Design and investigation of scalable multicast recursive protocols for wired and wireless ad hoc networks

-I- First, a basic packet (BP) with a size of maximum transfer unit (MTU) is used a
benchmark. The BP is a packet which has an IP header, with one source and one
destination, and its payload.

-I- Secondly, Multicast packets (MPs) are always of a bigger size than a BP due to the
fact that there might be a multicast group address or a protocol header in the multicast
packets. However, the control messages (CMs) (in SEM and SReM) are usually of a
size of less than MTU (for SEM) or far less than MTU (for SReM). For simplicity,
we treat them as multicast packets with a size of MTU.

-I- Thirdly, assuming that the processing cost to be 1 ( unit ) if a packet with a size of
BP is needed to be processed at a node and the delivering cost of this packet to be 1
as well if it is delivered via a link with a cost of 1.

Depending on the previous assumptions, the processing cost at node k is given by

S

Pcos t (Nk ) = MkMP × — + M ,                         (1)

S _BP

where _M and M are the number of destinations in multicast packets and that in
^M k , MP            k,CM

control messages at node k, S _MP and S _BP are the size of a multicast packet and the size
of a BP (i.e. MTU), respectively. In this simulation, the values of MTU fixed at 576 octets,
i.e., the minimum size of packets required for routers. When the size of multicast packets is
over MTU, a fragment processing for packets is needed, which might happen for Xcast
multicast packets, but not being considered in our simulation.

Correspondingly, the delivering cost for one multicast packet over a link i is given by

S

D cos t ( Li) = Li × ( -M^ + J₁C_m ),                                      (2)

S _BP

WhereJ _i,CM and L _i are the number of destinations in control messages and the cost over
a link I, respectively.

Based on previous discussion, the average processing cost ( p cos t ) at a node and average
delivering cost ( D_ra t ) over a link are given by,

P c_0s t = ɪ ∑ P_cost ( N_t )^{,                                                               (3)}

cost t

N t∈T

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