10 CHAPTER 1: 3COM ROUTER INTRODUCTION
New Features of the
3Com Router 1.x New features have been added to the 3Com Router1.10.
Support New Interfaces E3 and CE3 Interfaces
Both E3 and E1 are part of the ITU-T digital carrier architecture and are used in
most regions beyond North America. The data transmission speed of E3 is
34.368 Mbps and the line code is HDB3. E3/CE3 interfaces support the link layer
protocols including PPP, HDLC, Frame Relay, LAPB, and X.25, as well as the
network protocol such as IP. Similar to E1/CE1, E3/CE3 interfaces can work in two
operating modes, namely, E3 mode and CE3 mode.
■When working in E3 mode, an E3/CE3 interface is a timeslot-less interface of
the bandwidth of 34.368 Mbps.
■When working in CE3 mode, it can multiplex/demultiplex 16 channels of E1
signals. The E3-to-E1 multiplexing is compliant with the G.751 and G.742
provisions of ITU-T. In addition, each E1 interface can be divided into 32
timeslots.
E1-F/T1-F Interface
E1-F and T1-F interfaces refer to the fractional E1 and T1 interfaces, which are
equivalent to the simplified CE1/PRI and CT1/PRI interfaces. In essence, they are a
low-cost approach to E1/T1 access. In a simple E1 or T1 access application
requiring neither division of multiple channel groups nor ISDN PRI, either the E1-F
or T1/F interface will be a good choice.
Null Interface
The functions of the Null interface are similar to those of null devices supported by
many operating systems. It is always in UP status, but cannot forward data packets
or configure IP addresses or encapsulate other protocols. Null interface is a virtual
interface with software characteristics. Any network data packet sent to this
interface will be dropped.
FRoIP and FRoISDN Frame Relay over IP
As IP networks have gained wider acceptance, Frame Relay (FR) applications have
relied on IP networks for data communication and interconnection between
networks. FRoIP technology enables IP networks to carry FR data by establishing a
GRE tunnel across the IP network to connect the two FR networks at both ends of
the IP network.
Frame Relay over ISDN
Frame Relay over ISDN provides a method for accessing the Frame Relay network
based on ISDNs and the related devices. This shortens the time for users to access
and lowers the cost of leased lines.
The Frame Relay over ISDN is mainly used in the following two aspects:
■The simplest application is to take Frame Relay over ISDN as the main
communications method. That is, all the routers support Frame Relay over
ISDN, and the individual routers can directly access the Frame Relay networks
(without TA adapters) to communicate.