Lan Interworking Via Spanning Devices 1171 Repeaters

A repeater is nothing more than a regenerative repeater (see Section 6.6). It extends a LAN. It does not provide any kind of segmentation of a LAN, except the physical regeneration of the signal. Multiple LANs with common protocols can be interconnected with repeaters, in effect making just one large segment. A network using repeaters must avoid multiple paths, as any kind of loop would cause data to circulate indefinitely and could ultimately make the network crash. The multiple path concept is shown in Figure 11.14.

The following example shows how a loop can be formed. Suppose two repeaters connect CSMA/CD LAN segments as shown in Figure 11.14. Station #1 initiates an interchange with station #3, both on the same segment (upper in the figure). As data packets or frames are transmitted on the upper segment, each repeater will transmit them unnecessarily to the lower segment. Each repeater will receive the repeated packet on the lower segment and retransmit it once again on the upper segment. As one can see, any

LAN segment #2

Figure 11.14 Repeaters in multiple paths. (Courtesy of Hewlett-Packard Co., Ref. 9.)

LAN segment #2

Figure 11.14 Repeaters in multiple paths. (Courtesy of Hewlett-Packard Co., Ref. 9.)

6The adding of dummy octets (bytes) to meet minimum frame length requirements.

traffic introduced into this network will circulate indefinitely around the loop created by the two repeaters. On larger networks the effects can be devastating, although perhaps less apparent (Ref. 9).

Was this article helpful?

0 0

Post a comment