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Multimedia Services in the Internet. Dr. Dorgham Sisalem s [email protected] Goals. Overview of multimedia service Understanding of multimedia services in the Internet Understanding of the general pictures Transport protocols, signaling, traffic types, QoS

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Multimedia services in the internet

Multimedia Services in the Internet

Dr. Dorgham Sisalem

[email protected]


  • Overview of multimedia service

  • 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 speach recognition

    • Audio and video hardware

    • MMS or video over GSM

    • Where to get the latest movies or how to copy a DVD


  • Pre-requirements

    • Good understanding of IP networking principles

  • 2-Hour credit

  • Exam

    • 10-12 10.07.07

  • Office hours: After the lecture

  • Contact:

    • [email protected]

  • Slides:


  • (RFCs and drafts)

  • (SIP tutorial)

  • XXXX

  • 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“


  • 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.

Topics introduction
Topics: Introduction

  • Introduction to Internet

    • Very brief covering

      • Difference between IP and PSTN

      • Basic concepts

      • Transport protocols: TCP, UDP, RTP

        • Why use UDP for VoIP and TCP for signaling?

        • What is the difference between RTP and RTCP

    • You are expected to have visited the networking lecture of Prof. Wolisz

Topics voip
Topics: VoIP

  • What is VoIP

  • Signaling

  • Addressing

  • Intelligent services

  • Deployment problems: NAT, emergency

  • Integration with PSTN

Topics voip1
Topics: VoIP

What happens during this registration?

Topics voip2
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?

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?

Problems of voip
Problems of VoIP

  • Why doesn’t VoIP work over my DSL link

    • What are the problems of network address tarnslators?

    • How to deal with firewalls

  • Regulatory issues

    • How can I call the 110?

  • Scalability

    • How do I build a reliable carrier-grade VoIP infrastructure

  • Security

    • What kind of attacks can we expect

Group communication
Group Communication

  • What is the difference between broadcast and multicast

  • How does a conference bridge work

  • What solution is best fro which scenario?

Peer to peer networking
Peer-To-Peer Networking

  • How do P-2-P solutions work?

  • What solutions exist?

  • What is Skype?

  • Basic concepts and approaches

Instant messaging and presence
Instant Messaging and Presence

  • What is presence and IM

  • Basic concepts and approaches

  • What solutions and technologies exist

  • What are the current standards

  • Relation to VoIP


  • How are resources 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?

Public switched transport network pstn
Public Switched Transport Network (PSTN)

  • Exists now for around 100 years

  • 800 M Subscribers

  • Optimized for 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)



2 digits







11 to 5



Up to 40 digits

Pstn architecture in germany
PSTN Architecture in Germany




Ca. 50 HVSt


Ca. 550 KVSt


Ca. 500 OVSt



Ca. 40 M Teilnehmer

Ref. Prof. Dr.-Ing. Habil. Lutz Winkler, FH Mittweida

Routing in pstn
Routing in PSTN

Ref. Prof. Dr.-Ing. Habil. Lutz Winkler, FH Mittweida

Switching in pstn
Switching in PSTN

Capacity 100

99 calls active


Ref. Prof. Dr.-Ing. Habil. Lutz Winkler, FH Mittweida

Resource sharing tdm
Resource Sharing (TDM)

  • Time division multiplexing (TDM)

    • Allocate a time slot to a each call

      • Resources are guaranteed

    • May under utilize channel with idle senders

    • Applicable only for a fixed number of flows

    • Requires precise timers

1 link, 30kb/s speed

10 kb/s


10 kb/s

10 kb/s

Intelligent service in pstn
Intelligent Service in PSTN

Ref. Prof. Dr.-Ing. Habil. Lutz Winkler, FH Mittweida

Intelligent service in pstn1
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)

Example of free call
Example of Free Call

  • Allow calls to a generic number: No costs for the caller, final location decided based on time of day ….

Ref. Prof. Dr.-Ing. Habil. Lutz Winkler, FH Mittweida

General words
General Words

  • Since more than 20 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 xcountries and uses the TCP/IP protocols to form a single, cooperativevirtual network”. (Comer)

  • intranet:connection of different LANs within anorganization

    • Private

    • may use leased lines

    • usually small, but possibly hundreds of routers

    • may be connected to the Internet (or not), often by firewall

Packet switched communication
Packet Switched Communication

End Users

End Users


Data Packets (Voice, Video, Games, Signaling…)

What s a network
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

What s a protocol
What‘s a Protocol?

  • Protocol: rules by which active network elements communicate witheach 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, ...)

Protocol mechanisms what do protocols do for a living
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

Architectural requirements of the internet
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

    • (A later discovery. How many ARPAnets could the worldsupport? A few hundred, maybe… ?)

End to end principle
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.

    • New applications can be introduced at end systems with no need for network upgrades.

Resource sharing statistical
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

1 link, 30kb/s speed

5 kb/s


20 kb/s

5 kb/s

Resource sharing statistical1
Resource Sharing (Statistical)

  • Statistical multiplexing

    • Resources are NOT guaranteed

    • Need Mechanisms to prevent congestion and domination

1 links, 30kb/s speed,

50% Loss

5 kb/s


50 kb/s

5 kb/s

Who runs the internet
Who runs the Internet?

  • “nobody”

  • standards: Internet Engineering Task Force (later. . . )

  • names: Internic (US), RIPE (Europe), . . .

  • numbers: IANA (Internet Assigned Numbers Authority)

  • network: ISPs (Internet Service Providers), NAPs (Network AccessPoints), DFN, . . .

  • fibres: telephone companies (mostly)

  • content: thousands of companies, universities, individuals, . . .

How big is the internet
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

What networks are there
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

An example network
An Example Network



Local Loop Carrier

Point of Presence

Making the standards
Making the Standards

  • Internet Architecture Board: IAB

    • architectural oversight

    • elected by ISOC

  • Internet Engineering Steering Group (IESG)

    • approves standards

  • Internet Society: ISOC

    • Conferences

    • “hosts” IANA

  • Internet Assigned Number Authority: IANA

    • keeps track of numbers

    • delegates Internet address assignment

  • Internet Engineering Task Force: IETF

    • Define the problems and specify solutions to them

    • Run by interested people (people should contribute in person and not as company representatives)

Rfcs and drafts
RFCs and Drafts

  • “Request for Comments”, since 1969

  • most RFCs are not standards!

  • Internet drafts: working documents, but often used forprototypes

  • edited, but not refereed

  • numbered sequentially (Spetember 2002: more than 3600)

  • check the April 1 ones. . . (RFC 1149)


Tcp ip stack
TCP/IP Stack





Email ..








IP, IPv6










Internet protocol
Internet Protocol

  • Deliver an IP packet from host to host(s)

  • Connectionless, unreliable

    • No loss handling

    • No flow or congestion control


















Internet names
Internet Names

  • Physical link address

    • Ethernet, ATM ...

    • Flat

  • IP address

    • Identify an interface

    • Topological

  • IP Name

    • Identify the object to reach

    • Hierarchical

Ip addresses
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:

  • Can generally be used in place of names

Internet packets
Internet Packets

  • A lot of headers describing the different layers






Ip header
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:

    • MBZ:

    • 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

Special addresses
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: (local interface)

  • Local broadcast: all 1 (receive by all members of link)

  • Multicast:


    • Do not describe a host or interface but a group of receivers

  • Reserved:

Ipv6 why move to another protocol
IPv6: Why move to another protocol?

  • Lack of IP addresses

    • Support for nearly endless range of addresses

  • Explosion of routing tables

    • Allow for better aggregation and routing hierarchies

  • Better handling of options

    • Reduce complexity of IP header

  • Better support for management and administration

    • auto configuration and renumbering

    • Support plug&play

  • Need for better support for mobile and secure communication

    • Remove the need for network address translators

      • Really?

  • Better support for QoS (which is not correct)

IPv4 vs. IPv6 Header

  • 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 flowlabel field

  • options in Extension Headers

  • 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

Ip names
IP Names

host name(has IP address)

organization administering



subnames to left

organization type or country

Getting from a to b1
Getting from A to B

  • Know name: need to know IP address

    • Domain Name System (DNS)

  • Know IP address: need to know the way

Getting from a to b2

Getting From A to B

Name to IP Address

Domain name system
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.


  • 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.: is for academic institutions in the United Kingdom.

    • New generic top level domains (gTLD)

      • .biz, .tv, .name, .aero ...

  • Note: No single entity manages every node.

Dns hierarchical name space
DNS hierarchical name space

unnamed root

top level domains




Maintained by DeNIC









  • 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




Resolvers and n ame s ervers
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.

Dns operation
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.


  • nslookup


Hierarchical pstn routing
Hierarchical PSTN Routing





Distributed ip routing
Distributed IP Routing








Ip routing
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?

Ip routing goals
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

Ip routing1
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.





Ip routing2
IP Routing

  • DB initialization: description of the entities that are directly connected;

  • DB update: messages from neighboring gateways.

  • Decision taken based on topology and updated continously

    • No gurantee that two packets will follow the same path

  • ifconfig (ipconfig)

  • Netstat


Intra domain routing
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