(b) What is the packetization delay if the encoding is 8kbps (1 kB/sec), and we
ID: 3536106 • Letter: #
Question
(b) What is the packetization delay if the encoding is 8kbps (1 kB/sec), and we send 50 voice bytes per packet?
Suppose we have a largish number of ATM connections (rt-VBR fits this scenario best). All the connections together have an aggregate bandwidth of 100 cells/ms and a maximum burst of 4,000 cells. To handle all the connections, we obviously need a bandwidth of at least 100 cells/ms, but to guarantee a delay, we have to be able to clear a worst-case burst within the delay time. (There is a formula on the sheet to help with this.)
(d) What outbound bandwidth is needed, in cells/ms, to guarantee a maximum delay of 20 ms?
(e). What outbound bandwidth is needed, in cells/ms, to guarantee a maximum delay of 80 ms?
Explanation / Answer
1. (a) One of the sources of delay in packetized voice is the packetization delay, or fill time; this is the time a bit stream takes to fill the data portion of a packet. What is this delay if 160 bytes is sent per packet, and the encoding is 64kbps (8 kB/sec)?
(b) What is the packetization delay if the encoding is 8kbps (1 kB/sec), and we send 50 voice bytes per packet?
Suppose we have a largish number of ATM connections (rt-VBR fits this scenario best). All the connections together have an aggregate bandwidth of 100 cells/ms and a maximum burst of 4,000 cells. To handle all the connections, we obviously need a bandwidth of at least 100 cells/ms, but to guarantee a delay, we have to be able to clear a worst-case burst within the delay time. (There is a formula on the sheet to help with this.)
(d) What outbound bandwidth is needed, in cells/ms, to guarantee a maximum delay of 20 ms?
(e). What outbound bandwidth is needed, in cells/ms, to guarantee a maximum delay of 80 ms?
4. (c). What distinguishes the ATM realtime classes (CBR, rt-VBR) from the nonrealtime classes, in terms of traffic guarantees needed?
(d). Give one difference between ATM Available Bit Rate (ABR) traffic and nonrealtime Variable Bit Rate (nrt-VBR) traffic.
2. The GCRA (General Cell Rate Algorithm) is as follows.
GRCA(T,Ï„): T = average time between packets, Ï„ represents time variation
Suppose the current cell is expected at time tat, and actually arrives at time t.
Case 1: t < tat – τ (packet arrived too EARLY): the packet is nonconforming. Do not change tat
Case 2: t ≥ tat – τ: The packet is conforming. Set tatnew = max(t,tat) + T
(a). Consider the following packet arrival times. Which ones are conforming for GCRA(4,2)? Also give the tat values for each cell. T=4, τ=2. Hint: complete full columns in left-to-right order, first tat and then conformance. Don’t forget tatnew = max(t,tat) + T
Related Questions
Navigate
Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.