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Installation and Operation Manual Chapter 1 Introduction

Egate-100 Ver. 4.0 Functional Description 1-23

RX Traffic Path

The traffic received from TDM ports is assumed by Egate-100 to be traffic arriving

from a non-LCAS GFP transmitter. Egate-100 hence treats the data according to

the following:

• VCAT header extraction: The VCAT header is extracted from the first timeslot

of each multiframe.

• Frame Delineation: The frame border is recognized by synchronization on the

core header which contains the frame length & CRC16 on the length. The GFP

LINK is kept in sync state if the cHEC is correct per frame. To ensure that the

GFP LINK is always synchronized, the transmitter in Egate-100 generates idle

frames, with the Delta parameter equal to 2.

• Single-bit error correction: The GFP receiver has the ability to correct a

single-bit error in Thec or Chec or Ehec. This function is always active. The

single-bit error correction on Chec is not active when the GFP signal is in

Presync or hunt state.

The data is also descrambled (during sync state) before the packets are

transferred to the bridge.

Payload FCS / CRC 32 of Ethernet packet check: The GFP receiver checks that the

payload FCS (if enabled) or the CRC32 of Ethernet is correct. If incorrect, it

discards the packet.

GFP over PDH actual bandwidth: GFP mapping over a PDH signal involves the

following overhead:

• The PDH signal works in multiframe mode. For E1, TS0 is used for frame

synchronization, and for T1, the F bit is used.

• Space is also reserved for a VCAT header every multiframe.

From this it can be determined that the actual PDH rate for GFP frames is as

follows:

• For E1 links: (2.048Mbs –64Kbps – 64/16 k) = 1.98Mbs

• For T1 links: (1.544Mbs –8Kbps – 64/24 k) ~1.533Mbs. The overall

calculation must also take into account the following overhead for GFP

encapsulation:

• Chec_O (Core header encapsulation) – four bytes (always added to the

packet)

• Thec_O (Type header encapsulation) – four bytes (always added to the

packet)

• Ehec_O (Linear extension header encapsulation) – four bytes (optional;

user-configurable)

• P_FCS (Payload FCS -CRC32) – four bytes (optional; user-configurable).

The maximum PPS (packets per second) that can be generated on the PDH is thus

determined as follows (where P_SIZE is the packet size, and other parameters are

as described above):

• For E1 links: PPS =1.98Mbs/ 8/ ( P_SIZE + Chec_O + Thec_O + Ehec_O + P_FCS )

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