Multimedia Systems 2010/2011

Transcription

1 Multimedia Systems 2010/2011 Networks Prof. Dr. Paul Müller University of Kaiserslautern Department of Computer Science Integrated Communication Systems ICSY

2 Sitemap 2

3 Outline Network basics for Multimedia Data Network Types and Services Switching ISO/OSI Reference Model Network QoS Mechanisms Network Technologies Considered for Multimedia Ethernet ISDN ATM Internet Access Technologies Protocols Considered for Multimedia IP Integrated Services Resource Reservation Protocol Differentiated Services Multiprotocol Label Switching Real-Time Transport Protocol 3

4 Network basics for Multimedia Data Network types Switching concepts ISO/OSI model Layer Description Terminology Mechanisms for Network QoS 4

5 Network Types and Services (1) Network Services Physical Type Telephone Voice (1:1 and 1:n), Fax, Video, Text, Data,... cable (copper, fiber) wireless, satellite Telephone (mobile) Voice, Fax, Text, Data,... wireless + cable Internet Data, Text, Voice, Audio, Video,... Intranet Data, Text, Voice, Audio, Video,... cable (copper, fiber), wireless, satellite cable (copper, fiber), wireless Cable TV Video, Audio, Videotext, Data cable (copper) Satellite TV Video, Audio, Videotext satellite Broadcast TV Video, Audio, Videotext wireless Broadcast Radio Audio, Text wireless 5

6 Network Types and Services (2) Additionally very specialized Networks: Bank connections Controlling (traffic, machines, in house systems,...) Supervising (alarm systems, gas pipes, street lights,...) 6

7 Size versus Time of Transmission 7

8 Circuit Switching Provide a "physical" link: connection A, B established connection C, B blocked Advantages: guaranteed bandwidth and delay worldwide available Disadvantages: bandwidth not scalable bad efficiency (bandwidth usage) 8

9 Packet Switching Handle independent packages: A+C sending packages of different size to B Packet may get lost because of congestion Advantages: high efficiency (bandwidth usage) bandwidth is scalable Disadvantages: no guaranteed delay (bandwidth) 9

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. Advantages: high efficiency (bandwidth usage) bandwidth is scalable guaranteed bandwidth and delay Disadvantages: rare availability 10

11 ISO / OSI Reference Model (1) 11

12 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. (3) The network layer defines how data 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. 12

13 ISO / OSI Reference Model (3) (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). 13

14 Layer 1 Data Types electrical or optical signals Devices Repeater Hub extends physical segments to logical segments boosts electrical or optical signals is a multiport repeater is a shared medium like a bus Connectivity 14

15 Layer 2 (1) Data Types frames Devices Bridge connects logical segments to broadcast domains provides connectivity on layer 2 by forwarding frames between two logical segments a frame will be forwarded if the receiver resides on the other segment the receiver's location is unknown the destination address is a broadcast address needs information about directly connected network segments only automatically collects layer 2 addresses to be able to make forwarding decision 15

16 Layer 2 (2) Devices Switch is a multi-port bridge provides dedicated connections between all ports, i.e. does not realize a shared medium Connectivity 16

17 Layer 3 (1) Data Types packets Devices provides connectivity on layer 3, by interpreting packets and making routing decisions a router port is an endpoint of a network segment may connect different types of layer 2 networks needs information about the whole network topology receives external information to make a routing decision static information may be configured by an administrator dynamic information may be collected by routing protocols 17

18 Layer 3 (2) Connectivity 18

19 Layer 4-7 Data Types protocol data arbitrary application specific data Applications Client Process requests some information receives payload Server Process waiting for information requests sends payload One process may be client and server on different levels (e.g. FTP) Connectivity on the same levels (e.g. peer-to-peer protocols) 19

20 Terminology (1) Data types: layer 1: signals layer 2: frames layer 3: packets Repeating: boosting electrical or optical signals Forwarding: is the task of moving a frame or packet from one interface (or port) to another interface Bridging or switching: depending on layer 2 addresses deciding whether a frame needs to be forwarded, identifying the output port and performing the forwarding bridging/switching is a layer 2 functionality 20

21 Terminology (2) Routing: depending on layer 3 addresses and routing information deciding to which output port a packet needs to be forwarded and performing the forwarding forwarding a packet includes the generation of a new frame routing is a layer 3 functionality Combined devices: switching-hubs oder route-switches denote combined devices 21

22 Topologies (1) Complete mesh: ideal performance high reliability only for networks with small expansion connections Ring: reliability absorb drop out of one link easier cabling n connections Star: reliability drop out of one link affects a single endsystem only node in the middle is single point of failure complex cabling for large extent networks n connections 22

23 Topologies (2) Combination: Tree: large networks often combine different topologies Example: the B-WIN network of the DFN (Deutsches Forschungsnetz) uses a combination of ring and star topology is a combination of star topologies Irregular: some applications may require specialized topologies 23

24 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 24

25 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 classbased) 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 25

26 Shaping vs Policing (image source: Cisco.com) shaping: keep a traffic characteristic, increases delay! policing: monitor the traffic characteristic, increases loss rate! 26

27 Leaky Bucket (Shaping) 27

28 Token Bucket (Policing) 28

29 Shaping vs Policing ideal: shaping at client side, policing at provider side usually both done by provider Several instances enable control of multiple traffic parameters Example: 1. Token Bucket: average rate 2. Leaky Bucket: peak rate it's not necessary to drop non conforming packets, these may be marked and dropped preferably in case of high load assigned to a class with lower priority 29

30 Packet Scheduling / Queuing 1 FIFO best effort service only prior admission control and policing may improve fairness 30

31 Packet Scheduling / Queuing 2 (Strict) Priority Queuing different services according to bandwidth and delay unfair, because starvation of low priority flows possible 31

32 Packet Scheduling / Queuing 3 Weighted Fair Queuing (WFQ) each queue receives a portion of the available bandwidth resources round robin according to weight of queues, guarantees fairness 32

33 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 also 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 33

34 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. 34

35 4.2. 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 35

36 Ethernet History: Xerox Corp.: R. Metcalfe (PHD at the M.I.T.) and D. Boggs Standardized by IEEE there are vendor specific Ethernet variants, e.g. Ethernet V2 The original article from Robert M. Metcalfe and David R. Boggs Xerox Palo Alto Research Center 36

37 Ethernet Characteristics: Bus topology Several physical media: coax cable, twisted-pair, fiber Bus characteristics: max. segment size min. distance between nodes Repeater/Hub/Switches for longer distances access protocol CSMA/CD (Carrier Sense Multiple Access with Collision Detection) 37

38 Ethernet: CSMA/CD Protocol (1) 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 CSMA/CD is a medium access (MAC) protocol A shard medium provides half-duplex communication (HDX) only Collisions are not errors, they are part of the distributed channel arbitration mechanism 38

39 Ethernet: CSMA/CD Protocol (2) 39

40 Ethernet: CSMA/CD Protocol (3) 1. Station A determines there is no data on the bus and starts sending data. 2. Before the data of A has arrived at station B, station B has determined there is no data on the bus and starts sending data also, leading to a collision. 3. The scrambled data spreads over the bus, station B recognizes the collision. 4. After recognizing the collision station B must send a jam signal with a length equal to 32 bits. 5. Station A recognizes the collision when the scrambled data arrives at station A or at least when the jam signal arrives, station A sends a jam signal also. 6. The bus is empty after some waiting time. A station must continuously send data for at least twice the network transit delay of the signal in order to recognize a collision. Since the transmission speed is fixed the station must send a sufficient number of bits. 40

41 100 Mbit/s Ethernet 100 Mbit/s Ethernet New physical layers 100 Base-TX (802.3u) max length 100 m 100 Base-T4 (802.3u) max. length 100 m 100 Base-T2 (802.3y) max. length 100 m (no fullduplex mode) 100 Base-FX (802.3u) max. length 150m - 10km The slot time is still 64 bytes the physical network must be much smaller, e.g. max of 205m for coax cable no problem when using star topology with switches and 100m twisted pair cables 41

42 New Features (1) full duplex mode (FDX) peer-to-peer only no CSMA/CD lower delay and jitter auto-negotiation of bandwidth and HDX/FDX mode by modified and backward compatible link integrity pulses 100 Mbit/s device changes to 10 Mbit/s if receiving old integrity pulses flow control with CSMA/CD a switch could send jam signals reducing traffic at an ingress port with FDX a PAUSE frame is defined the receiver of a PAUSE frame has to slow down uses a special multicast address is not forwarded by the receiver 42

43 Gigabit Ethernet 1 Gbit/s Ethernet 1 Gbit/s over category 5 cables is specified problems with crosstalk may still occur special testing is required several new physical layers with single mode fiber distances of up to 5 km are possible slot time is extended to 512 bytes for HDX mode (which requires CSMA/CD) if necessary a frame extension (null-data) is added after the CRC with 64 byte packets a throughput of only around 100 Mbit/s could be achieved frame bursting defines the concatenation of frames for HDX Gigabit Ethernet to improve performance a burst must not exceed bit frames are separated by special signals 43

44 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 44

45 ISDN: 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 45

46 ISDN: Interfaces ISDN User Interfaces Basic Rate Interface 2 data channels (B channel) with 64 Kbit/s 1 signaling channel (D channel) with 16 Kbit/s Primary Rate Interface: 30 data channels (B channel) with each 64 Kbit/s in Europe 1 signaling channel (D channel) with 64 Kbit/s ISDN Protocol Reference Model Extensions to ISO/OSI: User plane: for user data Control plane: for connection management Packet oriented D channel signaling Channels: A - 4kHz analog B - 64 Kbps digital PCM C - 8 or 16 Kbps digital D - 16 or 64 Kbps digital signaling E - 64 Kbps digital internal signaling H - 384, 1536 or 1920 Kbps digital 46

47 ISDN: Topology + Interfaces Star topology, different technologies in LAN and WAN Formats are defined for Interfaces only Interfaces are described as reference points 47

48 ISDN: Network Access Time Division Multiplexing maps several 64 Kbps channels to one faster channel A frame consists of a header and a fixed number of slots A frame is generated each 125 micro-sec The slot size is 8 bit During signaling a fixed mapping between channels and slot numbers is defined; this is called Synchronous Time Division Multiplexing (STDM) The mapping is valid for two adjacent devices only Technology: Synchronous Digital Hierarchy (SDH) or SONET 48

49 ISDN: Addresses Defined by the ITU in E.164 Format: Prefixes are not part of the number (the prefix in Germany is 0 ) Digits are represented as binary coded decimals (BCD) 8 bytes are used to represent 15 digits Example: is used in Germany to identify an international number 49 is the country code for Germany 631 is the area code for Kaiserslautern 205 is the subscriber number of the university 2263 is a sub address (called "extension"), it is used within a private network only 49

50 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) 50

51 B-ISDN (Broadband ISDN) / ATM Standardization: ITU recommendations (former CCITT) ATM Forum (organization of vendors, specifications only) Characteristics: For LAN and WAN networks For private and public networks Support of fine granular Quality of Service Suitable for all media types Low and high bandwidth is supported Connection oriented Technology: Cell Switching ATM Asynchronous Transfer Mode 51

52 4.2.4 ATM = Asynchronous Transfer Mode Reference Model According to ITU-T Recommendation I.113 asynchronous means: "... it is asynchronous in the sense that the recurrence of cells containing information from an individual user is not necessarily periodic." (I113) Higher layer provide end-to-end services ATM Adaption Layer (AAL): adaption of service data to cells (48 bytes) 53 byte cells handled by ATM Layer: 5 byte header (VPI, VCI, HEC) switching/multiplexing of cells 52

53 ATM Layer Overview Examples: 53

54 ATM: Traffic Contract No error detection and correction, but mechanisms to guarantee Quality of Service 54

55 ATM: Service Categories 1 55

56 ATM: Service Categories 2 Distribution of bandwidth CBR: constant bit rate VBR: variable bit rate, i.e. constant bandwidth up to SCR for a short time (max. burst size) more bandwidth usage up to PCR is possible ABR: available bit rate, i.e. network provides feedback of bandwidth available UBR: unspecified bit rate, i.e. best-effort SCR = sustainable cell rate, PCR = peak cell rate, MBS = maximum burst size duration of a burst: (MBS-1)/PCR; time between two bursts: MBS/SCR 56

57 Quality of Service Parameter QoS Acronym Parameter Name Negotiated? peak-to-peak Cell Delay Variation YES maxctd max. Cell Transfer Delay YES CLR Cell Loss Ratio YES CER Cell Error Ratio NO SECBR Severely Errored Cell Block Ratio NO CMR Cell Misinsertion Rate NO Probability for exceeding maxctd must be less than CLR 57

58 ATM: Network Access ATM = "Asynchronous Transfer Mode" because the "Asynchronous Time Division Multiplexing" (ATDM) is used STDM uses slots; ATDM uses cells The sequence of the cells on a link is not fixed (asynchronous) A sender defines a useful sequence Enables arbitrary bandwidth for each connection High efficiency because no empty cells must be sent if no data is available Reservation of bandwidth can be handled by the cell multiplexer Each cell has a header identifying the connection a cell belongs to 58

59 ATM: Cells Cells are packets of a constant size Simplifies scheduling of the multiplexer Small size enables low delay even on low bandwidth links Overhead of cell header ~9,43% Cell header Basically: identifier of the connection VPI = Virtual Path Identifier VCI = Virtual Channel Identifier Payload type Label data or management information Cell loss priority In case of congestion drop cells with CLP=1 first Header Error Control CRC for the first 4 header bytes 59

60 ATM: Virtual Path/Circuit ATM is connection oriented Links: Virtual paths (VP) build a logical topology on top of the physical topology Virtual Circuits Channels(VC) are connections on virtual paths Physical link: connects two physical devices Virtual Circuit Channel: connects two end-systems Virtual Path: link <= path <= circuit Connections may be point-to-point (full-duplex) point-to-multipoint (half-duplex) VPs are static = permanent virtual path (PVP) VCs may be static or dynamic = permanent or switched virtual channel (PVC/SVC) 60

61 ATM: Characteristics of VC/VP Logical association between the endpoints of a link (individual link) Virtual Channel Characteristics: Bi-directional data transfer Guaranteed sequential delivery Error detection by HEC and correction of single bit errors QoS characteristic associated with each virtual channel connection and with each direction of a channel Virtual Path Characteristics : Route through a network Carries various VCs VP also has a QoS (the limit for all VCs) 61

62 ATM: Path switching Switching with regard to VPI only VCI are left unchanged 62

63 ATM: Circuit Switching Switching with regard to VPI and VCI If the VCI is used for switching, this means the VP ends at that switch VCs of one path could be spread over several new paths 63

64 ATM: Switching Table 64

65 ATM: Usability for Multimedia Data QoS parameters: Isochronism: is available guaranteed bandwidth (fixed, variable, feedback) low delay and low delay variation (not guaranteed) Multicast capability: uni-directional point-to-multipoint is available Flexibility: bandwidth on demand, limited by physical links and actual system load several traffic types CBR, RT-VBR, NRT-VBR, ABR and UBR independent of physical media mainly used for WAN or in LAN for backbones, ATM to the desktop was available but was too expensive to be accepted widely Efficiency: high bandwidth utilization statistical multiplexing increases utilization, VBR channels: SUM of "sustained cell rates" must be <= 100% SUM of "peak cell rates may be > 100% Costs: a complex and therefore an expensive technology 65

66 Evolution of Internet Access Technologies Success of multimedia systems requires for many services a broadband Internet connection. Economic requirement: Connect consumers costeffectively -- at home and mobile 80's 90's 200x analog access emerging: WiMAX future: ISDN, GSM (GPRS et al.) xdsl (>160Kbit/s), cable, powerline, satellite, WLAN (hot-spots), UMTS 4th generation wireless networks, fiber-to-the-home (FTTH) 66

67 Criteria for Internet Access Technologies A variety of technologies exist for realizing Internet access for devices Classification of technologies possible by means of throughput mobility area coverage / availability effort / costs 67

68 Development of Mobile Technologies GSM to UMTS development: increasing bandwidths 68

69 UMTS Services and Applications Anywhere-anytime communication Multimedia services Telephony Video conferencing Entertainment (interactive gaming, music on demand, video streaming, etc.) Personal Services Remote monitoring and control (e.g. of the home) Mobile banking Location-based services What movies are playing here? Where is the next Italian restaurant Mobile Internet access 69

70 UMTS Requirements and Challenges Global access using a single device Global standard Unified spectrum High coverage Seamless handover Support of multimedia services High data rates Variable bandwidths Symmetrical and asymmetrical data transfer Circuit-switched and packetswitched transfer High speech (and multimedia) quality Extendable multi-service network Easy to deploy new services Convergence of telephony and Internet services Operator services Tight control over network resources by network operator Sophisticated charging functionality Backward compatibility to 2G systems(gsm) 70

71 4.3. Protocols (Layer 3-7) 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 (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 71

72 TCP/IP Suite 72

73 IP Protocol (RFC 791) 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) 73

74 IP Header Version: version of IP header IHL: TOS: Length: ID: 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 length in bytes including the IP header serial number Flags, Frag. Offset: used for fragmentation TTL: Time To Live decremented by each machine to pass t Protocol: layer 4 protocol, e.g. 1=ICMP, 6=TCP, 17=UDP he packet Checksum: checksum for the IP header Options: security, record route, timestamp, source routes 74

75 IP Address Classes An IP address is a unique identifier for an end system Each address consists of two parts (hierarchy levels): a network address a host address Usage of classes is out-dated 75

76 IP Addresses and Netmasking Classless inter-domain routing (CIDR) Different network masks enable multiple level of hierarchies Prefix notation: IP-Address/n n = number of bits used for netmask Example: /24 IP Address: dotted decimal format 83 F hexadecimal format binary format Netmask: binary format FF FF F8. 0 hexadecimal format dotted decimal format 76

77 Routing Routers are used to connect networks Routing: making a local forwarding decision based on global topology information, this decision must take into account QoS guarantees / assurances How to obtain topology information: Default routing Static or non adaptive routing Does not take into account changes of the network Dynamic or adaptive routing, requires routing protocols Identifies the topology of the network automatically Different metrics are used to describe distances Number of hops Available bandwidth Error rates 77

78 Routing Hierarchy Interior Gateway Protocol (IGP) Routing within a LAN or administrative domain Each node may know the whole (local) topology Examples: Routing Information Protocol (RIP), IGRP, OSPF Exterior Gateway Protocol (EGP) Between Service Providers (ISPs), e.g. Example: Border Gateway Protocol (BGP), may be used exterior (EBGP) and interior (IBGP) Routing Protocol types Distance-Vector: distribute local routing table to all neighbors. The paths with the lowest advertised costs are added to the local routing table (routing bassed on "direction signs") Link-State: each router maintains at least a partial map of the network topology. Changes of a link state are flooded through the network (routing bassed on (partial) topology "maps"). 78

79 UDP (RFC 768) / TCP (RFC 793) 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: segment 79

80 UDP Header Source Port, Destination Port: port number of sender and receiver 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: 2*4 byte IP source and destination address 1 byte 0 1 byte protocol 2 byte IP header length 80

81 TCP Header Source Port, Destination Port: port number of sender and receiver 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: urgent pointer is valid ack: ack number is valid psh: push data to level above rst: reset connection syn: synchronize seq. Number fin: close this side of the connection Window: amount of data the sender is willing to accept (flow control) Urgent Pointer: points to last byte of urgent data Options: e.g. maximum segment size 81

82 TCP Service Mechanisms Retransmission default: Go-back-n strategy, simple and robust mechanism but resource consuming widely used: selective acknowledgement, retransmit lost packet 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 [TCP Summary] [TCP High Performance issues] 82

83 IPv6 Development of IPv 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 Coexistence with the old IPv the IETF agreed to specification named IPv6 (RFC1883) Changes to other protocols of the TCP/IP suite are specified in RFC

84 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 84

85 IP Header Extension Hop-by-Hop options: For example: extending the payload length, enabling datagrams of more than bytes (so called jumbograms) or exchange information between routers Routing: Full or partial routing path of a datagram Fragmentation: Similar to IPv4 fragmentation but fragmentation is handled only by endsystems Authentication: Identification of the sender Encryption security payload: Information about encrypted payload Destination options: Information that should be interpreted by the destination only 85

86 IPv6 Further Topics Experimental IPv6 networks exist, see the JOIN project of the DFN IPv6 is supported by most system software: AIX, BSD, HP-UX, Linux, Solaris, Windows To install the IPv6 Protocol for Windows XP: at the command prompt, type: "ipv6 install" Many topics are still discussed: geo based IPv6 addresses IPv6 over IPv4, IPv4 over IPv6, IPv6 to IPv4 (6to4) renumbering auto configuration use of the flow label field security mobility... 86

87 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 87

88 Integrated Services (RFC 1633) Integrated Services (IntServ) is a reservation based model. The intention is to guarantee individual QoS profiles for each flow. What is a flow? A flow is a stream of packets originated from the same application session The term "flow" describes semantically coherence of data Categories of applications Elastic applications, no delivery requirements as long as the packets reach the destination, e.g. TCP traffic (machine to machine) 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) Real Time Intolerant (RTI) applications, demand minimal delay and jitter, e.g. interactive application or videoconferences (human to human) 88

89 IntServ: Service Classes Service Classes Guaranteed Service for RTI applications Guaranteed amount of bandwidth Deterministic upper bound for delay Controlled Load Service for RTT applications Provides a service equivalent to an unloaded network Most packets will reach the destination The average delay is guaranteed Best Effort Service for all other applications standard use of IP 89

90 IntServ: Components 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. 90

91 IntServ: Packet Classifier Packet Classifier: Determines the QoS class for each packet May cooperate with routing mechanisms, packets of the same flow should always use the same path Arbitrary parts of the packet header may be used for classification IP-addresses and port numbers of the sender and/or receiver Application data like frame types of a video stream (e.g. MPEG) For IPv6 the flow label should be used Potential problems: IP fragmentation must be avoided (RSVP compute a minimum MTU for a multicast tree) Variable header length may require the interpretation of protocols IP-level security prevents access to higher layer protocols 91

92 IntServ: Packet Scheduler Packet Scheduler: The QoS capabilities of a Layer-2 network could be utilized to implement the packet scheduler functionality Manages access to the Layer-2 network in order to guarantee the requested QoS Some methods for the QoS implementation Priority queuing Weighted fair queuing Packet level traffic shaping Potential problems: The IntServ model can not guarantee QoS if anywhere in the data path a non IntServ capable router must be passed a non QoS capable Layer-2 network must be shared with a non IntServ capable node 92

93 IntServ: Admission and Policy Control Admission Control resource management decides whether the local system is able to support the requested traffic flow Policy Control is optional determines whether the requester has administrative permissions to make the reservation If either check fails the request is rejected, PDUs of that flow may be discarded or forwarded with a lower priority 93

94 RSVP - Resource Reservation Protocol (RFC 2210) RSVP is a general signaling protocol for QoS control services The signaled objects are opaque for RSVP A main focus of RSVP is to support multicast communication Unicasts are treated as special cases of multicast only RSVP performs receiver oriented reservations Support different requirements of many receivers Support heterogeneous networks RSVP uses soft-states, i.e. signaled information is valid for a fixed time interval only Simplifies cooperation with connection less IP Reservations must be refreshed periodically Resource consuming Prevents usage of RSVP in large networks Merging of reservation supports multiple senders in a multicast environment 94

95 RSVP Receiver oriented Reservation (1) RSVP implements hybrid negotiation 95

96 RSVP Receiver oriented Reservation (2) A PATH message is sent from sender to receiver The sender specifies its traffic specification (sender TSpec) The sender specifies its traffic characteristic (ADSPEC) Detection of path characteristics Detected bandwidth limitations, minimum packet size (MTU), may modify ADSPEC RSVP capable nodes get to know their RSVP capable neighbors 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 The RESV message travels the path backward, perform reservations The receiver application determines the required resource reservation and replies with Traffic specification (receiver Tspec) Requested Service Specification (receiver Rspec) 96

97 Differentiated Services RFC 2475 Differentiated Services (DiffServ, DS) is a model to differentiate services on the Internet. The key goals are: fast determination of a service class for a (IP) packet being scalable The key concepts are: traffic classification and service realization are separated each DiffServ domain has its own set of services traffic classification is done only at the border of a DiffServ domain assume that only a few different static services are required it is sufficient to specify services in long term contracts many flows will receive the same service, i.e. will share the resources of a service admission and usage control is necessary in order to guarantee a specific QoS 97

98 DiffServ Domains Example: 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 98

99 DiffServ Codepoint RFC 2474 Within a DiffServ domain each packet is marked by a 6-bit codepoint. All packets with the same codepoint build a so called "Behavior Aggregate" which is also called "Aggregate". IPv4: The Codepoint overwrites the TOS field in the IPv4 header Some routers use the precedent bits of the TOS field, therefore some DiffServ domains may use a limited Codepoint of 3 bits IPv6: The Codepoint overwrites the priority field of the IPv6 header 99

100 DiffServ Traffic Classification Logical view of packet classification and conditioning: Classification: Meter: performed at ingress node depends on Service Level Agreement (SLA) between user and provider based on packet data or an already assigned codepoint perform policing according to a specified traffic profile (average bandwidth, peakbandwidth, burstsizes,...) Marker: assigns a 6-bit codepoint different codepoints may be assigned to "in-profile" and "out-of-profile" packets Shaper/Droper: may delay or drop "out-of-profile" packets (traffic conditioning) 100

101 DiffServ Per-Hop-Behavior (1) The Per-Hop-Behavior (PHB) describes the service of a specific aggregate. 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) A PHB is described by the externally observable forwarding behavior A PHB is identified by the codepoint of each IP packet PHBs may be specified by: resource description (buffer usage, bandwidth,...) priorities relative to other PHBs observable traffic characteristics (delay, loss,...) Example: guarantee a minimal bandwidth allocation of X% of a link, with proportional fair sharing of any excess link capacity 101

102 DiffServ Per-Hop-Behavior (2) Suggested PHB types: default PHB, standard IP service = best-effort service codepoint: Class-Selector PHB, provides backward compatibility to IPv4 precedent bits codepoint: xxx000, x = 0 or 1 Assured Forwarding PHB (RFC 2597), defines four traffic classes and three drop precedence per class. According to the SLA buffer and bandwidth resources will be assigned to each class. Out-of- Profile traffic may be marked with a higher drop precedence Drop Precedence Class 1 Class 2 Class 3 Class 4 Low drop precedence Medium drop precedence High drop precedence Expedited Forwarding PHB (RFC 2598), guarantees a specified bandwidth (according to the SLA) codepoint

103 Multiprotocol Label Switching (MPLS) RFC 3031 MPLS is a traffic-engineering model Main goals: replace complex routing decisions by much more simpler packet forwarding (switching) technologies enable traffic engineering, i.e. explicit control of data flows separate signaling and data flow interact with existing: routing protocols, L2 and L3 protocols and QoS capabilities Basic concepts: 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) classify packets at the domain borders, i.e. assign a packet to a Forward Equivalence Class (FEC) packets of the same FEC are marked with a label, within a MPLS domain packets may be forwarded (switched) based on that label. Note: conventional routing is like assigning a packet to an FEC in each router 103

104 MPLS Example LER = Label Edge Router: add and remove labels LSR = Label Switching Router: forward packets based on labels FEC = Forwarding Equivalence Class 104

105 MPLS Label Encoding A label is a short fixed length locally significant identifier for an FEC. For most Layer-3 technologies the label is encoded in a so called Shim-Header: Lable (20 bit) = the identifier of an FEC Exp (3 bit) = experimental, suggestion: use as a diffserv 3-bit codepoint S (1 bit) = marker for last lable on stack TTL (8 bit) = time to live, copied from higher layer protocols, e.g. IP 105

106 MPLS Label Placement Insert Header in Ethernet Frame: Multiple lables are stacked: Use VPI/VCI field of ATM for MPLS label: 106

107 MPLS and QoS MPLS lables can be mapped to ATM cell headers. ATM can be integrated in an MPLS environment and the ATM QoS capabilities can be utilized for FECs MPLS is able to offer services similar to IntServ and can even interact with IntServ Contraint-based routing-ldp (CR-LDP), extends the LDP by resource reservation request, which is similar to ATM VBR QoS Traffic characteristic specification RSVP-TE, extends the RSVP protocol by lable distribution for MPLS. Thus it is possible to request a resource reservation within an MPLS domain in the same way as in an IntServ environment MPLS lables can be used to support DiffServ The 3-bit "extension field" of the MPLS lable can be used to differentiate 8 DiffServ classes Portions of the MPLS lable can be used/mapped to a DiffServ codepoint 107

108 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 supporting DiffServ utilizing ATM for IP traffic request resource reservation for each FEC, by extending label distribution with qos parameters (RSVP-TE or CR-LDP) Advantages of MPLS connection setup or connection release is not required 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 MPLS is protocol independent 108

109 RTP - Real-Time Transport Protocol (RFC 1889) 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 109

110 RTP - Scenario many-to-many communication (e.g. video conference) 110

111 RTP - Definitions RTP-Session: Mixer: is a set of participants each participant is identified by a host and a destination port address each medium is carried in a separate RTP-session is an intermediate system that receives data from one or more sources, possibly changes the data format and combines packets in some manner a mixer will make timing adjustments and generate an own timing for combined data Translator: is an intermediate system that forwards data without changing media or synchronization encryption and addresses may be changed multicast may be mapped to unicast and vice versa 111

112 RTP - Header the payload type is defined by the applications profile the sequence number enables receivers to detect lost RTP-PDUs 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 SSRC identifies the last sync. entity; it is unique within a session CCSR identifies the contributor of a source 112

113 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 113

114 Interesting Links Routing Basics dbook/routing-basics.html Size of BGB Tables Internetworking Technology Handbook dbook/ito_doc.html Its Latency TCP - How it works Visualroute 114

115 Prof. Dr. Paul Müller Integrated Communication Systems ICSY University of Kaiserslautern Department of Computer Science P.O. Box 3049 D Kaiserslautern Phone: +49(0)