Internet Working 16th lecture last

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Internet Working16th lecture (last)

• Chair of Communication Systems
• Department of Applied Sciences
• University of Freiburg
• 2005

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Internet Workingadministrational stuff

• Last lecture for this semester
• Thursday is inaugural lecture at the faculty
• Friday is written exam starting at 10am sharp
• Grades in oral or written exams will be sent to
  the examinations office (an will be available
  there beginning of winter term)
• If you need a special printed paper please tell
  us/send an email, so we could prepare it it
  will be available at the secretaries of the
  computing department

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Internet WorkingLast lecture SIP

• We talked on and demonstrated SIP session
  initialization protocol
• Telephony over IP networks
• Only session setup
• compression, packet transport left to other
  services like RTP and RTCP
• the latter define container and control protocols
  for multimedia data streams
• This lecture
• H.323 as another standard for VoIP
• Quality of Service in IP networks

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Internet Workinginternet telephony - standards

• Two main VoIP standards
• H.323 standard developed by Telcos - ITU
• SIP internet standard (last lecture)
• H.32x series defines not only VoIP but classical
  telefony too (H.324) and ISDN (H.320)
• 1996 the first version 1 was introduces, today
  modern equipment is using version 5
• family of protocols defines the transmission of
  multimedia content in realtime over unreliable
  networks
• protocol suite consists of several modules
  terminal, gateway, gatekeeper, MCU (multipoint
  controller unit)

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Internet WorkingH.323 - components
Paketorientiertes Netzwerk
H.320 Endpunkt
ISDN
Andere Telefonnetze
SIP
klass. Telefonie
Analoges Telefon
SIP Client
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Internet Working H.323 terminals, gateway

• Terminals
• communication end points
• hardware modules like (IP Telephones) or software
  (softphones)
• used mainly for audio communication, but video
  and Data possible too
• Gateways
• interface to other types of telefony networks
• seamless translation
• translates in realtime between two protocol
  stacks and their respective formats
• or interface to another H.323 gateway

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Internet Working H.323 gatekeeper, MCU

• Gatekeeper
• manager of a zone
• call and access control
• address translation
• multi controller unit (MCU)
• allows multipoint connections
• e.g. for video conferences with more than two
  partners

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Internet WorkingH.323 - protocol

• layered protocol
• precall control
• control of the calls itself
• media control
• transport of media data
• H.323 is not TCP/IP dependent and can be used
  over ISDN too

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Internet WorkingH.323 - SIP

• handle rather the same type of services
• H.323 was developed for telecommunication, not
  primerily for IP networks
• SIP is directly focused for the Internet use
• H.323 is able to handle video conferences and
  offers more complex telefony functions
• SIP much simpler, but clearer and easier to
  understand/implement, scales better
• SIP might take over, but many products implement
  H.323 so it is not dead by now

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Internet WorkingH-protocols and codecs

• codecs encode and decode analog data for
  transport over digital networks (independent of
  network type)
• g series codecs are defined for audio, h series
  for video streams
• rather common pulse code modulation (PCM)
• sampling -gt quantisation -gt encoding
• G.711 8000 Hz x 256 Q.-Intervalle 64 kbit/s
• well known standard for ISDN telephone networks
• codecs might offer compression and voice activity
  detection (or silence detection)

ampling
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Internet WorkingH-protocols and codecs

• how to select suitable codecs (different for
  voice, music, ...)
• tradeoff between bandwidth and qualitty
• rather subjective criterion (mean opion score)
• different popular voice codecs compared

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Internet Workingbandwidth and codecs

• needed bandwidth for a multimedia session depends
  on the demands of the codec used
• often this bandwidth is needed full-duplex
• rather big overhead through headers
• e.g. packets travelling over ethernet
• 18 Byte ethernet, 20 Byte IP, 8 Byte UDP, 12 Byte
  RTP
• 58 Byte header information / 120 Byte for
  codec (depending on samples and data rate)

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Internet Workingbandwidth and codecs

• Imaging a VoIP call over standard DSL connection
  with 128kbit/s upstream
• one would think that two PCM connections are
  possible
• but one connection with header overhead will
  consume around 80kbit/s
• even if we have a 192kbit/s uplink we need clever
  bandwidth management, because 192-26432 does
  not leave much space for other packets
• if a connection is used for other types of data
  (ftp, p2p, ...) too, you have small VoIP (180
  Byte) and big data packets (1500 Byte) to handle,
  queuing delays to avoid, ...

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Internet Workingbandwidth challenges

• we are in packet orientated networks
• Most router implementations
• use only First-Come-First-Serve (FCFS)
• Limited packet processing and transmission
  scheduling
• To mitigate impact of best-effort protocols,
  we can
• Buffer content at client and control playback to
  remedy jitter
• Adapt compression level to available bandwidth
• or Just add more bandwidth and enhance caching
  capabilities (over-provisioning)!
• latter is possible for many network setups, but
  e.g. often not for DSL uplinks (or only at not
  competitive prices)

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Internet Workingsolutions to bandwidth obstacles

• Options
• Need major change of the protocols
• Incorporate resource reservation (bandwidth,
  processing, buffering), and new scheduling
  policies
• Set up service level agreements with
  applications, monitor and enforce the agreements,
  charge accordingly
• Need moderate changes (Differentiated
  Services)
• Use two traffic classes for all packets and
  differentiate service accordingly
• Charge based on class of packets
• Network capacity is provided to ensure first
  class packets incur no significant delay at
  routers

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Internet WorkingQuality of Service (QoS) intro

• Talked last lecture on new protocols like RTP,
  RTCP and RSVP concentrate now on bandwidth
  management
• IETF groups are working on proposals to provide
  QOS control in IP networks, e.g., going beyond
  best effort to provide some assurance for QOS
• Work in Progress includes RSVP, Differentiated
  Services, and Integrated Services
• Simple model for sharing and congestion
  studies

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Internet WorkingQuality of Service (QoS) intro

• Consider a phone application at 1Mbps and an FTP
  application sharing a 1.5 Mbp/s link.
• bursts of FTP can congest the router and cause
  audio packets to be dropped.
• want to give priority to audio over FTP
• PRINCIPLE 1 Marking of packets is needed for
  router to distinguish between different classes
  and new router policy to treat packets accordingly

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Internet WorkingQuality of Service (QoS) intro

• Applications misbehave (audio sends packets at a
  rate higher than 1Mbp/s assumed above)
• PRINCIPLE 2 provide protection (isolation) for
  one class from other classes
• Require Policing Mechanisms to ensure sources
  adhere to bandwidth requirements Marking and
  Policing need to be done at the edges

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Internet WorkingQuality of Service (QoS) intro

• Alternative to Marking and Policing allocate a
  set portion of bandwidth to each application
  flow can lead to inefficient use of bandwidth if
  one of the flows does not use its allocation
• PRINCIPLE 3 While providing isolation, it is
  desirable to use resources as efficiently as
  possible

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Internet WorkingQuality of Service (QoS) intro

• Cannot support traffic beyond link capacity
• Two phone calls each requests 1 Mbp/s
• PRINCIPLE 4 Need a Call Admission Process
  application flow declares its needs, network may
  block call if it cannot satisfy the needs

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Internet WorkingQuality of Service (QoS)
packet scheduling

• Scheduling choosing the next packet for
  transmission
• FIFO
• Priority Queue
• Round Robin
• Weighted Fair Queuing

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Internet WorkingQuality of Service (QoS)
packet scheduling
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Internet WorkingQuality of Service (QoS)
packet scheduling

• Policing mechanisms
• (Long term) Average Rate
• 100 packets per sec or 6000 packets per min??
• crucial aspect is the interval length
• Peak Rate
• e.g., 6000 p p minute Avg and 1500 p p sec Peak
• (Max.) Burst Size
• Max. number of packets sent consecutively, e.g.
  over a short period of time
• Units of measurement
• Packets versus bits

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Internet WorkingQuality of Service (QoS)
packet scheduling

• Token Bucket mechanism, provides a means for
  limiting input to specified Burst Size and
  Average Rate.
• Bucket can hold b tokens
• tokens are generated at a rate of r token/sec
• unless bucket is full of tokens.
• Over an interval of length t, the number of
  packets that are admitted is less than or equal
  to (r t b)

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Internet WorkingQuality of Service (QoS)
routing

• QoS routing multiple restraints
• A request specifies the desired QoS requirements
• e.g., BW, Delay, Jitter, packet loss, path
  reliability etc
• Two type of constraints
• Additive e.g., delay
• Maximum (or Minimum) e.g., Bandwidth
• Task
• Find a (min cost) path which satisfies the
  constraints
• if no feasible path found, reject the connection

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Internet WorkingQuality of Service (QoS)
classification of packets

• But often to complicated/impossible to define a
  path first, so use mechanism on
  per-hop-behavior (PHB) - simply let routers
  decide on each hop what to do
• Big advantage over protocols like RSVP no state
  to be kept
• Give routers hints how to handle different
  packets
• Packet is marked in the Type of Service (TOS) in
  IPv4, and Traffic Class in IPv6
• 6 bits used for Differentiated Service Code Point
  (DSCP) and determine PHB that the packet will
  receive
• 2 bits are currently unused

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Internet WorkingQuality of Service (QoS)
classification of packets

• It may be desirable to limit traffic injection
  rate of some class user declares traffic profile
  (eg, rate and burst size) traffic is metered and
  shaped if non-conforming

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Internet WorkingQuality of Service (QoS)
classification of packets

• PHB result in a different observable (measurable)
  forwarding performance behavior
• PHB does not specify what mechanisms to use to
  ensure required PHB performance behavior
• Examples
• Class A gets x of outgoing link bandwidth over
  time intervals of a specified length
• Class A packets leave first before packets from
  class B

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Internet WorkingQuality of Service (QoS)
classification of packets

• PHBs under consideration
• Expedited Forwarding departure rate of packets
  from a class equals or exceeds a specified rate
  (logical link with a minimum guaranteed rate)
• Assured Forwarding 4 classes, each guaranteed a
  minimum amount of bandwidth and buffering each
  with three drop preference partitions
• But AF and EF are not even in a standard track
  yet research ongoing
• Virtual Leased lines and Olympic services are
  being discussed
• Impact of crossing multiple ASs and routers that
  are not DS-capable

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Internet WorkingQuality of Service (QoS)
conclusion

• In most cases bandwidth suffices
• But you may have to connect a flatsharing
  community of students over a single DSL line
• Provide Internet services for a student dormitory
  over a WLAN link with limited capacity
• Congested lines may render the whole service
  unusable
• SSH gets unbearable delays
• Mail download via POP or IMAP takes hours
• Even filesharing does not work ACK to
  downloaded packets have to wait to long ...

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Internet WorkingQuality of Service (QoS)
conclusion

• Linux kernel includes many types of QoS features
• Hierarchy token bucket (HTB)
• Statistical fair queuing (SFQ)
• Hierarchical Fair Service Curve Packet Scheduler
• ...
• The iproute2 package is used to handle traffic
  classes (tc command)
• Linux packet filter is able to mark packets so
  they could be handled later in QoS queues

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Internet WorkingQuality of Service (QoS)
conclusion

• Adding capacity is often not an issue, but you
  can experiment with QoS on a linux machine used
  as a router
• many embedded router devices use linux as OS
• they often offer basic features for QoS / traffic
  shaping or these features could be added by end
  user (alternative firmwares for such routers,
  e.g. for the popular Linksys WRT54G(S)
• That way you might solve a range of bandwidth
  related problems without the need to upgrade the
  connection
• Nevertheless at corporate level it is often
  cheaper just to add bandwidth than starting a
  sophisticated QoS management on switch and IP
  level

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Internet Workingconclusion of the lecture

• Gave a broad overview on network related issues
  with focus on IP networks
• Defined a model for network protocol layering
• talked on network layer IP v4 / v6
• routing on this layer
• transport layer brief introduction on TCP
  there could be talked much more on, left out UDP
  ...
• physical and data link layer several lower
  layer protocols and techniques for transportation
  of bitstreams
• encoding digital data into analogous signals

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Internet Workingconclusion of the lecture OSI
layers and examples
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Internet Workingconclusion of the lecture

• many topics were not or rather short covered
• range of lectures which focus on
• network security
• network programming
• dynamic networks and routing protocols
• network applications
• unfortunately the lecture plan was not available
  (either from the Dekanat nor the
  Studiendekan), so we could not give an
  extensive overview on constitutive lectures

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Internet Workingconclusion of the lecture

• courses of the professorship next semester
• range of seminars covering
• blocked course on network filtering, content
  blocking, law and possibilities
• blocked course on two major communication
  services email and web in october (17 - 21th)
• advanced seminar on telecommunication
  technologies, protocols, ...
• preliminary discussions are on Thursday (from 2pm
  ...)
• we do not know which kind of courses will be
  offered next summer

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Internet Workingend for today and this semester!!

• Thanks to our hiwis
• Rui Zhou
• Roman Malytskyy
• Helping preparation of practical courses
• Discussing and defining excercises
• Correcting excercises
• Preparing services
• ...
• Please hand back the lecture evaluation sheets
  now or bring them with you on Friday
• Have nice summer holidays!!
  

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