multimedia Data
• QoS parameters:
– No end-to-end guarantees possible
– No priorities supported
• Isochronism:
– not available
• Multicast capability:
– Multicast group addressing supported
– Broadcast group addressing supported
• Flexibility:
– formerly fixed bandwidth of 10 Mbit/s, Ethernet derivatives up to 10 GBit/s
• Efficiency:
– with CSMA/CD: low throughput at high utilization because of collisions
– bad efficiency for small frames because padding is required to ensure the necessary
minimum frame size
• Costs:
– Low cost technology enables dedicate connected systems
– 10/100 Mbit/s guaranteed bandwidth per host in small LANs
October 9, 2009
Simon Schwantzer
ICSY Lab, University of Kaiserslautern, Germany – http://www.icsy.de
25

QoS Mechanisms
Networks
Integrated Services Digital Network
• Standardization:
– ITU recommendations (former CCITT)
– ETSI and ANSI standards
• Characteristics:
– Public, digital, end-to-end network
– Implements digital bit pipe
• Based on 64 Kbit/s data rate
• Multiple full duplex data channels
– Support for multiple media and services within one network:
• Voice, low quality video, image data, text data,
• supplementary services
– Common signaling channel with common set of signaling protocols
• Technology:
– Circuit switching
– Fixed bandwidth channel assignment
October 9, 2009
Simon Schwantzer
ICSY Lab, University of Kaiserslautern, Germany – http://www.icsy.de
26

QoS Mechanisms
Networks
ISDN: Usability for Multimedia Data
• QoS parameters:
– guaranteed bandwidth
– low delay and low delay variation (not guaranteed, e.g. Satellite links with significantly higher
delay)
• Isochronism:
– guaranteed by design principles
• Multicast capability:
– no multicast capabilities
• Flexibility:
– fixed bandwidth
– although ISDN is used for end-to-end communications, it is mainly a WAN technology
– independent of physical media
• Efficiency:
– low bandwidth utilization
• Costs:
– expensive bandwidth (Telecom ports include WAN connectivity)
October 9, 2009
Simon Schwantzer
ICSY Lab, University of Kaiserslautern, Germany – http://www.icsy.de
27

QoS Mechanisms
Networks
Protocols (Layer 3-7)
A protocol defines the rules and formats for the exchange of data.
• Examples for typical protocol tasks:
– Layer 3: End-to-end connectivity (host-to-host)
– Layer 4: Process-to-Process connectivity
– Reliable communication
• Error detection
• Error recovery, e.g. forward error correction or retransmission
– Resource management
• avoid congestion, by flow control
– within the network
– within end systems
• Priorization
• Resource reservation
– Support for specialized media types
• Content description
• Timing / Synchronization Information
– And more ...
October 9, 2009
Simon Schwantzer
ICSY Lab, University of Kaiserslautern, Germany – http://www.icsy.de
28

QoS Mechanisms
Networks
TCP/IP Suite
October 9, 2009
Simon Schwantzer
ICSY Lab, University of Kaiserslautern, Germany – http://www.icsy.de
29

QoS Mechanisms
Networks
Simon Schwantzer
IP Protocol
• Development of IP
– DARPA: Defense Advanced Research Projects Agency
• The research aim was to build a network that is tolerant to extensive damage, e.g. by a
nuclear strike
• 1973/1974 development of TCP/IP, a replacement of NCP (Network Control Protocol)
• Since 1975 the ARPANET was controlled by the DoD
• In the early 80'ies the military part was extracted from the ARPANET
• Since 1983 exclusive use of TCP/IP, defining the term Internet
– IP is specified in RFC 791
– "This document is based on six earlier editions of the ARPA Internet Protocol
Specification ..."
• IP characteristics
– Provides end-to-end communication
– Connection less, i.e. state less protocol
– Provides unreliable transfer of packets
– Packets may be reordered during transmission
– Error messages are handled by the separate protocol ICMP (Internet Control
Message Protocol)
October 9, 2009
ICSY Lab, University of Kaiserslautern, Germany – http://www.icsy.de
30

QoS Mechanisms
Networks
IP Header
Version: version of IP header
IHL:
TOS:
IP header length in 32 bit words (5+ no. of
options)
Type Of Service
precedence ~ priority; D,T,R if set optimize
for Delay, Throughput, Reliability
Flags, Frag.
Offset:
TTL:
Protocol:
used for fragmentation
Time To Live, decremented by each
machine to pass the packet
layer 4 protocol, e.g. 1=ICMP, 6=TCP,
17=UDP
Length: length in bytes including the IP header Checksum: checksum for the IP header
ID: serial number Options: security, record route, timestamp,
source routes
October 9, 2009
Simon Schwantzer
ICSY Lab, University of Kaiserslautern, Germany – http://www.icsy.de
31

QoS Mechanisms
Networks
• Transport protocols (Layer 4)
– Provides process to process
connectivity
– Uses port number to identify
processes. An IP address and a
port number is a unique
identifier for a service.
• Characteristics
– Closely related to IP
– UDP offers a connectionless
and unreliable transport
service
• Nearly the same service as IP
• Data unit name: datagram
UDP / TCP
– TCP offers a connection
oriented and reliable
transport service
• Recognition of lost data
• Retransmission of lost data
• Reordering of data
• Delete duplicate data
• Flow control
– With respect to network
congestion
– With respect to buffer
overflow at the receiver
side
• User data is handled as a
stream of bytes
– User data is split into
segments
• Data unit name: segment
October 9, 2009 Simon Schwantzer ICSY Lab, University of Kaiserslautern, Germany – http://www.icsy.de 32

QoS Mechanisms
Networks
TCP Flow Control
• Avoid network congestion
If multiple identical ACKs indicate packet loss, then slow start +
congestion avoidance:
October 9, 2009
Simon Schwantzer
ICSY Lab, University of Kaiserslautern, Germany – http://www.icsy.de
33

QoS Mechanisms
Networks
TCP Flow Control
If timeout indicate packet loss, then slow start + restart slow start +
congestion avoidance:
October 9, 2009
Simon Schwantzer
ICSY Lab, University of Kaiserslautern, Germany – http://www.icsy.de
34

QoS Mechanisms
Networks
TCP Service Mechanisms
• Retransmission
– default: Go-back-n strategy, simple and robust mechanism but
resource consuming
– widely used: selective acknowledgement, retransmit lost package
only
– in general retransmission causes unpredictable delay
• Flow control
– Slow start and congestion avoidance realize considerate resource
usage
• enabling fair and cooperative bandwidth sharing
• may cause high jitter
• TCPs service mechanisms were designed for reliable data transfer
TCP is not suitable for real-time communications
October 9, 2009
Simon Schwantzer
ICSY Lab, University of Kaiserslautern, Germany – http://www.icsy.de
35

QoS Mechanisms
Networks
IPv6
• Development of IPv6
– 1993 the IETF called for the development of an IP next generation
IPng (RFC 1550)
– Improvements required
• Larger address space
• Reduce size of routing tables
• Simplification of the protocol, to allow routers to process packets faster
• Better security
• Pay more attention to Type of Service
• Aid multicasting
• Support roaming
• Easier extension of the protocol
• Coexistance with the old IPv4
– 1995 the IETF agreed to specification named IPv6 ( RFC1883 )
• Changes to other protocols of the TCP/IP suite are specified in RFC 1884-1887
October 9, 2009
Simon Schwantzer
ICSY Lab, University of Kaiserslautern, Germany – http://www.icsy.de
36

QoS Mechanisms
Networks
IPv6 Header
Version: version of IP header
Priority: 0-7 for non real time data, 8-15 for real-time data
Flow Label: may be used to identify a flow, RFC 1809 discusses how the flow label
could be used
Payload length: length of the datagram without the header
Next header: options are placed in separate extension header; next header identifies
an option or the protocol above IPv6
Hop limit: same as Time to Live of IPv4
Addresses: • there are 7*10 23 IPv6 addresses per square meter of the world
enabling well structured addresses Support of provider based
addresses
• and geographic based addresses
October 9, 2009
Simon Schwantzer
ICSY Lab, University of Kaiserslautern, Germany – http://www.icsy.de
37

QoS Mechanisms
Networks
QoS in Data Networks
IP Service Models
Traffic-Engineering
Concept
Network Technology
Best Effort DiffServ IntServ MPLS ATM
QoS
Guarantees
no aggregated flow based
flow based and
aggregated
flow based and
aggregated
QoS
Parameter
no
• long term
• static
• within a domain
• per flow
• dynamic
• end-to-end
Support for:
• DiffServ
• IntServ
• ATM
• per flow (channel) or
per path
• dynamic or static
• end-to-end or within a
domain
October 9, 2009
Simon Schwantzer
ICSY Lab, University of Kaiserslautern, Germany – http://www.icsy.de
38

QoS Mechanisms
Networks
RTP - Real-Time Transport Protocol
• Consists of two closely-linked parts:
– the real-time transport protocol (RTP), carries data with real-time properties
– the RTP control protocol (RTCP), monitors QoS and distributes this information to all
participants of a session
• RTP makes no reservations and does not guarantee any service
• RTP is a protocol framework, not a complete protocol
– a profile specification defines payload types and may extend RTP
– a payload specification defines payload formats and encoding types must be specified
– therefore RTP will typically be part of an application
• The purpose of RTP is to provide additional information for real-time media
streams
– payload type, may change dynamically
– sequence number, to determine the order (and loss) of the incoming data
– timestamp, to enable synchronized and constant output of the data
– contributor identifier, distinguish different contributors
– ...
October 9, 2009
Simon Schwantzer
ICSY Lab, University of Kaiserslautern, Germany – http://www.icsy.de
39

QoS Mechanisms
Networks
RTCP - RTP Control Protocol
• RTP enables receiver to monitor the QoS:
– Delay, jitter, PDU loss rate
• RTCP periodically transmits control packets between all
participants of an RTP session:
– the primary function is to provide feedback about the QoS
– carries transport-level identifiers for RTP sources, the canonical name
(the SSRC may change over the time; the canonical name is fixed, e.g.
a user name)
– the rate of sent RTCP packets depends on the number of participants
in order to make RTCP scalable
– optionally, further information about the participants could be
distributed to realize a simple session control
October 9, 2009
Simon Schwantzer
ICSY Lab, University of Kaiserslautern, Germany – http://www.icsy.de
40

Questions?
Contact: Simon Schwantzer, schwantzer@informatik.uni-kl.de, http://www.icsy.de
October 9, 2009 Simon Schwantzer ICSY Lab, University of Kaiserslautern, Germany – http://www.icsy.de 41

Links
• Ethernet: Distributed Packet Switching for Local Computer Networks
http://haya.informatik.uni-kl.de:11000/diverses/Ethernet.html
• Routing Basics
http://www.cisco.com/en/US/docs/internetworking/technology/handbo
ok/Routing-Basics.html
• Size of BGB Tables
http://bgp.potaroo.net/
• Internetworking Technology Handbook
http://www.cisco.com/univercd/cc/td/doc/cisintwk/ito_doc/
• Its Latency
http://www.potaroo.net/papers/isoc/2004-01/latency.html
• TCP - How it works
http://www.potaroo.net/papers/isoc/2004-07/tcp1.html
• Visualroute
http://www.webhits.de/english/index.shtml?visualroute.html
October 9, 2009
Simon Schwantzer
ICSY Lab, University of Kaiserslautern, Germany – http://www.icsy.de
42