Protocols for Multimedia on the Internet

1
Protocols for Multimedia on the Internet

• Raj Jain The Ohio State UniversityColumbus, OH
  43210Jain_at_cse.ohio-State.Edu
• http//www.cse.ohio-state.edu/jain/

2
Overview

• Integrated services
• Resource Reservation Protocol RSVP
• Integrated Services over ATM
• RSVP over ATM
• Real-time Transport Protocol RTP, RTCP
• Real-Time Streaming Protocol RTSP

3
Multimedia on the Internet

• Specify source traffic requirements
• Protocols to create and maintain resource
  reservations
• Routing protocols that support QoS and multicast
  
• Transport protocols for error and flow control
• Access control
• Packet scheduler to provide QoS

4
Multimedia on the Internet

• Specify source traffic requirements Flow specs
  from INTSERV working group
• Protocols to create and maintain resource
  reservations RSVP
• Routing protocols that support QoS and multicast
  MOSPF, IGMP
• Transport protocols for error and flow control
  RTP
• Access control Connection admission based on
  usage, packet dropping
• Packet scheduler to provide QoS Weighted Fair
  Queueing

5
IGMP

• Internet Group Management Protocol
• Used by hosts to report multicast membership
• Join-IP-Multicast Group (address, interface)
• Leave-IP-Multicast Group (address, interface)
• Ref RFC 1112 (Version 1)

Routers
Hosts
6
IGMP Operation

• One "Querier" router per link
• Every 60-90 seconds, querier broadcasts "query"
  to all-systems (224.0.0.1) with TTL 1
• After a random delay of 0-10 seconds, hosts
  respond for each multicast group
• Everyone hears responses and stops the delay
  timer ? One response per group
• Non-responding groups are timed-out
• IGMP V2 is an internet-draft. IGMP V3 is being
  designed.

7
Integrated Services

• Best Effort Service
• Controlled-Load Service Performance as good as
  in an unloaded datagram network. No quantitative
  assurances. (Min throughput)
• Guaranteed Service
• Firm bound on data throughput and delay.
• Every element along the path must provide delay
  bound.
• Is not always implementable, e.g., Ethernet.
• Delay jitter or average delay not guaranteed or
  minimized.

8
Flow Specification

• Flow Spec Traffic Spec QoS Spec TSpec
  RSpec
• TSpec Peak rate (p), bucket rate (r), bucket
  size (b), max datagram size (M), min policed unit
  (m)
• All datagrams less than m are counted as m bytes
• Peak rate may be unknown or unspecified
• RSpec Allocated Rate (R) and delay slack (S) S
  Extra acceptable delay over that obtainable
  with RZero slack Þ Reserve exactly R.
• RSpec specified only for guaranteed rate service.
  Not for controlled load service.

9
IS-Capable Router Components
RoutingProcess
ReservationProcess
PolicyControl
Admission Control
PacketClassifier
Packet Scheduler
10
IS Router Components (Cont)

• Packet Scheduler Manages queues and timers for
  different streams
• Classifier Each incoming packet is examined to
  determine its classPackets in the same flow may
  have preemptable (CLP) attribute
• Admission Control Determine whether a new flow
  can be granted without affecting existing flows
• Reservation Setup Protocol RSVP

11
RSVP

• Resource ReSerVation Protocol
• Internet signaling protocol
• Carries resource reservation requests through the
  network
• Receiver initiated reservations ? Scales well
• Sets up reservations at each hop
• RSVP does not find routes. Multicast routing
  protocols do.

12
Path Messages

• Sources send quasi-periodic PATH messages to
  multicast address
• Path message contain Flow spec
• Sender Template Data format, Src Address, Src
  Port
• TSpec Traffic Characteristics. Not changed.
• ADSpec Network path resource/service
  availabilityAccumulated along the path.

13
Reservation Requests

• Receivers must join multicast address to receive
  path messages
• Receivers generate reservation (RESV) requests
• RESV messages contain resources to be reserved
• RESV messages are forwarded along the reverse
  path of PATH messages

14
Reservation (Cont)

• Requests are checked for resource availability
  (admission control) and administrative
  permissions (policy control)
• Two or more RESV messages for the same source
  over the same link are merged.
• Routers maintain a soft state. The receivers
  have to refresh periodically.
• Heterogeneous Receivers Sources divide traffic
  into several flows. Each flow is a separate RSVP
  flow. Receivers join one or more flows. Each RSVP
  flow is homogeneous.

15
Reservation (Cont)

• ResV messages contain Flow Spec Filter Spec
• Filter Spec Defines the packets in the flowUsed
  in packet classifier
• Flow Spec Used in packet schedulerContents
  depends upon the service.Will generally include
  TSpec and RSpec.

16
RSVP Reservation Styles

• Fixed Filter One pipe per source
• Wildcard Filter One pipe for all sources on a
  session
• Shared-Explicit Sources explicitly identified
  (Reserve for sources S3 or S4)

17
RSVP Status

• Still an internet draft (Sep 1997)Submitted to
  IESG area director.
• Multivendor interoperability demo at Sep'95
  Interop.
• Product announced by Cisco.
• Unresolved Issues
• Accounting and charging
• Authentication and access control
• Session groups

18
RSVP vs UNI

• UNI 4.0 adds leaf initiated join.

19
Integrated Services on ATM

• Guaranteed service Peak rate, rate, and bucket
  depth for sender and Peak rate, rate, and bucket
  depth for receiver ps, rs, bs, pr, rr, br
• Separate sender and receiver specs allow receiver
  heterogeneity
• Receiver Rspec also has an allocated rate R gt rr
  to reduce delay

20
Int. Services on ATM

• Guaranteed service rtVBR (or CBR)PCR p_r, SCR
  R, MBS b_r
• Controlled load service nrtVBR (or ABR with
  MCR)PCR p_r, SCR r_r, MBS b_r
• Best effort UBR (or ABR)
• Excess can be carried on a separate VC
• ATM rate should be 10 higher than IP rates to
  account for 5 byte header/48 byte payload

21
RSVP over ATM
Src
Rcvr

• RSVP control messages on QoS or best effort VCs?
• Multiple RSVP sessions on one QoS VC?
• RSVP control is receiver oriented Þ Receiver
  generates RESV messages.Þ In ATM, either the
  subnet sender sets-up the VC or the receiver sets
  up the VC with backward direction traffic
  parameters (Not in pt-mpt VCs)
• VC Teardown No explicit RSVP close Þ timeout

22
RSVP Over ATM (Cont)

• Dynamic QoS RSVP allows QoS modification. ATM
  does not Þ Need new VC setup. Use old VC until
  the new VC is setup.
• Encapsulation LLC encapsulation. If only IP, VC
  based multiplexing is better

IP
IPX
IP
IPX
LLC Header
23
RSVP Multicast over ATM

• QoS Heterogeneity
• End-point identification
• Multicast data distribution
• Multicast receiver transitions

24
QoS Heterogeneity
R1
R2
Src
R3
R4

• Use a different VC for each QoS?
• If one VC, who pays?
• If a new receiver comes in with a larger QoS
  Increase the QoS before accepting the receiver.

25
End-point Identification

• Multicast end-points may not be identified if
  egress is tunneled(NHRP gives next hop only for
  unicast addresses)

R
R
R
26
Multicast Data Distribution

• QoS Þ Use VC mesh
• Multicast Server (MCS) Þ No QoS Þ Set break bits
  indicating service not supported
• LANE 1.0 Þ No QoS

Src
Src
R1
R1
MCS
R2
R2
R3
R3
VC Mesh
27
Multicast Receiver Transitions

• Partially set new QoS pt-mpt VC.
• Should the data be sent to old, new, or both VCs?
• Both Þ Duplicate, One Þ Loss.
• Rule Use old VC until all nodes have been added
  Þ No duplication
• Moving a VC from one QoS to another.
• Should add (remove) be done first?
• Rule Add first Þ Duplicates.

28
RSVP Control Management

• PATH messages to Multicast. RESV messages to
  unicast.Þ Need both multicast and unicast VCs.
• Can data use the same signaling VCs?
• Can different flow share these signaling VCs?
• Should these be multiple point-to-point VCs or
  point-to-multipoint VCs?

29
Desired Changes to ATM

• Heterogeneous Point-to-Multipoint Variegated
  VCs
• QoS renegotiation
• Group Address
• Lightweight Signaling

30
Summary

• TCP/IP protocols suite is being extended to allow
  multimedia on Internet
• Signaling protocol RSVP
• Integrated Services GS rtVBR, CLS nrtVBR
• RSVP over ATM Many issues
• Transport Protocol RTP, RTCP, RTSP

31
References

• For a detailed list of references see
  http//www.cse.ohio-state.edu/jain/refs/mul_refs
  .htm
• "Specification of Guaranteed Quality of
  Service", 7/7/1997,http//www.internic.net/inter
  net-drafts/draft-ietf-intserv-guaranteed-svc-08.t
  xt
• "Specification of the Controlled-Load Network
  Element Service", 5/29/1997, http//www.internic.n
  et/internet-drafts/draft-ietf-intserv-ctrl-load-sv
  c-05.txt

32
References (Cont)

• "Resource ReSerVation Protocol (RSVP) -- Version
  1 Functional Specification", 6/16/1997,
  http//www.internic.net/internet-drafts/draft-ietf
  -rsvp-spec-16.txt
• RFC 1889, RTP A Transport Protocol for
  Real-Time Applications
• "Real Time Streaming Protocol (RTSP)",
  08/02/1997, http//www.internic.net/internet-draft
  s/draft-ietf-mmusic-rtsp-03.txt

33
References (Cont)

• The MBONE information web, http//www.mbone.com/
• RFC 1819, Internet Stream Protocol Version 2
  (ST2) Protocol Specification - Version ST2
• SDP Session Description Protocol, 3/26/97,
  http//www.internic.net/internet-drafts/draft-iet
  f-mmusic-sdp-03.txt

34
References

• Voice Over IP (VoIP) Forum mailing list
  voip-tech-request_at_vocaltec.com
• E. Crawley, et al, "A Framework for Integrated
  Services and RSVP over ATM," draft-ietf-issll-atm-
  framework-00.txt, July 24, 1997

35
IETF Multimedia Working Groups

• Audio/Video Transport (avt)
• Integrated Services (intserv)
• Integrated Services over Specific Link Layers
  (issll)
• Resource Reservation Setup Protocol (rsvp)
• MBONE deployment working group (mboned)
• Multiparty Multimedia Session Control (mmusic)
• Multicast Extensions to OSPF (mospf)
• Inter-Domain Multicast Routing (idmr)

36
Working Groups (Cont)

• QoS-based Routing (qosr)

37
RTP

• Real-Time Transport Protocol
• Not really an L4 protocol. Common parts of
  several applications. Uses UDP for multiplexing
  and checksum.
• Supports unicast and multicast delivery
• Source and payload type identification
• Sequencing, Timing, and Synchronization
• Source merging Multiple contributing sources for
  a combined stream produced by an RTP mixer.
  32-bit Synchronizing source (SSRC) id.
• Stream translation High-speed to low speed

38
RTP (Cont)

• What RTP Does not Do?
• Reliable data delivery
• Quality of service guarantees
• Resource reservations (RSVP)
• Delivery of encryption key to participants
• RTP provides a general framework for applications
  to be able to do these ? Application Level
  Framing
• Two components RTP and Control (RTCP)? Simple
  RTP header
• Particular codings need additional parameters ?
  RTP Profiles documents

39
RTCP

• Real-Time Transport Control Protocol
• Convey information about participants
• Convey information about relationships among
  sessions
• Monitor application performance ? Feedback on
  quality of data
• Automatically adjusts overhead (Report frequency
  based on participant count)

40
RTCP Packet Types

• Sender Report (SR) Packets/bytes sent, lost
• Receiver Report (RR) Packets/bytes received,
  lost, jitter
• Source Description (SDES)
• End of participation (BYE)
• Application Specific functions (APP)

41
RTSP

• Real time streaming protocol
• Application level protocol similar to hyper-text
  transfer protocol (HTTP/1.1) for audio/video
• Maintains state ? Setup/teardown messages
• RTSP messages use TCP, UDP, ...
• Data transfer is done separately using TCP,
  RTP/UDP, ...
• Uses URLs, e.g., rtsp//media.example.com554/twis
  ter/audiotrack
• Both servers and clients can issue requests.
  HTTP servers do not issue requests.

42
RTSP Methods

• Setup Start a new session
• Teardown
• Redirect
• Play
• Record
• Pause
• Describe Tell me about session X
• Announce A session X will take place at t
• Get_parameter Get server/client statistics
• Set_parameter
• Options I can accept only these options.

43
Thank You!
44
RTP Frame Format

• V Version Number
• P Padding bytes present flag
• X Header extension flag
• M Marker
• Timestamp Sampling instant of the first byte

45
RTSP Terminology

• Media Stream Single audio/video
• Presentation S streams with one time axis
• Media Server Provides playback/recording of
  streams
• A single presentation could come from multiple
  servers
• Session One per stream

46
RTSP (Cont)

• Subsequent messages on the same or different
  connections.
• All RTSP requests are acked unless sent to a
  multicast group

47
MBone

• Internet Multicast backbone
• Set of routers with IP multicasting
• IP multicast address start with 1110...
  (binary), 224.0.0.0 to 239.255.255.255 (decimal)

NWnet
MIDnet
NEARnet
PSC
BARRNet
NCAR
Cornell
Merit
JvNC
UIUC
Alternet
NSI
Hawaii
ARPA
MCNC
SURA
GATech
SDSC
SESQUI
48
MBone (Cont)

• Uses radio/TV station paradigm Sender is
  allocated a multicast address. It starts
  transmitting on that address
• Anyone can listen by tuning into the multicast
  address by sending an Internet Group Management
  Protocol (IGMP) request to router to join the
  multicast
• The router provides a connection to the nearest
  point
• First audiocast in March 1992 IETF meeting to 20
  sites. Now over 600 hosts in over 15 countries
• Multicast routers setup tunnels between them.
  Tunnel direct connection

49
Tunnels
S
A
B
C

• Implemented by encapsulating the entire packet in
  another IP header.
• Each tunnel has a cost. Least cost path is found
  by exchanging distance-vectors with neighbors.

50
Internet Bandwidth Scarcity

• Each stream requires 100 to 300 kbps. Use 500
  kbps for design. A few tunnels can saturate the
  host. Four on SPARC 1, six on SPARC 10.Maximum
  two tunnels over T1.
• Each packet has a time to live (TTL). TTL is
  decremented at each router.The packet is
  forwarded iff its TTL is over a threshold.
• Pruning If a multicast router gets a packet for
  which it has no listeners, it sends a message to
  the upstream multicast router to stop sending.

51
SDP

• Session Description Protocol
• Used by session directory tool on MBone to
  announce sessions
• Currently SDP V2
• Examples Netlab Seminarsi Seminars on
  recent advances in networkingo
  maf_at_net.osu.educ 224.5.17.11 127 2873397496
  2873404696m audio 3456 0m video 2232 0

52
ST2

• Stream protocol
• Connection oriented IP. IPv5
• Uses IP addressing, routing tables
• Source oriented Sources setup real-time stream
  using a flow specification.
• Stream Message Control Protocol (SCMP)Like
  ICMP. Used to setup/teardown flows.Connect,
  Accept, Disconnect, Refuse, Change, Join
• Single rate for all destinations.
• Implementations in DEC, NeXT, Mac, PC, SGI, Sun

53
IGMP Version 2

• Querier election method
• Messages include "maximum response time"
• "Leave group" message to reduce leave
  latencySent only if the host that responded to
  the last query leaves
• Querier then issues a "membership query" with a
  short response time
• Already implemented. RFC soon.
• Ref http//www.internic.net/internet-drafts/draft
  -ietf-idmr-igmp-v2-06.txt

54
R
rr