This chapter is from the book
This chapter is from the book
This chapter is from the book
Transceiver Types
The choice of optics is based on the connectivity distance between two nodes. In general, optics meant for smaller distances are cheaper than those meant for longer distances. Each type of optical fiber has a suffix to denote the reach and optical lanes. For example, in 400G-SR8, SR stands for short reach, which is up to 100 m, and 8 denotes the number of optical lanes; 400G-SR8 can have 8 optical lanes of 53 Gbps each, which are multiplexed to support 400 Gbps bandwidth.
Table 4-1 lists the transceiver types and the reach and mode of optical fiber with which it can be used.
Table 4-1 Transceiver Types
Transceiver |
Full Form |
Reach |
Mode |
|---|---|---|---|
VR |
Very short reach |
50 m |
MMF |
SR |
Short reach |
100 m |
MMF |
DR |
Data center reach |
500 m |
SMF |
FR |
Far reach |
2 km |
SMF |
LR |
Long reach |
10 km |
SMF |
ZR |
Extended reach |
>80 km |
DWDM |
CR |
Copper |
Up to 7 m for passive Direct Attach Cable (DAC) type Up to 10 m for active Direct Attach Cable (DAC) type |
|
The length of the cable and type of optics needed are determined based on the design option chosen—for example, top-of-rack, middle-of-row, or end-of-row. Within a rack, copper-based Active Electrical Cable (AEC) has good potential. Across racks, Active Optical Cable (AOC) has good potential. Very short reach (VR) optics support is being added currently and may be suitable in AI/ML clusters.
Figure 4-12 illustrates an example of top-of-rack server-to-leaf connectivity and leaf-to-spine connectivity in the rail-optimized design. This topology requires cables of varying length within the rack.
)
Figure 4-13 illustrates an example of middle-of-row and end-of-row design server-to-leaf connectivity and leaf-to-spine connectivity in the rail-optimized design. This topology requires cables of similar lengths from a rack, but across the rack, the cable length varies.
)
