Implementation of multicast communication in internet
Individual hosts are configured as members of different multicast groups
One particular user may a member of many multicast groups
For a one multicast can be few members/nodes
IP Multicast group is identified by Class D address (224.0.0.0 – 239.255.255.255)
Every IP datagram send to a multicast group is transferred to all members of group
TEST CASE GENERATION GENERATION BLOCK BOX APPROACH
IP Multicasting
1. “
”
IP Multicasting
Background knowledge, What is IP Multicasting
Applications and Architecture
IGMP
Multicast routing
Reverse Path Forwarding (RPF)
Multicast distribution
PIM and Mapping and Rendezvous point
Address translation
2. IP Multicasting
“Implementation of multicast communication in
internet”
Individual hosts are configured as members of different multicast groups
One particular user may a member of many multicast groups
For a one multicast can be few members/nodes
IP Multicast group is identified by Class D address (224.0.0.0 –
239.255.255.255)
Every IP datagram send to a multicast group is transferred to all members
of group
3. Applications
Situations where multiple end points need to receive identical info at same
time
News/Sports/Stocks/Weather updates
Teleconferencing (Audio, Video, White board etc…)
Distance learning
Data replication
Stream video
Issues
Complexity
Early days routers are not configured to do multicasting in proper
manner
4. IP Multicasting components
IP multicast addressing (how we address
IP Group management
Multicast routing
Multicasting is UDP based
Best effort delivery
No congestion avoidance
Added complexity
IP Multicasting considerations
7. Multicast Address translation
In Ethernet Mac addresses a multicast address is identified by setting the
lowest bit of the most left byte
First 4 bytes -> Class D address
Special Class D addresses
224.0.0.1 really means all systems on this subnet
224.0.0.2 means all routers on this subnet
224.0.1.1 is for NTP (Network Time Protocol) used for synchronizing
machines
224.0.0.9 is for RIP-2 (a routing protocol).
8. Internet Group Management Protocol (IGMP)
Use by host to notify the local router that it wishes to receive (or stop
receiving) multicast traffic for given destination node or group
IGMP operates on physical network
Eg: single Ethernet segment
IGMP supports
Joining a multicast group
Query membership
Send membership reports
IGMP snooping
Send multicast only to needed ports
9. Multicast Routing
Source can determine who can be the member of group and who will not
be
Required mechanism
Packet forwarding can send multiple copies of same packet
Multicast routing algorithm which builds spanning tree
Two types of trees
Source Tree
Shared Tree
Single copy replicate in network
Routing tables are different in the two trees
10. Protocol Independent Multicast (PIM)
Router to router signal protocol
Use by a router to notify an upstream router that it wishes to receive (or
stop receiving) multicast traffic
Three main classifications of PIM
Dense
Sparse
Sparse dense
Source specific
Bidirectional
12. PIM-SM Rendezvous Point (RP)
PIM-SM uses a router called Rendezvous Point
The purpose of RP to allow, the first hop router to find out the IP address of
the source for a particular group.
The receiver don’t know the source address
A RP is mandatory for PIM Sparse Mode
PIM-SM Rendezvous Point Discovery
Static RP configuration
Dynamic RP configuration
13. Multicast advantages
Enhanced scalability
Network utilization is independent of the number of receivers
Network handle replication
Reduce resource utilization
Controls network bandwidth and reduces server and router load
Deterministic performance
Subscriber number 1 and subscriber number 10000 have identical
experience
14. Summery
IP Multicasting is somewhat similar to “spreading of virus”
Replication at each router
Functions are layered
IGMP to handle host to router
PIM to inter router signaling
Different message formats for IP Multicasting
Scalability accommodate more functions and features
15. References
[1] YouTube. “Lecture - 32 IP Multicasting”. Youtube.com. [Online]. Available
https://www.youtube.com/watch?v=TApIo_BiX6U [Accessed: 3 Aug2014].
[2] YouTube. “Cisco Live 2014: IP Multicast Concepts, Design and Troubleshooting
(Melbourne)”. Youtube.com. [Online]. Available https://www.youtube.com/watch?v=l9RJdrdjDU8
[Accessed: 3 Aug2014].
Hinweis der Redaktion
The flow of the presentation mentioned in this slide.
At the end of the presentation there will be two slides stating a “summery” and “references”.
3 modes of operations
Unicast : One sender to one receiver
Broadcast: One sender to all receivers
Multicast: One /Many sender/senders to many receivers in the group
There for “Multicasting” is “1 to Many” or “Many to Many”
IP Multicasting more concern on from where the packets come from
In IP Multicasting, packet replicating happens inside the network
Developing multicast-enabled applications is ostensibly simple. Having datagram access allows any application to send to a multicast address. A multicast application need only increase the Internet Protocol (IP) time-to-live (TTL) value to more than 1 (the default value) to allow outgoing datagrams to traverse routers. To receive a multicast datagram, applications join the multicast group, which transparently generates an [IGMPv2, IGMPv3] group membership report.
This apparent simplicity is deceptive, however. Enabling multicast support in applications and protocols that can scale well on a heterogeneous network is a significant challenge. Specifically, sending constant bit rate data streams, reliable data delivery, security, and managing many-to-many communications all require special consideration. Some solutions are available, but many of these services are still active research areas.
IP Multicast considerations in detail
Multicast is UDP based
No flow control
Sequencing
Error correction
Retransmission
Best effort delivery
Sender has no idea if all the subscribers have received the data. Subscribers don’t know if they have missed a packet. Applications should handled missed packets
No congestion avoidance
Slow start hence might result in network congestion
Added complexity
If we have the bandwidth available then unicast delivery model may be a simple option.
Adding protocol mean adding complexity
Right hand side, source pours multicast to network
Left hand side, nodes that receive the multicast
No control plan from receiver to sender
A device can be multicast sender/receiver at same time
Layer 2: Host to Router protocol : IGMP
Layer 3: Multicast Routing protocol
IP Multicast only support UDP as higher layer (Connectionless datagram oriented protocol)
So use UDP as transport layer protocol
“IP” takes part in normal routing protocol
“IP Multicast” takes care of multicast routing protocol
Mapping process
Suppose in this 1110, the first 4 bits and suppose this is the class D address and we are looking at the first byte of that address and the first four bits 1110 identifies that this is a class D address. Then this bit is actually ignored and then we have a 23 bit address. This 23 bit address comes straight to the Ethernet address. So these 7 bits, these 8 bits and these 8 bits are matched straight to the last 3 bytes of the Ethernet address. For the first three bytes of the Ethernet address we have a one here showing that this is multicast. Actually the Ethernet address with 01, 00, 5e in the first 3 bytes are reserved for IP multicast. So 01, 00 and this is 101 is 5e and 1110 is e. So, this is 01, 00, 5e and this is first 3 bytes, this is reserved for multicast and this part comes straight away.
IGMP : Joining group
Receiver sends IGMP membership report to router
Once received, send it to LAN and to host
Second receiver asks for same
That report is redundant ( since router is already doing what it suppose to do)
IGMP : Maintaining group
A host does not want multicast any more
It sends IGMP leave message to Router
Router check if is there any one still need it
If still need, still forward (Switch also knows)
IGMP : Leaving
Last host on the network say that it doesn’t need multicasting anymore
Router turnoff packet sending
Advantages of IGMP snooping
Hosts only receive MC traffic that they request
Fast
Multicast routing protocol
This is an additional service by router since unicast is already there
Building spanning tree between all members of multicast group
Source tree
Packet goes directly from source to receiver
Receiver needs knowledge of receiver
Traffic travel from source to receiver
Packets are replicated at branches
Provide optimal routing
Representation (S,G)
Shared tree
Packets don’t go directly from source to receiver
Flows through an arbitrary point : “Rendezvous point”
Root is common
Less state required
PIM-SM Router-Router Signaling
Each PIM router forms neighbor relationship with adjacent PM router at every 30 seconds
When PIM router wants to receive a multicast stream it sends a “PIM Join” message
When want to stop receiving send “Prune” message
Tree formed from destination
Each potential destination reach up-to source
For each recipient minimize path cost
RPF forward: forward only if receive from neighbor
PIM-SM operation
Advantages of Source Specific Multicasting
Easy to configure and maintain
Efficient network usage
Enforce security
PIM-SSM mapping
Use PIM-SSM in the network when we have hosts that only supports IGMP v2
Mapping can used as an interim measure until IGMP v3 is supposed on all hosts
Two ways to map
* PIM-SSM is static mapping
* PIM-SSM dynamic mapping (DNS)
Following drawbacks can be identified
Issues with multicast source
Issues with receiver
Underlying network issues
MC network misconfiguration