Transcript Document

Multicast Communication
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The Basics of Group Communication
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Quality of Service
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Types of communication
Integrated Services (IntServ)
Resource Reservation Protocol (RSVP)
ST2
MBone
Reference
R. Wittman and M. Zitterbart, Multicast Communication,
Protocols and Applications, ISBN 1-55860-645-9, 2001.
Network Architecture and Design
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Unicast Communication (1:1)
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One packet for each receiver
Network Architecture and Design
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Multicast Communication (1:n)
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One packet to many receivers
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Routers replicate the packet
Like mailing lists
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One email to many receivers
Network Architecture and Design
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Unicast Vs. Multicast
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Unicast
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With 3 receivers, sender must replicate the stream 3 times.
Consider good quality audio/video streams are about
1.5Mb/s (a T1).
Each additional receiver requires another 1.5Mb/s of
capacity on the sender network.
Multiple duplicate streams over expensive WAN links.
Multicast
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Source transmits one stream of data for 3 receivers.
Replication happens inside routers and switches.
WAN links only need one copy of the data, not 3 copies.
Network Architecture and Design
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How Multicast works?
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Nodes consist groups
Each group is identified by a single IP address
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Class-D addresses
Groups may be of any size and members of
groups may be located anywhere in the
Internet.
Members of groups can join and leave (IGMP).
Senders need not be members.
Network Architecture and Design
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Class–D Addresses
1 110
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Class-D IP address
In “dotted decimal” notation:
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group ID
224.0.0.0 — 239.255.255.255
Nodes that support class-D addresses
consist the Multicast Backbone (MBone)
Network Architecture and Design
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Other Types of Communication
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Concast Communication (m:1).
Multipeer/multipoint (m:n).
Broadcast.
Anycast.
Network Architecture and Design
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Anycast
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Distance between client and server is
usually large
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High response time
Bandwidth binding in many links
Inflexible in topology changes
Need for many service points
Network Architecture and Design
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What is Anycast Routing?
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A means of selecting and communicating
with anyone of a set of distributed
servers or service access points within a
network
The router delivers the datagram to the
nearest member of the group.
Appropriate for server-based applications
Network Architecture and Design
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Unicast Routing Example
FTP Request
Database Request
Database Server
FTP Server
Network Architecture and Design
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Anycast Routing Example
FTP Request
Database Request
Database Server group
FTP Server group
Resolver
Network Architecture and Design
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Anycast Routing - Resolver
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Close to client
Maintains
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Anycast group membership
Selects web server according to:
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Best response time
Best server processing time
Network Architecture and Design
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Multicast Communication
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The Basics of Group Communication
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Quality of Service
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Types of communication
Integrated Services (IntServ)
Resource Reservation Protocol (RSVP)
ST2
MBone
Network Architecture and Design
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IntServ
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Change Internet service to provide QoS
IntServ is not a protocol but a
framework.
Usage of RSVP or ST2.
Supports three classes of services
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Best Effort
Controlled Load Services
Guaranteed Services
Network Architecture and Design
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IntServ
An analogy: Travel by airplane
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Unreserved seat = Best Effort
Reserved Seat = Controlled Load
Charter your own flight = Guaranteed
Service
Network Architecture and Design
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IntServ
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Best Effort
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Controlled Load
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Bandwidth is not reserved
Per-packet delay is not guaranteed
Bandwidth is reserved
Per-packet delay is not guaranteed
Performs like a lightly loaded Best Effort network
Guaranteed Service
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Bandwidth is reserved
Per-packet delay is guaranteed
Performs like having your own network
Network Architecture and Design
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IntServ
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Traffic Flow
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Multimedia IP traffic is correlated.
Each packet from a sender to a receiver is
part of a flow.
IntServ provides QoS for a Flow, not
individual packets.
Flow specification generally same as TCP
connection (IP Address/Port).
Need for reservation setup mechanism.
Network Architecture and Design
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RSVP
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What is RSVP?
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RSVP: Resource Reservation Protocol
Application reserve resources in order to specify
desired QoS to net.
Multicast friendly, receiver-oriented.
Why run RSVP?
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Allows precise allocation of network resources.
Guarantees on quality of service.
Heterogeneous bandwidth support for multicast.
Network Architecture and Design
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RSVP Operation
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Sender advertises PATH messages to
receiver
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PATH = TSpec + AdSpec
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TSpec: Specify the traffic characteristics
AdSpec:
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Contain information about the path’s resources
Updated in every RSVP capable router
Help receivers calculate the resources needed to
obtain desired QoS
Network Architecture and Design
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RSVP Operation (cont)
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Receiver reserves resources using RESV
messages
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RESV = Rspec + filterspec + policy data
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Rspec: Specify the bandwidth needed
Filterspec: How reservations are distributed to data
streams and users.
Travel upstream in reverse direction of Path
message
Routers receive the RESV messages and make
the reservation (if available resources are more
than Rspec resources)
Network Architecture and Design
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RSVP Example
R2
R3
PATH
2
1
PATH
R4
R1
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Host A
24.1.70.210
Host B
128.32.32.69
R5
1. An application on Host A creates a session,
128.32.32.69/4078, by communicating with the
RSVP daemon on Host A.
3. The PATH message follows the next hop path
through R5 and R4 until it gets to Host B. Each
router on the path creates soft session state with
the reservation parameters.
2. The Host A RSVP daemon generates a PATH
message that is sent to the next hop RSVP
router, R1, in the direction of the session
address, 128.32.32.69.
Network Architecture and Design
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RSVP Example
R2
R3
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PATH
RESV
PATH
R4
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RESV
R1
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Host A
24.1.70.210
Host B
128.32.32.69
R5
4. An application on Host B communicates
with the local RSVP daemon and asks for a
reservation in session 128.32.32.69/4078. The
daemon checks for and finds existing session
state.
6. Reservation has been made and data flow
begins with the guaranteed QoS.
5. The Host B RSVP daemon generates a
RESV message that is sent to the next hop
RSVP router, R4, in the direction of the source
address, 24.1.70.210.
Network Architecture and Design
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Internet Stream Protocol Version 2 (ST2)
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The communication process takes place
in three separate steps:
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Establishment of an ST2 stream
Transfer of user data
Termination of an ST2 stream.
Different protocols are applied
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ST2
SCMP (Stream Control Message Protocol)
Network Architecture and Design
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RSVP Vs. ST2
ST2
RSVP
Functionality
Signaling protocol and
data transfer.
Signaling.
Connection Types
Connection-oriented,
multicast, multipeer.
Short-lived
connections, multicast.
Reservations
Sender or Receiver
oriented
Receiver-oriented
Modifications
QoS and receiver
group through explicit
messages
QoS and receiver
group through periodic
messages
Error Handling
Complex control and
correction
Periodic message
exchange
Heterogeneity
No
Yes
Network Architecture and Design
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The MBone
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An “interconnected” set of multicastcapable routers, providing the IP
multicast service in the Internet
Can be thought of as a virtual network,
overlaid on the Internet
Network Architecture and Design
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Mbone - Example
Tunnel
Simple Router
Multicast Router
Source Node
Destination Node
Network Architecture and Design
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MBone Tunnels
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A method for sending multicast packets
through multicast-ignorant routers
IP multicast packet is encapsulated in a
unicast packet addressed to far end of tunnel
IP header,
IP header,
transport header
dest = unicast dest = multicast
and data…
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A tunnel acts like a virtual point-to-point link
Each end of tunnel is manually configured
with unicast address of the other end
Network Architecture and Design
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End of Third Lecture
Network Architecture and Design
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