The GFP Frame Structure

PROBLEMS 45 . . . OC-48 STM-16 OC-12 STM-4 12 OC-3 STM-1 Figure 2.26 SONETSDH virtual concatenation. capacity of the OC-48STM-16 payload is split into an OC-12STM-4 subrate payload, which is used to carry voice; the rest is split into 12 OC-3STM-1s, which can be used to carry data either individually or virtually concatenated.

2.8.2 Link Capacity Adjustment Scheme LCAS

The number of subrate payloads allocated to an application is typically determined in advance. However, the transmission rate of the application can indeed vary over time. In view of this, it can be useful to dynamically vary the number of subrate payloads allocated to an application. This can be done using the link capacity adjustment scheme LCAS. In LCAS, signaling messages are exchanged between the originating and terminating SONETSDH node to determine and adjust the number of required subrate payloads. LCAS makes sure that the adjustment process is done without losing any data. PROBLEMS 1. Consider the DS1 and E1 signals: a How many voice calls are multiplexed in a DS1 signal? b How many voice calls are multiplexed in an E1 signal? c Why is there a difference in the number of voice calls carried in a DS1 signal and in an E1 signal? 2. Consider a time slot in the DS1 frame. Every sixth frame, the 8th bit is robbed and is used for signaling. What is the data rate of this signaling channel? 3. What is fractional T1? 4. In SONET, identify the differences between a section, a line, and a path. 5. In SONET, what is a virtual tributary group? What is a virtual tributary? Give an example of a virtual tributary. 6. Explain how an adddrop SONETSDH multiplexer works. 7. Two IP routers are connected via an OC-3c link by using packet over SONET PoS. Assume that 33 of the resulting HDLC frames are 50 bytes long, and the rest are 1500 bytes long. What is the rate of transmission of IP packets? 8. Consider the 1:1 and 1:N protection schemes in a point-to-point fiber link. Which of these two schemes provides better protection? Why? 9. Consider the two-fiber bidirectional line switched ring 2F-BLSR shown in Figure 2.18. What is the total available capacity of the ring for the transmission of the working traffic from ADM 1 to ADM 2: 46 SONETSDH AND THE GENERIC FRAME PROCEDURE GFP a When all fibers are working? b When fibers 2 and 8 fail? c When fiber 12 fails after fibers 2 and 8 have failed? 10. Explain how the virtual concatenation scheme works. Why does it have to be implemented only at the originating and terminating nodes?