21.5
SYSTEM DEPTH--A NETWORK MANAGEMENT PROBLEM
545
Bridge
E3 multiplex
Frame
relay
Bridge
Frame
relay
384 k
E1 channel
bank
E3 multiplex
384 k
E1 channel
bank
Microwave
terminal
Microwave
terminal
RPTR
RPTR
585 km
RPTR
RPTR
VAX
DEC-
NET
VAX
DEC-
NET
CSMA/CD LAN
CSMA/CD LAN
Figure 21.1
A typical multilevel network requiring a network management system. Note multiple
convergences.
DS1 or T1 has a frame rate of 8000 frames a second. Each frame is delineated with
a framing bit or F-bit. With modern alignment and synchronization algorithms, to main-
tain framing repetition of the F-bit 8000 times a second is excessive and unnecessary.
Advantage was taken of F-bit redundancy by the development of the extended superframe
(ESF). The ESF consists of 24 consecutive DS1 frames. With 24 frames we expect to
have 24 framing bits. Of these, only six bits need to be used for framing, six are used for
a cyclic redundancy check (CRC-6) on the superframe, and the remaining 12 bits form a
4-kbps data link for network control and maintenance. It is this channel that can serve as
transport for network management information. It can also serve as an ad hoc test link.
Our present concern is in-service monitoring. For instance, we can get real-time error
performance with the CRC-6, giving us a measure of errored seconds and severely errored
seconds in accordance with ITU-T Rec. G.821 (Ref 4). Such monitoring can be done with
test equipment such as the HP
4
37702A or HP 37741A.
Permanent monitoring can be carried out using typically Newbridge network monitoring
equipment, which can monitor an entire T1 or E1 network for frame alignment loss,
4
HP stands for Hewlett-Packard, a well-known manufacturer of electronics test equipment. HP spun off the
test equipment line to Agilent Technologies.
Summary :
21.5 SYSTEM DEPTH--A NETWORK MANAGEMENT PROBLEM 545 Bridge E3 multiplex Frame relay Bridge Frame relay 384 k E1 channel bank E3 multiplex 384 k E1 channel bank Microwave terminal Microwave terminal RPTR RPTR 585 km RPTR RPTR VAX DEC- NET VAX DEC- NET CSMA/CD LAN CSMA/CD LAN Figure 21.1 A typical multilevel network requiring a network management system.
Tags :
network,frame,test,equipment,monitoring,rptr,framing,frames,bits,fbit,channel,management,link