Compact SFP (CSFP) – What it is and when it is used?

SFP-type and BiDi SFP-type optical modules are very popular and widely used in optical communication, while CSFP (Compact Small Form-Factor Pluggable) optical transceivers are much rarer. In this article, we would like to explain the main difference between SFP, BiDi SFP, and Compact SFP, mention in which scenarios Compact SFPs are mostly used, which vendors in which platforms support them, and how it relates to the EDGE Optical Solutions CSFP portfolio.

SFP, BiDi SFP, and Compact SFP (CSFP) differences.

As an old Chinese proverb goes: “One Picture is Worth Ten Thousand Words”, let’s start with a Picture where we can see detailed differences between SFP, BiDi SFP, and Compact SFP (CSFP) optical modules link construction principles:

SFP principle:

We know that for one of the most widely used product types in our industry, SFP, we have 2 ports, one is TX, which is used to transmit the signal, and the other port is RX, which is used to receive the signal. This communication requires 2 optical fiber connections. To make a connection, we simply use 2pcs of this product type, put them in Site A and in Site B, correctly plug optical cables, and we will get the link up and communication can start.

BiDi SFP principle:

If we go further, BiDi SFP modules are also very popular. The key advantage of BiDi SFP compared to regular SFP is that we only need to use 1 optical fiber to make the same 1xGE transfer. In situations where fiber resources are scarce or an operator needs to rent out fiber, BiDi SFP brings significant benefit to the network design and can reduce the cost significantly. BiDi SFPs work in pairs; there are A-side and B-side modules. A side modules on standard distances 3-40km have Tx: 1310nm and Rx:1490nm or Tx:1310nm and Rx:1550nm, while B Side modules on standard distances will have Tx:1490nm, Rx:1310nm or Tx:1550nm and Rx:1310nm. We should connect them accordingly in pairs, Tx:1310nm/Rx:1490nm A side together with Tx:1490nm/Rx:1310nm B side, OR Tx:1310nm/Rx:1550nm A side together with Tx:1550nm/Rx:1310nm B side, and we will get the link running.

Compact SFP (CSFP) principle:

Compact SFP (CSFP) goes even further, by using the same SFP port, we can have 2 BiDi bidirectional streams of traffic, thus we can get 2xGE out from one SFP port. The only thing that is required is that the equipment line card support CSFP, and actually, not so many vendor equipment have been designed to accept CSFP modules.

When is Compact SFP (CSFP) used?

Most commonly, CSFP is used in Central Office/Aggregation site operating at Tx1&Tx2:1490nm Rx1&Rx2:1310nm, and it gets connected to 2 CPE sites, which have simple BiDi SFP operating in Tx:1310nm Rx:1490 at each site. Compact SFP (CSFP) major application is to use it in an FTTx scenario where we have (point-to-point) connections from Central Office/Aggregation Site to (CPE) Customer Premises Equipment. With the help of CSFP, we can double the Central Office/Aggregation Site port density (we can achieve 2xGE from one aggregation site port) and reduce power consumption in the Central Office as we use 2 times fewer ports.

Which Vendor platforms support Compact SFP (CSFP)?

Most popular vendors that support Compact SFP are Cisco, Huawei, and Nokia (ex. Alcatel), and here as well we need to be careful, as not all Cisco, Huawei, and Nokia (ex. Alcatel) platforms will support Compact SFPs.

Cisco Catalyst 4500 and GLC-2BX-D:

One of the most popular Cisco platforms that supports CSFP optical modules is the Cisco Catalyst 4500 Series, which, when used with the X4640-CSFP-E line card, accepts CSFP optical modules. Normally, in this line card, we can have 40xGE as 40 SFP ports are available, but if we use CSFP optical modules in the same 40 SFP ports, we can get 80xGE.

More details about this line card from Cisco Datasheet: Table 6: Ordering Information:

The most popular Cisco Compact SFP (CSFP) product is: GLC-2BX-D

Huawei S5700-LI Series and CSFP-GE-FE-BXD1:

If we check Huawei, then Huawei supports CSFP in their S5700-LI Series Gigabit Enterprise Switches. More particularly, in the following model: S5700-52X-LI-48CS-AC, it supports 48xGE CSFP ports or 24xGE SFP ports, 4xCombo 10/100/1000Base-T Ethernet ports, and 4x10GE SFP+ ports.

You can find the link to the datasheet ---> here.

Huawei MA5600T OLT can accept CSFP when equipped with H802OPGD or H802OPGE P2P Interface boards, which, by use of CSFP optical modules, can achieve 48xGE instead of 24xGE in case SFP modules are used. Huawei Compact SFP (CSFP) product code is: CSFP-GE-FE-BXD1 (part number: 02310TEE) (Datasheet).

Nokia (ex. Alcatel) and CSFP:

Nokia (ex. Alcatel) has several series with line cards that can be equipped with CSFP optical modules. For example, Nokia 7750 Service Router and 7450 Ethernet Service Switch can support 160-port GE CSFP/SFP IMM interface card, which normally have 80xGE when used with SFP optical modules, and we can get up to 160xGE per line card if we use CSFP optical modules. (Source)

As well, Nokia XRS 7950 can be equipped with a 36/72-port GE SFP/CSFP Compact XMA line card, which will support CSFP optical modules. (Source)

The same goes for the Nokia 7210 Service Access Switch series, where we can use an 11/22-port GE IMM-b line card and get up to 22 x cSFP 100/1000 Mb/s. (Source)

Other vendors and CSFP

Other equipment manufacturers have designed their equipment to be used with CSFP modules, such as:

Allied Telesis - SwitchBlade x3106 is designed for high-density FTTX support AT-SBx31GC40 line card, which can be equipped with CSFP transceivers to increase the port density. Allied Telesis CSFP part numbers are AT-SPBD20DUAL-14 (for 20km) and AT-SPBD40DUAL-14 (for 40km version).

Zhone - MXK Terabit Access Platform can be equipped with MXK-AEX20-FE/GE-CSFP Active Ethernet line card, which supports CSFP optical modules. More particularly, 3 types of CFP modules are available (Source):

Keymile has the MileGate SUE16 line card designed for FTTH scenarios where we can use CSFP optical modules and connect up to 480 subscribers from one MileGate 2510 subrack. (Source)

Calix E7-20 GPON system supports E7-20 GE-24x P2P Ethernet line card, which supports 12 CSFP sockets, which, when equipped with CSFP transceivers, will help to improve the traffic density.

The Zyxel CLC1320G-55 fiber-based Gigabit Ethernet Line Card has 16 ports for SFP transceivers and 4 for CSFP/SFP.

Ceragon FiberAir IP-20 all outdoor Microwave series can be equipped with CSFP modules. Ceragon CSFP Module Recommendations (Source):

Compact SFP (CSFP) in the EDGE Optical Solutions portfolio?

In this table, we have summarized the EDGE Optical Solutions CSFP portfolio and the matching relationship with other vendor CSFP optical modules and their part numbers. Many of the vendors follow the MSA standard, and EDGE CSFP modules can be easily used in their platforms. For detailed information, please click on Part Number.

If any questions/comments, feel free to write: sales@edgeoptic.com or call 00371-22084457