wahlpflichtfach multimediasysteme - icsy.de network device for this layer is called a bridge. 3. the...

ICSY Lab, University of Kaiserslautern, Germany – http://www.icsy.deSimon Schwantzer

University of KaiserslauternIntegrated Communication Systems

http://www.icsy.de

Wahlpflichtfach Multimediasysteme

Kapitel 5: Netzwerke

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[email protected]

Simon Schwantzer Wahlpflichfach Multimediasysteme

TU Kaiserslautern

Oktober 2009

9. Oktober 2009


Overview

• Switching

• ISO/OSI Reference Model

• QoS Mechanisms

• Networks– Ethernet– ISDN– TCP/IP– RTP

2October 9, 2009


SWITCHING

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SwitchingISO / OSI Reference

Model

ISO / OSI Reference Model

Network QoS Mechanisms


Circuit Switching• Provide a "physical" link:

connection A, B establishedconnection C, B blocked

• Advantages:– guaranteed bandwidth and delay– worldwide available

• Disadvantages:– bandwidth not scalable– bad efficiency (bandwidth usage)

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Model

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Packet Switching• Handle independent packages:

A+C sending packages of different size to BPacket may get lost because of congestion

• Advantages:– high efficiency (bandwidth usage)– bandwidth is scalable

• Disadvantages:– no guaranteed delay (bandwidth)

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Model

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Cell Switching• 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

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Model

October 9, 2009


ISO / OSI REFERENCE MODEL

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ISO / OSI Reference ModelSwitching QoS Mechanisms

Switching QoS Mechanisms

Networks



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ISO / OSI (Layer 1-3)

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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.

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2The 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.

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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. Pr

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October 9, 2009


ISO / OSI (Layer 4-7)

4The 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.

5The session layer establishes and terminates connections and arranges sessions to logical parts. TCP and RPC provide some functions at this layer.

6The presentation layer takes care of data type conversion. Protocols residing at this layer are used to provide interoperability between heterogeneous computer systems.

7The 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).

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QOS MECHANISMS

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QoS MechanismsISO / OSI Reference

Model Networks

ISO / OSI Reference Model Networks

Switching


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

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Model Networks

October 9, 2009


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

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Model Networks

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Shaping vs. Policing

• policing: monitor the traffic characteristic, increases loss rate!

• shaping: keep a traffic characteristic, increases delay!

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Model Networks

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Packet Scheduling / Queueing

• FIFO– best effort service only

– prior admission control and policing may improve fairness

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Model Networks



• (Strict) Priority Queueing– different services

according to bandwidth and delay

– unfair, because starvation of low priority flows possible

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Model Networks



• Weighted Fair Queueing(WFQ)– each queue receives a

portion of the available bandwidth resources

– round robin according to weight of queues, guarantees fairness

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Model Networks


IsochronismAn 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.

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Model Networks

October 9, 2009


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.

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Model Networks

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NETWORKS

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NetworksQoS Mechanisms

QoS Mechanisms


October 9, 2009


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

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October 9, 2009


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

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October 9, 2009


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, VLAN-

tagging (IEEE 802.3Q), priorities (IEEE 802.3p), link aggregation (IEEE 802.3ad)23


October 9, 2009


Ethernet: Frame

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MAC = Medium Access Control LLC = Logical Link control

SNAP = Sub-network Access Protocol DSAP = Destination Service Access Point

SSAP = Source Service Access Point cntl = controlorg code= organization code CRC = Cyclic Redundancy Check


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

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October 9, 2009


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

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October 9, 2009


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)

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October 9, 2009


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 ...

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TCP/IP Suite

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October 9, 2009


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)30


October 9, 2009


IP Header

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October 9, 2009

Version: version of IP header Flags, Frag. Offset:

used for fragmentation

IHL: IP header length in 32 bit words (5+ no. of options)

TTL: Time To Live, decremented by each machine to pass the packet

TOS: Type Of Service precedence ~ priority; D,T,R if set optimize for Delay, Throughput, Reliability

Protocol: 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


UDP / TCP• 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

– 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: segmentOctober 9, 2009 32



TCP Flow Control• Avoid network congestion

If multiple identical ACKs indicate packet loss, then slow start + congestion avoidance:

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TCP Flow ControlIf timeout indicate packet loss, then slow start + restart slow start + congestion avoidance:

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October 9, 2009


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

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October 9, 2009


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

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October 9, 2009

http://www.ietf.org/rfc/rfc1550.txt�

http://www.ietf.org/rfc/rfc1883.txt�


IPv6 Header

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October 9, 2009

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*1023 IPv6 addresses per square meter of the world enabling well structured addresses Support of provider based addresses

• and geographic based addresses


QoS in Data Networks

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October 9, 2009

IP Service ModelsTraffic-Engineering Concept

Network Technology

Best Effort DiffServ IntServ MPLS ATM

QoSGuarantees

no aggregated flow basedflow based and aggregated

flow based and aggregated

QoSParameter

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


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– ...

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October 9, 2009


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

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October 9, 2009


Questions?

October 9, 2009 41

Contact: Simon Schwantzer, [email protected], http://www.icsy.de


Links• Ethernet: Distributed Packet Switching for Local Computer Networks

http://haya.informatik.uni-kl.de:11000/diverses/Ethernet.html

• Routing Basicshttp://www.cisco.com/en/US/docs/internetworking/technology/handbook/Routing-Basics.html

• Size of BGB Tableshttp://bgp.potaroo.net/

• Internetworking Technology Handbook http://www.cisco.com/univercd/cc/td/doc/cisintwk/ito_doc/

• Its Latencyhttp://www.potaroo.net/papers/isoc/2004-01/latency.html

• TCP - How it workshttp://www.potaroo.net/papers/isoc/2004-07/tcp1.html

• Visualroutehttp://www.webhits.de/english/index.shtml?visualroute.html

42October 9, 2009

http://haya.informatik.uni-kl.de:11000/diverses/Ethernet.html�

http://www.cisco.com/en/US/docs/internetworking/technology/handbook/Routing-Basics.html�

http://www.cisco.com/en/US/docs/internetworking/technology/handbook/Routing-Basics.html�

http://bgp.potaroo.net/�

http://www.cisco.com/univercd/cc/td/doc/cisintwk/ito_doc/�

http://www.potaroo.net/papers/isoc/2004-01/latency.html�

http://www.potaroo.net/papers/isoc/2004-07/tcp1.html�

http://www.webhits.de/english/index.shtml?visualroute.html�

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