1. 1 Multimedia Services in the Internet Dorgham Sisalem / Sven Ehlert FhG Fokus sisalem@fokus.fhg.de sip:sisalem@iptel.org

2. 2 Lecture Overview Introduction to the Course –Goals –Administrative Stuff –Topics covered Basic Networking Principles Refresh –PSTN –IP Networking –Routing

3. 3GoalsGoals Overview of multimedia service (SIP) Understanding of multimedia services in the Internet Understanding of the general pictures –Transport protocols, signaling, traffic types, QoS Practical experience with protocols and applications Basic knowledge of the different involved protocols and concepts We are not dealing with: –Audio and video compression –Web programming –Image processing or speech recognition –Audio and video hardware –MMS or video over GSM –Where to get the latest movies or how to copy a DVD

4. 4StructureStructure Pre-requirements –Good understanding of IP networking principles 2-Hour credit Written exam on 11.7 –There is no second exam date –There are no other exam means (oral …) Office hours: After the lecture Contact: –sisalem@fokus.fraunhofer.de Slides –http://www.tkn.tu-berlin.de/curricula/ss06/vl-mkn/index.html –Basically still valid but will be updated soon

5. 5ReferencesReferences www.ietf.org (RFCs and drafts)www.ietf.org www.iptel.org (SIP tutorial)www.iptel.org www.cs.columbia.edu/~hgs/internet Schulzrinne Overviewwww.cs.columbia.edu/~hgs/internet Stevens, „TCP/IP Illustarted, V1“ (basic protocols) Ferguson, Huston, „Quality of Service“ (general QoS stuff) Henry Sinnreich and Alan B. Johnston „Internet Communication Using SIP: Delivering VoIP and Multimedia Services with Session Initiation Protocol“ Olivier Hersent, David Gurle, Jean-Pierre Petit,“IP Telephony“ Huitema, „IPv6“ Wikipedia

6. 6AcknowledgementsAcknowledgements Slides based on work of Henning Schulzrinne, Jim Kurose, Michael Smirnov, Georg Carle, Jiri Kuthan, Heikki Waris, Kevin Fall, Jim Chou, Thinh Nguyen, Vishal Misra, Steve Deering, Geert Heijenk, Ofer Hadar, John Floroiu, Nick McKeown, Eric D. Siegel, Ibrahim Matta, Steven Low, Vincent Roca, Nitin H. Vaidya, Charles Lang as well many other anonymous contributers.

7. 7 Topics: Introduction Introduction to Internet –Very brief covering Difference between IP and PSTN Basic concepts Transport protocols: TCP, UDP, SCTP, RTP –Why use UDP for VoIP and TCP for signaling? –What are the benefits of SCTP –What is the difference between RTP and RTCP –You are expected to have visited the networking lecture of Prof. Wolisz

8. 8 Topics: VoIP What is VoIP Signaling Addressing Intelligent services Deployment problems: NAT, emergency Integration with PSTN

9. 9 Topics: VoIP What happens during this registration?

10. 10 Topics: VoIP What does this address mean? How do we find the other side? How do we call a PSTN number? What happens when we press call?

11. 11 VoIP in UMTS What does IMS stand for? Basic concepts of UMTS What is the difference to normal VoIP? How does it work? Why a special version?

12. 12 Problems of VoIP Why doesn’t VoIP work over my DLS link –What are the problems of network address translators? –How to deal with firewalls Regulatory issues –How can I call the 110? QoS –Is it true that VoIP has bad voice quality

13. 13StreamingStreaming How are resource described? What happens when we press play? (signaling) What does it mean when it says “buffering” or ran out of buffer What protocols exist and how do they work?

14. 14 Peer-To-Peer Networking How do P-2-P solutions work? What solutions exist? What is Skype? Basic concepts and approaches

15. 15 Instant Messaging and Presence What is presence and IM Basic concepts and approaches What solutions and technologies exist What are the current standards –ICQ, Yahoo, MSN, etc is NOT a standard Relation to VoIP

16. 16 Group Communication What is the difference between broadcast and multicast How does a conference bridge work What solution is best for which scenario?

17. 17 Quality of Service (QoS) Control Why is the voice communication over the Internet not understandable some times? What can we do at the end system to improve the QoS? What can we do in the network to improve the QoS? Why can’t we find a network that deploys QoS concepts

18. 18 Public Switched Transmission Network PSTN

19. 19 Public Switched Transport Network (PSTN) Exists now for around 100 years 800 M Subscribers Supports Voice and Data (Fax) services Guaranteed bandwidth share In one country only a few exist –usually a big one controlling the whole network Cost of switching equipment high (A few millions for a carrier grade switching component Signaling to session establishment and control based on SS7 Hierarchical address structure (E.164) International Identity 1-3 digits National Identity 2-to-5 digits User Identity 11 to 5 digits Subaddress Up to 40 digits

20. 20 PSTN Architecture in Germany AVSt Auslandvermittlungsstelle Ca. 50 HVSt Hauptvermittlungsstelle Ca. 550 KVSt Knotenvermittlungsstelle Ca. 500 OVSt Ortvermittlungsstelle Ca. 40 M Teilnehmer Fernnetz Ortsnetz Ref. Prof. Dr.-Ing. Habil. Lutz Winkler, FH Mittweida

21. 21 Routing in PSTN Ref. Prof. Dr.-Ing. Habil. Lutz Winkler, FH Mittweida

22. 22 Switching in PSTN Ref. Prof. Dr.-Ing. Habil. Lutz Winkler, FH Mittweida Capacity 100 99 calls active busy

23. 23 Resource Sharing (TDM) Time division multiplexing (TDM) –May under utilize channel with idle senders –Applicable only for a fixed number of flows –Requires precise timers –Resources are guaranteed Multiplexer 1 link, 30kb/s speed 10 kb/s

24. 24 Intelligent Service in PSTN Ref. Prof. Dr.-Ing. Habil. Lutz Winkler, FH Mittweida

25. 25 Intelligent Service in PSTN Service switching point (SSP): A switch enhanced with logic for identifying IN services Service Transfer Point (STP): Interface of the switch to the IN environment Service Control Point (SCP): Control the execution of the service Service Management System (SMS): Control and manage the available services and provide the interface for adding new ones Intelligent Peripheral: Additional components for providing certain services such as announcements Feature Node: Execute services provided by private entities (similar to SCP)

26. 26 PSTN Summary Guaranteed Quality of Service Intelligence in the Network Signaling and Media tightly coupled Scalability and Extension difficulties

27. 27 Introduction to the Internet

28. 28 General Words Since 21 Years with the same technology (TCP/IP) Moved from 4 sites in 1968 to around 200 M hosts today Flat addressing and routing architecture Based on packet switching (the) Internet: “collection of networks and routers that spans x countries and uses the TCP/IP protocols to form a single, cooperative virtual network”. (Comer) intranet: connection of different LANs within an organization –Private –may use leased lines –usually small, but possibly hundreds of routers –may be connected to the Internet (or not), often by firewall

29. 29 Packet Switched Communication End Users Data Packets (Voice, Video, Games, Signaling…) Router

30. 30 What‘s a network? Host: Communication end point (PC, PDA, cell phone, coffee machine...) Link: carry bits from one place to another (or maybe to many other places) Switch/gateway/router: move bits between links, forming internetwork –IP router receives a packet from one interface and sends it out over another 1 2 1 2

31. 31 What‘s a Protocol? Protocol: rules by which active network elements communicate with each other protocols = “algorithms + data structures” –formats of messages exchanged –actions taken on receipt of messages –how to handle errors –hardware/operating-system independent real-life examples: –rules for meetings –conversational rules (interrupts, request for retransmission,...)

32. 32 Protocol Mechanisms (What Do Protocols Do for a Living?) All or some of the following: –addressing/naming: manage identifiers –fragmentation: divide large message into smaller chunks to fit lower layer –resequencing: reorder out-of-sequence messages –error control: detection and correction of errors and losses retransmission; forward error correction –flow control: avoid flooding/overwhelming of slower receiver –congestion control: avoid flooding of slower network nodes/links

33. 33 Architectural Requirements of the Internet Generality –Support ANY set of diverse applications, Heterogeneity –Interconnect ANY set of network technologies Robustness –More important than efficiency Extensibility –More important than efficiency Scalability

34. 34 End-to-End Principle Foundation of the Internet architecture: Dumb network, smart end systems –(Exact opposite of telephone network!) Dumb networks: require only least common service –Datagram service: no connection state in routers –Best effort: all packets treated equally. –Can lose, duplicate, reorder packets. Smart hosts: –Maintain state to enhance service for applications. –“Fate-sharing”-- If a host crashes and loses communication state, applications that are communicating share this fate.

35. 35 Resource Sharing (Statistical) Statistical multiplexing –Traffic is sent on demand, so channel is fully utilized if there is traffic to send –Any number of flows Multiplexer 5 kb/s 1 link, 30kb/s speed 20 kb/s 5 kb/s

36. 36 Resource Sharing (Statistical) Statistical multiplexing –Resources are NOT guaranteed –Need Mechanisms to prevent congestion and domination Multiplexer 5 kb/s 1 links, 30kb/s speed, 50% Loss 50 kb/s 5 kb/s

37. 37 Who runs the Internet? “nobody” standards: Internet Engineering Task Force names: Internet Corporation for Assigned Names and Numbers (ICANN) numbers: IANA (Internet Assigned Numbers Authority) network: ISPs (Internet Service Providers), NAPs (Network Access Points), DFN,... fibres: telephone companies (mostly) content: thousands of companies, universities, individuals,...

38. 38 How big is the Internet? Many measures: –networks (routed entities) –domains, host names (but: several names per host!) –directly (continuously) attached hosts (“ping’able”) –IP-connected hosts (SLIP, PPP) –firewalled hosts –e-mail reachable As of January 2006, over 1 billion people use the Internet according to Internet World Stats

39. 39 Host Count

40. 40 What Networks are There? Access (ISP): –Carry data from users Core –Carry data from access Network peering points –Connect networks together Some enterprises might be connected directly to core networks

41. 41 An Example Network USER Local Loop Carrier Point of Presence Backbone

42. 42 RFCs and Drafts “Request for Comments”, since 1969 most RFCs are not standards! Internet drafts: working documents, but often used for prototypes edited, but not refereed numbered sequentially (Jan 2006: more than 4000) check the April 1 ones... (RFC 1149) ftp://ds.internic.net/rfc

43. 43 TCP/IP Stack Link Network Transport Application Transport Network TCP/IP Host Router Ethernet Cable, UMTS IP, IPv6 TCP, UDP, SCTP VoIP Email..

44. 44 Internet Protocol Deliver an IP packet from host to host(s) Connectionless, unreliable –No loss handling –No flow or congestion control UDP TCP RTP VoIP AALx GPRSV.xSONETEthernetATM PPP IPv4/IPv6 DNS FTPHTTPSMTP ICMP

45. 45 Internet Names Physical link address –Ethernet, Token Ring, FDDI.. –Flat IP address –Identify an interface –Topological IP Name –Identify the object to reach –Hierarchical

46. 46 IP Addresses Identify an interface not host: –A host can have more than 1 address IP addresses are 32-bit numbers (4.3 billion of them!) Divided into parts: (network prefix, host number) 4 decimal numbers, called “dotted quad” Each (decimal) number is one byte –Example: 128.32.25.12 Can generally be used in place of names

47. 47 Special Addresses Private addresses: Only of meaning inside an intranet –172.16 through 172.31 16 –192.168.0 through 192.168.255 256 Loopback: 127.0.0.1 (local interface) Local broadcast: all 1 (receive by all members of link) Multicast: –224.0.0.0 239.255.255.255 –Do not describe a host or interface but a group of receivers Reserved: 240.0.0.0 255.255.255.255

48. 48 Internet Packets A lot of headers describing the different layers PhyIPUDP/ TCP Body

49. 49 IP Header Version: 4 or 6 Header length: number of 32 bit words of header Type of Service: delay, throughput, reliability, monetary Total length: length of packet in bytes Identification: identify packet Flag: –Do not fragment –More fragments Fragmentation offset: Distance from the first bit of the original packet Time-to-Live: Avoid loops Protocol: Which protocol is used (TCP, UDP, ICMP..) Header Checksum: Calculated over IP header Source address: Address of sender Destination address: Address of receiver

50. 50 IPv6: Why move to another protocol? Lack of IP addresses –Support for nearly endless range of addresses Better handling of options –Reduce complexity of IP header Better support for management and administration –auto configuration and renumbering –Support plug&play Higher Packet sizes (Jumbograms) Need for better support for mobile and secure communication –Remove the need for network address translators Really?

51. 51 IPv4 vs. IPv6 Header 14 fields, at least 20 octets 32 bit addresses fragmented packet processing at every hop header checksum recalculation at every hop variable Options field for extra processing information 8 fields, fixed 40 octet size 128 bit addresses fragmentation only in endpoints, or lower layer –Usage of Path MTU discovery no checksums –Already in lower layers new 20 bit flow label field options in Extension Headers

52. 52 IP Names Oxany.fokus.fhg.de host name (has IP address) organization type or country Organization administering subnames to left organization administering host

53. 53 Getting From A to B

54. 54 Getting from A to B Know name: need to know IP address –Domain Name System (DNS) Know IP address: need to know the way

55. 55 Getting From A to B Name to IP Address

56. 56 Domain Name System The Domain Name System (DNS) is a distributed database that is used by TCP/IP applications to… –map between hostnames and IP addresses, –and to provide application routing information. Distributed database: –No single site on the Internet “knows it all.” –Each site maintains its own database and runs a server that other systems on the Internet can query. DNS is the client/server protocol.

57. 57DomainsDomains Top level domains –arpa domain Special domain for address-to-name mappings –generic (organizational) domains 3-character domains (e.g. edu, com, org, …) –Country (geographical) domains 2-character domains Found in ISO 3166 Some countries form second-level domains –e.g.:.ac.uk is for academic institutions in the United Kingdom. –New generic top level domains (gTLD).biz,.name,,info... Note: No single entity manages every node.

58. 58 DNS hierarchical name space arpa comedugovintmilnetorg deus unnamed root wsu eecsmath gazoo top level domains Node labels up to 63 characters. Root node has null label. Comparisons are case insensitive. Domain name formed as follows: start at node and work toward root use a “dot” to separate labels Maintained by DeNIC

59. 59 Resolvers and Name Servers Applications (clients and servers) contact a DNS server by calling functions in a library known as a resolver. –The resolver is accessed through the functions gethostbyname() and gethostbyaddr(). –The resolver code is in a system library and is linked into the application.

60. 60 DNS Operation What does a server do when it does not have the requested information? –Every name server must know how to contact the root name servers (via IP address). –Name server contacts a root server –Root servers know the name and IP address of all the second-level domains –Each names server caches information from recent queries.

61. 61PracticalPractical nslookup http://www.internic.org

62. 62 Routing Packets from A to B

63. 63 Hierarchical PSTN Routing 030 040 050060

64. 64 Distributed IP Routing Enterprise Access Core PictureTel 193.175.135.21 195.37.78.225

65. 65 IP Routing How to get from A to B? –Different paths are possible!! –Neither A nor B know the best path in advance!! Goal: set routing tables for packet forwarding in hosts and routers, typically based on some optimality criterion. Questions: –who determines entries? –based on what information (hops, delay, cost,...) ? –how often does it change (hop vs. delay)? –where is routing information stored? –algorithm used to compute routes?

66. 66 IP Routing: Goals scalability “safe” interconnection of different organizations adopt quickly to changes in topology avoid routing loops or at least terminate them quickly self-healing, robust Distributed: No central component to determine the path efficient: can’t use 90% of bandwidth for routing info multiple metrics (QOS, price, politics,...) à not yet routes should be (near) “optimal” can’t have all hosts/networks in single table à hierarchical

67. 67 IP Routing Every router needs to determine the next hop to which to send the data Routing database: one entry for every possible destination in the system: –Destination address: the IP address of the host or network; –Next hop: the first router along the route to the destination; –Interface: the physical network which must be used to reach the first hop –Metric: a number, indicating the distance to the destination; –Timer: the amount of time since the entry was last updated; –Flags and other internal information. 1 2 1 2

68. 68 Intra-Domain Routing Set the routes inside an autonomous system (AS) –AS: a a collection of routers and system administered by one entity –Has a AS number assigned by IANA Different ASs might use different intra-domain routing schemes Changes in one AS do not effect other domains AS connects to another AS through one or more border routers Enterprise Access Core