User's Manual

Doc. No.
Rev.
Date
DRAFT
1.01
2012-01-27
Damm Cellular Systems A/S, Denmark
TetraFlex
®
7.5 Manual - IP Backbone network layout and
configuration
TetraFlex® 7.5 Manual 2-161
2.16.10 Applicable router techniques
As described previously in this document the router network between the nodes must provide
both unicast transport and multicast transport. Damm Cellular Systems A/S recommends the
use of Cisco products and especially the 1841 modular router has been tested and found
suitable for this purpose.
The following is a brief sketch of the techniques in use in the router network to form a routing
that can cater for the needs of the TetraFlex multisite environment.
2.16.10.1 VPN
Using IPSec with 3DES encryption on all traffic between the routers maintains security and
integrity of the voice and data transported between the nodes in the network.
2.16.10.2 Multicast networking
Multicast is a 1-to-many routing scheme. As opposed to unicast which is 1-to-1, the multicast
allows a sender of information to address several receivers by sending one instance of the
data. The multicast network replicates the sent data as applicable.
2.16.10.2.1 Routing multicast:
Protocol-Independent Multicast (PIM) is a family of multicast routing protocols that can
provide one-to-many and many-to-many distribution of data over the Internet. The "protocol-
independent" part refers to the fact that PIM does not include its own topology discovery
mechanism, but instead uses routing information supplied by other traditional routing
protocols such as Border Gateway Protocol (BGP) or in this specific case static routing entry.
The way PIM is routing is known as RPF, reverse path forwarding. The routing path of
multicast packets is based upon the routing path for unicast packets – but is turning it around
by 180 degrees. In unicast – the routing table is built on destination i.e. where the packet
needs to go. In multicast the routing is based on where the packet comes from. In popular,
the PIM forwards packets on all interfaces belonging to a multicast group – except for the
receiving interface.
A sub configuration of PIM is PIM Sparse Mode (PIM-SM).This version explicitly builds
unidirectional shared trees rooted at a Rendezvous Point (RP) per group, and optionally
creates shortest-path trees per source. PIM-SM generally scales fairly well for wide-area
usage.
2.16.10.2.2 Group management in multicast:
The control of members of the multicast environment, i.e. the nodes around the network that
need to send or receive multicast traffic is done by Internet Group Management Protocol
(IGMP). IGMP is used by IP hosts and adjacent multicast routers to establish multicast group
memberships. It is an integral part of the IP multicast specification, like ICMP for unicast
connections.
The TetraFlex release 7 supports version 3 of IGMP. Default setting in Cisco is version 2, but
can be changed through configuration.