Hans Erikson M6ONE: The Backbone

The first thing many researchers the cause of severe problam m the n+rwork and one for the hoar. .Io dif- like me do when they come to NSFnet backbone, saturation of ferentiate between the classes, star, work is read their email. The sec- major international links rendering with 0, I or 2 bits that are set followed ond thing on my list is to check them useless as well as sites being by a zero bit. Class A addresses start what is on the MBone-the completely disconnected due to with binary “0” and are in the range Multicast Backbone, which is a Connrction Management 0.0.0.0 to 127.255.255.255, class B virtual network on “top” of the Protocol (ICMP) responses flooding starts with “lo” with a range of Internet providing a multicasting the networks. We will expand on this 128.0.0.0 to 191.255.255.255, and facility to the Internet. There might later in this article. class C starts with “I IO” with a range be video from the Space Shuttle, a of 192.0.0.0 to 223.255.255.255. No[ seminar from Xerox, a plenary ses- Multicasting Background all addresses are available for host sion from an interesting conference When we talk about MBone we somr- addresses, however, as some are de- or a software demonstration for the times mean thr virtual network that fined for specific uses (e.g., broadcasr Swedish prime minister. implements multicasting, sometimes addresses). Class D is indicated by It all started in March 1992 when we refer to the applications that run “I 110” at the start, giving an ad- the first audiocast on the Internet on top of MBone (vat, nv, ivs, for ex- dress range of 224.0.0.0 t” took place from the Internet Engi- ample), and often we mea” every- 239.255.255.255. This class has been nrering Task Force (IETF) meeting thing. We will come back to the appli- reserved for multicast addresses. in San Diego. At that event 20 sites cations that are in use on MBone later When a host wishes tojoin a muh- listened to the audiocast. Two years in this article, but for now we will con- cast group, that is, get packets with a later, at the IETF meeting in Scattle centrate on the MBone proper, the specific , the host about 567 hosts in 15 countries tuned multicasting virtual network. issues a” Internet Group Manage- in to the two parallel broadcasting First let us define what is meant by ment Protocol (IGMP) request. The channels (audio and video) and also the different types of “casting.” The multicast router for that subnet will talked back (audio) and joined the usual way packets are sent on the then inform the other routers so that discussions! The networking commu- Intrrnet is unicasting, that is, one such packets will get to this subner nity now takes it for grantrd that the host is sending to another specific sin- and eventually be placed on the local- IETF meetings will be distributed via gle host. Broadcasting is when one area network (IAN) where the host is MBone. MBone has also been used to host sends to all hosts on the same connected. Frequently, the local distribute experimental data from a subnet. Normally, the routers be- router will poll the hosts on the IAN robot at the bottom of the Sea of Cor- tween one subnet and another subnet if they are still listening to the multi- tee (as will be described later) as well will not let broadcast packets pass cast group. If not, no more such as a late Saturday night feature movie through. Multicasting is when one packets will be placed onto the LAN. WAX or the Dmovely sf Televmon host sends to a group of hosts. When doing multicasting utilizing Among the Bee.~ by David Blair. On the link level (e.g., Ethernet) MBone, the sender does not know As soon as some crucial tools ex- multicasting has been defined for who will receive the packets. The isted, the usage just exploded. Many some time. On the network level (In- sender.just sends to a” address and it people started using MBone for con- terface Protocol or IP) it started with is up to the receivers to join that ferences, weather maps, research the work of Steve Deering of Xerox group (i.e., multicast address). An- experiments, to follow the Space PARC when he developed multicast other style of multicasting is where Shuttle, for rxample. At thr Swedish at the IP level [3]. The IP address the sender specifies who should re- Institute of Computer Science (SICS) space is divided into different classes. ceive the multicast. This gives more we saw our contribution to the Swed- A” IP address is four bytes and the control over the distribution, but one ish University Network SUNET, in- address classes A, B and C divide the drawback is that it does not scale well. crease from 26GB per month in Feb- addresses into a network part and a Having thousands of receivers is al- ruary 1993 to 69GB per month in host part. The difference between the most impossible to handle this way. March 1993. This was mainly due to classes is the balance between bits des- This second style of multicasting has multicast tmff,c as SICS at that time ignating network and hosts. Class A been used in ST-2 [6, 81. was the major connection point be- addresses have one byte for the net- tween the U.S. and Europe in work and three for host, B addresses MBone Today MBone. have two bytes for each, and class C As previously mentioned, MBonc 1s a MBone has also (in)directIy been addresses have three bytes for the virtual network running on “top” of