How to contact Acknowledgements Prof. Dr. Paul MГјller Raum: 34/312 Telefon: 0631/205в€’2263 eMail: [email protected]в€’kl.de Bernd Reuther Raum: 32/344 Telefon: 0631/205в€’2161 eMail: [email protected]в€’kl.de TU Darmstadt Stephan G. Eick Bellв€’Labs Dr. Andreas U. Mauthe Fa. TecMath Dr. Peter Thomas Fa. TecMath Uni Mannheim Technische UniversitГ¤t Kaiserslautern: Prof. Dr. Hans Irtel Dipl.в€’Inform. Bernd Reuther Dipl.в€’Ing. Dirk Henrici Dirk Henrici Raum: 36/414 Telefon: 0631/205в€’2891 eMail: [email protected]в€’kl.de How to contact Prof. Dr. Ralf Steinmetz 1 Literature Acknowledgements 2 Sitemap вЂў Ralf Steinmetz Multimediaв€’Technologie. Grundlagen, Komponenten und Systeme. 3. Auflage Springerв€’Verlag 2000 вЂў Andreas Holzinger Basiswissen Multimedia Band 1: Technik Vogel Buchverlag 2001 вЂў Guojun Lu Communication and Computing for Distributed Multimedia Systems Artech House 1996 вЂў FranГ§ois Fluckinger Understanding Networked Multimedia, applications and technology Prentice Hall 1995 вЂў Andrew S. Tanenbaum Computer Networks, third edition Prentice Hall 1994 Literature 3 Sitemap 4 Overview Chapter 4 4.1. Network Basics for Multimedia Data 4.1 Network basics for Multimedia Data в™¦ Network types в—Љ Switching concepts в™¦ ISO/OSI model в—Љ Layer Description в—Љ Terminology в™¦ Network Quality of Service Overview 4.2 Network Technologies Considered for Multimedia 4.3 Protocols Considered for Multimedia Overview Chapter 4 5 4.1.1. Network Types and Services (1) Network Telephone Telephone (mobile) Internet Intranet Cable TV, Satellite TV Broadcast TV Broadcast Radio 6 Network Types and Services (2) Services Voice (1:1 and 1:n), Fax, Video, Text, Data, ... Voice, Fax, Text, Data, ... Physical Type cable (copper, fiber) wireless, satellite wireless + cable cable (copper, fiber), wireless, Data, Text, Voice, Audio, Video, ... satellite Data, Text, Voice, Audio, Video, ... cable (copper, fiber), wireless Video, Audio, Videotext, Data cable (copper) Video, Audio, Videotext satellite Video, Audio, Videotext wireless Audio, Text wireless 4.1.1. Network Types and Services (1) 4.1. Network Basics for Multimedia Data Additionally very specialized Networks: вЂў Bank connections вЂў Controlling (traffic, machines, in house systems, ...) вЂў Supervising (alarm systems, gas pipes, street lights, ...) 7 Network Types and Services (2) 8 Size versus Time of Transmission Circuit Switching Provide a "physical" link: connection A, B established connection C, B blocked Advantages: Disadvantages: Size versus Time of Transmission Circuit Switching 10 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. Handle independent packages: A+C sending packages of different size to B Packet may get lost because of congestion Disadvantages: вЂў bandwidth not scalable вЂў bad efficiency (bandwidth usage) 9 Packet Switching Advantages: вЂў guaranteed bandwidth and delay вЂў worldwide available Advantages: вЂў high efficiency (bandwidth usage) вЂў bandwidth is scalable вЂў no guaranteed delay (bandwidth) Packet Switching Disadvantages: 11 вЂў high efficiency (bandwidth usage) вЂў bandwidth is scalable вЂў guaranteed bandwidth and delay вЂў rare availability Cell Switching 12 4.1.2. ISO / OSI Reference Model (1) ISO / OSI Reference Model (2) 1 The physical layer defines electric signaling on the transmission channel; how bits are converted into electric current, light pulses or any other physical form. Serial_line is an example of the physical layer. A network device for this layer is called a repeater. 2 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. Technology (usually hardware) Protocols (usually software) 3 4.1.2. ISO / OSI Reference Model (1) 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. 13 ISO / OSI Reference Model (2) ISO / OSI Reference Model (3) 14 Layer 1 4 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. 5 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). Data Types вЂў electrical or optical signals Devices вЂў Repeater в™¦ extends physical segments to logical segments в™¦ boosts electrical or optical signals вЂў Hub в™¦ is a multiport repeater в™¦ is a shared medium like a bus Connectivity ISO / OSI Reference Model (3) 15 Layer 1 16 Layer 2 (1) Layer 2 (2) Devices Data Types вЂў Switch в™¦ is a multiв€’port bridge в™¦ provides dedicated connections between all ports, i.e. does not realize a shared medium вЂў frames Devices вЂў Bridge в™¦ connects logical segments to broadcast domains в™¦ provides connectivity on layer 2 by forwarding frames between two logical segments в™¦ a frame will be forwarded if в—Љ the receiver resides on the other segment в—Љ the receiver's location is unknown в—Љ the destination address is a broadcast address в™¦ needs information about directly connected network segments only в™¦ automatically collects layer 2 addresses to be able to make forwarding decision Layer 2 (1) Connectivity 17 Layer 2 (2) Layer 3 (1) 18 Layer 3 (2) Data Types Connectivity вЂў packets Devices вЂў provides connectivity on layer 3, by interpreting packets and making routing decisions вЂў a router port is an endpoint of a network segment вЂў may connect different types of layer 2 networks вЂў needs information about the whole network topology в™¦ receives external information to make a routing decision в™¦ static information may be configured by an administrator в™¦ dynamic information may be collected by routing protocols Layer 3 (1) 19 Layer 3 (2) 20 Layer 4 в€’ 7 Terminology (1) Data Types Data types: вЂў protocol data вЂў arbitrary application specific data Repeating: Applications Forwarding: вЂў Client Process в™¦ requests some information в™¦ receives payload вЂў Server Process в™¦ waiting for information requests в™¦ sends payload вЂў One process may be client and server в™¦ on different levels (e.g. FTP) в™¦ on the same levels (e.g. peerв€’toв€’peer protocols) Bridging or switching: вЂў layer 1: signals вЂў layer 2: frames вЂў layer 3: packets вЂў boosting electrical or optical signals вЂў is the task of moving a frame or packet from one interface (or port) to another interface вЂў depending on layer 2 addresses deciding whether a frame needs to be forwarded, identifying the output port and performing the forwarding вЂў bridging/switching is a layer 2 functionality Connectivity Layer 4 в€’ 7 21 Terminology (1) Terminology (2) Routing: Combined devices: Topologies (1) вЂў depending on layer 3 addresses and routing information deciding to which output port a packet needs to be forwarded and performing the forwarding вЂў forwarding a packet includes the generation of a new frame вЂў routing is a layer 3 functionality Complete mesh: Ring: вЂў switchingв€’hubs oder routeв€’switches denote combined devices Star: Terminology (2) 22 23 вЂў ideal performance вЂў high reliability вЂў only for networks with small expansion вЂў connections вЂў reliability в™¦ absorb drop out of one link вЂў easier cabling вЂў n connections вЂў reliability в™¦ drop out of one link affects a single endsystem only в™¦ node in the middle is single point of failure вЂў complex cabling for large extent networks вЂў n connections Topologies (1) 24 Topologies (2) Combination: Tree: Irregular: Speed versus Distance вЂў large networks often combine different topologies вЂў Example: the Bв€’WIN network of the DFN (Deutsches Forschungsnetz) uses a combination of ring and star topology вЂў is a combination of star topologies вЂў some applications may require specialized topologies Topologies (2) 25 Quality of Service Overview Speed versus Distance 26 Network QoS Quality of Servcie (QoS) denotes the wellв€’defined and managable behaviour of a system according to measurable parameters. In this chapter we consider the Networkв€’QoS for Layerв€’2 Quantitative criteria: The implementation of QoS requires the availability of resource management mechanisms. Different layers of a system will use different QoS parameters, each layer may also have several subв€’layers. вЂў throughput вЂў delay вЂў delay variation вЂў error rate Network capabilities: вЂў isochronism вЂў multicast capability Quality of Service Overview 27 Network QoS 28 Throughput Endв€’toв€’End Delay The bit rate between two communication endpoints is the number of binary digits that the network is capable of delivering and accepting per time unit The endв€’toв€’end delay is the sum of the following delays: вЂў access delay the time between the request to send a data block and the emission of the first bit вЂў network transit delay the time between emission of the first bit of a data block and its reception at the destination endsystem (network transit delay is also called latency) вЂў transmission delay the time between emission of the first and the last bit of a data block вЂў The commonly used time unit is one second, but often the actually observed time unit is another one в™¦ ISDN offers a throughput of 8 bit per 125 μs вЂў distinguish individual and aggregate bit rates вЂў access speed versus bit rate в™¦ access speed refers to the frequency at which bits may be sent or received вЂў bit rate could be constant or variable вЂў burstiness в™¦ peak bit rate (PBR): maximum bit rate during a short time interval в™¦ mean bit rate (MBR): averaged bit rate over a longer time interval в™¦ burstiness is the relation between PBR and MBR Throughput 29 Roundв€’Tripв€’Delay (RTT) Endв€’toв€’End Delay 30 Delay Variation The Delay variation relates to variation of endв€’toв€’end delay вЂў also called "Jitter" вЂў distinguish average and maximum delay variation Originator of delay variation вЂў the physical environment causes jitter in magnitude of nano seconds вЂў intermediate switches/routers may cause jitter by в™¦ variation of medium access time, e.g. CSMA/CD (usually microв€’seconds) в™¦ store and forward switching delays, e.g. by internal node congestion (microв€’seconds) в™¦ waiting time caused by flow control mechanisms (microв€’ or even milliв€’seconds) In ISDN there is only a physical jitter, whereby in IP networks all types of jitter occur. вЂў The RTT is also called response time вЂў RTT is a good metric for interactive applications Roundв€’Tripв€’Delay (RTT) 31 Delay Variation 32 Error Rates 1 Error Rates 2 Error types: Error types: вЂў data alternation, i.e. inversion of bits в™¦ caused by the physical environment в™¦ metrics are: bit error rate (BER), packet error rare (PER), cell error rate (CER) вЂў data loss в™¦ caused by congestion в™¦ or caused by defective physical infrastructure в™¦ metrics are: packet loss rate (PLR) or cell loss rate (CLR) вЂў Data duplication, miss insertion or wrong delivery в™¦ is a rare incident, but may be caused by data alternation or loss в™¦ also caused by hackers to provoke unusual system behavior в™¦ miss insertion and wrong delivery may cause serious problems, therefore some techniques use countermeasurements especially to avoid these problems вЂў outв€’ofв€’order delivery в™¦ caused by changing routing paths Mechanisms to avoid problems: 1. Error detection, e.g. using CRC 2. Error handling methods вЂў discarding, i.e. handle all error types like data loss вЂў notification, includes discarding вЂў recovery, error correction or retransmission Error Rates 1 33 Isochronism Error Rates 2 34 Multicasting An endв€’toв€’end network connection is called isochronous if the bit rate and the jitter over the connection life time is guaranteed and the jitter is also small Multicasting is the capability to replicate data at certain internal points. Replicated data is forwarded to endsystems which are part of a multicast group. Isochronism therefore simply defines the requirements of continuous media streams. Remark: вЂў The property of media like audio and video, that must be sampled and played in regular intervals is also called isochrony вЂў Isochronism does not define quantitative values for jitter or probabilities refereed to by guaranteed. вЂў If a jitter may be considered small depends on the application. вЂў Multicast avoids or minimizes the multiple transport of the same data over the same network segments вЂў broadcast is a special case of multicast вЂў data duplication must be supported by forwarding engines in switches вЂў multicast types в™¦ oneв€’toв€’many unidirectional в™¦ oneв€’toв€’many biв€’directional в™¦ manyв€’toв€’many Note: The mulitcast or broadcast capability on OSI Layerв€’2 is usually a prerequisite for the realization of multicast on Layerв€’3. Isochronism 35 Multicasting 36 4.2. Networks 4.2.1. Ethernet Different network characteristics lead to different usability for the transport of multimedia data: History: вЂў QoS guarantees: в™¦ bandwidth в™¦ delay в™¦ delay variation вЂў Xerox Corp.: R. Metcalfe (PHD at the M.I.T.) and D. Boggs вЂў Standardized by IEEE 802.3 в™¦ there are vendor specific Ethernet variants, e.g. Ethernet V2 вЂў The original article from Robert M. Metcalfe and David R. Boggs Xerox Palo Alto Research Center вЂў Isochronism вЂў Multicast capability вЂў Flexibility: в™¦ bandwidth в™¦ traffic types в™¦ distance (LAN, WAN) в™¦ physical media вЂў Efficiency/Utilization of physical media вЂў Costs 4.2. Networks 37 4.2.1. Ethernet Ethernet Ethernet: Usability for Multimedia Data Characteristics: QoS parameters: вЂў Bus topology Isochronism: вЂў Several physical media: coax cable, twistedв€’pair, fiber Multicast capability: вЂў Bus characteristics: в™¦ max. segment size в™¦ min. distance between nodes в™¦ Repeater/Hub/Switches for longer distances Flexibility: вЂў access protocol CSMA/CD (Carrier Sense Multiple Access with Collision Detection) Efficiency: [ Details ] Costs: Ethernet 38 39 вЂў No endв€’toв€’end guarantees possible вЂў No priorities supported вЂў not available вЂў Multicast group addressing supported вЂў Broadcast group addressing supported вЂў formerly fixed bandwidth of 10 Mbit/s, Ethernat derivatives up to 10 GBit/s вЂў short distances (a so called "WAN Ethernet" is currently under develope) вЂў with CSMA/CD: low throughput at high utilization because of collisions вЂў bad efficieny for small frames because padding is required to ensure the necessary minimum frame size вЂў Low cost technology enables dedicate connected systems 10/100 Mbit/s guaranteed bandwidth per host in small LANs Ethernet: Usability for Multimedia Data 40 4.2.2. Token Ring Token Ring Usability for Multimedia Data History: QoS parameters: вЂў Introduced by IBM 1985 вЂў Standardized by IEEE 802.5 (ECMA 89, ISO 8802/5) вЂў No bandwidth guarantees, but “reservation” possible by use of 4 priority classes, e.g. high priority for continuousв€’media data traffic вЂў Priority Classes вЂў Priority Use 0 normal data transfer 1в€’3 available for data transfer 4 bridges 5в€’6 reserved 7 station management вЂў Bounded delay because of: в™¦ Token Holding Time в™¦ Deterministic access Characteristics: вЂў Ring topology вЂў Shielded coax cable (double) at 4 or 16 MBit/s вЂў Ring characteristics: в™¦ Maximal 260 stations per ring в™¦ Bridges to connect several rings Isochronism: вЂў Token controls media access: в™¦ Rotates on ring в™¦ Owner of token may send data в™¦ Priority fields Multicast capability: [ Details ] Flexibility: вЂў not available вЂў Multicast group addressing supported вЂў Broadcast group addressing supported вЂў bandwidth of 4 or 16 Mbit/s вЂў short distances Efficiency: 4.2.2. Token Ring 41 Token Ring Usability for Multimedia Data вЂў high throughput at high utilization Costs: вЂў complex protocol 42 4.2.3. Token Bus “expensive” hardware The Token Bus protocol was developed to meet the requirements of factory automation Characteristics: вЂў Specified in IEEE 802.4 вЂў Bus topology вЂў Shielded coax cable вЂў Defines a logical ring of stations в™¦ The order depends on MAC addresses в™¦ The MAC protocol is even more complex than for Token Ring вЂў Frame format is nearly the same than for IEEE 802.5 вЂў Priorities are only used to sort frames before sending Token Ring Usability for Multimedia Data 43 4.2.3. Token Bus 44 4.2.4. FDDI (Fiber Distributed Data Interface) FDDI Traffic Types History: вЂў Based on IEEE 802.5 (Token Protocol) вЂў Standardized (ANSI X3T9.5, ISO 9314) Ring Characteristics: вЂў Optical LAN at 100 MBit/s вЂў Up to 200 km in length with up to 2 km distance between two stations вЂў Up to 500 stations FDDI modes: вЂў Nonв€’restricted mode: residual bandwidth, timed token protocol, 8 priority levels вЂў Restricted mode: residual bandwidth shared between two stations, “restricted token” вЂў Synchronous: packet switched, guaranteed bandwidth, limited delay Protocol Characteristics: вЂў Timer controlled token protocol вЂў Bidding process at (reв€’)configuration time вЂў Early token release option FDDI II offers an additional mode: вЂў Isochronous: circuit switched, guaranteed bandwidth, fixed delay [ Details ] 4.2.4. FDDI (Fiber Distributed Data Interface) 45 FDDI Traffic Types FDDI: Usability for Multimedia Data (1) QoS parameters: FDDI: Usability for Multimedia Data (2) Performance guarantees in asynchronous mode: Multicast capability: вЂў Similar to Token Ring, but longer latency (20 bit per station instead of 2 bit) вЂў No guarantees if synchronous and asynchronous traffic on the ring вЂў Restricted mode for two stations: в™¦ Low delay в™¦ No other asynchronous traffic on the ring allowed Flexibility: Performance guarantees in synchronous mode: Efficiency: вЂў Guaranteed bandwidth with maximum delay (variation up to 100 ms) вЂў Time for reservation of synchronous bandwidth relatively long вЂў Buffering for packets coming too early: buffer space for TTRT duration, isochronous mode in FDDI II Isochronism: 46 Costs: вЂў Multicast group addressing supported вЂў Broadcast group addressing supported вЂў fixed bandwidth of 100 Mbit/s вЂў suitable for short and long distances вЂў High throughput at high utilization вЂў fiber is expensive, especially for short distance connections вЂў complex protocol “expensive” hardware вЂў available in FDDI II only FDDI: Usability for Multimedia Data (1) 47 FDDI: Usability for Multimedia Data (2) 48 4.2.5. DQDB DQDB: Traffic Types Queued Arbitrated (QA) Slots: (Distributed Queue Dual Bus) вЂў Allocated through “distributed queue” MAC procedure вЂў Similar to asynchronous data traffic in FDDI Previously QPSX: Queued Packet Switch Asynchronous part stable (IEEE 802.6), Isochronous part not standardized Preв€’Arbitrated (PA) Slots: вЂў Assigned to a specific node by the Frame Generator вЂў Identified by VCI in slot header вЂў Ignored by the distributed queue medium access procedure вЂў Number and timing of PA slots is variable вЂў Slot contains: в™¦ 48 usable bytes (every 125 μs) в™¦ n * 64 Kbit/s channel Design goals, compatibility with вЂў IEEE 802.x MAC frame formats вЂў Bв€’ISDN cell structure and speed Bus characteristic: вЂў Dual slotted bus, 125μs frame rate (125 μs = 8000 frames/s) Traffic modes: вЂў Asynchronous (packet switching) traffic вЂў Isochronous (circuit switching) traffic [ Details ] 4.2.5. DQDB 49 DQDB: Traffic Types DQDB: Usability for Multimedia Data QoS parameters: DQDB: Usability for Multimedia Data (2) Multicast capability: Performance guarantees for asynchronous traffic: вЂў Four priorities: High priority traffic is always sent before traffic of a lower priority вЂў Fairness problems: stations near to a bus head have a better chance to send data in this direction Flexibility: Performance guarantees for isochronous traffic: вЂў Guaranteed bandwidth, reservation is possible вЂў Fixed delay вЂў Few implementations Isochronism: Efficiency: вЂў is available DQDB: Usability for Multimedia Data 50 Costs: 51 вЂў not available вЂў usable for LAN and WAN, e.g. DQDB connection between Perth and Melbourne (3.500 km). вЂў different physical media with different line speed available (30/45/140/155 Mbit/s, fullв€’duplex) вЂў High throughput at high utilization вЂў High load leads to unfairness вЂў Data always travels to the bus head, a receiver does not remove data. If receivers would remove data, then efficiency could be increased. вЂў no market DQDB: Usability for Multimedia Data (2) 52 4.2.6. ISDN: Integrated Services Digital Network ISDN: Interfaces ISDN User Interfaces: Standardization: Channels: вЂў Basic Rate Interface в™¦ 2 data channels (B channel) with 64 Kbit/s в™¦ 1 signaling channel (D channel) with 16 Kbit/s вЂў Primary Rate Interface: в™¦ 30 data channels (B channel) with each 64 Kbit/s in Europe в™¦ 1 signaling channel (D channel) with 64 Kbit/s вЂў ITU recommendations (former CCITT) вЂў ETSI and ANSI standards Characteristics: вЂў Public, digital, endв€’toв€’end network вЂў Implements digital bit pipe в™¦ Based on 64 Kbit/s data rate в™¦ Multiple full duplex data channels вЂў Support for multiple media and services within one network: в™¦ Voice, low quality video, image data, text data, в™¦ supplementary services вЂў Common signaling channel with common set of signaling protocols A в€’ 4kHz analog B в€’ 64 Kbps digital PCM C в€’ 8 or 16 Kbps digital D в€’ 16 or 64 Kbps digital signaling E в€’ 64 Kbps digital internal signaling H в€’ 384, 1536 or 1920 Kbps digital ISDN Protocol Reference Model: вЂў Extensions to ISO/OSI: вЂў User plane: for user data вЂў Control plane: for connection management вЂў Packet oriented D channel signaling Technology: вЂў Circuit switching вЂў Fixed bandwidth channel assignment [ Details ] 4.2.6. ISDN:Integrated Services Digital Network 53 ISDN: Usability for Multimedia Data QoS parameters: ISDN: Interfaces 4.2.7. Bв€’ISDN (Broadband ISDN) / ATM вЂў guaranteed bandwidth вЂў low delay and low delay variation (not guaranteed, e.g. Satellite links with significantly higher delay) Standardization: Characteristics: Isochronism: Multicast capability: Flexibility: Efficiency: Costs: 54 вЂў guaranteed by design principals вЂў no multicast capabilities вЂў fixed bandwidth вЂў although ISDN is used for endв€’toв€’end communications, it is mainly a WAN technology вЂў independent of physical media Technology: вЂў ITU recommendations (former CCITT) вЂў ATM Forum (organization of vendors, specifications only) вЂў For LAN and WAN networks вЂў For private and public networks вЂў Support of fine granular Quality of Service в™¦ Suitable for all media types вЂў Low and high bandwidth is supported вЂў Connection oriented вЂў Cell Switching вЂў ATM – Asynchronous Transfer Mode вЂў low bandwidth utilization вЂў expensive bandwidth (Telecom ports includes WAN connectivity) ISDN: Usability for Multimedia Data 55 4.2.7. Bв€’ISDN (Broadband ISDN) / ATM 56 4.2.8. ATM = Asynchronous Transfer Mode ATM Layer Overview Examples: According to ITUв€’T Recommendation I.113 asynchronous means: Reference Model " ... it is asynchronous in the sense that the recurrence of cells containing information from an individual user is not necessarily periodic." (I113) вЂў Higher layer provide endв€’toв€’end services вЂў ATM Adaption Layer (AAL): в™¦ adaption of service data to cells (48 bytes) вЂў 53 byte cells handled by ATM Layer: в™¦ 5 byte header (VPI, VCI, HEC) в™¦ switching/multiplexing of cells [ Details ] 4.2.8. ATM = Asynchronous Transfer Mode 57 ATM: Traffic Contract ATM Layer Overview 58 ATM: Service Categories 1 No error detection and correction, but ... ... mechanisms to guarantee Quality of Service ATM: Traffic Contract 59 ATM: Service Categories 1 60 ATM: Service Categories 2 Quality of Service Parameter Distribution of bandwidth QoS Acronym peakв€’toв€’peak maxCTD CLR CER SECBR CMR вЂў CBR: fixed constant bandwidth вЂў VBR: fixed constant bandwidth up to sustained cell rate for a short time (max. burst size) more bandwidth usage is possible вЂў ABR: variable bandwidth based on feedback of the network вЂў UBR: bestв€’effort Parameter Name Cell Delay Variation max. Cell Transfer Delay Cell Loss Ratio Cell Error Ratio Severely Errored Cell Block Ratio Cell Misinsertion Rate Negotiated? YES YES YES NO NO NO Probability for exceeding maxCTD must be less than CLR ATM: Service Categories 2 61 ATM: Usability for Multimedia Data QoS parameters: Isochronism: Multicast capability: Flexibility: Efficiency: Costs: Quality of Service Parameter 62 4.3. Protocols (Layer 3в€’7) Examples for typical protocol tasks: вЂў guaranteed bandwidth (fixed, variable, feedback) вЂў low delay and low delay variation (not guaranteed) вЂў Layer 3: Endв€’toв€’end connectivity (hostв€’toв€’host) вЂў Layer 4: Processв€’toв€’Process connectivity вЂў Reliable communication в™¦ Error detection в™¦ Error recovery (forward error correction or retransmission) вЂў Resource management в™¦ avoid congestion, by flow control в—Љ within the network в—Љ within end systems в™¦ Priorization в™¦ Resource reservation вЂў Support for specialized media types в™¦ Content description в™¦ Timing / Synchronization Information вЂў And more ... вЂў is available вЂў uniв€’directional pointв€’toв€’multipoint is available вЂў bandwidth on demand, limited by physical links and actual system load вЂў several traffic types CBR, RTв€’VBR, NRTв€’VBR, ABR and UBR вЂў independent of physical media вЂў mainly used for WAN or in LAN for backbones, ATM to the desktop was available but was too expensive to be accepted widely вЂў high bandwidth utilization вЂў statistical multiplexing increases utilization, VBR channels: в™¦ SUM of "sustained cell rates" must be <= 100% в™¦ SUM of "peak cell rates” may be > 100% вЂў a complex and therefore an expensive technology ATM: Usability for Multimedia Data 63 4.3. Protocols (Layer 3в€’7) 64 TCP/IP Suite 4.3.1. IP Protocol (RFC 791) Development of IP вЂў DARPA: Defense Advanced Research Projects Agency в™¦ The research aim was to build a network that is tolerant to extensive damage, e.g. by a nuclear strike в™¦ 1973/1974 development of TCP/IP, a replacement of NCP (Network Control Protocol) в™¦ Since 1975 the ARPANET was controlled by the DoD в™¦ In the early 80'ies the military part was extracted from the ARPANET в™¦ Since 1983 exclusive use of TCP/IP, defining the term Internet вЂў IP is specified in RFC 791 вЂў "This document is based on six earlier editions of the ARPA Internet Protocol Specification ..." IP characteristics вЂў Provides endв€’toв€’end communication вЂў Connection less, i.e. state less protocol вЂў Provides unreliable transfer of packets вЂў Packets may be reordered during transmission вЂў Error messages are handled by the separate protocol ICMP (Internet Control Message Protocol) [ Details ] TCP/IP Suite 65 4.3.1. IP Protocol (RFC 791) IP Header 66 Routing Routers are used to connect networks Routing: making a local forwarding decision based on global topology information How to get topology information: Version: version of IP header used for fragmentation IHL: Time To Live, decremented by each machine to pass the packet layer 4 protocol, e.g. 1=ICMP, 6=TCP, 17=UDP TOS: Length: ID: Flags, Frag. Offset: IP header length in 32 bit words (5+ no. TTL: of options) Protocol: Type Of Service precedence ~ priority; D,T,R if set optimize for Delay, Throughput, Reliability length in bytes including the IP header Checksum: serial number Options: IP Header вЂў Default routing вЂў Static or non adaptive routing в™¦ Does not take into account changes of the network вЂў Dynamic or adaptive routing, requires routing protocols в™¦ Identifies the topology of the network automatically в™¦ Different metrics are used to describe distances в—Љ Number of hops в—Љ Available bandwidth в—Љ Error rates в—Љ ... checksum for the IP header security, record route, timestamp, source routes 67 Routing 68 4.3.2. UDP (RFC 768) / TCP (RFC 793) UDP Header Transport protocols (Layer 4) вЂў Provides process to process connectivity вЂў Uses port number to identify processes. An IP address and a port number is a unique identifier for a service. Characteristics Source Port, port number of sender and receiver Destination Port: Length: length of the UDP datagram Checksum: the checksum covers the UDP pseudo header and the UDP data The UDP pseudo header includes the UDP Header and 12 bytes of the IP header: вЂў Closely related to IP вЂў UDP offers a connectionless and unreliable transport service в™¦ Nearly the same service as IP в™¦ Data unit name: datagram вЂў TCP offers a connection oriented and reliable transport service в™¦ Recognition of lost data в™¦ Retransmission of lost data в™¦ Reordering of data в™¦ Delete duplicate data в™¦ Flow control в—Љ With respect to network congestion в—Љ With respect to buffer overflow at the receiver side в™¦ User data is handled as a stream of bytes в—Љ User data is split into segments в™¦ Data unit name: segment вЂў 2*4 byte IP source and destination address вЂў 1 byte 0 вЂў 1 byte protocol вЂў 2 byte IP header length 4.3.2. UDP (RFC 768) / TCP (RFC 793) 69 TCP Header UDP Header 70 Options: e.g. maximum segment size Source Port, port number of sender and receiver Destination Port: Sequence Number: TCP counts every byte of a stream This is the number of the first data byte Ack Number: If the ACK control bit is set this field contains the value of the next sequence number the sender expects to receive Data Offset: number of 32 bit words in the TCP header Flags: urg ack psh urg: urgent pointer is valid psh: push data to level above syn: synchronize seq. number rst syn ack: ack number is valid rst: reset connection fin: close this side of the connection fin Window: amount of data the sender is willing to accept (flow control) Urgent Pointer: points to last byte of urgent data TCP Header 71 TCP Header 72 TCP Flow Control (1) TCP Flow Control (2) avoid overflow of receiver buffers (sliding window): Avoid network congestion If multiple identical ACKs indicate packet loss, then slow start + congestion avoidance: вЂў ACKs may advance left side of window вЂў advertised windows size may advance right side of window If timeout indicate packet loss, then slow start + restart slow start + congestion avoidance: TCP Flow Control (1) 73 TCP Flow Control (2) 74 TCP Service Mechanisms Retransmission вЂў Goв€’backв€’n strategy в™¦ Simple and robust mechanism в™¦ Resource consuming в™¦ Causes unpredictable delay Flow control вЂў Slow start and congestion avoidance realize considerate resource usage в™¦ This enables fair and cooperative bandwidth sharing в™¦ May cause high jitter TCPs service mechanisms were designed for reliable data transfer TCP is not suitable for realв€’time communications TCP Flow Control (2) 75 TCP Service Mechanisms 76 4.3.3. IPv6 IPv6 Header Development of IPv6 вЂў 1993 the IETF called for the development of an IP next generation IPng (RFC 1550) вЂў Improvements required в™¦ Larger address space в™¦ Reduce size of routing tables в™¦ Simplification of the protocol, to allow routers to process packets faster в™¦ Better security в™¦ Pay more attention to Type of Service в™¦ Aid multicasting в™¦ Support roaming в™¦ Easier extension of the protocol в™¦ Coexistance with the old IPv4 Version: version of IP header Priority: 0в€’7 for non real time data, 8в€’15 for realв€’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 вЂў 1995 the IETF agreed to specification named IPv6 (RFC1883) в™¦ Changes to other protocols of the TCP/IP suite are specified in RFC 1884в€’1887 [ Details ] 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 вЂў Support of provider based addresses вЂў and geographic based addresses 4.3.3. IPv6 77 IPv6 Header IP Header Extension Hopв€’byв€’Hop options: Routing: Fragmentation: Authentication: Encryption security payload: Destination options: 78 IPv6 Further Topics Experimental IPv6 networks exist, see the JOIN project of the DFN вЂў extending the payload length, enabling datagrams of more than 65535 bytes (so called jumbograms) вЂў Information exchange between routers IPv6 is supported by most system software: AIX, BSD, HPв€’UX, Linux, Solaris, Windows To install the IPv6 Protocol for Windows XP: вЂў Full or partial routing path of a datagram at the command prompt, type: "ipv6 install" вЂў Similar to IPv4 fragmentation but fragmentation is handled only by endsystems Many topics are still discussed: в™¦ geo based IPv6 addresses в™¦ IPv6 over IPv4, IPv4 over IPv6, IPv6 to IPv4 (6to4) в™¦ renumbering в™¦ auto configuration в™¦ use of the flow label field в™¦ security в™¦ mobility в™¦ ... вЂў Identification of the sender вЂў Information about encrypted payload вЂў Information that should be interpreted by the destination only IP Header Extension 79 IPv6 Further Topics 80 QoS in Data Networks IP Service Models QoS Guarantees QoS Parameter Best Effort no DiffServ aggregated IntServ flow based no long term per flow static dynamic within a domain endв€’toв€’end Trafficв€’Engineering Concept MPLS flow based and aggregated support for: вЂў DiffServ вЂў IntServ вЂў ATM 4.3.4. Integrated Services (RFC 1633) Network Technology ATM flow based and aggregated per flow (channel) or per path dynamic or static What is a flow? вЂў A flow is a stream of packets originated from the same application session вЂў The term "flow" describes semantical coherence of data Categories of applications endв€’toв€’end or within a domain QoS in Data Networks Integrated Services (IntServ) is a reservation based model. The intention is to guarantee individual QoS profiles for each flow. вЂў Elastic applications, no delivery requirements as long as the packets reach the destination, e.g. TCP traffic (machine to machine) вЂў Real Time Tolerant (RTT) applications, demand weak bounds for the maximum transfer delay, also some packet loss is acceptable, e.g. streamed video (machine to human) вЂў Real Time Intolerant (RTI) applications, demand minimal delay and jitter, e.g. interactive application or videoconferences (human to human) 81 IntServ: Service Classes 4.3.4. Integrated Services (RFC 1633) 82 IntServ: Components Service Classes вЂў Guaranteed Service for RTI applications в™¦ Guaranteed amount of bandwidth в™¦ Deterministic upper bound for delay вЂў Controlled Load Service for RTT applications в™¦ Provides a service equivalent to an unloaded network в™¦ Most packets will reach the destination в™¦ The average delay is guaranteed вЂў Best Effort Service for all other applications в™¦ standard use of IP The Reservation Setup Agent is the only component that communicates with other nodes. The Resource Reservation Protocol (RSVP) was designed to meet the signaling requirements of IntServ. IntServ: Service Classes 83 IntServ: Components 84 IntServ: Packet Classifier IntServ: Packet Scheduler Packet Classifier: Packet Scheduler: вЂў The QoS capabilities of a Layerв€’2 network could be utilized to implement the packet scheduler functionality вЂў Manages access to the Layerв€’2 network in order to guarantee the requested QoS вЂў Some methods for the QoS implementation в™¦ Priority queuing (there is one queue for each QoS class) в™¦ Weighted fair queuing (place a packet within a queue depending on the QoS class) в™¦ Packet level traffic shaping (avoid peaks of traffic) вЂў Determines the QoS class for each packet вЂў May cooperate with routing mechanisms, packets of the same flow should always use the same path вЂў Arbitrary parts of the packet header may be used for classification в™¦ IPв€’addresses and port numbers of the sender and/or receiver в™¦ Application data like frame types of a video stream (e.g. MPEG) вЂў For IPv6 the flow label should be used Potential problems: Potential problems: вЂў IP fragmentation must be avoided (RSVP compute a minimum MTU for a multicast tree) вЂў Variable header length may require the interpretation of protocols вЂў IPв€’level security prevents access to higher layer protocols IntServ: Packet Classifier вЂў The IntServ model can not guarantee QoS if anywhere in the data path в™¦ a non IntServ capable router must be passed в™¦ a non QoS capable Layerв€’2 network must be shared with a non IntServ capable node 85 IntServ: Admission and Policy Control IntServ: Packet Scheduler 86 4.3.5. RSVP в€’ Ressource Reservation Protocol RFC 2210 Admission Control RSVP is a general signaling protocol for QoS control services вЂў resource management вЂў decides whether the local system is able to support the requested traffic flow вЂў The signaled objects are opaque for RSVP Policy Control A main focus of RSVP is to support multicast communication вЂў is optional вЂў determines whether the requester has administrative permissions to make the reservation вЂў Unicasts are treated as special cases of multicast only вЂў RSVP performs receiver oriented reservations в™¦ Support different requirements of many receivers в™¦ Support heterogeneous networks If either check fails the request is rejected, PDUs of that flow may be discarded or forwarded with a lower priority RSVP uses softв€’states, i.e. signaled information is valid for a fixed time interval only вЂў Simplifies cooperation with connection less IP вЂў Reservations must be refreshed periodically в™¦ Resource consuming в™¦ Prevents usage of RSVP in large networks Merging of reservation supports multiple senders in a multicast environment IntServ: Admission and Policy Control 87 4.3.5. RSVP в€’ Ressource Reservation ProtocolRFC 2210 88 RSVP Receiver oriented Reservation (1) RSVP Receiver oriented Reservation (2) A PATH message is sent from sender to receiver вЂў The sender specifies its traffic characteristic вЂў Detection of path characteristics в™¦ Detected bandwidth limitations, minimum packet size (MTU) в™¦ RSVP capable nodes get to know their RSVP capable neighbors вЂў RSVP does not perform routing; routing is done by standard components which do not know anything about QoS A RESV message is sent from receiver to sender вЂў The RESV message travels the path backward вЂў The receiver determines the required resource reservation в™¦ Traffic specification (Tspec) в™¦ Requested Service Specification (Rspec) RSVP Receiver oriented Reservation (1) 89 RSVP Reservation Types & Merging (1) RSVP Receiver oriented Reservation (2) 90 RSVP Reservation Types & Merging (2) Distinct Reservation (or Fixed Filter Style) Reservations are merged, dependent on their reservation type вЂў A receiver requests reservations for each sender вЂў Example: all senders send different types of data in parallel вЂў Example for distinct reservation: Shared Reservation вЂў Wild card Filter Type: в™¦ A receiver requests one reservation for all senders within a multicast tree в™¦ Senders may be added or removed without changing the reservations for the resource tree в™¦ Example: all senders require the same resources but not at the same time вЂў Shared Explicit Reservation: в™¦ A receiver requests one reservation for an explicit defined set of senders в™¦ Shared explicit reservation may be combined with distinct reservations RSVP Reservation Types & Merging (1) 91 RSVP Reservation Types & Merging (2) 92 4.3.6. Differentiated Services RFC 2475 DiffServ Domains Differentiated Services (DiffServ, DS) is a model to differentiate services on the Internet. Example: The key goals are: вЂў fast determination of a service class for a (IP) packet вЂў being scalable The key concepts are: вЂў traffic classification and service realization are separated вЂў each DiffServ domain has its own set of services вЂў traffic classification is done only at the border of a DiffServ domain вЂў assume that only a few different static services are required в™¦ it is sufficient to specify services in long term contracts в™¦ many flows will receive the same service, i.e. will share the resources of a service в™¦ admission and usage control is necessary in order to guarantee a specific QoS 4.3.6. Differentiated Services RFC 2475 SLA = Service Level Agreement, between user and provider Aggregation = all traffic flows that will receive the same service PHB = Per Hop Behaviour, is the externally observable forwarding behavior 93 DiffServ Domains DiffServ Codepoint RFC 2474 94 DiffServ Traffic Classification Within a DiffServ domain each packet is marked by a 6в€’bit codepoint. Logical view of packet classification and conditioning: All packets with the same codepoint build a so called "Behavior Aggregate" which is also called "Aggregate". IPv4: Classification: вЂў The Codepoint overwrites the TOS field in the IPv4 header вЂў Some routers use the precedent bits of the TOS field, therefore some DiffServ domains may use a limited Codepoint of 3 bits вЂў performed at ingress node вЂў depends on Service Level Agreement (SLA) between user and provider вЂў based on packet data or an already assigned codepoint IPv6: Meter: вЂў The Codepoint overwrites the priority field of the IPv6 header вЂў perform usage control according to a specified traffic profile (average bandwidth, peakв€’bandwidth, burstsizes, ...) Marker: вЂў assigns a 6в€’bit codepoint вЂў different codepoints may be assigned to "inв€’profile" and "outв€’ofв€’profile" packets Shaper/Droper: DiffServ Codepoint RFC 2474 95 DiffServ Traffic Classification 96 вЂў may delay or drop "outв€’ofв€’profile" packets (traffic conditioning) DiffServ Perв€’Hopв€’Behavior (1) The Perв€’Hopв€’Behavior (PHB) describes the service of a specific aggregate. вЂў DiffServ does not define a fixed set of parameters describing a PHB, i.e. DiffServ does not specifiy the service types which may be supported by a DiffServ domain (except the default PHB) вЂў A PHB is described by the externally observable forwarding behavior вЂў A PHB is identified by the codepoint of each IP packet PHBs may be specified by: вЂў ressource description (buffer usage, bandwidth, ...) вЂў priorities relative to other PHBs вЂў observable traffic characteristics (delay, loss, ...) вЂў Example: guarantee a minimal bandwidth allocation of X% of a link, with proportional fair sharing of any excess link capacity DiffServ Traffic Classification 97 DiffServ Perв€’Hopв€’Behavior (1) DiffServ Perв€’Hopв€’Behavior (2) 98 4.3.7. Multiprotocol Label Switching (MPLS) RFC 3031 Suggested PHB types: MPLS is a trafficв€’engineering model вЂў default PHB, standard IP service = bestв€’effort service codepoint: 000000 Goal: вЂў Classв€’Selector PHB, provides backward compatibility to IPv4 precedent bits codepoint: xxx000, x = 0 or 1 вЂў replace complex routing decisions by much more simpler packet forwarding (switching) technologies вЂў Assured Forwarding PHB (RFC 2597), defines four traffic classes and three drop precedence per class. According to the SLA buffer and bandwidth ressources will be assigned to each class. Outв€’ofв€’Profile traffic may be marked with a higher drop precedence Drop Precedence Class 1 Class 2 Class 3 Class 4 Low drop precedence 001010 010010 011010 100010 Medium drop precedence 001100 010100 011100 100100 High drop precedence 001110 010110 011110 100110 Basic concepts: вЂў assume that there are many packets in a network domain that will be treated in an equivalent manner equivalence = the packets leave the domain at the same (logical) link (and the packets receive the same QoS) вЂў classify packets at the domain borders, i.e. assign a packet to a Forward Equivalence Class (FEC) вЂў packets of the same FEC are marked with a label, within a MPLS domain packets may be forwarded (switched) based on that label. вЂў Note: conventional routing is like assigning a packet to an FEC in each router вЂў Expedited Forwarding PHB (RFC 2598), guarantees a specified bandwidth (according to the SLA) codepoint 101110 DiffServ Perв€’Hopв€’Behavior (2) 99 4.3.7. Multiprotocol Label Switching(MPLS) RFC 3031 100 MPLS Example MPLS Label Encoding A label is a short fixed length locally significant identifier for an FEC. For most Layerв€’3 technologies the label is encoded in a so called Shimв€’Header: exp = experimental, suggestion: use as a diffserv 3в€’bit codepoint s = 1 в€’> bottom of stack ttl = time to live Insert Header in Ethernet Frame: Use VPI/VCI field of ATM for MPLS label LSR FEC = Label Switching Router = Forwarding Equivalence Class MPLS Example 101 MPLS Label Assignment & Distribution MPLS Label Encoding 102 MPLS Label Stack Example Use of downstream label assignment: Example, assume the following label bindings: For FEC 1 and FEC 2: Label L1 between, LSR7 and LSR 6, LSR 6 and LSR4, LSR4 and LSR3 Label distribution is done by modified routing protocols or with a special Label Distribution Protocol (LDP) Example: For FEC 1: Label L6 between LSR3 and LSR2 Label L9 between LSR2 and LSR1 LSR 3 may inform LSR 2 to use Label "L6" for all packets with an IP destination address of 131.x.x.x LSR 2 may choose to use the same or another label for the link between LSR1 and LSR 2 What happens when a packet is traveling from LSR1 to LSR7: LSR1: assign packet to FEC 1 = push label "L9" on Stack LSR2: swap label "L9" to "L6" and forward packet to LSR3 LSR3: swap label "L6" to "L1" and forward packet to LSR4 LSR4: swap label "L1" to "L1" push a label "x" of the MPLS domain 2 on stack and MPLS Label Assignment & Distribution 103 MPLS Label Stack Example 104 forward the packet to LSR 8 or 9 of domain 2 ... the apcket travels within domain 2 to LSR 6 ... LSR6: pop label "x" swap label "L1" to "L1" and foward packet to LSR 7 LSR7: pop label "L1" and route packet based on IP addresses MPLS Remarks MPLS was not designed to support any QoS. Identification of flows or "traffic aggregates" makes QoS implementation much easier. MPLS may support QoS by вЂў supporting DiffServ вЂў utilizing ATM for IP traffic вЂў extend label distribution with qoS parameters Advantages of MPLS вЂў connection setup or connection release is not required вЂў is limited by domains, i.e. networks belonging to different administrative domains do not need to cooperate. Therefore MPLS may be utilized in parts of a network only, e.g. WAN or backbones вЂў MPLS is protocol independent MPLS Label Stack Example 105 4.3.8. RTP в€’ Realв€’Time Transport Protocol RFC 1889 MPLS Remarks 106 RTP в€’ Scenario Consists of two closelyв€’linked parts: вЂў the realв€’time transport protocol (RTP), carries data with realв€’time properties вЂў 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 вЂў a profile specification defines payload types and may extend RTP вЂў a payload specification defines payload formats and encoding types must be specified вЂў therefore RTP will typically be part of an application manyв€’toв€’many communication (e.g. video conference) 4.3.8. RTP в€’ Realв€’Time Transport ProtocolRFC 1889 107 RTP в€’ Scenario 108 RTP в€’ Definitions RTP в€’ Header RTPв€’Session: вЂў is a set of participants вЂў each participant is identified by a host and a destination port address вЂў each medium is carried in a separate RTPв€’session Mixer: вЂў is an intermediate system that receives data from one or more sources, possibly changes the data format and combines packets in some manner вЂў a mixer will make timing adjustments and generate an own timing for combined data вЂў the payload type is defined by the applications profile вЂў the sequence number enables receivers to detect lost RTPв€’PDUs вЂў the timestamp reflects a sampling instant. i.e. the timestamp unit depends on the encoding and does not need to correspond with the system clock вЂў SSRC identifies the last sync. entity; it is unique within a session вЂў CCSR identifies the contributor of a source Translator: вЂў is an intermediate system that forwards data without changing media or synchronization вЂў encryption and addresses may be changed вЂў multicast may be mapped to unicast and vice versa RTP в€’ Definitions 109 RTP в€’ Header RTCP в€’ RTP Control Protocol 110 Interesting Links RTP enables receiver to monitor the QoS: Routing Basics http://www.cisco.com/univercd/cc/td/doc/cisintwk/ito_doc/routing.htm вЂў Delay, jitter, PDU loss rate Size of BGB Tables http://bgp.potaroo.net/ RTCP periodically transmits control packets between all participants of an RTP session: вЂў the primary function is to provide feedback about the QoS вЂў carries transportв€’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) вЂў the rate of sent RTCP packets depends on the number of participants in order to make RTCP scalable вЂў optionally, further information about the participants could be distributed to realize a simple session control Internetworking Technology Handbook http://www.cisco.com/univercd/cc/td/doc/cisintwk/ito_doc/ Its Latency http://www.potaroo.net/papers/isoc/2004в€’01/latency.html TCP в€’ How it works http://www.potaroo.net/papers/isoc/2004в€’07/tcp1.html Visualroute http://www.webhits.de/english/index.shtml?visualroute.html RTCP в€’ RTP Control Protocol 111 Interesting Links 112