In Fig. 2-35, the user data rate for OC-3 is stated to be 148.608 Mbps. Show how this number can

In Fig. 2-35, the user data rate for OC-3 is stated to be...

Key Concepts

Gross, SPE, and User Data Rates

The gross rate is the total bit rate transmitted over the line, including both overhead and payload. The SPE rate represents the bit rate available for transport of the payload after initial frame alignment, but before the removal of specific SONET pointer and mapping overheads. The user data rate is the net rate available for actual user data after all overhead has been accounted for. Knowledge of how these rates interrelate and how overhead is subtracted is key to understanding SONET performance parameters.

Multiplexing Hierarchy in SONET

SONET establishes a multiplexing hierarchy where lower-rate signals are combined to form higher-rate aggregate signals (e.g., OC-3 is formed by multiplexing multiple STS-1 frames, and similarly, OC-3072 is built from many lower-rate channels). Each level of multiplexing involves adding additional overhead and mapping considerations, so the derivation of user data rates at higher orders involves scaling the corresponding rates from constituent channels, while accounting for the cumulative overhead introduced at each level.

SONET Framing and Structure

SONET (Synchronous Optical Network) is built on a structured frame format that repeats at regular intervals. Each frame contains a fixed number of bytes and consists of both overhead and payload sections. The framing structure determines how the raw bit rate (gross rate) is divided into transport overhead and the Synchronous Payload Envelope (SPE), which further contains the user data. Understanding this structure is essential for computing the various data rates in a SONET signal.

Overhead and Synchronous Payload Envelope (SPE)

Within each SONET frame, overhead bytes are used for management, synchronization, and error correction, meaning they do not carry user data. The payload, encapsulated in the Synchronous Payload Envelope (SPE), is what actually carries the user information. The ratio of payload to the total frame size is a crucial parameter to determine when deriving the effective (user) data rate from the gross line rate.

Transcript

00:01 Shown is the graph of traffic on an internet service providers t1 deadline from midnight to 8 a .m.

00:11 Where d is a data throughput measured in megabits per second.

00:16 We will use simpson's rule to estimate the total amount of data transmitted during that time period.

00:25 So we have a graphic or graph of data throughput d in terms of time.

00:40 Hours and the data is given in megabits per second.

00:47 And we have a graph, we don't put here, which you have in this stage of the problem, of the problem.

00:55 And then you can expect the graph in order to take out the values of the hours that we are interested in.

01:09 There are one hour intervals so we have to determine the value of t at t equals 0 1 2 3 up to 8 that is intervals of length 1 hour so at 0 if you look at the graph here you have the value 0 .35 remember t is given in megableness beats per second while t is given in hours and because we have seconds here and hours here we're going to do some conversion but we first put the values that we take out from the graph so at zero we have 0 .35 time one hour we have 0 .31 at 2 we get 0 .4 at 3 we are about 0 .5 at 4 we get 0 .51 at 5 we have 0 .56 at 6 0 .56 again at 7 0 .81 and at 8 we have 0 .888.

03:01 So these are the values of d and at 8 we have 0 .88.

03:07 So these are the values of d in megabits per second at values of t in hours each one hour time period that is at zero hours at one hour two hours so on up to eight hours so we have here eight intervals or sub intervals we have one here two three four five six seven eight sub intervals so n is eight and the step size age is one hour.

03:49 That is, each subventable has length one hour.

03:53 But, as i said, we are working the measure of data transmitted in megabits per second.

04:01 So we have to consider time here in seconds.

04:06 That corresponds to 3 ,600 seconds.

04:13 So this is the time we get to consider the step size in the second.

04:20 Seconds we have to consider for the formula of simpson's rule, which in this case has eight sub -intervals.

04:27 So it's s -8...

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