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15-744: Computer Networking Multicast Routing Example Applications Overview

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Multicast Routing

•ꢀ Unicast: one source to one destination •ꢀ Multicast: one source to many destinations •ꢀ Two main functions:

•ꢀ Efficient data distribution •ꢀ Logical naming of a group

15-744: Computer Networking

L-20 Multicast

2

  • Example Applications
  • Overview

•ꢀ IP Multicast Service Basics

•ꢀ Broadcast audio/video •ꢀ Push-based systems •ꢀ Software distribution •ꢀ Web-cache updates

•ꢀ Multicast Routing Basics •ꢀ Overlay Multicast •ꢀ Reliability

•ꢀ Teleconferencing (audio, video, shared whiteboard, text editor)
•ꢀ Multi-player games •ꢀ Server/service location •ꢀ Other distributed applications

•ꢀ Congestion Control

  • 3
  • 4

1

  • IP Multicast Architecture
  • Multicast – Efficient Data Distribution

  • Src
  • Src

Service model

Hosts

Host-to-router protocol
(IGMP)

Routers

Multicast routing protocols
(various)

  • 5
  • 6

  • Multicast Router Responsibilities
  • IP Multicast Service Model (rfc1112)

•ꢀ Each group identified by a single IP address •ꢀ Groups may be of any size •ꢀ Members of groups may be located anywhere in

•ꢀ Learn of the existence of multicast groups
(through advertisement)

•ꢀ Identify links with group members

the Internet

•ꢀ Establish state to route packets

•ꢀ Replicate packets on appropriate interfaces •ꢀ Routing entry:
•ꢀ Members of groups can join and leave at will •ꢀ Senders need not be members •ꢀ Group membership not known explicitly •ꢀ Analogy:

  • Src, incoming interface
  • List of outgoing interfaces

•ꢀ Each multicast address is like a radio frequency, on which anyone can transmit, and to which anyone can tune-in.

  • 7
  • 8

2

  • IP Multicast Addresses
  • Multicast Scope Control – Small TTLs

  • •ꢀ Class D IP addresses
  • •ꢀ TTL expanding-ring search to reach or find

a nearby subset of a group

•ꢀ 224.0.0.0 – 239.255.255.255

  • 1 1 1 0
  • Group ID

s

•ꢀ How to allocated these addresses?

1

•ꢀ Well-known multicast addresses, assigned by IANA

2

•ꢀ Transient multicast addresses, assigned and reclaimed dynamically, e.g., by “sdr” program

3

  • 9
  • 11

  • Multicast Scope Control – Large TTLs
  • Overview

•ꢀ Administrative TTL Boundaries to keep multicast traffic within an administrative domain, e.g., for privacy or resource reasons

•ꢀ IP Multicast Service Basics

•ꢀ Multicast Routing Basics

•ꢀ Overlay Multicast •ꢀ Reliability

The rest of the Internet

TTL threshold set on interfaces to these links, greater than the diameter of the admin. domain

•ꢀ Congestion Control

An administrative domain

  • 12
  • 13

3

  • IP Multicast Architecture
  • Multicast Routing

•ꢀ Basic objective – build distribution tree for

Service model

multicast packets

Hosts

•ꢀ Multicast service model makes it hard

•ꢀ Anonymity

Host-to-router protocol
(IGMP)

Routers

•ꢀ Dynamic join/leave

Multicast routing protocols
(various)

  • 14
  • 15

  • Shared vs. Source-based Trees
  • Source-based Trees

•ꢀ Source-based trees

Router
S

R

Source

•ꢀ Separate shortest path tree for each sender

Receiver

•ꢀ DVMRP, MOSPF, PIM-DM, PIM-SM

R
R

•ꢀ Shared trees

•ꢀ Single tree shared by all members •ꢀ Data flows on same tree regardless of sender •ꢀ CBT, PIM-SM

R

S
S

R

  • 16
  • 17

4

  • Shared Tree
  • Shared vs. Source-Based Trees

•ꢀ Source-based trees

Router

•ꢀ Shortest path trees – low delay, better load distribution •ꢀ More state at routers (per-source state) •ꢀ Efficient for in dense-area multicast

S

R

Source Receiver

R
R

•ꢀ Shared trees

•ꢀ Higher delay (bounded by factor of 2), traffic concentration

RP

R

S

•ꢀ Choice of core affects efficiency •ꢀ Per-group state at routers

S

•ꢀ Efficient for sparse-area multicast

R

•ꢀ Which is better? ꢀ extra state in routers is bad!

  • 18
  • 19

  • Routing Techniques
  • Routing Techniques

•ꢀ Flood and prune

•ꢀ Core based protocols

•ꢀ Begin by flooding traffic to entire network •ꢀ Prune branches with no receivers •ꢀ Examples: DVMRP, PIM-DM

•ꢀ Specify “meeting place” aka core •ꢀ Sources send initial packets to core •ꢀ Receivers join group at core

•ꢀ Unwanted state where there are no receivers

  • •ꢀ Requires mapping between multicast group
  • •ꢀ Link-state multicast protocols

address and “meeting place”

•ꢀ Routers advertise groups for which they have receivers to entire network
•ꢀ Compute trees on demand

•ꢀ Examples: CBT, PIM-SM

•ꢀ Example: MOSPF

•ꢀ Unwanted state where there are no senders

  • 20
  • 21

5

  • Distance-Vector Multicast Routing
  • Example Topology

•ꢀ DVMRP consists of two major components:

  • G
  • G

•ꢀ A conventional distance-vector routing protocol
(like RIP)
•ꢀ A protocol for determining how to forward multicast packets, based on the routing table

•ꢀ DVMRP router forwards a packet if

S

•ꢀ The packet arrived from the link used to reach the source of the packet (reverse path forwarding check – RPF)
•ꢀ If downstream links have not pruned the tree

G

  • 22
  • 23

  • Broadcast with Truncation
  • Prune

  • G
  • G
  • G
  • G

Prune (s,g)
Prune (s,g)

  • S
  • S

  • G
  • G

  • 24
  • 25

6

Graft
Steady State

  • G
  • G

  • G
  • G

  • G
  • G

Report (g)
Graft (s,g)
Graft (s,g)

  • S
  • S

G
G

26

27

  • Overview
  • Supporting Multicast on the Internet

•ꢀ IP Multicast Service Basics •ꢀ Multicast Routing Basics

•ꢀ Overlay Multicast

Application

?

At which layer should multicast be implemented?

?

IP

•ꢀ Reliability

Network

•ꢀ Congestion Control

Internet architecture

  • 28
  • 29

7

  • IP Multicast
  • End System Multicast

MIT1
MIT

MIT
Berkeley

UCSD
Berkeley
UCSD
MIT2 CMU1
CMU

routers end systems multicast flow

CMU
CMU2
Berkeley

MIT1

Overlay Tree

MIT2
UCSD

•ꢀ Highly efficient

CMU1
CMU2

•ꢀ Good delay

  • 30
  • 31

Potential Benefits Over IP Multicast
Concerns with End System Multicast

•ꢀ Self-organize recipients into multicast delivery

•ꢀ Quick deployment

overlay tree

•ꢀ All multicast state in end systems

•ꢀ Must be closely matched to real network topology to be efficient

•ꢀ Performance concerns compared to IP Multicast

•ꢀ Increase in delay

•ꢀ Computation at forwarding points simplifies support for higher level functionality

MIT1
MIT

•ꢀ Bandwidth waste (packet duplication)

Berkeley

  • MIT1
  • MIT1

Berkeley
Berkeley

MIT2
UCSD

UCSD
MIT2
MIT2
UCSD

CMU1

CMU1

CMU1

CMU

  • End System Multicast
  • IP Multicast

CMU2
CMU2

CMU2

  • 32
  • 33

8

  • Overview
  • Implosion

•ꢀ IP Multicast Service Basics

  • Packet 1 is lost
  • All 4 receivers request a resend

Resend request

  • S
  • S

•ꢀ Multicast Routing Basics •ꢀ Overlay Multicast

•ꢀ Reliability

1 2

  • R1
  • R1

  • R2
  • R2

•ꢀ Congestion Control

  • R3
  • R4
  • R3
  • R4

  • 34
  • 35

  • Retransmission
  • Exposure

Packet 1 does not reach R1; Receiver 1 requests a resend
Packet 1 resent to all 4 receivers

•ꢀ Re-transmitter

Resend request

•ꢀ Options: sender, other receivers

Resent packet

  • S
  • S

•ꢀ How to retransmit

  • 1 2
  • 1

•ꢀ Unicast, multicast, scoped multicast, retransmission group, …

1

  • R1
  • R1

•ꢀ Problem: Exposure

  • R2
  • R2

  • R3
  • R4
  • R3
  • R4

  • 36
  • 37

9

Scalable Reliable Multicast (SRM)
Ideal Recovery Model

Packet 1 reaches R1 but is lost before reaching other Receivers
Only one receiver sends NACK to the nearest S or R with packet

•ꢀ Originally designed for wb

Resend request Resent packet

Repair sent only to

•ꢀ Receiver-reliable

  • S
  • S

those that need packet

  • 1 2
  • 1

•ꢀ NACK-based

•ꢀ Every member may multicast NACK or

  • R1
  • R1

retransmission

1

  • R2
  • R2

  • R3
  • R4
  • R3
  • R4

  • 38
  • 39

SRM Request Suppression
Deterministic Suppression

  • Packet 1 is lost; R1 requests
  • Packet 1 is resent; R2 and R3 no

  • longer have to request a resend
  • resend to Source and Receivers

3d

Time

Resend request
Resent packet

  • S
  • S

ddata
2d

  • 1 2
  • 1

X

dd

  • R1
  • R1

dd

  • repair
  • nack

= Sender
3d

  • R2
  • R2

= Repairer = Requestor

X

4d d

Delay = C1ꢀdS,R
Delay varies

by distance

  • R3
  • R3

X

  • 40
  • 41

10

SRM Star Topology

Packet 1 is lost; All Receivers request resends

SRM: Stochastic Suppression

Packet 1 is resent to all Receivers

0

Time

Resend request
Resent packet

  • S
  • S

ddata

  • 1 2
  • 1

1d

X

repair

session msg d

d
2
NACK
3
2d

  • R2
  • R3
  • R4
  • R2
  • R3
  • R4

= Sender

Delay = U[0,D2] ꢀdS,R

= Repairer = Requestor

Delay is same length

  • 42
  • 43

  • SRM (Summary)
  • Overview

•ꢀ IP Multicast Service Basics •ꢀ Multicast Routing Basics •ꢀ Overlay Multicast

•ꢀ NACK/Retransmission suppression

•ꢀ Delay before sending •ꢀ Delay based on RTT estimation •ꢀ Deterministic + Stochastic components

•ꢀ Periodic session messages

•ꢀ Full reliability

•ꢀ Reliability

•ꢀ Estimation of distance matrix among members

•ꢀ Congestion Control

  • 44
  • 45

11

  • Multicast Congestion Control
  • Video Adaptation: RLM

•ꢀ What if receivers have very
•ꢀ Receiver-driven Layered Multicast •ꢀ Layered video encoding

100Mb/s

different bandwidths?
•ꢀ Each layer uses its own mcast group •ꢀ On spare capacity, receivers add a layer •ꢀ On congestion, receivers drop a layer •ꢀ Join experiments used for shared learning

100Mb/s

R
S

•ꢀ Send at max?

R

1Mb/s
???Mb/s

•ꢀ Send at min?

1Mb/s

R

•ꢀ Send at avg?

R

56Kb/s

  • 46
  • 47

Layered Media Streams
Drop Policies for Layered Multicast

•ꢀ Priority

R1 joins layer 1, joins layer 2 joins layer 3

•ꢀ Packets for low bandwidth layers are kept, drop queued packets for higher layers

R2
10Mbps
R1

•ꢀ Requires router support

10Mbps

•ꢀ Uniform (e.g., drop tail, RED)

R2 join layer 1, join layer 2 fails at layer 3

512Kbps
S
R

•ꢀ Packets arriving at congested router are dropped regardless of their layer

R
10Mbps

128Kbps

•ꢀ Which is better?

R3

R3 joins layer 1, fails at layer 2

  • 48
  • 49

12

  • RLM Intuition
  • RLM Intuition

•ꢀ Uniform

•ꢀ Better incentives to well-behaved users •ꢀ If oversend, performance rapidly degrades •ꢀ Clearer congestion signal •ꢀ Allows shared learning

•ꢀ Priority

•ꢀ Can waste upstream resources •ꢀ Hard to deploy

•ꢀ RLM approaches optimal operating point

•ꢀ Uniform is already deployed •ꢀ Assume no special router support

  • 50
  • 51

  • RLM Join Experiment
  • Join Experiments

•ꢀ Receivers periodically try subscribing to higher layer

Layer
4

•ꢀ If enough capacity, no congestion, no drops

ꢀ Keep layer (& try next layer)

32

•ꢀ If not enough capacity, congestion, drops

ꢀ Drop layer (& increase time to next retry)

•ꢀ What about impact on other receivers?

1
Time

  • 52
  • 53

13

RLM Scalability?

•ꢀ What happens with more receivers? •ꢀ Increased frequency of experiments?

•ꢀ More likely to conflict (false signals) •ꢀ Network spends more time congested

•ꢀ Reduce # of experiments per host?

•ꢀ Takes longer to converge

•ꢀ Receivers coordinate to improve behavior

54

14

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  • Introduction to IP Multicast Routing

    Introduction to IP Multicast Routing

    Introduction to IP Multicast Routing by Chuck Semeria and Tom Maufer Abstract The first part of this paper describes the benefits of multicasting, the Multicast Backbone (MBONE), Class D addressing, and the operation of the Internet Group Management Protocol (IGMP). The second section explores a number of different algorithms that may potentially be employed by multicast routing protocols: - Flooding - Spanning Trees - Reverse Path Broadcasting (RPB) - Truncated Reverse Path Broadcasting (TRPB) - Reverse Path Multicasting (RPM) - Core-Based Trees The third part contains the main body of the paper. It describes how the previous algorithms are implemented in multicast routing protocols available today. - Distance Vector Multicast Routing Protocol (DVMRP) - Multicast OSPF (MOSPF) - Protocol-Independent Multicast (PIM) Introduction There are three fundamental types of IPv4 addresses: unicast, broadcast, and multicast. A unicast address is designed to transmit a packet to a single destination. A broadcast address is used to send a datagram to an entire subnetwork. A multicast address is designed to enable the delivery of datagrams to a set of hosts that have been configured as members of a multicast group in various scattered subnetworks. Multicasting is not connection oriented. A multicast datagram is delivered to destination group members with the same “best-effort” reliability as a standard unicast IP datagram. This means that a multicast datagram is not guaranteed to reach all members of the group, or arrive in the same order relative to the transmission of other packets. The only difference between a multicast IP packet and a unicast IP packet is the presence of a “group address” in the Destination Address field of the IP header.
  • Shortest Path Bridging IEEE 802.1Aq

    Shortest Path Bridging IEEE 802.1Aq

    Shortest Path Bridging IEEE 802.1aq NANOG49 June 13-16/2010 Peter Ashwood-Smith Fellow [email protected] Abstract 802.1aq Shortest Path Bridging is being standardized by the IEEE as an evolution of the various spanning tree protocols. 802.1aq allows for true shortest path routing, multiple equal cost paths, much larger layer 2 topologies, faster convergence, vastly improved use of the mesh topology, single point provisioning for logical membership (E-LINE/E-LAN/E-TREE etc), abstraction of attached device MAC addresses from the transit devices, head end and/or transit multicast replication , all while supporting the full suit of 802.1 OA&M. 2 Outline • Challenges • What is 802.1aq/SPB • Applications • How does it work • Example (won’t cover but included here) 3 Challenges • L2 networks that scale to ~1000 bridges. • Use of arbitrary mesh topologies. • Use of (multiple) shortest paths. • Efficient broadcast/multicast routing and replication points. • Avoid address learning by tandem devices. • Get recovery times into 100’s of millisecond range for larger topologies. • Good scaling without loops. • Allow creation of very many logical L2 topologies (subnets) of arbitrary span. • Maintain all L2 properties within the logical L2 topologies (transparency, ordering, symmetry, congruence, shortest path etc). • Reuse all existing Ethernet OA&M 802.1ag/Y.1731 4 Example STP 36 nodes 1- Can’t use these links SOURCE ROOT A1.. A100 DEST 2 - LEARN A1..A100 5 Outline • Challenges • What is 802.1aq/SPB • Applications • How does it work 6 What is 802.1aq/SPB • IEEE protocol builds on 802.1 standards • A new control plane for Q-in-Q and M-in-M – Leverage existing inexpensive ASICs – Q-in-Q mode called SPBV – M-in-M mode called SPBM • Backward compatible to 802.1 – 802.1ag, Y.1731, Data Center Bridging suite • Multiple loop free shortest paths routing – Excellent use of mesh connectivity – Currently 16, path to 1000’s including hashed per hop.
  • IP Multicast

    IP Multicast

    Data Communication & Networks G22.2262-001 Session 10 - Main Theme IP Multicast Dr. Jean-Claude Franchitti New York University Computer Science Department Courant Institute of Mathematical Sciences 1 Agenda Introduction to Multicast Multicast Addresses IP Multicast Reliable Multicast Pragmatic General Multicast (PGM) Reliable Multicast Protocol (RMP) Conclusion 2 Part I Introduction to Multicast 3 Cast Definitions Unicast - send to one destination (198.122.15.20) General Broadcast - send to EVERY local node (255.255.255.255) Directed Broadcast - send to subset of nodes on LAN (198.122.15.255) Multicast - send to every member of a Group of “interested” nodes (Class D address). RFC 1112 (an easy read!) 4 Why Multicast, Why Not Unicast? Unicast: Many applications require same message sent to many nodes (10, 100, 1000, n) Same message transits network n times. n messages requires n*(CPU time) as 1 message Need to deliver “timely” information. Message arrives at node n >> node 1 5 Why Multicast, Why Not Broadcast? Broadcast: Send a copy to every machine on the net Simple, but inefficient All nodes “must” process the packet even if they don’t care Wastes more CPU cycles of slower machines (“broadcast radiation”) General broadcast cannot be routed Directed broadcast is limited in scope (to machines on same sub-net or same domain) 6 Multicast Applications News/sports/stock/weather updates Software distribution Video-conferencing, shared whiteboards Distributed interactive gaming or simulations Email distribution lists Database replication 7 IP Multicast - Concepts Message sent to multicast “group” of receivers Senders need not be group members Each group has a “group address” Groups can have any size End-stations (receivers) can join/leave at will Data Packets are UDP (uh oh!) 8 IP Multicast Benefits Distribution tree for delivery/distribution of packets (i.e., scope extends beyond LAN) Tree is built by multicast routing protocols.