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Internet. Foreleser: Carsten Griwodz Email: griff@ifi.uio.no. Multicast. Receiver. Sender. Receiver. Receiver. Receiver. Sender. Receiver. Receiver. Multicast. Multicast Definition Unicast: 1:1 communication Multicast: 1:n communication Tasks

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    1. Internet Foreleser: Carsten Griwodz Email: griff@ifi.uio.no 1

    2. Multicast 2

    3. Receiver Sender Receiver Receiver Receiver Sender Receiver Receiver Multicast • Multicast Definition • Unicast: 1:1 communication • Multicast: 1:n communication • Tasks • To send data to a group of end systems • one-time sending instead of • multiple sending • To maintain the overall load at a low level • Results • Lower network load • Lower load on the sender • Condition: group addressing • Group membership may change, managed for example by

    4. Internet Multicast • Multicast • Means to create trees, to address them, to modify them ... • IP Multicast Model • Shared Tree • tree may be used by several senders • Source Tree • tree is used by exactly one sender • Properties / Fields of Activity / Topics • Group addressing • Routing • Reliable multicast • temporally limited and error free

    5. IP Multicast: Concepts • Virtual Overlay Network • isolated solutions capable of multicasting • connected worldwide through several tunnels • logical tree structure • Dynamic, anonymous group model • no restrictions regarding the participants (location/number) • dynamic group membership • one host may be a member of several groups at the same time • sender does not have to be a member of the group • no restrictions regarding the group’s duration

    6. 7 24 0 Network Host 14 16 1 0 Network Host 21 8 1 1 0 Network Host 28 1 1 1 0 Multicast address 28 1 1 1 1 Reserved Prefix (binary) Usage Fraction 0000 0000 Reserved (including IPv4) 1/256 0000 0001 Unassigned 1/256 … … … 1111 1110 10 Link local use addresses 1/1024 1111 1110 11 Site local use address 1/1024 1111 1111 Multicast 1/256 IP Multicast • Addresses • IPv4 • 28 bit, i. e. > 250 Mio. Groups • IPv6 • 120 bit • Types of group addresses • Permanent • e. g. all ES and IS on one LAN, • all IS (router) on one LAN, ... • Temporary • Internet Group Management Protocol (IGMP) • RFC 1112 • dynamic definition of group memberships

    7. IP Multicast • Scoping rules • Two ways of limiting multicast group size • TTL scoping • Administrative scoping • TTL scoping • Original, first used in MBone • Limits distribution based on TTL field • Administrative scoping • Set of RFCs • Limits distribution based on addresses

    8. TTL Do not forward outside … 1 - 15 Organization 16 - Country 32 - Continent 64 - World-wide 128 - Low bandwidth tunnels IP Multicast • TTL scoping • IPv4 scoping style • Introduced for the Multicast backbone • Not covered by RFCs • Still in use

    9. Multicast address grouping in IPv4 8 8 8 8 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 1 1 0 0 1 0 0 1 0 0 0 1 0 0 0 1 0 0 0 0 0 0 0 0 0 1 1 0 1 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 1 0 1 0 0 0 0 1 x 0 0 x x 1 x 0 0 0 1 x x 0 1 x 0 x 0 0 0 0 0 x 0 x 1 0 0 1 x 0 x 0 x 1 x x 1 0 0 x 0 0 0 0 0 0 0 0 0 0 x 0 x 1 x x 1 0 0 0 0 0 0 x 1 1 x 0 x 0 x x 0 1 0 0 0 x x 1 0 x 0 x 0 x 0 x 0 x 1 1 0 0 x 0 x 0 x 0 x 1 0 0 x x 1 x x x 0 1 x 0 x 0 1 x 0 x x x x 0 x x x 1 x 1 0 x 0 x x 0 x 0 x x 1 0 x x 1 0 x 0 x 0 0 0 x 1 x x x x x 0 1 x x 1 0 x 0 x x 1 0 x x x 0 x x x 0 1 1 x x 0 1 0 x x x 1 x 1 1 0 x 0 x x 0 x x 0 x x x 1 1 x x x x x x 0 x x 1 x x x x x x 0 x 1 0 1 x 0 x x x x x x 0 1 x x x x x x x x 0 x 1 x x 0 1 x x 0 x x x x 0 1 x x x 1 1 0 x x x x 1 x x x x 0 x 1 x 0 x x x x 0 x x x 1 x x x 0 x x x 1 x x 0 1 x x IP Multicast Address Assignment Local Network Control Block Internetwork Control Block Ad-Hoc Control Block ST Multicast Groups SDP/SAP Block DIS Transient Block reserved Source Specific Multicast Block GLOP Block reserved Administratively Scoped Block

    10. IP Multicast Address Assignment • Multicast address grouping in IPv4 • Local network control block • For control traffic in one LAN • Internetwork control block • For control traffic forwarded through the entire Internet • Ad-hoc control block • First-come first-serve • ST multicast groups • Used by ST-II (the connection-oriented network layer protocol with version number 5) • SDP/SAP block • Exclusively for SAP messages

    11. IP Multicast Address Assignment • Multicast address grouping in IPv4 • DIS transient block • Historical – may be reassigned • Source specific multicast block • No allocation required • Routers must build one tree per (source IP address, multicast destination address) • GLOP block • Addresses that can be requested using a global allocation mechanism • Multicast address dynamic client allocation protocol (MADCAP) • Addresses are requested for some time • Administratively scoped block • Like administrative scoping in IPv6, next slide

    12. Administrative scoping in IPv6 scop is a 4-bit multicast scope value used to limit the scope of the multicast group 8 4 4 112 1 1 1 1 1 1 1 1 flags scop Group ID 0 0 0 T scop meaning 0 reserved 1 Interface-local scope 2 Link-local scope 3 reserved 4 Admin-local scope 5 Site-local scope 6 (unassigned) 7 (unassigned) 8 Organization-local scope 9 (unassigned) A (unassigned) B (unassigned) C (unassigned) D (unassigned) E Global scope F reserved IP Multicast Address Assignment • T=0 • Permanently assigned (“well-known”) multicast address, assigned by IANA (Internet Assigned Number Authority) • T=1 • Non-permanently assigned (“transient”) address

    13. IP Multicast Address Assignment • Administrative scoping in IPv4 • Interface-local • Only inside one machine • Link-local • Only inside a single LAN or on one point-to-point connection • Admin-local • Smallest scope that can not be automatically configured • Site-local • Inside one site • Where all nodes have the same subnet ID • Organization-local • Multiple sites of one organization • Global

    14. plen Number of bits used for network prefix network prefix Identifies the prefix of a subnet group id A multicast group id that is unique for the subnet Unicast-prefix scoping in IPv6 0 0 1 1 IP Multicast Address Assignment 8 4 4 8 8 64 32 1 1 1 1 1 1 1 1 flags scop reserved plen network prefix group id • flags • Must be 0011 • scop • As before

    15. Multicast Routing 15

    16. 1 2 1 1 2 2 2 2 1 1 Spanning Tree Multicast source IS Spanning tree for group 1 Spanning tree for group 2 Spanning tree for source IS • Principle • Global knowledge of the multicast group’s spanning tree (Multicast Tree), • Initially only local knowledge • Distribution of Information • First IS adapts spanning tree to the specific groupi.e. aligning (propagating) the spanning tree by • distance vector routing or link state routing

    17. Spanning Tree • Principle • all IS must know the multicast tree • i.e. each IS • knows to which group it belongs • but does not know (initially) which other IS belong to the group as well • distribution of this information • depends on the underlying routing protocol • here: Link State Routing

    18. Spanning Tree with Link State Routing • Link State Routing • All IS send link state packets periodically • Containing information • distance to neighbours • expanded by information on multicast group • By broadcast to all the others • Each IS calculates a multicast tree • From the now locally available and complete state information • Based on the information about the multicast tree • IS determines the outgoing lineson which packets have to be transmitted

    19. Reverse Path Forwarding with Pruning • Pruning • Feedback in order to stop data transfer • Feedback is generated by IS without interested end systems • Principle • Sender sends first multicast packet to everybody, using the broadcast method Reverse Path Forwarding • Then apply adaptation (Pruning) • Because broadcasting too resource consuming

    20. Reverse Path Forwarding with Pruning • Reverse Path Forwarding • When a multicast packet arrives at an IS • from origin S • on an interface I • Test whether it would send unicast packets to S via I • Yes • Deliver multicast packet to all connected end systems in the multicast group(they must have registered themselves using IGMP) • Forward multicast packet on all interfaces to other routers except I • No • Drop packet (assume it’s a duplicate)

    21. Reverse Path Forwarding with Pruning • Pruning • When a multicast packet arrives from S on interface I • If • No directly connected end system is registered • Non-Membership-Reports (NMRs) are received from all IS reachable via interfaces other than I • Then • Send a Non-Membership-Report (NMR) to the previous IS that forwarded the packet • Do not forward messages for the group any more • Flooding and pruning must be repeated after some time • To find end-systems that have joined • Benefit • Pruning only on trees that are actually used • Unused trees are cut coarsely • Optimized for many receivers

    22. Core-Based Tree Core IS Non-Core IS • Also known as "Trees with Rendezvous Points“ • Principle • the core is selected (an IS which is central to the group) • the group’s spanning tree from this node/IS is determined • the sender transmits a packet to this central IS • the core transmits this packet via the spanning tree • Properties • simple central calculation • one tree common to all n senders (instead of n trees) • route to the central IS may not be optimized

    23. Truncated Reverse Path Forwarding • Principle • Enhancement of broadcast routing approach"Reverse-Path-Broadcast“

    24. Reverse Path Broadcast • Motivation • When packets are forwarded,they are forwarded over all edges (not including the incoming one) • Better if over only one suitable edge • Algorithm: packet from source S to destination • Has packet arrived via an IS entry over which packets may also be sent to station/source S? • Yes • Packet used the best route until now • Select the edges at which the packets arrived that were routed to S • Forward over those edges • No • Discard packet (is most likely a duplicate)

    25. Reverse Path Broadcast • In the example • A can learn by inspecting the unicast packets • that it is located on the unicast path from B to S • X can learn by packets failing to appear • that it is not located on the unicast path from B to S • This information is used by the RPB algorithm

    26. Reverse Path Broadcast • In the example with the RPB algorithm • X does not forward a broadcast packet from S to B, because X knows • that B does not receive unicast packets via X • but sends them over a different node instead with • this other node then receiving the broadcast packet

    27. Truncated Reverse Path Forwarding • Principle • Enhancement of broadcast routing approach"Reverse-Path-Broadcast“ • Here packets are sent only on edge/leaf links which • Contain group members • Contain additional routers in their path (known from the message exchange between the routers) • Algorithm (when packet arriving at IS) • Has this packet arrived from the same connection over which packets are sent to this station? • Yes • Packet used the most favorable route up to now • Select all subnetwork edges/leaf links (not incl. the incoming one) that • Contain group members, or • Contain additional routes within their path • Forward over those edges • No • discard packet (is probably duplicate)

    28. Truncated Reverse Path Forwarding • Comment on selecting the outgoing paths • Recognizing leaf links by sending router messages • Exchange membership information via IGMP • Uncoupling of subnetworks only (no pruning procedure)

    29. Additional Procedures & Topics • Additional Variations • Steiner Trees (optimizing network resources) • Distance Vector Multicast Routing Protocol (DVMRP) • Flooding and pruning approach • Hierarchic DVMRP • Two-tiered, non-overlapping domains/subnetworks • Multicast Open Shortest Path First (MOSPF) • Based on link state routing OSPF • Protocol Independent Multicast – Dense Mode (PIM-DM) • Similar to DVMRP • Protocol Independent Multicast – Sparse Mode (PIM-SM) • For groups with small spatial density • Related to core-based trees

    30. Additional Procedures & Topics • Objectives • Optimizations • Constraints • Optimizations • Edge optimization • e. g. path with largest bandwidth • Path optimization • e. g. path with the lowest overall costs • Constraints • Edge limited • e. g. find a path that adheres to the constraints at every edge • Path limited • e. g. path which does not exceed a certain overall delay

    31. Mobile IP 31

    32. Mobile IP • Motivation • Networked society demands for & enables mobility • at work • private environment • Infrastructure: wireless communication technologies • spreading more and more • e.g. hotspots with IEEE 802.11 • End systems: laptops, palmtops are getting more and more powerful • Mobility using Internet technology • Mobile IP • Adds mobility to the Internet • History • developed by the Internet Engineering Task Force (IETF) • proposed standard in 1996 (RFC 2002) • obsoleted by RFC3344 • There are many more RFCs and drafts in this area, seehttp://www.ietf.org/html.charters/mobileip-charter.html

    33. Problems & Challenges • IP address of end system • Belong to organizational entity • Contains topological information • Intermediate systems • Use the IP address for routing definition • Network information, or • Subnet information (part of host-Id), or • Only end system information (part of host-Id) • Change of physical subnet implies • Either: Change of IP address • Or: Change entries in routing tables • Problems • How to connect mobile end system to the Internet? • With existing address but from a different location • Routing to mobile end system does not work • Changing IP address • DNS updates take to long time • TCP connections break • Changing entries in routing tables • Does not scale with the number of mobile hosts and frequent changes in the location

    34. Problems & Challenges with Mobility in the Internet • (simple) Possible solutions • Use new IP address at each respective location Information of own IP address maintained at many locations • (e.g. DNS), update impractical, problems with IPSec Communication with other systems has to be interrupted when changing location • Modified routing definitioni.e. routers to make use of complete IP address Router tables with millions of entries, extremely high costs Security problems • (secure change of routes)

    35. Requirements • Basic requirement • Mobile end system uses the same IP address allover • Transparency • Compatibility requirements • No modifications on existing • (non-mobile) end system necessary • IS (i.e. routers) • Tables • Protocols • Interoperability with TCP/IP protocol-suite • Possibility to adapt existing applications • Solution should be independentfrom an underlying wireless network technology

    36. Requirements • Performance requirements • No overhead with mobile end system in stationary cases • Should have solid scaling characteristics • Quantity of administrative protocol messages should be low because • often lower bandwidth of wireless networks • limited battery performance of mobile end system • Security requirements • E.g. all registration messages have to be protected

    37. Components Cell Home agent Mobile host Home LAN WAN Correspondent node Foreign LAN • Mobile Node (MN), mobile host • moves to different location • uses permanent IP address • Correspondend Node (CN) • Communication partner to mobile node • Home Agent (HA) • IS (router) in the home network of the mobile host • knows the mobile hosts, which are not "at home" at the moment • knows the current location of the mobile host • tunnels IP packets (re-routes them) to the mobile host’s location

    38. Components Cell Home agent • Foreign Agent (FA) • IS (router) in the foreign network • mobile hosts log on to the foreign agents • unpacks tunneled IP packets • re-routes them to their respective mobile host • assigns addresses (CoA) to the visiting Mobile Node • Care-of-Address (CoA) • Tunnel endpoint of the Mobile Node while abroad Mobile host Home LAN Foreign agent WAN Correspondent node Foreign LAN

    39. Protocol Overview Cell Home agent • A mobile host moves to a foreign network • The foreign agent periodically sends out agent advertisements • thereby the mobile host receives a care-of-address • care-of-address is used to inform the home agent of the new location • The home agent intercepts and redirects the IP packets which are intended for the mobile host to its new address • this is done by means of an IP tunnel • Once the mobile host is back in its home network • it de-registers from its home agent Mobile host Home LAN Foreign agent WAN Correspondent node Foreign LAN

    40. Protocol Overview Cell Home agent • The mobile IP protocol consists out of three independent functions • Agent discovery • Registration • Tunneling Mobile host Home LAN Foreign agent WAN Correspondent node Foreign LAN

    41. Agent Discovery • Procedure used by the mobile host to determine if • it is in its home network • it is in a foreign network • it has moved into another (additional) foreign network (move detection) • Message type: Agent Advertisements • transmitted by home or foreign agent • to offer their services to mobile hosts • determines in which network the mobile host is • if it is in a foreign network it receives a care-of-address from Agent Advertisement • Message type: Agent Solicitations • transmitted from the mobile host • if it cannot/does not want to wait any longer for the agent advertisement

    42. Agent Discovery • The care-of-address is • temporary IP address for the mobile host • specific for the foreign network • defines the location of the mobile host • i.e. it is the IP address transmitted to the home agent and to which the IP packets, which are intended for the mobile host, are re-routed

    43. Registration Agent discovery (incl. advertisements) Requests service Mobile host Foreign agent FA relays request to HA WAN FA relays Status to MH Home agent HA accepts or denies

    44. Registration • Main purpose • to transmit the new care-of-address of the mobile host to the home agent • Home agent • logs the current care-of-addresses in a table • each registration has a period of validity • The mobile host registers itself • when it is in a new network • when the old registration expires • Note • authentications of registration messages done using the MD5 algorithm

    45. Tunneling Correspondent node Packet is sent to the mobile host’s home address Home agent Foreign agent Packet is tunneled to the foreign agent

    46. Tunneling • IP packets of the correspondent node to the mobile host are routed to the home agent • Home agent performs IP-in-IP Encapsulation • original packets are "encapsulated" into surrounding IP packets • destination is current care-of-address • IP packet is routed to the care-of-address • this process is called Tunneling • The foreign agent is the finishing point of the tunnel • unpacks the packet • transfers it to the mobile host according to the original home address

    47. A Few Additional Aspects Sender is given foreign agents address Correspondent node Packet is sent to the mobile host’s home address Tunnel to the foreign agent Home agent Foreign agent Packet is tunneled to the foreign agent

    48. A Few Additional Aspects • Redirecting the packets from the mobile host to the correspondent host can • be sent directly to the correspondent host • by using the care-of-address as the sender’s address • or, for security reasons, be done • by means of reverse tunneling • i.e. the packets are "re-tunneled" to the home agent • note: route optimization • If no foreign agent is available, a mobile host itself can assume this function • the mobile host gets a colocated care-of-address from a foreign network, • e.g. via the "Dynamic Host Configuration Protocol" (DHCP) • this address is then used exclusively by the mobile host • it transmits this address to its home agent • and represents the tunnel’s finishing point

    49. Mobile IP: Problems • Without special care • Reverse tunneling may be necessary for • Firewalls • Streaming servers with destination check • Mandatory in RTSP • Tunneling • IP in IP has an additional header • Reduces the max MTU size • Large increase in delay • End-to-end distance • IP in IP processing • Increase in jitter and loss • No reasonable interaction • With multicast • Subscribe to groups through the tunnel • With reservation protocols • E.g. RSVP relies on multicast