Information Technology Reference
In-Depth Information
Application
Presentation
Session
Transport
TCP or SPX
Network
IP or IPX
Ethernet/
Token Ring/
ISDN/FDDI/
ATM
Data link
Physical
Figure 25.8
Typical technologies used in network communications
25.4 Routers, bridges and repeaters
Networks connect to other networks through repeaters, bridges or routers. A repeater corre-
sponds to the physical layer of the OSI model and routes data from one network segment to
another. Bridges route data using the data link layer (with the media access control address
(MAC) address), and routers route data using the network layer (that is, using a network ad-
dress, such as an IP address). Normally, at the data-link layer, the transmitted data is known
as a data frame, while at the network layer it is referred to as a data packet. Figure 25.9 illus-
trates the three interconnection types.
25.4.1 Repeaters
All network connections suffer from a reduction in signal strength (attenuation) and digital
pulse distortion. Thus, for a given cable specification and bit rate, each connection will have
a maximum length of cable that can be used to transmit the data reliably. Repeaters can be
used to increase the maximum interconnection length, and may do the following:
•
Clean signal pulses.
•
Pass all signals between attached segments.
•
Boost signal power.
•
Possibly translate between two different media types (such as fibre to twisted-pair cable).
